Fig. 7: Flexiblity is inversely correlated with myonuclear number.

a A comparison of the cross-sectional area of tibialis anterior muscle in Δ2w and Δ3w mice at postnatal (P) day 42 revealed similar effects on cell size, despite differences in myonuclear number (n = 3–7 biologically independent animals). b Assessment of the myonuclear domain in isolated EDL myofibers from Δ3w mice at P42 (n = 3 biologically independent animals). c Total RNA levels normalized to muscle weight in the various groups of mice (n = 5–10 biologically independent animals). d Normalized RNA levels from (c) were normalized again to the average number of nuclei/myofiber (n = 5–10 biologically independent animals). A significant increase in the amount of RNA per myonucleus is observed in Δ2w muscle, but remains unchanged in Δ3w muscle. e Concentration of transcripts coding for key skeletal muscle structural genes (Acta1, Myh1, Myh4, Tnnt3, and Tnnc2) on a per nuclear basis are increased in Δ2w and Δ3w muscle compared to controls (n = 3–8 biologically independent animals). Δ2w muscle has a larger increase in transcript concentration per nucleus than Δ3w, despite having fewer myonuclei per fiber. To obtain these values, relative transcript levels were determined by semi-quantitative qPCR from P42 samples, which were then normalized to total RNA and average myonuclear numbers for each genotype. f Abundance of transcripts on a per nuclear basis in wild-type tibialis anterior across developmental time points (n = 3–7 biologically independent animals). Statistical analyses and data presentation: a, two-sided unpaired t-test. c, d One-way ANOVA with a Tukey correction for multiple comparisons; significance compared to control group. e, Acta1 (both groups), Myh1 (Δ2w only): Mann–Whitney test. Myh1 (Δ3w only), Myh4, Tnnt3, and Tnnc2 (both groups): two-sided unpaired t-test with Welch’s correction. f One-way ANOVA with Tukey correction for multiple comparisons. Acta1 was analyzed with one-way ANOVA with Kruskal–Wallis correction for multiple comparisons. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001. Data are represented as mean ± SD. Source data are provided as a Source Data file.