Mechanism of an Evolutionary Change in Development

大多数无脊椎动物门包含的物种， 生命周期中的一个阶段。在某些情况下， 改变或消除幼虫期的趋势。 关于发育过程中的变异是如何产生的，我们知之甚少 在进化过程中。在此建议中，开发了一个模型系统 并被用来研究进化背后的机制 发展的变化。该模型系统由两个紧密相连的 海鞘的相关种类，显示出不同的幼虫形态 并且能够进行种间杂交。眼斑裸花金龟 (the有尾目物种）发展一个传统的尾巴（或有尾目） 幼虫，其中包含脑色素细胞，脊索，和尾巴 肌肉细胞相比之下，Molgula occulta（无尾物种） 发育出无尾（或无尾）幼虫，缺乏脑色素 细胞、脊索和分化的肌肉细胞。杂交种 是由无尾目的卵和 有尾目动物发育出脑色素细胞和脊索 但不形成分化的肌肉细胞，这表明两者都 母体和合子的变化发生在进化过程中， 无尾发育该提案结合了胚胎学和 分子方法1）表征母体和合子 从有尾目到无尾目幼虫转变的变化 发展，2）检查负责的分子机制 因为无尾类动物缺乏肌细胞分化， 3)以确定无尾两栖类的亲缘关系， 有尾目海鞘预计结果将提供更多 全面了解 发展中的进化变化。

Most invertebrate phyla contain species which include a larval phase in their life cycle. In certain instances, however, there has been a tendancy to modify or eliminate the larval phase. Little is known about how modifications in development arise during evolutoin. In this proposal, a model system is developed and exploited to study the mechanisms underlying evolutionary changes in development. This model system consists of two closely related species of ascidians that exhibit different larval forms and are capable of interspecific hybridizatrion. Molgula oculata (the urodele species) develops a conventional tailed (or urodele) larva, which contains brain pigment cells, a notochord, and tail muscle cells. In contrast, Molgula occulta (the anural species) develops a tailless (or anural) larva, which lacks brain pigment cells, a notochord, and differentiated muscle cells. Hybrids produced by fertilizing eggs of the anural speies with sperm of the urodele species develop a brain pigment cell and notochrod but do not form differentiated muscle cells, suggesting that both maternal and zygotic changes have occured during the evolution of anural development. This proposal combines embryological and molecular approaches 1) to characterize the maternal and zygotic changes involved in the switch from urodele to anural larval development, 2) to examine the molecular mechanisms responsible for lack of muscle cell differentiation in the anural species and 3) to determine the phylogenetic realtionship of anural and urodele ascidians. The results are expected to provide a more comprehensive understanding of the mechanisms underying evolutionary changes in development.