Like many men, male fruit flies have a considerable array of schemes for courting females, from tender touching to solo serenades. But in a surprising find, it appears that in flies all these acts of gallantry are controlled by a single gene active in small clusters of cells in the fly brain. The gene, called fruitless (fru), is the first shown to control a complex set of behaviors in an animal.
Biologists have known since the 1970s that flies with a mild mutation in fru are bisexual, courting both males and females. But in the new study, published in today's issue of Cell, a team of geneticists led by Bruce Baker of Stanford University, Jeff Hall of Brandeis University, Barbara Taylor of Oregon State University, and Steve Wasserman of the University of Texas Southwestern Medical Center in Dallas show that males with more severe mutations aren't just indiscriminate, but sexless.
The flies lose the will to follow other flies, play courtship songs on their wings, and attempt copulation. Along with evidence that the protein encoded by fru is present in only 500 of the fly's 10,000 central nervous system cells and that it is a transcription factor--a protein that turns other genes on or off--the finding suggests that fru is a high-level regulatory gene that somehow gets specific brain centers to coordinate male courtship behavior, the scientists say.
"It's a real breakthrough," says Dean Hamer, a researcher at the National Institutes of Health who studies whether sexual orientation in humans has a hereditary component. "It confirms what everyone suspected but no one had really proven--that sexual behavior can indeed be genetically programmed in an animal."
Hamer and other researchers caution that the study sheds little direct light on sexuality in humans, because the genes that determine sex in flies and mammals are unrelated. But according to Michael McKeown, a developmental geneticist at the Salk Institute in La Jolla, California, fru's presence in nine small clusters of fly nerve cells--including several previously mapped by Hall as "courtship centers"--may begin to give researchers "a handle on how the neural circuits that generate complex behaviors are put together."
For more details, see News story in this week's issue of Science.