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mammalian retina; transgenic; signal transduction; single cell RT-PCR; gene expression profiling
Abstract:
We investigated the expression of Gγ13, a recently discovered G protein subunit, and a selection of Gβ subunits in retinal bipolar cells, by using a transgenic mouse strain in which green fluorescent protein is strongly expressed in a single type of cone bipolar cell. The cells have ON morphology, and patch-clamp recordings in slices confirmed that they are of the physiological ON type. Immunohistochemistry showed that Gγ13 is expressed in rod bipolar cells and ON cone bipolar cells, where it is colocalized in the dendrites with Gαo. ON and OFF cone bipolar cells and rod bipolar cells were identified among dissociated cells by their green fluorescence and/or distinct morphology. Hybridization of single-cell polymerase chain reaction products with cDNA probes for G protein subunits Gβ1 to 5 showed that Gβ3, Gβ4, and Gγ13 are coexpressed in ON bipolar cells but not present in OFF bipolar cells. Gβ1, 2, and 5 are expressed in partially overlapping subpopulations of cone bipolar cells. Gγ13 and Gβ3 and/or Gβ4, thus, seem selectively to participate in signal transduction by ON bipolar cells.
