NETRINS AND SEMAPHORINS AND AXONAL GUIDANCE

这项提案将研究神经网络蛋白和信号蛋白的作用，轴突 在Zebrafish的指导下。 semaphorins和netrins的发现 导致对化学吸引和排斥机制的评价， 轴突导向 然而，我们对体内作用的理解， 这些分子还不完整 1. semaphorins是一个大型的 分子家族，但其功能方面仅为3所知 信号蛋白该提案将研究2个以上的体内作用 信号蛋白 2.显然，几种机制协调工作， 来引导轴突 我们现在对个体如何 netrins和semaphorins的工作，但还不知道这些分子如何 共同引导特定的生长锥。这一建议将看到如何 这些分子协同工作以引导脊髓连合轴突。 3. 连合生长锥首先向中线延伸，然后远离中线 从中枢神经系统中线 他们是如何做到这一点，尽管存在的 双侧对称的引导线索，如化学吸引性netrins 在中枢神经系统腹侧中线表达，并没有得到很好的理解。 这个提议测试了一种解释这种行为的机制。 基于我们对斑马鱼netrin和semaphorins的分析， 这些分子在其他生物体中的作用，一个模型， 生成了2个netrin和2个semaphorins，用于路径查找， 脊髓连合轴突 该模型的关键特征是， 连合生长锥改变它们对这些分子的反应， 腹侧中线，可能是与地板相互作用的结果 板连合生长锥在同侧腹侧延伸 因为它们被屋顶分泌的Sema Z2排斥 由腹侧分泌的Netrin-1a和Netrin-1b吸引 分别为绳索和底板的一半;在底板处暂停 重新编程，然后向腹侧延伸到对侧， 因为他们对Sema Z2不敏感或被Sema Z2吸引， 对Netrin-1b不敏感或排斥，对Netrin-1b不敏感或保持 被Netrin-1a吸引此外，Sema Z7现在表示为 背索排斥生长锥， 在背索中纵向延伸。 我们的基本策略是 操纵信号蛋白和netrin，并确定这如何影响 斑马鱼胚胎中生长锥的行为。 此外，我们将 通过检查连合来测试模型中提出的冗余 脊髓中的生长锥缺少顶板和底板， 它们缺乏包括Sema Z2和Netrin-1b在内的分子 源自屋顶和地板。

This proposal will examine the role of netrins and semaphorins for axon guidance in the zebrafish. The discovery of semaphorins and netrins has lead to an appreciation of chemoattractive and repulsive mechanisms for axon guidance. However, our understanding of the in vivo action of these molecules is still incomplete. 1. The semaphorins are a large family of molecules, but aspects of their function is only known for 3 semaphorins. This proposal will examine the in vivo action of 2 more semaphorins. 2. It is clear that several mechanisms work coordinately to guide axons. We now have some understanding of how individual netrins and semaphorins work, but do not yet know how these molecules work together to guide specific growth cones. This proposal will see how these molecules work in concert to guide spinal commissural axons. 3. Commissural growth cones first extend toward the midline and then away from the midline in the CNS. How they do this despite the presence of bilaterally symmetric guidance cues, such as chemoattractive netrins expressed at the ventral midline of the CNS, is not well understood. This proposal tests a mechanism that accounts for this behavior. Based upon our analysis of netrins and semaphorins in zebrafish and the actions of these molecules in other organisms, a model that incorporates 2 netrins and 2 semaphorins was generated to account for pathfinding by spinal commissural axons. The critical feature of the model is that commissural growth cones change their responses to these molecules at the ventral midline, perhaps as a result of interactions with the floor plate. Commissural growth cones extend ventrally on the ipsilateral side of the cord because they are repulsed by Sema Z2 secreted by the roof plate and attracted by Netrin-1a and Netrin-1b secreted by the ventral half of the cord and floor plate, respectively; pause at the floor plate to reprogram themselves; and then extend ventrally on the contralateral side because they are insensitive to or attracted by Sema Z2, insensitive to or repulsed by Netrin-1b, and insensitive to or remain attracted to Netrin-1a. Furthermore, Sema Z7 which is now expressed by the dorsal cord repulses the growth cones so that they now turn to extend longitudinally in the dorsal cord. Our basic strategy will be to manipulate semaphorins and netrins and determine how this affects the behavior of growth cones in zebrafish embryos. In addition, we will test the redundancy proposed in the model by examining commissural growth cones in spinal cords missing both the roof and floor plate so that they are devoid of molecules including Sema Z2 and Netrin-1b derived from the roof and floor plate.