NEXT GENERATION GENOME EDITING TECHNOLOGIES Next-Generation-Genome-Editing-Technologies | Page 9
Making precise and correct changes in target genome has been a dream for researchers. Luckily,
we live in an era where dreams can become reality. A similar boon was given to the domain of
gene editing when a tool based on bacterial nuclease known as CRISPR –associated protein-9
(CAS9) came into spotlight. Isolated from Streptococcus pyogenes, CAS9 became most efficient
tool after TALENs. It is a known fact that CRISPR and CAS are essential in providing adaptive
immunity to bacterial and archaeal species, by enabling them to eliminate the invading genetic
material. There are three types of CRISPR mechanisms and type II is studied most:
The attacking viral DNA is cut into small fragments and integrated into CRSIPR locus between
small repeats.
These loci are then transcribed and are processed to give CRISPR RNA or CrRNA.
CrRNA then guides endonucleases which cleave the target foreign DNA based on
complimentary sequence.
Disadvantages:
Offsite effects: There were cases when changes were made to similar but not identical sites.
This led to formation of offsite mutation that had potential to cause collateral damage.
Mosaicism: Organism with a mutant allele in only some of its cell can also result in a
problematic production, as nucleases may not have cut DNA at one of the cell stages of
embryonic development.
Multiple alleles: Production of organism with multiple mutation sites is also possible. Therefore,
extra step of breeding might be required to separate organism with single mutation.