Usage share of web browsers and Long non-coding RNA: Difference between pages

From Wikipedia, the free encyclopedia
(Difference between pages)
Content deleted Content added
m gen fixes: rm 'of' between month and year, using AWB
 
Drmed36 (talk | contribs)
 
Line 1: Line 1:
Long [[Non-coding_RNA|noncoding RNAs]] (long ncRNAs) are generally considered (somewhat arbitrarily) as non-protein coding transcripts longer than 200 [[nucleotide]]s. This limit is due to practical considerations including the separation of RNAs in common experimental protocols. Additionally, this limit distinguishes long ncRNAs from small regulatory RNAs such as [[microRNA|microRNAs]] (miRNAs), [[Small_interfering_RNA|short interfering RNAs]] (siRNAs), [[Piwi-interacting RNA|Piwi-interacting RNAs]] (piRNAs), [[snoRNA|small nucleoloar RNAs]] (snoRNAs) etc.
[[Image:Usage share of web browsers.png|thumb|300px|The usage share of web browsers described in this chart. Source from Net Applications<ref>[http://marketshare.hitslink.com/report.aspx?qprid=0&qptimeframe=Q&qpsp=38 Market share for browsers, operating systems and search engines<!-- Bot generated title -->]</ref>
{{legend|#0000ff|[[Internet Explorer]] (72.22%)}}
{{legend|#ff9900|[[Mozilla Firefox]] (19.48%)}}
{{legend|#cccccc|[[Safari (web browser)|Safari]] (6.39%)}}
{{legend|#ff0000|[[Opera (web browser)|Opera]] (0.71%)}}
{{legend|#66cc33|[[Netscape (web browser)|Netscape]] (0.68%)}}
{{legend|#ffff00|[[Google Chrome|Chrome]] (0.26%)}}
{{legend|#00ffff|Other (0.26%)}}]]
'''Usage share''', in '''[[web browser]]''' statistics is the percentage of visitors to a group of web sites that use a particular browser. For example, when it is said that [[Internet Explorer]] has 74% usage share, it means Internet Explorer is used by 74%<ref>[http://marketshare.hitslink.com/report.aspx?qprid=0&qptimeframe=Q&qpsp=37 Market share for browsers, operating systems and search engines]</ref> of visitors that visit a given set of sites. Typically, the [[user agent]] string is used to identify which browser a visitor is using. The concept browser percentages for the Web audience in general is sometimes called '''browser penetration'''.


===Abundance of long ncRNAs===
==Overestimation and underestimation==
Note that measuring browser usage in terms of the number of requests (page hits) made by each [[user agent]] can be misleading. Not all requests are generated by a user, as a user agent can make requests at regular time intervals without user input. In this case, the usage of that user agent would then be overestimated. Some examples:


A recent study found only one fifth of transcription across the human genome is associated with protein-coding genes ([[#ref17510325|Kapranov 2007]]), indicating at least four-times more long noncoding than coding RNA sequences. However, it is large-scale cDNA sequencing projects such as FANTOM (functional annotation of mouse cDNA) that reveal the complexity of this transcription ([[#ref16141072|Carninci 2005]]). The FANTOM3 project identified ~35,000 noncoding transcripts from ~10,000 distinct loci that bear many signatures of mRNAs, including 5’capping, splicing and poly-adenylation, but have little or no open reading frame ([[#ref16141072|Carninci 2005]]). While the abundance of long ncRNAs was unanticipated, this number nevertheless represents a conservative lower estimate since it omitted many singleton transcripts and non-polyadenylated transcripts (tiling array show more than 40% of transcripts are non-polyadenylated) ([[#ref15790807|Cheng 2005]]). However, unambiguously identifying ncRNAs within these cDNA libraries is challenging since it can be difficult to distinguish protein-coding transcripts from noncoding transcripts.
*A web browser that refreshes the [[webpage]] at a regular time interval.
*Most [[browsers]] generate additional page hits by refreshing webpages when user navigates back through page history; only a few [[browsers]] (like [[Opera (web browser)|Opera]]) reuse cached content without resending requests to server.<ref>{{cite web|url=http://my.opera.com/yngve/blog/2007/02/27/introducing-cache-contexts-or-why-the|title=Opera Cache Contexts vs Security}}</ref><ref>{{cite web|url=http://sharovatov.wordpress.com/2008/06/03/http-history-lists-and-back-button/|title=HTTP History Lists and Back Button}}</ref>
*A feed reader that requests the [[RSS (file format)|RSS]] or [[Atom (standard)|Atom]] feed at a regular time interval.
*Extra files like [[Cascading Style Sheets|CSS]] hacks and [[JavaScript]] hacks are often sent to Internet Explorer.
*[[Gecko layout engine|Gecko]]-based browsers (such as [[Mozilla Firefox|Firefox]]) can [[Link prefetching|link prefetch]] web pages, increasing hits. Link prefetching in Gecko-based browsers is used on pages with enhanced [[Markup language|markup]], including Google search results.<ref>{{cite web|url=http://www.google.com/help/features.html#prefetch|title=Google feature list}}</ref>
*A user who revisits a site shortly after changing or upgrading browsers may be double-counted under some methodologies; overall numbers at the time of a new version's release may be skewed.<ref>{{cite web |url=http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9102398 |title=Firefox 3.0 boosts Mozilla's market share |accessdate=2008-06-27 |author=Gregg Keizer |date=2008-06-23 |work=Computerworld |publisher=IDG }}</ref>
*Certain anti-virus products fake their user-agent to appear to be popular browsers. This is done to trick attack sites that might display clean content to the scanner, but not to the browser. The Register reported in June 2008 that traffic from AVG Linkscanner, using an IE6 user-agent, outstripped human link clicks by nearly 10 to 1. <ref>{{cite web |url=http://www.theregister.co.uk/2008/06/26/avg_disguises_fake_traffic_as_ie6/ |title=AVG disguises fake traffic as IE6 |accessdate=2008-09-05 |author=Cade Metz |date=2008-06-26 |work=The Register }}</ref>


===Genomic organisation of long ncRNAs===
It is also possible to underestimate the usage share by using the number of requests, for example:


The current landscape of the mammalian genome is described as numerous ‘foci’ of transcription that are separated by long stretches of intergenic space ([[#ref16141072|Carninci 2005]]). While long ncRNAs are located and transcribed within the intergenic stretches, the majority are transcribed as complex, interlaced networks of overlapping sense and antisense transcripts that often includes protein-coding genes ([[#ref17486121|Kapranov 2007]]). Genomic sequences within these transcriptional foci are often shared within a number of different coding and noncoding transcripts in the sense and antisense directions ([[#ref17571346|Birney 2007]]) giving rise to a complex hierarchy of overlapping isoforms. For example, 3012 out of 8961 cDNAs previously annotated as truncated coding sequences within FANTOM2 were later designated as genuine ncRNA variants of protein-coding cDNAs ([[#ref16141072|Carninci 2005]]). While the abundance and conservation of these interleaved arrangements suggest they have biological relevance, the complexity of these foci frustrates easy evaluation.
*A graphical browser typically results in more hits than a text browser, as it downloads files referred to by the [[HTML]] document (e.g., [[digital image|image]], CSS, and JavaScript).
*Many [[Internet browser|browsers]] and [[download manager]]s spoof a different [[User agent#Example user-agent strings|user agent string]] to the [[web server]] to prevent erroneous or malicious browser sniffing which could result in receiving broken or incompatible code, or being completely blocked, and thus increasing the statistics for other browsers (as an example, prior to version 9, the [[Opera (web browser)|Opera]] web browser had "Identify as Internet Explorer" as the default user setting)
*Most recent browsers block third-party [[spyware]].
*Text-based and audio-based browsers do not download any [[Web bug|webbugs]] at all.
*Gecko-based browsers since Firefox 1.5 and Opera uses fast [[Document Object Model]] (DOM) caching. JavaScript is only executed on pageload from net or disk cache, but not if it is loaded from DOM cache. This can have an impact on JavaScript based tracking of browser statistics.[http://developer.mozilla.org/en/docs/Using_Firefox_1.5_caching]
*Firefox blocked [[Alexa Internet|Alexa]] toolbars from its extension page for quite some time, this makes the estimates of Net Applications inaccurate.
*[[Ad filtering]] is popular through methods such as the Firefox extension [[Adblock]].


===Conservation of long ncRNAs===
==Present to 1999==
===Net Applications===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Global usage share data from: [http://www.netapplications.com Net Applications]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]]
! style="width:6em" | [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! style="width:6em" | [[Chrome (web browser)|Chrome]]
! Source
|-
| Q3 2008 || 72.22% || 0.68% || 0.09% || 19.48% || 0.71% || 6.39% || 0.26% || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qpcal=1&qptimeframe=Q&qpsp=38 Q3 2008]
|-
| Q2 2008 || 73.81% || 0.62% || 0.11% || 18.43% || 0.71% || 6.14% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qpcal=1&qptimeframe=Q&qpsp=37 Q2 2008]
|-
| Q1 2008 || 75.06% || 0.62% || 0.33% || 17.35% || 0.67% || 5.78% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=36 Q1 2008]
|-
| Q4 2007 || 77.37% || 0.64% || 0.09% || 15.84% || 0.62% || 5.24% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=35 Q4 2007]
|-
| Q3 2007 || 78.85% || 0.76% || 0.11% || 14.69% || 0.51% || 4.80% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=34 Q3 2007]
|-
| Q2 2007 || 78.76% || 0.83% || 0.15% || 14.92% || 0.46% || 4.66% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=33 Q2 2007]
|-
| Q1 2007 || 79.38% || 0.77% || 0.19% || 14.35% || 0.50% || 4.70% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=32 Q1 2007]
|-
| Q4 2006 || 80.69% || 0.86% || 0.23% || 13.50% || 0.56% || 4.06% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=31 Q4 2006]
|-
| Q3 2006 || 82.88% || 0.88% || 0.26% || 11.89% || 0.62% || 3.30% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=30 Q3 2006]
|-
| Q2 2006 || 84.03% || 0.98% || 0.32% || 10.67% || 0.57% || 3.25% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=29 Q2 2006]
|-
| Q1 2006 || 85.01% || 1.09% || 0.36% || 9.77% || 0.53% || 3.10% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=28 Q1 2006]
|-
| Q4 2005 || 85.88% || 1.25% || 0.43% || 9.00% || 0.54% || 2.80% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=27 Q4 2005]
|-
| Q3 2005 || 86.74% || 1.92% || 0.48% || 7.97% || 0.55% || 2.24% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=26 Q3 2005]
|-
| Q2 2005 || 87.24% || 1.62% || 0.59% || 8.08% || 0.52% || 1.89% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=25 Q2 2005]
|-
| Q1 2005 || 89.02% || 1.89% || 0.67% || 6.17% || 0.49% || 1.70% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=24 Q1 2005]
|-
| Q4 2004 || 91.35% || 2.09% || 0.80% || 3.66% || 0.51% || 1.50% || || [http://marketshare.hitslink.com/report.aspx?qprid=0&qpmr=15&qpdt=1&qpct=3&qptimeframe=Q&qpsp=23 Q4 2004]
|}


Many small RNAs, such as microRNAs or snoRNAs, exhibit strong conservation across diverse species ([[#ref15965474|Bentwich 2005]]). In contrast, long ncRNAs generally lack strong conservation which is often cited as evidence of non-functionality ([[#ref15851065|Brosius 2005]]; [[#ref17277804|Struhl 2007]]). However, many well-described long ncRNAs, such as Air and Xist, are poorly conserved ([[#ref11437441|Nesterova 2001]]), suggesting that ncRNAs may be subject to different selection pressures ([[#ref16290135|Pang 2006]]). Unlike mRNAs, which have to conserve the codon usage and prevent frameshift mutations in a single long ORF, selection may conserve only short regions of long ncRNAs that are constrained by structure or sequence-specific interactions. Therefore we may see selection act only over small regions of the long ncRNA transcript. Nevertheless, despite low conservation of long ncRNAs generally, it should be noted that many long ncRNAs still contain strongly conserved elements. For example 19% of highly conserved phastCons elements occur in known introns, and another 32% in unannotated regions ([[#ref16024819|Siepel 2005]]). Furthermore, a representative set of human long ncRNAs exhibit small, yet significant, reductions in substitution and insertion/deletion rates indicative of purifying selection that conserve the integrity of the transcript at the levels of sequence, promoter and splicing ([[#ref17387145|Ponjavic 2007]]).
Among other browsers, Net Applications gives the following breakdown from the third quarter of 2008:
*[[Opera Mini]] - 0.05%
*[[PlayStation 3|Playstation]] - 0.04%
*[[Konqueror]] - 0.02%
*[[Blazer (web browser)|Blazer]] - 0.02%
*[[Microsoft Pocket Internet Explorer]] - 0.02%
*[[WebTV]] - 0.01%
*[[NetFront]] - 0.01%
*[[IBM Lotus Notes]] - 0.00%


