An assessment of genome-editing efficiency of a newly developed Cas9 in C. elegans

Minimizing the off-target effects of the programmable genome editing tool CRISPR/Cas9 is critical for its potential therapeutic applications. A recent study reported a new Cas9 variant, SuperFi-Cas9, that dramatically reduces off-target DNA cleavage while retaining on-target DNA cleavage activity in in vitro assays. Here we evaluated the genome editing potential of SuperFi-Cas9 by examining its efficiency in mutagenizing targeted genes in the nematode C. elegans . We found that gene mutagenesis rates induced by SuperFi-Cas9 through either non-homologous end joining or homology-directed repair were much lower than those by the wild type Cas9, indicating that Super-Cas9 had very low in vivo DNA cleavage activity. Our results also suggest that C. elegans may serve as an excellent model system for assessing in vivo genome-editing efficiency of newly-developed Cas9 variants.