Fig. 4

Muscle pathology results from elevated Myomerger expression in myofibers. A qPCR analysis reveals elevated levels of Myomerger in the TA and rectus femoris muscles of homozygous mice compared to heterozygous mice after 2 weeks of induction. B Quantification of Western blots demonstrates elevated Myomerger protein content in the TA and rectus femoris muscles of iMymg/Mymg mice compared to iMymg mice after 2 weeks of induction. C Serum CK levels in iMymg/Mymg mice are elevated after 2 weeks of Myomerger expression. Levels are also significantly higher than 2 weeks of Myomerger expression in iMymg mice. D Quantification of the proportion of IgM⁺ myofibers reveals elevated levels of damage in the soleus and TA muscles after 2 weeks of Myomerger expression. E Myofiber stiffness is reduced after 2 weeks of Myomerger expression in myofibers by atomic force microscopy. Each bar represents the average stiffness of three myofibers from a given mouse. F Representative sections of the TA muscle from iMymg/Mymg mice after 8 weeks of Myomerger expression revealed a lack of significantly elevated proportion of IgM⁺ myofibers (G). H Elevated levels of centrally nucleated myofibers were observed in the soleus, TA, and rectus femoris. Scale bar = 100 μm. I Muscle mass to tibia length ratios were reduced in the TA and rectus femoris after 8 weeks of Myomerger expression in myofibers. J Myofiber size, quantified by minimum Feret’s diameter, was quantified in the soleus, TA, and rectus femoris. Statistical analyses and presentation: data are presented as mean ± SEM; A and C One-way ANOVA with a Tukey’s post hoc test compared samples from the same muscle; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. B, D–E, and G–J two-tailed Student’s t test, identical muscles were compared in D and G–J; stiffness values were compared between the two groups using average values from each mouse for E; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001