Figure 3. Expression and localization of utrophin in wild-type, desmin^−/−, mdx^4cv and dko muscles at 11 weeks of age.

A) Frozen sections of the gastrocnemius muscles immunolabelled with antibodies to utrophin A and α-bungarotoxin (α-BTX). Utrophin was restricted to the neuromuscular junctions in wild-type and desmin^−/− muscles. Utrophin was expressed on the extrasynaptic sarcolemma in the mdx^4cv and dko muscles. Note the increased utrophin expression on the sarcolemma of dko fibers compared with the mdx^4cv muscles. Scale bar  = 50 µm. B) Western blot analyses of utrophin A expression in whole gastrocnemius muscle lysates from wild-type (n = 3), desmin^−/− (n = 3), mdx^4cv (n = 7) and dko (n = 6) mice. Quantitation of utrophin expression in whole muscle lysates is shown below the immunoblots. C) Maximal utrophin fluorescence intensity was significantly increased on the sarcolemma of dko fibers compared with mdx^4cv fibers. Furthermore, maximal fluorescence intensity was significantly increased in dko fibers compared to mdx:utrophin double knockout fibers expressing microutrophin^ΔR4–R21. N = 4. D) We found no change in utrophin mRNA when comparing whole gastrocnemius muscle lysates when utrophin mRNA was normalized to the housekeeping gene Ywhaz. N = 4. E) Utrophin prevents muscle degeneration and regeneration in dko gastrocnemius muscles as demonstrated by the reduced proportion of fibers with central nuclei. N = 4. All bar graphs show the mean +/− S.D. *P<0.05 and ***P<0.001 compared to wild-type; ^# P<0.05 and ^### P<0.001 compared to mdx^4cv.