Direct involvement of N-cadherin-mediated signaling in muscle differentiation

Cell-cell interactions, mediated by members of the cadherin family of Ca2+-dependent adhesion molecules, play key roles in morphogenetic processes as well as in the transduction of long-range growth and differentiation signals. In muscle differentiation cell adhesion is involved in both early stages of myogenic induction and in later stages of myoblast interaction and fusion. In this study we have explored the involvement of a specific cadherin, namely N-cadherin, in myogenic differentiation. For that purpose we have treated different established lines of cultured myoblasts with beads coated with N-cadherin-specific ligands, including a recombinant N-cadherin extracellular domain, and anti-nr-cadherin antibodies. Immunofluorescent labeling for cadherins and catenins indicated that treatment with the cadherin-reactive beads for several hours enhances the assembly of cell-cell adherens-type junctions. Moreover, immunofluorescence and immunoblotting analyses indicated that treatment with the beads for 12-24 h induces myogenin expression and growth arrest, which are largely independent of cell plating density. Upon longer incubation with the beads (2-3 d) a major facilitation in the expression of several muscle-specific sarcomeric proteins and in cell fusion into myotubes was observed. These results suggest that surface clustering or immobilization of N-cadherin can directly trigger signaling events, which promote the activation of a myogenic differentiation program.