How do non-myelinating glia ensheath axons?

项目总结 轴突的胶质包膜是神经系统的一种保守特征，对正常的神经系统是必不可少的。 功能。轴突包裹的损害或丢失是包括多发性硬化症在内的许多衰弱情况的基础， 脑白质营养不良、周围神经病变和CMT疾病。尽管我们做了多年的工作，但我们对 控制神经胶质发育、神经胶质-轴突通讯和长轴突包膜的分子通路，包括 髓鞘形成，还远远没有完成。我们对非髓鞘形式的轴突包膜的理解尤其 稀疏，尽管人类的大多数外周轴突(~70%)是无髓鞘的，并被Remak包裹 雪旺细胞。为了解决我们理解中的这一差距，我们建议使用遗传易驯化的果蝇模型来 表征促进轴突神经胶质包膜的新分子机制，并研究其功能作用 非髓鞘包裹对轴突健康和体内功能的影响。在果蝇中，特殊的神经胶质细胞称为包裹神经胶质细胞 (WG)以一种与脊椎动物Remak SCs非常相似的方式包裹外周轴突。最近的研究(包括我们 自己的初步数据)发现，许多控制脊椎动物髓鞘形成的基因也控制着轴突 WG在果蝇中的包膜，支持这些形式的包膜之间的强大分子保守。我们有 利用苍蝇进行了大规模的RNAi筛选，寻找新型的鞘调控因子，并鉴定了 轴突的神经胶质包膜需要一些令人兴奋的新基因。一位从屏幕上脱颖而出的候选人， 盘状结构域受体(DDR)编码一种进化上保守的受体酪氨酸激酶，由胶原蛋白激活。 我们发现WG中DDR的丢失导致轴突包膜的严重缺陷：尽管WG可以生长 沿着神经的纵向，它们未能在捆绑的轴突之间插入突起，从而对它们进行分类和包裹。有趣的是， 小鼠DDR1在少突胶质细胞中高表达，详细的表达谱显示mDdr1表达 在发育过程中包裹开始时和损伤后重新髓鞘形成时增加，但功能 MDDR在包膜或髓鞘形成中的作用尚未被研究。我们的初步工作也确定了 第15/XVIII型胶原同源复合体是轴突包膜所必需的，可能是作为DDR的配体。 在目标1中，我们将描述DDR在促进轴突包膜中的作用，确定其行动的自主性，以及 进行结构功能分析，以确定体内DDR信号的关键方面。在目标2中，我们将调查 并直接检验了MP以自分泌方式激活DDR的模型 WG上的受体。最后，在目标3中，我们将利用屏幕上识别的许多基因，这些基因具有轻微到 探讨非髓鞘鞘对神经元健康和生理功能的影响 使用行为分析和活体生理学研究。我们的工作将定义DDR和MP的机制基础 在神经组装和轴突的神经胶质包膜过程中的信号转导，并有助于确定 复杂神经系统中的非髓鞘形式的包膜。

Project summary Glial ensheathment of axons is a conserved feature of nervous systems that is essential for proper nervous system function. Impairment or loss of axonal wrapping underlies many debilitating conditions including multiple sclerosis, leukodystrophies, peripheral neuropathies, and CMT diseases. Despite many years of work our understanding of the molecular pathways that control glial development, glial-axon communication, and ensheathment of long axons, including myelination, is far from complete. Our understanding of non-myelinating forms of axon ensheathment is particularly sparse, despite the fact that the majority of peripheral axons (~70%) in humans are unmyelinated and encased by Remak Schwann cells. To address this gap in our understanding we propose to use the genetically tractable model Drosophila to characterize novel molecular mechanisms that promote glial ensheathment of axons and to study the functional roles of non-myelinating ensheathment in axon health and function in vivo. In Drosophila, specialized glia called wrapping glia (WG) ensheath peripheral axons in a manner closely resembling vertebrate Remak SCs. Recent studies (including our own preliminary data) have found that many genes that control the formation of vertebrate myelin also control axon ensheathment by WG in the fly, supporting strong molecular conservation between these forms of ensheathment. We have taken advantage of the fly to conduct a large-scale RNAi screen for novel regulators of ensheathment, and have identified a number of exciting new genes required for glial ensheathment of axons. One candidate to emerge from the screen, discoidin domain receptor (Ddr), encodes an evolutionarily conserved receptor tyrosine kinase activated by collagens. We show that loss of Ddr in WG results in profound defects in axonal ensheathment: although WG can grow longitudinally along the nerve they fail to insert processes between bundled axons to sort and ensheath them. Intriguingly, murine Ddr1 is highly expressed in oligodendrocytes and detailed expression profiling reveals that mDdr1 expression increases at the onset of wrapping during development and with the initiation of remyelination after injury, but functional roles for mDdr in ensheathment or myelination has not been investigated. Our preliminary work has also identified the Type XV/XVIII collagen homolog Multiplexin as required for axon ensheathment, possibly by acting as a ligand for Ddr. In Aim 1 we will characterize the role of Ddr in promoting axonal ensheathment, determine its autonomy of action, and perform a structure function analysis to define key aspects of Ddr signaling in vivo. In Aim 2 we will investigate the role of Mp in driving ensheathment and directly test our model that Mp acts in an autocrine fashion to activate the Ddr receptor on WG. Finally, in Aim 3 we will take advantage of the many genes identified in the screen that have mild to strong ensheathment defects to probe the function of non-myelinating ensheathment on neuronal health and physiology using behavioral assays and in vivo physiological studies. Our work will define the mechanistic basis of Ddr and Mp signaling during nerve assembly and glial ensheathment of axons, and help define the enigmatic but essential functions of non-myelinating forms of ensheathment in complex nervous systems.