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S. Finkelstein, E. S. Lobanova, V. Y. Arshavsky; Knockout of the Rod Transducin Gamma Subunit Induces Cell Death. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4472.
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Transducin is a prototypic heterotrimeric G-protein mediating visual signaling in vertebrate photoreceptor cells. Despite the central role of transducin in phototransduction, little is known about the mechanisms that regulate its expression. Transducin consists of three subunits: alpha, beta and gamma. It was shown previously that knockout of transducin alpha subunit makes rod photoreceptors insensitive to light, results in the mislocalization of transducin beta/gamma subunits from rod outer segments, but has no effect on the expression levels of other subunits and does not have any significant effect on the rod morphology. To further probe the mutual dependency of transducin subunits’ expression levels, we analyzed the retina phenotype of the ‘reciprocal’ mouse model: the rod transducin gamma knockout.
Retinas from transducin gamma subunit knockout or wild type mice of different ages were used for morphological analysis or for studying the expression levels of transducin subunit on both protein and mRNA levels by quantitative western blotting or qRT-PCR, respectively.
We have found that knockout of transducin gamma subunit causes a marked reduction ion the expression level of other transducin subunits and resu,lts in a progressive photoreceptor loss which begins at 3 weeks of age and becomes prominent in 6 weeks old mice, at which point ~1/3 of photoreceptors are lost. We also found, that retinal degeneration in rod transducin gamma knockout mouse was not rescued by the knockout of either of its major interacting partners in rods: transducin subunit and phosducin.
Our findings indicate that the expression of all transducin subunits in rods is critically dependent on the expression of the gamma subunit. They also suggest that the production of transducin beta subunit without its constitutive gamma subunit partner sufficiently stresses rod photoreceptors to induce apoptotic cell death.
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