Fig. 5. Inhibition of p38 promotes myogenesis of pre-existing myoblasts. Cultures were established from distal limb mesenchyme (A-F) or proximal limb mesenchyme (G-L). Proximal cultures contain more MyHC-positive cells compared to distal cultures (compare G with A). After 6 days, there are fewer detectable muscle cells in untreated distal cultures (B) compared with proximal cultures (H), but many more cartilage nodules form from distal mesenchyme (E) than from proximal mesenchyme (K). Following 6 days of treatment with SB202190, in both distal and proximal cultures, there is a decrease in nodule formation and an increase in the formation of foci of MyHC-positive cells. The muscle cells in treated proximal cultures (I), however, are much more prevalent, stain more intensely and are more highly organized into parallel arrays compared with muscle cells of distal cultures (C), and there are more cartilage nodules in the distal cultures (F) compared with the proximal cultures (L). Bars, fluorescence images (A-C, G-I) 750 µm; bright-field images (D-F, J-L) 1.5 mm.