Caenorhabditis elegans
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Video loop with Caenorhabditis elegans ( ⚥ ) under a simple transmitted light microscope |
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| Caenorhabditis elegans | ||||||||||||
| ( Maupas , 1900) |
Caenorhabditis elegans is a nematode from the group of rhabditides , which is mainlyresearchedas a model organism in developmental biology and genetics . The name is of Greco-Latin origin and means "elegant new rod" (Greek caeno 'new', rhabditis 'rod-shaped'; Latin elegans 'elegant').
features
anatomy
Adult individuals are only about a millimeter long and 65 µm (0.065 mm) in diameter . Part of the species population consists of hermaphrodites (hermaphrodites) , which can reproduce through self-fertilization. These are so-called consecutive hermaphrodites, which means that these animals first produce sperm in their gonads (gonads), which are stored in a sperm library , and then they form oocytes . The other part of the species population consists of pure males who copulate with the hermaphrodites and can thus sexually produce new offspring.
In addition, the species has a relatively simple nervous system, the main elements of which are a circumpharyngeal nerve ring ( looped around the isthmus of the pharynx), a ventral (on the abdomen) and a dorsal (on the back) nerve cord, and several nerve nodes (ganglia) in the head - and tail region. It consists of 302 nerve cells in adult hermaphrodites. Up to 2015, 383 nerve cells were known in adult males, before another pair of neurons was described under the name “MCMs” (from English mystery cells of the male ). The total number of nerve cells in males is 385. Compared to the hermaphrodites, the neurons of the males are predominantly located in the region of the specialized tail (the "MCMs", which are located in the head region, are an exception) and control the mating behavior.
The phenomenon of cell constancy ( eutelia ), which occurs in C. elegans not only in the cells of the nervous system, is not least of all decisive for the use of the species as a model organism in biological and medical research (see below ): every adult hermaphrodite always has precise characteristics 959, each adult male has exactly 1031 somatic cell nuclei (that is, a male has fewer non-neuronal somatic cells than a hermaphrodite).
habitat
C. elegans normally lives in the soil of temperate climates, the temperature optimum is between 4 ° C and 30 ° C. There the worm feeds on bacteria that break down dead organic material.
Life cycle
The hermaphrodite lays around 300 eggs during its life, from which the L1 larvae hatch. This is followed by 3 further larval stages ( L2 , L3 and L4 ), which arise from moults. The adult stage is reached after about 8 hours at a room temperature of 25 ° C. The adult stage is visually distinguished from the other stages by having a vulva . It should be noted that these are not actual larval stages, but juvenile stages .
Permanent stage (permanent larva)
Under unfavorable environmental conditions, such as a high population density or food shortage, the L2 larva develops into a permanent larvae stage (preduration "similar to L2 stage" and then duration "similar to L3 / L4 stage"), which can last for 3 months. The formation of the permanent stage is induced by the permanent pheromone (a cholesterol derivative , steroid ). The permanent stage differs morphologically from the normal larval stages. It is thinner in shape than the normal L2 stage. The permanent larva has a thicker cuticle and a smaller mouth opening, which protects it from drying out. ( Anatomy and metabolism are very different from the other stages). While the early stages are very active and looking for food, the later stages are passive and lie next to each other on the agar plates . However, they can be animated to flee again by touch stimuli. The passive behavior prevents you from burning too much of the stored resources. If the permanent stage comes into contact with food, it develops into the L4 larva.
Biological model organism
In the 1960s, Caenorhabditis elegans was introduced to science by the developmental biologist Sydney Brenner ( Nobel Prize in Medicine 2002) as an object of observation for cell biology and developmental biology.
Caenorhabditis elegans is characterized by the so-called Eutelia . The developmental fate of the individual cells is generally determined at the beginning of the cleavage (mosaic development). However, the development of C. elegans is not a prime example of a deterministic, cell-autonomous development. The developmental fate of each cell is clearly controlled by certain predecessor cells ( mosaic development ). Brenner researched the cellular regulation of this determination . In connection with this, H. Robert Horvitz investigated programmed cell death . The results of basic research on Caenorhabditis elegans can be applied to a wide range of organisms, including vertebrates and thus also humans . See also Let-7 in this context .
