Orchestra-like-human-circadian clock has many conductors

Researchers have challenged the prevailing wisdom about how our body clocks are organized, and suggest that interactions among neurons that govern circadian rhythms are more complex than originally thought.

Orie Shafer, a University of Michigan assistant professor of molecular, cellular and developmental biology and U-M doctoral student Zepeng Yao looked at the circadian clock neuron network in fruit flies, which is functionally similar to that of mammals, but at only 150 clock neurons is much simpler.

Previously, scientists thought that a master group of eight clock neurons acted as pacemaker for the remaining 142 clock neurons-think of a conductor leading an orchestra-thus imposing the rhythm for the fruit fly circadian clock. It is thought that the same principle applies to mammals.

When researchers genetically changed the clock speeds of only the group of eight master pacemakers they could examine how well the conductor alone governed the orchestra. They found that without the environmental cues, the orchestra didn't follow the conductor as closely as previously thought.

Some of the fruit flies completely lost sense of time, and others simultaneously demonstrated two different sleep cycles, one following the group of eight neurons and the other following some other set of neurons.

The findings suggest that instead of a group of master pacemaker neurons, the clock network consists of many independent clocks, each of which drives rhythms in activity.