Buhr Ethan D, Takahashi Joseph S
Department of Ophthalmology, University of Washington, 1959 NE Pacific St, 356485 BB-857 HSB, Seattle, WA 98195, USA.
Handb Exp Pharmacol. 2013(217):3-27. doi: 10.1007/978-3-642-25950-0_1.
Mammals synchronize their circadian activity primarily to the cycles of light and darkness in the environment. This is achieved by ocular photoreception relaying signals to the suprachiasmatic nucleus (SCN) in the hypothalamus. Signals from the SCN cause the synchronization of independent circadian clocks throughout the body to appropriate phases. Signals that can entrain these peripheral clocks include humoral signals, metabolic factors, and body temperature. At the level of individual tissues, thousands of genes are brought to unique phases through the actions of a local transcription/translation-based feedback oscillator and systemic cues. In this molecular clock, the proteins CLOCK and BMAL1 cause the transcription of genes which ultimately feedback and inhibit CLOCK and BMAL1 transcriptional activity. Finally, there are also other molecular circadian oscillators which can act independently of the transcription-based clock in all species which have been tested.
哺乳动物主要通过环境中的昼夜明暗循环来同步其昼夜活动。这是通过眼部光感受器将信号传递到下丘脑的视交叉上核（SCN）来实现的。来自SCN的信号使全身独立的生物钟同步到适当的相位。能够调节这些外周生物钟的信号包括体液信号、代谢因子和体温。在个体组织层面，数千个基因通过基于局部转录/翻译的反馈振荡器和全身信号的作用进入独特的相位。在这个分子钟中，蛋白质CLOCK和BMAL1导致基因转录，这些基因最终反馈并抑制CLOCK和BMAL1的转录活性。最后，在所有已测试的物种中，也存在其他分子昼夜振荡器，它们可以独立于基于转录的生物钟发挥作用。
