Transgenic Mouse Model of Nougaret Night Blindness

Abstract

Abstract: : Purpose: To elucidate the mechanism of the Nougaret form of dominant stationary night blindness linked to a G38D mutation in the rod transducin–α subunit (Tα). Methods: Trangenic mouse lines expressing the EE–tagged mutant TαG38D on the Tα +/+, +/–, and –/– backgrounds have been generated. Expression of TαG38D and several major phototransduction proteins in transgenic retinas was examined by Western blotting. Localization and light–dependent translocation of TαG38D were investigated by immunofluorescence staining of mouse retinal sections. The properties of TαG38D in ROS preparations isolated from transgenic mice were analyzed using GTPγS binding, single–turnover GTPase, and PDE6 binding/activation assays. The photoresponses and visual sensitivities of mice expressing TαG38D were analyzed by electroretinography and vision–dependent behavior. Results: The levels of TαG38D expression on the Tα +/+, +/–, and –/– backgrounds were estimated at ∼20%, 25%, and 30–35%, respectively, of the native Tα in control mice. The retinal morphology of the transgenic mice was normal, and TαG38D was properly localized to the OS in dark–adapted retinas. Translocation of TαG38D in response to a bright–light exposure was similar to that of the native Tα, but appeared to be deficient under the conditions of moderate illumination (∼200 lux). TαG38D did not interfere with the localization or translocation of the native Tα. Biochemical characterization of TαG38D showed reduced GTPase activity and a marked impairment of the effector function. Mice expressing TαG38D both in the absence and presence of normal transducin had reduced visual sensitivity as evaluated by electroretinography and vision–dependent behavior analysis. Conclusions: The reduced ability of TαG38D to activate PDE6 and the slow rate of recovery due to decreased GTPase activity of the mutant are likely to represent the major mechanisms underlying the Nougaret form of night blindness.

Keywords: photoreceptors • signal transduction