title: Prolonged light exposure induces widespread phase shifting in the circadian clock and visual pigment gene expression of the Arvicanthis ansorgei retina.
abstract: OBJECTIVE
  Prolonged periods of constant lighting are known to perturb circadian clock function at the molecular, physiological, and behavioral levels. However, the effects of ambient lighting regimes on clock gene expression and clock outputs in retinal photoreceptors--rods, cones and intrinsically photosensitive retinal ganglion cells--are only poorly understood.
  
  
  METHODS
  Cone-rich diurnal rodents (Muridae: Arvicanthis ansorgei) were maintained under and entrained to a 12 h:12 h light-dark cycle (LD; light: ~300 lux). Three groups were then examined: control (continued maintenance on LD); animals exposed to a 36 h dark period before sampling over an additional 24 h period of darkness (DD); and animals exposed to a 36 h light period before sampling over an additional 24 h period of light (~300 lux, LL). Animals were killed every 3 or 4 h over 24 h, their retinas dissected, and RNA extracted. Oligonucleotide primers were designed for the Arvicanthis clock genes Per1, Per2, Cry1, Cry2, and Bmal1, and for transcripts specific for rods (rhodopsin), cones (short- and mid-wavelength sensitive cone opsin, cone arrestin, arylalkylamine N-acetyltransferase) and intrinsically photosensitive retinal ganglion cells (melanopsin). Gene expression was analyzed by real-time PCR.
  
  
  RESULTS
  In LD, expression of all genes except cone arrestin was rhythmic and coordinated, with acrophases of most genes at or shortly following the time of lights on (defined as zeitgeber time 0). Arylalkylamine N-acetyltransferase showed maximal expression at zeitgeber time 20. In DD conditions the respective profiles showed similar phase profiles, but were mostly attenuated in amplitude, or in the case of melanopsin, did not retain rhythmic expression. In LL, however, the expression profiles of all clock genes and most putative output genes were greatly altered, with either abolition of daily variation (mid-wavelength cone opsin) or peak expression shifted by 4-10 h.
  
  
  CONCLUSIONS
  These data are the first to provide detailed measures of retinal clock gene and putative clock output gene expression in a diurnal mammal, and show the highly disruptive effects of inappropriate (nocturnal) lighting on circadian and photoreceptor gene regulation.
authors.affiliation: Department of Neurobiology of Rhythms, Institute for Cellular and Integrative Neurosciences, Strasbourg, France.
authors.forename: Corina
authors.initials: C
authors.lastname: Bobu
authors.forename: Cristina
authors.initials: C
authors.lastname: Sandu
authors.forename: Virginie
authors.initials: V
authors.lastname: Laurent
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Felder-Schmittbuhl
authors.forename: David
authors.initials: D
authors.lastname: Hicks
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D057906:Circadian Clocks / Q000235:genetics* / Q000528:radiation effects; D025461:Feedback, Physiological / Q000528:radiation effects; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000528:radiation effects*; D008027:Light; D051189:Murinae / Q000235:genetics* / Q000502:physiology; D009928:Organ Specificity / Q000235:genetics / Q000528:radiation effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012160:Retina / Q000378:metabolism* / Q000528:radiation effects*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000528:radiation effects; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000528:radiation effects; D012168:Retinal Pigments / Q000235:genetics* / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism / Q000528:radiation effects; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism; D017299:Rod Opsins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000528:radiation effects; D000099210:Melanopsin
chemical_list: D047068:Arylalkylamine N-Acetyltransferase; D012333:RNA, Messenger; D012168:Retinal Pigments; D012243:Rhodopsin; D017299:Rod Opsins; D000099210:Melanopsin