An Comprehensive Analysis of Circadian Clock Controlled Genes in Central and Peripheral Clock Systems.

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The central circadian oscillator is located at the suprachiasmatic nucleus (SCN) of the mammalian brain. The circadian fluctuation of electrophysiological activities or humoral factors produced by the SCN regulates the peripheral rhythms. Elucidation of molecular mechanisms generating circadian rhythms requires comprehensive analyses of the clock and clock controlled genes. In this study, we have established an easier screening system of gene expression at the cellular level than that at the individual level. Firstly, we constructed a new transgenic rat in which the mouse Per1 gene promoter is linked to a luciferase reporter. Light emission from the SCN of the mPer1::luc transgenic rat line was robustly rhythmic, and persisted for up to 32 days in static culture, indicating that the promoter in the mPer1::luc transgene was fully functional. Then several SCN derived cell lines were established from the embryonic brain of the transgenic rat. Of 584 cloned lines, 12 lines expressed NCAM, in addition to the circadian rhythms of light output for more than 8 cycles. The time dependent phase advance or delay of the rhythm was accomplished after the treatment of a cell line with the most robust oscillation by forskolin, and the phase response curve obtained by forskolin was consistent with that obtained in the behavioral rhythm by light. Although a stable Rat1 transfectant with the Per1::luc reporter had circadian rhythms after the stimulation by forskolin, Dex, or PMA, the rhythms were not as robust as those we recorded from the SCN derived cell lines and always damped out after about 6 cycles in culture. Therefore, each of two lines could be regarded as the cellular models of the central or peripheral circadian oscillator, and the profiles of gene expression in these cells were analyzed by DNA microarrays..