Cas9-triggered chain ablation of cas9 as a gene drive brake

We designed and synthesized a transgene system that we named Cas9-triggered chain ablation (CATCHA). The CATCHA transgene encodes a guide RNA (gRNA) that is expressed ubiquitously from a U6:2 promoter. The gRNA targets a site within the DNA sequence of cas9. The guide RNA is flanked by homology arms (of 1,042 bp and 1,003 bp) that match the cas9 sequences next to the gRNA-specified cleavage site (Fig. 1a). In the presence of both CATCHA and cas9, Cas9 proteins will be guided to cleave the cas9 genomic locus from which Cas9 proteins are expressed. Upon repair of the cleaved cas9 by homology-directed repair (HDR), the cas9 locus will be converted to CATCHA. Such conversion in heterozygous offspring favors amplification of CATCHA in the cas9- carrying population