Mitochondrial base editor DdCBE cause substantial DNA off-target editing in nuclear genome

DdCBE was recently developed to install base conversion in mitochondrial genome of several species including human cells. However, genome wide off-target profile has yet been interrogated for DdCBE with the rigorous method such as GOTI (genome-wide off-target analysis by two-cell embryo injection). Therefore, we performed 2-cell embryo injection of DdCBE targeting two loci in mouse mitochondrial genome and whole genome off-target analysis in mouse embryos. High on-target efficiency with up to 72% was achieved in edited cells derived from injected blastomere. Furthermore, bystander editing close to on-target loci was observed in mitochondrial genome, which is similar to recent findings. Notably, we further found DdCBE unexpectedly generate substantial off-target events identified by GOTI in nuclear genome. Our results suggest a high-fidelity DdCBE with reduced bystander editing and genome-wide off-target activity is required for precise base editing in mitochondrial DNA while preserving integrity of nuclear genome.