Figure 5. Utrophin maintains the integrity of the dko muscle membrane in a fiber-type specific manner.

A) Shown are frozen sections of the lateral portion of the gastrocnemius muscle immunolabeled with monoclonal antibodies to fiber types 1a (blue), 2a (red), 2d/x (black) and 2b (green; left panel) or utrophin (green; right panel) and Evan's blue dye (EBD; red; right panel). Note that the uneven distribution of utrophin expression in the mdx^4cv muscles correlated with patches of adjacent membrane permeable fibers that labeled with EBD. However, an increase in utrophin expression in the dko myofibers excluded EBD from the 1a, 2a and 2d/x fiber types. The dko fast 2b fibers, which lacked utrophin, were permeable to EBD. Scale bar  = 500 µm. B) Bars show the mean +/− S.D. percentage of centrally nucleated fibers in distinct fiber types. Note that all dko muscle fiber types had significantly less myonuclei than the mdx^4cv fibers (^## P<0.01 and ^### P<0.001). The dko fast 2b fibers had more central nuclei than the 1a, 2a and 2d/x fiber types (^@@@P<0.001). The mdx^4cv fast 2b fibers had more central nuclei than the 1a, 2a and 2d/x fiber types (**P<0.01). C) Bars show the mean +/− S.D. total number of EBD positive fibers in the gastrocnemius muscles. ***P<0.001 compared with mdx^4cv myofibers. D) Bars show the mean +/− S.D. area of type 1a, 2a, 2d/x and 2b muscle fiber types. ***P<0.001 compared with wild-type myofibers. ^### P<0.001 compared with mdx^4cv myofibers. ^@@@P<0.001 compared with desmin^−/− myofibers. All experiments were from n = 4 mice.