Pre– and post–synaptic localization at the outer plexiform layer of dystrophins Dp427, Dp260 and Dp140 : functionnal implications.

Abstract

Abstract: : Purpose: The reduction of the b–wave amplitude of the electroretinogram (ERG) observed in Duchenne Muscular Dystrophy (DMD) patients has been related to alteration of retinal neurotransmission. To elucidate the role of dystrophins in this phenotype we first analyzed the cellular localization of the three products of the DMD gene expressed at the outer plexiform layer (OPL): Dp427, Dp260 and Dp140. Using different DMD mouse models we test by different approaches (cellular biology, electrophysiological techniques) the role of dystrophins in the clustering of neurotransmitter receptors as well as others membrane proteins implicated in the neurotransmission. Methods: The precise cellular localization of dystrophins on mice retina was analyzed by double–immunocytochemical labeling using a panspecific antibody directed against all the DMD gene products, and specific cell markers: anti–PSD95 (whole photoreceptor terminal), anti–PKCa and anti–G0a (ON bipolar cell), anti calbindin (horizontal cell). All fluorescence specimens were viewed by using a confocal microscope. By the patch–clamp technique we record currents induced by glutamate and GABA on bipolar cells and photoreceptor enzymatically dissociated from the control and mutant dystrophin mice. Results: We observed the colocalisation of dystrophins immunolabeling with photoreceptor terminals and bipolar cell tips markers. We also showed juxtaposition of dystrophins and horizontal cells labeling. Double immunolabeling have shown an overlap of dystrophins and mGluR6 staining, a receptor required for b–wave generation. The functionnal implications of dystrophins are studied by patch–clamp technique. Conclusions: Our results showed that dystrophins are localized in pre– and post–synaptic neurons of the OPL. In the bases of these observations it is tempting to postulate that perturbation of the clustering of receptor and/or ionic channels at pre– and post–synpatic membrane will be at the basis of the ERG phenotype.

Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells) • cytoskeleton • signal transduction