Urochordate Origins of Neural Crest and Muscle

[02:12 . 11]关于脊索动物门脊椎动物特征的起源，我们所知甚少。在这里，重点是尾脊索动物的发展方面，有望为这一进化和发展中的重要问题提供新的线索。总体目标是评估海鞘尾脊索动物的两个关键脊椎动物特征的起源：(1)迁移的神经嵴细胞和(2)诱导过程指定的幼虫肌肉组织。在当代发育生物学中使用的海鞘物种（例如，Ciona, Molgula， Styela和Halocynthia）表现出快速发育，高度流线型的蝌蚪幼虫。这些衍生的幼虫似乎缺乏迁移的神经嵴细胞，仅含有约40个尾肌细胞，这些细胞主要由定位的细胞质决定因子指定。流线型蝌蚪是为快速扩散而进化的，并不代表大多数海鞘幼虫。大多数海鞘物种的蝌蚪更大，发育缓慢，头部更复杂，尾巴更结实，这可能代表了真正的祖先状态。因此，Jeffery博士将在这里介绍腹水鞘（Ecteinascidia turbinata）作为一个实验系统来研究尾脊索动物中关键脊椎动物特征的起源。外ascidia是Ciona的近亲，它有一个巨大的蝌蚪幼虫，头部有预先形成的虹吸雏形，感觉器官扩大，咽鳃有裂缝，有一条强壮的尾巴，有1134个肌肉细胞。具有高度分化蝌蚪的海鞘的发展几乎被忽视了，现在已经成熟了，可以用现代技术进行分析。外海鞘系统将允许他结合各种实验胚胎学和分子方法，包括使用正在进行的Ciona基因组和EST数据库，来研究发育的进化。这一建议特别针对神经嵴和肌肉发育的腹膜外鞘胚胎。首先，他将利用活性染料和基因标记研究相结合的方法，确定外海鞘胚胎是否具有与脊椎动物神经嵴细胞同源的迁移细胞。他已经从DiI标记实验中获得了强有力的证据，证明存在迁移的神经嵴样细胞。他将确定神经嵴样细胞的胚胎来源、区域迁移模式和发育命运，并将其与脊椎动物神经嵴细胞的特性进行比较。其次，他将确定腹外海鞘尾部肌肉细胞的发育是由细胞质决定因素控制的，这是流线型幼虫腹外海鞘尾部肌肉特征的主要方式，还是由诱导过程控制的，这是脊椎动物肌肉特征的方法。这些研究将通过细胞谱系追踪、原位mRNA和蛋白质定位以及卵裂球分离和重组的结合来进行。这些研究的智力价值在于，它们将为尾脊索动物神经嵴细胞的进化史和尾肌发育机制提供新的信息。拟议的活动的更广泛的影响是，它将解决脊索动物门中关键脊椎动物特征的起源，并将我们未来的注意力集中在特定的脊索动物或非脊索动物群体上，以便绘制复杂脊椎动物身体计划的进化起点。最后，该研究计划通过将本科生纳入调查过程来促进研究中的通识教育。

0212110JefferyLittle is known about the origins of vertebrate features in the Phylum Chordata. Here, the focus is on aspects of urochordate development that are expected to shed new light on this important problem in evolution and development. The overall goal is to assess the origins of two key vertebrate features in the ascidian urochordates: (1) migratory neural crest cells and (2) larval musculature specified by inductive processes. The ascidian species used in contemporary developmental biology (e. g., Ciona, Molgula, Styela, and Halocynthia) exhibit rapidly developing, highly streamlined tadpole larvae. These derived larva appear to lack migratory neural crest cells and contain only about 40 tail muscle cells, which are primarily specified by localized cytoplasmic determinants. The streamlined tadpoles, which have evolved for rapid dispersal, are not representative of most ascidian larvae. Most ascidian species have larger, slowly developing tadpoles with more complex heads and robust tails, which are likely to represent the true ancestral state. Accordingly, Dr. Jeffery will introduce here the ascidian Ecteinascidia turbinata as an experimental system to study the origin of key vertebrate features in the urochordates. Ecteinascidia, a close relative of Ciona, has a giant tadpole larva exhibiting a head with preformed siphon rudiments, enlarged sensory organs, and pharyngeal gill slits, and a robust tail with 1134 muscle cells. The development of ascidians with highly differentiated tadpoles has been virtually ignored and is ripe for analysis using modern technologies. The Ecteinascidia system will permit him to combine a variety of experimental embryological and molecular approaches, including use of ongoing Ciona genomic and EST databases, to study the evolution of development. This proposal specifically addresses neural crest and muscle development in Ecteinascidia embryos. First, he will determine whether Ecteinascidia embryos have migratory cells homologous to vertebrate neural crest cells using a combination of vital dye and gene marking studies. He already has strong evidence from DiI marking experiments that migratory neural crest-like cells are present. He will determine the embryonic sources, regional migration patterns, and developmental fates of the neural crest-like cells, and compare their properties to vertebrate neural crest cells. Second, he will determine whether the development of tail muscle cells in Ecteinascidia is controlled by cytoplasmic determinants, the predominant means of tail muscle specification in ascidians with streamlined larvae, or by inductive processes, the method of muscle specification characteristic of vertebrates. These studies will be carried out by a combination of cell lineage tracing, in situ mRNA and protein localization, and blastomere isolation and recombination. The intellectual merit of these studies is that they will provide new information on the evolutionary history of neural crest cells and the mechanisms of tail muscle development in the urochordates. The broader impacts of the proposed activity is that it will address the origin of key vertebrate features in the Phylum Chordata and focus our future attention on particular chordate or non-chordate groups in order to chart the evolutionary beginnings of the complex vertebrate body plan. Finally, the research is planned to foster general education in research by incorporating undergraduate students into the investigative process.