Tick-Tock, Fruit Flies Have Multiple Clocks

If you thought the ticking of your biological clock was only in your head, brace yourself. While the brain has long seemed the master timekeeper for biological rhythms--controlling everything from normal fluctuations in body temperature to midafternoon slumps--now it turns out that some organisms have independent clocks throughout their bodies. In the current issue of Science comes a report that fruit flies have multiple cellular clocks that keep to a 24-hour schedule and can be set independently of the brain.

One of a cellular clock's mechanisms for keeping time is periodic fluctuations in the amount of a protein called PER. To track the production of PER, geneticist Steve Kay from Scripps Research Institute in La Jolla, California, and his colleagues took the DNA that regulates the expression of the per gene and fused it to the gene for luciferase, the enzyme that generates a firefly's light. When that DNA tries to activate the per gene, it causes luciferase to be produced instead of PER, and the fruit fly will luminesce. The researchers saw a periodic glowing of the transgenic fly as per production--and hence luciferase production--cycled on and off. But in addition to a glowing head, the insect's legs, wings, thorax, and abdomen also shone.

The research "shows clocks all over the place, all at once, in a very graphic fashion," marvels Martin Zatz, a physiologist at the National Institute of Mental Health in Rockville, Maryland. And because researchers have found the PER protein and another clock protein outside the brain in mammals as well as insects, there's a good chance that they too have multiple clocks.

If that proves to be the case, the implications are "quite provocative," says Joseph Takahashi, a clock biologist at Northwestern University in Evanston, Illinois. These apparently independent clocks--they function even when disconnected from the brain or from other parts of the body, and can be reset by exposure to light--may help various parts of the body tailor their protein production to suit the needs of the hour, Takahashi says. Eyes, for example, may produce different mixtures of photoreceptor proteins at different times of day to make adjustments for night vision, while muscles might rev up their metabolism in anticipation of daytime activities.

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