Hypothalamic expression of thyroid-activating and -inactivating enzyme genes in relation to photorefractoriness in birds and mammals.

Watanabe, Tsuyoshi; Yamamura, Takashi; Watanabe, Miwa; Yasuo, Shinobu; Nakao, Nobuhiro; Dawson, Alistair; Ebihara, Shizufumi; Yoshimura, Takashi. 2007 Hypothalamic expression of thyroid-activating and -inactivating enzyme genes in relation to photorefractoriness in birds and mammals. American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 292. R568-R572.

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Photorefractoriness is the insensitivity of gonadal development to the stimulatory effects of long photoperiods in birds and to the inhibitory effects of short photoperiods in small mammals. Its molecular mechanism remains unknown. Recently, it has been shown that reciprocal expression of thyroid hormone-activating enzyme [type 2 deiodinase (Dio2)] and-inactivating enzyme [type 3 deiodinase (Dio3)] genes in the mediobasal hypothalamus is critical for photoperiodically induced gonadal growth. Since thyroid hormones are required not only for photoinduction, but also for the induction of photorefractoriness, we examined the expression of these genes in relation to photorefractoriness in birds and mammals. Transfer of birds to long photoperiods induced strong expression of Dio2. This was maintained in tree sparrow when they later became photorefractory, but decreased somewhat in quail. In hamsters, transfer to long photoperiods also induced strong expression of Dio2. High values were not maintained under long photoperiods, and, indeed, expression decreased at the same rate as in animals transferred to short photoperiods. There was no renewed expression of Dio2 associated with testicular growth as animals became refractory to short photoperiods. Expression of Dio3 was high under short photoperiods and low under long photoperiods in all the animals examined, except for the short photoperiod-refractory hamsters. Our present study revealed complex regulation of deiodinase genes in the photoinduction and photorefractory processes in birds and mammals. These gene changes may be involved in the regulation of photorefractoriness, as well as photoinduction.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Programmes pre-2009 publications > Biodiversity
UKCEH and CEH Sections/Science Areas: Watt
Additional Information. Not used in RCUK Gateway to Research.: Full text available from journal website
Additional Keywords: Eurasian tree sparrow, Japanese quail, Djungarian hamster
NORA Subject Terms: Biology and Microbiology
Ecology and Environment
Date made live: 22 Apr 2008 11:11 +0 (UTC)

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