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G. Y. Ko, L. Shi, D. Trump, M. L. Ko; Retinoschisin Is Under Circadian Control in the Chick Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):181. doi: https://doi.org/.
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Retinoschisin is a 224 amino acid protein secreted mainly from retina photoreceptors and bipolar cells. Previously, retinoschisin was also shown to be present in rodent pineal glands. The purpose of this study was to investigate the circadian regulation of retinoschisin, as well as whether the secretion of retinoschisin is an L-type voltage-gated calcium channel (VGCC)-dependent process, since the L-type VGCCs are essential in neurotransmitter release in photoreceptors.
Chick embryos (E10) were entrained under 12:12 hr light-dark (LD) cycles in ovo for 6 days and kept in constant darkness (DD) for 1 day. On the second day of DD, retinas were dissected at different circadian time points and prepared for quantitative RT-PCR and western immunoblotting for the expression of retinoschisin mRNA and protein. Whole retina cultures and dissociated retina cultures were also used in this study to detect the secreted retinoschisin in the media. Co-immunoprecipitation and mammalian two-hybrid assays were used to determine the interaction between retinoschisin and the VGCCα1 subunit.
The mRNA level, protein expression, and secretion of retinoschisin were under circadian control. The mRNA level peaked at CT 12, while the protein level peaked at CT 16. Using a membrane biotinylation assay, we found that treatment with the L-VGCC inhibitor nitrendipine diminished the circadian regulation of retinoschisin secretion, but nitrendipine did not completely block the synthesis or secretion of retinoschisin. We also found that there was a protein-protein interaction between retinoschisin and the VGCCα1 subunit using co-immunoprecipitation and mammalian two-hybrid luciferase assays.
Retinoschisin is under circadian control from mRNA to protein expression in chick retinas, and L-type VGCCs are part of the circadian output pathway to regulate the secretion of retinoschisin. The circadian regulation of retinoschisin is also through the same Ras-Erk-CaMKII pathway that regulates the cGMP-gated ion channels and L-type VGCCs. Furthermore, there is a protein-protein interaction between retinoschisin and the VGCCα1 subunit.Supported by: TX A&M Start-up fund and NIH RO1 EY017452.
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