Oxygen tension modulates the mitochondrial genetic bottleneck and influences the segregation of a heteroplasmic mtDNA variant

Most humans carry a mixed population of mitochondrial DNA (mtDNA heteroplasmy) affecting ~1-2% of molecules, but rapid percentage shifts occur over one generation leading to severe mitochondrial diseases. A decrease in the amount of mtDNA within the developing female germ line appears to play a role, but other sub-cellular mechanisms have been implicated. Establishing an in vitro model of early mammalian germ cell development from embryonic stem cells, here we show the reduction of mtDNA content is modulated by oxygen and reaches a nadir immediately before germ cell specification. The observed genetic bottleneck was accompanied by a decrease in mtDNA replicating foci and the segregation of heteroplasmy, which were both abolished at higher oxygen levels. Thus, differences in oxygen tension during early development can modulate mtDNA segregation, facilitating germ-line purification, and contribute to tissue-specific somatic mutation loads. Overall design: Single-cell RNA seq for 768 cells from mice embryo.

绝大多数人体均携带线粒体DNA（mitochondrial DNA，mtDNA）异质性（heteroplasmy），该现象会影响约1%~2%的DNA分子，且在单代个体间会发生快速的比例变化，进而引发严重的线粒体疾病。发育中的雌性生殖细胞系内的mtDNA含量减少似乎发挥了一定作用，但其他亚细胞机制也被证实参与该过程。本研究通过胚胎干细胞构建了早期哺乳动物生殖细胞发育的体外模型，结果显示mtDNA含量的减少受氧气浓度调控，并在生殖细胞特化前夕达到最低点。观察到的遗传瓶颈伴随mtDNA复制焦点的减少与异质性的分离，而在高氧环境下这两种现象均会被消除。因此，早期发育过程中的氧张力差异可调控mtDNA的分离过程，促进生殖系纯化，并影响组织特异性体细胞突变负荷。整体实验设计：对来自小鼠胚胎的768个细胞进行单细胞RNA测序（Single-cell RNA seq）。