There's quite a good biological explanation to the traditional 'nine to five' office shift. Scientists have found that certain genes are switched in the body only once every 12 or 8 hours. These are responsible fore keeping us actively involved in the work at hand.
The findings by researchers at the University of Pennsylvania School of Medicine and the Salk Institute for Biological Studies indicated that shorter cycles of the circadian rhythm are also biologically encoded.
Already, scientists know that some genes are controlled by the clock and are turned on only one time during each 24-hour cycle.
In the new study, researchers looked at gene activity in the mouse liver every hour for 48 hours using a novel time-sampling approach.
They also found 10-fold more genes controlled by the 24-hour clock than previously reported.
This the first report where researchers have found other periodicities than the 24-hour cycle functioning in a live animal.
According to researchers, 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.
"The principal frequency, which is not a surprise, is the 24-hour cycle, and it is the most prevalent. What was a surprise to us - although we set up the experiment to see exactly this - are the 12-hour and the 8-hour cycles," said senior author John Hogenesch, PhD, Associate Professor of Pharmacology in the Institute for Translational Medicine and Therapeutics at Penn.
To uncover these shorter oscillations, researchers 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 4 percent of all of the genes expressed in the liver.
In addition, 260 genes were expressed on a 12-hour cycle and 63 genes were expressed on an 8-hour cycle.
The researchers saw similar 12-hour gene expression patterns in five other tissues.
"There is an obvious biological basis to a 12-hour rhythm. The 12-hour genes predicted dusk and dawn. These are two really, really stressful transitions that your body goes through and your mind goes through. Anybody who has young children realizes that they are more likely to cry around those times - and you're more likely to cry with them," said Hogenesch.
The shift in gene expression controlled by these harmonics 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 8-hour rhythms, 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 8-hour cycle," he said.
The study appears in the April issue of PLoS Genetics