ABR: Evolution of Left-Right Asymmetry in Chordates using Cephalochordates as a Proxy for the Ancestral Chordate

ABR：使用头索动物作为祖先脊索动物的代理的脊索动物左右不对称的进化

• 批准号: 1353688
• 负责人: Linda Holland
• 金额: $ 64.29万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1353688&HistoricalAwards=false
• 关键词: ABR; Evolution; Left; Right; Asymmetry

Linda Z. Holland, P.I. PROPOSAL NUMBER: 1353688 PROPOSAL TITLE: ABR: Evolution of Left-Right Asymmetry in Chordates using Cephalochordates as a Proxy for the Ancestral ChordateNontechnical description/broader impacts Cephalochordates (amphioxus and lancelets) are closely related to vertebrates but simpler both structurally and at the gene level as their genomes have not undergone the two rounds of whole-genome duplication that occurred in ancestral vertebrates. While these duplications are useful for humans as a defect in one gene can often be compensated for by a duplicate, the lack of gene duplication in amphioxus makes it ideal for determining how individual genes work together to create an embryo and adult. Because amphioxus is so vertebrate-like, the genetic mechanisms that pattern, for example, the kidney or brain are fundamentally the same for both groups. The difference is that vertebrates have created additional complexity by elaborating upon these basic mechanisms. A major outstanding question is how left/right (LR) asymmetry evolved. Vertebrates are superficially symmetric, but internal organs are asymmetrically arranged across the left/right (LR) axis. This study aims to elucidate the genetic mechanisms of LR asymmetry using two distant amphioxus genera (Branchiostoma and Asymmetron). Importantly, hybrids between the two genera yield larvae intermediate in asymmetry. This study has far reaching implications for understanding gene networks and how they evolve. A collaboration with bioinformaticians will help identify genes that are active at particular developmental stages. It will give undergraduates research experience. During 2013-2014, 13 undergraduates including 6 under-represented minorities participated in research in the Holland laboratory. One postdoctoral fellow will be trained. Results will be presented at meetings and published in scientific journals. Outreach with the Birch Aquarium at Scripps and the San Diego Unified Schools' Enhancing Science Education through Technology program will give middle school students virtual tours of the Holland laboratory with direct interactions via SKYPE. The work will foster cross-disciplinary education via exchanges of students/postdocs between the PI and collaborators, allowing bioinformatics students to learn biology and biology students to learn bioinformatics. Technical descriptionThe basal chordate amphioxus has long been thought to hold clues to vertebrate origins. This proposal addresses a major unresolved question: What is the genetic basis of LR asymmetry in chordates and how has it changed during evolution? The specific aim is to elucidate the evolution of LR asymmetry in chordates using two distant amphioxus genera (Branchiostoma and Asymmetron) as proxies for ancestral chordates. Except for left-sided expression of the conserved triad of Nodal, Lefty and Pitx in embryos of both vertebrates and amphioxus, the fundamental genetic basis of LR patterning in chordates is elusive. It is proposed that specification of LR asymmetry begins with skewed maternal Nodal and is refined by BMP suppressing Nodal on the right. The simplicity of amphioxus embryos allows dissection of gene networks starting with the egg and ending with a vertebrate-like embryo. Branchiostoma and Asymmetron offer the "Goldilocks Principle"- alike enough to be sure that two structures are homologous and unlike enough to elucidate genetic differences in LR asymmetry. Hybrids between the two genera have intermediate asymmetry. The Holland lab pioneered research on B. floridae, was the first to study Asymmetron development and establish year-round breeding of both species in the laboratory. sequencing the A. lucayanum genome and is currently sequencing the A. lucayanum genome. The two genera are similar, but LR asymmetries differ in several respects. Importantly, Branchiostoma has gonads on both sides, but Asymmetron has them only on the right. The approach combines in situ hybridization, antibody labeling, manipulating gene function, RNA-Seq and bioinformatics. Comparisons of the molecular basis of LR patterning and germ cell migration in both species will elucidate the fundamental basis of LR asymmetry in chordates and test the overall hypothesis that vertebrates evolved from an amphioxus-like ancestor. The results promise to be applicable not just to cephalochordates but also to vertebrates and may transform ideas on evolution of the myriad variations vertebrates added to the basic theme of a small non-yolky embryo gastrulating by invagination.

