1 Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University , Nagoya, Japan .
2 Division of Seasonal Biology, National Institute for Basic Biology , Okazaki, Japan .
Thyroid. 2018 Jan;28(1):4-10. doi: 10.1089/thy.2017.0186. Epub 2017 Oct 5.
Seasonal changes in various physiological events have been reported in humans, including metabolism, immune function, and mood. However, the molecular and endocrine basis of these seasonal changes remains unclear.
Animals that breed seasonally, such as Japanese quail and the Siberian hamster, have sophisticated seasonal mechanisms, and hence they provide excellent opportunities to understand the underlying processes. Functional genomic analysis in quail uncovered the photoperiodic signal transduction pathway, which regulates avian seasonal reproduction: a long-day stimulus induces secretion of thyrotropin (TSH) from the pars tuberalis (PT) of the anterior pituitary gland. This PT-derived TSH locally activates thyroid hormone within the hypothalamus, which in turn induces gonadotropin-releasing hormone and then gonadotropin secretion, leading to gonadal growth.
Studies using TSH receptor-null mice confirmed the involvement of PT-derived TSH in mammalian seasonal reproduction. The pars distalis of the anterior pituitary gland is the major source of circulating TSH. Although the pars distalis and PT are in close proximity, tissue-specific glycosylation of circulating TSH alters its function to avoid cross talk.
人类的许多生理事件都存在季节性变化，包括代谢、免疫功能和情绪。然而，这些季节性变化的分子和内分泌基础仍不清楚。
季节性繁殖的动物，如日本鹌鹑和仓鼠，具有复杂的季节性机制，因此它们为理解潜在的过程提供了极好的机会。鹌鹑的功能基因组分析揭示了调节鸟类季节性繁殖的光周期信号转导途径：长日照刺激诱导垂体柄中叶细胞（PT）分泌促甲状腺素（TSH）。这种由 PT 衍生的 TSH 在局部激活下丘脑内的甲状腺激素，进而诱导促性腺激素释放激素和促性腺激素的分泌，导致性腺生长。
使用 TSH 受体缺失小鼠的研究证实了 PT 衍生的 TSH 参与了哺乳动物的季节性繁殖。垂体前叶的垂体远侧部是循环 TSH 的主要来源。尽管垂体远侧部和 PT 彼此靠近，但循环 TSH 的组织特异性糖基化改变了其功能以避免串扰。
