Could the CRISPR-Cas9 genome editing system be replaced by the NgAgo-gDNA system?

Abstract

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated protein-9 nuclease (Cas9) system is a new genome editing tool developed from the bacterial (Streptococcus pyogenes) adaptive immune mechanism. The CRISPR-Cas9 system sequence-specifically cleaves target sequence under the guide from single guide RNA (sgRNA) and the presence of protospacer-adjacent motif (PAM) in the target sequence. Another genome editing tool was recently developed and was named as the NgAgo-gDNA system. The NgAgo nuclease cleaves target sequence by binding to 5’-phophorylated 24-nucleotide single-strand guide DNA (gDNA). Here we have briefly introduced both the CRISPR-Cas9 and NgAgo-gDNA systems and compared them in their genome editing conditions, cleavage fidelity and efficiency as well as their application area. The NgAgo-gDNA system may have advantages in editing animal genomes due to the availability and convenience of artificially synthesized gDNAs. The NgAgo-gDNA system also benefits multiple target genes and shows higher efficiency in editing GC-rich genes with higher editing fidelity and less target sequence restriction. However, the transfected gDNA may also be integrated into an organism genome, which may lead to unexpected mutations or ethic issues. On the other hand, the current study showed that the best cleavage activity of NgAgo was observed at 37oC, which may restrict its application in some of organisms. In addition, the NgAgo-gDNA system may not be easily applied to edit plant genomes due to the unavailability of gDNA in plants. Thus, the CRISPR-Cas9 system could not be replaced by the NgAgo-gDNA system and both systems may have their own application potential in gene functional annotation and organism improvement as well as disease control. The NgAgo-gDNA system may have its advantages in human/animal genome editing whereas the CRISPR-Cas9 system has been proven to benefit plant genome modification.