AXON GUIDANCE IN THE SPINAL CORD

轴突导向其目标是第一步， 选择性神经连接的发展。的长远目标 在这个建议中描述的实验是确定细胞和 轴突和生长锥引导下的分子事件 在哺乳动物中枢神经系统内的目标。工作 集中在脊髓中连合神经元轴突的导航 在他们的轨迹中，一条绳索指向一个中间目标， 位于脊髓腹侧中线的细胞。的投影 连合神经元是定型的，发生在两个阶段，最初的 腹侧延伸局限于脊髓的外侧边缘， 随后的突起朝向中线的内侧和腹侧。 这种刻板的途径可能是由于存在几种不同的 引导线索这项建议的目的是审查其性质， 这些提示的功能。 初步的实验表明， 连合轴突最初的腹侧延伸仅限于 表达细胞外基质成分的脊髓神经上皮， 由抗体INO识别，并且可能包含层粘连蛋白-乙酰肝素 硫酸蛋白多糖复合物。细胞外基质的作用 将在体外检查限制连合轴突的生长。的 将检查INO复合体上连合轴突的延伸。在 此外，针对INO的抗体调节轴突生长的能力， 扩展将被确定。最后，受体在连合中的作用 将检查基质中糖蛋白的轴突。 我们已经证明底板细胞释放一种趋化因子， 影响体外连合轴突的生长方向， 负责连合轴突向地板的内侧轨迹 体内平板。这提供了第一个实验证据， 向化性与中枢神经系统发育的关系 系统向化作用将详细研究，重点是 热带因子作用的时间进程和范围。此外，本发明还提供了一种方法， 将确定因子的生化性质， 有助于其纯化和分析其作用机制。 拟议中的实验应能增进我们对自然的理解， 事件的调节和相互作用导致发展 一组中枢神经元的轨迹，脊髓的连合神经元， 线.这些信息还将使我们能够确定其中有多少人 这些机制可能会被用于发展中国家的其他地区。 神经系统最初轴突延伸的许多机制 并且轴突投射向适当靶的引导也可以 对轴突的再生至关重要理解这些机制 对于我们治疗退行性或发育性疾病的能力至关重要 的神经系统。

The guidance of axons towards their targets is one of the first steps in the development of selective neural connections. The long term aim of the experiments described in this proposal is to determine the cellular and molecular events that underly the guidance of axons and growth cones towards their targets within the mammalian central nervous system. The work focuses on the navigation of the axons of commissural neurons in the spinal cord towards an intermediate target in their trajectory, the floor plate cells at the ventral midline of the spinal cord. The projection of commissural neurons is stereotyped and occurs in two stages, the initial ventral extension being confined to the lateral edge of the spinal cord and the subsequent projection directed medially and ventrally to the midline. This stereotyped pathway may be due to the presence of several distinct guidance cues. The purpose of this proposal is to examine the nature and function of these cues. Preliminary experiments have revealed that the pathway taken during the initial ventral extension of commissural axons is restricted to a region of spinal cord neuroepithelium expressing an extracellular matrix component, recognized by the antibody INO, and probably comprising a laminin-heparan sulphate proteoglycan complex. The role of the extracellular matrix in restricting the growth of commissural axons will be examined in vitro. The extension of commissural axons on the INO complex will be examined. In addition, the ability of antibodies directed against INO to modulate axonal extension will be determined. Finally, the role of receptors on commissural axons for the glycoproteins in the substratum will be examined. We have shown that floor plate cells release a chemoattractant factor that influences the direction of growth of commissural axons in vitro and may be responsiblefor the medial trajectory of commissural axons towards the floor plate in vivo. This provides the first experimental evidencefor the involvement of chemotropism in the developmentof the central nervous system. The chemotropic effect will be examined in detail with emphasis on the time course and range of the action of the tropic factor. In addition, the biochemical properties of the factor will be determined in order to facilitate its purification and the analysis of its mechanism of action. The proposed experiments should enhance our understanding of the nature, regulation and interaction of events leading to the developmental trajectory of one set of central neurons, commissural neurons of the spinal cord. The information will also permit us to determine how many of these mechanisms are likely to be used in other parts of the developing central nervous system. Many of the mechanisms underlying initial axonal extension and the guidance of axonal projections towards appropriate targets may also be essential for regeneration of axons. Understandingthese mechanisms is fundamental to our ability to treat degenerative or developmental disorders of the nervous system.