Department of Neurology, Haukeland University Hospital, Bergen, Norway; Department of Clinical Medicine, University of Bergen, Bergen, Norway.
Wellcome Centre for Mitochondrial Research, Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.
Neurobiol Aging. 2018 Mar;63:120-127. doi: 10.1016/j.neurobiolaging.2017.10.024. Epub 2017 Dec 8.
Mitochondrial DNA (mtDNA) deletions accumulate with age in postmitotic cells and are associated with aging and neurodegenerative disorders such as Parkinson's disease. Although the exact mechanisms by which deletions form remain elusive, the dominant theory is that they arise spontaneously at microhomologous sites and undergo clonal expansion. We characterize mtDNA deletions at unprecedented resolution in individual substantia nigra neurons from individuals with Parkinson's disease, using ultradeep sequencing. We show that the number of deleted mtDNA species per neuron is substantially higher than previously reported. Moreover, each deleted mtDNA species shows significant differences in sequence composition compared with the remaining mtDNA population, which is highly consistent with independent segregation and clonal expansion. Deletion breakpoints occur consistently in regions of sequence homology, which may be direct or interrupted stretches of tandem repeats. While our results support a crucial role for misannealing in deletion generation, we find no overrepresentation of the 3'-repeat sequence, an observation that is difficult to reconcile with the current view of replication errors as the source of mtDNA deletions.
线粒体 DNA（mtDNA）缺失在有丝分裂后细胞中随年龄的增长而积累，并与衰老和神经退行性疾病（如帕金森病）有关。尽管缺失形成的确切机制仍不清楚，但主流理论认为它们自发地在微同源位点形成，并发生克隆扩增。我们使用超高深度测序，以空前的分辨率描述了帕金森病患者个体黑质神经元中的 mtDNA 缺失。我们表明，每个神经元中缺失的 mtDNA 种类数量明显高于之前的报道。此外，与剩余的 mtDNA 群体相比，每个缺失的 mtDNA 种类在序列组成上都有显著差异，这与独立分离和克隆扩增高度一致。缺失的断点始终发生在序列同源性区域，这些区域可能是直接的或串联重复的中断区域。虽然我们的结果支持错误配对在缺失产生中的关键作用，但我们没有发现 3'重复序列的过度表达，这一观察结果与当前将复制错误视为 mtDNA 缺失来源的观点难以调和。