The poor conservation of ncRNAs may be the result of recent and rapid adaptive selection. For instance, ncRNAs may be more pliant to evolutionary pressures than protein-coding genes, as evidenced by the existence of many lineage specific ncRNAs, such as Xist or Air ([[#ref16290135|Pang 2006]]). Indeed, those conserved regions of the human genome that are subject to recent evolutionary change relative to the chimpanzee genome occurs mainly in noncoding regions, many of which are transcribed ([[#ref17040131|Pollard 2006]]; [[#ref16915236|Pollard 2006]]). This includes a ncRNA, HAR1, which has undergone rapid evolutionary change in humans and is specifically expressed in the Cajal-Retzious cells in the human neocortex ([[#ref16915236|Pollard 2006]]). The observation that many functionally validated RNAs are evolving quickly ([[#ref16290135|Pang 2006]]; [[#ref15475259|Smith 2004]]), may result from these sequences having more plastic structure-function constraints, and we may expect a great deal of evolutionary innovation to occur in such sequences. This is supported by the existence of thousands of sequences in the mammalian genome that show poor conservation at the primary sequence level but have evidence of conserved RNA secondary structures ([[#ref16751343|Torarinsson 2006]]; [[#ref18096747|Torarinsson 2008]]).
===TheCounter.com===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Global usage share data from: [http://www.thecounter.com/stats/ TheCounter.com Global Statistics]'''
|-
! style="width:10em" | Period
! style="width:6em" |[[Internet Explorer]]
! style="width:6em" |[[Netscape Navigator]]
! style="width:6em" |[[Netscape (web browser)|Netscape]] / [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" |[[Opera (web browser)|Opera]]
! style="width:6em" |[[Safari (web browser)|Safari]]
! Sources
|-
| 2008 Q3 || 76.33% || 0.07% || 17.97% || 0.84% || 3.76% || [http://www.thecounter.com/stats/2008/July/browser.php Jul 2008], [http://www.thecounter.com/stats/2008/August/browser.php Aug 2008], [http://www.thecounter.com/stats/2008/September/browser.php Sep 2008]
|-
| 2008 Q2 || 78.30% || 0.06% || 16.36% || 0.81% || 3.41% || [http://www.thecounter.com/stats/2008/April/browser.php Apr 2008], [http://www.thecounter.com/stats/2008/May/browser.php May 2008], [http://www.thecounter.com/stats/2008/June/browser.php Jun 2008]
|-
| 2008 Q1 || 78.80% || 0.06% || 15.87% || 0.79% || 3.32% || [http://www.thecounter.com/stats/2008/January/browser.php Jan 2008], [http://www.thecounter.com/stats/2008/February/browser.php Feb 2008], [http://www.thecounter.com/stats/2008/March/browser.php Mar 2008]
|-
| 2007 Q4 || 81.14% || 0.06% || 13.81% || 0.67% || 3.21% || [http://www.thecounter.com/stats/2007/October/browser.php Oct 2007], [http://www.thecounter.com/stats/2007/November/browser.php Nov 2007], [http://www.thecounter.com/stats/2007/December/browser.php Dec 2007]
|-
| 2007 Q3 || 81.63% || 0.06% || 13.49% || 0.66% || 3.00% || [http://www.thecounter.com/stats/2007/July/browser.php Jul 2007], [http://www.thecounter.com/stats/2007/August/browser.php Aug 2007], [http://www.thecounter.com/stats/2007/September/browser.php Sep 2007]
|-
| 2007 Q2 || 82.97% || 0.06% || 12.41% || 0.64% || 2.87% || [http://www.thecounter.com/stats/2007/April/browser.php Apr 2007], [http://www.thecounter.com/stats/2007/May/browser.php May 2007], [http://www.thecounter.com/stats/2007/June/browser.php Jun 2007]
|-
| 2007 Q1 || 83.69% || 0.06% || 11.57% || 0.57% || 2.92% || [http://www.thecounter.com/stats/2007/January/browser.php Jan 2007], [http://www.thecounter.com/stats/2007/February/browser.php Feb 2007], [http://www.thecounter.com/stats/2007/March/browser.php Mar 2007]
|-
| 2006 Q4 || 84.11% || 0.05% || 11.13% || 0.60% || 2.80% || <!-- this link leads to data from October 2005 [http://www.thecounter.com/stats/2006/October/browser.php Oct 2006], -->[http://www.thecounter.com/stats/2006/November/browser.php Nov 2006], [http://www.thecounter.com/stats/2006/December/browser.php Dec 2006]
|-
| 2006 Q3 || 84.48% || 0.06% || 10.56% || 0.73% || 2.27% || [http://www.thecounter.com/stats/2006/July/browser.php Jul 2006], [http://www.thecounter.com/stats/2006/August/browser.php Aug 2006], [http://www.thecounter.com/stats/2006/September/browser.php Sep 2006]
|-
| 2006 Q2 || 86.32% || 0.05% || 9.03% || 0.70% || 1.89% || [http://www.thecounter.com/stats/2006/April/browser.php Apr 2006], [http://www.thecounter.com/stats/2006/May/browser.php May 2006], [http://www.thecounter.com/stats/2006/June/browser.php Jun 2006]
|-
| 2006 Q1 || 90.01% || 0.05% || 6.77% || 0.58% || 1.40% || [http://www.thecounter.com/stats/2006/January/browser.php Jan 2006], [http://www.thecounter.com/stats/2006/February/browser.php Feb 2006], [http://www.thecounter.com/stats/2006/March/browser.php Mar 2006]
|-
| 2005 Q4 || 87.25% || 0.07% || 8.60% || 0.71% || 1.83% || [http://www.thecounter.com/stats/2005/October/browser.php Oct 2005], [http://www.thecounter.com/stats/2005/November/browser.php Nov 2005], [http://www.thecounter.com/stats/2005/December/browser.php Dec 2005]
|-
| 2005 Q3 || 87.58% || 0.07% || 8.42% || 0.67% || 1.60% || [http://www.thecounter.com/stats/2005/July/browser.php Jul 2005], [http://www.thecounter.com/stats/2005/August/browser.php Aug 2005], [http://www.thecounter.com/stats/2005/September/browser.php Sep 2005]
|-
| 2005 Q2 || 90.90% || 0.09% || 6.02% || 0.51% || 0.99% || [http://www.thecounter.com/stats/2005/April/browser.php Apr 2005], [http://www.thecounter.com/stats/2005/May/browser.php May 2005], [http://www.thecounter.com/stats/2005/June/browser.php Jun 2005]
|-
| 2005 Q1 || 90.77% || 0.11% || 5.73% || 0.54% || 1.00% || [http://www.thecounter.com/stats/2005/January/browser.php Jan 2005], [http://www.thecounter.com/stats/2005/February/browser.php Feb 2005], [http://www.thecounter.com/stats/2005/March/browser.php Mar 2005]
|-
| 2004 Q4 || 90.98% || 0.18% || 5.10% || 0.68% || 0.77% || [http://www.thecounter.com/stats/2004/October/browser.php Oct 2004], [http://www.thecounter.com/stats/2004/November/browser.php Nov 2004], [http://www.thecounter.com/stats/2004/December/browser.php Dec 2004]
|-
| 2004 Q3 || 92.70% || 0.20% || 3.57% || 0.65% || 0.73% || [http://www.thecounter.com/stats/2004/July/browser.php Jul 2004], [http://www.thecounter.com/stats/2004/August/browser.php Aug 2004], [http://www.thecounter.com/stats/2004/September/browser.php Sep 2004]
|-
| 2004 Q2 || 95.04% || 0.32% || 2.37% || 0.51% || 0.67% || [http://www.thecounter.com/stats/2004/April/browser.php Apr 2004], [http://www.thecounter.com/stats/2004/May/browser.php May 2004], [http://www.thecounter.com/stats/2004/June/browser.php Jun 2004]
|-
| 2004 Q1 || 94.28% || 0.36% || 2.70% || 0.52% || || [http://www.thecounter.com/stats/2004/January/browser.php Jan 2004], [http://www.thecounter.com/stats/2004/February/browser.php Feb 2004], [http://www.thecounter.com/stats/2004/March/browser.php Mar 2004]
|-
| 2003 Q2 || 94.43% || 1.45% || 2.22% || 0.66% || || [http://www.thecounter.com/stats/2003/April/browser.php Apr 2003], [http://www.thecounter.com/stats/2003/May/browser.php May 2003], [http://www.thecounter.com/stats/2003/June/browser.php Jun 2003]
|-
| 2003 Q1 || 94.18% || 1.77% || 2.15% || 0.65% || || [http://www.thecounter.com/stats/2003/January/browser.php Jan 2003], [http://www.thecounter.com/stats/2003/February/browser.php Feb 2003], [http://www.thecounter.com/stats/2003/March/browser.php Mar 2003]
|-
| 2002 Q4 || 93.94% || 2.31% || 1.67% || 0.83% || || [http://www.thecounter.com/stats/2002/October/browser.php Oct 2002], [http://www.thecounter.com/stats/2002/November/browser.php Nov 2002], [http://www.thecounter.com/stats/2002/December/browser.php Dec 2002]
|-
| 2002 Q3 || 93.32% || 3.04% || 1.36% || 0.94% || || [http://www.thecounter.com/stats/2002/July/browser.php Jul 2002], [http://www.thecounter.com/stats/2002/August/browser.php Aug 2002], [http://www.thecounter.com/stats/2002/September/browser.php Sep 2002]
|-
| 2002 Q2 || 92.47% || 4.13% || 1.13% || 0.82% || || [http://www.thecounter.com/stats/2002/April/browser.php Apr 2002], [http://www.thecounter.com/stats/2002/May/browser.php May 2002], [http://www.thecounter.com/stats/2002/June/browser.php Jun 2002]
|-
| 2002 Q1 || 92.40% || 4.67% || 0.93% || 0.52% || || [http://www.thecounter.com/stats/2002/January/browser.php Jan 2002], [http://www.thecounter.com/stats/2002/February/browser.php Feb 2002], [http://www.thecounter.com/stats/2002/March/browser.php Mar 2002]
|-
| 2001 Q4 || 90.83% || 5.23% || 0.71% || 0.36% || || [http://www.thecounter.com/stats/2001/October/browser.php Oct 2001], [http://www.thecounter.com/stats/2001/November/browser.php Nov 2001], [http://www.thecounter.com/stats/2001/December/browser.php Dec 2001]
|-
| 2001 Q3 || 88.43% || 6.49% || 0.26% || 0.31% || || [http://www.thecounter.com/stats/2001/July/browser.php Jul 2001], [http://www.thecounter.com/stats/2001/August/browser.php Aug 2001], [http://www.thecounter.com/stats/2001/September/browser.php Sep 2001]
|-
| 2001 Q2 || 87.99% || 7.46% || 0.27% || 0.28% || || [http://www.thecounter.com/stats/2001/April/browser.php Apr 2001], [http://www.thecounter.com/stats/2001/May/browser.php May 2001], [http://www.thecounter.com/stats/2001/June/browser.php Jun 2001]
|-
| 2001 Q1 || 86.80% || 9.84% || 0.30% || 0.22% || || [http://www.thecounter.com/stats/2001/January/browser.php Jan 2001], [http://www.thecounter.com/stats/2001/February/browser.php Feb 2001], [http://www.thecounter.com/stats/2001/March/browser.php Mar 2001]
|-
| 2000 Q4 || 83.95% || 12.61% || 0.14% || 0.14% || || [http://www.thecounter.com/stats/2000/October/browser.php Oct 2000], [http://www.thecounter.com/stats/2000/November/browser.php Nov 2000], [http://www.thecounter.com/stats/2000/December/browser.php Dec 2000]
|-
| 2000 Q3 || 82.76% || 14.35% || 0.04% || 0.14% || || [http://www.thecounter.com/stats/2000/July/browser.php Jul 2000], [http://www.thecounter.com/stats/2000/August/browser.php Aug 2000], [http://www.thecounter.com/stats/2000/September/browser.php Sep 2000]
|-
| 2000 Q2 || 80.30% || 17.54% || 0.02% || 0.12% || || [http://www.thecounter.com/stats/2000/April/browser.php Apr 2000], [http://www.thecounter.com/stats/2000/May/browser.php May 2000], [http://www.thecounter.com/stats/2000/June/browser.php Jun 2000]
|-
| 2000 Q1 || 79.09% || 19.25% || 0.00% || 0.13% || || [http://www.thecounter.com/stats/2000/January/browser.php Jan 2000], [http://www.thecounter.com/stats/2000/February/browser.php Feb 2000], [http://www.thecounter.com/stats/2000/March/browser.php Mar 2000]
|-
! Period
! [[Internet Explorer]]
! [[Netscape Navigator]]
! [[Netscape (web browser)|Netscape]] / [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! [[Opera (web browser)|Opera]]
! [[Safari (web browser)|Safari]]
! Sources
|-
|}


== Long ncRNA functions ==
===OneStat.com===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Global usage share data from [http://www.onestat.com OneStat.com]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape Navigator]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| February 2008 || 83.27% || || 0.14% || 13.76% || 0.55% || 2.18% || [http://www.onestat.com/html/aboutus_pressbox57-firefox-mozilla-ie-browser-market-share.html 2008-02-18]
|-
| June 2007 || 84.66% || || 0.11% || 12.72% || 0.61% || 1.79% || [http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html 2007-07-02]
|-
| January 2007 || 85.81% || || 0.13% || 11.69% || 0.58% || 1.64% || [http://www.onestat.com/html/aboutus_pressbox50-microsoft-internet-explorer-7-usage.html 2007-01-22]
|-
| November 2006 || 85.24% || || 0.11% || 12.15% || 0.69% || 1.61% || [http://www.onestat.com/html/aboutus_pressbox49-microsoft-internet-explorer-7-usage.html 2006-11-06]
|-
| October 2006 || 85.85% || || 0.12% || 11.49% || 0.69% || 1.61% || [http://www.onestat.com/html/aboutus_pressbox48-microsoft-internet-explorer-usage.html 2006-10-09]
|-
| July 2006 || 83.05% || || 0.16% || 12.93% || 1.00% || 1.84% || [http://www.onestat.com/html/aboutus_pressbox44-mozilla-firefox-has-slightly-increased.html 2006-07-09]
|-
| May 2006 || 85.17% || || 0.15% || 11.79% || 0.79% || 2.02% || [http://www.onestat.com/html/aboutus_pressbox42_microsoft_internet_explorer_has_slightly_increased.html 2006-05-15]
|-
| January 2006 || 85.82% || || 0.16% || 11.23% || 0.77% || 1.88% || [http://www.onestat.com/html/aboutus_pressbox41_mozilla_firefox_usage_share.html 2006-01-31]
|-
| [[November 2]], [[2005]] || 85.45% || || 0.26% || 11.51% || 0.77% || 1.75% || [http://www.onestat.com/html/aboutus_pressbox40_browser_market_firefox_growing.html 2005-11-02]
|-
| [[April 27]], [[2005]] || 86.63% || || 1.08% || 8.69% || 1.03% || 1.26% || [http://www.onestat.com/html/aboutus_pressbox37.html 2005-04-27]
|-
| [[February 28]], [[2005]] || 87.28% || || 1.11% || 8.45% || 1.09% || 1.21% || [http://www.onestat.com/html/aboutus_pressbox36.html 2005-02-28]
|-
| [[November 22]], [[2004]] || 88.90% || || || 7.35% || 1.33% || 0.91% || [http://www.onestat.com/html/aboutus_pressbox34.html 2004-11-22]
|-
| [[May 28]], [[2004]] || 93.9% || || || 2.1% || 1.02% || 0.71% || [http://www.onestat.com/html/aboutus_pressbox30.html 2004-05-28]
|-
| [[January 19]], [[2004]] || 94.8% || || || 1.8% || 0.8% || 0.48% || [http://www.onestat.com/html/aboutus_pressbox26.html 2004-01-19]
|-
| [[July 28]], [[2003]] || 95.4% || 0.6% || 1.9% || 1.6% || 0.6% || 0.25% || [http://www.onestat.com/html/aboutus_pressbox23.html 2003-07-28]
|-
| [[February 3]], [[2003]] || 95.2% || 1.0% || 1.9% || 1.2% || 0.7% || 0.11% || [http://www.onestat.com/html/aboutus_pressbox18.html 2003-02-03]
|-
| [[December 16]], [[2002]] || 95.0% || 1.1% || 1.9% || 1.1% || 0.8% || || [http://www.onestat.com/html/aboutus_pressbox15.html 2002-12-16]
|-
| [[September 30]], [[2002]] || 94.9% || 1.2% || 1.8% || 0.8% || 0.9% || || [http://www.onestat.com/html/aboutus_pressbox11.html 2002-09-30]
|-
| [[June 21]], [[2002]] || 95.3% || 1.9% || 1.5% || 0.4% || 0.7%|| || [http://www.onestat.com/html/aboutus_pressbox7.html 2002-06-24]
|-
| [[April 29]], [[2002]] || 96.6% || 2.1% || 0.7% || || 0.5%|| || [http://www.onestat.com/html/aboutus_pressbox4.html 2002-04-29]
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape Navigator]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
|}


{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''USA usage share data from [http://www.onestat.com OneStat.com]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| June 2007 || 75.69% || 0.17% || 19.65% || 0.61% || 3.77%
||[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
| January 2007 || 78.13% || 0.18% || 16.11% || 0.73% || 3.68%
||[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
|}


===Long ncRNAs in the regulation of gene transcription===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Canadian usage share data from [http://www.onestat.com OneStat.com]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| June 2007 || 75.76% || 0.13% || 16.47% || 0.69% || 5.72%
||[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
| January 2007 || 79.00% || 0.14% || 14.13% || 0.71% || 4.70%
|[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
|}


====Long ncRNAs in gene-specific transcription====
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''UK usage share data from [http://www.onestat.com OneStat.com]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| June 2007 || 86.00% || 0.10% || 11.22% || 0.53% || 1.61%
|[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
| January 2007 || 86.72% || 0.10% || 10.86% || 0.49% || 1.78%
|[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
|}


In eukaryotes, RNA transcription is a tightly regulated process. NcRNAs can target different aspects of this process, targeting transcriptional activators or repressors, different components of the transcription reaction including [[RNA_polymerase_II|RNA polymerase (RNAP) II]] and even the DNA duplex to regulate gene transcription and expression ([[#ref16723972|Goodrich 2006]]). In combination these ncRNAs may comprise a regulatory network that, including transcription factors, finely control the gene expression in complex eukaryotes
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Australian usage share data from [http://www.onestat.com OneStat.com]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]] / [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| June 2007 || 66.42% || 0.24% || 26.32% || 4.05% || 1.86%
|[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
| January 2007 || 65.71% || 0.24% || 26.68% || 4.28% || 1.77%
|[http://www.onestat.com/html/aboutus_pressbox53-firefox-mozilla-browser-market-share.html Onestat.com pressbox]
|-
|}


NcRNAs modulate the function of transcription factors by several different mechanisms, including functioning itself as a co-regulator, modifying transcription factor activity, or by regulating the association and activity of co-regulators. For example, the ncRNA Evf-2 functions as a co-activator for the homeobox transcription factor [[DLX2|Dlx2]], which fulfils important roles in forebrain development and neurogenesis ([[#ref16705037|Feng 2006]]; [[#ref12223397|Panganiban 2002]]). [[Sonic hedgehog]] induces transcription of Evf-2 from an ultraconserved element located between the [[DLX5|Dlx5]] and [[DLX6|Dlx6]] genes during forebrain development ([[#ref16705037|Feng 2006]]). Evf-2 then recruits the Dlx2 transcription factor to the same ultraconserved element whereby Dlx2 subsequently induces expression of Dlx5. The existence of other similar ultra- or highly conserved elements within the mammalian genome that are both transcribed and fulfil enhancer function suggest Evf-2 may be illustrative of a generalised mechanism that tightly regulates important developmental genes with complex expression patterns during vertebrate growth ([[#ref17086198|Pennacchio 2006]]; [[#ref18176564|Visel 2008]]). Indeed the transcription and expression of similar noncoding ultraconserved elements was recently shown to be abnormal in human leukaemia and contribute towards apoptosis in colon cancer cells, suggesting an involvement in tumorogenesis ([[#ref17785203|Calin 2007]]).
===ADTECH===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Europe usage share data from: [http://adtech.info/ ADTECH]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]]
! style="width:6em" | [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| Q1 2008 || 76.2% || || 2.6% || 18.1% || 1.0% || 1.7% || [http://www.adtech.info/news/pr-08-07_en.htm 2008-04-08]
|-
| Q4 2007 || 76.0% || || 2.9% || 18.0% || 1.0% || 1.6% || [http://www.adtech.info/news/pr-08-03.htm 2008-01-31]
|-
| July 2007 || 77.5% || || 3.9% || 15.5% || 0.9% || 1.6% || [http://www.adtech.info/news/pr-07-18.html 2007-08-23]
|-
| February 2007 || 77.34% || || 5.11% || 14.34% || 0.85% || 1.63% || [http://www.adtech.info/news/pr-07-7.html 2007-03-20]
|-
| February–April 2006 || 83.36% || 0.38% || 0.82% || 12.38% || 0.77% || 1.67% || [http://www.adtech.info/news/pr-06-5.html 2006-06-13]
|-
| September 2005 || 83.31% || 0.61% || 1.06% || 12.41% || 0.90% || 1.40% || [http://www.adtech.info/news/pr-05-10.html 2005-11-14]
|-
| June 2005 || 85.10% || 0.60% || 1.05% || 10.11% || 1.21% || 1.34% || [http://www.adtech.info/news/pr-05-5.html 2005-06-27]
|-
| March 2005 || 86.73% || 0.71% || 1.14% || 8.96% || 1.12% || || rowspan=3 | [http://www.adtech.info/news/pr-05-4.html 2005-04-21]
|-
| February 2005 || 87.57% || 0.76% || 1.26% || 7.85% || 1.05% ||
|-
| January 2005 || 87.13% || 0.85% || 1.33% || 7.43% || 1.70% ||
|-
| [[November 30]], [[2004]] || 89.47% || 0.92% || 2.50% || 5.51% || 1.01% || || rowspan=2 | [http://www.adtech.info/news/pr-04-8.html 2004-12-02]
|-
| [[November 16]], [[2004]] || 90.56% || 0.89% || 2.38% || 4.56% || 1.07% ||
|-
| September 2004 || 92.63% || 0.82% || 2.10% || 2.91% || 1.00% || || [http://www.adtech.info/news/pr-04-4.html 2004-10-19]
|-
| [[August 30]], [[2004]] || 93.08% || 0.95% || 2.18% || 2.15% || 0.89% || || [http://www.adtech.info/news/pr-04-8.html 2004-12-02]
|-
| August 2004 || 92.78% || 0.91% || 2.82% || 1.69% || 1.06% || || rowspan=2 | [http://www.adtech.info/news/pr-04-4.html 2004-10-19]
|-
| July 2004 || 93.08% || 0.97% || 2.62% || 1.64% || 0.99% ||
|-
| January–April 2004 || 94.72% || 1.49% || 2.50% || || 0.73% || || [http://adtech.info/NewsPresse/framepresse.php?lang_id=en&node=4&current=119 2004-06-02]
|-
! Date
! [[Internet Explorer]]
! [[Netscape]]
! [[Mozilla Application Suite|Mozilla]]
! [[Mozilla Firefox|Firefox]]
! [[Opera (web browser)|Opera]]
! [[Safari (web browser)|Safari]]
! Source
|}


