The Biological Clock

Biological clocks count off 24-hour intervals in most forms of life. Genetics has revealed that related molecular timepieces are at work in fruit flies, mice and humans by Michael W. Young

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You have to fight the urge to fall asleep at 7:00 in the evening. You are ravenous at 3 P.M. but have no appetite when suppertime rolls around. You wake up at 4:00 in the morning and cannot get back to sleep. This scenario is familiar to many people who have flown from the East Coast of the U.S. to California, a trip that entails jumping a three-hour time difference. During a weeklong business trip or vacation, your body no sooner acclimatizes to the new schedule than it is time to return home again, where you must get used to the old routine once more.

Nearly every day my colleagues and I put a batch of Drosophila fruit flies through the jet lag of a simulated trip from New York to San Francisco or back. We have several refrigerator-size incubators in the laboratory: one labeled "New York" and another tagged "San Francisco." Lights inside these incubators go on and off as the sun rises and sets in those two cities. (For consistency, we schedule sunup at 6 A.M. and sundown at 6 P.M. for both locations.) The temperature in the two incubators is a constant, balmy 77 degrees Fahrenheit.

The flies take their simulated journey inside small glass tubes packed into special trays that monitor their movements with a narrow beam of infrared light. Each time a fly moves into the beam, it casts a shadow on a phototransistor in the tray, which is connected to a computer that records the activity. Going from New York to San Francisco time does not involve a five-hour flight for our flies: we simply disconnect a fly-

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GIVING FRUIT FLIES JET LAG is helping researchers such as the author (above) understand the molecular basis of the biological clocks of a variety of other organisms, including humans. The tiny flies are kept in small glass tubes (photograph at left) packed into trays equipped with sen sors that record the insects' activity. When a tray from an incubator kept at New York time, where it is dark at 7:30 P.M., is moved to another incubator simulating San Francisco time, where it is three hours earlier and still light, the levels of key proteins in the flies' brains plunge.

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