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O. G. Kisselev, L. Rikimaru, P. D. Lukasiewicz, A. Hennig, S. J. Fliesler; Visual Function in a Mouse Mutant Lacking Rod-Specific G-Protein Gamma Subunit. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2993.
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© ARVO (1962-2015); The Authors (2016-present)
Phototransduction in retinal rod photoreceptor cells relies on the classic mechanism of high-yield signal amplification mediated by the heterotrimeric G-protein transducin, Gt. In order to further understand the role of the Gt-gamma subunit in rod phototransduction, retina development and protein distribution, we developed and characterized a mouse mutant lacking the gene for this protein, GNGT.
GNGT(-/-) mice were generated by homologous recombination. Retinal morphology was examined by light microscopy over a 1-14 mo time course, compared to wildtype (WT) controls. Expression levels of rhodopsin, transducin and several other key phototransduction proteins were studied by quantitative Western Blot analysis. Light-dependent subcellular distribution of transducin and arrestin were examined by immunohistochemistry. Visual function was assessed by electroretinography (ERG).
Retinal development in GNGT(-/-) mice was comparable to that in WT and GNGT(-/+) littermates, including rod outer segment (ROS) maturation. GNGT(-/-) retinas exhibited slow, progressive ROS shortening; by 14 mo, retinas contained only residual photoreceptor layers and were notably thinner, yet maintained all other typical morphological features. Rhodopsin expression levels in GNGT(-/-) retinas were identical to those in GNGT(-/+) and WT mice. Rod Gt alpha subunit expression was reduced 10-fold in GNGT(-/-) retinas, relative to that in GNGT(-/+) and GNGT(+/+) mice. Scotopic ERG a- and b-wave amplitudes were significantly reduced in GNGT(-/-) mice compared to 10-wk WT mice, while photopic b-waves appeared normal. ERGs of 6- and 14-mo old GNGT(-/-) mice were further compromised, including no recordable scotopic a-waves and reduced b-waves at 14 mo, while photopic b-waves were comparable to 14-mo WT mice. Anti-rhodopsin immunostaining of ROS in all three genotypes at 10 wk postnatal was robust and comparable. Immunostaining with anti-rod Gt alpha was reduced in GNGT(-/-) retinas relative to WT and GNGT(-/+) mice. Interestingly, GNGT(-/-) retinas displayed light-dependent translocation of Gt alpha between rod outer and inner segments, similar to that in GNGT(-/+) and WT retinas.
GNGT(-/-) retinas develop normally, but display slow progressive loss of rod photoreceptors. Loss of rod Gt gamma is accompanied by a partial reduction of rod Gt-alpha subunit. Rod Gt beta-gamma subunits appear responsible for the sensitivity of photoresponses.
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