Presence and importance of connexin43 during myogenesis.

We analyzed the expression of connexin(Cx)43 in proliferating and differentiating C(2)C(12) cells and in myoblasts obtained from newborn mice. Cx43 was present in both cell types and under both conditions. The functional role of gap junctional communication (GJC) during terminal differentiation was evaluated in C(2)C(12) myoblasts in the presence or absence of the gap junction blocker 18beta-glycyrrhetinic acid (beta-GA). Differentiation was temporally analyzed through myogenin expression, activity of creatine kinase (CK), and yield of multinucleated cells. In cells treated with beta-GA, the CK activity and myotube formation were reversibly blocked. While in control cultures positive myogenin expression was seen in cell clusters, in beta-GA treated cultures the myogenin immunoreactivity was detected in few, preferentially sparse cells. The role of Cx43 during terminal differentiation was evaluated in cultures of myoblasts obtained from Cx43(Cre-ER(T)/fl) transgenic mice. Inducible deletion of Cx43 was obtained upon activation of Cre-ER(T) via 4-OH-tamoxifen applications. Cx43 deletion led to a drastic decrease in myogenin expression at 24 h of differentiation as compared to myoblasts from control mice. Our results indicate that Cx43-containing gap junctions are required for normal skeletal muscle terminal differentiation. These channels might provide a pathway for the intercellular transfer of signals involved in myogenesis.