Department of Cell and Molecular Physiology, and UNC-Neuroscience Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7545, USA.
J Neurosci. 2010 Apr 7;30(14):4868-76. doi: 10.1523/JNEUROSCI.5951-09.2010.
The formation of paranodal axo-glial junctions is critical for the rapid and efficient propagation of nerve impulses. Genetic ablation of genes encoding the critical paranodal proteins Caspr, contactin (Cont), and the myelinating glia-specific isoform of Neurofascin (Nfasc(NF155)) results in the disruption of the paranodal axo-glial junctions, loss of ion channel segregation, and impaired nerve conduction, but the mechanisms regulating their interactions remain elusive. Here, we report that loss of immunoglobulin (Ig) domains 5 and 6 in Nfasc(NF155) in mice phenocopies complete ablation of Nfasc(NF155). The mutant mice lack paranodal septate junctions, resulting in the diffusion of Caspr and Cont from the paranodes, and redistribution of the juxtaparanodal potassium channels toward the nodes. Although critical for Nfasc(NF155) function, we find that Ig5-6 are dispensable for nodal Nfasc(NF186) function. Moreover, in vitro binding assays using Ig5-6 deletion constructs reveal their importance for the association of Nfasc(NF155) with Cont. These findings provide the first molecular evidence demonstrating domain-specific requirements controlling the association of the paranodal tripartite complex in vivo. Our studies further emphasize that in vivo structure/function analysis is necessary to define the unique protein-protein interactions that differentially regulate the functions of Neurofascins during axonal domain organization.
连接蛋白（paranodal axo-glial junctions）的形成对于神经冲动的快速有效传播至关重要。编码连接蛋白关键蛋白 Caspr、神经联络蛋白（contactin，Cont）和髓鞘特异性神经束蛋白（Neurofascin，NF155）的基因缺失会破坏连接蛋白，导致离子通道分离，从而损害神经传导，但调节它们相互作用的机制仍不清楚。在这里，我们报告小鼠 NF155 中的免疫球蛋白（Ig）结构域 5 和 6 的缺失可模拟 NF155 的完全缺失。突变小鼠缺乏连接蛋白分隔连接，导致 Caspr 和 Cont 从连接蛋白扩散，连接蛋白旁钾通道重新分布到节点。尽管 Ig5-6 对 NF155 的功能至关重要，但我们发现 Ig5-6 对于 NF186 的功能并非不可或缺。此外，使用 Ig5-6 缺失构建体的体外结合实验揭示了它们对于 NF155 与 Cont 结合的重要性。这些发现为体内连接蛋白复合体的形成提供了首个分子证据，证明了特定结构域对于连接蛋白复合体形成的重要性。我们的研究进一步强调，需要进行体内结构/功能分析，以确定在轴突结构组织过程中差异调节神经束蛋白功能的独特蛋白-蛋白相互作用。