Local ncRNAs can also recruit transcriptional programmes to regulate adjacent protein-coding gene expression. The RNA binding protein TLS, binds and inhibits the [[P300/CBP|CREB-binding protein and p300]] histone acetyltransferease activities on a repressed gene target, cyclin D1. The recruitment of TLS to the promoter of cyclin D1 was directed by lowly expressed long ncRNAs tethered to 5’ regulatory regions in response to DNA damage signals ([[#ref18509338|Wang 2008]]). Moreover, these local ncRNAs act cooperatively as ligands to modulate the activities of TLS. More broadly, this mechanism allows the cell to harness RNA-binding proteins, which make up one of the largest classes within the mammalian proteome, and integrate their function in transcriptional programs.
===W3 Counter===
*Note: W3 Counter only lists the top 10 Browsers by Version. This is one of the reasons why Opera fluctuates between 0.7% and 1.2% in the table below, as some versions only make it into the top 10 occasionally. This site counts the last 25,000 page views from each site making relatively small sites contribute a lot more to the statistics than in an overall count.
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Global usage share data from: [http://www.w3counter.com/globalstats.php W3 Counter]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Mozilla Application Suite|Mozilla]]
! style="width:6em" | [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| Aug 31, 2008 || 58.46% || || 31.40% || 1.55% || 1.80% || [http://www.w3counter.com/globalstats.php?date=2008-08-31 2008-08-31]
|-
| Jul 31, 2008 || 60.65% || 0.58% || 29.68% || 1.08% || 1.90% || [http://www.w3counter.com/globalstats.php?date=2008-07-31 2008-07-31]
|-
| Jun 30, 2008 || 61.43% || 0.60% || 29.02% || 1.13% || 2.02% || [http://www.w3counter.com/globalstats.php?date=2008-06-30 2008-06-30]
|-
| May 31, 2008 || 61.56% || 0.62% || 28.86% || 1.15% || 2.16% || [http://www.w3counter.com/globalstats.php?date=2008-05-31 2008-05-31]
|-
| Apr 30, 2008 || 61.66% || 0.58% || 28.79% || 1.14% || 2.31% || [http://www.w3counter.com/globalstats.php?date=2008-04-30 2008-04-30]
|-
| Mar 31, 2008 || 61.66% || 0.61% || 28.39% || 1.11% || 2.50% || [http://www.w3counter.com/globalstats.php?date=2008-03-31 2008-03-31]
|-
| Feb 29, 2008 || 61.67% || 0.65% || 28.38% || 1.07% || 2.54% || [http://www.w3counter.com/globalstats.php?date=2008-02-29 2008-02-29]
|-
| Jan 31, 2008 || 61.79% || 0.52% || 28.39% || 1.02% || 2.42% || [http://www.w3counter.com/globalstats.php?date=2008-01-31 2008-01-31]
|-
| Dec 1, 2007 || 62.36% || 0.56% || 27.77% || 1.41% || 1.84% || [http://www.w3counter.com/globalstats.php?date=2007-12-01 2007-12-01]
|-
| Nov 10, 2007 || 62.55% || 0.59% || 27.56% || 1.39% || 1.95% || [http://www.w3counter.com/globalstats.php?date=2007-11-10 2007-11-10]
|-
| Oct 30, 2007 || 62.41% || 0.60% || 27.70% || 1.35% || 1.99% || [http://www.w3counter.com/globalstats.php?date=2007-10-30 2007-10-30]
|-
| Sept 20, 2007 || 66.22% || 0.61% || 25.45% || 1.22% || 1.76% || [http://www.w3counter.com/globalstats.php?date=2007-09-20 2007-09-20]
|-
| Aug 30, 2007 || 66.20% || 0.61% || 25.43% || 1.22% || 1.76% || [http://www.w3counter.com/globalstats.php?date=2007-08-30 2007-08-30]
|-
| July 30, 2007 || 66.41% || 0.65% || 25.11% || 1.16% || 1.75% || [http://www.w3counter.com/globalstats.php?date=2007-07-30 2007-07-30]
|-
| June 30, 2007 || 66.20% || 0.71% || 25.08% || 0.69% || 1.81% || [http://www.w3counter.com/globalstats.php?date=2007-06-30 2007-06-30]
|-
| May 30, 2007 || 66.69% || 0.73% || 24.55% || 1.22% || 1.85% || [http://www.w3counter.com/globalstats.php?date=2007-05-30 2007-05-30]
|-
! Date
! [[Internet Explorer]]
! [[Mozilla Application Suite|Mozilla]]
! [[Mozilla Firefox|Firefox]]
! [[Opera (web browser)|Opera]]
! [[Safari (web browser)|Safari]]
! Source
|}


====Long ncRNAs regulating basal transcription machinery====
===XiTi===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Europe usage share data from: [http://xiti.com/ XiTi] [http://xitimonitor.com/ <span style=" color:#474747;">XiTi</span>''<span style=" color:#82A316;">Monitor</span>''] '''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]]
! style="width:6em" | [[Mozilla Firefox|Firefox]]
! style="width:6em" | [[Opera (web browser)|Opera]]
! style="width:6em" | [[Safari (web browser)|Safari]]
! Source
|-
| March 2008 || 65.0% || 0.5% || 28.8% || 3.3% || 2.3% ||rowspan="6" | [http://www.xitimonitor.com/en-us/browsers-barometer/firefox-march-2008/index-1-2-3-127.html 2008-04-30]
|-
| February 2008 || 65.6% || 0.5% || 28.5% || 3.2% || 2.2%
|-
| January 2008 || 66.1% || 0.5% || 28.0% || 3.2% || 2.1%
|-
| December 2007 || 66.1% || 0.5% || 28.0% || 3.3% || 2.0%
|-
| November 2007 || 66.9% || 0.5% || 27.3% || 3.2% || 1.9%
|-
| October 2007 || 67.5% || 0.4% || 27.0% || 3.1% || 1.8%
|-
| September 2007|| 66.6% || 0.3% || 27.7% || 3.4% || 1.8% || [http://www.xitimonitor.com/en-us/browsers-barometer/firefox-september-2007/index-1-2-3-110.html 2007-10-30]
|-
| July 2-8, 2007 || 66.5% || 0.3% || 27.8% || 3.5% || 1.7% || [http://www.xitimonitor.com/en-us/browsers-barometer/firefox-july-2007/index-1-2-3-102.html 2007-07-18]
|-
|}


NcRNAs also target general transcription factors required for the [[RNA polymerase II|RNAP II]] transcription of all genes ([[#ref16723972|Goodrich 2006]]). These general factors include components of the initiation complex that assemble on promoters or involved in transcription elongation. A ncRNA transcribed from an upstream minor promoter of the dihydrofolate reductase (DHFR) gene forms a stable RNA-DNA triplex within the major promoter of DHFR to prevent the binding of the transcriptional co-factor [[Transcription Factor II D|TFIID]] ([[#ref17237763|Martianov 2007]]). This novel mechanism of regulating gene expression may in fact represent a widespread method of controlling promoter usage given that thousands of such triplexes exist in eukaryotic chromosome ([[#ref2434928|Lee 1987]]). The U1 ncRNA can induce transcription initiation by specifically binding to and stimulating [[Transcription Factor II H|TFIIH]] to phosphorylate the C-terminal domain of RNAP II ([[#ref12389039|Kwek 2002]]). In contrast the ncRNA 7SK, is able to repress transcription elongation by, in combination with [[HEXIM1|HEXIM1]]/[[HEXIM2|2]], forming an inactive complex that prevents the [[P-TEFb|PTEFb]] general transcription factor from phosphorylating the C-terminal domain of RNAP II ([[#ref12389039|Kwek 2002]]; [[#ref11604515|Yang 2001]]; [[#ref14580347|Yik 2003]]), thereby repressing global elongation under stressful conditions. These examples which bypass specific modes of regulation at individual promoters to mediate changes directly at the level of initiation and elongation transcriptional machinery provides a means of quickly affecting global changes in gene expression.
===WebSideStory===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''USA usage share data from: [http://www.websidestory.com WebSideStory]'''
|-
! style="width:10em" | Date
! style="width:6em" | [[Internet Explorer]]
! style="width:6em" | [[Netscape (web browser)|Netscape]] / [[Mozilla Application Suite|Mozilla]]
! style="width:6em" | [[Mozilla Firefox|Firefox]]
! Source
|-
| June 2006 || 86.64% || || 9.95% || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=891&year=2006 July 19, 2006]
|-
| [[January 5]], [[2006]] || 87.63% || || 8.88% || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=927&year=2006 Jan. 12, 2006]
|-
| [[November 4]], [[2005]] || 88.16% || 1.61% || 8.13% || [http://blogs.websidestory.com/datainsights/2005/11/looking_foxy_on_its_oneyear_an.php November 10, 2005]
|-
| [[September 23]], [[2005]] || 88.46% || 1.69% || 7.86% || [http://blogs.websidestory.com/datainsights/2005/09/firefox_cools_down_1.php September 27, 2005]
|-
| [[April 29]], [[2005]] || 88.86% || 2.23% || 6.75% || [http://www.websidestory.com/products/web-analytics/datainsights/spotlight/05-10-2005.html May 10, 2005]
|-
| [[February 18]], [[2005]] || 89.85% || 2.47% || 5.69% || rowspan="4" | [http://www.websidestory.com/products/web-analytics/datainsights/spotlight/02-28-2005.html Feb. 28, 2005]
|-
| [[January 14]], [[2005]] || 90.28% || 2.64% || 4.95%
|-
| [[December 3]], [[2004]] || 91.80% || 2.83% || 4.06%
|-
| [[November 5]], [[2004]] || 92.89% || 2.95% || 3.03%
|-
| [[October 8]], [[2004]] || 93.21% || 3.05% || 2.66% || rowspan="2" | [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=978&year=2004 December 13, 2004]
|-
| [[June 4]], [[2004]] || 95.48% || 3.53% ||
|-
| [[August 26]], [[2002]] || 95.97% || 3.39% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1044&year=2002 August 28, 2002]
|-
| [[October 25]], [[2001]] || 89.03% || 10.47% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1088&year=2001 October 31, 2001]
|-
| [[April 25]], [[2001]] || 86.61% || 13.10% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1107&year=2001 May 1, 2001]
|-
| [[February 21]], [[2001]] || 87.71% || 12.01% || || rowspan="2" | [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1120&year=2001 February 22, 2001]
|-
| [[June 18]], [[2000]] || 86.08% || 13.90% ||
|-
| [[August 2]], [[1999]] || 75.31% || 24.68% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1183&year=1999 August 9, 1999]
|-
| [[April 6]], [[1999]] || 68.75% || 29.46% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1195&year=1999 April 7, 1999]
|-
| [[March 1]], [[1999]] || 66.90% || 31.21% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1198&year=1999 March 2, 1999]
|-
| [[February 8]], [[1999]] || 64.60% || 33.43% || || [http://www.websidestory.com/company/news-events/press-releases/view-release.html?id=1120&year=2001 February 22, 2001]
|-
! Date
! [[Internet Explorer]]
! [[Netscape (web browser)|Netscape]] / [[Mozilla Application Suite|Mozilla]]
! [[Mozilla Firefox|Firefox]]
! Source
|}


The ability to quickly mediate global changes is also apparent in the rapid expression of noncoding repetitive sequences. The short interspersed nuclear ([[SINE]]) [[Alu sequence|Alu elements]] in humans and analogous B1 and B2 elements in mice have succeeded in becoming the most abundant mobile elements within the genomes, comprising ~10% of the human and ~6% of the mouse genome, respectively ([[#ref11237011|Lander 2001]]; [[#ref12466850|Waterston 2002]]). These elements are transcribed as ncRNAs by [[RNA_polymerase_III|RNAP III]] in response to environmental stresses such as heat shock ([[#ref7784180|Liu 1995]]), where they then bind to RNAP II with high affinity and prevent the formation of active pre-initiation complexes ([[#ref15565108|Allen 2004]]; [[#ref15300239|Espinoza 2004]]; [[#ref17307818|Espinoza 2007]]; [[#ref18313387|Mariner 2008]]). This allows for the broad and rapid repression of gene expression in response to stress ([[#ref15565108|Allen 2004]]; [[#ref18313387|Mariner 2008]]).
==1998 and earlier==
===GVU WWW User Survey===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: [http://www.cc.gatech.edu/gvu/user_surveys/ GVU WWW User Survey]'''
|-
! style="width:18%" | Date
! [[Mosaic (web browser)|Mosaic]]
! [[Netscape Navigator]]
! [[Internet Explorer]]
! style="width:36%" | Source
|-
| October 1998 || || 64% || 32.2% || [http://www.cc.gatech.edu/gvu/user_surveys/survey-1998-10/graphs/technology/q41.htm Primary Browser in 12 Months]
|-
| April 1998 || || 70% || 22.7% || [http://www.cc.gatech.edu/gvu/user_surveys/survey-1998-04/graphs/technology/q15.htm Browser Expected to Use in 12 Months]
|-
| October 1997 || || 59.67% || 15.13% || [http://www.gvu.gatech.edu/user_surveys/survey-1997-10/graphs/technology/Browser_You_Expect_to_Use_in_12_Months.html Browser Expected to Use in 12 Months]
|-
| April 1997 || || 81.13% || 12.13% || [http://www.gvu.gatech.edu/user_surveys/survey-1997-04/graphs/use/Browser_You_Expect_to_Use_in_12_Months.html Browser Expected to Use in 12 Months]
|-
| October 1996 || || 80.45% || 12.18% || [http://www.cc.gatech.edu/gvu/user_surveys/survey-10-1996/graphs/use/Browser_You_Expect_To_Use_In_12_Months.html Browser Expected to Use in 12 Months]
|-
| April 1996 || || 89.36% || 3.76% || [http://www.cc.gatech.edu/gvu/user_surveys/survey-04-1996/graphs/use/intend_browser.html Browser Expected to Use in 12 Months]
|-
| April 1995 || 9% || 54% || || [http://berghel.net/col-edit/cybernautica/jan-feb96/pcai961.php Hal Berghel's Cybernautica - "A Web Monopoly"]
|-
| October 1994 || 68% || 18% || || [http://www.cc.gatech.edu/gvu/user_surveys/survey-09-1994/graphs/Browser.html Result Graph - Browser]
|-
| January 1994 || 97% || || || [http://www.cc.gatech.edu/gvu/user_surveys/survey-01-1994/graphs/results-general.html General Results Graphs]
|}


