Many MC13 cells had fused into myotubes and myofibers at 6 weeks after transplantation in the nonlacerated muscle (A–D). The injected sites were positive for α-SMA (E, F), but negative for vimentin (G, H). At 9 weeks after transplantation, most of the β-galactosidase-expressing myofibers had matured and become larger than at 6 weeks after transplantation (I–L). However, the injected sites were negative for both α-SMA (M, N) and vimentin (O, P).