What is CRISPR/Cas9?
The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR Associated (Cas) system was first discovered in bacteria and provides sequence specific adaptive immunity against foreign DNA. Following its initial demonstration, scientists successfully tuned CRISPR system into a gene-editing tool enables permanent modification of targeted genes in living organisms.
The CRISPR genome editing system requires two components, a guide RNA (gRNA) and a non-specific CRISPR-associated endonuclease (Cas9). gRNA is a short synthetic RNA guides Cas9 to the specific location in the genome sequence. The gRNA and Cas9 complex is like a pair of scissors that can cleave both strands of DNA upon recognition of particular DNA sequences. By simply redesigning the targeting sequence in the gRNA, we can change the genomic target of Cas9.
After both strands are cut, the break is repaired by endogenous DNA repair mechanisms: non-homologous end joining (NHEJ) or homology-directed repair (HDR). HDR uses donor DNA containing a desired sequence resulting in the correction of a disease-causing mutation.