Clock gene expression in the submandibular glands

Clock genes, which mediate molecular circadian rhythms, are expressed in a circadian fashion in the suprachiasmatic nucleus and in various peripheral tissues. To establish a molecular basis for circadian regulation in the salivary glands, we examined expression profiles of clock- related genes and salivary gland- characteristic genes. Clock- related genes - including Per1, Per2, Cry1, Bmal1, Dec1, Dec2, Dbp, and Rev- erb alpha- showed robust circadian expression rhythms in the submandibular glands in 12: 12- hour light- dark conditions. In addition, a robust circadian rhythm was observed in amylase 1 mRNA levels, whereas the expression of other salivary- glandcharacteristic genes examined was not rhythmic. The Clock mutation resulted in increased or decreased mRNA levels of Per2, Bmal1, Dec1, Dec2, and Dbp, and in Cry1-/- background, Cry2 disruption also increased or decreased mRNA levels of these clock- related genes and the amylase 1 gene. These findings indicate that the Clock- and Cry- dependent molecular clock system is active in the salivary glands.