A dissection of the functional sequences within Alu RNA transcripts has drafted a modular structure analogous to the organization of domains in protein transcription factors ([[#ref18313380|Shamovsky 2008]]). The Alu RNA contains two ‘arms’, each of which may bind one RNAP II molecule, as well as two regulatory domains that are responsible for RNAP II transcriptional repression in vitro ([[#ref18313387|Mariner 2008]]). These two loosely-structured domains may even be concatenated to other ncRNAs such as B1 elements to impart their repressive role ([[#ref18313387|Mariner 2008]]). The abundance and distribution of Alu elements and similar repetitive elements throughout the mammalian genome may be partly due to these functional domains being co-opted into other long ncRNAs during evolution, with the presence of functional repeat sequence domains being a common characteristic of several known long ncRNAs including Kcnq1ot1, Xlsirt and Xist ([[#ref14505360|Mattick 2003]]; [[#ref18299392|Mohammad 2008]]; [[#ref11780141|Wutz 2002]]; [[#ref12676327|Zearfoss 2003]]).
===Dataquest===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: Dataquest'''
|-
! style="width:18%" | Date
! [[Internet Explorer]]
! [[Netscape Navigator]]
! style="width:36%" | Source
|-
| 1997 || 39.4% || 57.6% || rowspan="3" | [http://news.zdnet.com/2100-3513_22-996866.html Browser wars: High price, huge rewards]
|-
| 1996 || 20% || 73%
|-
| 1995 || 2.9% || 80.1%
|}


In addition to [[heat shock]], the expression of [[SINE]] elements (including Alu, B1 and B2 RNAs) increases during cellular stress such as viral infection ([[#ref2581137|Singh 1985]]) in some cancer cells ([[#ref15593371|Tang 2005]]) where they may similarly regulate global changes to gene expression. The ability of Alu and B2 RNA to bind directly to RNAP II provides a broad mechanism for to repress transcription ([[#ref15300239|Espinoza 2004]]; [[#ref18313387|Mariner 2008]]). Nevertheless, there are specific exceptions to this global response where Alu or B2 RNAs are not found at activated promoters of genes undergoing induction, such as the heat shock genes ([[#ref18313387|Mariner 2008]]). This additional hierarchy of regulation that exempts individual genes from the generalised repression also involves a long ncRNA, heat shock RNA-1 (HSR-1). HSR-1 is present in all cells in an inactive state, but upon stress is activated to induce the expression of heat shock genes ([[#ref17018852|Shamovsky 2006]]). This activation involves a conformational alteration to the structure of HSR-1 in response to rising temperatures, thereby permitting its interaction with the transcriptional activator HSF-1 that subsequently undergoes trimerisation and induces the expression of heat shock genes ([[#ref17018852|Shamovsky 2006]]). More broadly, these examples illustrate a regulatory circuit nested witin ncRNAs whereby Alu or B2 RNAs repress general gene expression, while other ncRNAs, such as HSR-1, activate the expression of specific genes.
===EWS Web Server at UIUC===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: [http://www.ews.uiuc.edu/bstats/latest.html EWS Web Server at UIUC]'''
|-
! style="width:18%" | Date
! [[Mosaic (web browser)|Mosaic]]
! [[Internet Explorer]]
! [[Netscape Navigator]]
! style="width:36%" | Source
|-
| Q4 1998 || || 50.43% || 46.87% || [http://www.ews.uiuc.edu/bstats/months/9810-month.html Oct 1998], [http://www.ews.uiuc.edu/bstats/months/9811-month.html Nov 1998], [http://www.ews.uiuc.edu/bstats/months/9812-month.html Dec 1998]
|-
| Q3 1998 || || 47.90% || 48.97% || [http://www.ews.uiuc.edu/bstats/months/9807-month.html Jul 1998], [http://www.ews.uiuc.edu/bstats/months/9808-month.html Aug 1998], [http://www.ews.uiuc.edu/bstats/months/9809-month.html Sep 1998]
|-
| Q2 1998 || || 43.17% || 53.57% || [http://www.ews.uiuc.edu/bstats/months/9804-month.html Apr 1998], [http://www.ews.uiuc.edu/bstats/months/9805-month.html May 1998], [http://www.ews.uiuc.edu/bstats/months/9806-month.html Jun 1998]
|-
| Q1 1998 || || 39.67% || 57.63% || [http://www.ews.uiuc.edu/bstats/months/9801-month.html Jan 1998], [http://www.ews.uiuc.edu/bstats/months/9802-month.html Feb 1998], [http://www.ews.uiuc.edu/bstats/months/9803-month.html Mar 1998]
|-
| Q4 1997 || || 35.53% || 62.23% || [http://www.ews.uiuc.edu/bstats/months/9710-month.html Oct 1997], [http://www.ews.uiuc.edu/bstats/months/9711-month.html Nov 1997], [http://www.ews.uiuc.edu/bstats/months/9712-month.html Dec 1997]
|-
| Q3 1997 || || 32.40% || 64.93% || [http://www.ews.uiuc.edu/bstats/months/9707-month.html Jul 1997], [http://www.ews.uiuc.edu/bstats/months/9708-month.html Aug 1997], [http://www.ews.uiuc.edu/bstats/months/9709-month.html Sep 1997]
|-
| Q2 1997 || 0.37% || 27.67% || 69.77% || [http://www.ews.uiuc.edu/bstats/months/9704-month.html Apr 1997], [http://www.ews.uiuc.edu/bstats/months/9705-month.html May 1997], [http://www.ews.uiuc.edu/bstats/months/9706-month.html Jun 1997]
|-
| Q1 1997 || 0.60% || 22.87% || 74.33% || [http://www.ews.uiuc.edu/bstats/months/9701-month.html Jan 1997], [http://www.ews.uiuc.edu/bstats/months/9702-month.html Feb 1997], [http://www.ews.uiuc.edu/bstats/months/9703-month.html Mar 1997]
|-
| Q4 1996 || 1.20% || 19.07% || 77.13% || [http://www.ews.uiuc.edu/bstats/months/9610-month.html Oct 1996], [http://www.ews.uiuc.edu/bstats/months/9611-month.html Nov 1996], [http://www.ews.uiuc.edu/bstats/months/9612-month.html Dec 1996]
|-
| Q3 1996 || 2.47% || 13.97% || 80.37% || [http://www.ews.uiuc.edu/bstats/months/9607-month.html Jul 1996], [http://www.ews.uiuc.edu/bstats/months/9608-month.html Aug 1996], [http://www.ews.uiuc.edu/bstats/months/9609-month.html Sep 1996]
|-
| Q2 1996 || 6.93% || 9.60% || 82.77% || [http://www.ews.uiuc.edu/bstats/months/9604-month.html Apr 1996], [http://www.ews.uiuc.edu/bstats/months/9605-month.html May 1996], [http://www.ews.uiuc.edu/bstats/months/9606-month.html Jun 1996]
|}


====Long ncRNA transcribed by RNA polymerase III====
===International Data Corporation===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: International Data Corporation'''
|-
! style="width:18%" | Date
! [[Internet Explorer]]
! [[Netscape Navigator]]
! style="width:36%" | Source
|-
| 1997 || 23% || 51% || rowspan="2" | [http://www.cnn.com/TECH/computing/9810/08/browser.idg/ Behind the numbers: Browser market share]
|-
| 1996 || 16% || 55%
|}


Many of the ncRNAs that interact with general transcription factors or RNAP II itself (including 7SK, Alu and B1 and B2 RNAs) are transcribed by RNAP III ([[#ref17977614|Dieci 2007]]), thereby decoupling the expression of these ncRNAs from the RNAP II transcriptional reaction they regulate. RNAP III also transcribes a number of additional novel ncRNAs, such as BC2, BC200 and some microRNAs and snoRNAs, in addition to the highly-expressed infrastructural ‘housekeeping’ ncRNA genes such as tRNAs, 5S rRNAs and snRNAs ([[#ref17977614|Dieci 2007]]). The existence of an RNAP III-dependent ncRNA transcriptome that regulates its RNAP II-dependent counterpart was supported by a recent study that described a novel set of ncRNAs transcribed by RNAP III with sequence homology to protein-coding genes. This prompted the authors to posit a ‘cogene/gene’ functional regulatory network ([[#ref17264081|Pagano 2007]]), showing that one of these ncRNAs, 21A, regulates the expression its antisense partner gene, [[CENPF|CENP-F]] in trans.
===ZD Market Intelligence===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: ZD Market Intelligence'''
|-
! style="width:18%" | Date
! [[Internet Explorer]]
! [[Netscape Navigator]]
! style="width:36%" | Source
|-
| January 1998 || 39% || 54% || rowspan="2" | [http://www.cnn.com/TECH/computing/9810/08/browser.idg/ Behind the numbers: Browser market share]
|-
| January 1997 || 21% || 63%
|}


===Long noncoding RNAs in post-transcriptional regulation===
===Zona Research===
{| class="wikitable" style="width: auto; table-layout: fixed;"
|+ '''Usage share data from: Zona Research'''
|-
! style="width:18%" | Date
! [[Internet Explorer]]
! [[Netscape Navigator]]
! style="width:36%" | Source
|-
| July 1998 || 45% || 54% || rowspan="3" | [http://www.cnn.com/TECH/computing/9810/08/browser.idg/ Behind the numbers: Browser market share]
|-
| September 1997 || 36% || 62%
|-
| January 1997 || 28% || 70%
|}


In addition to regulating transcription, ncRNAs also control various aspects of post-transcriptional mRNA processing. Similar to small regulatory RNAs such as microRNAs and snoRNAs, these functions often involve complementary base pairing with the target mRNA. The formation of RNA duplexes between complementary ncRNA and mRNA may mask key elements within the mRNA required to bind trans-acting factors, potentially effecting any step in post-transcriptional gene expression including pre-mRNA processing and splicing, transport, translation, and degradation.
===AdKnowledge===

{| class="wikitable" style="width: auto; table-layout: fixed;"
====Long ncRNAs in splicing====
|+ '''Usage share data from: AdKnowledge'''

|-
The [[RNA splicing|splicing]] of mRNA can induce its translation and functionally diversify the repertoire of proteins it encodes. The [[ZEB2|Zeb2]] mRNA, which has a particularly long 5’UTR, requires the retention of a 5’UTR intron that contains an internal ribosome entry site for efficient translation ([[#ref18347095|Beltran 2008]]). However, retention of the intron is dependent on the expression of an antisense transcript that complements the intronic 5’ splice site ([[#ref18347095|Beltran 2008]]). Therefore, the ectopic expression of the antisense transcript represses splicing and induces translation of the Zeb2 mRNA during mesenchymal development. Similarly, the expression of an overlapping antisense Rev-ErbAα2 transcript controls the alternative splicing of the thyroid hormone receptor ErbAα2 mRNA to form two antagonistic isoforms ([[#ref1657988|Munroe 1991]]).
! style="width:18%" | Date

! [[Internet Explorer]]
====Long ncRNAs in translation====
! [[Netscape Navigator]]

! style="width:36%" | Source
NcRNA may also apply additional regulatory pressures during [[translation (biology)|translation]], a property particularly exploited in neurons where the dendritic or axonal translation of mRNA in response to synaptic activity contributes to changes in synaptic plasticity and the remodelling of neuronal networks. The RNAP III transcribed BC1 and BC200 ncRNAs, that previously derived from tRNAs, are expressed in the mouse and human central nervous system, respectively ([[#ref7684772|Tiedge 1993]]; [[#ref1706516|Tiedge 1991]]). BC1 expression is induced in response to synaptic activity and synaptogenesis and is specifically targeted to dendrites in neurons ([[#ref9647652|Muslimov 1998]]). Sequence complementarity between BC1 and regions of various neuron-specific mRNAs also suggest a role for BC1 in targeted translational repression ([[#ref16330711|Wang 2005]]). Indeed it was recently shown that BC1 is associated with translational repression in dendrites to control the efficiency of dopamine [[Dopamine receptor D2|D2]] receptor-mediated transmission in the [[striatum]] ([[#ref17699670|Centonze 2007]]) and BC1 RNA-deleted mice exhibit behavioural changes with reduced exploration and increased anxiety ([[#ref15302134|Lewejohann 2004]]).
|-

| June 1998 || 46% || 52% || rowspan="3" | [http://www.cnn.com/TECH/computing/9810/08/browser.idg/ Behind the numbers: Browser market share]
====Long ncRNAs in siRNA-directed gene regulation====
|-

| March 1998 || 42% || 57%
In addition to masking key elements within single-stranded RNA, the formation of double stranded RNA duplexes can also provide a substrate for the generation of endogenous siRNAs (endo-siRNAs) in Drosophila and mouse oocytes ([[#ref18691963|Golden 2008]]). The annealing of complementary sequences, such as antisense or repetitive regions between transcripts, forms a RNA duplex that may be processing by for Dicer-2 into endo-siRNAs. Alternatively, long ncRNAs that form extended intramolecular hairpins may also be processed into siRNAs, compellingly illustrated by the esi-1 and esi-2 transcripts ([[#ref18463631|Czech 2008]]). Endo-siRNAs generated from these transcripts seem particularly useful in suppressing the spread of mobile transposon elements within the genome in the germline. However, the generation of endo-siRNAs from antisense transcripts or pseudogenes may also silence the expression of their functional counterparts via RISC effector complexes, acting as an important node that integrates integrate various modes of long and short RNA regulation, as exemplified by the [[Xist]] and Tsix (see above) ([[#ref18535243|Ogawa 2008]]).
|-

| January 1998 || 36% || 61%
===Long ncRNAs in epigenetic regulation===
|}

Epigenetic modifications, including histone and DNA methylation, histone acetylation and sumolyation, affect many aspects of chromosomal biology, primarily including regulation of large numbers of genes by remodeling broad chromatin domains ([[#ref17304537|Kiefer 2007]]; [[#ref17603471|Mikkelsen]]). While it has been known for some time that RNA is an integral component of chromatin ([[#ref2911567|Nickerson]]; [[#ref18000552|Rodriguez-Campos 2007]]), it is only recently that we are beginning to appreciate the means by which RNA is involved in pathways of chromatin modification ([[#ref18555785|Chen]]; [[#ref17604720|Rinn]]; [[#ref16497925|Sanchez-Elsner]]).

In Drosophila, long ncRNAs induce the expression of the homeotic gene, Ubx, by recruiting and directing the chromatin modifying functions of the trithorax protein Ash1 to Hox regulatory elements ([[#ref16497925|Sanchez-Elsner]]). Similar models have been proposed in mammals, where strong epigenetic mechanisms are thought to underlie the embryonic expression profiles of the Hox genes that persist throughout human development ([[#ref17690303|Mazo]]; [[#ref17604720|Rinn]]). Indeed, the human Hox genes are associated with hundreds of ncRNAs that are sequentially expressed along both the spatial and temporal axes of human development and define chromatin domains of differential histone methylation and RNA polymerase accessibility ([[#ref17604720|Rinn]]). One ncRNA, termed HOTAIR, that originates from the HOXC locus represses transcription across 40 kb of the HOXD locus by altering chromatin trimethylation state. HOTAIR is thought to achieve this by directing the action of Polycomb chromatin remodeling complexes in trans to govern the cells epigenetic state and subsequent gene expression. Components of the Polycomb complex, including Suz12, EZH2 and EED, contain RNA binding domains that may potentially bind HOTAIR and probably other similar ncRNAs ([[#ref9742080|Denisenko]]; [[#ref16141073|Katayama 2005]]). This example nicely illustrates a broader theme whereby ncRNAs recruit the function of a generic suite of chromatin modifying proteins to specific genomic loci, underscoring the complexity of recently published genomic maps ([[#ref17603471|Mikkelsen]]). Indeed the prevalence of long ncRNAs associated with protein coding genes may contribute to localised patterns of chromatin modifications that regulate gene expression during development. For example, the majority of protein-coding genes have antisense partners, including many tumour suppressor genes that are frequently silenced by epigenetic mechanisms in cancer ([[#ref18185590|Yu]]). A recent study observed an inverse expression profile of the p15 gene and an antisense ncRNA in leukaemia ([[#ref18185590|Yu]]). A detailed analysis showed the p15 antisense ncRNA was able to induce changes to heterochromatin and DNA methylation status of p15 by an unknown mechanism, thereby regulating p15 expression ([[#ref18185590|Yu]]). Therefore misexpression of the associated antisense ncRNAs may subsequently silence the tumour suppressor gene contributing towards oncogenesis.

====Imprinting====

Many emergent themes of ncRNA-directed chromatin modification were first apparent within the phenomenon of imprinting, whereby only one allele of a gene is expressed from either the maternal or paternal chromosome. Imprinted genes are generally clustered together on chromosomes, suggesting the imprinting mechanism acts upon local chromosome domains rather than individual genes. These clusters are also often associated with long ncRNAs whose expression is correlated with the repression of the linked protein-coding gene on the same allele ([[#ref17445943|Pauler]]). Indeed, detailed analysis has revealed a crucial role for the ncRNAs Kcnqot1 and Igf2r/Air in directing imprinting ([[#ref16117633|Braidotti]]).

