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Circannual variation in thyroid hormone deiodinases in a short-day breeder.
MedLine Citation:
PMID:  23282080     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
At temperate latitudes many mammals and birds show internally timed, long-term changes in seasonal physiology, synchronised to the seasons by changing day length (photoperiod). Photoperiodic control of thyroid hormone levels in the hypothalamus dictates the timing. This is effected through reciprocal regulation of thyroid hormone deiodinase gene expression. The local synthesis of Type 2 deiodinase (Dio2) promotes triiodothyronine (T3) production and summer biology, while Type 3 deiodinase (Dio3) promotes T3 degradation and winter biology. Here, we investigated the extent to which hypothalamic expression of Dio2 and Dio3 is circannually regulated in the Soay sheep, a short day breeding mammal. Male sheep were exposed to long photoperiod (LP, 16-h light/24-h) or short photoperiod (SP, 8-h light/24-h), for up to 28 weeks to establish 4 different endocrine states: i) LP animals in a spring/summer-like state of reproductive arrest; ii) LP refractory (LPR) animals showing spontaneous reproductive reactivation; iii) SP animals showing autumn/winter-like reproductive activation, and iv) SP refractory (SPR) animals showing spontaneous reproductive arrest. A complex pattern of hypothalamic Dio2 and Dio3 expression was observed, revealing distinctive photoperiod-driven and internally timed effects for both genes. The patterns of expression differed both spatially and temporally, with phases of peak Dio2 expression in the median eminence and tuberoinfundibular sulcus as well as in the paraventricular zone (PVZ) (maximal under LP), whereas Dio3 expression was always confined to the PVZ (maximal under SP). These effects likely reflect the distinct roles of these enzymes in the localized control of hypothalamic T3 levels. The spontaneous decline in Dio2 and spontaneous increase in Dio3 in LPR animals occurred with a corresponding decline in thyroid stimulating hormone beta subunit (TSHβ) expression in the neighbouring pars tuberalis (PT), but this relationship did not hold for the corresponding Dio2 increase/Dio3 decrease seen in SPR animals. We conclude that internally timed and spatially regulated changes in Dio2 and Dio3 expression may drive the cycling between breeding and non-breeding states in long lived seasonal species, and may be either PT-dependent or PT-independent at different phases of the circannual cycle. © 2013 British Society for Neuroendocrinology.
Authors:
Cristina Sáenz de Miera; Elodie A Hanon; Hugues Dardente; Michael Birnie; Valérie Simonneaux; Gerald A Lincoln; David G Hazlerigg
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-1-2
Journal Detail:
Title:  Journal of neuroendocrinology     Volume:  -     ISSN:  1365-2826     ISO Abbreviation:  J. Neuroendocrinol.     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-1-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8913461     Medline TA:  J Neuroendocrinol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
© 2013 British Society for Neuroendocrinology.
Affiliation:
School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, Scotland, United Kingdom; Département de Neurobiologie des Rythmes CNRS UPR-3212, Institut des Neurosciences Cellulaires et Intégratives, Université de Strasbourg, 67084, Strasbourg, France.
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