Hypothalamic thyroid hormone catabolism acts as a gatekeeper for the seasonal control of body weight and reproduction.
Seasonal adaptations in physiology exhibited by many animals involve an interface between biological timing and specific neuroendocrine systems, but the molecular basis of this interface is unknown. In this study of Siberian hamsters, we show that the availability of thyroid hormone within the hypothalamus is a key determinant of seasonal transitions. The expression of the gene encoding type III deiodinase (Dio3) and Dio3 activity in vivo (catabolism of T(4) and T(3)) is dynamically and temporally regulated by photoperiod, consistent with the loss of hypothalamic T(3) concentrations under short photoperiods. Chronic replacement of T(3) in the hypothalamus of male hamsters exposed to short photoperiods, thus bypassing synthetic or catabolic deiodinase enzymes located in cells of the ependyma of the third ventricle, prevented the onset of short-day physiology: hamsters maintained a long-day body weight phenotype and failed to undergo testicular and epididymal regression. However, pelage moult to a winter coat was not affected. Type II deiodinase gene expression was not regulated by photoperiod in these hamsters. Collectively, these data point to a pivotal role for hypothalamic DIO3 and T(3) catabolism in seasonal cycles of body weight and reproduction in mammals.
Barrett
Perry
P
Rowett Research Institute, Greenburn Road, Buckburn, Aberdeen AB21 9SB, United Kingdom. P.Barrett@Rowett.ac.uk
Ebling
Francis J P
FJ
Schuhler
Sandrine
S
Wilson
Dana
D
Ross
Alexander W
AW
Warner
Amy
A
Jethwa
Preeti
P
Boelen
Anita
A
Visser
Theo J
TJ
Ozanne
Daniel M
DM
Archer
Zoe A
ZA
Mercer
Julian G
JG
Morgan
Peter J
PJ
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology; D006224:Cricetinae; D004435:Eating / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006197:Hair / Q000502:physiology; D007031:Hypothalamus / Q000201:enzymology / Q000502:physiology*; D007453:Iodide Peroxidase / Q000235:genetics / Q000378:metabolism; D008297:Male; D008660:Metabolism; D010641:Phenotype; D017111:Phodopus; D017440:Photoperiod; D012098:Reproduction / Q000502:physiology*; D012621:Seasons; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*; D000097564:Iodothyronine Deiodinase Type II
D007453:Iodide Peroxidase; D013974:Thyroxine; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II; C117274:iodothyronine deiodinase type III