title: Low temperature-induced circulating triiodothyronine accelerates seasonal testicular regression.
abstract: In temperate zones, animals restrict breeding to specific seasons to maximize the survival of their offspring. Birds have evolved highly sophisticated mechanisms of seasonal regulation, and their testicular mass can change 100-fold within a few weeks. Recent studies on Japanese quail revealed that seasonal gonadal development is regulated by central thyroid hormone activation within the hypothalamus, depending on the photoperiodic changes. By contrast, the mechanisms underlying seasonal testicular regression remain unclear. Here we show the effects of short day and low temperature on testicular regression in quail. Low temperature stimulus accelerated short day-induced testicular regression by shutting down the hypothalamus-pituitary-gonadal axis and inducing meiotic arrest and germ cell apoptosis. Induction of T3 coincided with the climax of testicular regression. Temporal gene expression analysis over the course of apoptosis revealed the suppression of LH response genes and activation of T3 response genes involved in amphibian metamorphosis within the testis. Daily ip administration of T3 mimicked the effects of low temperature stimulus on germ cell apoptosis and testicular mass. Although type 2 deiodinase, a thyroid hormone-activating enzyme, in the brown adipose tissue generates circulating T3 under low-temperature conditions in mammals, there is no distinct brown adipose tissue in birds. In birds, type 2 deiodinase is induced by low temperature exclusively in the liver, which appears to be caused by increased food consumption. We conclude that birds use low temperature-induced circulating T3 not only for adaptive thermoregulation but also to trigger apoptosis to accelerate seasonal testicular regression.
authors.affiliation: Laboratory of Animal Physiology (K.I., Y.A., E.Y., H.O., I.M., Y.N., W.O., T.Y.), Avian Bioscience Research Center (Y.A., T.Y.), Graduate School of Bioagricultural Sciences, Department of Genetics (Y.H.), Division of Stress Adaptation and Recognition, Research Institute of Environmental Medicine, and Institute of Transformative Bio-molecules (T.Y.), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan; Department of Applied Biochemistry (N.A., A.T., M.I.), Faculty of Agriculture, Center for Bioscience Research and Education (M.I.), Utsunomiya University, Utsunomiya 321-8505, Japan; Utsunomiya University Center for Optical Research and Education (M.I.), Utsunomiya, Tochigi 321-8585, Japan; Department of Biology and Center for Medical Life Science (K.T.), Waseda University, Tokyo 162-8480, Japan; Division of Germ Cell Biology (S.Y.), National Institute for Basic Biology, Okazaki 444-8787, Japan; Division of Seasonal Biology (T.Y.), National Institute for Basic Biology, Okazaki 444-8585, Japan; and Animal Physiology and Neurobiology Section (V.M.D.), Department of Biology, Laboratory of Comparative Endocrinology, KU Leuven, B-3000 Leuven, Belgium.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ikegami
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Atsumi
authors.forename: Eriko
authors.initials: E
authors.lastname: Yorinaga
authors.forename: Hiroko
authors.initials: H
authors.lastname: Ono
authors.forename: Itaru
authors.initials: I
authors.lastname: Murayama
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nakane
authors.forename: Wataru
authors.initials: W
authors.lastname: Ota
authors.forename: Natsumi
authors.initials: N
authors.lastname: Arai
authors.forename: Akinori
authors.initials: A
authors.lastname: Tega
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iigo
authors.forename: Veerle M
authors.initials: VM
authors.lastname: Darras
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Tsutsui
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Shosei
authors.initials: S
authors.lastname: Yoshida
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshimura
mesh_terms: D000818:Animals; D017209:Apoptosis; D003080:Cold Temperature; D003370:Coturnix / Q000502:physiology*; D005215:Fasting / Q000378:metabolism; D005786:Gene Expression Regulation; D007453:Iodide Peroxidase / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D008540:Meiosis; D017440:Photoperiod; D013094:Spermatozoa / Q000502:physiology; D013737:Testis / Q000502:physiology*; D014284:Triiodothyronine / Q000097:blood*; D000097564:Iodothyronine Deiodinase Type II
chemical_list: D007453:Iodide Peroxidase; D007986:Luteinizing Hormone; D014284:Triiodothyronine; D000097564:Iodothyronine Deiodinase Type II