Coupling of a core post-translational pacemaker to a slave transcription/translation feedback loop in a circadian system.
Coupling of a core post-translational pacemaker to a slave transcription/translation feedback loop in a circadian system.
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DOI：
10.1371/journal.pbio.1000394
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发表时间：
2010-06-15
期刊：
影响因子：
9.8
通讯作者：
Johnson CH
中科院分区：
文献类型：
--
作者：
Qin X;Byrne M;Xu Y;Mori T;Johnson CH
对蓝藻昼夜节律生物钟的分析揭示了转录/翻译反馈环和生化振荡器之间复杂的相互依赖性。蓝细菌是唯一可以在体外重建昼夜节律振荡器的生物钟模型系统。潜在的昼夜节律机制似乎包含两个子组件：翻译后振荡器（PTO）和转录/翻译反馈环（TTFL）。假设 PTO 和 TTFL 在蓝藻中作为双振荡器系统运行。然而，我们发现它们具有明确的层级相互依赖性——PTO 是核心起搏器，而 TTFL 是从属振荡器，当 PTO 停止时，它会迅速衰减。通过对过表达实验和突变时钟蛋白的分析，我们发现昼夜节律系统依赖于 PTO，并且抑制 PTO 会导致基于 TTFL 的阻尼振荡，其温度补偿在不同代谢条件下不稳定。数学模型表明实验数据与驱动 TTFL 的核心 PTO 兼容；组合式 PTO/TTFL 系统具有抗噪音能力。此外，该模型还表明了 TTFL 可以馈入 PTO 的机制，以便新合成的时钟蛋白可以相移或夹带核心 PTO 起搏器。通过将体内昼夜节律系统引入新的时钟蛋白合成周期来调节 PTO 中时钟蛋白的磷酸化状态，这一预测得到了实验测试和证实。在蓝细菌中，PTO 是自我维持的核心起搏器，可以独立于 TTFL 运行，但当 PTO 的磷酸化状态被钳制时，TTFL 会减弱。然而，TTFL 可以向 PTO 提供引导输入。据我们所知，这项研究是第一个从实验和理论上研究生物钟动态的研究，其中 PTO 与 TTFL 耦合。这些结果对真核生物钟系统具有重要意义，因为它们可以解释 TTFL 如何看起来是核心昼夜节律时钟装置，而实际上真正的起搏器是嵌入式生化振荡器。从细菌到人类，许多生物体已经进化出昼夜节律机制，以在每日时间范围内调节生物过程。在蓝细菌中，这种循环调节的最小系统可以在体外由三种蛋白质（称为 KaiA、KaiB 和 KaiC）重建。这种三蛋白振荡器被认为通过涉及 KaiC 节律性磷酸化的翻译后机制调节体内的周期性活动。尽管这种翻译后振荡器（PTO）足以在体外产生节律，但体内蓝藻昼夜节律系统还包括转录/翻译反馈环（TTFL）。 PTO 和 TTFL 的确切作用以及它们在体内形成完整时钟系统中的相互依赖性尚不清楚。通过操纵体内野生型和突变型时钟蛋白的表达，我们在此表明蓝藻昼夜节律系统依赖于 PTO 提供的生化振荡器，并且抑制 PTO 会导致 TTFL 产生残余阻尼（从属）振荡。数学模型表明，实验数据与 PTO 作为起搏器驱动 TTFL 活动的机制兼容。此外，我们的分析提出了一种机制，通过该机制 TTFL 可以反馈到 PTO，从而新合成的 Kai 蛋白夹带核心 PTO 起搏器。因此，PTO和TTFL似乎具有明确的分层相互依赖性：PTO是一个自我维持的核心起搏器，可以独立于TTFL振荡，但TTFL是一个从属振荡器，当PTO中KaiC的磷酸化状态被钳制时，它会阻尼。真核生物中的核心昼夜节律起搏器被认为是 TTFL，但我们对蓝细菌的研究结果对真核生物钟系统具有重要意义，因为它们可以解释 TTFL 如何看似核心时钟，而实际上真正的起搏器是嵌入式生化振荡器。
Analysis of the cyanobacterial circadian biological clock reveals a complex interdependence between a transcription/translation feedback loop and a biochemical oscillator. Cyanobacteria are the only model circadian clock system in which a circadian oscillator can be reconstituted in vitro. The underlying circadian mechanism appears to comprise two subcomponents: a post-translational oscillator (PTO) and a transcriptional/translational feedback loop (TTFL). The PTO and TTFL have been hypothesized to operate as dual oscillator systems in cyanobacteria. However, we find that they have a definite hierarchical interdependency—the PTO is the core pacemaker while the TTFL is a slave oscillator that quickly damps when the PTO stops. By analysis of overexpression experiments and mutant clock proteins, we find that the circadian system is dependent upon the PTO and that suppression of the PTO leads to damped TTFL-based oscillations whose temperature compensation is not stable under different metabolic conditions. Mathematical modeling indicates that the experimental data are compatible with a core PTO driving the TTFL; the combined PTO/TTFL system is resilient to noise. Moreover, the modeling indicates a mechanism by which the TTFL can feed into the PTO such that new synthesis of clock proteins can phase-shift or entrain the core PTO pacemaker. This prediction was experimentally tested and confirmed by entraining the in vivo circadian system with cycles of new clock