The role of the Casein kinase I epsilon (CKIε) as a key regulator of mammalian circadian clock has not been known a decade ago. By analyzing naturally mutated tau hamster of which free running period is shorter about 4h than wild type hamster, it was revealed that this dramatic change in circadian rhythm is due to the point mutation on casein kinase I epsilon. CKIε is crucial for the generation of the transcriptional-translational feedback loop which endows the circadian clock with endogenocity and cell-autonomy. Phosphorylating the core clock gene, Period(PER), CKIε regulates its degradation or nuclear localization on post-translational level. How the tau mutation on CKIε makes 4 hour shorter period in hamster, however, has not been divulged in detail at molecular level. hPER2 and CKIδ whose mutation was reported to cause familial advanced sleep phase syndrome(FASPS) are related to CKIε but there is no model to explain their exact mechanism. This paper is focused on the understanding the mechanism of molecular clock in vivo by introducing dominant negative CKIε (CKIεDN) into mouse system. Transgenic mice designed to overexpress CKIεDN in liver specific manner showed the in vivo effect of CKIεDN on mPER pattern. mPER1, 2 level in the liver of the transgenic mice is elevated relative to the wild type and have delayed phase. mPER1,2 is remained in the transgenic mouse liver lysate at ZT4 although in wild type mouse liver at this time they are already degraded and not detected. Delayed shift of mPER2 oscillation phase accompanies the elevated mPer2 mRNA level which peaks about 4 hr later than wild type. In summary, CKIε dominant negative form results in delayed and elevated transcription and translation of mPER and doesn’t shorten or lengthen contrary to tau mutation. In addition, by disrupting liver clock specifically, the uncoupling effect of the liver clock from the central oscillator, SCN, can be obtained. Wheel running test shows that disrupted liver clock in the transgenic mice does not change the free running period (τ) but affect the locomotor activity under food restricted condition. Core body temperature monitoring also designates that changes in PER pattern in transgenic mouse liver reduce the amplitude of fluctuation of daily temperature oscillation. From locomotor and temperature monitoring of the CKIεDN transgenic mice, it is demonstrated that liver is the peripheral clock vital for food entrainment and homeostasis of body temperature controlling the metabolism under its circadian rhythm mechanism.
