title: Diurnal and circadian regulation of connexin 36 transcript and protein in the mammalian retina.
abstract: OBJECTIVE
  Gap junctional coupling between rod and cone photoreceptor cells is regulated by light and the circadian clock, and contributes to retinal light adaptation. Phosphorylation of connexin 36 (Cx36) has been proposed as the mechanism involved. We investigated whether retinal Cx36 is also regulated at the level of transcript and protein expression.
  
  
  METHODS
  At specific time points in a diurnal or circadian cycle, Cx36 protein was assessed by Western blotting and immunohistochemistry, and Cx36 transcript by quantitative real time PCR in a melatonin-deficient (C57BL6/FVB) and two melatonin-proficient (C3H(+/+) and C3H(rd/rd)) mouse strains.
  
  
  RESULTS
  In C57BL6/FVB mice during a diurnal cycle, Cx36 protein expression was rhythmic, peaking at approximately zeitgeber time (ZT) 20. However, this rhythm was not maintained in the circadian cycle. In C3H(+/+) mice levels of Cx36 protein were higher at night and subjective night relative to day and subjective day, respectively. These patterns of Cx36 expression were localized primarily to the outer plexiform layer in both strains. Cx36 transcript expression was higher at night and subjective night relative to day and subjective day in C57BL6/FVB and C3H(+/+) mice. Rhythmic expression of Cx36 transcript was lost in retinally degenerate C3H(rd/rd) mice.
  
  
  CONCLUSIONS
  The results suggested the circadian control of Cx36 protein expression is dependent on melatonin, whereas the circadian regulation of Cx36 transcript expression may be controlled directly by the circadian clock. In addition to post-translational modification, regulation of Cx36 transcript and protein expression may be important during retinal light adaptation.
authors: Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, John Radcliffe Hospital, United Kingdom.
authors: Christiana
authors: C
authors: Katti
authors: Rachel
authors: R
authors: Butler
authors: Sumathi
authors: S
authors: Sekaran
mesh_terms: D000818:Animals; D015153:Blotting, Western; D057906:Circadian Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D017630:Connexins / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D008550:Melatonin / Q000502:physiology; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D012160:Retina / Q000378:metabolism*; D000097004:Gap Junction delta-2 Protein
chemical_list: D017630:Connexins; D008550:Melatonin; D012333:RNA, Messenger; D000097004:Gap Junction delta-2 Protein