Dystrophin and a dystrophin-related protein in intrafusal muscle fibers, and neuromuscular and myotendinous junctions

To determine whether or not and how dystrophin exists in neuromuscular junctions (NMJs) and myotendinous junctions (MTJs), we studied the mid-belly and peripheral portions of control and mdx muscles, immunohistochemically and immunoelectrophoretically, using six kinds of polyclonal antibodies, and an antibody against a dystrophin-related protein (DRP). In controls these regions and the polar region of intrafusal muscle fibers showed a rather clearer immunohistochemical dystrophin reaction than those of extrafusal muscle fibers with all antibodies used. In the muscles of mdx mice NMJs only showed a positive dystrophin reaction with the c-terminal antibody, that is, no reaction with the other five antibodies, and MTJs in mdx showed a positive reaction with the c-terminal antibody and a faint to negative reaction with the other five antibodies. In biopsied human muscles NMJs and MTJs also showed a clear reaction with all ten antibodies, i.e., six polyclonal and four monoclonal ones. Although an immunohistochemical DRP reaction was clearly seen at NMJs, only a faint or no reaction was seen on MTJs and on intrafusal muscle fibers in both mouse and human materials. Western blot analysis of control mouse muscle for dystrophin showed a clearer band for the peripheral portion, which contains many MTJs, than for the mid-belly portion. These data suggest that dystrophin really exists on MTJs, and that dystrophin and DRP exist on NMJs in mouse and human muscles.