IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi, 110 007, India.
IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi, 110 007, India.
J Photochem Photobiol B. 2017 Apr;169:13-20. doi: 10.1016/j.jphotobiol.2017.02.016. Epub 2017 Feb 24.
The avian circadian pacemaker system is comprised of independent clocks in the retina, pineal and hypothalamus, as shown by daily and circadian oscillations of core clock genes (Per2, Cry1, Bmal1 and Clock) in several birds including migratory blackheaded buntings (Emberiza melanocephala). This study investigated the extra-hypothalamic brain circadian clocks in blackheaded buntings, and measured Per2, Cry1, Cry2, Bmal1 and Clock mRNA expressions at 4h intervals over 24h beginning 1h after light-on in the left and right telencephalon, optic tectum and cerebellum, the brain regions involved in several physiological and cognitive functions. Because of seasonal alterations in the circadian clock dependent brain functions, we measured daily clock gene oscillations in buntings photoperiod-induced with the non-migratory state under short days (SDnM), and the pre-migratory (LDpM), migratory (LDM) and post-migratory (refractory, LDR) states under long days. Daily Per2 oscillations were not altered with changes in the photoperiodic states, except for about 2-3h phase difference in the optic tectum between the SDnM and LDpM states. However, there were about 3-5h differences in the phase and 2 to 4 fold change in the amplitude of daily Bmal1 and Cry1 mRNA oscillations between the photoperiod-induced states. Further, Cry2 and Clock genes lacked a significant oscillation, except in Cb (Cry2) and TeO and Rt (Clock) under LDR state. Overall, these results show the presence of circadian clocks in extra-hypothalamic brain regions of blackheaded buntings, and suggest tissue-dependent alterations in the waveforms of mRNA oscillations with transitions in the photoperiod-induced seasonal states in a long-day species.
鸟类的生物钟系统由视网膜、松果体和下丘脑中的独立时钟组成，这一点已被证明，包括迁徙性黑头鹀在内的几种鸟类的核心生物钟基因（Per2、Cry1、Bmal1 和 Clock）存在日常和昼夜节律波动。本研究调查了黑头鹀的额外下丘脑脑生物钟，并在光照后 1 小时开始，以 4 小时为间隔测量了 24 小时内左、右脑大脑皮层、视顶盖和小脑中 Per2、Cry1、Cry2、Bmal1 和 Clock mRNA 的表达，这些脑区参与了许多生理和认知功能。由于生物钟相关脑功能随季节而变化，我们在短日照（SDnM）、非迁徙状态下测量了黑头鹀的每日时钟基因波动，在长日照下测量了迁徙前（LDpM）、迁徙（LDM）和迁徙后（恢复期，LDR）状态。除了视顶盖在 SDnM 和 LDpM 状态之间的相位差约为 2-3 小时外，每日 Per2 波动没有因光周期状态的变化而改变。然而，在光周期诱导状态之间，Bmal1 和 Cry1 mRNA 波动的相位差异约为 3-5 小时，振幅变化约为 2 到 4 倍。此外，Cry2 和 Clock 基因除了在 LDR 状态下 Cb（Cry2）、TeO 和 Rt（Clock）中缺乏明显的波动外，其余基因都缺乏明显的波动。总的来说，这些结果表明，黑头鹀的额外下丘脑脑区存在生物钟，并且表明在长日照物种中，随着光周期诱导的季节性状态的转变，mRNA 波动的波形存在组织依赖性变化。
