Photoperiod regulates multiple gene expression in the suprachiasmatic nuclei and pars tuberalis of the Siberian hamster (Phodopus sungorus).
Photoperiod regulates the seasonal physiology of many mammals living in temperate latitudes. Photoperiodic information is decoded by the master circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and then transduced via pineal melatonin secretion. This neurochemical signal is interpreted by tissues expressing melatonin receptors (e.g. the pituitary pars tuberalis, PT) to drive physiological changes. In this study we analysed the photoperiodic regulation of the circadian clockwork in the SCN and PT of the Siberian hamster. Female hamsters were exposed to either long or short photoperiod for 8 weeks and sampled at 2-h intervals across the 24-h cycle. In the SCN, rhythmic expression of the clock genes Per1, Per2, Cry1, Rev-erbalpha, and the clock-controlled genes arginine vasopressin (AVP) and d-element binding protein (DBP) was modulated by photoperiod. All of these E-box-containing genes tracked dawn, with earlier peak mRNA expression in long, compared to short, photoperiod. This response occurred irrespective of the presence of additional regulatory cis-elements, suggesting photoperiodic regulation of SCN gene expression through a common E-box-related mechanism. In long photoperiod, expression of Cry1 and Per1 in the PT tracked the onset and offset of melatonin secretion, respectively. However, whereas Cry1 tracked melatonin onset in short period, Per1 expression was not detectably rhythmic. We therefore propose that, in the SCN, photoperiodic regulation of clock gene expression primarily occurs via E-boxes, whereas melatonin-driven signal transduction drives the phasing of a subset of clock genes in the PT, independently of the E-box.
School of Biological Sciences, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK. j.johnston@abdn.ac.uk
Jonathan D
JD
Johnston
Francis J P
FJ
Ebling
David G
DG
Hazlerigg
D000818:Animals; D001127:Arginine Vasopressin / Q000235:genetics; D001683:Biological Clocks / Q000235:genetics*; D018797:Cell Cycle Proteins; D002940:Circadian Rhythm / Q000235:genetics*; D006224:Cricetinae; D056931:Cryptochromes; D004268:DNA-Binding Proteins / Q000235:genetics; D024721:E-Box Elements / Q000235:genetics*; D005260:Female; D005420:Flavoproteins / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics*; D015694:Gene Products, rev / Q000235:genetics; D005809:Genes, Regulator / Q000235:genetics; D008550:Melatonin / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics; D056950:Period Circadian Proteins; D017111:Phodopus; D010775:Photic Stimulation; D017440:Photoperiod; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics
D018797:Cell Cycle Proteins; C538964:Cry1 protein, mouse; D056931:Cryptochromes; D004268:DNA-Binding Proteins; D005420:Flavoproteins; D015694:Gene Products, rev; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D014157:Transcription Factors; D001127:Arginine Vasopressin; D008550:Melatonin