Expanding the CRISPR Toolbox with ErCas12a in Zebrafish and Human Cells

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR associated (Cas) effector proteins enable the targeting of DNA double-strand breaks (DSBs) to defined loci based on a variable length RNA guide specific to each effector. The guide RNAs are generally similar in size and form, consisting of a ~20 nucleotide sequence complementary to the DNA target and an RNA secondary structure recognized by the effector. However, the effector proteins vary in Protospacer Adjacent Motif (PAM) requirements, nuclease activities, and DNA binding kinetics. Recently, ErCas12a, a new member of the Cas12a family, was identified in Eubacterium rectale . Here, we report the first characterization of ErCas12a activity in zebrafish and human cells. Using a fluorescent reporter system, we show that CRISPR/ErCas12a elicits strand annealing mediated DNA repair more efficiently than CRISPR/Cas9. Further, using our previously reported gene targeting method that utilizes short homology, GeneWeld, we demonstrate the use of CRISPR/ErCas12a to integrate reporter alleles into the genomes of both zebrafish and human cells. Together, this work provides methods for deploying an additional CRISPR/Cas system, thus increasing the flexibility researchers have in applying genome engineering technologies.