Laminins and their receptors control nearly all aspects of peripheral nerve development and myelination. Laminin mutants cause a dysmyelinating neuropathy in man (congenital muscular dystrophy, MDC1 A) and mouse (dystrophic, dy) that manifests impaired Schwann cell-axon interactions, altered myelination and nodes of Ranvier formation. A laminin receptor, dystroglycan, also interacts with periaxin, mutated in Charcot-Marie-Tooth 4F (CMT4F). In the previous grant period we used conditional mutagenesis to disrupt singly or multiply the major laminin receptors in Schwann cells of transgenic mice, and have determined that (31 integrins are crucial for Schwann cell-axon interactions during radial sorting, dystroglycan is important for organization of nodes of Ranvier, and both dystroglycan and a6-34 integrin confer myelin stability. The emerging view is that laminin receptors have both specific and overlapping functions. In addition they control both radial and longitudinal morphogenesis of myelinated fibers, and thereby organize even molecules on the axon, at a distance from the basal lamina. The overall goal of this proposal is to understand how this occurs, defining the mechanism of action of single laminins or receptors, and the signaling pathways that they activate. We will take advantage of the unique group of conditional alleles and Cre transgenes that we produced or collected, that allow us to disrupt laminin receptors and relevant signaling molecules in Schwann cells of transgenic mice. We will combine morphological and biochemical analysis in vivo with studies of mutant cultures, time-lapse microscopy and a unique technique that preserves cytoarchitecture of live teased fibers. Combining these techniques, we will probe molecular effectors of pi integrin, of dystroglycan at nodes of Ranvier, and participation of dystroglycan with periaxin in compartmentalization of the Schwann cell cytoplasm. Observation of transport of fluorescent molecules in compartments of myelinated internodes will combine """"""""live teasing"""""""" with photoactivation and time lapse microscopy. This comprehensive approach will establish the role of the different laminins/receptors/signaling pathways in peripheral nerve, and thereby clarify the pathogenesis of MDC1A and CMT4F mutations. The information produced by these experiments will collectively form a basis for developing treatment stategies of MDC1A, CMT4F and other hereditary neuropathies, and to promote nerve regeneration and remyelination in all neuropathies.
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