Identification, Development and Function of Rapidly Adapting Mechanoreceptors

描述（由申请人提供）：触觉，包括对形状和纹理的感知，在我们的日常生活中是必不可少的。三叉神经节和背根神经节（DRG）神经元亚群是介导这一过程的初级感觉神经元，分为快速（RA）和慢适应（SA）机械感受器。它们的分子身份、在形状和质地感知方面的独特功能以及发育机制在很大程度上是未知的。最近，我发现一小部分表达酪氨酸激酶受体Ret的DRG神经元是难以捉摸的RA机械受体，Ret信号传导对它们的发育至关重要。在本申请中，我建议通过实验来阐明Ret和TrkB信号控制RA机械受体的存活、外周末端器官形成、中枢投射和生理特性的机制。此外，我建议建立新的触觉辨别行为试验和体感神经元特异性白喉毒素（DTA）小鼠系，以测试RA机械受体在触觉辨别中的体内功能。具体目的1：验证Ret和TrkB对于RA机械感受器存活是冗余的假设，以及TrkB在RA机械感觉DRG神经元中自主作用于迈斯纳小体形成的假设。为此，我们将生成Ret和TrkB双敲除小鼠和TrkB条件敲除小鼠来验证我的假设。具体目的2：探讨Ret信号传导指导RA机械受体中枢投射的机制。为此，我将可视化单个Ret null RA机械受体在早期发育期间的中枢轴突投影，以确定原发性轴突投影缺陷的性质。此外，我将鉴定Ret的内源性配体和共受体及其来源，建立其作用机制。特异性目的3：确定Ret信号是否调节RA机械受体的生理特性。在这个目的中，将检查RA机械受体的生理特性，其中Ret在发育早期被切除或在成人中被急性激活或抑制。目的4：开始建立RA机械受体在体内的功能作用。为了研究各种机械感受器的独特功能，我将开发新的行为分析来测试小鼠的触觉辨别。此外，我将生成体感觉神经元特异性条件DTA小鼠系。总之，这些新的检测方法和试剂将使我能够解决RA机械感受器的作用，以及未来在触觉辨别过程中更多的DRG神经元群体。

DESCRIPTION (provided by applicant): Touch sensation, including the perception of form and texture, is essential for our daily lives. Subpopulations of trigeminal and dorsal root ganglion (DRG) neurons are primary sensory neurons mediating this process, and are classified as either rapidly (RA) or slowly adapting (SA) mechanoreceptors. Their molecular identities, unique functions in the context of form and texture perception, and mechanisms of development are largely unknown. Recently, I discovered that a small population of DRG neurons that express the receptor tyrosine kinase Ret are the elusive RA mechanoreceptors and that Ret signaling is essential for their development. In this application, I propose experiments to elucidate the mechanisms by which Ret and TrkB signaling control survival, peripheral end organ formation, central projections, and physiological properties of RA mechanoreceptors. In addition, I propose to develop new tactile discrimination behavior assays and a somatosensory neuron specific diphtheria toxin (DTA) mouse line to test the in vivo functions of RA mechaoreceptors during tactile discrimination. Specific Aim 1: To test the hypothesis that Ret and TrkB are redundant for survival of RA mechanoreceptors and that TrkB functions in RA mechanosensory DRG neurons autonomously for Meissner corpuscle formation. In this aim, Ret and TrkB double knockout mice and TrkB conditional knockout mice will be generated to test my hypothesis. Specific Aim 2: To address the mechanism by which Ret signaling directs central projections of RA mechanoreceptors. For this purpose, I will visualize the central axonal projections of individual Ret null RA mechanoreceptors during early development to establish the nature of the primary axonal projection deficit. In addition, I will identify the endogenous ligand and co-receptor of Ret, and their sources, to establish the mechanism of action. Specific Aim 3: To determine whether Ret signaling modulates the physiological properties of RA mechanoreceptors. In this aim, physiological properties of RA mechanoreceptors in which Ret is either ablated early during development or acutely activated or inhibited in adults will be examined. Aim 4: To begin to establish the functional roles of RA mechanoreceptors in vivo. To study the unique functions of various mechanoreceptors, I will develop new behavioral assays to test tactile discrimination in mice. In addition, I will generate a somatosensory neuron specific conditional DTA mouse line. Together, these new assays and reagent will enable me to address the role of RA mechanoreceptors and, in the future additional populations of DRG neurons during tactile discrimination. PUBLIC HEALTH RELEVANCE: Texture and form discrimination and the perception of touch are fundamental and important for our daily lives. Our study aims to reveal the development and unique functions of newly identified somatosensory neurons implicated in discriminative touch sensation. Insights from this study will be useful for guiding future strategies at promoting nerve regeneration after spinal cord injury.