OREGON STATE UNIVERSITY

Gene for sexual behavior identified in flies

12/12/1996

CORVALLIS - A group of scientists have identified a single gene that dictates all aspects of sexual preference and behavior in male fruit flies.

The research, to be announced Friday in the professional journal Cell, is perhaps the first study to ever successfully pinpoint a clear genetic basis for such a complex behavior in any adult animal, the scientists said.

The findings cannot be directly correlated to the control of human sexual preference and behavior. But the researchers said in their report the data is relevant and "there is a variety of evidence in vertebrates, including humans, suggesting that male sexual behavior, including sexual orientation, has a genetic component."

"Flies, other animals and even humans share many similarities in their genes," said Barbara Taylor, a co-principal investigator on the study and assistant professor of zoology at Oregon State University.

"It's quite astounding, even in a fly, to find a single gene that has such a profound influence on sexual behavior," Taylor said. "But based on this, I would be surprised if similar mechanisms did not exist in humans."

The study was published by researchers from four institutions, including Taylor at OSU; Bruce Baker, a professor of biology, and research associate Lisa Ryner at Stanford University; Jeffrey Hall, a professor of biology at Brandeis University; and Steven Wasserman, an associate professor of molecular biology and oncology at the University of Texas Southwestern Medical Center.

Taylor, who is an expert on the genetics and neuroanatomy of fruit flies, said the new discoveries relate to the fly gene "fruitless," which geneticists already knew could influence sexual orientation - mutant male flies that lack the fruitless gene will court other males as well as females. But this latest study shows the fruitless gene does far more than that.

Among the impacts: - The fruitless gene is a master gene that controls not only sexual orientation but all, or nearly all, aspects of the male fly's elaborate courtship ritual, from its first interest in a female through its rhythmic courtship song and its attempts to mate.

- The gene is part of a group of genes that work together to govern all aspects of a fly's sex life, including development of male and female organs.

- The fruitless gene works by becoming activated in only a few cells in the fly's brain, where it carries out "command and control" functions to coordinate the complex events of male courtship.

"We never really expected to find a single gene regulating so many behaviors," Taylor said. "And it's very focused. The fruitless gene has a controlling impact on sexual behavior, but not much else, and it does this by being expressed in just a few hundred cells out of a few hundred thousand."

It's clear at this point, Taylor said, that genetics are the dominant player in sexual behavior for fruit flies. But even those tiny insects can also be influenced by external environmental forces.

"Flies can learn, be trained, and respond to their environment," Taylor said. "If you raise flies in a social environment, we can even see physical changes in their brain."

So it's difficult, Taylor said, to extrapolate the implications of this research for higher animal species, including humans. Obviously social and environmental influences can also have a major impact on human sexual preference and behavior, she said, but the genetic component must be considered seriously.

Studies by other scientists, Taylor said, have made it clear that there are genetic links between flies, humans and other animals that are retained intact after millions of years of separate evolution.

"There are a series of master genes called homeotic genes, which control physical structure and formation, that are similar in flies, mice and humans," Taylor said. "There's a pair of genes involved in immune system function that's the same in flies and humans."

Research has been done with less success in humans trying to identify genes that control complex behaviors, Taylor said.

The fruit fly study is the first to prove such a dominant genetic influence by a single animal gene.

"We're just beginning to scratch the surface in exploring how genes can influence behavior," Taylor said. "With our new findings about the fruitless gene in fruit flies, we have one solid example. It's like a master blueprint for male sexual behavior."