Chemical Modification and Transformation Strategies of Guide RNAs in CRISPR-Cas9 Gene Editing Systems.

The CRISPR (clustered regularly interspaced short palindromic repeat)-Cas9 (CRISPR-associated protein 9) is a most powerful tool and has been widely used in gene editing and gene regulation since its discovery. However, wild-type CRISPR-Cas9 suffers from off-target effects and low editing efficiency. To overcome these limitations, engineered Cas9 proteins have been extensively investigated. In addition to Cas9 protein engineering, chemically synthesized guide RNAs have been developed to improve the efficiency and specificity of genome editing as well as spatiotemporal controllability, which broadens the biological applications of CRISPR-Cas9 gene editing system and increases their potentials as therapeutics. In this review, we summarize the latest research advances in remodeling guide RNAs through length optimization, chemical modifications, and conditional control, as well as their powerful applications in gene editing tools and promising therapeutic agents.