A model for elimination of defective mitochondrial genomes

总结 这项研究的主要目的是揭示消除缺陷线粒体的机制。 基因组（mtDNA）通过遗传和表观遗传过程。动物细胞线粒体DNA的异质性状态 允许有缺陷的mtDNA积累，具有潜在的复制优势。质量控制系统功能 来移除这些有害的线粒体基因组。我们发现一个大的带有缺失的 mtDNA在C. elegans，uaDf 5，其通常稳定地维持在与野生型mtDNA的异质状态 随着成年年龄的增长，WT-mtDNA增加，这种增加的负担会传递给年长母亲的后代。 这种有缺陷的线粒体DNA也在缺乏以下两种质量控制系统的突变体中升高：线粒体自噬（粉红色）， 1（-））或生殖系程序性细胞死亡（PCD; ced-13（-））。然而，出乎意料的是，我们发现， pink-1和ced-13功能被消除，相反的情况发生：uaDf 5被快速和完全去除， 有效地治愈动物的线粒体疾病。更令人吃惊的是， pink-1（-）或ced-13（-）单突变的母亲与缺乏PINK-1和CED-13的男性也表现出快速的 删除缺失的mtDNA，这种效应发生，而不管不同的后代基因型。这些 这些发现使我们假设，这些杂交的起始遗传事件（IGE）触发了一个强有力的 跨代表观遗传过程，区分并有效地去除缺陷mtDNA。与这些 基础性的发现，我们将探讨这一惊人的mtDNA质量控制过程的机制。在Aim中 1，我们将分析IgE触发的uaDf 5去除对其年龄依赖性积累的影响， 分析其发展时间。我们将测试这种消除过程是否对其他线粒体DNA具有普遍性。 删除，并评估大小和序列位置对去除过程的影响。我们将调查 线粒体自噬和PCD途径中的其他组分是否在激活清除中显示协同作用，并将测试 假设增强的线粒体分裂可能允许区分和消除uaDf 5。在Aim中 2、分析线粒体DNA质量表观遗传代际传递的基础 控制过程。我们将评估我们发现的WT-mtDNA的急剧扩增 发生在uaDf 5被去除的世代之前，是去除过程所需的，并且uaDf 5是 需要触发这种放大。我们将研究IGE是否拮抗线粒体UPR， 其保护uaDf 5不被去除。我们将测试IGE是由父亲的特定触发的假设。 PINK-1和CED-13的丢失。最后，我们将评估IGE激活的表观遗传过程是否通过 通过细胞核或细胞质/线粒体。这些研究将有助于我们了解 健康的线粒体基因组得以维持，这是对衰老、神经变性和 线粒体疾病

SUMMARY The major objective of the proposed research is to unveil mechanisms that eliminate defective mitochondrial genomes (mtDNA) through genetic and epigenetic processes. The heteroplasmic state of mtDNA in animal cells allows accumulation of defective mtDNAs with potential replicative advantage. Quality control systems function to remove such deleterious mitochondrial genomes. We found that the abundance of a large deletion-bearing mtDNA in C. elegans, uaDf5, that is normally stably maintained in a heteroplasmic state with wild-type mtDNA (WT-mtDNA) increases with adult age and that this increased burden is passed onto offspring of older mothers. This defective mtDNA is also elevated in mutants lacking either of two quality control systems: mitophagy (pink- 1(-)) or germline programmed cell death (PCD; ced-13(-)). Unexpectedly, however, we found that when both pink-1 and ced-13 functions are eliminated, the opposite occurs: uaDf5 is rapidly and completely removed, effectively curing the animal of mitochondrial disease. Even more startling, descendants of crosses between pink-1(-) or ced-13(-) single mutant mothers with males lacking both PINK-1 and CED-13 also show rapid removal of the deleted mtDNA, and this effect occurs irrespective of the differing descendant genotypes. These findings lead us to hypothesize that an initiating genetic event (IGE) from these crosses triggers a potent transgenerational epigenetic process that discriminates and effectively removes defective mtDNA. With these foundational findings, we will investigate the mechanisms of this striking mtDNA quality control process. In Aim 1, we will analyze the effect of the IGE-triggered removal of uaDf5 on its age-dependent accumulation and analyze its developmental timing. We will test whether the elimination process is general to other mtDNA deletions and assess the impact of size and sequence location on the removal process. We will investigate whether other components in the mitophagy and PCD pathways show synergy in activating removal and will test the hypothesis that enhanced mitochondrial fission may allow for discrimination and elimination of uaDf5. In Aim 2, we will analyze the basis for the apparently epigenetic transgenerational transmission of the mtDNA quality control process. We will evaluate the hypothesis that the dramatic amplification of WT-mtDNA that we found occurs prior to the generations in which uaDf5 is removed is required for the removal process and that uaDf5 is required to trigger this amplification. We will investigate whether the IGE antagonizes the mitochondrial UPR, which protects uaDf5 from removal. We will test the hypothesis that the IGE is triggered specifically by paternal loss of PINK-1 and CED-13. Finally, we will assess whether the IGE-activated epigenetic process is transmitted through the nucleus or cytoplasm/mitochondria. These studies will contribute to our understanding of how a healthy mitochondrial genome is maintained, a problem of premier importance to aging, neurodegeneration, and mitochondrial disease.