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D. T. Organisciak, R. M. Darrow, L. S. Barsalou; Translocation of Crystallin Proteins in Photoreceptor Cells During the Day and Night. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4656.
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Crystallins present in post mitotic tissues such as retina may serve a protective, chaperone-like role and reportedly migrate within cells during stress. In this study we examined the time course of crystallin translocation within rat photoreceptors by determining their presence or absence in rod outer segments (ROS) at various circadian times.
Male Sprague-Dawley rats reared in dim cyclic light (lights on 8am-8pm) or darkness to the age of 60 days were dark adapted and then sacrificed at 4 hr intervals during the day or night. Retinas were excised, vitreous removed, and ROS purified by discontinuous sucrose gradient ultracentrifugation. ROS were prepared from 8 retinas per timepoint (1, 5, 9am and 1, 5, 9pm) in 3 separate experiments and used for gel electrophoresis/western analysis. In some experiments RPE was isolated from the remaining eye cups. The 1 D-gel separated proteins were visualized by Coomassie staining or transferred to PVDF membranes for Western analysis of crystallins, actin or other proteins.
In cyclic-reared animals, α-, ß- and γ-crystallin protein levels were elevated beginning at 5am, peaked during late morning into early afternoon and declined thereafter. Crystallin immunoreactivity was lowest at 9pm and 1am. Dark-reared animals exhibited a later onset of crystallin staining with peak levels detected during the afternoon to evening hours. In both types of rats crystallin levels were lowest at 1am, the period of greatest light damage susceptibility. ROS contain relatively high levels of αB-crystallin with low levels of γ-crystallins. RPE contains low levels of both α-crystallins and high levels of γ-crystallins, indicating that the changes seen in ROS are not a result of RPE contamination.
The appearance of crystallins within rat ROS exhibits differences which depend on previous light rearing environment as well as time of day. These changes appear to occur by protein translocation within photoreceptors and to occur in a circadian manner which may be linked to protection against retinal light damage. Our findings suggest that crystallin translocation is only one example of protein trafficking within photoreceptors that may occur in response to environmental stress or genetic disease.
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