Organization of myelinated axons by Caspr and Caspr2 requires the cytoskeletal adapter protein 4.1B.
Caspr and Caspr2 regulate the formation of distinct axonal domains around the nodes of Ranvier. Caspr is required for the generation of a membrane barrier at the paranodal junction (PNJ), whereas Caspr2 serves as a membrane scaffold that clusters Kv1 channels at the juxtaparanodal region (JXP). Both Caspr and Caspr2 interact with protein 4.1B, which may link the paranodal and juxtaparanodal adhesion complexes to the axonal cytoskeleton. To determine the role of protein 4.1B in the function of Caspr proteins, we examined the ability of transgenic Caspr and Caspr2 mutants lacking their 4.1-binding sequence (d4.1) to restore Kv1 channel clustering in Caspr- and Caspr2-null mice, respectively. We found that Caspr-d4.1 was localized to the PNJ and is able to recruit the paranodal adhesion complex components contactin and NF155 to this site. Nevertheless, in axons expressing Caspr-d4.1, Kv1 channels were often detected at paranodes, suggesting that the interaction of Caspr with protein 4.1B is necessary for the generation of an efficient membrane barrier at the PNJ. We also found that the Caspr2-d4.1 transgene did not accumulate at the JXP, even though it was targeted to the axon, demonstrating that the interaction with protein 4.1B is required for the accumulation of Caspr2 and Kv1 channels at the juxtaparanodal axonal membrane. In accordance, we show that Caspr2 and Kv1 channels are not clustered at the JXP in 4.1B-null mice. Our results thus underscore the functional importance of protein 4.1B in the organization of peripheral myelinated axons.
Horresh
Ido
I
Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel.
Bar
Vered
V
Kissil
Joseph L
JL
Peles
Elior
E
D000818:Animals; D001369:Axons / Q000502:physiology*; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000502:physiology*; D002461:Cell Line, Transformed; D003593:Cytoplasm / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D051662:Kv1.1 Potassium Channel / Q000378:metabolism; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D008840:Microfilament Proteins; D009154:Mutation / Q000235:genetics; D009413:Nerve Fibers, Myelinated / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D016900:Neurofilament Proteins / Q000378:metabolism; D009469:Neuromuscular Junction / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D015222:Sodium Channels / Q000378:metabolism; D014162:Transfection / Q000379:methods; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000502:physiology*
C403049:CNTNAP2 protein, human; D015816:Cell Adhesion Molecules, Neuronal; C116887:EPB41L3 protein, human; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; D015222:Sodium Channels; D025521:Tumor Suppressor Proteins; C051774:neurofilament protein H; D051662:Kv1.1 Potassium Channel