BASAL LAMINA MOLECULES ARE CONCENTRATED IN MYOGENIC REGIONS OF THE MOUSE LIMB BUD

Molecular components of basal lamina, such as laminin, stimulate the d ifferentiation of skeletal muscle cells in culture, while interstitial matrix components such as fibronectin are inhibitory. However, the ro le of extracellular matrix (ECM) molecules in muscle cell differentiat ion in the embryo is less well understood. As a first step toward unde rstanding the role of the ECM in embryonic myogenesis, the localizatio n of basal lamina molecules in the mouse limb bud before and during mu scle cell differentiation was determined by immunofluorescence. Lamini n, collagen type IV and nidogen (entactin) were concentrated in myogen ic regions of the limb bud both before and during differentiation of s keletal muscle cells. Punctate immunofluorescence for basal lamina mol ecules was concentrated in dorsal and ventral premuscle and muscle mas ses, when compared with other regions of limb mesenchyme. In contrast, immunofluorescence for fibronectin, an interstitial extracellular mat rix molecule, was decreased in premuscle and muscle masses. These resu lts suggest that basal lamina components play an important stimulatory role in early stages of skeletal muscle differentiation in the develo ping mouse limb bud.