Sample numbers and statistical analysis

sqRT‐PCR (human tissue panel) was performed n = 3 per isoform using individually synthesised cDNA template mixes, quantified on separate agarose gels. All qRT‐PCR reactions were conducted in triplicate, numbers as follows. C2C12 myogenesis and C3H studies were performed using cDNA synthesized from up to 4 or 6 wells, respectively (nonpooled), with standard deviation calculated if n ≥ 3 separate cDNA preparations used. For prepooled samples (aorta‐/skeletal muscle‐derived mdx mesoangioblasts, D16 and D351 clonal cell lines, mouse total embryo, human embryonic tissue), three separate cDNA preparations were performed in triplicate. Data presented in colour scale (Figs 1B–C, 2A–B) are presented in numerical form in Table S1–S2. Postnatal mouse tissue samples were extracted from n ≥ 3 subjects; two tailed t‐tests and P‐values on data in Fig. 2A were conducted using Prism7 (GraphPad, La Jolla, USA) and listed in Table S2.

Utrophin isoforms exhibit species‐ and isoform‐specific transcript levels. (A) The postnatal mouse response to dystrophin‐deficiency is tissue and isoform specific. Quantitative RT‐PCR (qRT‐PCR) analysis of tissue samples sourced from control (wt) C57BL/10 and mdx C57BL/10 mouse tissue at the 2‐week precrisis period (upper panel) and during the degeneration‐regeneration period in mdx during which total Utrn levels are elevated (6‐weeks; lower panel). Values for wt are at the left and for mdx at the right as denoted below each pair of columns. Utrn‐C/D mRNAs were greatly lowered in comparison to other isoforms (Table S2). P values represent differences between wild‐type and mdx tissues at the same time point (P < 0.0001••• P < 0.001••, P < 0.05•, 99% cl). qRT‐PCR analysis of Utrn‐A,‐A′ and ‐F levels in specific hindlimb muscles (tibilialis anterior, quadricep and soleus) compared to diaphragm (Fig. 2A) is provided in Fig. S9. (B) Selective upregulation of utrophin isoforms during C2C12 myogenesis. qRT‐PCR analysis of endogenous Utrn mRNA levels in myoblasts (myob) and differentiating (diff) myotubes sampled at days 3, 6 and 9, with corresponding mRNA profiles illustrated below. For (A and B), values are represented as a colour scale under (B), standardised to 28s cDNA for each time‐point. Numerical values obtained for all sample sets and additional statistical data are provided in Table S2. (C–D) Species‐specific utrophin mRNA myogenic profiles are mirrored in skeletal muscle mesoangioblasts (MABs). qRT‐PCR of utrophin mRNA isoform levels in wild‐type, mdx/DMD myogenic cell lines (left panel; white columns, myoblast, black columns, myotubes as outlined in the legend) and in dystrophin‐deficient skeletal muscle mesoangioblasts (MAB, grey columns, right panel). Values too low to be visualised by scale are provided numerically (upper value; myoblast, lower value; myotube). Numerical values for (A–B) sample sets are provided in Table S2.