CRISPR-Cas9 System: Opportunities and Concerns.

Abstract

Currently, a new revolutionary genome-editing tool is opening new avenues for gene engineering. It is known as the clustered regularly interspaced short palindromic repeats (CRISPR)11 and the CRISPR-associated (Cas) 9 system. In general, the CRISPR-Cas system has been evolved in archaea and bacteria as part of their adaptive immune mechanisms. Mechanistic aspects of the system can be found in the literature. Among the 3 CRISPR-Cas system types that were found in these organisms, the type II system in Streptococcus pyogenes is the most widely applied. The type II (CRISPR-Cas9) system includes the RNA-guided Cas9 nuclease, which binds to specific DNA sequences (complementary to the RNA-guide sequence) and creates double-stranded breaks on the DNA. The dsDNA breaks can be repaired via homology-directed repair (HDR) or nonhomologous end-joining (NHEJ). Based on this principle, the Cas9 and the guide-RNA were modified in various ways to improve the efficiency and specificity of this system, to expand its potential for different applications. This system can be used for altering specific genetic loci through insertions, deletions, point mutations, and sequence inversions. More recently, the system was modified to act as a genome regulator, by tethering effector domains to the Cas9 or guide-RNA, and as a visualization tool by fusing with marker molecules. This multiplex capacity of engineering CRISPR-Cas9 enabled scientists to apply this system for genome modifications in a variety of organisms, like Arabidopsis, Drosophila, Caenorhabditis elegans, zebrafish, mosquitoes, mice, primates, and humans. Lately, the CRISPR-Cas9 gene editing has been used in human embryos and generated several ethical questions and concerns. In this Q&A, 5 experts from around the world discuss the capabilities of the CRISPR-Cas9 system in editing genomes and discuss the associated ethical concerns. The interest for using the CRISPR-Cas9 system to targeted genome editing is rapidly emerging. The efficiency …