Recursive Editing improves homology-directed repair through retargeting of undesired outcomes

CRISPR-Cas induced HDR methods tend to have a low efficiency. Here the authors report an HDR improvement strategy, Recursive Editing, that selectively retargets undesired indel outcomes to create additional opportunities for HDR; they introduce REtarget, a tool for Recursive Editing experimental design. CRISPR-Cas induced homology-directed repair (HDR) enables the installation of a broad range of precise genomic modifications from an exogenous donor template. However, applications of HDR in human cells are often hampered by poor efficiency, stemming from a preference for error-prone end joining pathways that yield short insertions and deletions. Here, we describe Recursive Editing, an HDR improvement strategy that selectively retargets undesired indel outcomes to create additional opportunities to produce the desired HDR allele. We introduce a software tool, named REtarget, that enables the rational design of Recursive Editing experiments. Using REtarget-designed guide RNAs in single editing reactions, Recursive Editing can simultaneously boost HDR efficiencies and reduce undesired indels. We also harness REtarget to generate databases for particularly effective Recursive Editing sites across the genome, to endogenously tag proteins, and to target pathogenic mutations. Recursive Editing constitutes an easy-to-use approach without potentially deleterious cell manipulations and little added experimental burden.

Automated summary

This study presents a HDR improvement strategy called Recursive Editing, which selectively retargets undesired indel outcomes to create more opportunities for HDR. The authors introduce a software tool called REtarget for the design of Recursive Editing experiments. By using REtarget-designed guide RNAs, Recursive Editing can simultaneously enhance HDR efficiency and reduce undesired indels. This approach proves to be easy to use and has little experimental burden.