Assembly and expression of isoforms of laminin in cultured muscle cells.

Abstract

Glycoproteins of the extracellular matrix regulate cellular behavior during development and in some human diseases. The assembly and expression of the extracellular matrix glycoprotein laminin were studied during myogenic differentiation in cultures of a mouse mesenchymal stem cell line, immortalized rodent myoblast cell lines, and primary adult and neonate mouse muscle cells. Three isoforms of laminin were identified and characterized at the biochemical level. The three isoforms were assembled from related biosynthetic intermediates in three distinct intracellular pathways dependent on the stage of cellular muscle differentiation. Two of the isoforms were expressed early and late, respectively, in muscle differentiation pathway and were associated with the expression of muscle-specific transcription factors. The deposition of the laminin isoforms into the extracellular matrix was also developmentally regulated during the myogenic differentiation events. These results suggest that laminin isoforms have important functions during development of the mammalian skeletal musculature.