Urochordate Origins of Neural Crest and Muscle

0212110关于脊索动物门中脊椎动物特征的起源，人们知之甚少。在这里，重点放在尿索发育的各个方面，这些方面有望为这一进化和发展中的重要问题提供新的线索。总的目标是评估脊椎动物的两个关键特征的起源：(1)迁徙的神经脊细胞和(2)由诱导过程指定的幼虫肌肉。现代发育生物学中使用的海鞘类物种(如乔纳属、莫古拉属、海鞘属和盐生属)表现出发育迅速、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脊细胞，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素指定。为了快速扩散而进化的流线型蝌蚪，并不是大多数海鞘幼虫的代表。大多数海鞘物种都有更大、发育缓慢的蝌蚪，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博士将在这里介绍海鞘动物Eteinascidia turbinata作为研究尾索动物关键脊椎动物特征起源的实验系统。Eteinascidia是Ciona的近亲，有一只巨大的蝌蚪幼虫，头上有预先形成的虹吸状痕迹，感觉器官增大，咽部裂开，尾巴粗壮，有1134个肌肉细胞。具有高度分化的蝌蚪的海鞘的发育几乎被忽视了，使用现代技术进行分析的时机已经成熟。Eteinascidia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，以研究发育的进化。这项建议专门针对外周血吸虫胚胎中的神经脊和肌肉发育。首先，他将结合活性染料和基因标记研究，确定外囊尾虫胚胎是否有与脊椎动物神经脊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脊样细胞。他将确定神经脊样细胞的胚胎来源、区域迁移模式和发育命运，并将它们的特性与脊椎动物的神经脊细胞进行比较。其次，他将确定尾部肌肉细胞的发育是由细胞质决定因素控制的，还是由诱导过程控制的，细胞质决定因素是流线型幼虫尾部肌肉指定的主要方式，还是脊椎动物特有的肌肉指定方法。这些研究将通过结合细胞谱系追踪、原位mRNA和蛋白质定位以及卵裂球分离和重组来进行。这些研究的学术价值在于，它们将为脊神经细胞的进化史和尾部肌肉发育的机制提供新的信息。拟议活动的更广泛影响是，它将解决脊椎动物脊索动物门的关键特征的起源，并将我们未来的注意力集中在特定的脊索类或非脊索类群上，以便绘制复杂脊椎动物身体计划的进化起点。最后，这项研究计划通过将本科生纳入调查过程来培养研究中的通识教育。

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.