Since then, its popularity as a model organism has continued to grow. The easy handling of the animals on agar plates , with bacteria as food ( E. coli strains: OP50 and HB101) and its developmental properties (including Eutelia, simple structure formation, transparency ) have favored its triumph in the laboratory. Today, alongside the bacterium Escherichia coli , the fruit fly Drosophila melanogaster and the thale cress Arabidopsis thaliana, it is one of the best-researched organisms in the world. It is no longer just developmental biology that draws knowledge from research on worms, as well as many other areas of the world Biology such as physiology , ecology , genomics , neurobiology , evolutionary biology and cell biology use the model organism. This research is often carried out on an interdisciplinary basis and also with a view to gaining medical knowledge.
Caenorhabditis elegans was the first fully sequenced multicellular cell ( metazoon ) in 1998 . The six chromosomes and the genome of the mitochondrion together contain 100,281,426 base pairs and 23,217 genes . In 2003, the genome of the closely related species Caenorhabditis briggsae was completely deciphered in order to enable comparison of closely related species.
In 2006, the American biologist Andrew Z. Fire , a student of Sydney Brenner , and Craig C. Mello received the Nobel Prize in Medicine for their research into RNA interference , a method by which genes can be specifically "silenced" . This work was carried out on Caenorhabditis elegans . The third Nobel Prize associated with Caenorhabditis elegans was awarded in 2008 when the American biologist Martin Chalfie, together with Osamu Shimomura and Roger Y. Tsien, received the Nobel Prize in Chemistry for the introduction of the green fluorescent protein (GFP) into basic biomedical research. Martin Chalfie's work was carried out on Caenorhabditis elegans . Chalfie had also joined Sydney Brenner's team at Cambridge University in 1977 .
Studies on Caenorhabditis elegans also provided numerous insights into the relationship between certain external stimuli , the receiving nerve cells , the behavior patterns triggered by them and the underlying genetic makeup of the respective populations or individuals. Thus, for example, determined experimentally, that that representatives of the phenomenon of certain strains and wild populations of C. elegans tend in food intake aggregations form ( English social feeding ), while others do not ( solitary feeding ), among others, the activity of specific genes depends on the structure of certain ion channels (so-called TRP channels ) in certain sensory cells (so-called Nozizeptorneuronen ) encoding, potentially for the perception of harmful substances are responsible of the food the worms, bacteria such as E. coli , are produced . Experiments with C. elegans have also made some significant advances in studying the origins of Parkinson's disease at the cellular level.
See also
Developmental biology: on the development of the roundworm
literature
- William B. Wood: The Nematode Caenorhabditis Elegans . Cold Spring Harbor Laboratory Press, 1988, ISBN 978-087969433-3
Web links
- Caenorhabditis elegans at the National Center for Biotechnology Information (NCBI)
- The wormbase
- Wormatlas (A database of behavioral and structural anatomy of Caenorhabditis elegans )
- WormBook (The online review of C. elegans biology)
- Caenorhabditis Genome Sequencing Project (with links)
Individual evidence
- ↑ a b Travis A. Jarrell, Yi Wang, Adam E. Bloniarz, Christopher A. Brittin, Meng Xu, J. Nichol Thomson, Donna G. Albertson, David H. Hall, Scott W. Emmons: The Connectome of a Decision- Making Neural Network. In: Science. Volume 337, No. 6093, 2012, pp. 437–444, doi: 10.1126 / science.1221762 (alternative full text access : wormwiring.org )
- ↑ Michele Sammut, Steven J. Cook, Ken CQ Nguyen, Terry Felton, David H. Hall, Scott W. Emmons, Richard J. Poole, Arantza Barrios: Glia-derived neurons are required for sex-specific learning in C. elegans. In: Nature. Volume 526, No. 7573, 2015, pp. 385–390, doi: 10.1038 / nature15700 , PMC 4650210 (free full text)
- ↑ MapView entry
- ↑ Proteome at UniProt
- ↑ C. elegans Sequencing Consortium: Genome sequence of the nematode C. elegans: a platform for investigating biology . In: Science . tape 282 , no. 5396 , 1998, pp. 2012–2018 , doi : 10.1126 / science.282.5396.2012 , PMID 9851916 .
- ↑ Mario de Bono, David M. Tobin, M. Wayne Davis, Leon Avery, Cornelia I. Bargmann: Social feeding in Caenorhabditis elegans is induced by neurons that detect aversive stimuli. In: Nature. Volume 419, No. 6910, 2002, pp. 899–903, doi: 10.1038 / nature01169 , PMC 3955269 (free full text)
- ↑ Anthony L. Gaeta, Kim A. Caldwell, Guy A. Caldwell: Found in Translation: The Utility of C. elegans Alpha-Synuclein Models of Parkinson's Disease . In: Brain Sciences . tape 9 , no. 4 , 2019, 73, doi : 10.3390 / brainsci9040073 .