All animals have internal clocks to help them track along with the 24-hour cycle of light and dark. New work with fruit flies reveals that the insects have two cellular clocks that coordinate their daily schedule--one for the morning and one for the night.
Like other crepuscular animals, fruit flies have two peaks of activity, one at dusk and the other at dawn, when the flies are busy mating and looking for food. Scientists have made progress in dissecting the inner workings of the fly's clock. They've found several genes, for example, that are required for a working clock. They've also found that these genes are expressed in two groups of about 100 neurons each, the ventral lateral neurons (LNV) and the dorsal lateral neurons (LND). How the clock controls behavior has remained a mystery. Now, two independent teams shed new light on the issue in papers published 14 October in Nature.
A team led by François Rouyer, a neurobiologist at the Alfred Fessard Institute of Neurobiology in Gif-sur-Yvette, France, studied a breed of fruit fly with a mutated copy of per, one of the central clock genes. When they restored the per gene to the LNV neurons, the flies once again buzzed around in the morning. Restoring per in the LND neurons brought back the evening foraging. Rouyer concludes that the flies rely on two internal alarm clocks.
A different approach was used by a team led by Michael Rosbash, a neurobiologist at Brandeis University in Waltham, Massachusetts. Rather than using mutant flies, they delivered a suicide gene to kill specific groups of neurons in wild-type flies. By knocking out either the LNV or LND neurons, they arrived at the same double-clock model as Rouyer's team.
"The findings in these two papers provide truly exciting new insight," says Serge Daan, a neurobiologist at the University of Groningen, the Netherlands, because it clinches a longstanding theory that crepuscular animals run on two separate internal clocks. He adds that the next step is to find out how the two clocks are interconnected.