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 extra-fusal 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.