Almost all the genes at the Kcnq1 loci are maternally inherited, except the paternally expressed antisense ncRNA Kcnqot1 ([[#ref10369866|Mitsuya]]). Transgenic mice with truncated Kcnq1ot fail to silence the adjacent genes, suggesting that Kcnqot1 is crucial to the imprinting of genes on the paternal chromosome ([[#ref16702402|Mancini-Dinardo]]). It appears that Kcnqot1 is able to direct the trimethylation of lysine 9 (H3K9me3) and 27 of histone 3 (H3K27me3) to an imprinting centre that overlaps the Kcnqot1 promoter and actually resides within a Kcnq1 sense exon ([[#ref15516932|Umlauf]]). Similar to HOTAIR (see above), Eed-Ezh2 Polycomb complexes are recruited to the Kcnq1 loci paternal chromosome, possibly by Kcnqot1, where they may mediate gene silencing through repressive histone methylation ([[#ref15516932|Umlauf]]). A differentially methylated imprinting centre also overlaps the promoter of a long antisense ncRNA Air that is responsible for the silencing of neighbouring genes at the Igf2r locus on the paternal chromosome ([[#ref11845212|Sleutels]]; [[#ref11562346|Zwart]]). The presence of allele-specific histone methylation at the Igf2r locus suggests Air also mediates silencing via chromatin modification ([[#ref12456662|Fournier]]).

====Xist and X-chromosome inactivation====

The inactivation of a X-chromosome in female placental mammals is directed by one of the earliest and best characterized long ncRNAs, Xist ([[#ref17869504|Wutz 2007]]). The expression of Xist from the future inactive X-chromosome, and its subsequent coating of the inactive X-chromosome, occurs during early embryonic stem cell differentiation. Xist expression is followed by irreversible layers of chromatin modifications that include the loss of the histone (H3K9) acetylation and H3K4 methylation that are associated with active chromatin, and the induction of repressive chromatin modifications including H4 hypoacetylation, H3K27 trimethylation ([[#ref17869504|Wutz 2007]]), H3K9 hypermethylation and H4K20 monomethylation as well as H2AK119 monoubiquitylation. These modifications coincide with the transcriptional silencing of the X-linked genes ([[#ref14749728|Morey]]). Xist RNA also localises the histone variant macroH2A to the inactive X–chromosome ([[#ref9634239|Costanzi 1998]]). There are additional ncRNAs that are also present at the Xist loci, including an antisense transcript Tsix, which is expressed from the future active chromosome and able to repress Xist expression by the generation of endogenous siRNA ([[#ref18535243|Ogawa]]). Together these ncRNAs ensure that only one X-chromosome is active in female mammals.

====Telomeric noncoding RNAs====

Telomeres form the terminal region of mammalian chromosomes and are essential for stability and aging and play central roles in diseases such as cancer ([[#ref17876321|Blasco 2007]]). Telomeres have been long considered transcriptionally inert DNA-protein complexes until it was recently shown that telomeric repeats may be transcribed as telomeric RNAs (TelRNAs) ([[#ref18157120|Schoeftner 2008]]) or telomeric repeat-containing RNAs ([[#ref17916692|Azzalin]]). These ncRNAs are heterogenous in length, transcribed from several sub-telomeric loci and physically localise to telomeres. Their association with chromatin, which suggests an involvement in regulating telomere specific heterochromatin modifications, is repressed by SMG proteins that protect chromosome ends from telomere loss ([[#ref17916692|Azzalin]]). In addition, TelRNAs block telomerase activity in vitro and may therefore regulate telomerase activity ([[#ref18157120|Schoeftner 2008]]). Although early, these studies suggest an involvement for telomeric ncRNAs in various aspects of telomere biology.

== Long noncoding RNAs in disease ==

Recent recognition that long ncRNAs function in various aspects of cell biology has focused increasing attention on their potential to contribute towards disease aetiology. A handful of studies have implicated long ncRNAs in a variety of disease states and support an involvement and co-operation in oncogenesis.

While many association studies have identified long ncRNAs that are aberrantly expressed in disease states, we have little understanding of their contribution within disease etiology. Expression analyses that compare tumor cells and normal cells have revealed changes in the expression of ncRNAs in several forms of cancer. For example, the ncRNA OCC-1 (overexpressed in colon carcinoma-1) is overexpressed in colon carcinoma cells ([[#ref11890990|Pibouin]]). Similarly, in prostate tumours, one of two overexpressed ncRNAs, PCGEM1, is correlated with increased proliferation and colony formation suggesting an involvement in regulating cell growth ([[#ref16569192|Fu]]). NEAT2 was originally identified as an abundantly expressed ncRNA that is upregulated during metastasis of early-stage non-small cell lung cancer and its overexpression is an early prognostic marker for poor patient survival rates ([[#ref16569192|Fu]]). More recently, the highly conserved mouse homologue of NEAT2 was found to be highly expressed in hepatocellular carcinoma ([[#ref16878148|Lin]]). Despite a number of long ncRNAs having aberrant expression in cancer, their function and potential role in tumourogenesis is relatively unknown. For example, the ncRNAs HIS-1 and BIC have been implicated in oncogenesis and growth control, but their function in normal cells is unknown ([[#ref15738415|Eis]]; [[#ref9094986|Li]]). In addition to cancer, ncRNAs also exhibit aberrant expression in other disease states. Overexpression of PRINS is associated with psoriasis susceptibility, with PRINS expression being elevated in the uninvolved epidermis of psoriatic patients compared with both psoriatic lesions and healthy epidermis ([[#ref15855153|Sonkoly]]).

Genome-wide profiling revealed that many transcribed noncoding ultraconserved regions exhibit distinct profiles in various human cancer states ([[#ref17785203|Calin]]). An analysis of chronic lymphocytic leukaemia, colorectal carcinoma and hepatocellular carcinoma found that all three cancers exhibited aberrant expression profiles for ultraconserved ncRNAs relative to normal cells. Further analysis of one ultraconserved ncRNA suggested it behaved like an oncogene by mitigating apoptosis and subsequently expanding the number of malignant cells in colorectal cancers ([[#ref17785203|Calin]]). Many of these transcribed ultraconserved sites that exhibit distinct signatures in cancer are found at fragile sites and genomic regions associated with cancer. It seems likely that the aberrant expression of these ultraconserved ncRNAs within malignant processes results from important functions they fulfil in normal human development.

Recently a number of association studies examining single nucleotide polymorphisms (SNPs) associated with disease states have been mapped to long ncRNAs. For example, SNPs that identified a susceptibility locus for myocardial infarction mapped to a long ncRNA, MIAT (myocardial infarction associated transcript) ([[#ref17066261|Ishii]]). Similarly, genome-wide association studies identified a region associated with coronary artery disease ([[#ref17440112|Pasmant]]) that encompassed a long ncRNA, ANRIL that associates with a high-risk haplotype for coronary artery disease and is expressed in tissues and cell types affected by atherosclerosis ([[#ref17440112|Pasmant]]).

The complexity of the transcriptome, and our evolving understanding of its structure may inform a reinterpretation of the functional basis for many natural polymorphisms associated with disease states. Many SNPs associated with certain disease conditions are found within noncoding regions and the complex networks of noncoding transcription within these regions make it particularly difficult to elucidate the functional effects of polymorphisms. For example, a SNP both within the truncated form of ZFAT and the promoter of an antisense transcript increases the expression of ZFAT not through increasing the mRNA stability, but rather by repressing the expression of the antisense transcript ([[#ref15294872|Shirasawa]]).

The ability of long ncRNAs in regulating associated protein-coding genes may contribute towards disease if the long ncRNAs misexpression deregulates a protein coding genes with clinical significance. Similarly, an antisense long ncRNA that regulates the expression of the sense BACE1 gene, a crucial enzyme in Alzheimer’s disease etiology, exhibits elevated expression in several regions of the brain in individuals with Alzheimer's disease ([[#ref18587408|Faghihi]]). Alteration of the expression of ncRNAs may also mediate changes at an epigenetic level to effect gene expression and contribute to disease aetiology. For example, the induction of an antisense transcript by a genetic mutation led to the DNA methylation and silencing of sense genes, causing β-thalassemia in a patient ([[#ref12730694|Tufarelli]]).


==See also==
*[[Usage share of desktop operating systems]]
*[[Web browser]]
*[[Layout engine]]
*[[Market share]]
*[[Browser wars]]


