Involvement of CLOCK:BMALI heterodimer in serum-responsive mPerl induction

A rapid induction of mouse periodI (mPerI) gene expression is supposed to be critical in the clock gene regulation, especially in the phase resetting of the clock, but its molecular mechanism is poorly understood. Based on the previous finding that the process does not involve de novo synthesis of proteins, we postulated the involvement of CLOCK:BMALI heterodimer, a positive regulator of circadian oscillator, in the rapid induction of mPerI transcription. To test this hypothesis, we utilized CLOCKDelta19, a dominant-negative mutant, to suppress the function of CLOCK:BMALI in vitro. Serum-evoked rapid increases of mperI mRNA expression and promoter activity were significantly blunted when CLOCK:BMALI function was interfered with. Furthermore, DNA binding activity of CLOCK:BMALI heterodimer to five E-boxes of mPerI promoter markedly increased shortly after serum shock. Taken together, these results suggest that CLOCK:BMALI heterodimer is not only a core component of negative feedback loop driving circadian oscillator, but also involved in the rapid induction of mPerI during phase resetting of the clock.