Interestingly, NaV1.2 and KCNQ3 exhibit significant variability in their mobility, ranging from slowly mobile to essentially

immobile populations, on different axon segments. It is not yet clear whether this variation corresponds to differences in the composition of ion channel complexes (Rasband, 2010 and Zhang et al., 2011) that may affect their association with the cytoskeleton, and mobility, either regionally along the length of an axon or between different axons. As axon transection (Figure 2A) and BFA treatment (Figure 2C; Campenot et al., 2003) arrest axonal transport, our selleck kinase inhibitor data do not establish whether the vesicles that transport ion channels and cytoskeletal components to the node are already present within the axon or require export from the soma, representing newly synthesized proteins. Together, these findings support a model of sequential node assembly that relies on distinct sources. NF186, which pioneers PNS node formation (Dzhashiashvili et al., 2007, Lambert et al., 1997, Sherman et al., 2005 and Thaxton et al., Epacadostat cost 2011), together with NrCAM, diffuses to the node where it is initially “trapped” via gliomedin interactions. NF186

then recruits ankyrin G, which accumulates with a slight delay (Lambert et al., 1997), and thereby sodium channels and βIV spectrin (Dzhashiashvili et al., 2007), which are delivered by transport. Triton X-100 extraction studies (Figure S4C) support the notion that adhesion molecules are not part of a preformed complex with ion channels and cytoskeletal elements that redistributes en masse to the node. Whether sodium channels, ankyrin G, and βIV spectrin are transported as a complex themselves, akin to that of the presynaptic complex (Jin and Garner, 2008), or are transported separately and assemble locally at the node, is not yet known. In potential support that ankyrin G and

ion channels may be targeted separately to the node, sodium channels Florfenicol accumulated in the absence of ankyrin G at a small number (∼20%) of the newly formed heminodes and nodes in the transected axon and BFA experiments (Figure S2A). These occasional channel accumulations are consistent with an earlier report that sodium channels can accumulate at heminodes during remyelination of Wldslow-transected axons ( Tzoumaka et al., 1995). In view of the effects of BFA and transection on transport, these sodium channels would appear to accumulate by a transport-independent mechanism—potentially via redistribution of the subset of channels that are diffusible along the axon ( Figures 3C and 3D). Unexpectedly, these results also indicate that a subset of sodium channels are neither bound to nor dependent on ankyrin G for targeting to the node. These findings contrast with our previous report that assembly of the node, in particular the accumulation of sodium channels, is strictly dependent on ankyrin G expression ( Dzhashiashvili et al., 2007).