α-Actin overexpression in Srf-deleted SCs rescues fusion and hypertrophic growth upon overload. (A) TA muscle sections immunostained for dystrophin (green) and nuclear staining with DAPI for control, mutant, and Mut/Act⁺ mice untreated (No CTX) and 30 d after CTX-induced muscle injury (30D after CTX). (B) Mean CSA (square micrometers) of TA muscles untreated (0) and 30 d after CTX-induced injury in control, mutant, and Mut/Act⁺ mice (n = 5–9 muscles from n = 4–7 mice). (C) Number of nuclei (DAPI) within the dystrophin⁺ sarcolemma per myofiber in untreated (0) and 30 d after CTX-induced injury of control, mutant, and Mut/Act⁺ TA muscles (n = 5–11 muscles from n = 4–7 mice). (D) Ratio of plantaris mass (milligrams) to body weight (grams) before (SO) and after 3 and 5 wk of CH in control, mutant, and Mut/Act⁺ mice (n = 5–16 muscles from n = 4–9 mice). (E) Mean CSA (square micrometers) of plantaris before (SO) and after 3 and 5 wk of CH in control, mutant, and Mut/Act⁺ mice (n = 5–15 muscles from n = 4–9 mice). (F) Number of nuclei (DAPI) within the dystrophin⁺ sarcolemma per myofiber before (SO) and after 3 and 5 wk of CH in control, mutant, and Mut/Act⁺ plantaris muscles (n = 6–11 muscles from n = 4–6 mice). Data are mean ± SEM. *, P < 0.05; **, P < 0.01.