Developmental Mechanisms of Body Plan Evolution

虽然有几百万种动物，但它们只分为35个基本的身体计划（门）。 这项建议是研究成年棘皮动物不寻常的身体计划的发展，由于它经历了彻底的重组，为身体计划进化提供了一个独特的模型。 棘皮动物与脊索动物有关。 这一共同祖先是双侧的，但棘皮动物的祖先通过从原始祖先的左侧产生其主要身体轴而产生了新的身体计划。 此外，棘皮动物进化成五室放射状对称。 新的身体结构必须包括发育的重组，这一点在棘皮动物幼虫左侧组织的副产物--成体原基的形成中表现得很明显。 与发育研究中最常用的模型系统不同，棘皮动物在发育过程中改变了它们的身体平面，从幼虫的双侧对称转变为成虫的五角对称。 这种发展变化与它们的进化历史是平行的。 由于棘皮动物进化和棘皮动物发育的关键步骤是产生左右不对称和五配体的过程，因此该项目将重点关注这些过程。 棘皮动物成虫的发育研究很少。Heliocidaris erythrogramma是一种具有非常大的卵的海胆，仅在四天内就直接发育成青少年成虫，并且非常适合研究成虫发育。 本研究将采用以下方法：（1）通过显微外科技术研究该胚胎中自主和局部诱导相互作用的不对称性发展机制。 组织特异性基因标记将用于分析这些过程中操作的胚胎。 (2)本论文将探讨脊椎动物中参与不对称性发生的调控基因的作用，以及H.红细胞增多症。 (3)将通过在H.红带胚 这个项目的结果将提供一个深入了解的机制，基础上的进化修改的发育过程，并将产生理解的发展不对称的胚胎。

Although there are several million species of animals, they fall into groups representing only 35 basic body plans (phyla). This proposal is to study development of the unusual body plan of adult echinoderms, which, because of the radical reorganization it has undergone, offers a unique model for body plan evolution. Echinoderms are related to chordates. Thier common ancestor was bilateral, but the echinoderm ancestor produced a new body plan by generation of its major body axis from the original ancestral left side. In addition, echinoderms evolved a pentameral, radial symmetry. The new body plan had to have involved a reorganization of development, and this is evident in the formation of the adult rudiment as an outgrowth of left-side tissues of the echinoderm larva. Unlike the model systems most used in studies of development, echinoderms transform their body plan in development, making a transformation from the bilateral symmetry of the larva to the pentameral radial symmetry of the adult. This developmental transformation parallels their evolutionary history. As the crucial steps in echinoderm evolution as well as in echinoderm development are the processes that produce left-right asymmetry and pentamery, the project will focus on these. Development of the echinoderm adult has been little studied. Heliocidaris erythrogramma, a sea urchin with a very large egg develops directly into a juvenile adult in only four days, and is highly amenable to study of adult development. The study will use the following approaches: (1) The mechanisms of development of the asymmetries will be studied by microsurgical techniques to investigate autonomous and local inductive interactions in this embryo. Tissue-specific gene markers will be used to analyze these processes in operated embryos. (2) The roles of regulatory genes involved in asymmetry generation in vertebrates will be investigated, and genes involved in development of asymmetry in H. erythrogramma identified. (3) The function of genes implicated in symmetry determination will be tested by over/ectopic expression experiments into appropriate cells of the H. erythrogramma embryo. The results of this project will provide an insight into the mechanisms that underlie evolutionary modifications of developmental processes, and will yield understanding of the development of asymmetries in embryos.