title: Laminin assembles into separate basement membrane and fibrillar matrices in Schwann cells.
abstract: Laminins are important for Schwann cell basement membrane assembly and axonal function. In this study, we found that exogenous laminin-1, like neuromuscular laminins-2/4, formed two distinct extracellular matrices on Schwann cell surfaces, each facilitated by laminin polymerization. Assembly of one, a densely-distributed reticular matrix, was accompanied by a redistribution of cell-surface dystroglycan and cytoskeletal utrophin into matrix-receptor-cytoskeletal complexes. The other, a fibrillar matrix, accumulated in separate zones associated with pre-existing beta1-integrin arrays. The laminin-1 fragment E3 (LG-modules 4-5), which binds dystroglycan and heparin, inhibited reticular-matrix formation. By contrast, beta1-integrin blocking antibody (Ha2/5) prevented fibrillar assembly. Ultrastructural analysis revealed that laminin treatment induced the formation of a linear electron-dense extracellular matrix (lamina densa) separated from plasma membrane by a narrow lucent zone (lamina lucida). This structure was considerably reduced with non-polymerizing laminin, fully blocked by E3, and unaffected by Ha2/5. Although it formed in the absence of type IV collagen, it was nonetheless able to incorporate this collagen. Finally, cell competency to bind laminin and form a basement membrane was passage-dependent. We postulate that laminin induces the assembly of a basement membrane on competent cell surfaces probably mediated by anchorage through LG 4-5. Upon binding, laminin interacts with dystroglycan, mobilizes utrophin, and assembles a 'nascent' basement membrane, independent of integrin, that is completed by incorporation of type IV collagen. However, the fibrillar beta1-integrin dependent matrix is unlikely to be precursor to basement membrane.
authors.affiliation: Department of Pathology & Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
authors.forename: Maria V
authors.initials: MV
authors.lastname: Tsiper
authors.forename: Peter D
authors.initials: PD
authors.lastname: Yurchenco
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D001485:Basement Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D024141:Collagen Type IV / Q000378:metabolism / Q000648:ultrastructure; D003598:Cytoskeletal Proteins / Q000378:metabolism / Q000648:ultrastructure; D049030:Dystroglycans; D005109:Extracellular Matrix / Q000378:metabolism* / Q000648:ultrastructure; D007797:Laminin / Q000378:metabolism* / Q000494:pharmacology / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D011108:Polymers / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012155:Reticulin / Q000378:metabolism / Q000648:ultrastructure; D012583:Schwann Cells / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D024141:Collagen Type IV; D003598:Cytoskeletal Proteins; D007797:Laminin; D008562:Membrane Glycoproteins; D011108:Polymers; D012155:Reticulin; C121346:laminin 1; C102645:laminin alpha 2; D049030:Dystroglycans