Genome editing

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Genome editing or genome surgery , in German often genome editing , is a collective term for molecular biological techniques for the targeted modification of DNA , including the genome of plants, animals and humans.

Mode of action

Graphic to clearly explain genome editing

So-called designer endonucleases are used to introduce targeted changes in the genome of complex organisms . These enzymes cut double-stranded DNA at a predetermined target sequence, thereby creating double-strand breaks. The double-strand breaks in turn activate DNA repair processes in the cell, such as non-homologous end-joining (NHEJ) or homologous repair , which is also referred to as homology directed repair (HDR). While genes are specifically inactivated using NHEJ, HDR can be used to insert specific mutations or entire DNA segments into the genome .

The journal Nature Methods named Genome Editing 2011 Method of the Year.

Enzymes

The frequently used classes of designer nucleases include zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALENs), the CRISPR / Cas method , the CRISPR / Cpf1 system and meganucleases (modified homing endonucleases ). In zinc finger nuclease, TALEN and meganuclease, DNA is specifically recognized by a specific protein part, while in CRISPR systems it is mediated by a specific RNA.

Applications

Genome editing is used for targeted changes to the genome of microorganisms ( white genetic engineering ), plants ( green genetic engineering ), animals ( red genetic engineering ) and humans ( gene therapy ). The genome editing can be used to selectively destroy a gene ( gene knockout ) in the genome for the insertion of a gene at a specific location ( gene knockin ), or for correction of a point mutation can be used in a gene.

Base editing

A new, precise method of genome editing consists of changing individual bases in the DNA sequence (base editing). Here a mutated form of the Cas9 nuclease , which can no longer cut the DNA, is coupled with a deaminase. This fusion protein is able to recognize a specific DNA sequence with the sgRNA and changes a base by deamination. In the case of fusion with cytidine deaminase, the cytidine is converted into uracil , which is replaced with thymidine through DNA repair and replication . This mutates the base pair CG to TA. Alternatively, Cas9 can be coupled with an adenosine deaminase , so that the adenosine is converted into inosine, which is replaced with guanosine after DNA repair and replication . In this case the base pair AT is converted to GC. The efficiency of base editing is between 5% and 50% and, since the DNA is not cut, undesirable changes are less frequent.

Regulatory Aspects

There is currently no unanimous opinion as to whether genome-edited organisms should be classified as genetically modified organisms (GMOs) and whether the guidelines applicable to GMOs should be applied. The association of national science academies of member states of the European Union ( EASAC ) points out that the regulation of genome editing should not cover the technology as such, but the specific applications in the individual subject areas. At the moment, the possible applications in agriculture, but also the possible use in medicine, are in the foreground.

Plant breeding

Experts from various countries have suggested that genome-edited plants, provided they do not contain foreign DNA, are to be treated as plants from conventional breeding. This opinion takes into account the fact that genome-edited plants are often indistinguishable from conventionally grown plants and that they can also be grown by conventional methods.

A ruling by the European Court of Justice (ECJ) on July 25, 2018 equates genome-edited plants with genetically modified organisms (GMOs). The Court argues that genome editing makes a naturally impossible change in the genetic material of a plant. He states that genome editing is not to be equated with induced mutagenesis , which is excluded from regulation, since it has been used in conventional plant breeding for decades. This assessment is criticized by many scientists. They point out that genome editing results in a much more precise change in the genome than is the case with induced mutagenesis , in which genes are changed aimlessly by radiation or genotoxic chemicals. The Central Commission for Biosafety (ZKBS) does not see any scientific basis for the interpretation of the GMO Directive by the ECJ with regard to genome editing. In a statement on the ECJ ruling, the Bioeconomy Council points out that all products that are manufactured using the new process must go through a very complex and expensive approval procedure. He advocates a risk-based approval and approval process. This widespread criticism of the ECJ ruling is not shared by everyone and reflects the fundamental controversy about genetic engineering in general.

In the USA, a number of genome-edited plants have been released for commercial cultivation without restrictions by the USDA . Before developing the plant in question, a company can clarify with the USDA whether regulation is necessary or not. This preliminary query accelerates the development of new plants considerably. Similar provisions apply in Argentina, Australia, Brazil and Japan, among others.

The internationally different approval regulations for genome-edited plants represent a problem that cannot be solved by the supervisory authorities, since without prior knowledge of the genetic changes it is very time-consuming to check imported foods. In a specific case, it will not be possible to decide whether a mutation was caused by genome editing or spontaneously.

Therapy in humans

The use of genome editing in humans caused general consternation in November 2018 due to the work of the Chinese scientist He Jiankui . According to his own statements, he deactivated the CCR5 receptor in several human embryos in order to make the children then born immune to HIV . The Chinese researcher's approach contradicts both international and Chinese ethical guidelines. Obviously, globally binding regulations are urgently needed.

literature

  • S. Chandrasegaran, D. Carroll: Origins of Programmable Nucleases for Genome Engineering. In: Journal of molecular biology. [electronic publication before printing] October 2015, doi: 10.1016 / j.jmb.2015.10.014 . PMID 26506267 .

Web links

Individual evidence

  1. ↑ BBAW : Genome surgery in humans. (PDF) p. 10 , accessed on November 2, 2018 .
  2. ↑ see for example genome editing: patent dispute over Crispr has been decided
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  4. ↑ Christien Bednarski, Toni Cathomen: Customized Genome Designer Nucleases in Use. In: BIOspectrum. 21, 2015, pp. 22-24. doi: 10.1007 / s12268-015-0528-4
  5. ↑ R. Wilkinson, B. Wieden Issue: A CRISPR method for genome engineering. In: F1000prime reports. Volume 6, 2014, p. 3, ISSN  2051-7599 . doi: 10.12703 / P6-3 . PMID 24592315 . PMC 3883426 (free full text).
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  7. ↑ KM Esvelt, HH Wang: Genome-scale engineering for systems and synthetic biology . In: Mol Syst Biol . tape 9 , no. 1 , 2013, p. 641 , doi : 10.1038 / msb.2012.66 , PMID 23340847 , PMC 3564264 (free full text).
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  20. ↑ Court of Justice of the European Union: Organisms obtained by mutagenesis are genetically modified organisms (GMOs) and are fundamentally subject to the obligations set out in the GMO Directive. Retrieved February 13, 2019 .
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  22. ↑ ZKBS: Genome Editing - Effects of the ECJ judgment on plant breeding. Retrieved February 13, 2019 .
  23. ^ Bioeconomy Council: Genome Editing: Europe needs a new genetic engineering law. In: BÖRMEMO January 07, 19, 2019, accessed on February 13, 2019 .
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  29. ^ ZEIT online: Emmanuelle Charpentier: Crispr discoverer criticizes genetic experiments on babies. Retrieved February 20, 2019 .
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