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J. Cell Biol.,
Volume 145, Number 3, May 3, 1999 619-631
Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
The transition of laminin from a monomeric
to a polymerized state is thought to be a crucial step in
the development of basement membranes and in the
case of skeletal muscle, mutations in laminin can result
in severe muscular dystrophies with basement membrane defects. We have evaluated laminin polymer and
receptor interactions to determine the requirements for
laminin assembly on a cell surface and investigated
what cellular responses might be mediated by this transition. We found that on muscle cell surfaces, laminins preferentially polymerize while bound to receptors that
included dystroglycan and 
7
1 integrin. These receptor interactions are mediated through laminin COOH-terminal domains that are spatially and functionally distinct from NH2-terminal polymer binding sites. This
receptor-facilitated self-assembly drives rearrangement of laminin into a cell-associated polygonal network, a process that also requires actin reorganization
and tyrosine phosphorylation. As a result, dystroglycan
and integrin redistribute into a reciprocal network as
do cortical cytoskeleton components vinculin and dystrophin. Cytoskeletal and receptor reorganization is dependent on laminin polymerization and fails in response to receptor occupancy alone (nonpolymerizing
laminin). Preferential polymerization of laminin on cell
surfaces, and the resulting induction of cortical architecture, is a cooperative process requiring laminin-
receptor ligation, receptor-facilitated self-assembly, actin reorganization, and signaling events.
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