Article

Expression of laminin receptors in Schwann cell differentiation: Evidence for distinct roles

Neuropathology Unit, Department of Neuroscience and DIBIT, San Raffaele Scientific Institute, 20132 Milan, Italy.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 08/2003; 23(13):5520-30.
Source: PubMed

ABSTRACT Schwann cells require laminin-2 throughout nerve development, because mutations in the alpha2 chain in dystrophic mice interfere with sorting of axons before birth and formation of myelin internodes after birth. Mature Schwann cells express several laminin receptors, but their expression and roles in development are poorly understood. Therefore, we correlated the onset of myelination in nerve and synchronized myelinating cultures to the appearance of integrins and dystroglycan in Schwann cells. Only alpha6beta1 integrin is expressed before birth, whereas dystroglycan and alpha6beta4 integrin appear perinatally, just before myelination. Although dystroglycan is immediately polarized to the outer surface of Schwann cells, alpha6beta4 appears polarized only after myelination. We showed previously that Schwann cells lacking beta1 integrin do not relate properly to axons before birth. Here we show that the absence of beta1 before birth is not compensated by other laminin receptors, whereas coexpression of both dystroglycan and beta4 integrin is likely required for beta1-null Schwann cells to myelinate after birth. Finally, both beta1-null and dystrophic nerves contain bundles of unsorted axons, but they are predominant in different regions: in spinal roots in dystrophic mice and in nerves in beta1-null mice. We show that differential compensation by laminin-1, but not laminin receptors may partially explain this. These data suggest that the action of laminin is mediated by beta1 integrins during axonal sorting and by dystroglycan, alpha6beta1, and alpha6beta4 integrins during myelination.

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    • "Transgenic mice which possess a mutation in the c1 laminin gene of Schwann cells have severely disrupted peripheral nerves, Schwann cells do not extend processes between axons, do not produce a continuous basement membrane, show reduced sodium channel clustering at nodes of Ranvier, and have reduced nerve conduction velocity (Chen and Strickland, 2003; Yu et al., 2005). In the peripheral nerves of laminin a2 mutant mice, the basement membrane is also disrupted, axons have reduced Schwann cell ensheathment and myelination; however , the phenotype is perhaps relatively mild, as there is a compensatory increase in laminins a4 and a1 isoforms (Patton et al., 1997; Previtali et al., 2003b). The importance of laminin–integrin interaction in Schwann cells in radial sorting, axonal maturation and myelination is described in further detail by Colognato and Tzvetanova (2011). "
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    • "Laminins are also recognized by 'non-integrin' receptors including dystroglycan. In peripheral nerves, laminins expressed in the basal lamina play a pivotal role in Schwann cell-axon interactions (Uziyel et al. 2000; Wallquist et al. 2005; Yang et al. 2005), acting both through Schwann cell integrin and dystroglycan receptors at the different steps of myelin formation (Feltri et al. 2002; Previtali et al. 2003). For the CNS, blocking antibodies to dystroglycan receptors do not affect oligodendrocyte survival but prevent oligodendroglial production of complex membrane sheets and myelin segments when added on dorsal root ganglia neurons in vitro (Colognato et al. 2007), suggesting that dystroglycan receptors may have a specific role in the regulation of terminal stages of myelination. "
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    • "Also, transgenic laminin α5 chain expression promoted myelination [67]. Laminin α1 chain is also suggested to compensate the deficiency of laminin α2 chain, and actually transgenic expression of laminin α1 chain rescued radial sorting defect of spinal roots of dy3K/dy3K mice [74] [75]. In addition, inactivation of all known laminin isoforms in Schwann cells led to radial sorting defect in both spinal roots and sciatic nerve [68]. "
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