Evidence for an endogenous per1- and ICER-independent seasonal timer in the hamster pituitary gland.
Most mammals use changing annual day-length cycles to regulate pineal melatonin secretion and thereby drive many physiological rhythms including reproduction, metabolism, immune function, and pelage. Prolonged exposure to short winter day lengths results in refractoriness, a spontaneous reversion to long-day physiological status. Despite its critical role in the timing of seasonal rhythms, refractoriness remains poorly understood. The aim of this study was therefore to describe cellular and molecular mechanisms driving the seasonal secretion of a key hormone, prolactin, in refractory Syrian hamsters. We used recently developed single cell hybridization and reporter assays to show that this process is initiated by timed reactivation of endocrine signaling from the pars tuberalis (PT) region of the pituitary gland, a well-defined melatonin target site, causing renewed activation of prolactin gene expression. This timed signaling is independent of per1 clock gene expression in the suprachiasmatic nuclei and PT and of melatonin secretion, which continue to track day length. Within the PT, there is also a continued short day-like profile of ICER expression, suggesting that the change in hormone secretion is independent of cAMP signaling. Our data thus identify the PT as a key anatomical structure involved in endogenous seasonal timing mechanisms, which breaks from prevailing day length-induced gene expression.
School of Biological Sciences, University of Manchester, UK.
Jonathan D
JD
Johnston
Felino R A
FR
Cagampang
J Anne
JA
Stirland
Amanda-Jayne F
AJ
Carr
Michael R H
MR
White
Julian R E
JR
Davis
Andrew S I
AS
Loudon
D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology; D006224:Cricetinae; D051786:Cyclic AMP Response Element Modulator; D004268:DNA-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D017403:In Situ Hybridization; D008297:Male; D008550:Melatonin / Q000097:blood; D008647:Mesocricetus; D009687:Nuclear Proteins / Q000235:genetics*; D017440:Photoperiod; D010902:Pituitary Gland / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D011388:Prolactin / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D012621:Seasons; D013493:Suprachiasmatic Nucleus / Q000378:metabolism
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; D051786:Cyclic AMP Response Element Modulator; D011388:Prolactin; D008550:Melatonin