Dual function of Gβ5 in regulating dendritic morphology and light responses of rod bipolar cell

Abstract

Purpose : Gβ5 and R7RGS proteins are obligate partners required for normal light response and dendritic morphology of rod bipolar cells (RBC), wherein Gβ5/RGS7 and Gβ5/RGS11 are redundant GTPase accelerating proteins for Gαo. RGS7/RGS11 double knockout (711dKO) mice phenocopy RBC defects of global Gβ5^-/- mice. We determined here whether prolonged Gao activation is sufficient to recapitulate RBC defects of Gβ5^-/- mice and whether these anatomical and functional deficits are separable.

Methods : We have floxed the Gnb5 and Gnao genes and used Chx10Cre mouse to generate retina-specific Gβ5 and Gαo knockout mice. To express a RGS-insensitive Gαo in the retina, we generated a compound heterozygous Gαo^flox/G184S mouse line and mated it into the Chx10Cre driver. Protein levels were determined by Western blotting. Immunofluorescence staining (IF) with various post- and pre-synaptic markers was used to examine RBC dendritic morphology. A custom image analysis program was developed to quantify the shortest distance distribution between neighboring photoreceptor ribbons and RBC dendritic tips. Light responses were determined by Electroretinography (ERG). RBC responses to puffed mGluR6 antagonist CPPG were determined by patch clamp recording in acute retinal slices.

Results : RBC dendritic defects were readily found in retina-specific Gβ5^-/-, Gαo^-/- and Chx10Cre/Gαo^flox/G184S and 711dKO mouse retinas. The number of synaptic contacts, defined as < 1 μm in distance between neighboring RBC dendritic tips and photoreceptor ribbons, decreased in both retina-specific Gβ5^-/- and Chx10Cre/Gαo^flox/G184S retinas. Moreover, there was no recordable scotopic ERG b-waves in retina-specific Gαo-/- and Chx10Cre/Gαo^flox/G184S, or in 711dKO mice. However, a noticeable but small b-wave could be recorded in Chx10/Gαo^flox/G184S mice when inter-flash intervals increased from 1.7 to ≥ 15 seconds. RBCs of retina-specific Gβ5^-/-, Gαo^-/- mice or 711dKO mice showed no responses to CPPG puffs, while a discernable but small response was recorded in Chx10Cre/Gαo^flox/G184S mice.

Conclusions : Our data demonstrate that prolonged Gαo activation causes RBC morphological defect in straight Gβ5^-/- and 711dKO mice and further reveal that Gβ5 may have a previously unappreciated role in RBC light response pathway.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.