alpha-dystroglycan isoforms are differentially distributed in adult rat retina

alpha-Dystroglycan (alpha -DG) is a laminin/agrin receptor expressed in skeletal muscle as well as in nervous system and other tissues. Glycosylation of the core protein of alpha-DG is extensive, variable from tissue to tissue, and functionally relevant. To address differential glycosylation of alpha-DG in the retina, we have investigated the distribution of this protein using two different antibodies: 1B7 directed against the core protein of alpha-dystroglycan, and IIH6 directed against a carbohydrate moiety (Ervasti and Campbell [1993] J Cell Biol 122:809-823). Monoclonal antibody 1B7 recognizes a broader band than IIH6, which seems to recognize only a subset of alpha-DG forms in retina. These data reflect the existence of differentially glycosylated isoforms of alpha-DG. Monoclonal antibody 1B7 shows an extensive staining for alpha-DG in the inner limiting membrane as well as in the ganglion cell and inner plexiform layers labeling Müller cell processes, whereas monoclonal antibody IIH6 staining is restricted to the inner limiting membrane and blood vessels. Our data indicate that there are distinct isoforms of alpha-DG that are localized in apposition to basal lamina in the inner limiting membrane and blood vessels or within the parenchyma of the retina along Müller glia. Both isoforms are expressed in a Müller cell line in culture and coimmunoprecipitate with beta-dystroglycan. These data suggest that DGs may participate in organizing synapses and basement membrane assembly in the retina.