Dovzhenok Andrey A, Baek Mokryun, Lim Sookkyung, Hong Christian I
Department of Mathematical Sciences, University of Cincinnati, Cincinnati, Ohio.
Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio.
Biophys J. 2015 Apr 7;108(7):1830-1839. doi: 10.1016/j.bpj.2015.01.043.
Autonomous circadian oscillations arise from transcriptional-translational feedback loops of core clock components. The period of a circadian oscillator is relatively insensitive to changes in nutrients (e.g., glucose), which is referred to as "nutrient compensation". Recently, a transcription repressor, CSP-1, was identified as a component of the circadian system in Neurospora crassa. The transcription of csp-1 is under the circadian regulation. Intriguingly, CSP-1 represses the circadian transcription factor, WC-1, forming a negative feedback loop that can influence the core oscillator. This feedback mechanism is suggested to maintain the circadian period in a wide range of glucose concentrations. In this report, we constructed a mathematical model of the Neurospora circadian clock incorporating the above WC-1/CSP-1 feedback loop, and investigated molecular mechanisms of glucose compensation. Our model shows that glucose compensation exists within a narrow range of parameter space where the activation rates of csp-1 and wc-1 are balanced with each other, and simulates loss of glucose compensation in csp-1 mutants. More importantly, we experimentally validated rhythmic oscillations of the wc-1 gene expression and loss of glucose compensation in the wc-1(ov) mutant as predicted in the model. Furthermore, our stochastic simulations demonstrate that the CSP-1-dependent negative feedback loop functions in glucose compensation, but does not enhance the overall robustness of oscillations against molecular noise. Our work highlights predictive modeling of circadian clock machinery and experimental validations employing Neurospora and brings a deeper understanding of molecular mechanisms of glucose compensation.
自主昼夜节律振荡源自核心生物钟组件的转录-翻译反馈回路。昼夜节律振荡器的周期对营养物质（如葡萄糖）的变化相对不敏感，这被称为“营养补偿”。最近，一种转录抑制因子CSP-1被鉴定为粗糙脉孢菌昼夜节律系统的一个组件。csp-1的转录受昼夜节律调控。有趣的是，CSP-1抑制昼夜节律转录因子WC-1，形成一个可影响核心振荡器的负反馈回路。这种反馈机制被认为能在广泛的葡萄糖浓度范围内维持昼夜节律周期。在本报告中，我们构建了一个包含上述WC-1/CSP-1反馈回路的粗糙脉孢菌昼夜节律钟数学模型，并研究了葡萄糖补偿的分子机制。我们的模型表明，葡萄糖补偿存在于一个狭窄的参数空间范围内，其中csp-1和wc-1的激活率相互平衡，并模拟了csp-1突变体中葡萄糖补偿的丧失。更重要的是，我们通过实验验证了wc-1基因表达的节律振荡以及模型预测的wc-1(ov)突变体中葡萄糖补偿的丧失。此外，我们的随机模拟表明，依赖CSP-1的负反馈回路在葡萄糖补偿中起作用，但不会增强振荡对分子噪声的整体稳健性。我们的工作突出了昼夜节律钟机制的预测建模以及利用粗糙脉孢菌进行的实验验证，并加深了对葡萄糖补偿分子机制的理解。