==References==
==References==
<div class="references-small">
{{reflist}}


*<cite id=ref15565108>{{cite journal |author=Allen E, Xie Z, Gustafson AM, Sung GH, Spatafora JW and Carrington JC |title=Evolution of microRNA genes by inverted duplication of target gene sequences in Arabidopsis thaliana |journal=Nat Genet|volume=36 |issue=12 |pages=1282-90 |year=2004 |pmid=15565108 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15565108 }}</cite>
==External links==
*<cite id=ref17916692>{{cite journal |author=Azzalin CM, Reichenbach P, Khoriauli L, Giulotto E and Lingner J |title=Telomeric repeat containing RNA and RNA surveillance factors at mammalian chromosome ends |journal=Science|volume=318 |issue=5851 |pages=798-801 |year=2007 |pmid=17916692 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17916692 }}</cite>
*[http://upsdell.com/BrowserNews/stat.htm Chuck Upsdell's Browser Stats] lists web stats from many different stats sources and gives the approximate current usage share of the most popular layout engines.
*<cite id=ref18347095>{{cite journal |author=Beltran M, Puig I, Pena C, Garcia JM, Alvarez AB, Pena R, Bonilla F and de Herreros AG |title=A natural antisense transcript regulates Zeb2/Sip1 gene expression during Snail1-induced epithelial-mesenchymal transition |journal=Genes Dev|volume=22 |issue=6 |pages=756-69 |year=2008 |pmid=18347095 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18347095 }}</cite>
*[http://www.w3schools.com/browsers/browsers_stats.asp W3Schools' Browser Statistics] lists the web stats only from the W3 Schools site, which gives the approximate usage share of browsers among "people with an interest for web technologies."
*<cite id=ref15965474>{{cite journal |author=Bentwich I, Avniel A, Karov Y, Aharonov R, Gilad S, Barad O, Barzilai A, Einat P, Einav U, Meiri E, et al. |title=Identification of hundreds of conserved and nonconserved human microRNAs |journal=Nat Genet|volume=37 |issue=7 |pages=766-70 |year=2005 |pmid=15965474 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15965474 }}</cite>
*<cite id=ref17571346>{{cite journal |author=Birney E, Stamatoyannopoulos JA, Dutta A, Guigo R, Gingeras TR, Margulies EH, Weng Z, Snyder M, Dermitzakis ET, Thurman RE, et al. |title=Identification and analysis of functional elements in 1% of the human genome by the ENCODE pilot project |journal=Nature|volume=447 |issue=7146 |pages=799-816 |year=2007 |pmid=17571346 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17571346 }}</cite>
*<cite id=ref17876321>{{cite journal |author=Blasco MA |title=Telomere length, stem cells and aging |journal=Nat Chem Biol|volume=3 |issue=10 |pages=640-9 |year=2007 |pmid=17876321 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17876321 }}</cite>
*<cite id=ref16117633>{{cite journal |author=Braidotti G, Baubec T, Pauler F, Seidl C, Smrzka O, Stricker S, Yotova I and Barlow DP |title=The Air noncoding RNA: an imprinted cis-silencing transcript |journal=Cold Spring Harb Symp Quant Biol|volume=69 |pages=55-66 |year=2004 |pmid=16117633 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16117633 }}</cite>
*<cite id=ref15851065>{{cite journal |author=Brosius J |title=Waste not, want not--transcript excess in multicellular eukaryotes |journal=Trends Genet|volume=21 |issue=5 |pages=287-8 |year=2005 |pmid=15851065 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15851065 }}</cite>
*<cite id=ref17785203>{{cite journal |author=Calin GA, Liu CG, Ferracin M, Hyslop T, Spizzo R, Sevignani C, Fabbri M, Cimmino A, Lee EJ, Wojcik SE, et al. |title=Ultraconserved regions encoding ncRNAs are altered in human leukemias and carcinomas |journal=Cancer Cell|volume=12 |issue=3 |pages=215-29 |year=2007 |pmid=17785203 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17785203 }}</cite>
*<cite id=ref16141072>{{cite journal |author=Carninci P, Kasukawa T, Katayama S, Gough J, Frith MC, Maeda N, Oyama R, Ravasi T, Lenhard B, Wells C, et al. |title=The transcriptional landscape of the mammalian genome |journal=Science|volume=309 |issue=5740 |pages=1559-63 |year=2005 |pmid=16141072 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16141072 }}</cite>
*<cite id=ref17699670>{{cite journal |author=Centonze D, Rossi S, Napoli I, Mercaldo V, Lacoux C, Ferrari F, Ciotti MT, De Chiara V, Prosperetti C, Maccarrone M, et al. |title=The brain cytoplasmic RNA BC1 regulates dopamine D2 receptor-mediated transmission in the striatum |journal=J Neurosci|volume=27 |issue=33 |pages=8885-92 |year=2007 |pmid=17699670 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17699670 }}</cite>
*<cite id=ref18555785>{{cite journal |author=Chen X, Xu H, Yuan P, Fang F, Huss M, Vega VB, Wong E, Orlov YL, Zhang W, Jiang J, et al. |title=Integration of external signaling pathways with the core transcriptional network in embryonic stem cells |journal=Cell|volume=133 |issue=6 |pages=1106-17 |year=2008 |pmid=18555785 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18555785 }}</cite>
*<cite id=ref15790807>{{cite journal |author=Cheng J, Kapranov P, Drenkow J, Dike S, Brubaker S, Patel S, Long J, Stern D, Tammana H, Helt G, et al. |title=Transcriptional maps of 10 human chromosomes at 5-nucleotide resolution |journal=Science|volume=308 |issue=5725 |pages=1149-54 |year=2005 |pmid=15790807 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15790807 }}</cite>
*<cite id=ref9634239>{{cite journal |author=Costanzi C and Pehrson JR |title=Histone macroH2A1 is concentrated in the inactive X chromosome of female mammals |journal=Nature|volume=393 |issue=6685 |pages=599-601 |year=1998 |pmid=9634239 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=9634239 }}</cite>
*<cite id=ref18463631>{{cite journal |author=Czech B, Malone CD, Zhou R, Stark A, Schlingeheyde C, Dus M, Perrimon N, Kellis M, Wohlschlegel JA, Sachidanandam R, et al. |title=An endogenous small interfering RNA pathway in Drosophila |journal=Nature|volume=453 |issue=7196 |pages=798-802 |year=2008 |pmid=18463631 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18463631 }}</cite>
*<cite id=ref9742080>{{cite journal |author=Denisenko O, Shnyreva M, Suzuki H and Bomsztyk K |title=Point mutations in the WD40 domain of Eed block its interaction with Ezh2 |journal=Mol Cell Biol|volume=18 |issue=10 |pages=5634-42 |year=1998 |pmid=9742080 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=9742080 }}</cite>
*<cite id=ref17977614>{{cite journal |author=Dieci G, Fiorino G, Castelnuovo M, Teichmann M and Pagano A |title=The expanding RNA polymerase III transcriptome |journal=Trends Genet|volume=23 |issue=12 |pages=614-22 |year=2007 |pmid=17977614 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17977614 }}</cite>
*<cite id=ref15738415>{{cite journal |author=Eis PS, Tam W, Sun L, Chadburn A, Li Z, Gomez MF, Lund E and Dahlberg JE |title=Accumulation of miR-155 and BIC RNA in human B cell lymphomas |journal=Proc Natl Acad Sci U S A|volume=102 |issue=10 |pages=3627-32 |year=2005 |pmid=15738415 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15738415 }}</cite>
*<cite id=ref15300239>{{cite journal |author=Espinoza CA, Allen TA, Hieb AR, Kugel JF and Goodrich JA |title=B2 RNA binds directly to RNA polymerase II to repress transcript synthesis |journal=Nat Struct Mol Biol|volume=11 |issue=9 |pages=822-9 |year=2004 |pmid=15300239 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15300239 }}</cite>
*<cite id=ref17307818>{{cite journal |author=Espinoza CA, Goodrich JA and Kugel JF |title=Characterization of the structure, function, and mechanism of B2 RNA, an ncRNA repressor of RNA polymerase II transcription |journal=Rna|volume=13 |issue=4 |pages=583-96 |year=2007 |pmid=17307818 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17307818 }}</cite>
*<cite id=ref18587408>{{cite journal |author=Faghihi MA, Modarresi F, Khalil AM, Wood DE, Sahagan BG, Morgan TE, Finch CE, St Laurent G, 3rd, Kenny PJ and Wahlestedt C |title=Expression of a noncoding RNA is elevated in Alzheimer's disease and drives rapid feed-forward regulation of beta-secretase |journal=Nat Med|volume=14 |issue=7 |pages=723-30 |year=2008 |pmid=18587408 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18587408 }}</cite>
*<cite id=ref16705037>{{cite journal |author=Feng J, Bi C, Clark BS, Mady R, Shah P and Kohtz JD |title=The Evf-2 noncoding RNA is transcribed from the Dlx-5/6 ultraconserved region and functions as a Dlx-2 transcriptional coactivator |journal=Genes Dev|volume=20 |issue=11 |pages=1470-84 |year=2006 |pmid=16705037 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16705037 }}</cite>
*<cite id=ref12456662>{{cite journal |author=Fournier C, Goto Y, Ballestar E, Delaval K, Hever AM, Esteller M and Feil R |title=Allele-specific histone lysine methylation marks regulatory regions at imprinted mouse genes |journal=Embo J|volume=21 |issue=23 |pages=6560-70 |year=2002 |pmid=12456662 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12456662 }}</cite>
*<cite id=ref16569192>{{cite journal |author=Fu X, Ravindranath L, Tran N, Petrovics G and Srivastava S |title=Regulation of apoptosis by a prostate-specific and prostate cancer-associated noncoding gene, PCGEM1 |journal=DNA Cell Biol|volume=25 |issue=3 |pages=135-41 |year=2006 |pmid=16569192 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16569192 }}</cite>
*<cite id=ref18691963>{{cite journal |author=Golden DE, Gerbasi VR and Sontheimer EJ |title=An inside job for siRNAs |journal=Mol Cell|volume=31 |issue=3 |pages=309-12 |year=2008 |pmid=18691963 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18691963 }}</cite>
*<cite id=ref16723972>{{cite journal |author=Goodrich JA and Kugel JF |title=Non-coding-RNA regulators of RNA polymerase II transcription |journal=Nat Rev Mol Cell Biol|volume=7 |issue=8 |pages=612-6 |year=2006 |pmid=16723972 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16723972 }}</cite>
*<cite id=ref17066261>{{cite journal |author=Ishii N, Ozaki K, Sato H, Mizuno H, Saito S, Takahashi A, Miyamoto Y, Ikegawa S, Kamatani N, Hori M, et al. |title=Identification of a novel non-coding RNA, MIAT, that confers risk of myocardial infarction |journal=J Hum Genet|volume=51 |issue=12 |pages=1087-99 |year=2006 |pmid=17066261 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17066261 }}</cite>
*<cite id=ref17510325>{{cite journal |author=Kapranov P, Cheng J, Dike S, Nix DA, Duttagupta R, Willingham AT, Stadler PF, Hertel J, Hackermuller J, Hofacker IL, et al. |title=RNA maps reveal new RNA classes and a possible function for pervasive transcription |journal=Science|volume=316 |issue=5830 |pages=1484-8 |year=2007 |pmid=17510325 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17510325 }}</cite>
*<cite id=ref17486121>{{cite journal |author=Kapranov P, Willingham AT and Gingeras TR |title=Genome-wide transcription and the implications for genomic organization |journal=Nat Rev Genet|volume=8 |issue=6 |pages=413-23 |year=2007 |pmid=17486121 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17486121 }}</cite>
*<cite id=ref16141073>{{cite journal |author=Katayama S, Tomaru Y, Kasukawa T, Waki K, Nakanishi M, Nakamura M, Nishida H, Yap CC, Suzuki M, Kawai J, et al. |title=Antisense transcription in the mammalian transcriptome |journal=Science|volume=309 |issue=5740 |pages=1564-6 |year=2005 |pmid=16141073 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16141073 }}</cite>
*<cite id=ref17304537>{{cite journal |author=Kiefer JC |title=Epigenetics in development |journal=Dev Dyn|volume=236 |issue=4 |pages=1144-56 |year=2007 |pmid=17304537 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17304537 }}</cite>
*<cite id=ref12389039>{{cite journal |author=Kwek KY, Murphy S, Furger A, Thomas B, O'Gorman W, Kimura H, Proudfoot NJ and Akoulitchev A |title=U1 snRNA associates with TFIIH and regulates transcriptional initiation |journal=Nat Struct Biol|volume=9 |issue=11 |pages=800-5 |year=2002 |pmid=12389039 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12389039 }}</cite>
*<cite id=ref11237011>{{cite journal |author=Lander ES, Linton LM, Birren B, Nusbaum C, Zody MC, Baldwin J, Devon K, Dewar K, Doyle M, FitzHugh W, et al. |title=Initial sequencing and analysis of the human genome |journal=Nature|volume=409 |issue=6822 |pages=860-921 |year=2001 |pmid=11237011 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11237011 }}</cite>
*<cite id=ref2434928>{{cite journal |author=Lee JS, Burkholder GD, Latimer LJ, Haug BL and Braun RP |title=A monoclonal antibody to triplex DNA binds to eucaryotic chromosomes |journal=Nucleic Acids Res|volume=15 |issue=3 |pages=1047-61 |year=1987 |pmid=2434928 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2434928 }}</cite>
*<cite id=ref15302134>{{cite journal |author=Lewejohann L, Skryabin BV, Sachser N, Prehn C, Heiduschka P, Thanos S, Jordan U, Dell'Omo G, Vyssotski AL, Pleskacheva MG, et al. |title=Role of a neuronal small non-messenger RNA: behavioural alterations in BC1 RNA-deleted mice |journal=Behav Brain Res|volume=154 |issue=1 |pages=273-89 |year=2004 |pmid=15302134 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15302134 }}</cite>
*<cite id=ref9094986>{{cite journal |author=Li J, Witte DP, Van Dyke T and Askew DS |title=Expression of the putative proto-oncogene His-1 in normal and neoplastic tissues |journal=Am J Pathol|volume=150 |issue=4 |pages=1297-305 |year=1997 |pmid=9094986 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=9094986 }}</cite>
*<cite id=ref16878148>{{cite journal |author=Lin R, Maeda S, Liu C, Karin M and Edgington TS |title=A large noncoding RNA is a marker for murine hepatocellular carcinomas and a spectrum of human carcinomas |journal=Oncogene|volume=26 |issue=6 |pages=851-8 |year=2007 |pmid=16878148 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16878148 }}</cite>
*<cite id=ref7784180>{{cite journal |author=Liu WM, Chu WM, Choudary PV and Schmid CW |title=Cell stress and translational inhibitors transiently increase the abundance of mammalian SINE transcripts |journal=Nucleic Acids Res|volume=23 |issue=10 |pages=1758-65 |year=1995 |pmid=7784180 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=7784180 }}</cite>
*<cite id=ref16702402>{{cite journal |author=Mancini-Dinardo D, Steele SJ, Levorse JM, Ingram RS and Tilghman SM |title=Elongation of the Kcnq1ot1 transcript is required for genomic imprinting of neighboring genes |journal=Genes Dev|volume=20 |issue=10 |pages=1268-82 |year=2006 |pmid=16702402 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16702402 }}</cite>
*<cite id=ref18313387>{{cite journal |author=Mariner PD, Walters RD, Espinoza CA, Drullinger LF, Wagner SD, Kugel JF and Goodrich JA |title=Human Alu RNA is a modular transacting repressor of mRNA transcription during heat shock |journal=Mol Cell|volume=29 |issue=4 |pages=499-509 |year=2008 |pmid=18313387 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18313387 }}</cite>
*<cite id=ref17237763>{{cite journal |author=Martianov I, Ramadass A, Serra Barros A, Chow N and Akoulitchev A |title=Repression of the human dihydrofolate reductase gene by a non-coding interfering transcript |journal=Nature|volume=445 |issue=7128 |pages=666-70 |year=2007 |pmid=17237763 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17237763 }}</cite>
*<cite id=ref14505360>{{cite journal |author=Mattick JS |title=Challenging the dogma: the hidden layer of non-protein-coding RNAs in complex organisms |journal=Bioessays|volume=25 |issue=10 |pages=930-9 |year=2003 |pmid=14505360 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=14505360 }}</cite>
*<cite id=ref17690303>{{cite journal |author=Mazo A, Hodgson JW, Petruk S, Sedkov Y and Brock HW |title=Transcriptional interference: an unexpected layer of complexity in gene regulation |journal=J Cell Sci|volume=120 |issue=Pt 16 |pages=2755-61 |year=2007 |pmid=17690303 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17690303 }}</cite>
*<cite id=ref17603471>{{cite journal |author=Mikkelsen TS, Ku M, Jaffe DB, Issac B, Lieberman E, Giannoukos G, Alvarez P, Brockman W, Kim TK, Koche RP, et al. |title=Genome-wide maps of chromatin state in pluripotent and lineage-committed cells |journal=Nature|volume=|year=2007 |pmid=17603471 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17603471 }}</cite>
*<cite id=ref10369866>{{cite journal |author=Mitsuya K, Meguro M, Lee MP, Katoh M, Schulz TC, Kugoh H, Yoshida MA, Niikawa N, Feinberg AP and Oshimura M |title=LIT1, an imprinted antisense RNA in the human KvLQT1 locus identified by screening for differentially expressed transcripts using monochromosomal hybrids |journal=Hum Mol Genet|volume=8 |issue=7 |pages=1209-17 |year=1999 |pmid=10369866 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=10369866 }}</cite>
*<cite id=ref18299392>{{cite journal |author=Mohammad F, Pandey RR, Nagano T, Chakalova L, Mondal T, Fraser P and Kanduri C |title=Kcnq1ot1/Lit1 noncoding RNA mediates transcriptional silencing by targeting to the perinucleolar region |journal=Mol Cell Biol|volume=28 |issue=11 |pages=3713-28 |year=2008 |pmid=18299392 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18299392 }}</cite>
*<cite id=ref14749728>{{cite journal |author=Morey C, Navarro P, Debrand E, Avner P, Rougeulle C and Clerc P |title=The region 3' to Xist mediates X chromosome counting and H3 Lys-4 dimethylation within the Xist gene |journal=Embo J|volume=23 |issue=3 |pages=594-604 |year=2004 |pmid=14749728 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=14749728 }}</cite>
*<cite id=ref1657988>{{cite journal |author=Munroe SH and Lazar MA |title=Inhibition of c-erbA mRNA splicing by a naturally occurring antisense RNA |journal=J Biol Chem|volume=266 |issue=33 |pages=22083-6 |year=1991 |pmid=1657988 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=1657988 }}</cite>
*<cite id=ref9647652>{{cite journal |author=Muslimov IA, Banker G, Brosius J and Tiedge H |title=Activity-dependent regulation of dendritic BC1 RNA in hippocampal neurons in culture |journal=J Cell Biol|volume=141 |issue=7 |pages=1601-11 |year=1998 |pmid=9647652 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=9647652 }}</cite>
*<cite id=ref11437441>{{cite journal |author=Nesterova TB, Barton SC, Surani MA and Brockdorff N |title=Loss of Xist imprinting in diploid parthenogenetic preimplantation embryos |journal=Dev Biol|volume=235 |issue=2 |pages=343-50 |year=2001 |pmid=11437441 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11437441 }}</cite>
*<cite id=ref2911567>{{cite journal |author=Nickerson JA, Krochmalnic G, Wan KM and Penman S |title=Chromatin architecture and nuclear RNA |journal=Proc Natl Acad Sci U S A|volume=86 |issue=1 |pages=177-81 |year=1989 |pmid=2911567 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2911567 }}</cite>
*<cite id=ref18535243>{{cite journal |author=Ogawa Y, Sun BK and Lee JT |title=Intersection of the RNA interference and X-inactivation pathways |journal=Science|volume=320 |issue=5881 |pages=1336-41 |year=2008 |pmid=18535243 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18535243 }}</cite>
*<cite id=ref17264081>{{cite journal |author=Pagano JM, Farley BM, McCoig LM and Ryder SP |title=Molecular basis of RNA recognition by the embryonic polarity determinant MEX-5 |journal=J Biol Chem|volume=282 |issue=12 |pages=8883-94 |year=2007 |pmid=17264081 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17264081 }}</cite>
*<cite id=ref16290135>{{cite journal |author=Pang KC, Frith MC and Mattick JS |title=Rapid evolution of noncoding RNAs: lack of conservation does not mean lack of function |journal=Trends Genet|volume=22 |issue=1 |pages=1-5 |year=2006 |pmid=16290135 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16290135 }}</cite>
*<cite id=ref12223397>{{cite journal |author=Panganiban G and Rubenstein JL |title=Developmental functions of the Distal-less/Dlx homeobox genes |journal=Development|volume=129 |issue=19 |pages=4371-86 |year=2002 |pmid=12223397 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12223397 }}</cite>
*<cite id=ref17440112>{{cite journal |author=Pasmant E, Laurendeau I, Heron D, Vidaud M, Vidaud D and Bieche I |title=Characterization of a germ-line deletion, including the entire INK4/ARF locus, in a melanoma-neural system tumor family: identification of ANRIL, an antisense noncoding RNA whose expression coclusters with ARF |journal=Cancer Res|volume=67 |issue=8 |pages=3963-9 |year=2007 |pmid=17440112 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17440112 }}</cite>
*<cite id=ref17445943>{{cite journal |author=Pauler FM, Koerner MV and Barlow DP |title=Silencing by imprinted noncoding RNAs: is transcription the answer? |journal=Trends Genet|volume=23 |issue=6 |pages=284-92 |year=2007 |pmid=17445943 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17445943 }}</cite>
*<cite id=ref17086198>{{cite journal |author=Pennacchio LA, Ahituv N, Moses AM, Prabhakar S, Nobrega MA, Shoukry M, Minovitsky S, Dubchak I, Holt A, Lewis KD, et al. |title=In vivo enhancer analysis of human conserved non-coding sequences |journal=Nature|volume=444 |issue=7118 |pages=499-502 |year=2006 |pmid=17086198 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17086198 }}</cite>
*<cite id=ref11890990>{{cite journal |author=Pibouin L, Villaudy J, Ferbus D, Muleris M, Prosperi MT, Remvikos Y and Goubin G |title=Cloning of the mRNA of overexpression in colon carcinoma-1: a sequence overexpressed in a subset of colon carcinomas |journal=Cancer Genet Cytogenet|volume=133 |issue=1 |pages=55-60 |year=2002 |pmid=11890990 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11890990 }}</cite>
*<cite id=ref17040131>{{cite journal |author=Pollard KS, Salama SR, King B, Kern AD, Dreszer T, Katzman S, Siepel A, Pedersen JS, Bejerano G, Baertsch R, et al. |title=Forces shaping the fastest evolving regions in the human genome |journal=PLoS Genet|volume=2 |issue=10 |pages=e168 |year=2006 |pmid=17040131 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17040131 }}</cite>
*<cite id=ref16915236>{{cite journal |author=Pollard KS, Salama SR, Lambert N, Lambot MA, Coppens S, Pedersen JS, Katzman S, King B, Onodera C, Siepel A, et al. |title=An RNA gene expressed during cortical development evolved rapidly in humans |journal=Nature|volume=443 |issue=7108 |pages=167-72 |year=2006 |pmid=16915236 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16915236 }}</cite>
*<cite id=ref17387145>{{cite journal |author=Ponjavic J, Ponting CP and Lunter G |title=Functionality or transcriptional noise? Evidence for selection within long noncoding RNAs |journal=Genome Res|volume=|year=2007 |pmid=17387145 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17387145 }}</cite>
*<cite id=ref17604720>{{cite journal |author=Rinn JL, Kertesz M, Wang JK, Squazzo SL, Xu X, Brugmann SA, Goodnough LH, Helms JA, Farnham PJ, Segal E, et al. |title=Functional demarcation of active and silent chromatin domains in human HOX loci by noncoding RNAs |journal=Cell|volume=129 |issue=7 |pages=1311-23 |year=2007 |pmid=17604720 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17604720 }}</cite>
*<cite id=ref18000552>{{cite journal |author=Rodriguez-Campos A and Azorin F |title=RNA Is an Integral Component of Chromatin that Contributes to Its Structural Organization |journal=PLoS ONE|volume=2 |issue=11 |pages=e1182 |year=2007 |pmid=18000552 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18000552 }}</cite>
*<cite id=ref16497925>{{cite journal |author=Sanchez-Elsner T, Gou D, Kremmer E and Sauer F |title=Noncoding RNAs of trithorax response elements recruit Drosophila Ash1 to Ultrabithorax |journal=Science|volume=311 |issue=5764 |pages=1118-23 |year=2006 |pmid=16497925 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16497925 }}</cite>
*<cite id=ref18157120>{{cite journal |author=Schoeftner S and Blasco MA |title=Developmentally regulated transcription of mammalian telomeres by DNA-dependent RNA polymerase II |journal=Nat Cell Biol|volume=10 |issue=2 |pages=228-36 |year=2008 |pmid=18157120 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18157120 }}</cite>
*<cite id=ref17018852>{{cite journal |author=Shamovsky I and Nudler E |title=Gene control by large noncoding RNAs |journal=Sci STKE|volume=2006 |issue=355 |pages=pe40 |year=2006 |pmid=17018852 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17018852 }}</cite>
*<cite id=ref18313380>{{cite journal |author=Shamovsky I and Nudler E |title=Modular RNA heats up |journal=Mol Cell|volume=29 |issue=4 |pages=415-7 |year=2008 |pmid=18313380 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18313380 }}</cite>
*<cite id=ref15294872>{{cite journal |author=Shirasawa S, Harada H, Furugaki K, Akamizu T, Ishikawa N, Ito K, Ito K, Tamai H, Kuma K, Kubota S, et al. |title=SNPs in the promoter of a B cell-specific antisense transcript, SAS-ZFAT, determine susceptibility to autoimmune thyroid disease |journal=Hum Mol Genet|volume=13 |issue=19 |pages=2221-31 |year=2004 |pmid=15294872 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15294872 }}</cite>
*<cite id=ref16024819>{{cite journal |author=Siepel A, Bejerano G, Pedersen JS, Hinrichs AS, Hou M, Rosenbloom K, Clawson H, Spieth J, Hillier LW, Richards S, et al. |title=Evolutionarily conserved elements in vertebrate, insect, worm, and yeast genomes |journal=Genome Res|volume=15 |issue=8 |pages=1034-50 |year=2005 |pmid=16024819 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16024819 }}</cite>
*<cite id=ref2581137>{{cite journal |author=Singh K, Carey M, Saragosti S and Botchan M |title=Expression of enhanced levels of small RNA polymerase III transcripts encoded by the B2 repeats in simian virus 40-transformed mouse cells |journal=Nature|volume=314 |issue=6011 |pages=553-6 |year=1985 |pmid=2581137 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2581137 }}</cite>
*<cite id=ref11845212>{{cite journal |author=Sleutels F, Zwart R and Barlow DP |title=The non-coding Air RNA is required for silencing autosomal imprinted genes |journal=Nature|volume=415 |issue=6873 |pages=810-3 |year=2002 |pmid=11845212 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11845212 }}</cite>
*<cite id=ref15475259>{{cite journal |author=Smith NG, Brandstrom M and Ellegren H |title=Evidence for turnover of functional noncoding DNA in mammalian genome evolution |journal=Genomics|volume=84 |issue=5 |pages=806-13 |year=2004 |pmid=15475259 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15475259 }}</cite>
*<cite id=ref15855153>{{cite journal |author=Sonkoly E, Bata-Csorgo Z, Pivarcsi A, Polyanka H, Kenderessy-Szabo A, Molnar G, Szentpali K, Bari L, Megyeri K, Mandi Y, et al. |title=Identification and characterization of a novel, psoriasis susceptibility-related noncoding RNA gene, PRINS |journal=J Biol Chem|volume=280 |issue=25 |pages=24159-67 |year=2005 |pmid=15855153 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15855153 }}</cite>
*<cite id=ref17277804>{{cite journal |author=Struhl K |title=Transcriptional noise and the fidelity of initiation by RNA polymerase II |journal=Nat Struct Mol Biol|volume=14 |issue=2 |pages=103-5 |year=2007 |pmid=17277804 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17277804 }}</cite>
*<cite id=ref15593371>{{cite journal |author=Tang RB, Wang HY, Lu HY, Xiong J, Li HH, Qiu XH and Liu HQ |title=Increased level of polymerase III transcribed Alu RNA in hepatocellular carcinoma tissue |journal=Mol Carcinog|volume=42 |issue=2 |pages=93-6 |year=2005 |pmid=15593371 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15593371 }}</cite>
*<cite id=ref7684772>{{cite journal |author=Tiedge H, Chen W and Brosius J |title=Primary structure, neural-specific expression, and dendritic location of human BC200 RNA |journal=J Neurosci|volume=13 |issue=6 |pages=2382-90 |year=1993 |pmid=7684772 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=7684772 }}</cite>
*<cite id=ref1706516>{{cite journal |author=Tiedge H, Fremeau RT, Jr., Weinstock PH, Arancio O and Brosius J |title=Dendritic location of neural BC1 RNA |journal=Proc Natl Acad Sci U S A|volume=88 |issue=6 |pages=2093-7 |year=1991 |pmid=1706516 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=1706516 }}</cite>
*<cite id=ref16751343>{{cite journal |author=Torarinsson E, Sawera M, Havgaard JH, Fredholm M and Gorodkin J |title=Thousands of corresponding human and mouse genomic regions unalignable in primary sequence contain common RNA structure |journal=Genome Res|volume=16 |issue=7 |pages=885-9 |year=2006 |pmid=16751343 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16751343 }}</cite>
*<cite id=ref18096747>{{cite journal |author=Torarinsson E, Yao Z, Wiklund ED, Bramsen JB, Hansen C, Kjems J, Tommerup N, Ruzzo WL and Gorodkin J |title=Comparative genomics beyond sequence-based alignments: RNA structures in the ENCODE regions |journal=Genome Res|volume=18 |issue=2 |pages=242-51 |year=2008 |pmid=18096747 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18096747 }}</cite>
*<cite id=ref12730694>{{cite journal |author=Tufarelli C, Stanley JA, Garrick D, Sharpe JA, Ayyub H, Wood WG and Higgs DR |title=Transcription of antisense RNA leading to gene silencing and methylation as a novel cause of human genetic disease |journal=Nat Genet|volume=34 |issue=2 |pages=157-65 |year=2003 |pmid=12730694 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12730694 }}</cite>
*<cite id=ref15516932>{{cite journal |author=Umlauf D, Goto Y, Cao R, Cerqueira F, Wagschal A, Zhang Y and Feil R |title=Imprinting along the Kcnq1 domain on mouse chromosome 7 involves repressive histone methylation and recruitment of Polycomb group complexes |journal=Nat Genet|volume=36 |issue=12 |pages=1296-300 |year=2004 |pmid=15516932 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=15516932 }}</cite>
*<cite id=ref18176564>{{cite journal |author=Visel A, Prabhakar S, Akiyama JA, Shoukry M, Lewis KD, Holt A, Plajzer-Frick I, Afzal V, Rubin EM and Pennacchio LA |title=Ultraconservation identifies a small subset of extremely constrained developmental enhancers |journal=Nat Genet|volume=|year=2008 |pmid=18176564 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18176564 }}</cite>
*<cite id=ref16330711>{{cite journal |author=Wang H, Iacoangeli A, Lin D, Williams K, Denman RB, Hellen CU and Tiedge H |title=Dendritic BC1 RNA in translational control mechanisms |journal=J Cell Biol|volume=171 |issue=5 |pages=811-21 |year=2005 |pmid=16330711 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16330711 }}</cite>
*<cite id=ref18509338>{{cite journal |author=Wang X, Arai S, Song X, Reichart D, Du K, Pascual G, Tempst P, Rosenfeld MG, Glass CK and Kurokawa R |title=Induced ncRNAs allosterically modify RNA-binding proteins in cis to inhibit transcription |journal=Nature|volume=454 |issue=7200 |pages=126-30 |year=2008 |pmid=18509338 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18509338 }}</cite>
*<cite id=ref12466850>{{cite journal |author=Waterston RH, Lindblad-Toh K, Birney E, Rogers J, Abril JF, Agarwal P, Agarwala R, Ainscough R, Alexandersson M, An P, et al. |title=Initial sequencing and comparative analysis of the mouse genome |journal=Nature|volume=420 |issue=6915 |pages=520-62 |year=2002 |pmid=12466850 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12466850 }}</cite>
*<cite id=ref17869504>{{cite journal |author=Wutz A and Gribnau J |title=X inactivation Xplained |journal=Curr Opin Genet Dev|volume=17 |issue=5 |pages=387-93 |year=2007 |pmid=17869504 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=17869504 }}</cite>
*<cite id=ref11780141>{{cite journal |author=Wutz A, Rasmussen TP and Jaenisch R |title=Chromosomal silencing and localization are mediated by different domains of Xist RNA |journal=Nat Genet|volume=30 |issue=2 |pages=167-74 |year=2002 |pmid=11780141 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11780141 }}</cite>
*<cite id=ref11604515>{{cite journal |author=Yang S, Tutton S, Pierce E and Yoon K |title=Specific double-stranded RNA interference in undifferentiated mouse embryonic stem cells |journal=Mol Cell Biol|volume=21 |issue=22 |pages=7807-16 |year=2001 |pmid=11604515 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11604515 }}</cite>
*<cite id=ref14580347>{{cite journal |author=Yik JH, Chen R, Nishimura R, Jennings JL, Link AJ and Zhou Q |title=Inhibition of P-TEFb (CDK9/Cyclin T) kinase and RNA polymerase II transcription by the coordinated actions of HEXIM1 and 7SK snRNA |journal=Mol Cell|volume=12 |issue=4 |pages=971-82 |year=2003 |pmid=14580347 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=14580347 }}</cite>
*<cite id=ref18185590>{{cite journal |author=Yu W, Gius D, Onyango P, Muldoon-Jacobs K, Karp J, Feinberg AP and Cui H |title=Epigenetic silencing of tumour suppressor gene p15 by its antisense RNA |journal=Nature|volume=451 |issue=7175 |pages=202-6 |year=2008 |pmid=18185590 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=18185590 }}</cite>
*<cite id=ref12676327>{{cite journal |author=Zearfoss NR, Chan AP, Kloc M, Allen LH and Etkin LD |title=Identification of new Xlsirt family members in the Xenopus laevis oocyte |journal=Mech Dev|volume=120 |issue=4 |pages=503-9 |year=2003 |pmid=12676327 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=12676327 }}</cite>
*<cite id=ref11562346>{{cite journal |author=Zwart R, Sleutels F, Wutz A, Schinkel AH and Barlow DP |title=Bidirectional action of the Igf2r imprint control element on upstream and downstream imprinted genes |journal=Genes Dev|volume=15 |issue=18 |pages=2361-6 |year=2001 |pmid=11562346 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=11562346 }}</cite>


