Experimental and Computational Insights into the Mechanism that CHRONO Regulates the Circadian Clock

The pace of the endogenous circadian clock is important for organisms to maintain homeostasis. CHRONO has been shown to play an important role in regulating the period of the mammalian clock and has recently been implicated to function in several important physiological aspects. To function properly, CHRONO needs to enter the nucleus to repress transcription. However, how CHRONO enters the nucleus and regulates the circadian clock remains unknown. Here, we report the nuclear localization signal of CHRONO and the genome-scale cistrome of CHRONO. We show that CHRONO acts as a transcriptional repressor on Jun/Fos complexes in addition to the classical BMAL1/CLOCK complexes. We further developed a mathematical model and the model simulations strongly agreed with our findings that CHRONO acts on both REV-ERBα and BMAL1 to regulate the circadian period. The model also sheds light on the fact that CHRONO cycles in most of the mammalian tissues. Thus, our experimental and computational approaches reveal the molecular mechanisms of an important circadian component, CHRONO. To investigate the function of CHRONO, we constructed CHRONO knock out cell lines,and performed gene expression profiling analysis using data obtained from RNA-seq of U2OS-WT and U2OS-CHRONO-/- cells with three replications respectively.