Axon Guidance in the Olfactory System

描述（由申请人提供）：嗅觉感觉神经元（OSN）的发生是一个持续的过程，从发育早期开始并持续到成人。它要求新生成的轴突成功地穿过固有层和筛板，进入中枢神经系统。神经发育事件的中断可导致多种疾病，包括自闭症、脆性X染色体、缺脑畸形和卡尔曼综合征。我的最终目标是提高我们对驱动和调节轴突生长的机制的理解。具体来说，我的目标是研究嗅觉通路的发展，并测试dishevelded （Dvl）蛋白影响轴突引导和突触形成的假设。轴突引导信号、细胞粘附分子和气味受体诱导的活性都与OSN轴突最终精确靶向特定肾小球有关。然而，OSN轴突将轴突从嗅上皮（OE）延伸到嗅球（OB）的机制仅被部分理解，并且经常存在争议。同样，在OB中，参与在osn和投射神经元之间建立突触的分子也不太清楚。Wnt分泌的分子通过卷曲（Fz）受体参与许多过程，包括轴突引导和突触形成。我们最近在嗅觉系统中发现了几个这样的分子，其模式暗示了OSN轴突生长的作用。Fz激活后信号通路中的一个关键分子是Dvl。本提案包括系统表征所有三种Dvl （Dvl-1， -2和-3）分子和一些候选下游信号分子（如RhoA， Daam-1， ROCK）在嗅觉系统中的表达模式。蛋白质（Western blot和免疫组织化学）和mRNA （RT-PCR和原位杂交）的表达将被研究。Dvl分子的作用将通过子宫内电穿孔注射一种特征沉默RNA （siRNA）来评估，我最近优化了这种沉默RNA来标记OE中的osn。这项研究的结果将促进我们对Wnt-Fz信号通路（包括Dvls）在OSN轴突中的作用的理解。反过来，这将对理解嗅觉系统中的轴突引导和突触形成产生重大影响，并广泛地影响中枢神经系统的其他区域。

DESCRIPTION (provided by applicant): Olfactory sensory neuron (OSN) genesis is an ongoing process that begins early in development and continues in adults. It requires that newly generated axons successfully navigate through the lamina propria and the cribiform plate, into the central nervous system. Disruptions in neurodevelopmental events are responsible for a wide range of diseases, including Autism, Fragile X, Lissencephaly, and Kallman's syndrome. My ultimate goal is to improve our understanding of the mechanisms that drive and regulate axonal outgrowth. Specifically, my goal in this proposal is to study the development of the olfactory pathway and test the hypothesis that Dishevelled (Dvl) proteins influence both axon guidance and synapse formation. Axon guidance cues, cell adhesion molecules, and odor receptor induced activity have all been implicated in the precise final targeting of OSN axons to specific glomeruli. However, the mechanisms used by OSN axons to extend an axon from the olfactory epithelium (OE) toward the olfactory bulb (OB) are only partially understood, and often controversial. Similarly, the molecules involved in establishing the synapses between the OSNs and the projection neurons in the OB are not well understood. Wnt secreted molecules, acting through Frizzled (Fz) receptors are implicated in many processes, including axon guidance and synapse formation. We recently found several of these molecules in the olfactory system, in a pattern suggestive of a role in OSN axon outgrowth. One key molecule in the signaling pathway after Fz activation is Dvl. This proposal includes a systematic characterization of the expression patterns of all three Dvl (Dvl-1, -2 and -3) molecules and some candidate downstream signaling molecules (e.g. RhoA, Daam-1, ROCK) in the olfactory system. Both protein (Western blot and immunohistochemistry), and mRNA (RT-PCR and in situ hybridization) expressions will be studied. The role of Dvl molecules will be assessed by injecting a characterized silencing RNA (siRNA) by in utero electroporation, which I recently optimized to label OSNs in the OE. The results from this proposal will promote our understanding of the role of the Wnt-Fz signaling pathways, including Dvls, in OSN axons. This, in turn, will have a significant impact on understanding axon guidance and synapse formation in the olfactory system, and broadly in other regions of the central nervous system. PUBLIC HEALTH RELEVANCE: Loss of the sense of smell is an early indicator of several major neurological diseases in humans including Alzheimer's disease, Parkinson's disease, and schizophrenia. As new neurons mature in the olfactory epithelium in the nasal cavity, they extend an axon that navigates long distances into the central nervous system. This project proposes understanding the mechanisms used by olfactory sensory neuron axons to grow into the olfactory bulb, which will give us the knowledge to manipulate them and use them in therapeutic strategies for neurodegenerative diseases, and perhaps provide new insights into the etiology of diseases such as Kallman's syndrome in which the olfactory system fails to properly develop.