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

A) Utrophin expression in gastrocnemius muscles compared to adjacent sections labeled for the different skeletal muscle fiber-types. Note that utrophin expression is restricted to the neuromuscular junctions and non-muscle cells in the wild-type muscles. Utrophin is also restricted to the neuromuscular junctions in most fast 2b fibers in desmin^−/− muscles, but remains on the sarcolemma of the type 1a, 2a and 2d/x fiber types. Utrophin is found on the extrasynaptic sarcolemma of mdx^4cv muscles, irrespective of fiber-type at 3 weeks of age. Regions where utrophin is lost from the extrasynaptic sarcolemma in mdx^4cv muscles have necrotic fibers (arrows). Utrophin expression is lost from most of the fast 2b fibers in the dko by 3 weeks of age, but is retained on the sarcolemma of 1a, 2a and 2d/x fiber types. Scale bar  = 50 µm. B) Western blot analyses of utrophin A expression in whole gastrocnemius muscle lysates from (n = 4), desmin^−/− (n = 4), mdx^4cv (n = 8) and dko (n = 8) mice. Quantitation of utrophin expression in whole muscle lysates is shown below the immunoblots. C) 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. *P<0.05, P<0.001 compared to wild-type. ^### P<0.001 compared to mdx^4cv.