Human cleaving embryos enable efficient mitochondrial base-editing with DdCBE

Mitochondrial diseases could be caused by heritable mutations in both mtDNA and nuclear DNA 1 , 2 , 3 . Because mitochondria membrane 4 insulated mtDNAs’ access from large ribonucleoprotein complex of Cas9 and sgRNA, mtDNAs are intractable for genetic modifications with RNA-guided CRISPR/Cas9 system commonly used for effectively editing nuclear DNA of different species. Although ZFN and TALEN have been previously engineered to successfully cut and eliminate mtDNA in a programmable way 5 , 6 , 7 , 8 , 9 , correction of disease-causing point mutations in mtDNA remained challenging. Recently, DddA-derived cytosine base editors (DdCBEs) have been developed to specifically induce C-to-T conversion in mtDNA by fusion of sequence-programmable TALE and split deaminase derived from interbacterial toxins 10 . DdCBE has been demonstrated to generate mutant zebrafish and mice carrying base-modified mtDNA by injecting DdCBE mRNA into zygotes 11 , 12 . However, the efficacy of DdCBE for specific installation of C-to-T conversion in mtDNA of human embryos remained to be investigated.