Loss of basement membrane, receptor and cytoskeletal lattices in a laminin-deficient muscular dystrophy.

Basement membrane laminins bearing the alpha2-subunit interact with alpha-dystroglycan and beta1-integrins, cell-surface receptors that are found within the rectilinear costameric lattices of skeletal muscle sarcolemma. Mutations of the alpha2 subunit are a major cause of congenital muscular dystrophy. To determine whether the costameres are altered as a result of laminin alpha2-mutations, the skeletal muscle surface of a dystrophic mouse (dy(2J)/dy(2J)) lacking the alpha2-LN domain was examined by confocal and widefield deconvolution immunomicroscopy. Although the dy(2J) dystrophic fibers possessed a normal-appearing distribution of alpha2-laminins and alpha-dystroglycan within a rectilinear costameric lattice at 6.5 weeks of age, by 11 weeks the surface architecture of these components were found to be disorganized, with frequent effacement of the circumferential and longitudinal lattice striations. The defect in the lattice organization was also noted to be a characteristic of type IV collagen, nidogen, perlecan, beta1(D)-integrin, dystrophin and vinculin. The development of this pattern change occurring only after birth suggests that although alpha2-laminins are not essential for the initial assembly of the costameric framework, they play a role in maintaining the stability and organization of the framework.