RETINAL ACCUMULATION OF THE PHOSDUCIN-T-BETA-GAMMA AND TRANSDUCIN COMPLEXES IN DEVELOPING NORMAL MICE AND IN MICE AND DOGS WITH INHERITED RETINAL DEGENERATION

Rod photoreceptors of mammalian retinas contain a 33-kDa phosphoprotein, phosducin, which complexes with the β,γ-subunits of transducin (Tβγ). The level of phosducin phosphorylation is modulated by light, suggesting that the phosducin/Tβγ complex has a pivotal role in light-regulated events that occur in photoreceptors. We have investigated, in developing mouse retinas, the age at which the complex is first detected and the subsequent accumulation of the phosducin/Tβγ complex during postnatal life. Western blot analysis detected immunoreactivity both for phosducin and Tβ in retinal homogenates of 3-day-old mice. Thereafter, the level of immunoreactivity for both proteins increased steadily, to reach adult levels in the next 2 postnatal weeks. Gel filtration analysis of extracts from immature mouse retina showed that phosducin and tβ co-eluted, like the phosducin/Tβγ complex of adult retina, as a 77-kDa complex, indicating that the phosducin/Tβγ complex is formed when photoreceptors first synthesize the components of the complex. While the levels of the phosducin/Tβγ complex increased steadily during the first 2 postnatal weeks, the subunits of transducin complex, Tα together with additional amounts of Tβγ, only started to appear around the 7-9th postnatal day, and the level of transducin complex increased sharply at 11-14 days to reach adult levels that are similar to those of phosducin/Tβγ complex. Similar studies of immature retinas from rd mouse, rds mouse, rcd Irish setter and erd Norwegian elkhound showed that the composition and level of accumulation of both phosducin/Tβγ and transducin were essentially normal in each case. The ability of rd mouse photoreceptors to form both the phosducin/Tβγ complex and transducin contrasts with the failure of rd photoreceptors to assemble a phosphodiesterase complex of normal composition and function. © 1990.