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L. Perez de Sevilla Muller, U. Janssen-Bienhold, K. Dedek, M. M. Kreuzberg, S. Maxeiner, S. Lorenz, K. Willecke, R. Weiler; Expression and Modulation of Connexin30.2, a Novel Gap Junction Protein in the Mammalian Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3052.
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Gap junctions are clusters of intercellular channels which connect the cytoplasm of two cells, providing direct intercellular communication. They are formed of proteins called connexins, and six connexins form a hexameric connexon. Two identical or two different connexons can form a homotypic or heterotypic gap junctions, respectively (for review see Söhl et al., 2005). The open probability of the gap junction channels can be regulated by different protein kinases. In the mammalian retina, four different connexins have so far been reported to build electrical synapses, and it is very likely that this list is not complete. Besides the direction selective and alpha ganglion cells, the connexin involved in the electrical coupling of the remaining ganglion cell types is unknown. Recently, a novel connexin, connexin30.2, was shown to be expressed in the central nervous system of the mouse (Kreuzberg et al., 2007). In this study we identified the cells expressing Cx30.2 in the mouse retina, and quantified the modulation of their coupling by phosphorylation.
A transgenic mouse line, in which the Cx30.2 coding region was deleted and replaced by the lacZ gene, was used to identify the cells expressing Cx30.2 in the ganglion cell layer of the mouse retina. We used immunohistochemistry and tracer coupling experiments to characterize the morphology of the cells expressing Cx30.2 and the modulation of their coupling by phosphorylation
In this mouse line, the LacZ signal was expressed in the nuclei of neurons located in the ganglion cell layer and in cells of the inner nuclear layer. We found at least six different types of Cx30.2-expressing ganglion cells. One of these was a giant ganglion cell type coupled to numerous displaced amacrine cells through gap junctions involving Cx30.2 and an unidentified protein. This heterotypic coupling was sensitive to modulation by protein kinase C but not by protein kinase A.
These data provide evidence of a new connexin in the mammalian retina which builds gap junctions modulated by protein kinase C.
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