Researchers have discovered that by increasing or decreasing the synapse strength of cells by modifying a "genderblind" (GB) gene, fruit flies can be made to demonstrate either homosexual or heterosexual behavior, respectively.
The scientists explained that adult fly brains have dual-track sensory circuits: one track triggers heterosexual behavior, the other homosexual. In heterosexuals, the homosexual circuit is blocked by a normal suppression of synapse strength. But when the GB gene was modified to not suppress synapse strength, the homosexual circuit became unblocked.
"It was amazing. I never thought we'd be able to do that sort of thing, because sexual orientation is supposed to be hard-wired," said David Featherstone, a researcher at the University of Illinois at Chicago who lead the study. "This fundamentally changes how we think about this behavior."
Many genes don't regulate synapse strength. The GB gene is a bit different than most genes because it has the unusual ability to transmit a neurotransmitter called glutamate out of glial cells. Changing the amount of glutamate outside these cells can affect the strength of the cells' synapses. Synapses provide the means for the nervous system to connect to and control other parts of the body, and therefore they play a key role in human and animal behavior.
When the flies' synapse strength was genetically increased, the flies no longer interpreted smells the same way. Specifically, the flies did not recognize male pheromones as a repulsive stimulus. In a sense, the flies were over-stimulated.
To the researchers' surprise, they could switch the flies' sexual orientation within a few hours after GB gene modification.
The researchers explain that, while other genes that alter sexual orientation have been discovered, 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 may help scientists understand specifically why males choose to mate with females.
The scientists also suggest that, by manipulating flies' responses to certain smells, it might be possible to domesticate them and turn them into useful pollinators instead of pests.
The study is published in Nature Neuroscience.
Via: University of Illinois at Chicago