Antiphase circadian expression between BMAL1 and period homologue mRNA in the suprachiasmatic nucleus and peripheral tissues of rats

BMAL1 is a putative transcription factor which is involved in circadian rhy thm generation in Drosophila. Northern blot analysis was performed to inves tigate the expression of rat BMAL1 mRNA in the suprachiasmatic nucleus (SCN ) and peripheral tissues. In the SCN, circadian expression of BMAL1 mRNA wh ich reaches its peak level at the time of dark-light transition was observe d, and the expression pattern was antiphase to those of two period (per) ho mologues, rPer1 and rPer2. However, no circadian oscillation for rat Clock mRNA was detected. The circadian expression of BMAL1 mRNA was also observed in peripheral tissues such as brain (excluding the SCN), eye, heart, kidne y, and lung. The amplitudes of BMAL1 and rPer2 mRNA expression levels were correlated between the different tissues, suggesting that the circadian exp ression of BMAL1 mRNA plays an important role in generating the circadian e xpression of per homologue genes in mammals. (C) 1998 Academic Press.