Different circadian expression profiles of clock genes in the mouse suprachiasmatic nucleus

The mammalian clock genes clock, BMAL1, and Periods, were cloned and demonstrated to localize in the suprachiasmatic nucleus (SCN), the mammalian circadian center. In the present study, we examined the daily mRNA expression profiles of these genes by quantitative in situ hybridization. Clock was constantly expressed in the mouse SCN in any circadian time, although mammalian Periods and BMAL1 were expressed in time-dependent manner: peaks of Periods appeared in the daytime but those of BMAL1 appeared in the nighttime. Digoxigenin-in situ hybridization demonstrated that all of these clock genes were expressed in most SCN cells. These findings suggest that clock genes were expressed in the SCN with the different expression profiles.