Mechanisms of Node of Ranvier Assembly

有髓轴突的朗维尔结对于通过跳跃传导的动作电位传播是至关重要的，并且是神经元的精致域组织特征的突出例子。节点由包括电压门控钠和钾通道的多聚体复合物、辅助β亚基、细胞粘附分子（CAM）和包括通道和CAM结合的锚蛋白G的细胞骨架复合物组成。我们最近的研究表明，节点组装从不同的来源。CAM，特别是NF 186，通过从轴突表面上的现有池重新分布，经由与许旺细胞相互作用的扩散捕获，在形成节点处积累。相比之下，通道和细胞骨架蛋白主要通过轴突运输传递到节点。令人惊讶的是，似乎也有一个池的钠通道，交通和积累在节点独立的运输和锚蛋白G。最后，我们的研究表明，有一个积极的计划，以清除结蛋白从nodal网站，进一步加强他们的选择性富集在节点。为了扩展这些发现并进一步阐明节点组装的机制，我们将研究节点组件的贩运和组装，以及它们是如何通过髓鞘共培养物中的实时成像策略从节点部位清除的。我们尤其会：ii）表征钠通道组分向节点的转运依赖性和非转运依赖性运输，分别包括锚蛋白G和NF 186的作用，并确定钠通道复合物是否局部组装，和i）研究结组分如何从结节部位清除，集中于NF 186以进一步检查其胞质区段的作用以及内吞作用和蛋白水解在清除NF 186的结间表面池中的作用。相关性：这些研究将阐明调节朗维尔结组装的机制，朗维尔结对神经纤维适当传导电脉冲的能力至关重要。因此，这项研究的结果可能对我们理解有髓纤维疾病的发病机制具有重要意义，包括导致异常神经传导的神经病变，并可能因此导致这些神经系统疾病的新治疗策略。

The nodes of Ranvier of myelinated axons are critical for action potential propagation by saltatory conduction and are a striking example of the exquisite domain organization characteristic of neurons. Nodes are comprised of a multimeric complex that includes voltage gated sodium and potassium channels, accessory beta subunits, cell adhesion molecules (CAMs), and a cytoskeletal complex that includes ankyrin G to which channels and CAMs bind. Our recent studies indicate that the node assembles from distinct sources. CAMs, notably NF186, accumulate at forming nodes by redistribution from existing pools on the axon surface via diffusion trapping from interactions with the Schwann cell. In contrast, channels and cytoskeletal proteins are delivered to the node primarily via axonal transport. Surprisingly, there also appears to be a pool of sodium channels that traffics and accumulates at the node independent of transport and of ankyrin G. Finally, our studies suggest there is an active program to clear nodal proteins from extranodal sites that further reinforces their selective enrichment at the node. To extend these findings and further elucidate the mechanisms of node assembly, we will investigate trafficking and assembly of components of the node, and how they are cleared from extranodal sites, by live imaging strategies in myelinating cocultures. In particular, we will: i) determine whether vesicles that transport components to the nodes segregate into those specific for CAMs and others for ion channels, and exhibit any domain specificity, ii) characterize transport-dependent and -independent trafficking of sodium channel components to the node, including the roles of ankyrin G and NF186, respectively, and determine whether the sodium channel complex assembles locally, and i) investigate how nodal components are cleared from extranodal sites, focusing on NF186 to examine further the role of its cytoplasmic segment and that of endocytosis and proteolysis in clearing the internodal, surface pool of NF186. Relevance: These studies will elucidate the mechanisms that regulate the assembly of the node of Ranvier, which is critical to the ability of nerve fibers to conduct electrical impulses appropriately. Findings in this study may therefore have important implications for our understanding of the pathogenesis of disorders of myelinated fibers, including neuropathies that result in aberrant nerve conduction, and may thereby lead to new therapeutic strategies for these neurological disorders.