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Shanti R. Tummala, Marie Fina, Anuradha Dhingra, Noga Vardi; Gαo1 is Required for the Proper Expression of mGluR6 Transduction Elements in ON-Bipolar Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4314.
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ON-bipolar cells respond to photoreceptor signals through the mGluR6-Go1-TRPM1 cascade. A recent study in mGluR6-/- mice found that while expression of the G-protein subunit Gαo and its potential partners Gβ3 and Gγ13 was similar to that in wild type, staining for TRPM1 and the mGluR6 cascade modulators Gβ5 and RGS11 in the dendritic tips was significantly reduced. A similar study in Gβ3-/- mice, on the other hand, found pronounced down-regulation of most cascade elements including mGluR6, Gαo, Gβ5, Gγ13, RGS11 and TRPM1. These results suggest a complex interdependence of expression and localization of the cascade elements. The purpose of this study was to determine if deletion of Gαo1 from ON-bipolar cells also results in the altered expression of these proteins.
Standard immnuocytochemistry was performed on age-matched wild type (CD57/BL6), GRM6:GFP (regarded as wild type) and Gαo1-/- mice.
In the wild type retina, immunostaining for the potential partners of Gαo1, namely Gβ3 and Gγ13, was strong in the dendrites and somas, and weak in the axons of ON-bipolar cells. Deletion of Gαo1 resulted in reduced staining for Gβ3 and Gγ13. Staining for mGluR6 in the wild type mice showed distinct puncta that were restricted to the OPL. In the Gαo1-/- mice, the intensity and number of these puncta were reduced. Staining for TRPM1 in the wild type was similarly punctate in the OPL, but was also present in the ON-bipolar cells somas. In the Gαo1-/- mice, staining for TRPM1 was retained in the somas, but the number of puncta in the OPL decreased. The known modulators of the cascade, Gβ5, RGS11 and R9AP, present as distinct puncta in the OPL of wild type mice, were absent in the Gαo1-/- mice, suggesting that deletion of Gαo1 down-regulates their expression.
Similar to the deletion of Gβ3, deletion of Gαo1 from ON-bipolar cells significantly alters the expression pattern of the G-protein hetero-trimer candidates, suggesting that their heteromeric form is required for normal expression. The reduction of receptor, channel, and modulators from the dendritic tips suggests that all these proteins are in a large complex whose stability and localization at the tip requires either the G-protein subunits themselves or normal activity that they confer to the cell.
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