Kataki Bidisha, Dixit Anand S
Department of Zoology, North-Eastern Hill University, Shillong, Meghalaya, India.
J Neuroendocrinol. 2025 Jun;37(6):e70023. doi: 10.1111/jne.70023. Epub 2025 Mar 19.
Seasonal transitions in avian reproductive cycles are governed by neuroendocrine adaptability. The molecular mechanisms behind seasonal regulation are still not fully understood in many species and remain an important area of ongoing research. Despite recognizing the importance of regulatory genes, gaps persist in comprehending the exact molecular processes that control the transitions between different reproductive phases. We investigated the expression patterns of Tsh-β (Thyroid-stimulating hormone subunit beta), Dio2 (Iodothyronine deiodinase 2), Dio3 (Iodothyronine deiodinase 3), and GnRH-I (Gonadotropin-releasing hormone I) mRNAs in regulating reproduction in both sexes of the Eurasian tree sparrow (Passer montanus). Adult tree sparrows (n = 4 for each sex) were procured from the wild, and mRNA expression of Tsh-β, Dio2, Dio3, and GnRH-I, along with gonadal size and body weight, was examined on a monthly basis for 1 year. Results revealed distinct annual cycles of Tsh-β, Dio2, Dio3, and GnRH-I mRNA expression and gonadal size in both sexes. Significantly higher expressions of Tsh-β, Dio2, and GnRH-I mRNA were observed during the breeding phase (April-May), while Dio3 expression was reported higher during the non-breeding phase. The synchronization in the pattern of increase in the Tsh-β, Dio2, and GnRH-I during the breeding phase is associated with gonadal growth, suggesting their potential involvement in regulating seasonal reproduction in tree sparrows. Thus, the control of the reproductive cycle in tree sparrows involves the actions of Tsh-β and Dio2/Dio3 leading to the activation and deactivation of GnRH-I via the HPG (hypothalamic-pituitary-gonadal) axis.
鸟类繁殖周期的季节性转变受神经内分泌适应性的调控。许多物种中季节性调节背后的分子机制仍未完全明了，仍是正在进行的研究的一个重要领域。尽管认识到调控基因的重要性，但在理解控制不同繁殖阶段之间转变的确切分子过程方面仍存在差距。我们研究了促甲状腺激素β亚基（Tsh-β）、碘甲腺原氨酸脱碘酶2（Dio2）、碘甲腺原氨酸脱碘酶3（Dio3）和促性腺激素释放激素I（GnRH-I）mRNA在欧亚树麻雀（Passer montanus）两性繁殖调控中的表达模式。从野外捕获成年树麻雀（雌雄各n = 4只），并在1年的时间里每月检测Tsh-β、Dio2、Dio3和GnRH-I的mRNA表达以及性腺大小和体重。结果显示，雌雄两性的Tsh-β、Dio2、Dio3和GnRH-I mRNA表达以及性腺大小均呈现明显的年度周期。在繁殖期（4月至5月）观察到Tsh-β、Dio2和GnRH-I mRNA的表达显著更高，而在非繁殖期Dio3的表达更高。繁殖期Tsh-β、Dio2和GnRH-I增加模式的同步与性腺生长相关，表明它们可能参与调节树麻雀的季节性繁殖。因此，树麻雀繁殖周期的控制涉及Tsh-β和Dio2/Dio3的作用，通过下丘脑-垂体-性腺（HPG）轴导致GnRH-I的激活和失活。
