By Sean Henahan, Access Excellence

PALO ALTO, CA (Dec. 14, 1996) A single gene appears to control virtually all aspects of sexual behavior in male fruit flies, according to a team of US researchers. The research is the first to pinpoint a single gene controlling a complex behavior in adult animals.

A gene called "fruitless" and nicknamed "fru" has long been known to influence sexual orientation in the fly Drosophila melanogaster. Previous studies showed that male flies with some mutations in the fru gene become bisexual - they cannot tell other males from female flies when courting.

The current study indicates that the fru gene is much more:

• A master gene that controls not only sexual orientation but all, or nearly all, the steps in the male fly's elaborate courtship ritual - from its first interest in a female through its rhythmic courting song, to its attempts to mate.

• Part of a group of genes that work together to govern all aspects of sex in these flies, including development of male and female organs.

• At work in a very small fraction of the cells in the fly's brain. The properties of the fru gene's target neurons suggest that they carry out command-and-control functions to set up and coordinate the complex events of male courtship and copulation.

"These findings on fru provide a starting point for a whole host of other studies, to learn how sexual behavior and sexual orientation are specified by genes and controlled by the nervous system," added Steven Wasserman, associate professor of molecular biology and oncology at UT Southwestern, an expert on the molecular genetics of fertility.

The new data suggests that the fru gene is involved in interactions between a handful of specific brain cells that in some way direct the various steps of male courtship behavior and copulation. The discovery gives genetic researchers a new tool for evaluating behavior and the organization of the nervous system.

Researchers from Stanford, the University of Texas Southwestern Medical Center, Brandeis University and Oregon State University reported these findings in the Dec. 13, 1996 issue of the journal Cell.