Laboratory of Seasonal Biology, Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Glasgow, UK.
J Exp Zool A Ecol Integr Physiol. 2022 Dec;337(9-10):890-901. doi: 10.1002/jez.2604. Epub 2022 May 10.
Seasonal cycles of environmental cues generate variation in the timing of life-history transition events across taxa. It is through the entrainment of internal, endogenous rhythms of organisms to these external, exogenous rhythms in environment, such as cycling temperature and daylight, by which organisms can regulate and time life history transitions. Here, we review the current understanding of how photoperiod both stimulates and terminates seasonal reproduction in birds. The review describes the role of external coincidence timing, the process by which photoperiod is proposed to stimulate reproductive development. Then, the molecular basis of light detection and the photoperiodic regulation of neuroendocrine timing of seasonal reproduction in birds is presented. Current data indicates that vertebrate ancient opsin is the predominant photoreceptor for light detection by the hypothalamus, compared to neuropsin and rhodopsin. The review then connects light detection to well-characterized hypothalamic and pituitary gland molecules involved in the photoperiodic regulation of reproduction. In birds, Gonadotropin-releasing hormone synthesis and release are controlled by photoperiodic cues via thyrotropin-stimulating hormone-β (TSHβ) independent and dependent pathways, respectively. The review then highlights the role of D-box and E-box binding motifs in the promoter regions of photoperiodic genes, in particular Eyes-absent 3, as the key link between circadian clock function and photoperiodic time measurement. Based on the available evidence, the review proposes that at least two molecular programs form the basis for external coincidence timing in birds: photoperiodic responsiveness by TSHβ pathways and endogenous internal timing by gonadotropin synthesis.
环境线索的季节性循环在跨分类群的生命史转折事件的时间上产生变化。正是通过生物体内部、内源性节律与环境外部、外源性节律的同步，如温度和日光的循环，生物体可以调节和控制生命史转折。在这里，我们回顾了光周期刺激和终止鸟类季节性繁殖的当前理解。该综述描述了外部巧合定时的作用，即光周期被提出刺激生殖发育的过程。然后，介绍了光检测的分子基础以及鸟类季节性生殖的神经内分泌定时的光周期调节。目前的数据表明，与神经肽和视蛋白相比，脊椎动物古老视蛋白是下丘脑光检测的主要光感受器。然后，该综述将光检测与特征明确的下丘脑和垂体分子联系起来，这些分子参与了生殖的光周期调节。在鸟类中，促性腺激素释放激素的合成和释放分别受光周期线索通过促甲状腺激素刺激激素-β（TSHβ）独立和依赖途径的控制。然后，该综述强调了 D 盒和 E 盒结合基序在光周期基因启动子区域中的作用，特别是 Eyes-absent 3，它是生物钟功能和光周期时间测量之间的关键联系。基于现有证据，该综述提出，至少有两个分子程序构成了鸟类外部巧合定时的基础：TSHβ 途径的光周期反应性和促性腺激素合成的内源性内部定时。
