SUBCELLULAR CONCENTRATION OF BETA-DYSTROGLYCAN IN PHOTORECEPTORS AND GLIAL-CELLS OF THE CHICK RETINA

Mutations in the dystrophin-glycoprotein complex cause muscle degenera tion and dysfunctions in the central nervous system, including an impa ired synaptic transmission in the outer plexiform layer (OPL) of the r etina. To investigate the basis for this ocular phenotype, we analyzed the distribution of beta-dystroglycan, a central member of the dystro phin-glycoprotein complex, in the chick retina by using the 43DAG/8D5 monoclonal antibody. This antibody reacted specifically with chick bet a-dystroglycan, as indicated by its staining of the neuromuscular junc tion, and its reactivity with a single 43-kilodalton band in Western b lots. In the retina, beta-dystroglycan was highly concentrated in the OPL and at the vitreal border of the retina, around the inner limiting membrane. Mechanically isolated and flat-mounted inner limiting membr anes were stained by the anti-beta-dystroglycan antibody, and this imm unoreactivity could be extracted by detergent, indicating that beta-dy stroglycan is associated with membranous structures bound to the basal lamina. Consistently, electron microscopy showed a concentration of b eta-dystroglycan in the endfeet of Muller glial cells exclusively in t he region of direct contact to the inner limiting membrane. In the OPL , beta-dystroglycan immunoreactivity was concentrated in the distal ex tensions of rod and cone terminals protruding into the outer plexiform layer. There, beta-dystroglycan codistributed with the alpha(1B) subu nit of the N-type voltage-gated calcium channel. By contrast to previo us reports, we did not detect beta-dystroglycan directly associated wi th the synaptic regions of conventional or ribbon synapses of the reti na. These results show that in the retina beta-dystroglycan is exclusi vely expressed by photoreceptors and glial cells and that beta-dystrog lycan is highly concentrated in subcellular regions of glial cell endf eet and photoreceptor terminals. Moreover, the colocalization of beta- dystroglycan with N-type calcium channels in the outer plexiform layer indicates that bath proteins might be part of a macromolecular comple x. (C) 1997 Wiley-Liss, Inc.