Trans-generational maintenance of mitochondrial DNA integrity in oocytes during early folliculogenesis

Mutations in mitochondrial DNA (mtDNA) can lead to mitochondrial and cellular dysfunction. However, recent studies suggest that there is purifying selection against mutant mtDNAs during transgenerational transmission. We investigated the mtDNA dynamics during ovarian follicle development. Using base-editing, we generated mice harboring a 3177 G>A mutation corresponding to the human Leber hereditary optic neuropathy (LHON)-related mtDNA mutation and confirmed the transgenerational reduction of mutant mtDNA. Using a mouse follicle culture system in which pathogenic mtDNA mutations were introduced in vitro followed by mtDNA sequencing and digital PCR, we found this germline heteroplasmy shift during early folliculogenesis was induced by the decrease of mutant mtDNA together with compensatory replication of wild-type mtDNA. In contrast, synonymous mtDNA mutations did not impact the mtDNA dynamics. These findings show that mice can eliminate certain pathogenic mtDNA mutations in the germline during early folliculogenesis, maintaining mitochondrial integrity across generations.