Retention of a cell adhesion complex at the paranodal junction requires the cytoplasmic region of Caspr.
An axonal complex of cell adhesion molecules consisting of Caspr and contactin has been found to be essential for the generation of the paranodal axo-glial junctions flanking the nodes of Ranvier. Here we report that although the extracellular region of Caspr was sufficient for directing it to the paranodes in transgenic mice, retention of the Caspr-contactin complex at the junction depended on the presence of an intact cytoplasmic domain of Caspr. Using immunoelectron microscopy, we found that a Caspr mutant lacking its intracellular domain was often found within the axon instead of the junctional axolemma. We further show that a short sequence in the cytoplasmic domain of Caspr mediated its binding to the cytoskeleton-associated protein 4.1B. Clustering of contactin on the cell surface induced coclustering of Caspr and immobilized protein 4.1B at the plasma membrane. Furthermore, deletion of the protein 4.1B binding site accelerated the internalization of a Caspr-contactin chimera from the cell surface. These results suggest that Caspr serves as a "transmembrane scaffold" that stabilizes the Caspr/contactin adhesion complex at the paranodal junction by connecting it to cytoskeletal components within the axon.
Gollan
Leora
L
Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel.
Sabanay
Helena
H
Poliak
Sebastian
S
Berglund
Erik O
EO
Ranscht
Barbara
B
Peles
Elior
E
D000595:Amino Acid Sequence; D000818:Animals; D001923:Brain Chemistry; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D015816:Cell Adhesion Molecules, Neuronal / Q000172:deficiency / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D058966:Contactins; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007365:Intercellular Junctions / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009479:Neuropeptides; D009900:Optic Nerve / Q000378:metabolism / Q000648:ultrastructure; D011901:Ranvier's Nodes / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D012584:Sciatic Nerve / Q000378:metabolism; D017384:Sequence Deletion; D019076:Transgenes / Q000235:genetics
C491323:CNTNAP1 protein, human; D015815:Cell Adhesion Molecules; D015816:Cell Adhesion Molecules, Neuronal; C491322:Cntnap1 protein, mouse; D058966:Contactins; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D009479:Neuropeptides; D011956:Receptors, Cell Surface; C028841:erythrocyte membrane band 4.1 protein; C120557:erythrocyte membrane protein band 4.1-like 1