Developmental patterning of the anterior neural plate in a simple chordate

描述（由申请人提供）：我们建议使用海鞘，玻璃海鞘，作为一个简单的脊索动物模型，研究关键的脊椎动物发育过程。玻璃海鞘胚胎和幼虫类似于简化的脊椎动物蝌蚪，具有突出的脊索，背侧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，被囊动物（尾索动物），如玻璃海鞘是最近的生活亲属的脊椎动物。玻璃海鞘具有许多特殊的功能，阐明脊椎动物的发育过程。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。蝌蚪仅由约2,000个细胞组成，这些细胞来自简单而明确的谱系，与C.优雅可以通过电穿孔用所需的转基因DNA转化数千个同步发育的胚胎。简而言之，脊椎动物关键发育过程的基因网络，如神经嵴的特化，在玻璃海鞘中高度保守，而在C。线虫、果蝇或其它无脊椎动物模型系统。Gans和Northcutt的“新头”理论提出，脊椎动物头部的大多数组织代表了新的创新，在无脊椎动物中没有同源的对应物。在脊椎动物中，这些组织来自颅神经嵴和基板，来自神经管和前神经板之间的边界。这一修订建议的重点是规范玻璃海鞘退化颅基板和神经嵴的前边缘的神经管。我们将使用细胞特异性标记方法、顺式调控分析、靶向错误表达测定、基因破坏方法、细胞分选技术和计算建模的组合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）确定控制口道和相关基板的特化和内陷的基因调控网络;（2）确定调控假定垂体特化的基因网络;和（3）表征色素耳石和单眼的特化， 并鉴定负责间充质和“合成”外生间充质定向迁移的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.