Photoperiod differentially regulates circadian oscillators in central and peripheral tissues of the Syrian hamster.
In many seasonally breeding rodents, reproduction and metabolism are activated by long summer days (LD) and inhibited by short winter days (SD). After several months of SD, animals become refractory to this inhibitory photoperiod and spontaneously revert to LD-like physiology. The suprachiasmatic nuclei (SCN) house the primary circadian oscillator in mammals. Seasonal changes in photic input to this structure control many annual physiological rhythms via SCN-regulated pineal melatonin secretion, which provides an internal endocrine signal representing photoperiod. We compared LD- and SD-housed animals and show that the waveform of SCN expression for three circadian clock genes (Per1, Per2, and Cry2) is modified by photoperiod. In SD-refractory (SD-R) animals, SCN and melatonin rhythms remain locked to SD, reflecting ambient photoperiod, despite LD-like physiology. In peripheral oscillators, Per1 and Dbp rhythms are also modified by photoperiod but, in contrast to the SCN, revert to LD-like, high-amplitude rhythms in SD-R animals. Our data suggest that circadian oscillators in peripheral organs participate in photoperiodic time measurement in seasonal mammals; however, circadian oscillators operate differently in the SCN. The clear dissociation between SCN and peripheral oscillators in refractory animals implicates intermediate factor(s), not directly driven by the SCN or melatonin, in entrainment of peripheral clocks.
Carr
Amanda Jayne F
AJ
School of Biological Sciences, University of Manchester, Oxford Road, M13 9P, Manchester, United Kingdom.
Johnston
Jonathan D
JD
Semikhodskii
Andrei G
AG
Nolan
Tania
T
Cagampang
Felino R A
FR
Stirland
J Anne
JA
Loudon
Andrew S I
AS
D000818:Animals; D001683:Biological Clocks / Q000235:genetics* / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D056931:Cryptochromes; D017931:DNA Primers; D029721:Drosophila Proteins; D005136:Eye Proteins / Q000502:physiology; D005420:Flavoproteins / Q000502:physiology; D005786:Gene Expression Regulation; D017403:In Situ Hybridization; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D056950:Period Circadian Proteins; D017440:Photoperiod; D017956:Photoreceptor Cells, Invertebrate; D016133:Polymerase Chain Reaction; D011388:Prolactin / Q000097:blood; D043562:Receptors, G-Protein-Coupled; D012621:Seasons; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013737:Testis / Q000502:physiology
D056931:Cryptochromes; D017931:DNA Primers; D029721:Drosophila Proteins; D005136:Eye Proteins; D005420:Flavoproteins; D056950:Period Circadian Proteins; D043562:Receptors, G-Protein-Coupled; C119828:cry protein, Drosophila; D011388:Prolactin