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

Abstract

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.

Keywords:

• CRISPR
• Cas-9
• sgRNA
• gene-editing
• mechanism
• applications

Abbreviations

AAVs, adeno-associated viral vectors; ABE, adenine base editor; Acr, anti-CRSPR; AVs, adeno-viral vectors; ATP, adenosine tri-phosphate; BCL11A, B-cell lymphoma 11 A; CAS-9, CRISPR-associated protein-9; CBE, cytidine base editor; CCR5, chemokine receptor type 5; CFTR, cystic fibrosis conductance transmembrane receptor; CRISPR, clustered regularly interspaced short palindromic repeat; CrRNA, CRISPR ribonucleic acid; DMD, Duchenne muscular dystrophy; DNA, deoxyribonucleic acid; DSBs, double-stranded breaks; HDR, homology-directed repair; LVs, lentivirus vectors; NHEJ, non-homologous end Jjining; PAM, protospacer adjacent motif; PD-1, programmed cell death-1; RNA, ribonucleic acid; TALENs, transcriptionactivator like effector nucleases; TRAC, T-cell receptor alpha; TRBC, T-cell receptor beta; TracrRNA, trans-activating CRISPR ribonucleic acid; ZFNs, zinc finger nucleases.

Ethics Approval and Consent to Participate

Not applicable.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no conflicts of interest for this work.

Additional information

Funding

No funding was received.