Assembly and Maintenance of Nodes of Ranvier Rely on Distinct Sources of Proteins and Targeting Mechanisms

We have investigated the source(s) and targeting of components to PNS nodes of Ranvier. We show adhesion molecules are freely diffusible within the axon membrane and accumulate at forming nodes from local sources, whereas ion channels and cytoskeletal components are largely immobile and require transport to the node. We further characterize targeting of NF186, an adhesion molecule that pioneers node formation. NF186 redistributes to nascent nodes from a mobile, surface pool. Its initial accumulation and clearance from the internode require extracellular interactions, whereas targeting to mature nodes, i.e., those flanked by paranodal junctions, requires intracellular interactions. After incorporation into the node, NF186 is immobile, stable, and promotes node integrity. Thus, nodes assemble from two sources: adhesion molecules, which initiate assembly, accumulate by diffusion trapping via interactions with Schwann cells, whereas ion channels and cytoskeletal components accumulate via subsequent transport. In mature nodes, components turnover slowly and are replenished via transport. [Display omitted] ► Diffusible surface pools of adhesion molecules redistribute to initiate node assembly ► Channels and cytoskeletal proteins are not diffusible; they are transported to nodes ► NF186 is targeted initially via ectodomain and later cytoplasmic domain interactions ► NF186 turns over in neurites but is stable at nodes and maintains their integrity Zhang et al provide new insights into the development of nodes of Ranvier. They find assembly is initiated by redistribution of mobile, surface pools of axonal adhesion molecules, whereas ion channels and cytoskeletal components require transport to this site. Once formed, nodes are highly stable.