Data from: Early replication dynamics of sex-linked mitochondrial DNAs in the doubly uniparental inheritance species Ruditapes philippinarum (Bivalvia Veneridae)

Mitochondrial homoplasmy, which is maintained by strictly maternal inheritance and a series of bottlenecks, is thought to be an adaptive condition for metazoans. Doubly uniparental inheritance (DUI) is a unique mode of mitochondrial transmission found in bivalve species, in which two distinct mitochondrial genome (mtDNA) lines are present, one inherited through eggs (F) and one through sperm (M). During development, the two lines segregate in a sex- and tissue-specific manner: females lose M during embryogenesis, whereas males actively segregate it in the germ line. These two pivotal events are still poorly characterized. Here we investigated mtDNA replication dynamics during embryogenesis and pre-adulthood of the venerid Ruditapes philippinarum using real-time quantitative PCR. We found that both mtDNAs do not detectably replicate during early embryogenesis, and that the M line might be lost from females around 24 h of age. A rise in mtDNA copy number was observed before the first reproductive season in both sexes, with the M mitochondrial genome replicating more than the F in males, and we associate these boosts to the early phase of gonad production. As evidence indicates that DUI relies on the same molecular machine of mitochondrial maternal inheritance that is common in most animals, our data are relevant not only to DUI but also to shed light on how differential segregations of mtDNA variants, in the same nuclear background, may be controlled during development.由严格母系遗传与一系列瓶颈效应维持的线粒体纯质性（mitochondrial homoplasmy），被认为是后生动物的适应性状态。双单亲遗传（Doubly uniparental inheritance, DUI）是双壳类物种中特有的线粒体传递模式，该模式下存在两套独立的线粒体基因组（mtDNA）系：一套经由卵子传递（F型），另一套经由精子传递（M型）。在发育进程中，两套线粒体基因组系呈现性别与组织特异性的分离模式：雌性个体在胚胎发生阶段会丢失M型线粒体基因组，而雄性个体则将其主动分配至生殖系中。目前学界对这两个关键事件的分子机制仍缺乏深入认知。本研究以帘蛤科菲律宾蛤仔（Ruditapes philippinarum）为研究对象，借助实时定量PCR（real-time quantitative PCR）技术，解析了其胚胎发生期与成年前期的线粒体DNA复制动态。研究结果显示，两套线粒体基因组在早期胚胎发生阶段均未出现可检测到的复制；且雌性个体的M型线粒体基因组可能在孵化后24小时左右发生丢失。在首个繁殖季来临前，雌雄个体的线粒体DNA拷贝数均出现显著上升：雄性个体中M型线粒体基因组的复制水平显著高于F型；我们将这一拷贝数提升与性腺发育的早期阶段相关联。已有研究证实，双单亲遗传依赖于多数动物共有的线粒体母系遗传分子机制，因此本研究的数据不仅对双单亲遗传领域具有重要参考价值，同时也为阐明在相同核背景下，线粒体DNA变异的差异化分离如何在发育过程中受到调控提供了新的研究视角。