Losing sleep: mutant flies need less shut-eye.

Most people require about 8 hours of sleep a night, but some lucky oddballs function well on 4 hours or even less. A new study in fruit flies provides evidence that genetics plays a strong role in determining who can get by with little rest. A single mutation in a gene that's also found in people can reduce the insects' sleep needs by about two-thirds.

Although researchers have been studying sleep for decades, they've made little progress in teasing out the genetic components that control this phenomenon. In 2000, a team discovered that the fruit fly Drosophila melanogaster sleeps, much as mammals do. A sleeping fly simply sits motionless, usually for many hours a day.

"We realized that if we really wanted to understand sleep, we'd have to take advantage of the powerful genetics of Drosophila," says Chiara Cirelli of the University of Wisconsin-Madison.

Searching for genes that affect sleep requirements, Cirelli and her colleagues rounded up more than 9,000 mutant lines of fruit flies. The researchers then observed several flies of each type to determine how long the insects sleep per day and how they behave after 24 hours of sleep deprivation.

Cirelli's team eventually narrowed its focus onto one line that they named minisleep flies. Unlike normal Drosophila, which spend 9 to 15 hours sleeping each day, minisleep flies doze only 4 to 5 hours daily.

When the flies were kept awake for 24 hours, the researchers discovered further differences. The scientists enforced the sleeping ban by tapping or shaking the insects' habitats whenever the creatures were immobile for longer than 5 minutes.

The normal sleep-deprived flies showed a delay in trying to escape from stimuli such as noise, vibration, or heat. However, minisleep flies reacted as rapidly as well-rested normal flies did.

The scientists traced the differences between normal and minisleep flies to a mutation on the X chromosome within a particular gene known as Shaker. Flies with mutations in this gene shake their legs when recovering from anesthesia.

Further investigations showed that the mutation in minisleep flies affects channels in nerve cell membranes and makes the cells extrasensitive to electrical signals. Having more-excitable nerve cells, says Cirelli, may keep minisleep flies awake longer. A similar mutation may be at play in people who require less sleep than normal, she notes.

The researchers report their results in the April 28 Nature.

Although the minisleep flies appear normal in other ways, their life span was about 2 weeks shorter than the typical 3 to 4 months of most fruit flies. These results are "an interesting, cautionary note" added to a growing body of evidence documenting the need for sleep, says Joan C. Hendricks, whose team 5 years ago discovered that fruit flies sleep (SN: 2/19/00, p. 117).