Molecular mechanism of photoperiodic time measurement in the brain of Japanese quail

Shinobu Yasuo, Miwa Watanabe, Masayuki Iigo, Takashi Yamamura, Nobuhiro Nakao, Tsuyoshi Takagi, Shizufumi Ebihara, Takashi Yoshimura

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


In most organisms living in temperate zones, reproduction is under photoperiodic control. Although photoperiodic time measurement has been studied in organisms ranging from plants to vertebrates, the underlying molecular mechanism is not well understood. The Japanese quail (Coturnix japonica) represents an excellent model to study this problem because of the rapid and dramatic photoperiodic response of its hypothalamic-pituitary-gonadal axis. Recent investigations of Japanese quail show that long-day-induced type 2 deiodinase (Dio2) expression in the mediobasal hypothalamus (MBH) plays an important role in the photoperiodic gonadal regulation by catalyzing the conversion of the prohormone thyroxine (T4) to bioactive 3,5,3′-triiodothyronine (T3). The T3 content in the MBH is approximately 10-fold higher under long than short days and conditions, and the intracerebroventricular infusion of T3 under short days and conditions mimics the photoperiodic gonadal response. While Dio2 generates active T3 from T4 by outer ring deiodination, type 3 deiodinase (Dio3) catalyzes the conversion of both T3 and T 4 into inactive forms by inner ring deiodination. In contrast to Dio2 expression, Dio3 expression in the MBH is suppressed under the long-day condition. Photoperiodic changes in the expression of both genes during the photoinduction process occur before the changes in the level of luteinizing hormone (LH) secretion, suggesting that the reciprocal changes in Dio2 and Dio3 expression act as gene switches of the photoperiodic molecular cascade to trigger induction of LH secretion.

Original languageEnglish
Pages (from-to)307-315
Number of pages9
JournalChronobiology International
Issue number1-2
Publication statusPublished - 2006
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Physiology
  • Physiology (medical)


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