Cells anchor to substrates by binding to extracellular matrix (ECM). In addition to this anchoring function however, cell-ECM binding is a mechanism for cells to sense their surroundings and to communicate and coordinate behaviour amongst themselves. Several ECM molecules and their receptors play essential roles in muscle development and maintenance. Defects in these proteins are responsible for some of the most severe muscle dystrophies at every stage of life from neonates to adults. However, recent studies have also revealed a role of cell-ECM interactions at much earlier stages of development as skeletal muscle forms. Here we review which ECM molecules are present during the early phases of myogenesis, how myogenic cells interact with the ECM that surrounds them and the potential consequences of those interactions. We conclude that cell-ECM interactions play significant roles during all stages of skeletal muscle development in the embryo and suggest that this "extracellular matrix dimension" should be added to our conceptual network of factors contributing to skeletal myogenesis.

Here, we determined ␣ subunit expression patterns at embryonic day (E) 11.5-E14.5. Differentiated myotomal myocytes express all ␣ subunits studied. As the muscle masses form both in trunk (E12.5) and limbs (E11.5-E12.5), laminin receptors ␣6␤1 and ␣7␤1 are undetectable, and an assembled laminin matrix is absent. Instead ␣1␤1, ␣4␤1, ␣5␤1, and an ␣v-containing integrin are expressed and unassembled laminin and fibronectin are abundant around myogenic cells. At E13.5-E14.5, ␣6␤1 and ␣7␤1 are expressed, and a laminin matrix forms around individual myotubes. Thus, myogenic cells change their integrin expression pattern during the course of primary myogenesis in the mouse, suggesting different roles for fibronectin-and laminin-containing matrices in this process.

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