Kadener Sebastian, Stoleru Dan, McDonald Michael, Nawathean Pipat, Rosbash Michael
Department of Biology, Brandeis University, Waltham, MA 02454, USA.
Genes Dev. 2007 Jul 1;21(13):1675-86. doi: 10.1101/gad.1552607. Epub 2007 Jun 19.
Many organisms use circadian clocks to keep temporal order and anticipate daily environmental changes. In Drosophila, the master clock gene Clock promotes the transcription of several key target genes. Two of these gene products, PER and TIM, repress CLK-CYC-mediated transcription. To recognize additional direct CLK target genes, we designed a genome-wide approach and identified clockwork orange (cwo) as a new core clock component. cwo encodes a transcriptional repressor that synergizes with PER and inhibits CLK-mediated activation. Consistent with this function, the mRNA profiles of CLK direct target genes in cwo mutant flies manifest high trough values and low amplitude oscillations. Because behavioral rhythmicity fails to persist in constant darkness (DD) with little or no effect on average mRNA levels in flies lacking cwo, transcriptional oscillation amplitude appears to be linked to rhythmicity. Moreover, the mutant flies are long period, consistent with the late repression indicated by the RNA profiles. These findings suggest that CWO acts preferentially in the late night to help terminate CLK-CYC-mediated transcription of direct target genes including cwo itself. The presence of mammalian homologs with circadian expression features (Dec1 and Dec2) suggests that a similar feedback mechanism exists in mammalian clocks.
许多生物体利用生物钟来维持时间秩序并预测日常环境变化。在果蝇中，主生物钟基因Clock促进几个关键靶基因的转录。其中两种基因产物，PER和TIM，抑制CLK-CYC介导的转录。为了识别其他直接的CLK靶基因，我们设计了一种全基因组方法，并确定了发条橙（cwo）作为一种新的核心生物钟组件。cwo编码一种转录抑制因子，它与PER协同作用并抑制CLK介导的激活。与此功能一致，cwo突变果蝇中CLK直接靶基因的mRNA谱表现出低谷值和低振幅振荡。由于行为节律性在持续黑暗（DD）中无法持续，而在缺乏cwo的果蝇中对平均mRNA水平几乎没有影响，转录振荡幅度似乎与节律性有关。此外，突变果蝇的周期较长，这与RNA谱所显示的晚期抑制一致。这些发现表明，CWO在深夜优先发挥作用，以帮助终止CLK-CYC介导的包括cwo自身在内的直接靶基因的转录。具有昼夜节律表达特征的哺乳动物同源物（Dec1和Dec2）的存在表明，哺乳动物生物钟中存在类似的反馈机制。
