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CRISPR means Clustered Regularly Interspaced Short Palindromic Repeats. These small DNA sequences were characterized by Mojica and collaborators in 1993 by studying bacteria found in salt marches. The researchers observed that these repeat sequences were framed pieces of unknown DNA. Thanks to extensive databases, these sequences were then identified to be DNA from bacterial viruses, known as bacteriophages. The CRISPR system works like a vaccination mechanism, giving the bacterium a targeted immune protection against encountered viruses. Bacteriophage DNA pieces are kept, like “a memory”, in the bacterial genome surrounded by these CRISPR sequences. This sequence is then transcribed into RNA, a single strand nucleic acid sequence, kind of like a DNA copy, containing the information of the virus sequence to be recognized. The Cas9 enzyme will use this RNA molecule guide to bind to the targeted virus sequence, cut its DNA and destroy it.

In 2012, two research teams produced in vitro the different actors of this technique, the enzyme and the guide RNA, and showed its interest as a tool for genome engineering (Gasiunas et al., 2012 and Jinek et al., 2012). Cas9 can indeed be programmed by linking it to a targeted RNA corresponding to the genome region to be cut. Furthermore, in eukaryotic cells, a piece of DNA may be introduced with the enzyme and the guide RNA, in order to be embedded in the sequence to replace the cut region. This technique permits the replacement of a damaged gene with its repaired copy or its inactivation in order to study its function. Other techniques can also do this type of genome editing but CRISPR/Cas9 is very simple, fast and therefore inexpensive.

The CRISPR/Cas9 technique is so promising that in August 2015, Bill Gates invested $120 million in the Editas Medicine Company, using this tool for medical applications. Several research teams have since published numerous applications of this technique in many species over the world. In plants CRISPR/Cas9 represents a unique alternative to conventional GMO. The specificity of this technique lies in the fact that there is no DNA integration from another specie but repair or modification of a gene already present naturally in the plant. The CRISPR/Cas9 opens a wide field of investigation in life sciences and suggests very promising research.

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Learn more

• Review « The Heroes of CRISPR” Lander ES. Cell. 2016 Jan 14;164(1-2):18-28. doi: 10.1016/j. Cell.2015.12.041. Review. PMID:26771483
• Review « Development and applications of CRISPR-Cas9 for genome engineering” Hsu PD, Lander ES, Zhang F. Cell. 2014 Jun 5;157(6):1262-78. doi: 10.1016/j.cell.2014.05.010.
• Movie Genome Editing with CRISPR-Cas9 McGovern Institute for Brain Research at MIT

Cited articles

• Mojica, F.J.M., Juez, G., and Rodrı´guez-Valera, F. (1993). Transcription at different salinities of Haloferax mediterranei sequences adjacent to partially modified PstI sites. Mol. Microbiol. 9, 613–621.
• Gasiunas, G., Barrangou, R., Horvath, P., and Siksnys, V. (2012). Cas9-crRNA ribonucleoprotein complex mediates specific DNA cleavage for adaptive immunity in bacteria. Proc. Natl. Acad. Sci. USA 109, E2579–E2586.
• Jinek, M., Chylinski, K., Fonfara, I., Hauer, M., Doudna, J.A., and Charpentier, E. (2012). A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science 337, 816–821.