Circadian oscillation of BMAL1, a partner of a mammalian clock gene Clock, in rat suprachiasmatic nucleus.

A superfamily gene which encodes a bHLH (basic helix-loop-helix)/PAS transcription factor, BMAL1, was cloned and sequenced from rat cDNA. A robust circadian rhythm of rat BMAL1 expression was detected by in situ hybridization in the suprachiasmatic nucleus (SCN), the site of the circadian clock, with the highest level at the subjective night. Less prominent and completely reversed circadian rhythms of rBMAL1 mRNA were observed in the piriform and parietal cortices. The hybridization signals of rBMAL1 mRNA were also detected in the olfactory bulb, hippocampus, and cerebellum. Since the product of rBMAL1 was recently demonstrated to dimerize with the protein of a mammalian clock gene, Clock, and the protein complex was shown to bind the E Box in the promoter region of mPer1 (a mouse homologue to Drosophila clock gene, Per), rBMAL1 possibly plays a critical role in the clock mechanism generating the circadian oscillation in rats.