protein synthesis that modulate the phosphorylation status of the clock proteins in the PTO. In cyanobacteria, the PTO is the self-sustained core pacemaker that can operate independently of the TTFL, but the TTFL damps when the phosphorylation status of the PTO is clamped. However, the TTFL can provide entraining input into the PTO. This study is the first to our knowledge to experimentally and theoretically investigate the dynamics of a circadian clock in which a PTO is coupled to a TTFL. These results have important implications for eukaryotic clock systems in that they can explain how a TTFL could appear to be a core circadian clockwork when in fact the true pacemaker is an embedded biochemical oscillator. Many organisms from bacteria to humans have evolved circadian mechanisms for regulating biological processes on a daily time scale. In cyanobacteria, a minimal system for such cyclical regulation can be reconstituted in vitro from three proteins, called KaiA, KaiB, and KaiC. This three-protein oscillator is believed to regulate the cyclical activities in vivo through a post-translational mechanism that involves rhythmic phosphorylation of KaiC. Although this post-translational oscillator (PTO) is sufficient for generating rhythms in vitro, the cyanobacterial circadian system in vivo also includes a transcriptional/translational feedback loop (TTFL). The precise roles of the PTO and the TTFL and their interdependence in forming the complete clock system in vivo are unclear. By manipulating wild-type and mutant clock protein expression in vivo, we here show that the cyanobacterial circadian system is dependent upon the biochemical oscillator provided by the PTO and that suppression of the PTO leads to a residual damped (slave) oscillation that results from the TTFL. Mathematical modeling shows that the experimental data are compatible with a mechanism in which the PTO acts as a pacemaker to drive the activity of the TTFL. Moreover, our analyses suggest a mechanism by which the TTFL can feed back into the PTO such that new synthesis of the Kai proteins entrains the core PTO pacemaker. Therefore, the PTO and TTFL appear to have a definite hierarchical interdependency: the PTO is a self-sustained core pacemaker that can oscillate independently of the TTFL, but the TTFL is a slave oscillator that damps when the phosphorylation status of KaiC in the PTO is clamped. The core circadian pacemaker in eukaryotes is thought to be a TTFL, but our results with cyanobacteria have important implications for eukaryotic clock systems in that they can explain how a TTFL could appear to be the core clock when in fact the true pacemaker is an embedded biochemical oscillator.
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影响因子：
64.8
作者：
HARDIN, PE;HALL, JC;ROSBASH, M
通讯作者：
ROSBASH, M
对昼夜节律振荡器的结构见解。
DOI：
10.1126/science.1150451
发表时间：
2008-10-31
期刊：
Science (New York, N.Y.)
影响因子：
--
作者：
Johnson CH;Egli M;Stewart PL
通讯作者：
Stewart PL
DOI：
10.1098/rspb.1995.0153
发表时间：
1995-09-22
影响因子：
4.7
作者：
GOLDBETER, A
通讯作者：
GOLDBETER, A
DOI：
10.1073/pnas.0403906101
发表时间：
2004-09-21
影响因子：
11.1
作者：
Nishiwaki, T;Satomi, Y;Kondo, T
通讯作者：
Kondo, T
影响因子：
16.8
作者：
Ito, Hiroshi;Kageyama, Hakuto;Kondo, Takao
通讯作者：
Kondo, Takao