Sb202190

All experiments were performed under the approval of the University of Otago Animal Ethics Committee. A total of 374 embryos (an average of 15.6 ± 0.5 embryos per litter) from 24 pregnant Wistar rats (ages 8 to 10 weeks old) were used. Pregnancies were determined by the presence of copulation plugs (embryonic day zero: E0). The embryos were extracted from the pregnant rats between gestation day E14 and E19 and decapitated after body weights were recorded (Table 2). These timepoints were chosen because gatherings of undifferentiated cells marking the site of formation of the muscles were seen on embryonic day 15 (E15). Primary myotubes appear on E16 and reach stability by day E17. E15-16 signifies primary myogenesis, E18-19 signifies secondary myogenesis and E17 signifies the one day gap (Harris et al., 1989) .
In a second set of experiments, pregnant rats (E17) were injected intraperitoneally (i.p.) with either SB202190 (A.G. Scientific Inc., Ca, USA) a potent p38 MAPK inhibitor (3 doses of 5 mg each over 24 h) or with dimethyl sulfoxide (DMSO) vehicle control (de Angelis et al., 2005) . A total of 42 and 43 embryos (E18) were collected respectively, the left legs dissected, cryosectioned (10 mm) and stored at -20°C until required. Tissue was also lysed and the myogenic populations isolated for Western blot analysis and mononucleated cell immunostaining and quantification.