Tracing the timing of monozygotic twinning using somatic mutations.

项目摘要 在这个提议中，我们的目标是证明一个关于单卵孪生时间的假设，这个假设是在1997年首次提出的。 世纪50年代该假说指出，同卵双生发生在不同阶段， 胚胎发生，并且可以通过出生时绒毛膜/羊膜的共享来推断时间。虽然这个简单的 许多教科书都采用了直觉假设，缺乏对这一假设的科学证明。 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标记， 早期胚胎发生中细胞谱系的条形码。我们将利用这些体细胞突变来追踪 具有不同程度绒毛膜性/绒毛膜性的单卵双胞胎的胚胎史。我们已经证明 这种胚胎体细胞突变的检测在测序平台上确实是可能的。与我们 生物信息学管道，我们希望证明这一假设，即同卵双生的时间与 同卵双胞胎共有的绒毛膜/绒毛膜状态。在目标1中，我们将对双胞胎家庭进行测序， 鉴定具有不同程度绒毛膜/绒毛膜双胞胎的胚胎体细胞突变， 以及双卵双胞胎。我们将比较和验证不同模式的胚胎体细胞突变， 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 双胞胎之间的基因差异。这将使我们能够估计与不同类型的孪生时间 绒毛膜性/绒毛膜性。在Aim 3中，我们将通过分离单个细胞来在单细胞水平上追踪孪生事件。 从每一个双胞胎中提取细胞来绘制双胞胎的细胞谱系树。 我们的研究将强调单卵双胞胎之间的不一致性，并证明普遍接受的 单卵双胞胎的绒毛膜性/双卵性与分裂时间相关的假说 单卵双胞胎事件。这将是第一项全面描述 单卵双胞胎从基因组学的角度使用胚胎体细胞突变。我们还将证明， 这些胚胎体细胞突变可以解释单卵双胞胎中的一些不一致性， 并非双胞胎中的所有不一致都应被称为非遗传病因。追踪胚胎体细胞 单细胞水平的突变将帮助我们精确地确定孪生事件的时间。因此，本研究将 增强我们对孪生的基本生物学的理解，并增加另一种解释机制， 单卵双胞胎的遗传不一致性，这也可能影响治疗和咨询的选择， 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.