How the circadian rhythm affects gene regulation

In recent years, scientists have discovered that biological clocks help organise a dizzying array of biochemical processes in the body — but exactly how the microscopic pacemakers in every cell in the body exert such a widespread influence has remained a mystery.

Now, a recent study provides direct evidence that biological clocks can influence the activity of a large number of different genes in an ingenious fashion: by causing chromosomes to coil more tightly during the day and to relax at night.

“The idea that the whole genome is oscillating is really cool,” said Carl Johnson, Prof of Biological Sciences at Vanderbilt University.

“The fact that oscillations can act as a regulatory mechanism is telling us something important about how DNA works — it is something DNA jockeys really need to think about.”

The research, published online in the Proceedings of the National Academy of Sciences, details how Johnson’s team used gel electrophoresis on cyanobacteria plasmids to measure the extent of supercoiling at different points of the day/night cycle.

The researchers found the plasmid is smaller and more tightly wound during periods of light than during periods of darkness. They also found that this rhythmic condensation disappears when the cyanobacteria are kept in constant darkness.

“This is one of the first pieces of evidence that the biological clock exerts its effect on DNA structure through the coiling of the chromosome and that this, in turn, allows it to regulate all the genes in the organism,” said Mark Woelfle, senior lecturer at the university.

The researchers see no reason why the bioclocks in higher organisms, including humans, do not operate in a similar fashion. “This could be a universal theme that we are just starting to decipher,” said Woelfle.