Researchers have discovered a gene involved in homosexual behavior in the tiny flies. They also found a way to turn homosexuality on and off with drugs.

Humans have a similar gene. But it's unclear what effect, if any, the gene has on homosexual behavior in people, said biologist David Featherstone of the University of Illinois at Chicago.

Featherstone and colleagues described their findings in the journal Nature Neuroscience.

The team led by Featherstone discovered that sexual orientation in fruit flies is controlled by a previously unknown regulator of synapse strength. Armed with this knowledge, the researchers found they were able to use either genetic manipulation or drugs to turn the flies' homosexual behavior on and off within hours.

Featherstone, associate professor of biological sciences at UIC, and his coworkers discovered a gene in fruit flies they called "genderblind," or GB. A mutation in GB turns flies bisexual.

But the GB gene became even more interesting when post-doctoral researcher Yael Grosjean noticed that all the GB mutant male flies were courting other males.

"It was very dramatic," said Featherstone. "The GB mutant males treated other males exactly the same way normal male flies would treat a female. They even attempted copulation."

Other genes that alter sexual orientation have been described, but most just control whether the brain develops as genetically male or female. It's still unknown why a male brain chooses to do male things and a female brain does female things. The discovery of GB provided an opportunity to understand why males choose to mate with females.

Featherstone and his colleagues reasoned that adult fly brains have dual-track sensory circuits, one that triggers heterosexual behavior, the other homosexual. When GB suppresses glutamatergic synapses, the homosexual circuit is blocked.

Further work showed precisely how this happens -- without GB to suppress synapse strength, the flies no longer interpreted smells the same way.

"Pheromones are powerful sexual stimuli," Featherstone said. "As it turns out, the GB mutant flies were perceiving pheromones differently. Specifically, the GB mutant males were no longer recognizing male pheromones as a repulsive stimulus."

Full article: In Fruit Flies, Homosexuality Is Biological But Not Hard-wired, Study Shows
Gene makes fruit flies bisexual: study | Chicago Sun-Times