MULTITISSUE CIRCADIAN EXPRESSION OF RAT PERIOD HOMOLOG (RPER2) MESSENGER-RNA IS GOVERNED BY THE MAMMALIAN CIRCADIAN CLOCK, THE SUPRACHIASMATIC NUCLEUS IN THE BRAIN

The period (per) gene, controlling circadian rhythms in Drosophila, is expressed throughout the body in a circadian manner. A homolog of Dro sophila per was isolated from rat and designated as rPer2. The rPER2 p rotein showed 39 and 95% amino acid identity with mPER1 and mPER2 (mou se homologs of per) proteins, respectively. A robust circadian fluctua tion of rPer2 mRNA expression was discovered not only in the suprachia smatic nucleus (SCN) of the hypothalamus but also in other tissues inc luding eye, brain, heart, lung, spleen, liver, and kidney. Furthermore , the peripheral circadian expression of rPer2 mRNA was abolished in S CN-lesioned rats that showed behavioral arrhythmicity. These findings suggest that the multitissue circadian expression of rPer2 mRNA was go verned by the mammalian brain clock SCN and also suggest that the rPer 2 gene was involved in the circadian rhythm of locomotor behavior in m ammals.