von Gall Charlotte, Noton Elizabeth, Lee Choogon, Weaver David R
Department of Neurobiology, Aaron Lazare Medical Research Building, Room 723, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605-2324, USA.
Eur J Neurosci. 2003 Jul;18(1):125-33. doi: 10.1046/j.1460-9568.2003.02735.x.
Biological rhythms in mammals are driven by a central circadian clock located in the suprachiasmatic nucleus (SCN). At the molecular level the biological clock is based on the rhythmic expression of clock genes. Two basic helix-loop-helix (bHLH)/PAS-containing transcription factors, CLOCK and BMAL1 (MOP3), provide the basic drive to the system by activating transcription of negative regulators through E box enhancer elements. A critical feature of circadian timing is the ability of the clockwork to be entrained to the environmental light/dark cycle. The light-resetting mechanism of the mammalian circadian clock is poorly understood. Light-induced phase shifts are correlated with the induction of the clock genes mPer1 and mPer2 and a subsequent increase in mPER1 protein levels. It has previously been suggested that rapid degradation of BMAL1 protein in the rat SCN is part of the resetting mechanism of the central pacemaker. Our study shows that BMAL1 and CLOCK proteins are continuously expressed at high levels in the mouse SCN, supporting the hypothesis that rhythmic negative feedback plays the major role in rhythm generation in the mammalian pacemaker. Using both immunocytochemistry and immunoblot analysis, our studies demonstrate that BMAL1 protein in the mouse SCN is not affected by a phase-resetting light pulse. These results indicate that rapid degradation of BMAL1 protein is not a consistent feature of resetting mechanisms in rodents.
哺乳动物的生物节律由位于视交叉上核（SCN）的中央昼夜节律时钟驱动。在分子水平上，生物钟基于时钟基因的节律性表达。两种含基本螺旋-环-螺旋（bHLH）/PAS的转录因子，CLOCK和BMAL1（MOP3），通过E盒增强子元件激活负调节因子的转录，为该系统提供基本驱动力。昼夜节律计时的一个关键特征是生物钟机制能够与环境光/暗周期同步。哺乳动物昼夜节律时钟的光重置机制尚不清楚。光诱导的相位偏移与时钟基因mPer1和mPer2的诱导以及随后mPER1蛋白水平的增加相关。此前有人提出，大鼠SCN中BMAL1蛋白的快速降解是中央起搏器重置机制的一部分。我们的研究表明，BMAL1和CLOCK蛋白在小鼠SCN中持续高水平表达，支持了节律性负反馈在哺乳动物起搏器节律产生中起主要作用的假说。通过免疫细胞化学和免疫印迹分析，我们的研究表明，小鼠SCN中的BMAL1蛋白不受相位重置光脉冲的影响。这些结果表明，BMAL1蛋白的快速降解不是啮齿动物重置机制的一致特征。
