Transfer of mitochondrial DNA into the nuclear genome during gene editing

Mitochondria serve as the cellular powerhouse, and their distinct DNA makes them a prospective target for gene editing to treat genetic disorders. However, the impact of genome editing on mitochondrial DNA (mtDNA) stability remains a mystery. Our study reveals previously unknown risks of genome editing that both nuclear and mitochondrial editing cause broad transfer of mitochondrial DNA segments into the nuclear genome in various cell types including human cell lines, primary T cells, retinal cells, and mouse embryos. Furthermore, drug-induced mitochondrial stresses and mtDNA breaks exacerbate this transfer of mtDNA into the nuclear genome. Notably, we observe that the newly developed mitochondrial base editor DdCBE can also cause widespread mtDNA integrations. However, we provide a practical solution to suppress the transfer of mtDNA by co-expressing TREX1 or TREX2 exonucleases during DdCBE editing. These findings also shed light on the origins of mitochondrial-nuclear DNA segments.