Engineered FnCas12a with enhanced activity through directional evolution in human cells.

CRISPR-Cas12a has been used to manipulate the human genome; however, low cleavage efficiency and stringent protospacer adjacent motif (PAM) hinder the use of Cas12a-based therapy and applications. Here, we have described a directional evolving and screening system in human cells to identify novel FnCas12a variants with high activity. By using this system, we identified IV-79 (enhanced activity FnCas12a, eaFnCas12a), which possessed higher DNA cleavage activity than wild-type (WT) FnCas12a. Furthermore, to widen the target selection spectrum, eaFnCas12a was engineered through site-directed mutagenesis. eaFnCas12a and eaFnCas12a-RR variant, used for correcting human RS1 mutation responsible for X-linked retinoschisis (XLRS), had a 3.28∼4.04-fold improved activity compared to WT. Collectively, eaFnCas12a and its engineered variants can be used for genome-editing applications that requires high activity.