title: Involvement of thyrotropin in photoperiodic signal transduction in mice.
abstract: Local thyroid hormone catabolism within the mediobasal hypothalamus (MBH) by thyroid hormone-activating (DIO2) and -inactivating (DIO3) enzymes regulates seasonal reproduction in birds and mammals. Recent functional genomics analysis in birds has shown that long days induce thyroid-stimulating hormone production in the pars tuberalis (PT) of the pituitary gland, which triggers DIO2 expression in the ependymal cells (EC) of the MBH. In mammals, nocturnal melatonin secretion provides an endocrine signal of the photoperiod to the PT that contains melatonin receptors in high density, but the interface between the melatonin signal perceived in the PT and the thyroid hormone levels in the MBH remains unclear. Here we provide evidence in mice that TSH participates in this photoperiodic signal transduction. Although most mouse strains are considered to be nonseasonal, a robust photoperiodic response comprising induced expression of TSHB (TSH beta subunit), CGA (TSH alpha subunit), and DIO2, and reduced expression of DIO3, was observed in melatonin-proficient CBA/N mice. These responses could not be elicited in melatonin-deficient C57BL/6J, but treatment of C57BL/6J mice with exogenous melatonin elicited similar effects on the expression of the above-mentioned genes as observed in CBA/N after transfer to short-day conditions. The EC was found to express TSH receptor (TSHR), and ICV injection of TSH induced DIO2 expression. Finally, we show that melatonin administration did not affect the expression of TSHB, DIO2, and DIO3 in TSHR-null mice. Taken together, our findings suggest that melatonin-dependent regulation of thyroid hormone levels in the MBH appears to involve TSH in mammals.
authors.affiliation: Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Ono
authors.forename: Yuta
authors.initials: Y
authors.lastname: Hoshino
authors.forename: Shinobu
authors.initials: S
authors.lastname: Yasuo
authors.forename: Miwa
authors.initials: M
authors.lastname: Watanabe
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nakane
authors.forename: Atsushi
authors.initials: A
authors.lastname: Murai
authors.forename: Shizufumi
authors.initials: S
authors.lastname: Ebihara
authors.forename: Horst-Werner
authors.initials: HW
authors.lastname: Korf
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshimura
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation / Q000502:physiology; D007453:Iodide Peroxidase / Q000235:genetics; D055537:Light Signal Transduction / Q000502:physiology*; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000235:genetics / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D017440:Photoperiod; D011989:Receptors, Thyrotropin / Q000235:genetics; D013972:Thyrotropin / Q000502:physiology*; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D008550:Melatonin; D011989:Receptors, Thyrotropin; D013972:Thyrotropin; D000097564:Iodothyronine Deiodinase Type II