Neurobiology Division, Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
PNAC Division, Medical Research Council Laboratory of Molecular Biology, Cambridge, CB2 0QH, United Kingdom.
Proc Natl Acad Sci U S A. 2022 Aug 23;119(34):e2203563119. doi: 10.1073/pnas.2203563119. Epub 2022 Aug 17.
The suprachiasmatic nucleus (SCN) of the hypothalamus is the principal clock driving circadian rhythms of physiology and behavior that adapt mammals to environmental cycles. Disruption of SCN-dependent rhythms compromises health, and so understanding SCN time keeping will inform management of diseases associated with modern lifestyles. SCN time keeping is a self-sustaining transcriptional/translational delayed feedback loop (TTFL), whereby negative regulators inhibit their own transcription. Formally, the SCN clock is viewed as a limit-cycle oscillator, the simplest being a trajectory of successive phases that progresses through two-dimensional space defined by two state variables mapped along their respective axes. The TTFL motif is readily compatible with limit-cycle models, and in and the negative regulators Frequency (FRQ) and Period (Per) have been identified as state variables of their respective TTFLs. The identity of state variables of the SCN oscillator is, however, less clear. Experimental identification of state variables requires reversible and temporally specific control over their abundance. Translational switching (ts) provides this, the expression of a protein of interest relying on the provision of a noncanonical amino acid. We show that the negative regulator Cryptochrome 1 (CRY1) fulfills criteria defining a state variable: ts-CRY1 dose-dependently and reversibly suppresses the baseline, amplitude, and period of SCN rhythms, and its acute withdrawal releases the TTFL to oscillate from a defined phase. Its effect also depends on its temporal pattern of expression, although constitutive ts-CRY1 sustained (albeit less stable) oscillations. We conclude that CRY1 has properties of a state variable, but may operate among several state variables within a multidimensional limit cycle.
视交叉上核（SCN）是驱动生理和行为昼夜节律的主要时钟，使哺乳动物适应环境周期。SCN 依赖性节律的破坏会损害健康，因此了解 SCN 的计时将为管理与现代生活方式相关的疾病提供信息。SCN 的计时是一个自我维持的转录/翻译延迟反馈环（TTFL），其中负调节因子抑制自身的转录。从形式上看，SCN 时钟被视为极限环振荡器，最简单的是沿各自轴映射的两个状态变量在二维空间中连续相位的轨迹。TTFL 基序很容易与极限环模型兼容，在 和 中，负调节因子频率（FRQ）和周期（Per）已被确定为各自 TTFL 的状态变量。然而，SCN 振荡器的状态变量的身份不太清楚。状态变量的实验鉴定需要对其丰度进行可逆和时间特异性控制。翻译开关（ts）提供了这种控制，感兴趣的蛋白质的表达依赖于提供非典型氨基酸。我们表明，负调节因子隐花色素 1（CRY1）满足定义状态变量的标准：ts-CRY1 剂量依赖性和可逆地抑制 SCN 节律的基线、幅度和周期，其急性撤回将 TTFL 释放到从定义的相位开始振荡。其作用还取决于其表达的时间模式，尽管组成型 ts-CRY1 维持（尽管不太稳定）振荡。我们得出结论，CRY1 具有状态变量的特性，但可能在多维极限环内的几个状态变量中运作。
