Borah Bijoy Krishna, Renthlei Zothanmawii, Trivedi Amit Kumar
Department of Zoology, Mizoram University, Aizawl, India.
Chronobiol Int. 2020 Apr;37(4):485-492. doi: 10.1080/07420528.2020.1726373. Epub 2020 Feb 12.
Circadian clock(s) allow an organism to be in synchrony with the surrounding environment and perform daily and seasonal physiological processes, including hibernation, migration, and reproduction. To cope with adverse environmental conditions, organisms have evolved various strategies. Insects undergo diapause, while some higher animals either migrate or hibernate/aestivate during unfavorable environmental conditions. Hibernation is an energy conservation strategy used to cope with adverse environmental conditions. Limited knowledge is available on the physiology of hibernation in non-mammalian vertebrates. Some studies suggest that metabolism is altered during amphibian hibernation, but nothing is known about the circadian clock. In the present study, we investigated daily oscillation of clock genes in the brain and liver of the terai tree frog () during two annual phases of life: breeding and hibernation. Adult male terai tree frogs were procured from their natural habitat on the Mizoram University campus (23°N 92°E) during their breeding and hibernation phases. Body mass and testes weight were recorded. Animals were sacrificed at six time points: ZT1, ZT5, ZT9, ZT13, ZT17, and ZT21 (ZT0, zeitgeber time 0, indicates the sunrise time at the respective time of the year; N = 5 frogs per time point). Quantitative real-time polymerase chain reaction (qPCR) was performed for clock genes (, and ) in the hypothalamus and liver. Our results showed that body and testes weights decreased during hibernation. Further, the hypothalamus retained daily clock gene oscillations during breeding and hibernation. However, the liver lost this daily oscillation during hibernation. The maintained rhythm in hypothalamus in contrast to other hibernating animals might be the result of the fact that these animals hibernate at a higher temperature and might be more alert. As the animals have no food intake during their hibernation season which might be the reason the animals loose their rhythm in liver clock genes. These results suggest that retaining daily clock gene oscillations in the hypothalamic clock could be important for internal time tracking and post-hibernation emergence.
生物钟使生物体能够与周围环境保持同步，并执行日常和季节性的生理过程，包括冬眠、迁徙和繁殖。为了应对不利的环境条件，生物体进化出了各种策略。昆虫会进入滞育状态，而一些高等动物在不利的环境条件下要么迁徙，要么冬眠/夏眠。冬眠是一种用于应对不利环境条件的节能策略。关于非哺乳动物脊椎动物冬眠生理学的知识有限。一些研究表明，两栖动物冬眠期间新陈代谢会发生变化，但对于生物钟却一无所知。在本研究中，我们调查了Terai树蛙（）在生命的两个年度阶段：繁殖期和冬眠期，其大脑和肝脏中生物钟基因的每日振荡情况。成年雄性Terai树蛙在其繁殖期和冬眠期从米佐拉姆大学校园（北纬23°，东经92°）的自然栖息地采集。记录体重和睾丸重量。在六个时间点处死动物：ZT1、ZT5、ZT9、ZT13、ZT17和ZT21（ZT0，授时时间0，表示一年中相应时间的日出时间；每个时间点n = 5只青蛙）。对下丘脑和肝脏中的生物钟基因（、和）进行定量实时聚合酶链反应（qPCR）。我们的结果表明，冬眠期间体重和睾丸重量下降。此外，下丘脑在繁殖期和冬眠期都保持着生物钟基因的每日振荡。然而，肝脏在冬眠期间失去了这种每日振荡。与其他冬眠动物相比，下丘脑维持的节律可能是因为这些动物在较高温度下冬眠，可能更警觉。由于动物在冬眠季节不进食，这可能是动物肝脏生物钟基因失去节律的原因。这些结果表明，下丘脑生物钟中维持生物钟基因的每日振荡对于内部时间追踪和冬眠后苏醒可能很重要。
