Axon Guidance and Olfactory Map Development

地形图是所有感官系统处理传入信息的手段。因此，寻找调节地形图发育的分子是神经生物学中的一个紧迫问题。经典地说，视网膜轴突到大脑的投射为研究神经映射提供了一个模型，其中存在外周感受器薄片到映射图上的直接、点对点映射。然而，与不同组织的地图的开发，如嗅觉地图，人们知之甚少。对不同气味作出反应的嗅觉神经元散布在感受器薄层中。然而，它们将轴突非常精确地投射到大脑中的特定目标(肾小球)。嗅觉纤维导航到靶点的分子机制，例如引导信号及其信号机制，基本上是未知的。我的实验室的长期目标是以果蝇为模型系统，阐明嗅轴突引导和正位图形成的分子和细胞机制。我们的初步数据表明，参与细胞骨架控制和细胞运动的两个信号分子，Dock(SH2/SH3适配器)和Pak(丝氨酸/苏氨酸激酶)，是精确定位苍蝇嗅觉轴突所必需的。在这个提议中，我们假设Dock和Pak在信号转导级联中发挥作用，准确地将嗅觉生长锥引导到它们的目标位置。我们的具体目标是：1)确定Dock和Pak在嗅轴突中调控的确切细胞事件。这将通过使用各种细胞命运和亚细胞标记对dock和pak突变体进行详细的表型分析来进行。2)阐明了Dock和Pak作用的分子机制。这将通过结构-功能研究以及对Dock和Pak基因在嗅轴突引导中的遗传上位性分析来实现。3)确定LIM-Kinase(一种丝氨酸/苏氨酸激酶)是否是PAK下游的一个新的信号成分。这将通过对纯化蛋白的体外激酶分析，以及对Pak和Lim-Kinase基因在嗅轴突投射中的遗传相互作用的分析来评估。这些实验有望提供关键的见解，并首次一瞥嗅觉生长锥体导向和嗅觉映射形成的分子机制。

Topographic maps are the means by which all sensory systems process afferent information. Hence, finding the molecules that regulate topographic map development is a pressing issue in neurobiology. Classically, projections of retinal axons to the brain has provided a model for the investigation of neural maps where there is direct, point- to-point mapping of the peripheral receptor sheet onto the map. However, development of maps with a different organization, like the olfactory map, is poorly understood. Olfactory neurons responsive to different odors are interspersed in the receptor sheet. Yet they project their axons with great precision to specific targets (glomeruli) in the brain. The molecular mechanisms by which olfactory fibers navigate to their targets, e.g. guidance cues and their signaling mechanisms, are essentially unknown. The long-term goal of my laboratory is to elucidate the molecular and cellular mechanisms of olfactory axon guidance and odotopic map development, using Drosophila as a model system. Our preliminary data indicated that two signaling molecules that are involved in cytoskeletal control and cellular motility, Dock (an SH2/SH3 adapter) and Pak (a serine/threonine kinase), are required for precise targeting of the fly olfactory axons. In this proposal, we hypothesize that Dock and Pak act in a signal transduction cascade to precisely steer olfactory growth cones to their targets. Our specific aims are to: 1) Identify the exact cellular events regulated by Dock and Pak in olfactory axons. This will be carried out through detailed phenotypic analyses of the dock and Pak mutants using a variety of cell-fate and subcellular markers. 2) Delineate the molecular mechanisms of Dock and Pak's function. This will be achieved through structure-function studies, and genetic epistatic analyses of dock and Pak genes in olfactory axon guidance. 3) Determine if Lim-Kinase (a serine/threonine kinase) is a novel signaling component downstream of Pak. This will be assessed through in vitro kinase assays with purified proteins, and analyses of the genetic interactions between Pak and Lim- kinase genes in the projections of olfactory axons. These experiments are expected to provide critical insights, and the first glimpse into the molecular mechanisms of olfactory growth cone steering and olfactory map formation.