Differential distribution of beta-dystroglycan in rabbit and rat retina

The distribution of the dystrophin-associated glycoprotein complex was investigated in rabbit and rat retina by using the monoclonal antibody 43DAG/8D5, which specifically recognizes beta-dystroglycan, a central component of the complex. In cryostat sections of retinae from both species, the authors observed staining of blood vessels, continuous labeling around the vitreal border, and strong immunoreactivity in the outer plexiform layer (OPL). Electron microscopy showed that the immunoreactivity associated with the vitreal border of the retina was the result of a subcellular concentration of beta-dystroglycan in the endfeet of Müller glial cells. A similar concentration was observed in endfeet of perivascular astrocytes in the region of contact with the capillary basal lamina. In the OPL, beta-dystroglycan was associated with the terminals of both rods and cones. The label was almost exclusively found outside the synaptic area and was particularly strong in the extensions of the photoreceptor terminals protruding into the OPL. In the OPL of the rabbit retina, the authors found additional immunoreactivity associated with the tips of postsynaptic horizontal and bipolar cell processes. These results show that the dystrophin-associated glycoprotein complex is subcellularly concentrated in photoreceptor terminals and glial cell endfeet, and that the rabbit retina differs from the rat retina by the additional expression of this complex in bipolar and horizontal cells.