Differential daily expression of Per1 and Per2 mRNA in the suprachiasmaticnucleus of fetal and early postnatal mice

It is well known that there are circadian rhythms of 2-deoxyglucose uptake and neuronal firing in the rat suprachiasmatic nucleus (SCN) during fetal a nd early postnatal periods. A core clock mechanism in the mouse SCN appears to involve a transcriptional feedback loop in which CLOCK and BMAL1 functi on as positive regulators and three mPeriod (mPer) genes play a role in neg ative feedback. Per genes expression occurs not only in the adult SCN but a lso in the fetal SCN. However, the developmental change in these genes rema ins unclear. In this experiment, we examined the day-night pattern of expre ssion of Per1 and Per2 mRNA in the mouse SCN and cerebral cortex on embryon ic day 17, postnatal day 3, and in young adult mice under a light-dark cycl e. Daily rhythms of mRNA content were observed in mPer1 but not mPer2 in th e fetal SCN. Interestingly, the expression of mPer2 in the SCN was high thr oughout the entire day, and a significant daily rhythm of this gene was obs erved on postnatal day 6. The expression pattern of SCN mPer1 in constant d arkness was similar to that seen in the light-dark cycle. The present resul ts suggest that the daily oscillation of mPer1 but not of mPer2 in the SCN in fetal and early postnatal mice may be associated with the daily rhythms of 2-deoxyglucose uptake and neuronal firing.