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Abstract

The metabotropic glutamate receptor, mGluR6, and the G protein α subunit Gao are expressed in the ON-bipolar cells and have been suggested to mediate the ON-response. We set out to identify other signal transduction components in the bipolar cells using single cell RT-PCR, gene expression profiling and immunocytochemistry. Retinae were isolated from transgenic mice that expressed green fluorescent protein (GFP) in α subset of ON-bipolar cells, and dissociated into single cells. ON- and OFF- bipolar cells were identified by their green fluorescence and distinct morphology. Poly A+ RNAs from individual bipolar cells were reverse transcribed into cDNAs. The whole population of cDNAs was tailed with dATP and amplified with oligo (dT) attached adapter-primers. Hybridization of the PCR products with cDNA probes for G protein subunits Gb1, Gb3 and α newly identified Gg13, showed that Gb3 and Gg13 are co-expressed in ON−bipolar cells, but not in OFF−bipolar cells, while Gb1 is expressed in some, but not all, ON− and OFF- bipolar cells. Immunocytochemistry of retinal sections further confirmed that Gg13 is expressed in rod bipolar cells and ON-cone bipolar cells, with the strongest signal at the dendritic tips and axonal terminals. Double immunostaining indicated that Gg13 is colocalized with Gao in ON-bipolar cells. The functions of Gg13 in the retina remain to be determined and may be involved in visual signal transduction