琳达·Z·霍兰德 (Linda Z. Holland) 提案编号：1353688 提案标题：ABR：使用头索动物作为祖先脊索动物的代理的脊索动物左右不对称的进化非技术描述/更广泛的影响头索动物（文昌鱼和文昌鱼）与脊椎动物密切相关，但在结构和基因水平上都更简单因为他们的基因组没有经历这两次祖先脊椎动物中发生的多轮全基因组复制。虽然这些重复对人类有用，因为一个基因的缺陷通常可以通过重复来弥补，但文昌鱼缺乏基因重复，使其成为确定单个基因如何协同工作以产生胚胎和成体的理想选择。由于文昌鱼非常像脊椎动物，因此两个群体的肾脏或大脑等模式的遗传机制基本上是相同的。不同之处在于，脊椎动物通过阐述这些基本机制创造了额外的复杂性。 一个主要的悬而未决的问题是左/右（LR）不对称是如何演变的。脊椎动物表面上是对称的，但内脏器官在左/右 (LR) 轴上不对称排列。本研究旨在利用两个远缘文昌鱼属（Branchiostoma 和 Asymmetron）阐明 LR 不对称的遗传机制。重要的是，两个属之间的杂交产生不对称的中间幼虫。这项研究对于理解基因网络及其进化方式具有深远的影响。与生物信息学家的合作将有助于识别在特定发育阶段活跃的基因。它将为本科生提供研究经验。 2013-2014年间，包括6名少数族裔在内的13名本科生参与了荷兰实验室的研究。将培训一名博士后研究员。结果将在会议上公布并发表在科学期刊上。与斯克里普斯伯奇水族馆和圣地亚哥联合学校的“通过技术加强科学教育”计划的外展活动将为中学生提供虚拟参观荷兰实验室的机会，并通过 SKYPE 进行直接互动。 这项工作将通过 PI 和合作者之间的学生/博士后交流来促进跨学科教育，让生物信息学学生学习生物学，让生物学学生学习生物信息学。技术描述长期以来，人们一直认为基部脊索动物文昌鱼掌握着脊椎动物起源的线索。该提案解决了一个尚未解决的主要问题：脊索动物 LR 不对称的遗传基础是什么？它在进化过程中是如何变化的？具体目的是使用两个远缘文昌鱼属（Branchiostoma 和 Asymmetron）作为祖先脊索动物的代表来阐明脊索动物 LR 不对称性的进化。除了脊椎动物和文昌鱼胚胎中保守三联体 Nodal、Lefty 和 Pitx 的左侧表达外，脊索动物中 LR 模式的基本遗传基础是难以捉摸的。建议 LR 不对称性的规范从偏斜的母体 Nodal 开始，并通过 BMP 抑制右侧的 Node 进行细化。文昌鱼胚胎的简单性允许从卵开始到脊椎动物样胚胎结束的基因网络的解剖。文昌鱼和 Asymmetron 提供了“金发姑娘原理”——足够相似以确保两个结构是同源的，并且足够不同以阐明 LR 不对称性的遗传差异。两个属之间的杂交体具有中等不对称性。荷兰实验室开创了对 B. floridae 的研究，是第一个研究 Asymmetron 发育并在实验室中建立这两个物种的全年育种的实验室。 对 A. lucayanum 基因组进行测序，目前正在对 A. lucayanum 基因组进行测序。这两个属相似，但 LR 不对称性在几个方面有所不同。重要的是，文昌鱼两侧都有性腺，但不对称鱼只在右侧有性腺。该方法结合了原位杂交、抗体标记、操纵基因功能、RNA-Seq 和生物信息学。对两个物种的 LR 模式和生殖细胞迁移的分子基础进行比较，将阐明脊索动物中 LR 不对称的基本原理，并检验脊椎动物从文昌鱼类祖先进化而来的总体假设。这些结果有望不仅适用于头索动物，也适用于脊椎动物，并且可能会改变关于脊椎动物无数变异进化的想法，这些变异添加到小型非卵黄胚胎通过内陷进行原肠胚形成的基本主题中。