Tracing the timing of monozygotic twinning using somatic mutations.

项目总结 在这个建议中，我们的目标是证明关于同卵双胞胎的时间的假设，该假说最早是在 20世纪50年代。该假说指出，同卵双胞胎发生在不同的阶段 胚胎发生的时间可以通过出生时共用绒毛膜/羊膜来推断。虽然这很简单 而直觉假说在很多教材中都被纳入，缺乏科学的证明。 全基因组测序的出现现在允许我们使用胚胎体细胞突变作为分子 早期胚胎发育中细胞谱系的条形码。我们将利用这些体细胞突变来追踪 不同程度绒毛膜/羊膜性同卵双生子的胚胎史。我们已经证明了 在测序平台上检测这种胚胎体细胞突变确实是可能的。带着我们的 生物信息学流水线，我们希望证明同卵双胞胎的时间与 同卵双胞胎共有的绒毛膜/羊膜状态。在目标1中，我们将对双胞胎家庭进行排序 鉴定具有不同程度绒毛膜/羊膜性的同卵双胞胎胚胎体细胞突变 还有同卵双胞胎。我们将比较和验证胚胎体细胞突变的不同模式 不同类型的双胞胎。在目标2中，我们将创建孪生事件的模拟模型，以了解 这对双胞胎之间的基因组差异。这将使我们能够估计不同类型的双胞胎的时间 绒毛膜感染/羊膜感染。在Aim3中，我们将通过分离单个细胞来跟踪单细胞级别的孪生事件 从每一个双胞胎的细胞中画出双胞胎的细胞谱系树。 我们的研究将强调同卵双胞胎之间的不一致性，并证明人们普遍接受的 单卵双胞胎的绒毛膜/羊水与分裂时间相关的假说 同卵双胞胎事件。这将是第一个全面刻画不和谐的研究 从基因组学角度使用胚胎体细胞突变的同卵双胞胎。我们还将展示 这些胚胎体细胞突变可以解释同卵双胞胎中出现的一些不一致，而且 并不是双胞胎中所有的不一致都应该被称为非遗传病因。胚胎体细胞的示踪 单细胞水平的突变将帮助我们准确地确定双胞胎事件的时间。因此，这项研究将 加深我们对双胞胎的基本生物学的理解，并增加另一种解释机制 同卵双胞胎的遗传不协调，这也可能影响对 同卵双胞胎。

Project summary In this proposal, we aim to prove a hypothesis on the timing of monozygotic twinning that was first proposed in the 1950s. The hypothesis states that the monozygotic twinning occurs at different stages during embryogenesis, and that the timing can be inferred by the sharing of chorion/amnion at birth. While this simple and intuitive hypothesis was incorporated into many textbooks, the scientific proof of the hypothesis is lacking. The advent of whole-genome sequencing now allows us to use embryonic somatic mutations as molecular barcodes of cellular lineages in early embryogenesis. We will use these somatic mutations to trace the embryonic history of monozygotic twins with different degrees of chorionicity/amnionicity. We have shown that detection of such embryonic somatic mutations is indeed possible on sequencing platforms. With our bioinformatics pipeline, we hope to prove the hypothesis that the timing of monozygotic twinning is related to the status of chorions/amnions shared by the monozygotic twins. In Aim 1, we will sequence twin families to identify embryonic somatic mutations in monozygotic twins with varying degrees of chorionicity/amnionicity as well as dizygotic twins. We will compare and validate the different pattern of embryonic somatic mutations in different types of twins. In Aim 2, we will create a simulation model of the twinning event to understand the genomic differences between the twins. This will allow us to estimate the timing of twinning with different types of chorionicity/amnionicity. In Aim3, we will trace the twinning event at the single cell level by isolating single cells from each twin to draw the cellular lineage trees of the twins. Our study will emphasize the discordance between monozygotic twins and prove the commonly accepted hypothesis that the chorionicity/amnionicity of monozygotic twins is correlated with the timing of the splitting event of monozygotic twins. This will be the first study to comprehensively characterize the discordance of monozygotic twins from a genomics perspective using embryonic somatic mutations. We will also show that these embryonic somatic mutations can explain some of the discordance seen in monozygotic twins, and that not all discordance in the twins should be referred to as non-genetic etiology. Tracing the embryonic somatic mutations at the single cell level will help us precisely time the twinning event. Therefore, this study will enhance our understanding of the basic biology of twinning and add another mechanism of explanation to genetic discordance in monozygotic twins, which may also affect treatment and counselling options for the monozygotic twins.