Dissection of Complex Molecular Interactions of Neurofascin with Axonin-1, F11, and Tenascin-R, Which Promote Attachment and Neurite Formation of Tectal Cells

Abstract

Neurofascin is a member of the L1 subgroup of the Ig superfamily that promotes axon outgrowth by interactions with neuronal NgCAM-related cell adhesion molecule (NrCAM). We used a combination of cellular binding assays and neurite outgrowth experiments to investigate mechanisms that might modulate the interactions of neurofascin. In addition to NrCAM, we here demonstrate that neurofascin also binds to the extracellular matrix glycoprotein tenascin-R (TN-R) and to the Ig superfamily members axonin-1 and F11.Isoforms of neurofascin that are generated by alternative splicing show different preferences in ligand binding. While interactions of neurofascin with F11 are only slightly modulated, binding to axonin-1 and TN-R is strongly regulated by alternatively spliced stretches located in the NH2-terminal half, and by the proline-alanine-threonine-rich segment.In vitro neurite outgrowth and cell attachment assays on a neurofascin-Fc substrate reveal a shift of cellular receptor usage from NrCAM to axonin-1, F11, and at least one additional protein in the presence of TN-R, presumably due to competition of the neurofascin– NrCAM interaction. Thereby, F11 binds to TN-R of the neurofascin/TN-R complex, but not to neurofascin, whereas axonin-1 is not able to bind directly to the neurofascin/TN-R complex as shown by competition binding assays.In conclusion, these investigations indicate that the molecular interactions of neurofascin are regulated at different levels, including alternative splicing and by the presence of interacting proteins.

Versican V2 Assembles the Extracellular Matrix Surrounding the Nodes of Ranvier in the CNS

“…Considering all these observations, we propose a model, in which the accumulation of versican V2 around the CNS nodes of Ranvier forms the extracellular nucleation point for the subsequent assembly of the perinodal matrix. Accordingly, the deposition of the versican-enriched matrix at the nodes is likely to be initiated by a firm interaction of versican V2 with the nodal axolemma or, less probable, with the paranodal structure, while previously reported binding activities of its partner TnR and/or phosphacan to paranodal contactin (Brümmen-dorf et al, 1993;Peles et al, 1995) and neurofascin-155 (NF-155) (Volkmer et al, 1998) or to the nodal sodium channels (Srinivasan et al, 1998;Ratcliffe et al, 2000) may play either no or only subordinate roles in matrix anchoring. The prominent paranodal components contactin, NF-155, Caspr, and sulfatide [interacts with versican in vitro (Miura et al, 1999)] seem also not necessary for the selective deposition and binding of versican V2 at the nodes.…”

Contactin-1 regulates myelination and nodal/paranodal domain organization in the central nervous system

“…First, neuronal Contactin may be necessary for axon maturation. Contactin interactions with any or several of neuronal cell-surface proteins, including L1/NgCAM, RPTPα, NrCAM, neurofascin, and sodium channel-β1, may affect cellular mechanisms required for axon maturation (16,(32)(33)(34)(35). Second, as numbers of oligodendrocytes in optic nerves are comparable between genotypes, in Cntn1-KO the number of oligodendrocytes may be insufficient to match the demand of myelinating an increased number of small-diameter axons.…”

“…The parallel defects in Cntn1-KO mice with this latter phenotype raise the possibility that axonal Contactin, in addition to its role at paranodes, participates in stabilizing nodal complexes through NF186 or ECM interactions. Indeed, several studies documented Contactin interactions with various cytoskeleton-associated membrane proteins and ECM components, including neurofascins, NgCAM, NrCAM, RPTP-β/phosphacan, tenascin-R, and tenascin-C (32)(33)(34)(51)(52)(53).…”

The Expression of TAG-1 in Glial Cells Is Sufficient for the Formation of the Juxtaparanodal Complex and the Phenotypic Rescue of Tag-1 Homozygous Mutants in the CNS

“…Next to it, the paranodal glial loops tightly interact with the axon to form the paranodal junction, which insulates the node from the periaxonal internode. The paranodal complex comprises of the neurexin protein Caspr on the axon, and the Ig superfamily (IgSF) members contactin and neurofascin 155 on the axon and glial cell surface, respectively (Peles et al, 1997;Volkmer et al, 1998;Faivre-Sarrailh et al, 2000;Charles et al, 2002). Juxtaparanodes are the regions of the internode adjacent to the paranodes.…”