Agarwal Neha, Mishra Ila, Rani Sangeeta, Kumar Vinod
a IndoUS Center for Biological Timing, Department of Zoology , University of Delhi , Delhi , India.
b IndoUS Center for Biological Timing, Department of Zoology , University of Lucknow , Lucknow , India.
Chronobiol Int. 2018 May;35(5):617-632. doi: 10.1080/07420528.2017.1422742. Epub 2018 Jan 25.
We investigated if the duration and/or frequency of the light period affect 24-h rhythm of circadian clock genes in central and peripheral tissues of a non-photoperiodic songbird, the spotted munia (Lonchura punctulata), in which a circannual rhythm regulates the reproductive cycle. We monitored activity-rest pattern and measured 24-h mRNA oscillation of core clock (Bmal1, Clock, Per2, Cry1 and Cry2) and clock-controlled (E4bp4, Rorα and Rev-erbα) genes in the hypothalamus, retina, liver and gut of spotted munia subjected to an aberrant light-dark (LD) cycle (3.5L:3.5D; T7, T = period length of LD cycle) and continuous light (LL, 24L:0D), with controls on 24-h LD cycle (T24, 12L:12D). Munia exhibited rhythmic activity-rest pattern with period matched to T7 or T24 under an LD cycle and were arrhythmic with a scattered activity pattern and higher activity duration under LL. At the transcriptional level, both clock and clock-controlled genes showed a significant 24-h rhythm in all four tissues (except Clock in the liver) under 12L:12D, suggesting a conserved tissue-level circadian time generation in spotted munia. An exposure to 3.5L:3.5D or LL induced arrhythmicity in transcriptional oscillation of all eight genes in the hypothalamus (except Rev-erbα) and liver (except Bmal1 and Rev-erbα under T7 and Cry1 under LL). In the retina, however, all genes showed arrhythmic 24-h mRNA expression under LL, but not under T7 (except in E4bp4 and Rorα). Interestingly, unlike in the liver, Bmal1, Per2, Cry1, Rorα and Rev-erbα mRNA expressions were rhythmic in the gut under both T7 (except Rorα) and LL conditions. These results showed variable relationship of internal circadian clocks with the external light environment and suggested a weak coupling of circadian clocks between the central (hypothalamus and retina) and peripheral (liver and gut) tissues. We suggest tissue-level circadian clock regulation of daily physiology and behavior in the spotted munia.
我们研究了光照期的时长和/或频率是否会影响一种非光周期鸣禽——斑文鸟（Lonchura punctulata）的中枢和外周组织中昼夜节律钟基因的24小时节律，在斑文鸟中，年周期节律调节着生殖周期。我们监测了活动-休息模式，并测量了处于异常明暗（LD）周期（3.5L:3.5D；T7，T = LD周期的时长）和持续光照（LL，24L:0D）条件下的斑文鸟的下丘脑、视网膜、肝脏和肠道中核心生物钟（Bmal1、Clock、Per2、Cry1和Cry2）以及生物钟控制基因（E4bp4、Rorα和Rev-erbα）的24小时mRNA振荡情况，同时设置了处于24小时LD周期（T24，12L:12D）的对照组。在LD周期下，斑文鸟表现出与T7或T24时长匹配的节律性活动-休息模式，而在LL条件下则无节律，活动模式分散且活动时长增加。在转录水平上，在12L:12D条件下，所有四个组织中的生物钟基因和生物钟控制基因均表现出显著的24小时节律（肝脏中的Clock基因除外），这表明斑文鸟在组织水平上存在保守的昼夜节律时间产生机制。暴露于3.5L:3.5D或LL条件下会导致下丘脑（Rev-erbα基因除外）和肝脏（T7条件下的Bmal1和Rev-erbα基因以及LL条件下的Cry1基因除外）中所有八个基因的转录振荡出现无节律性。然而，在视网膜中，所有基因在LL条件下均表现出24小时mRNA表达无节律，但在T7条件下并非如此（E4bp4和Rorα基因除外）。有趣的是，与肝脏不同，在T7（Rorα基因除外）和LL条件下，肠道中的Bmal1、Per2、Cry1、Rorα和Rev-erbα mRNA表达均具有节律性。这些结果表明内部生物钟与外部光照环境之间存在可变关系，并表明中枢（下丘脑和视网膜）和外周（肝脏和肠道）组织之间的生物钟耦合较弱。我们认为斑文鸟的日常生理和行为存在组织水平的昼夜节律钟调节。
