FORMATION OF NEURAL PATHWAYS IN THE EMBRYO

本申请旨在探索潜在的机制 轴突寻路和目标识别在视网膜 胚胎爪蟾中枢神经系统的投射，一个系统， 非常适合这样的研究，因为最近 开发的体内延时系统，修改为 药物灌注。 这一建议，一个延续 长期研究这个系统，有三大目标。 的 首先是了解生长锥丝状伪足在 轴突导向 用细胞松弛素处理的视网膜轴突， 一个肌动蛋白解聚剂，不要在 个脑袋 在这个提议中， 在不同时间用细胞松弛素处理的单个轴突 和剂量，将与他们的寻路 行为 其次，越来越明显的是， 在文化中，可以通过生长来响应特定的暗示， 停止、转动或倒塌。 信号转导 必须使用各种级联来翻译这些 哪些信使系统 在发育中的大脑中有什么用途， 但是，还没有接触过。 其中一个目标是 建议，因此，调查的作用 第二信使系统在轴突引导中的作用， 在完整的胚胎大脑中的目标识别。 一 筛选程序的基础上的影响， 膜渗透剂已经被用于牵连 一些相关的信号通路，特别是G- 蛋白质级联，并建议其他途径，如 钙途径可能是无关的或多余的。 在 此外，已证明生长丝状伪足 是大脑中寻路所必需的，这表明， 这可能是信号转导的位点。 实验 建议以严格的方式执行这些建议， 区分不同解释的实验，以及 以分子的形式延伸这条通路。 第三，视网膜轴突dX到顶盖使用局部 神经上皮中的位置线索 证据表明 某些位置信息基因，如同源异型盒基因， 基因和配对盒基因，参与建立 在早期脊椎动物神经发生中的地形特征。 最近，已经表明，至少其中一些 基因可以直接调节特定的 细胞粘附分子，使得它们可能 因此也影响CNS中的轴突导航。 体内基因导入技术的进展使得 非洲爪蟾胚胎中的基因有可能错误表达， 神经系统 在这个提议中，爪蟾同源盒- 包含的基因包括有爪的，无远端的，Pax-6， 和神经节细胞或神经上皮细胞， 生长中的视网膜轴突通常会通过这些通道。 的 错误表达的胚胎将被检查的缺陷， 寻路和目标识别。

This application seeks to explore the underlying mechanisms of axonal pathfinding and target recognition in the retinal projection of the embryonic Xenopus CNS, a system which is very amenable to such studies because of a recently developed in vivo time-lapse system, modified for the perfusion of drugs. This proposal, a continuation of a long term study of this system, has three major goals. The first is to understand the role of growth cone filopodia in axonal guidance. Retinal axons treated with cytochalasin, an actin depolymerizer, do not pathfind properly in the brain. In this proposal, the filopodial activity of individual axons treated with cytochalasin at various times and doses, will be correlated with their pathfinding behavior. Second, it has become increasingly clear that growth cones in culture can to respond particular cues by growing, stopping, turning or collapsing. Signal transduction cascades of various sorts must be used to translate these signals into growth cone action Which messenger systems are used for which purpose in the developing brain, however, has not yet been approached. One goal of this proposal, therefore is to investigate the role of particular second messenger systems in axon guidance and target recognition in the intact embryonic brain. A screening procedure based on the effects of particular membrane permeant agents has already been used to implicate some of the signaling pathways involved, particularly a G- protein cascade, and to suggest that other pathways, like the calcium pathway may be uninvolved or redundant. In addition, it has been demonstrated that growth filopodia are necessary for pathfinding in the brain, suggesting that this may be the sites of signal transduction. Experiments are proposed to pursue these suggestions with rigorous experiments that distinguish alternate interpretations, and to extend the pathway molecularly. Third, retinal axons dX to the tectum using local positional cues in the neuroepithelium. Evidence suggests that certain positional information genes, such as homeobox genes and paired-box genes, are involved in establishing topographic identity during early vertebrate neurogenesis. Recently, it has been shown that at least some of these genes can directly regulate tahe expression of particular cell adhesion molecules, making it likely that they therefore also affect axonal navigation in the CNS. Advances in gene introduction technology in vivo have made it possible to misexpress genes tin the embryonic Xenopus nervous system. In this proposal, Xenopus homeobox- containing genes, including engrailed, distal-less, Pax-6, and ganglion cells or in the neuroepithelial cells through which the growing retinal axons normally navigate. The misexpressing embyros will be examined for defects in pathfinding and target recognition.