Analysis of mammalian circadian rhythms and Per1 transcriptional oscillation using Per1 tramsgenicm

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Many biochemical, physiological and behavioral processes in many organisms exhibit circadian rhythms. Circadian rhythms are driven by autonomous oscillators and entrained by daily light-dark cycles. The transcription of Per1, a mammalian clock gene, oscillates in a circadian manner in the mouse suprachiasmatic nucleus (SCN ; the central pacemaker of the mammalian circadian clock) with a peak in the daytime and a trough at night. In addition, the expression of mPer1 in the SCN is induced immediately by a light pulse even at night. Function of the circadian expression of the mammalian Per1 gene is a key question for the regulation of circadian rhythms. For elucidation of the molecular mechanisms controlling the mammalian circadian clock, the genomic sequences of the human and mouse Per1 genes in addition to their transcriptional start sites have been determined. Both of the genomic sequences consist of 23 exons spanning approximately 16 kb. Comparisons of both genes revealed five and one … More conserved segments in the 5' flanking regions and the first introns, respectively. These conserved segments contained several potential regulatory elements such as five E-boxes (the binding site for the Clock-Bmal1 complex). Transfection analyses using a series of deletion and point mutants of the mPer1 : : luc reporter showed that each of the five E-boxes was functional for the Per1 induction mediated by Clock and Bmal1. Second, we constructed transgenic rat lines with constitutive expression of the mouse Per1 gene using elongation 1 alpha or neural specific enolase promoters. Both the circadian period of locomoter activity and entrainment to light- dark cycles were severely affected in several transgenic lines. In addition, we measured the expression of the native (rat) Per1 and Per2 genes in the SCN and retina of the transgenic lines under DD conditions. The circadian expression of endogenous Per1 and Per2 genes was diminished in the transgenic lines. These results clearly indicate that the circadian expression and light induction of the mammalian Per1 gene is involved in rhythm generation and/or entrainment of the circadian clock. Less