Timed inhibition of CDC7 increases CRISPR-Cas9 mediated templated repair
Repair of double strand DNA breaks (DSBs) can result in gene disruption or precise gene modification via homology directed repair (HDR) from a templating donor DNA. During genome editing, altering cellular responses to DSBs may be an effective strategy to rebalance editing outcomes towards HDR and away from other repair pathways. To identify factors that regulate HDR from a double-stranded DNA donor (dsDonor), we utilized a pooled screen to define the consequences of thousands of individual gene knockdowns during Cas9-initiated HDR from a double strand plasmid donor. We find that templated dsDonor repair pathways are mostly genetically distinct from single strand donor DNA (ssDonor) repair but share aspects that include dependency upon the Fanconi Anemia (FA) pathway. We also identified several factors whose knockdown increases HDR and thus act as repressors of gene modification. Screening available small molecule inhibitors of these repressors revealed that the cell division cycle 7-related protein kinase (CDC7) inhibitor XL413 increases the efficiency of HDR by 2-3 fold in many contexts, including primary T-cells. XL413 stimulates HDR through cell cycle regulation, inducing an early S-phase cell cycle arrest that, to the best of our knowledge, is uncharacterized for Cas9-induced HDR. We anticipate that XL413 and other such rationally developed inhibitors will be useful tools for boosting the efficiency of gene modification.