Developmental Mechanisms of Body Plan Evolution

尽管世界上有数百万种动物，但它们可分为35种基本体型（门）。这个门出现在寒武纪的辐射中，已经存在了超过5亿年。对发育进化的研究揭示了两个重要的和意想不到的观察结果。首先，在关系密切的分类群中，完全不同的发育模式可以迅速进化。第二，主调控基因是高度保守的，即使在形态上完全不同的门中也是如此。这些结果表明，发育重组主要是通过现有基因和途径的共同选择发生的，我们可以利用保守调控基因的表达来确定身体计划的转变是如何发生的。本研究探讨棘皮动物的五分体形与其姊妹类群脊索动物的双侧对称体形的进化。这一建议侧重于将双边对称的身体计划转换为五分体计划的转换，并在不同的门中发现控制轴向决定的共享过程。提出的工作将寻求建立一个潜在的棘皮动物同源脊索在轴向结构的诱导。这种同源存在的假设可以通过定义脊椎动物轴向决定基因的棘皮动物同源物的表达模式来证实。该项目将利用一种仅在4天内就能直接发育成幼年的海胆。将从海胆中分离出与脊椎动物前-后和背-腹轴诱导通路相关的基因。该项目将表征基因的空间表达模式，以推断棘皮动物与脊椎动物轴向特征的同源性。轴向决定基因的功能将通过过/异位表达实验进行检测。最后，该项目将通过实验胚胎学和基因标记的使用来确定诱导过程在棘皮动物轴向决定中的作用。这种对诱导过程的测试将进一步测试两个形态不同但相关的门的发育过程的潜在同源性。该项目的结果将提供对发育过程的进化修改的见解，以及发育过程在限制形态进化过程中的作用。

Raff 9724003 Although there are several million species of animals, they fall into groups representing 35 basic body plans (phyla). The phyla appeared in the Cambrian radiation, and have existed for over a half billion years. The study of the evolution of development has revealed two important and unexpected observations. The first is that radically different developmental modes can evolve rapidly among closely related taxa. The second is that master regulatory genes are highly conserved, even among morphologically widely disparate phyla. These results suggest that developmental reorganization has occurred largely by co-option of existing genes and pathways, and that we can exploit the expression of conserved regulatory genes to determine how body plan transformations took place. This study investigates the evolution of the pentameral body plan of echinoderms with the bilaterally symmetric body plan of their sister group, the chordates. This proposal focuses on the transformations that have converted a bilaterally symmetric body plan into a pentameral one, and on finding shared processes that govern axial determination in disparate phyla. The proposed work will seek to establish a potential echinoderm homolog to the notochord in the induction of axial structures. The hypothesis that such a homolog exists can be confirmed by defining patterns of expression of echinoderm homologs of vertebrate axial determination genes. The project will exploit a sea urchin species that develops directly into a juvenile adult in only four days. Genes involved in specification of vertebrate anterior-posterior and dorsal-ventral axis induction pathways will be isolated from that sea urchin. The project will characterize spatial expression patterns of the genes to infer echinoderm homologs to vertebrate axial features. The function of axial determination genes will be tested by over/ectopic expression experiments. Finally, the project will determine the role of induction processes in axial determination in echin oderms by experimental embryology and use of gene markers. This testing of inductive processes will further test the potential homologies of developmental processes in two morphologically distinct but related phyla. The results of this project will provide an insight into the evolutionary modifications of developmental processes, and into the role of developmental processes in constraining the course of morphological evolution.