Department of Zoology, University of Delhi, Delhi 110 007, India.
Department of Zoology, CCS University, Meerut 250 004, India.
J Photochem Photobiol B. 2020 Oct;211:111995. doi: 10.1016/j.jphotobiol.2020.111995. Epub 2020 Aug 14.
A most crucial feature of biological adaptation is the maintenance of a close temporal relationship of behaviour and physiology with prevailing 24-h light-dark environment, which is rapidly changing with increasing nighttime illumination. This study investigated developmental effects of the loss of night on circadian behaviour, metabolism and gene expressions in diurnal zebra finches born and raised under LL, with controls on 12L:12D. Birds under LD were entrained, and showed normal body mass and a significant 24-h rhythm in both activity-rest pattern and mRNA expression of candidate genes that we measured. But, under LL, birds gained weight and accumulated lipid in the liver. Intriguingly, at the end of the experiment, the majority (4/5th) of birds under LL were rhythmic in activity despite arrhythmic expression in the hypothalamus of c-Fos (neuronal activity), Rhodopsin and Mel1-a genes (light perception), and clock genes (Bmal1, Per2 and Rev-erb β). In peripheral tissues, LL induced variable clock gene expressions. Whereas 24-h mRNA rhythm was abolished for Bmal1 in both liver and gut, it persisted for Per2 and Rev-erb β in liver, and for Per2 in gut. Further, we found under LL, the loss of 24-h rhythm in hepatic expression of Fasn and Cd36/Fat (biosynthesis and its uptake), and gut expression of Sglt1, Glut5, Cd36 and Pept1 (nutrient absorption) genes. As compared to LD, baseline mRNA levels of Fasn and Cd36 genes were attenuated under LL. Among major transporter genes, Sglt1 (glucose) and Cd36 (fat) genes were arrhythmic, while Glut5 (glucose) and Pept1 (protein) genes were rhythmic but with phase differences under LL, compared to LD. These results demonstrate dissociation of circadian behaviour from clock gene rhythms, and provide molecular insights into possible mechanisms at different levels (behaviour and physiology) that diurnal animals might employ in order to adapt to an emerging overly illuminated-night urban environment.
生物适应的一个最关键特征是行为和生理学与当前 24 小时光照-黑暗环境保持密切的时间关系，而随着夜间光照的增加，这种关系迅速变化。本研究调查了失去夜间对昼夜节律行为、代谢和基因表达的发育影响在昼行性斑马雀中，这些雀鸟在 LL 下出生和饲养，对照组为 12L:12D。在 LD 下，鸟类被驯化，表现出正常的体重和我们测量的候选基因的活动-休息模式和 mRNA 表达的显著 24 小时节律。但是，在 LL 下，鸟类体重增加，肝脏中积累脂肪。有趣的是，在实验结束时，尽管下丘脑的 c-Fos（神经元活动）、视蛋白和 Mel1-a 基因（光感知）和时钟基因（Bmal1、Per2 和 Rev-erb β）表达无节律，但大多数（4/5 只）LL 下的鸟类在活动中仍有节律。在周围组织中，LL 诱导了可变的时钟基因表达。虽然肝脏和肠道中 Bmal1 的 24 小时 mRNA 节律被消除，但肝脏中 Per2 和 Rev-erb β 以及肠道中 Per2 的节律仍然存在。此外，我们发现，在 LL 下，Fasn 和 Cd36/Fat（生物合成及其摄取）基因在肝脏中的表达和 Sglt1、Glut5、Cd36 和 Pept1（营养吸收）基因在肠道中的表达失去了 24 小时的节律。与 LD 相比，LL 下 Fasn 和 Cd36 基因的基线 mRNA 水平减弱。在主要转运基因中，Sglt1（葡萄糖）和 Cd36（脂肪）基因无节律，而 Glut5（葡萄糖）和 Pept1（蛋白质）基因节律，但与 LD 相比，LL 下有相位差异。这些结果表明昼夜行为与时钟基因节律分离，并为昼夜动物可能采用的不同水平（行为和生理学）的可能机制提供了分子见解，以适应新兴的过度照明夜间城市环境。
