Changes in TA myofiber size, SC number, and grip strength emerge between 3 and 5 months of age in ΔIg3-MuSK mice.
(a) Representative IHC images of 3- and 5-month-old WT and ΔIg3-MuSK TA used for Pax7+ quantification and myofiber size analysis. Pax7 (red) and laminin (green) staining; arrows indicate SCs. (b) At 3 months, myofiber minimum Feret diameter is equivalent in WT and ΔIg3-MuSK muscle (n=3 male mice, unpaired t-test, 3 mo. p=0.6). At 5 months, myofiber minimum Feret diameter is increased by about 10% (37 ±0.80µm and 41 ± 1.0µm in WT vs ΔIg3-MuSK, respectively; n=8 male mice, unpaired t-test p=0.006). (c) At 3 months of age, the number of Pax7+ cells per area is equivalent between WT and ΔIg3-MuSK muscle (n=10-11 male & female mice, unpaired t-test, p=0.6). At 5 months, the number of Pax7+ cells per area is reduced by almost half in ΔIg3-MuSK muscle (19±2.1 and 10.6±1.4mm2 in WT vs ΔIg3-MuSK, respectively; n=9-10 male & female mice, unpaired t-test, p=0.004). (d) At 3 months, grip strength is comparable between the two genotypes (n=10 males, unpaired t-test, p=0.64). In contrast, at 5 months, ΔIg3-MuSK mice have increased grip strength (n=6-10 males, unpaired t-test, p=0.029; see also Supplemental Fig. 2).