Wiring of Spiral Ganglion Neurons and Auditory Hair Cells by Secreted Semaphorins

大鼠螺旋神经节神经元与毛细胞联系的建立和维持 耳蜗对听觉功能至关重要，而这些连接的中断是公认的 感觉神经性听力损失的后果，以及人工耳蜗植入性能下降的原因。 尽管这些联系很重要，但SGN轴突引导和 突触发生在很大程度上是未知的。这项研究的长期目标是确定这些机制 负责听觉神经系统的发展，因此可以开发改进的治疗方法来治疗 人类的听力损失。本申请中概述的研究结果将定义三类 信号素(Sema3s)，一大类激活Neuropilin/Plexin(NRP/Plxn)辅助受体的分泌因子 对于SGN轴突的引导决策是必不可少的。从概念上讲，建议的 这项研究具有创新性，因为它将首次对SGN轴突引起的听力损失进行深入分析 引导缺陷，因为对耳蜗管内SGN纤维的精细加工知之甚少 与听力学评估有关。这项拟议的研究在技术上具有创新性，因为一只鼠标 允许标记、可视化和实时分析SGN-毛细胞相互作用的模型将是 使用。将定义在耳蜗中表达的特定的3类信号素的功能。功能获得性腺病毒感染实验和功能丧失小鼠模型将被用来测试 假设Sema3C吸引SGN，而Sema3A对不同的SGN种群进行排序。为了 在细胞内传递信号时，NRP必须与丛蛋白共受体结合。不同的SGN种群 差异表达丛状蛋白A3，从而确定丛状蛋白A3的功能。使用药理学，小鼠 模型和蛋白质截断实验，假设丛状蛋白A3在不同人群中激活 针对特定毛细胞群体的SGN将进行测试。这项研究的贡献将 意义重大，因为它将定义第一批分子信号通路之一，对 哺乳动物听觉系统内复杂传入神经模式的发展。

The establishment and maintenance of spiral ganglion neuron (SGN) connections with hair cells in the cochlea is critical to auditory function, and the disruption of these connections is both a well-recognized consequence of sensorineural hearing loss, and a cause of diminished cochlear implant performance. Despite the importance of these connections, the mechanisms required for SGN axon guidance and synaptogenesis are largely unknown. The long-term goal of this research is to define the mechanisms responsible for auditory nervous system development, so that improved therapies can be developed to treat hearing loss in humans. The results from the research outlined in this application will define how class-3 Semaphorins (Sema3s), a large family of secreted factors that activate Neuropilin/Plexin (Nrp/Plxn) coreceptors on growing axons, are essential for SGN axon guidance decisions. Conceptually, the proposed research is innovative because it will provide the first in-depth analysis of hearing loss caused by SGN axon guidance defects, as there is little known about how the elaboration of SGN fibers within the cochlear duct con-elates with audiological assessments. The proposed research is technically innovative because a mouse model that allows the labeling, visualization and analyses of SGN-hair cell interactions in real time will be used. The function of specific class-3 Semaphorins that are expressed in the cochlea will be defined. Gain-of-function adenovirus infection experiments, and loss-of-function mouse models, will be used to test the hypothesis that Sema3C attracts SGNs and that Sema3A sorts different populations of SGNs. In order to transmit a signal intracellularly, Nrps must bind to Plexin co-receptors. Distinct populations of SGNs differentially express PlexinA3, thus the function of PlexlnA3 will be determined. Using pharmacology, mouse models, and protein truncation experiments, the hypothesis that PlexinA3 activation in different populations of SGNs targets them to specific populations of hair cells will be tested. This contribution of this research will be significant because it will define one of the first molecular signaling pathways to contribute to the development of the complex afferent innervation pattern within the mammalian auditory system.