How do non-myelinating glia ensheath axons?

项目摘要 轴突的胶质鞘化是神经系统的一个保守特征，是正常神经系统所必需的 功能轴突包裹的损伤或丧失是许多衰弱性疾病的基础，包括多发性硬化症， 脑白质营养不良、周围神经病和CMT疾病。尽管多年的工作，我们的理解， 控制神经胶质发育、神经胶质-轴突通讯和长轴突鞘化的分子途径，包括 髓鞘形成还远未完成我们对轴突鞘化的非髓鞘形成形式的理解特别重要， 稀疏，尽管事实上，大多数外周轴突（约70%）在人类是无髓鞘和包裹的Remak 雪旺氏细胞。为了解决我们理解中的这一差距，我们建议使用遗传学上易于处理的果蝇模型， 表征促进轴突神经胶质鞘化的新分子机制，并研究 非髓鞘形成鞘在轴突健康和功能在体内。在果蝇中，一种特殊的神经胶质叫做包裹神经胶质 (WG)以非常类似于脊椎动物Remak SC的方式包裹外周轴突。最近的研究（包括 他自己的初步数据）发现，许多控制脊椎动物髓鞘形成的基因也控制轴突 在果蝇中，WG的包被，支持这些形式的包被之间的强分子保守性。我们有 利用果蝇进行大规模的RNAi筛选，寻找新的鞘化调节因子，并确定了 神经胶质鞘化轴突所需的一些令人兴奋的新基因。一个候选人从屏幕上出现， 盘状结构域受体（Ddr），编码由胶原激活的进化上保守的受体酪氨酸激酶。 我们发现WG中Ddr的缺失导致轴突包鞘的严重缺陷：尽管WG可以生长， 纵向沿着神经，它们不能在成束的轴突之间插入突起以将它们分类和包裹。有趣的是， 鼠Ddr 1在少突胶质细胞中高度表达，详细的表达谱显示mDdr 1表达 在发育过程中包裹开始时和损伤后髓鞘再生开始时增加，但功能性 尚未研究mDdr在鞘形成或髓鞘形成中的作用。我们的初步工作还确定了 XV/XVIII型胶原同源物多路复用蛋白，可能通过充当Ddr的配体而为轴突鞘化所需。 在目标1中，我们将描述Ddr在促进轴突鞘化中的作用，确定其自主作用， 进行结构功能分析，以确定体内Ddr信号传导的关键方面。在目标2中，我们将研究 直接测试我们的模型，即Mp以自分泌方式激活Ddr WG上的受体。最后，在目标3中，我们将利用在筛选中鉴定的许多基因，这些基因具有轻微的， 强鞘化缺陷，以探索非髓鞘形成鞘化对神经元健康和生理的功能 使用行为分析和体内生理学研究。我们的工作将确定Ddr和Mp的机制基础 信号在神经组装和神经胶质鞘的轴突，并帮助确定神秘的，但基本的功能， 复杂神经系统中的非髓鞘形成形式的鞘。

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.