Srf loss in SCs results in CH deficiency in plantaris muscle. (A) Immunostaining for Pax7 (green) and Srf (red) on single fibers fixed immediately after isolation (0 h) or maintained in culture for 24 h. White arrows indicate SC expressing both Srf and Pax7. (B) Proportion of SCs displaying Srf expression (Pax7⁺Srf⁺; n = 3). (C) Srf mutant mice were injected with TMX 1 wk before CH procedure and after CH. Plantaris muscles were isolated 1, 3, and 5 wk after surgery. (D) Plantaris muscle sections immunostained for dystrophin (green) and nuclear staining with DAPI for control and Srf Mutant mice before (SO) and after 3 wk of CH. (E) Ratio of plantaris mass (milligrams) to body weight (grams) before (SO) and after 1, 3, and 5 wk of CH in control and Mutant mice (n = 10–16 muscles from n = 6–9 mice). (F) Mean CSA (square micrometers) before (SO) and after 1, 3, and 5 wk of CH in control and mutant mice (n = 6–15 muscles from n = 5–9 mice). (G) Mean myofiber number before (SO) and after 1, 3, and 5 wk of CH in control and mutant mice (n = 8–14 muscles from n = 6–9 mice). Data are mean ± SEM. **, P < 0.01 versus SO; ^§§, P < 0.01.