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. 2023 Sep 22;8(18):e171878. doi: 10.1172/jci.insight.171878

Figure 2. Depletion of SMN specifically in skeletal muscle is sufficient to cause pathology.

Figure 2

(A) Confocal transverse section image of the calf muscle of a mutant mouse selectively depleted of the SMN protein in skeletal muscle tissue. Muscle cell–autonomous pathology is observed in the form of degenerating fibers penetrated by circulating IgG (asterisks), infiltrating microglia (arrows) and numerous myofibers containing abnormal, centrally positioned nuclei (arrowheads). Muscle was dual stained with antibodies against Iba-1 and mouse IgG to visualize microglia and damaged myofibers, respectively. Scale bar: 50 μm. (B) Kaplan-Meier survival curves depicting the correlation between SMN2 copies, and thus absolute SMN levels, in muscle and life span of the SMA mutants. P < 0.0001, log-rank test, n ≥ 16 mice of each cohort. (C) Enumeration of degenerating myofibers and cells harboring central nuclei in the gastrocnemius of mutants selectively depleted of SMN in skeletal muscle. Roughly nine times as many SMA fibers were found to display central nuclei compared with those that were degenerating (IgG-positive). *P < 0.05, ** P < 0.01, t tests, n ≥ 300 fibers from n ≥ 3 mice of each cohort. Panels adapted from Kim et al. (33).