A new era of gene editing -

CRISPR/Cas9

The acronym CRISPR/Cas9 stands for the long and complicated term “clustered regularly interspaced short palindromic repeats” (CRISPR) and CRISPR associated sequences (Cas), which describes a nucleic acid based and wide spread adaptive “immune system” of bacteria and archaea to repel invading viruses. CRISPR sequences were first described in 1987 (Ishino et al 1987), but the real function was just understood in 2005 (Bolotin et al 2005, Mojica et al. 2005). Basically the CRISPR/Cas9 system is able to detect and distinguish between foreign viral DNA fragments and bacterial DNA, based on this detection system, the CRISPR/Cas9 cleaves finally a specific viral sequence and safes the cell from the viral take-over. The CRISPR/Cas9 system produces at the same time a historical and distinct library of the intruders (viruses) in the bacterial genome to defend the cell against the same intruders.

In the following years of research, Prof. Emmanuelle Charpentier and Prof. Jennifer Doudna developed the idea to modify the natural CRISPR/Cas9 system and use it as a universal tool for gene editing. The general idea behind the gene editing system using CRISPR/Cas9 is, that you analyze the genome and if you spot a typo in the sequence which causes a disease you correct the this typo via introducing a double-strand break in the genome and giving the cell the correct template (typo free template), so the cell can use his own DNA repairing mechanisms to correct the typo. Generally they use a three component system composed of (1) tracer (a RNA molecule which is complementary to the sequence which is going to be modified), (2) “gene-scissor” (the Cas9 protein) and (3) Donor DNA. The tracer (1) aims the gene defect or more general, the part of the gene which should be modified. After the tracer recognizes the desired part, the “gene-scissor” (2) cuts these and the DNA-repairing systems of the cell use the donor DNA (3) to repair the recently cut gene. These very easy and all over applicable system, will be used to modify all different genes in various model organisms and finally in humans, to extinguish diseases and the hopefully the effects of aging.