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(Investigative Ophthalmology and Visual Science. 2008;49:1615-1621.)
© 2008 by The Association for Research in Vision and Ophthalmology, Inc.
DOI:  10.1167/iovs.07-1189
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Circadian Regulation of Retinoschisin in the Chick Retina

Michael L. Ko,1 Yilin Liu,1,2 Liheng Shi,1 Dorothy Trump,3 and Gladys Y.-P. Ko1

1From the Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas; and the 3Medical Genetics Research Group and Centre for Molecular Medicine, Faculty of Medical and Health Sciences, University of Manchester, Manchester, United Kingdom.

PURPOSE. To investigate the circadian regulation and acute illumination effects on the expression and secretion of retinoschisin from vertebrate retinas.

METHODS. Retinas were studied on the second day of constant darkness (DD) after several days of entrainment to 12-hour light/12-hour dark (LD) cycles in ovo or in vitro. Quantitative real-time PCR and Western immunoblotting were used to examine the mRNA and protein expressions of retinoschisin at different circadian time points. Pharmacologic treatments in whole retina and dissociated retinal cell cultures were used to investigate the cellular mechanisms underlying the circadian regulation of retinoschisin content and secretion. Different illumination conditions were given to examine changes in retinoschisin content in association with acute light/dark adaptation.

RESULTS. The mRNA level, protein expression, and secretion of retinoschisin were under circadian control, all of which were higher at night and lower during the day. The Ras, MAP kinase Erk, CaMKII pathway served as part of the circadian output regulating the rhythmicity of retinoschisin. Blockage of L-type VGCCs dampened the retinoschisin rhythm, but inhibition of L-type VGCCs did not completely abolish the secretion of retinoschisin. The protein expression of retinoschisin also responded to acute illumination changes.

CONCLUSIONS. The mRNA and protein expression, as well as retinoschisin secretion, are under circadian control. L-type VGCCs play a role in the circadian regulation of retinoschisin, but the molecular mechanism underlying retinoschisin secretion does not depend on L-type VGCCs. Protein expression of retinoschisin in response to acute illumination changes depends on previous light exposure experience.






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