There are a number ofmethods that biologist can employ to edit genes.
The most powerful andversatile method currently is the CRISPR/CAS9 technique. CRISPR stands forclustered regularly interspaced short palindromic repeats. The power of CRISPRcomes from its simplicity and diversity. CRISPR is an enzyme that causes doublestrand breaks (DSBs) in DNA in precise locations.
The way it finds the correctlocation to induce the DSB reminds me of how RNA polymerase and TFs work. TheCRISPR is introduced into the cell with a guide RNA (gRNA). The gRNA is a 20-nucleotidesequence, giving it extreme precision in locating a specific locus on the DNA.Once the gRNA finds the locus on the chromosome, it recruits the Cas9 (crisperassociated protein 9, a form of endonuclease) to the DNA strand kind of like howa sigma subunit or other TF binds RNA polymerase to a specific site.
Once theCas9 is bound to the DNA it then proceeds to catalyze the DSB, leaving stickyends behind at the cleavage sites. A new strand of synthesized DNA can then beintroduced into the gap, or an existing strand can simply be deleted. NHEJ(non-homologous end joining) DNA repair mechanism is then implemented to rejoinand ligate the sticky ends. Delivery methods for CRISPR vary extensively.Methods include such things as viral and non-viral vectors, transfection,electroporation, and microinjection (1).The practicalapplications of the CRISPR technique are numerous. There have been over 3,500published reports using CRISPR in the last couple years alone (1). I only havespace to discuss a few uses of this tool.
One of the leading areas of study for the application of CRISPR is ingerm line cells, where CIRSPR can be used to correct genetic abnormalities suchas inherited retinal degeneration, as just one example (2). Another area thathas received a lot of attention lately is the use of CRISPR in conjunction withgene drives to eliminate such diseases as malaria, which use mosquitos as avector to infect humans. A gene drive, at least theoretically, gives theselected gene 100% inheritance rate by incorporating the genes that createCRISPR proteins and gRNAs into the host genome. The goal with mosquitos is toengineer a gene that makes the mosquitos resistant to the malaria-causingparasite called plasmodium parasite. With the help of gene drive, this parasiteresistant gene could proliferate to the point where all mosquitos within thetarget species carry it, completely nullifying the vector for the parasite, andeliminating malaria. This method is also being investigated with regard to anumber of other diseases that use mosquitos as vectors (3). Many methods forcontrolling insect vectors have limited efficacy, whereas CRISPR technology inconjunction with gene drives have the potential for near complete efficacy.
Anotherpotentially use for CRISPR technology is for the investigation of neuraldiseases. CRISPR can be used to create neural models of human diseases withinanimals such as mice in order to conduct research that could not be done onhumans (4). This research focuses primarily on age related brain diseases suchas Alzheimer’s and huntingtins diseases. Not only can it be used to model thesediseases in animals, but once the diseases are better understood, it couldpotentially be used in human germ line cells to eliminate the disease in vitro,or in the zygote. In summary, CRISPRtechnology is a revolutionary tool in the field of genetics and genomics. It isvery easy to use compared to other similar tools. The uses for the tool varyextensively, and we have probably only begun to scratch the surface ofpractical applications for it.