Impaired regeneration resulting from a satellite cell deficit in p38-γ^−/− muscle. (A) Enumeration of total fiber number from wild-type and p38-γ^−/− TA muscle 21 d after CTX injury. Numbers were normalized to the contralateral TA muscle. Error bars represent ±SEM for n = 5–6. Asterisk denotes significance (P < 0.0003). (B–H) Immunofluorescent staining for Pax7 (C and F) from wild-type and p38-γ^−/− TA muscle. Nuclei were counterstained with DAPI (B and E). (D and G) Pax7-DAPI merged pictures. Representative pictures are shown, with arrowheads denoting Pax7-positive nuclei. Pax7-positive satellite cells were enumerated (H). Error bars represent standard error of the means (±SEM) for n = 10. Asterisk denotes significance (P < 0.0001). (I–O) Immunofluorescent staining for Pax7 (J and M) on freshly isolated single fibers from wild-type and p38-γ^−/− EDL muscle. Nuclei were counterstained with DAPI (I and L). (K and N) Pax7-DAPI merged pictures are shown. Representative pictures are shown, with arrowheads indicating Pax7-positive nuclei. Pax7-positive satellite cells were enumerated (O). Error bars represent ±SEM for n = 84 myofibers. Asterisk denotes significance (P < 0.0001). Bars, 25 µm.