Differential expression of dystrophin, utrophin and dystrophin-associated proteins in peripheral nerve

The dystrophin-glycoprotein complex is a novel laminin receptor in skeletal muscle. Dystrophin-associated proteins are comprised of an extracellular glycoprotein of 156 kDa (156DAG), transmembrane glycoproteins of 50 kDa (50DAG), 43 kDa (43DAG) and 35 kDa (35DAG), and a cytoskeletal protein of 59 kDa (59DAP). The laminin-binding 156DAG and 43DAG are encoded by a single gene and are now called alpha- and beta-dystroglycan, respectively. In neuromuscular junctions, utrophin, an autosomal homologue of dystrophin, is associated with sarcolemmal proteins identical or immunologically homologous to the dystrophin-associated proteins. Here we demonstrate the co-localization of Dp116 (a 116 kDa protein product of the DMD gene), full-size utrophin, alpha- and beta-dystroglycan, 59DAP and 35DAG in a thin rim surrounding the outermost layer of myelin sheath of peripheral nerve fibers. The alpha-dystroglycan in peripheral nerve had molecular weight of 120 kDa instead of 156 kDa, suggesting different levels of glycosylation between skeletal muscle and peripheral nerve. In sharp contrast to skeletal muscle, however, full-size dystrophin and 50DAG were undetectable in peripheral nerve. Our results demonstrate the varied expression of the components of the dystrophin/utrophin-glycoprotein complex between skeletal muscle and peripheral nerve suggesting the complex may exist in varied compositions and have varied functions in these two tissues.