The role of dystroglycan, a novel receptor of laminin and agrin, in cell differentiation.

Dystroglycan was originally identified as the extracellular and transmembrane constituents of a large oligomeric complex of sarcolemmal proteins associated with dystrophin, the protein product of the Duchenne muscular dystrophy (DMD) gene. During the last few years, dystroglycan has been demonstrated to be a novel receptor of not only laminin but also agrin, two major proteins of the extracellular matrix having distinct biological effects. The fact that the drastic reduction of dystroglycan in the sarcolemma, caused by the absence of dystrophin, leads to muscle cell death in DMD patients and mdx mice indicates that, as a laminin receptor, dystroglycan contributes to sarcolemmal stabilization during contraction and stretch of striated muscle cells. Dystroglycan is also expressed in the neuromuscular junction and non-muscle tissues such as kidney, brain and peripheral nerve, and, as a receptor of laminin/agrin, has been implicated in such diverse and specific developmental processes as epithelial morphogenesis, synaptogenesis and myelinogenesis. These findings point to the fundamental role of dystroglycan in the cellular differentiation process shared by many different cell types. In this paper, we review the recent publications on the biological functions of dystroglycan and discuss its roles in cell differentiation.