</div>
{{Web browsers}}


[[Category:Web browsers]]
[[Category:Usage share|Web browsers]]


[[Category:RNA]]
[[ms:Bahagian penggunaan pelayar web]]
[[Category:Non-coding RNA]]
[[ru:Доли веб-браузеров по использованию]]
[[zh:網頁瀏覽器的使用分佈]]

Revision as of 10:37, 11 October 2008

Long noncoding RNAs (long ncRNAs) are generally considered (somewhat arbitrarily) as non-protein coding transcripts longer than 200 nucleotides. This limit is due to practical considerations including the separation of RNAs in common experimental protocols. Additionally, this limit distinguishes long ncRNAs from small regulatory RNAs such as microRNAs (miRNAs), short interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), small nucleoloar RNAs (snoRNAs) etc.

Abundance of long ncRNAs

A recent study found only one fifth of transcription across the human genome is associated with protein-coding genes (Kapranov 2007), indicating at least four-times more long noncoding than coding RNA sequences. However, it is large-scale cDNA sequencing projects such as FANTOM (functional annotation of mouse cDNA) that reveal the complexity of this transcription (Carninci 2005). The FANTOM3 project identified ~35,000 noncoding transcripts from ~10,000 distinct loci that bear many signatures of mRNAs, including 5’capping, splicing and poly-adenylation, but have little or no open reading frame (Carninci 2005). While the abundance of long ncRNAs was unanticipated, this number nevertheless represents a conservative lower estimate since it omitted many singleton transcripts and non-polyadenylated transcripts (tiling array show more than 40% of transcripts are non-polyadenylated) (Cheng 2005). However, unambiguously identifying ncRNAs within these cDNA libraries is challenging since it can be difficult to distinguish protein-coding transcripts from noncoding transcripts.

Genomic organisation of long ncRNAs

The current landscape of the mammalian genome is described as numerous ‘foci’ of transcription that are separated by long stretches of intergenic space (Carninci 2005). While long ncRNAs are located and transcribed within the intergenic stretches, the majority are transcribed as complex, interlaced networks of overlapping sense and antisense transcripts that often includes protein-coding genes (Kapranov 2007). Genomic sequences within these transcriptional foci are often shared within a number of different coding and noncoding transcripts in the sense and antisense directions (Birney 2007) giving rise to a complex hierarchy of overlapping isoforms. For example, 3012 out of 8961 cDNAs previously annotated as truncated coding sequences within FANTOM2 were later designated as genuine ncRNA variants of protein-coding cDNAs (Carninci 2005). While the abundance and conservation of these interleaved arrangements suggest they have biological relevance, the complexity of these foci frustrates easy evaluation.

Conservation of long ncRNAs

Many small RNAs, such as microRNAs or snoRNAs, exhibit strong conservation across diverse species (Bentwich 2005). In contrast, long ncRNAs generally lack strong conservation which is often cited as evidence of non-functionality (Brosius 2005; Struhl 2007). However, many well-described long ncRNAs, such as Air and Xist, are poorly conserved (Nesterova 2001), suggesting that ncRNAs may be subject to different selection pressures (Pang 2006). Unlike mRNAs, which have to conserve the codon usage and prevent frameshift mutations in a single long ORF, selection may conserve only short regions of long ncRNAs that are constrained by structure or sequence-specific interactions. Therefore we may see selection act only over small regions of the long ncRNA transcript. Nevertheless, despite low conservation of long ncRNAs generally, it should be noted that many long ncRNAs still contain strongly conserved elements. For example 19% of highly conserved phastCons elements occur in known introns, and another 32% in unannotated regions (Siepel 2005). Furthermore, a representative set of human long ncRNAs exhibit small, yet significant, reductions in substitution and insertion/deletion rates indicative of purifying selection that conserve the integrity of the transcript at the levels of sequence, promoter and splicing (Ponjavic 2007).

The poor conservation of ncRNAs may be the result of recent and rapid adaptive selection. For instance, ncRNAs may be more pliant to evolutionary pressures than protein-coding genes, as evidenced by the existence of many lineage specific ncRNAs, such as Xist or Air (Pang 2006). Indeed, those conserved regions of the human genome that are subject to recent evolutionary change relative to the chimpanzee genome occurs mainly in noncoding regions, many of which are transcribed (Pollard 2006; Pollard 2006). This includes a ncRNA, HAR1, which has undergone rapid evolutionary change in humans and is specifically expressed in the Cajal-Retzious cells in the human neocortex (Pollard 2006). The observation that many functionally validated RNAs are evolving quickly (Pang 2006; Smith 2004), may result from these sequences having more plastic structure-function constraints, and we may expect a great deal of evolutionary innovation to occur in such sequences. This is supported by the existence of thousands of sequences in the mammalian genome that show poor conservation at the primary sequence level but have evidence of conserved RNA secondary structures (Torarinsson 2006; Torarinsson 2008).

Long ncRNA functions

Long ncRNAs in the regulation of gene transcription

Long ncRNAs in gene-specific transcription

In eukaryotes, RNA transcription is a tightly regulated process. NcRNAs can target different aspects of this process, targeting transcriptional activators or repressors, different components of the transcription reaction including RNA polymerase (RNAP) II and even the DNA duplex to regulate gene transcription and expression (Goodrich 2006). In combination these ncRNAs may comprise a regulatory network that, including transcription factors, finely control the gene expression in complex eukaryotes

NcRNAs modulate the function of transcription factors by several different mechanisms, including functioning itself as a co-regulator, modifying transcription factor activity, or by regulating the association and activity of co-regulators. For example, the ncRNA Evf-2 functions as a co-activator for the homeobox transcription factor Dlx2, which fulfils important roles in forebrain development and neurogenesis (Feng 2006; Panganiban 2002). Sonic hedgehog induces transcription of Evf-2 from an ultraconserved element located between the Dlx5 and Dlx6 genes during forebrain development (Feng 2006). Evf-2 then recruits the Dlx2 transcription factor to the same ultraconserved element whereby Dlx2 subsequently induces expression of Dlx5. The existence of other similar ultra- or highly conserved elements within the mammalian genome that are both transcribed and fulfil enhancer function suggest Evf-2 may be illustrative of a generalised mechanism that tightly regulates important developmental genes with complex expression patterns during vertebrate growth (Pennacchio 2006; Visel 2008). Indeed the transcription and expression of similar noncoding ultraconserved elements was recently shown to be abnormal in human leukaemia and contribute towards apoptosis in colon cancer cells, suggesting an involvement in tumorogenesis (Calin 2007).

Local ncRNAs can also recruit transcriptional programmes to regulate adjacent protein-coding gene expression. The RNA binding protein TLS, binds and inhibits the CREB-binding protein and p300 histone acetyltransferease activities on a repressed gene target, cyclin D1. The recruitment of TLS to the promoter of cyclin D1 was directed by lowly expressed long ncRNAs tethered to 5’ regulatory regions in response to DNA damage signals (Wang 2008). Moreover, these local ncRNAs act cooperatively as ligands to modulate the activities of TLS. More broadly, this mechanism allows the cell to harness RNA-binding proteins, which make up one of the largest classes within the mammalian proteome, and integrate their function in transcriptional programs.

Long ncRNAs regulating basal transcription machinery

NcRNAs also target general transcription factors required for the RNAP II transcription of all genes (Goodrich 2006). These general factors include components of the initiation complex that assemble on promoters or involved in transcription elongation. A ncRNA transcribed from an upstream minor promoter of the dihydrofolate reductase (DHFR) gene forms a stable RNA-DNA triplex within the major promoter of DHFR to prevent the binding of the transcriptional co-factor TFIID (Martianov 2007). This novel mechanism of regulating gene expression may in fact represent a widespread method of controlling promoter usage given that thousands of such triplexes exist in eukaryotic chromosome (Lee 1987). The U1 ncRNA can induce transcription initiation by specifically binding to and stimulating TFIIH to phosphorylate the C-terminal domain of RNAP II (Kwek 2002). In contrast the ncRNA 7SK, is able to repress transcription elongation by, in combination with HEXIM1/2, forming an inactive complex that prevents the PTEFb general transcription factor from phosphorylating the C-terminal domain of RNAP II (Kwek 2002; Yang 2001; Yik 2003), thereby repressing global elongation under stressful conditions. These examples which bypass specific modes of regulation at individual promoters to mediate changes directly at the level of initiation and elongation transcriptional machinery provides a means of quickly affecting global changes in gene expression.

