title: Circadian regulation of retinoschisin in the chick retina.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas 77843-4458, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Ko
authors.forename: Yilin
authors.initials: Y
authors.lastname: Liu
authors.forename: Liheng
authors.initials: L
authors.lastname: Shi
authors.forename: Dorothy
authors.initials: D
authors.lastname: Trump
authors.forename: Gladys Y-P
authors.initials: GY
authors.lastname: Ko
mesh_terms: D000818:Animals; D015153:Blotting, Western; D020746:Calcium Channels, L-Type / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002642:Chick Embryo; D002940:Circadian Rhythm / Q000502:physiology*; D003623:Dark Adaptation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000196:embryology* / Q000378:metabolism* / Q000528:radiation effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020703:ras GTPase-Activating Proteins / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D005136:Eye Proteins; D012333:RNA, Messenger; C108726:RS1 protein, human; D020703:ras GTPase-Activating Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D048049:Extracellular Signal-Regulated MAP Kinases