EXPRESSION OF LAMININ ISOFORMS IN MOUSE MYOGENIC CELLS IN-VITRO AND IN-VIVO

The expression of laminin-1 (previously EHS laminin) and laminin-2 (pr eviously merosin) isoforms by myogenic cells was examined in vitro and in vivo. No laminin alpha 2 chain-specific antibodies react with mous e tissues, so rat monoclonal antibodies were raised against the mouse laminin alpha 2 chain: their characterization is described here. Myobl asts and myotubes from myogenic cell lines and primary myogenic cultur es express laminin beta 1 and gamma 1 chains and form a complex with a 380 kDa alpha chain identified as laminin alpha 2 by immunofluorescen ce, immunoprecipitation and PCR. PCR from C2C12 myoblasts and myotubes for the laminin alpha 2 chain gene (LamA2) provided cDNA sequences wh ich were used to investigate the in vivo expression of mouse LamA2 mRN A in embryonic tissues by in situ hybridization. Comparisons were made with specific probes for the laminin alpha 1 chain gene (LamA1). LamA 2 but not LamA1 mRNA was expressed in myogenic tissues of 14-and 17-da y-old mouse embryos, while the laminin alpha 2 polypeptide was localiz ed in adjacent basement membranes in the muscle fibres. In situ hybrid ization also revealed strong expression of the LamA2 mRNA in the dermi s, indicating that laminin alpha 2 is expressed other than by myogenic cells in vivo. Immunofluorescence studies localized laminin alpha 2 i n basement membranes of basal keratinocytes and the epithelial cells o f hair follicles, providing new insight into basement membrane assembl y during embryogenesis. In vitro cell attachment assays revealed that C2C12 and primary myoblasts adhere to laminin-1 and -2 isoforms in a s imilar manner except that myoblast spreading was significantly faster on laminin-2. Taken together, the data suggest that laminins 1 and 2 p lay distinct roles in myogenesis.