Mechanisms of mitochondrial mutation rate variation across eukaryotes

项目总结 线粒体DNA(MtDNA)的高突变率是遗传性和年龄相关疾病的主要原因。 长期以来，有一种观点认为，人类和动物线粒体基因组的易突变性质 Models是与氧化磷酸化和能量有关的强烈代谢活动的副产品 转换。然而，最近的证据挑战了这一观点，人们越来越多地认识到 负责线粒体DNA复制和修复的酶机制的差异是高 人类线粒体DNA的突变率。线粒体DNA复制和修复途径的变异也可以解释为什么 一些真核生物谱系(如植物)能够抑制其线粒体基因组的突变率 异常低的水平。我们研究计划的一个主要主题是确定 负责真核细胞线粒体突变率的变异，从而帮助解决长期的 长期的不确定性，为什么人类的发病率如此之高。要克服相关的技术挑战 通过研究像新生突变这样的罕见事件，我们应用了多种创新的测序方法 可以检测超低频新DNA序列变异的技术，本质上是 在突变和受损碱基发生时捕获它们，并将它们映射到核苷酸水平的分辨率。我们的 今后的工作将解决两个主要问题。首先，植物线粒体是如何达到最低水平的 曾经观察到的点突变的比率(每十亿年每个位置不到一个替换)？这一行 调查将建立在我们最近的发现基础上，即植物-MSH1是维持低突变率所必需的 在植物细胞器基因组中。MSH1是MutS基因家族中神秘的成员，很可能是通过 巨型病毒的水平传播。我们将检验这一假设，即它是一个新的机制的一部分 导致双链断裂的错配修复，然后是基于模板的重组修复。 第二，线粒体如何修复紫外线引起的庞大的DNA损伤？我们将检验这一假设 线粒体包含一条先前未知的修复途径，与经典的核苷酸切除相似 维修(NER)。这一假说是由我们最近观察到的分歧真核生物暴露出来的 紫外线照射下的模型体系会导致携带受损碱基的线粒体DNA衍生的寡核苷酸的释放 在一致的位置，并表现出特有的长度轮廓，这是NER的一个标志。总体而言，这项研究 该计划将有助于确定为什么线粒体基因组表现出如此极端的突变率差异 真核生命之树。

PROJECT SUMMARY High mutation rates in mitochondrial DNA (mtDNA) are a major cause of inherited and age-related diseases. There is a longstanding view that the mutation-prone nature of mitochondrial genomes in humans and animal models is a byproduct of the intense metabolic activity associated with oxidative phosphorylation and energy conversion. However, recent evidence has challenged this idea, and there is growing recognition that differences in the enzymatic machinery responsible for mtDNA replication and repair are a key cause of high mutation rates in human mtDNA. Variation in mtDNA replication and repair pathways may also explain why some eukaryotic lineages (e.g., plants) are able to suppress mutation rates in their mitochondrial genomes to exceptionally low levels. An overarching theme of our research program is to identify the mechanisms responsible for variation in mitochondrial mutation rates across eukaryotes and thereby help resolve the long- term uncertainties about why rates are so high in humans. To overcome the technical challenges associated with investigating rare events like de novo mutations, we have applied multiple innovative sequencing technologies that can detect new DNA sequence variants present at ultra-low frequencies, essentially capturing mutations and damaged bases as they occur and mapping them to nucleotide-level resolution. Our future work will address two major questions. First, how do plant mitochondria achieve some of the lowest rates of point mutations ever observed (less than one substitution per site per billion years)? This line of investigation will build off our recent discovery that plant-MSH1 is necessary for maintaining low mutation rates in plant organelle genomes. MSH1 is enigmatic member of the MutS gene family which was likely acquired by horizontal transfer from giant viruses. We will test the hypothesis that it is part of a novel mechanism of mismatch repair that induces double-stranded breaks followed by template-based recombinational repair. Second, how do mitochondria repair bulky DNA damage introduced by UV? We will test the hypothesis that mitochondria contain a previously unrecognized repair pathway with similarities to classic nucleotide excision repair (NER). This hypothesis is motivated by our recent observation that exposure of divergent eukaryotic model systems to UV light results in the release of mtDNA-derived oligonucleotides that carry damaged bases at consistent positions and exhibit characteristic length profiles, a hallmark of NER. Overall, this research program will help determine why mitochondrial genomes exhibit such extreme mutation rate variation across the eukaryotic tree of life.