Fig. 1.

Schematic diagram of the mammalian circadian clock. a External cues, such as light, food, stress, and exercise, entrain the central (suprachiasmatic nucleus; SCN) and peripheral (peripheral tissues) clocks. Light directly entrains the SCN, whereas other stimuli reset the peripheral clocks, and entrainment depends on the timing of stimulation. b The molecular clock is regulated by transcriptional feedback loops of core clock genes, and oscillations of clock-regulated genes in each tissue are controlled by various transcriptional factors, including CLOCK/BMAL1, RORs, PPARs, REV-ERBs, SREBPs, DBP, TEF, and HLF