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D. K. Mojumder, T. G. Wensel; Variable Distribution of RGS7 and RGS11 in the Dendritic-Tips of ON-Bipolar Cells in the Murine Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):762.
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The light-evoked reduction in glutamate release by photoreceptors shuts off a G-protein (Go) mediated biochemical cascade linked to metabotropic glutamate receptor, mGluR6 in the dendritic tips of the ON-bipolar cells (ON-BPCs). This shut-off opens cation channels and depolarizes the ON-BPC. The fast kinetics of the ON-BPC responses imply that the slow intrinsic GTPase activity of the G subunit requires the action of a GTPase accelerating protein (GAP), a mechanism that operates in the photoreceptors. It has been reported that two GAP complexes, Gβ5-RGS11 and Gβ5-RGS7, are present in ON-BPC dendrites (Morgans et al., 2007, Eur. J.Neurosci. 26:2899). We asked if immunofluorescence for RGS7 and RGS11, were found across all ON bipolar cell dendritic terminals.
Single, double and triple immunolabeling were performed on paraformaldehyde fixed mouse eyes.
As reported previously, we observed prominent punctate RGS7, RGS11 and Gβ5 immunofluorescence in the outer plexiform layer (OPL) colocalized with staining for mGluR6, the marker of dendritic tips of the ON-BPC, but not for the pre-synaptic marker, ribeye, or for the horizontal cell marker, calbindin. Cell bodies in the INL that were RGS7, RGS11 or Gβ5 immunopositive, showed very little co-localization with Chx-10, indicating their presence in amacrine and not bipolar cell soma. RGS7, RGS11 and Gβ5 immunofluorescence was also found in the ganglion cell layer. Two prominent bands of immunofluorescence for both RGS7 and Gβ5 were seen in the inner-plexiform layer. Although Gβ5 staining seemed to be present in nearly all the ON-BPC dendritic tips, some did not stain for RGS11 and some did not stain for RGS7. RGS11 immunofluorescence was absent in some tips positive for other markers of rod-bipolar cell dendritic tips, including PKC-α, Gαo and mGlur6. RGS7 immunofluorescence was found to be characteristically absent from some tight clusters of mGlur6- and Gαo-positive putative ON-cone bipolar dendritic tips. Double immunofluorescence of RGS7 and Gβ5 or RGS11 and Gβ5 showed that numerous Gβ5-positive puncta in the OPL did not have RGS7 or RGS11 immunostaining.
There is a variable distribution of RGS7, RGS11, and Gβ5 in the dendritic tips of ON-bipolar cells in the murine retina. Some mGlur6-positive tips appear to contain RGS11 but not RGS7, and RGS7 is missing from dendritic tips of some cone ON-BPC, reflecting different functions for RGS complexes in subsets of ON-BPC.
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