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Birthe Dorgau, Helena Greb, Regina Herrling, Petra Bolte, Konrad Schultz, Reto Weiler, Ulrike Janssen-Bienhold; Expression and distribution of connexin50 in the mouse retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1172.
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© ARVO (1962-2015); The Authors (2016-present)
Horizontal cells (HC) are laterally connecting interneurons in the outer retina which form highly dynamic networks modulated by ambient light. HCs provide positive and negative feedback signals to photoreceptors (PR). An ephaptic mechanism is supposed to underlie negative feedback, mediated by connexin (Cx) hemichannels located in the dendritic tips of HCs, invaginating PR terminals. The axon-bearing B-type HCs of the mouse form two independent, coupled networks via dendro-dendritic and axo-axonal gap junctions (GJ). Both types of GJs are composed of Cx57. However, in Cx57-deficient mice, HC coupling is very strongly reduced (>90%) but not completely abolished, indicating the expression of at least one other connexin. Cx50 might be an interesting candidate because it was already found in the axonless A-type HCs of rabbits. In this study we investigated the subcellular distribution of Cx50 in the mouse retina.
By single cell RT PCR, we analyzed the expression of Cx50 transcripts in dissociated retinal neurons. Commercially available anti-Cx50 antibodies, whose specificity on retinal tissue was demonstrated by Western blot, were used to detect Cx50 proteins in individual cell types. Retina sections and whole-mounts were double-labeled with anti-Cx50 antibodies and different cell markers to determine the subcellular localization of Cx50. Results were confirmed with electron microscopy.
Cx50 mRNA expression was exclusively identified in isolated HCs and in Müller cells. Anti-Cx50 antibody stainings revealed that Cx50 immunoreactivity was mainly confined to the axon terminals (AT) and was rarely found along the dendrites of mouse HCs. Although Cx57 is also expressed on the AT network, we did not find a colocalization of both connexins, suggesting independent functions within the HC network. Double-labeling with PR terminal markers showed that Cx50 is located below PR terminals. Electron micrographs displayed no Cx50 immunosignal in dendritic tips of HCs, indicating that Cx50 is not involved in negative feedback mechanism.
These findings show the subcellular distribution of Cx50 in the mouse retina whereat Cx50 was found predominantly on ATs of HCs. As Cx50 is not colocalized with Cx57, our data suggest that Cx50 may form a separate network of only homomeric/homotypic GJ channels between ATs. Whether this Cx50-mediated network is also influenced by ambient light like Cx57 networks remains to be seen.
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