Axon Guidance and Olfactory Map Development

地形图是所有感觉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。传统上，视网膜轴突到大脑的投射提供了用于神经映射图的研究的模型，其中存在外周受体片到映射图上的直接点对点映射。然而，开发地图与不同的组织，如嗅觉地图，是知之甚少。嗅觉神经元对不同气味的反应散布在受体片层中。然而，它们将轴突精确地投射到大脑中的特定目标（肾小球）。嗅觉纤维导航到其目标的分子机制，例如引导线索及其信号传导机制，基本上是未知的。本实验室的长期目标是以果蝇为模型系统，阐明嗅觉轴突导向和嗅觉定位图发展的分子和细胞机制。我们的初步数据表明，参与细胞骨架控制和细胞运动的两种信号分子，Dock（SH 2/SH 3适配器）和Pak（丝氨酸/苏氨酸激酶），是精确靶向果蝇嗅觉轴突所必需的。在这个提议中，我们假设Dock和Pak在信号转导级联中精确地引导嗅觉生长锥到达它们的目标。我们的具体目标是：1）确定在嗅觉轴突中由Dock和Pak调节的确切细胞事件。这将通过使用各种细胞命运和亚细胞标记物对dock和Pak突变体进行详细的表型分析来进行。2)阐明Dock和Pak功能的分子机制。这将通过结构-功能研究，和遗传上位性分析的码头和帕克基因在嗅觉轴突的指导。3)确定Lim-Kinase（一种丝氨酸/苏氨酸激酶）是否是Pak下游的新型信号传导组分。这将通过纯化蛋白质的体外激酶测定和嗅觉轴突投射中Pak和Lim激酶基因之间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，并首次瞥见嗅觉生长锥转向和嗅觉地图形成的分子机制。

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.