The ability to quickly mediate global changes is also apparent in the rapid expression of noncoding repetitive sequences. The short interspersed nuclear (SINE) Alu elements in humans and analogous B1 and B2 elements in mice have succeeded in becoming the most abundant mobile elements within the genomes, comprising ~10% of the human and ~6% of the mouse genome, respectively (Lander 2001; Waterston 2002). These elements are transcribed as ncRNAs by RNAP III in response to environmental stresses such as heat shock (Liu 1995), where they then bind to RNAP II with high affinity and prevent the formation of active pre-initiation complexes (Allen 2004; Espinoza 2004; Espinoza 2007; Mariner 2008). This allows for the broad and rapid repression of gene expression in response to stress (Allen 2004; Mariner 2008).

A dissection of the functional sequences within Alu RNA transcripts has drafted a modular structure analogous to the organization of domains in protein transcription factors (Shamovsky 2008). The Alu RNA contains two ‘arms’, each of which may bind one RNAP II molecule, as well as two regulatory domains that are responsible for RNAP II transcriptional repression in vitro (Mariner 2008). These two loosely-structured domains may even be concatenated to other ncRNAs such as B1 elements to impart their repressive role (Mariner 2008). The abundance and distribution of Alu elements and similar repetitive elements throughout the mammalian genome may be partly due to these functional domains being co-opted into other long ncRNAs during evolution, with the presence of functional repeat sequence domains being a common characteristic of several known long ncRNAs including Kcnq1ot1, Xlsirt and Xist (Mattick 2003; Mohammad 2008; Wutz 2002; Zearfoss 2003).

In addition to heat shock, the expression of SINE elements (including Alu, B1 and B2 RNAs) increases during cellular stress such as viral infection (Singh 1985) in some cancer cells (Tang 2005) where they may similarly regulate global changes to gene expression. The ability of Alu and B2 RNA to bind directly to RNAP II provides a broad mechanism for to repress transcription (Espinoza 2004; Mariner 2008). Nevertheless, there are specific exceptions to this global response where Alu or B2 RNAs are not found at activated promoters of genes undergoing induction, such as the heat shock genes (Mariner 2008). This additional hierarchy of regulation that exempts individual genes from the generalised repression also involves a long ncRNA, heat shock RNA-1 (HSR-1). HSR-1 is present in all cells in an inactive state, but upon stress is activated to induce the expression of heat shock genes (Shamovsky 2006). This activation involves a conformational alteration to the structure of HSR-1 in response to rising temperatures, thereby permitting its interaction with the transcriptional activator HSF-1 that subsequently undergoes trimerisation and induces the expression of heat shock genes (Shamovsky 2006). More broadly, these examples illustrate a regulatory circuit nested witin ncRNAs whereby Alu or B2 RNAs repress general gene expression, while other ncRNAs, such as HSR-1, activate the expression of specific genes.

Long ncRNA transcribed by RNA polymerase III

Many of the ncRNAs that interact with general transcription factors or RNAP II itself (including 7SK, Alu and B1 and B2 RNAs) are transcribed by RNAP III (Dieci 2007), thereby decoupling the expression of these ncRNAs from the RNAP II transcriptional reaction they regulate. RNAP III also transcribes a number of additional novel ncRNAs, such as BC2, BC200 and some microRNAs and snoRNAs, in addition to the highly-expressed infrastructural ‘housekeeping’ ncRNA genes such as tRNAs, 5S rRNAs and snRNAs (Dieci 2007). The existence of an RNAP III-dependent ncRNA transcriptome that regulates its RNAP II-dependent counterpart was supported by a recent study that described a novel set of ncRNAs transcribed by RNAP III with sequence homology to protein-coding genes. This prompted the authors to posit a ‘cogene/gene’ functional regulatory network (Pagano 2007), showing that one of these ncRNAs, 21A, regulates the expression its antisense partner gene, CENP-F in trans.

Long noncoding RNAs in post-transcriptional regulation

In addition to regulating transcription, ncRNAs also control various aspects of post-transcriptional mRNA processing. Similar to small regulatory RNAs such as microRNAs and snoRNAs, these functions often involve complementary base pairing with the target mRNA. The formation of RNA duplexes between complementary ncRNA and mRNA may mask key elements within the mRNA required to bind trans-acting factors, potentially effecting any step in post-transcriptional gene expression including pre-mRNA processing and splicing, transport, translation, and degradation.

Long ncRNAs in splicing

The splicing of mRNA can induce its translation and functionally diversify the repertoire of proteins it encodes. The Zeb2 mRNA, which has a particularly long 5’UTR, requires the retention of a 5’UTR intron that contains an internal ribosome entry site for efficient translation (Beltran 2008). However, retention of the intron is dependent on the expression of an antisense transcript that complements the intronic 5’ splice site (Beltran 2008). Therefore, the ectopic expression of the antisense transcript represses splicing and induces translation of the Zeb2 mRNA during mesenchymal development. Similarly, the expression of an overlapping antisense Rev-ErbAα2 transcript controls the alternative splicing of the thyroid hormone receptor ErbAα2 mRNA to form two antagonistic isoforms (Munroe 1991).

Long ncRNAs in translation

NcRNA may also apply additional regulatory pressures during translation, a property particularly exploited in neurons where the dendritic or axonal translation of mRNA in response to synaptic activity contributes to changes in synaptic plasticity and the remodelling of neuronal networks. The RNAP III transcribed BC1 and BC200 ncRNAs, that previously derived from tRNAs, are expressed in the mouse and human central nervous system, respectively (Tiedge 1993; Tiedge 1991). BC1 expression is induced in response to synaptic activity and synaptogenesis and is specifically targeted to dendrites in neurons (Muslimov 1998). Sequence complementarity between BC1 and regions of various neuron-specific mRNAs also suggest a role for BC1 in targeted translational repression (Wang 2005). Indeed it was recently shown that BC1 is associated with translational repression in dendrites to control the efficiency of dopamine D2 receptor-mediated transmission in the striatum (Centonze 2007) and BC1 RNA-deleted mice exhibit behavioural changes with reduced exploration and increased anxiety (Lewejohann 2004).

Long ncRNAs in siRNA-directed gene regulation

In addition to masking key elements within single-stranded RNA, the formation of double stranded RNA duplexes can also provide a substrate for the generation of endogenous siRNAs (endo-siRNAs) in Drosophila and mouse oocytes (Golden 2008). The annealing of complementary sequences, such as antisense or repetitive regions between transcripts, forms a RNA duplex that may be processing by for Dicer-2 into endo-siRNAs. Alternatively, long ncRNAs that form extended intramolecular hairpins may also be processed into siRNAs, compellingly illustrated by the esi-1 and esi-2 transcripts (Czech 2008). Endo-siRNAs generated from these transcripts seem particularly useful in suppressing the spread of mobile transposon elements within the genome in the germline. However, the generation of endo-siRNAs from antisense transcripts or pseudogenes may also silence the expression of their functional counterparts via RISC effector complexes, acting as an important node that integrates integrate various modes of long and short RNA regulation, as exemplified by the Xist and Tsix (see above) (Ogawa 2008).

Long ncRNAs in epigenetic regulation

Epigenetic modifications, including histone and DNA methylation, histone acetylation and sumolyation, affect many aspects of chromosomal biology, primarily including regulation of large numbers of genes by remodeling broad chromatin domains (Kiefer 2007; Mikkelsen). While it has been known for some time that RNA is an integral component of chromatin (Nickerson; Rodriguez-Campos 2007), it is only recently that we are beginning to appreciate the means by which RNA is involved in pathways of chromatin modification (Chen; Rinn; Sanchez-Elsner).

In Drosophila, long ncRNAs induce the expression of the homeotic gene, Ubx, by recruiting and directing the chromatin modifying functions of the trithorax protein Ash1 to Hox regulatory elements (Sanchez-Elsner). Similar models have been proposed in mammals, where strong epigenetic mechanisms are thought to underlie the embryonic expression profiles of the Hox genes that persist throughout human development (Mazo; Rinn). Indeed, the human Hox genes are associated with hundreds of ncRNAs that are sequentially expressed along both the spatial and temporal axes of human development and define chromatin domains of differential histone methylation and RNA polymerase accessibility (Rinn). One ncRNA, termed HOTAIR, that originates from the HOXC locus represses transcription across 40 kb of the HOXD locus by altering chromatin trimethylation state. HOTAIR is thought to achieve this by directing the action of Polycomb chromatin remodeling complexes in trans to govern the cells epigenetic state and subsequent gene expression. Components of the Polycomb complex, including Suz12, EZH2 and EED, contain RNA binding domains that may potentially bind HOTAIR and probably other similar ncRNAs (Denisenko; Katayama 2005). This example nicely illustrates a broader theme whereby ncRNAs recruit the function of a generic suite of chromatin modifying proteins to specific genomic loci, underscoring the complexity of recently published genomic maps (Mikkelsen). Indeed the prevalence of long ncRNAs associated with protein coding genes may contribute to localised patterns of chromatin modifications that regulate gene expression during development. For example, the majority of protein-coding genes have antisense partners, including many tumour suppressor genes that are frequently silenced by epigenetic mechanisms in cancer (Yu). A recent study observed an inverse expression profile of the p15 gene and an antisense ncRNA in leukaemia (Yu). A detailed analysis showed the p15 antisense ncRNA was able to induce changes to heterochromatin and DNA methylation status of p15 by an unknown mechanism, thereby regulating p15 expression (Yu). Therefore misexpression of the associated antisense ncRNAs may subsequently silence the tumour suppressor gene contributing towards oncogenesis.

Imprinting

Many emergent themes of ncRNA-directed chromatin modification were first apparent within the phenomenon of imprinting, whereby only one allele of a gene is expressed from either the maternal or paternal chromosome. Imprinted genes are generally clustered together on chromosomes, suggesting the imprinting mechanism acts upon local chromosome domains rather than individual genes. These clusters are also often associated with long ncRNAs whose expression is correlated with the repression of the linked protein-coding gene on the same allele (Pauler). Indeed, detailed analysis has revealed a crucial role for the ncRNAs Kcnqot1 and Igf2r/Air in directing imprinting (Braidotti).

Almost all the genes at the Kcnq1 loci are maternally inherited, except the paternally expressed antisense ncRNA Kcnqot1 (Mitsuya). Transgenic mice with truncated Kcnq1ot fail to silence the adjacent genes, suggesting that Kcnqot1 is crucial to the imprinting of genes on the paternal chromosome (Mancini-Dinardo). It appears that Kcnqot1 is able to direct the trimethylation of lysine 9 (H3K9me3) and 27 of histone 3 (H3K27me3) to an imprinting centre that overlaps the Kcnqot1 promoter and actually resides within a Kcnq1 sense exon (Umlauf). Similar to HOTAIR (see above), Eed-Ezh2 Polycomb complexes are recruited to the Kcnq1 loci paternal chromosome, possibly by Kcnqot1, where they may mediate gene silencing through repressive histone methylation (Umlauf). A differentially methylated imprinting centre also overlaps the promoter of a long antisense ncRNA Air that is responsible for the silencing of neighbouring genes at the Igf2r locus on the paternal chromosome (Sleutels; Zwart). The presence of allele-specific histone methylation at the Igf2r locus suggests Air also mediates silencing via chromatin modification (Fournier).

Xist and X-chromosome inactivation

The inactivation of a X-chromosome in female placental mammals is directed by one of the earliest and best characterized long ncRNAs, Xist (Wutz 2007). The expression of Xist from the future inactive X-chromosome, and its subsequent coating of the inactive X-chromosome, occurs during early embryonic stem cell differentiation. Xist expression is followed by irreversible layers of chromatin modifications that include the loss of the histone (H3K9) acetylation and H3K4 methylation that are associated with active chromatin, and the induction of repressive chromatin modifications including H4 hypoacetylation, H3K27 trimethylation (Wutz 2007), H3K9 hypermethylation and H4K20 monomethylation as well as H2AK119 monoubiquitylation. These modifications coincide with the transcriptional silencing of the X-linked genes (Morey). Xist RNA also localises the histone variant macroH2A to the inactive X–chromosome (Costanzi 1998). There are additional ncRNAs that are also present at the Xist loci, including an antisense transcript Tsix, which is expressed from the future active chromosome and able to repress Xist expression by the generation of endogenous siRNA (Ogawa). Together these ncRNAs ensure that only one X-chromosome is active in female mammals.

Telomeric noncoding RNAs

Telomeres form the terminal region of mammalian chromosomes and are essential for stability and aging and play central roles in diseases such as cancer (Blasco 2007). Telomeres have been long considered transcriptionally inert DNA-protein complexes until it was recently shown that telomeric repeats may be transcribed as telomeric RNAs (TelRNAs) (Schoeftner 2008) or telomeric repeat-containing RNAs (Azzalin). These ncRNAs are heterogenous in length, transcribed from several sub-telomeric loci and physically localise to telomeres. Their association with chromatin, which suggests an involvement in regulating telomere specific heterochromatin modifications, is repressed by SMG proteins that protect chromosome ends from telomere loss (Azzalin). In addition, TelRNAs block telomerase activity in vitro and may therefore regulate telomerase activity (Schoeftner 2008). Although early, these studies suggest an involvement for telomeric ncRNAs in various aspects of telomere biology.

Long noncoding RNAs in disease

Recent recognition that long ncRNAs function in various aspects of cell biology has focused increasing attention on their potential to contribute towards disease aetiology. A handful of studies have implicated long ncRNAs in a variety of disease states and support an involvement and co-operation in oncogenesis.

While many association studies have identified long ncRNAs that are aberrantly expressed in disease states, we have little understanding of their contribution within disease etiology. Expression analyses that compare tumor cells and normal cells have revealed changes in the expression of ncRNAs in several forms of cancer. For example, the ncRNA OCC-1 (overexpressed in colon carcinoma-1) is overexpressed in colon carcinoma cells (Pibouin). Similarly, in prostate tumours, one of two overexpressed ncRNAs, PCGEM1, is correlated with increased proliferation and colony formation suggesting an involvement in regulating cell growth (Fu). NEAT2 was originally identified as an abundantly expressed ncRNA that is upregulated during metastasis of early-stage non-small cell lung cancer and its overexpression is an early prognostic marker for poor patient survival rates (Fu). More recently, the highly conserved mouse homologue of NEAT2 was found to be highly expressed in hepatocellular carcinoma (Lin). Despite a number of long ncRNAs having aberrant expression in cancer, their function and potential role in tumourogenesis is relatively unknown. For example, the ncRNAs HIS-1 and BIC have been implicated in oncogenesis and growth control, but their function in normal cells is unknown (Eis; Li). In addition to cancer, ncRNAs also exhibit aberrant expression in other disease states. Overexpression of PRINS is associated with psoriasis susceptibility, with PRINS expression being elevated in the uninvolved epidermis of psoriatic patients compared with both psoriatic lesions and healthy epidermis (Sonkoly).

Genome-wide profiling revealed that many transcribed noncoding ultraconserved regions exhibit distinct profiles in various human cancer states (Calin). An analysis of chronic lymphocytic leukaemia, colorectal carcinoma and hepatocellular carcinoma found that all three cancers exhibited aberrant expression profiles for ultraconserved ncRNAs relative to normal cells. Further analysis of one ultraconserved ncRNA suggested it behaved like an oncogene by mitigating apoptosis and subsequently expanding the number of malignant cells in colorectal cancers (Calin). Many of these transcribed ultraconserved sites that exhibit distinct signatures in cancer are found at fragile sites and genomic regions associated with cancer. It seems likely that the aberrant expression of these ultraconserved ncRNAs within malignant processes results from important functions they fulfil in normal human development.

Recently a number of association studies examining single nucleotide polymorphisms (SNPs) associated with disease states have been mapped to long ncRNAs. For example, SNPs that identified a susceptibility locus for myocardial infarction mapped to a long ncRNA, MIAT (myocardial infarction associated transcript) (Ishii). Similarly, genome-wide association studies identified a region associated with coronary artery disease (Pasmant) that encompassed a long ncRNA, ANRIL that associates with a high-risk haplotype for coronary artery disease and is expressed in tissues and cell types affected by atherosclerosis (Pasmant).

The complexity of the transcriptome, and our evolving understanding of its structure may inform a reinterpretation of the functional basis for many natural polymorphisms associated with disease states. Many SNPs associated with certain disease conditions are found within noncoding regions and the complex networks of noncoding transcription within these regions make it particularly difficult to elucidate the functional effects of polymorphisms. For example, a SNP both within the truncated form of ZFAT and the promoter of an antisense transcript increases the expression of ZFAT not through increasing the mRNA stability, but rather by repressing the expression of the antisense transcript (Shirasawa).

The ability of long ncRNAs in regulating associated protein-coding genes may contribute towards disease if the long ncRNAs misexpression deregulates a protein coding genes with clinical significance. Similarly, an antisense long ncRNA that regulates the expression of the sense BACE1 gene, a crucial enzyme in Alzheimer’s disease etiology, exhibits elevated expression in several regions of the brain in individuals with Alzheimer's disease (Faghihi). Alteration of the expression of ncRNAs may also mediate changes at an epigenetic level to effect gene expression and contribute to disease aetiology. For example, the induction of an antisense transcript by a genetic mutation led to the DNA methylation and silencing of sense genes, causing β-thalassemia in a patient (Tufarelli).


References