FIG. 1.

PI 3-kinase and p38 MAPK signaling pathways are essential for myogenesis. (A) Phase-contrast photomicrographs (×20 magnification) of C2 myoblasts in proliferative (GM) and differentiating (DM [24 to 96 h]) phases; arrows highlight myotube formations. (B) Western blot detection of MHC, MEF2, and caveolin-3 in differentiating C2 cells; total p38 protein levels are shown as a loading control. (C) Analysis (by Western blotting) of MHC expression after 72 h in DM in the presence or absence of the following kinase inhibitors: PD98059 (20 μM), SB203580 (5 μM), rapamycin (2 ng/ml), and LY294002 (10 μM). As a control, cells were also treated with vehicle alone (DMSO); total p38 protein levels are shown as a loading control. (D) Myoblast differentiation (in the presence or absence of the indicated inhibitors) was assessed by immunofluorescence (×20 magnification) with anti-MHC antibody (upper panels); cell nuclei were visualized by DAPI staining (middle panels), and cell morphology was examined by H and E staining (lower panels) (×5 magnification).