The investigators found ten-fold more genes controlled by the 24-hour clock, called circadian rhythm, than previously reported. Additionally, they have found other periodicities than the 24-hour cycle.
"The principal frequency is the 24-hour cycle. It is the most prevalent," says senior author John Hogenesch. "A surprise to us is the twelve-hour and the eight-hour cycles.” These findings have implications for better understanding disruptions to normal circadian rhythms that contribute to a host of pathologies such as cardiovascular and metabolic disease, cancer, and aging-related disorders.
To uncover the shorter oscillations, the team isolated RNA from the livers of mice every hour for 48 hours. Microarray analysis showed that more than 3,000 genes were expressed on a circadian rhythm – which account for approximately four percent of all of the genes expressed in the liver. Additionally, 260 genes were expressed on a twelve-hour cycle and 63 genes were expressed on an eight-hour cycle. The investigators saw similar twelve-hour gene expression patterns in five other tissues.
"There is an obvious biological basis to a twelve-hour rhythm," Hogenesch says. "The twelve-hour genes predicted dusk and dawn." The shift in gene expression can help an animal prepare for the behavioural and physiological changes that accompany the shift from light to dark and back. "We have less of a handle on the eight-hour rhythms," he says, "but the fact that we can see them reliably means to me there is the possibility that there could be a biological basis to an eight-hour cycle."
MEDICA.de; Source: University of Pennsylvania School of Medicine