Immunogold localization of the 43-kDa dystroglycan at the plasma membrane in control and dystrophic human muscle.

Immunofluorescence and immunogold labelling were used to localise the 43-kDa dystrophin-associated glycoprotein (43DAG) of the dystrophin-glycoprotein complex in control and Duchenne muscular dystrophy (DMD) biopsies. In control muscle 43DAG was localised by immunofluorescence to the periphery of the fibre and, by immunogold, was further delimited to the plasma membrane. The labelling was indistinguishable from that previously reported for the dystrophin C terminus. Moreover, the distance separating adjacent 43DAG labelling sites (120 nm mode) closely matched that separating dystrophin C-terminal sites. This is strong evidence supporting Ervasti & Campbell's model in which the DAG complex is bound close to the C terminus of dystrophin and in which the DAG complexes are separated by approximately the length of the dystrophin rod. In DMD, where there is a 80-90% reduction in the glycoprotein complex, a faint or locally patchy distribution of 43DAG was seen by immunofluorescence. Measurement of nearest-neighbour distances after immunogold labelling showed that in DMD the 43DAG was more dispersed, which is further evidence that dystrophin is normally involved in anchoring the DAGs in the plasma membrane. This is significant because the potential success of dystrophin gene therapy could depend not only on restoring dystrophin but also on restoring the lost DAGs.