May 2007
Volume 48, Issue 13
ARVO Annual Meeting Abstract  |   May 2007
Gß5-RGS Complexes in Retinal ON-Bipolar Cell Dendrites
Author Affiliations & Notes
  • C. W. Morgans
    Neurological Sciences Institute, Oregon Health & Science Univ, Beaverton, Oregon
  • T. G. Wensel
    Biochemistry, Baylor College of Medicine, Houston, Texas
  • R. L. Brown
    Neurological Sciences Institute, Oregon Health & Science Univ, Beaverton, Oregon
  • R. M. Duvoisin
    Neurological Sciences Institute, Oregon Health & Science Univ, Beaverton, Oregon
  • Footnotes
    Commercial Relationships C.W. Morgans, None; T.G. Wensel, None; R.L. Brown, None; R.M. Duvoisin, None.
  • Footnotes
    Support NIH Grant 5R03EY016078-02
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 54. doi:
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      C. W. Morgans, T. G. Wensel, R. L. Brown, R. M. Duvoisin; Gß5-RGS Complexes in Retinal ON-Bipolar Cell Dendrites. Invest. Ophthalmol. Vis. Sci. 2007;48(13):54.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose:: In photoreceptor outer segments (OS), activated rhodopsin is negatively coupled to a cation channel through the G-protein transducin, so that absorption of a photon by rhodopsin closes the channel and hyperpolarizes the cell. The metabotropic glutamate receptor of ON-bipolar cells (ON-BPCs), mGluR6, is similarly coupled to a cation channel through the G protein, Go. In both photoreceptor OS and ON-BPC dendrites, the slow intrinsic GTPase activity of the Gα subunit requires the action of a GTPase accelerating protein (GAP). In photoreceptor OS, the GAP activity is provided by the Gß5-RGS9 complex. We present evidence here for two similar complexes, Gß5-RGS11 and Gß5-RGS7, in ON-BPC dendrites, and propose that they accelerate the GTPase activity of Gαo.

Methods:: Immunohistochemistry and western blots were performed as described previously (Morgans et al., 2006). A Zeiss LSM510 confocal microscope was used to visualize the labeling. Immunoprecipitations were done as described by Hu and Wensel (2004).

Results:: Bright, punctate Gß5 immunofluorescence was observed in the OPL of the mouse retina associated with both rod and cone terminals. Double labeling with pre-synaptic (ribeye) and post-synaptic (calbindin and mGluR6) markers revealed that Gß5 is localized to the tips of ON-BPC dendrites. Identical staining was observed for RGS11 and RGS7, GGL-domain containing RGS proteins that form tightly bound complexes with Gß5. Immunolabeling of acutely dissociated rod-bipolar cells for Gß5 and RGS11 confirmed their localization to ON-BPC dendrites. Furthermore, in a mGluR6-deficient mouse, RGS11 was diffusely distributed in the BPCs, suggesting that mGluR6 is necessary for proper dendritic localization of the Gß5-RGS complex. We also find that R9AP, a protein known to anchor the Gß5-RGS9 complex in photoreceptor OS, is co-localized with mGluR6 in the OPL. Comparison of R9AP-/- and wild-type retinas revealed a differential dependence of RGS7 and RGS11 on R9AP. In the R9AP-/- retina, RGS11 is absent from the OPL whereas the levels of RGS7 are increased.

Conclusions:: The precise co-localization of the Gß5-RGS7 and Gß5-RGS11 complexes with mGluR6 in ON-BPC dendritic tips argues that they function specifically in the mGluR6 signal transduction pathway. They are likely to accelerate the GTPase activity of Gαo, thus accelerating the opening of ON-BPC cation channels and the depolarizing response to light.

Keywords: bipolar cells • signal transduction • retina: neurochemistry 

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