The molecular mechanism of the circadian oscillator as a transcriptional-translational feedback loop has been unraveled by genetic analysis in Drosophila and mammals. Circadian clocks are primarily synchronized with environmental time by the daylight cycle as an input signal to the SCN through the direct and indirect neural projections from retinal ganglion cells, however, other non-photic cues can also synchronize circadian clocks to 24-h/day.

Because the periodicity of the circadian clock only approximates that of the environment, circadian clocks have to be adjusted to 24-h/day period by environmental time cues. It has also revealed that in mammals circadian oscillators exist not only in the SCN but also in peripheral tissues, and even in immortalized cells. Using our developed IV-ROMS to screen 299 compounds, we found eight novel and four known molecules to be potential entrainment factors for circadian clocks, indicating that this assay system is a powerful and useful tool in initial screenings.Ĭircadian rhythms are endogenous self-sustained oscillations with approximately 24-hr rhythmicity that are manifested in various physiological and metabolic processes In mammals the circadian orchestration of these processes is governed by pacemaker cells located within the suprachiasmatic nuclei (SCN) of the hypothalamus. Here, we identified 15d-PGJ 2 as an entrainment factor in vitro. Furthermore, we showed that 15d-PGJ 2 transiently induces Cry1, Cry2, and Rorα mRNA expressions and that 15d-PGJ 2-induced entrainment signaling pathway is PPAR-γ – and MAPKs (ERK, JNK, p38MAPK)-independent. We demonstrated that one of the novel candidates, 15-deoxy-Δ 12,14-prostaglandin J 2 (15d-PGJ 2), a natural ligand of the peroxisome proliferator-activated receptor-γ (PPAR-γ), triggers the rhythmic expression of endogenous clock genes in NIH3T3 cells. Among them, four candidates (endothelin-1, all-trans retinoic acid, 9-cis retinoic acid, and 13-cis retinoic acid) have already been reported as the entrainment factors in vivo and in vitro. Using this IV-ROMS as the primary screening of entrainment factors for circadian clocks, we identified 12 candidates as the potential entrainment factor in a total of 299 peptides and bioactive lipids. We developed the in vitro real-time oscillation monitoring system (IV-ROMS) by measuring the activity of luciferase coupled to the oscillatory gene promoter using photomultiplier tubes and applied this system to screen and identify factors able to influence circadian rhythmicity.

Some candidates for endogenous entrainment factors have sporadically been reported, however, their details remain mainly obscure. Recent findings revealed that circadian oscillators exist in most organs, tissues, and even in immortalized cells, and that the oscillators in peripheral tissues are likely to be coordinated by SCN, the master oscillator. The circadian organization of these processes in mammals is governed by the master oscillator within the suprachiasmatic nuclei (SCN) of the hypothalamus. Circadian rhythms are endogenous, self-sustained oscillations with approximately 24-hr rhythmicity that are manifested in various physiological and metabolic processes.

Abi time clock