Figure 4. Little cellular pathology in young adult MyoD-iCre Smn^F7/– mutants bearing 2 SMN2 copies.

(A) Comparisons of body weights of controls and mutants harboring 1 or 2 SMN2 copies; 1-way ANOVA, n ≥ 10 mice of each cohort. (B) Western blot results showing selective depletion of SMN protein in skeletal muscle of a P30 MyoD-iCre SMN2^+/+ Smn^F7/– mutant. (C) Quantified levels of SMN protein in P30 mutant and control mice; t test, n ≥ 3 mice from each group. (D) Transverse sections of H&E-stained gastrocnemius muscles from a P30 mutant and control did not reveal major morphological differences between the two. Scale bar: 25 μm. Graphs of (E) myofiber areas, (F) fibers containing central nuclei, and (G) serum creatine kinase (CK) levels in young mutants and controls. NS: P > 0.05, t test, n > 150 fibers from n = 3 mice from each group for results in E and F; NS: P > 0.05, t test, n = 10 mice for CK values. (H) NMJs from the triceps of a P30 mutant and a control showing similar morphology of pre- and postsynaptic compartments in the 2 mice. Scale bar: 30 μm. (I) Graph of the extent of NMJ innervation in P30 mutants and controls. (J) Graph depicting endplate complexity in P30 mutants and control littermates. NS: P > 0.05, Fisher’s exact test, n ≥ 300 NMJs from n = 3 mice from each group of mice for analyses in I and J. **P < 0.01; ***P < 0.001.