Mechanism and Applications of CRISPR/Cas-9-Mediated Genome Editing.

Clustered regularly interspaced short palindromic repeat (CRISPR) and their associated protein (Cas-9) is the most effective, efficient, and accurate method of genome editing tool in all living cells and utilized in many applied disciplines. Guide RNA (gRNA) and CRISPR-associated (Cas-9) proteins are the two essential components in CRISPR/Cas-9 system. The mechanism of CRISPR/Cas-9 genome editing contains three steps, recognition, cleavage, and repair. The designed sgRNA recognizes the target sequence in the gene of interest through a complementary base pair. While the Cas-9 nuclease makes double-stranded breaks at a site 3 base pair upstream to protospacer adjacent motif, then the double-stranded break is repaired by either non-homologous end joining or homology-directed repair cellular mechanisms. The CRISPR/Cas-9 genome-editing tool has a wide number of applications in many areas including medicine, agriculture, and biotechnology. In agriculture, it could help in the design of new grains to improve their nutritional value. In medicine, it is being investigated for cancers, HIV, and gene therapy such as sickle cell disease, cystic fibrosis, and Duchenne muscular dystrophy. The technology is also being utilized in the regulation of specific genes through the advanced modification of Cas-9 protein. However, immunogenicity, effective delivery systems, off-target effect, and ethical issues have been the major barriers to extend the technology in clinical applications. Although CRISPR/Cas-9 becomes a new era in molecular biology and has countless roles ranging from basic molecular researches to clinical applications, there are still challenges to rub in the practical applications and various improvements are needed to overcome obstacles.