title: Rat photoreceptor circadian oscillator strongly relies on lighting conditions.
abstract: Mammalian retina harbours a self-sustained circadian clock able to synchronize to the light : dark (LD) cycle and to drive cyclic outputs such as night-time melatonin synthesis. Clock genes are expressed in distinct parts of the tissue, and it is presently assumed that the retina contains several circadian oscillators. However, molecular organization of cell type-specific clockworks has been poorly investigated. Here, we questioned the presence of a circadian clock in rat photoreceptors by studying 24-h kinetics of clock and clock output gene expression in whole photoreceptor layers isolated by vibratome sectioning. To address the importance of light stimulation towards photoreceptor clock properties, animals were exposed to 12 : 12 h LD cycle or 36 h constant darkness. Clock, Bmal1, Per1, Per2, Cry1, Cry2, RevErbα and Rorβ clock genes were all found to be expressed in photoreceptors and to display rhythmic transcription in LD cycle. Clock genes in whole retinas, used as a reference, also showed rhythmic expression with marked similarity to the profiles in pure photoreceptors. In contrast, clock gene oscillations were no longer detectable in photoreceptor layers after 36 h darkness, with the exception of Cry2 and Rorβ. Importantly, transcripts from two well-characterized clock output genes, Aanat (arylalkylamine N-acetyltransferase) and c-fos, retained sustained rhythmicity. We conclude that rat photoreceptors contain the core machinery of a circadian oscillator likely to be operative and to drive rhythmic outputs under exposure to a 24-h LD cycle. Constant darkness dramatically alters the photoreceptor clockwork and circadian functions might then rely on inputs from extra-photoreceptor oscillators.
authors.affiliation: Département de Neurobiologie des Rythmes, CNRS UPR 3212 - Université de Strasbourg, Institut des Neurosciences Cellulaires et Intégratives, Strasbourg, France.
authors.forename: Cristina
authors.initials: C
authors.lastname: Sandu
authors.forename: David
authors.initials: D
authors.lastname: Hicks
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Felder-Schmittbuhl
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics / Q000378:metabolism; D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D001683:Biological Clocks / Q000502:physiology*; D056926:CLOCK Proteins / Q000235:genetics / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D056931:Cryptochromes / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D008027:Light; D008297:Male; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1 / Q000235:genetics / Q000378:metabolism; D057095:Nuclear Receptor Subfamily 1, Group F, Member 2 / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins / Q000235:genetics / Q000378:metabolism; D017440:Photoperiod; D010786:Photoreceptor Cells / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000166:cytology / Q000502:physiology
chemical_list: D056930:ARNTL Transcription Factors; C538965:Cry1 protein, rat; C538968:Cry2 protein, rat; D056931:Cryptochromes; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D057095:Nuclear Receptor Subfamily 1, Group F, Member 2; C539024:Per1 protein, rat; C513311:Per2 protein, rat; D056950:Period Circadian Proteins; D016760:Proto-Oncogene Proteins c-fos; D056926:CLOCK Proteins; C520223:Aanat protein, rat; D047068:Arylalkylamine N-Acetyltransferase