Non-homologous DNA increases gene disruption efficiency by altering DNA repair outcomes
Cas9 endonuclease can be targeted to genomic sequences by varying the sequence of the single guide RNA (sgRNA). The activity of these Cas9-sgRNA combinations varies widely at different genomic loci and in different cell types. Thus, disrupting genes in polyploid cell lines, or using inefficient sgRNAs, can require extensive downstream screening to identify homozygous clones. We have found that linear, non-homologous oligonucleotide DNA greatly stimulates Cas9-mediated gene disruption in the absence of homology-directed repair. This stimulation greatly increases the frequency of clones with homozygous gene disruptions, even in polyploid cell lines, and rescues otherwise ineffective sgRNAs. The mechanism of enhanced gene disruption differs between human cell lines, stimulating deletion of genomic sequence and/or insertion of non-homologous oligonucleotide DNA at the edited locus in a cell line specific manner. Thus, the addition of non-homologous DNA appears to drive cells towards error-prone instead of error-free repair pathways, dramatically increasing the frequency of gene disruption.