Developmental patterning of the anterior neural plate in a simple chordate

描述(申请人提供)：我们建议使用海鞘，作为一个简单的脊索动物模型来研究脊椎动物的关键发育过程。Ciona胚胎和幼虫类似于简化的脊椎动物蝌蚪，有突出的脊索，背部中空的神经管和集中的大脑。最近的分子系统发育研究表明，脊索动物(尾索动物)是脊椎动物现存的最近的近亲。在阐明脊椎动物的发育过程方面，Ciona具有许多特殊的特征。基因组很小(约16,000个基因和160 Mb)，并且缺乏困扰脊椎动物功能遗传分析的全基因组复制事件。蝌蚪只由大约2000个细胞组成，这些细胞来自简单而明确的谱系，与线虫中看到的细胞相当。用所需的转基因DNA通过电穿孔转化数千个同步发育的胚胎是可能的。简单地说，脊椎动物关键发育过程的基因网络，如神经脊的指定，在Ciona中高度保守，但在线虫、果蝇或其他无脊椎动物模型系统中不是。甘斯和诺斯卡特的“新头部”理论提出，脊椎动物头部的大多数组织代表着新的创新，而无脊椎动物没有相应的组织。在脊椎动物中，这些组织来自于神经管和前神经板之间的交界处的颅神经脊和安慰剂。这一修订方案的重点是说明神经管前缘的颅骨原始安慰剂和神经脊的规格。我们将结合使用细胞特异性标记方法、顺式调控分析、靶向错误表达分析、基因干扰方法、细胞分类技术和计算模型来描绘控制这些过程的基因调控网络。研究计划包括以下三个具体目标：(1)确定支配口器和相关安慰剂的规格和内陷的基因调控网络；(2)确定调节假定的垂体腺规格的基因网络；(3)表征有色耳石和耳轮的规格， 并确定负责间充质和“合成”外胚间充质定向迁移的Twist靶基因。

DESCRIPTION (provided by applicant): We propose to use the sea squirt, Ciona intestinalis, as a simple chordate model to study key vertebrate developmental processes. Ciona embryos and larvae resemble simplified vertebrate tadpoles with a prominent notochord, dorsal hollow neural tube, and centralized brain. Recent molecular phylogenetic studies indicate that Tunicates (Urochordates) such as Ciona are the closest living relatives of the vertebrates. Ciona possesses a number of exceptional features for elucidating vertebrate developmental processes. The genome is small (~16,000 genes and 160 Mb) and lacks the whole-genome duplication events that bedevil functional genetic analyses in vertebrates. The tadpole is composed of only ~2,000 cells that arise from simple and well-defined lineages, comparable to those seen in C. elegans. It is possible to transform thousands of synchronously developing embryos with desired transgenic DNAs via electroporation. Simply put, the gene networks underlying key vertebrate developmental processes, such as specification of neural crest, are highly conserved in Ciona but not in C. elegans, Drosophila or other invertebrate model systems. The Gans and Northcutt "new head" theory proposed that most tissues of the vertebrate head represent novel innovations with no homologous counterparts in invertebrates. In vertebrates, these tissues arise from cranial neural crest and placodes, derived from the boundary between the neural tube and anterior neural plate. The focus of this revised proposal is the specification of the Ciona rudimentary cranial placodes and neural crest at the anterior border of the neural tube. We will use a combination of cell- specific labeling methods, cis-regulatory analysis, targeted misexpression assays, gene disruption methods, cell sorting techniques and computational modeling to delineate gene regulatory networks controlling these processes. The research plan includes the following three specific aims: (1) to determine gene regulatory networks governing the specification and invagination of the stomodeum and associated placodes; (2) to determine the gene networks regulating the specification of the putative pituitary; and (3) to characterize the specification of the pigmented otolith and ocellus, and identify Twist target genes responsible for the directed migration of mesenchyme and "synthetic" ectomesenchyme.