(A) Immunostains of NMJs in the triceps of PND9 controls and SMA mutants with or without Hspa8G470R; the modifier reduces denervation (asterisks) and the incidence of nerve terminals with abnormal NF varicosities (arrows). Scale bar: 20μm. Enumeration of NMJs in the three cohorts of mice displaying (B) nerve terminals abnormally swollen with NF protein and (C) denervated endplates. (D) Graphs depict relative enlargement of endplates in SMA-G470R+/+ versus SMA mutants. Note: **, ***, P < 0.01, P < 0.001, one-way ANOVA (panels B – D). Electrophysiological measures from EDL muscles of (E) PND75 SMA-G470R+/+ mutants and controls and (F) similarly aged controls with or without the variant illustrate the potentiating effect of the modifier on neurotransmission. Note: *, ***, P < 0.05, P < 0.001, t tests, N.S. – not significant. Data: mean ± SEM. See also Fig. S5.