Weiss Ron, Bartok Osnat, Mezan Shaul, Malka Yuval, Kadener Sebastian
Biological Chemistry Department, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
PLoS Genet. 2014 Apr 3;10(4):e1004252. doi: 10.1371/journal.pgen.1004252. eCollection 2014 Apr.
Most organisms use 24-hr circadian clocks to keep temporal order and anticipate daily environmental changes. In Drosophila melanogaster CLOCK (CLK) and CYCLE (CYC) initiates the circadian system by promoting rhythmic transcription of hundreds of genes. However, it is still not clear whether high amplitude transcriptional oscillations are essential for circadian timekeeping. In order to address this issue, we generated flies in which the amplitude of CLK-driven transcription can be reduced partially (approx. 60%) or strongly (90%) without affecting the average levels of CLK-target genes. The impaired transcriptional oscillations lead to low amplitude protein oscillations that were not sufficient to drive outputs of peripheral oscillators. However, circadian rhythms in locomotor activity were resistant to partial reduction in transcriptional and protein oscillations. We found that the resilience of the brain oscillator is depending on the neuronal communication among circadian neurons in the brain. Indeed, the capacity of the brain oscillator to overcome low amplitude transcriptional oscillations depends on the action of the neuropeptide PDF and on the pdf-expressing cells having equal or higher amplitude of molecular rhythms than the rest of the circadian neuronal groups in the fly brain. Therefore, our work reveals the importance of high amplitude transcriptional oscillations for cell-autonomous circadian timekeeping. Moreover, we demonstrate that the circadian neuronal network is an essential buffering system that protects against changes in circadian transcription in the brain.
大多数生物利用24小时的昼夜节律时钟来维持时间秩序并预测日常环境变化。在果蝇中，生物钟蛋白（CLK）和周期蛋白（CYC）通过促进数百个基因的节律性转录来启动昼夜节律系统。然而，目前尚不清楚高振幅转录振荡对于昼夜节律计时是否至关重要。为了解决这个问题，我们培育出了果蝇，在这些果蝇中，CLK驱动的转录振幅可以部分降低（约60%）或大幅降低（90%），而不影响CLK靶基因的平均水平。转录振荡受损导致蛋白振荡振幅降低，不足以驱动外周振荡器的输出。然而，运动活动的昼夜节律对转录和蛋白振荡的部分降低具有抗性。我们发现，大脑振荡器的弹性取决于大脑中昼夜节律神经元之间的神经通讯。事实上，大脑振荡器克服低振幅转录振荡的能力取决于神经肽PDF的作用，以及表达pdf的细胞具有与果蝇大脑中其他昼夜节律神经元组相等或更高的分子节律振幅。因此，我们的研究揭示了高振幅转录振荡对于细胞自主昼夜节律计时的重要性。此外，我们证明昼夜节律神经元网络是一个重要的缓冲系统，可以防止大脑中昼夜节律转录的变化。
