Molecular mechanisms in controlling development of touch-sensing neurons

描述（申请人提供）：触觉是我们日常生活、社会交往和性行为所必需的，它是由三叉神经（TG）和背根神经节（DRG）内的机械感觉神经元介导的。尽管触觉很重要，但人们对哺乳动物的触觉知之甚少。机械敏感性的分子基础，产生不同类型机械感觉神经元和回路的发育机制，以及它们的独特功能，在很大程度上是未知的。我们的长期目标是在分子、细胞和电路水平上了解不同类型哺乳动物机械感觉神经元的发育机制和功能，并以小鼠为模型系统。在此之前，我们发现一小部分表达神经营养受体酪氨酸激酶Ret的小鼠体感觉神经元发育成一种经典的哺乳动物机械感觉神经元，即快速适应（RA）机械受体。此外，我们确定了Ret在控制RA机械感受器发育中的核心作用，并发现Ret敲除小鼠中RA机械感受器的一种亚型Pacinian小体的外周末端器官未形成。然而，Ret指定RA机械受体不同亚型的信号靶点仍然难以捉摸。有趣的是，我们的初步研究已经确定了ETS转录因子Er81是太平洋小体神经元规范中Ret信号传导的重要靶点。我们建议阐明Ret/Er81信号通路在控制太平洋小体神经元发育中的作用。目的一：表征Er81在太平洋小体和触觉回路形成中的作用。我们将利用原位杂交和免疫染色技术彻底表征Er81在RA机械受体中不同发育阶段的表达。我们还将解决Er81缺失的太平洋小体神经元的主要缺陷，并使用组织特异性敲除小鼠来确定Er81是否不仅在神经元中需要，而且在太平洋小体形成的辅助细胞中也需要。最后，我们将通过在成年小鼠中消融Er81来探讨Er81是否需要维持太平洋小体。目的二：确定Ret如何调节Er81调控太平洋小体神经元的发育。我们将研究Ret信号是否需要和/或充分调节太平洋小体神经元Er81的转录、磷酸化和核定位。我们还将确定Er81对于介导Ret信号传导是否必要和/或充分。最后，我们将探讨Ret是否通过丝裂原活化蛋白激酶（MAPK）途径调控Er81。综上所述，本研究将确定(1)Er81是否是Ret信号通路控制太平洋小体神经元发育的新靶点；(2)Ret信号通路在体内如何调控Er81。这项研究的结果将大大提高我们对哺乳动物机械感受器如何发育的理解，并为损伤后轴突再生提供见解。

DESCRIPTION (provided by applicant): Touch sensation, which is essential for our daily life, social interactions and sexual behaviors, is mediated by mechanosensory neurons within the trigeminal (TG) and dorsal root ganglion (DRG). Despite its importance, touch sensation is poorly understood in mammals. The molecular basis of mechanosensitivity, the developmental mechanisms that generate different types of mechanosensory neurons and circuits, and their unique functions, are largely unknown. Our long-term goal is to understand, at the molecular, cellular and circuit levels, the developmental mechanisms and the function of different types of mammalian mechanosensory neurons, using mice as a model system. Previously, we discovered that a small population of mouse somatosensory neurons expressing the neurotrophic receptor tyrosine kinase Ret develops into a classic type of mammalian mechanosensory neuron, the rapidly adapting (RA) mechanoreceptors. Moreover, we established a central role for Ret in controlling the development RA mechanoreceptors and found that peripheral end organs of one subtype of RA mechanoreceptors, the Pacinian corpuscles, are not formed in Ret knock-out mice. However, the signaling targets of Ret to specify different subtypes of RA mechanoreceptors remain elusive. Interestingly, our preliminary studies have identified the ETS transcription factor Er81 as an important target of Ret signaling in the specification of Pacinian corpuscle neurons. We propose to elucidate the roles of a Ret/Er81 signaling pathway in controlling the development of Pacinian corpuscle neurons. Aim I: Characterize the function of Er81 in Pacinian corpuscle and touch circuit formation. We will thoroughly characterize the expression of Er81 in RA mechanoreceptors using in situ hybridization and immunostaining at different developmental stages. We will also address the primary deficits of Er81 null Pacinian corpuscle neurons and use tissue specific knockout mice to determine if Er81 is required not only in neurons but also in accessory cells for Pacinian corpuscle formation. Lastly, we will address whether Er81 is required for maintenance of Pacinian corpuscles by ablating Er81 in adult mice. Aim II: Determine how Ret regulates Er81 to control the development of Pacinian corpuscle neurons. We will examine if Ret signaling is required and/or sufficient for regulating Er81 transcription, phosphorylation and nuclear localization in Pacinian corpuscle neurons. We will also determine if Er81 is necessary and/or sufficient for mediating the Ret signaling. Finally, we will address if Ret regulates Er81 through the mitogen- activated protein kinase (MAPK) pathway. In summary, the proposed research will determine (1) if Er81 is a novel target of Ret signaling to control the development of Pacinian corpuscle neurons and (2) how Ret signaling regulates Er81 in vivo. Results from this research will greatly improve our understanding of how mammalian mechanoreceptors develop and provide insight into axonal regeneration after injuries.