Fig. 4. Acvr1^R206H/+ MuSCs fail to form properly fused myofibers.

a Representative images show that freshly isolated MuSCs from control and Acvr1^R206H/+ skeletal muscle have similar morphologies. b–d Representative images of control MuSCs after 2 days (b top) and 7 days (c top) in differentiation media (DM) show fusion into myotubes and normal myofibers are formed. Representative images of Acvr1^R206H/+ MuSCs after 2 days (b bottom) and 7 days (c bottom) in DM show that Acvr1^R206H/+ cells do not differentiate into normal myofibers and have reduced fusogenic efficiency. d Representative images of control and Acvr1^R206H/+ MuSCs that were stained for the mature muscle marker alpha-myosin heavy chain (α-MyHC) after 7 days in myogenic differentiation media are shown. e Quantification of fusion index (percent of total nuclei residing in cells with 3 or more nuclei) after 7 days in culture. All data are expressed as mean ± SEM; Scale bars for all images = 100 µm. n ≥ 3 mice for each group; N > 100 MuSCs (nuclei) per timepoint and genotype were analyzed. Statistical significance was determined by one-way ANOVA, ***p < 0.0001.