The recent
decades have witnessed what has been named as a Genomic Revolution. The most
recent discovery in this revolution is called CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas9 (an RNA-guided
endonuclease) system, a breakthrough new form of DNA editing. The system was
originally discovered in bacteria and archae in the late 80’s. Microbiologists
found in the genome of these organisms patterns of interspersed DNA whose function
had remained elusive for many years. Several decades after, through sequencing
of bacterial genomes, researchers discovered that these repeats were flanking
DNA sequences of virus origin that the bacteria had incorporated into their
chromosome. Moreover, these elements (CRISPR) were found to be in close
proximity to genes that coded for proteins (Cas enzymes) involved in DNA
cleavage and repair (Bolotin et al., Microbiology 2005; Mojica et al., J Mol
Evol 2005; Pourcel at al., Microbiology 2005). Over the following years it was found
that these viral sequences inserted at these specific loci constituted an
immune memory that allowed bacteria fighting invading nucleic acids –such as
virus- and blocking their propagation, and was the first evidence of an acquired
immunity used by bacteria to adapt against foreign DNA.
