-- Next, we took the hermaphrodite brain and we activated the genes that determine maleness, but only in the brain and not in the rest of the worm, Jorgensen says. Hermaphrodites with masculine brains were attracted to other hermaphrodites.
The results show sexual orientation is wired into the brain in both sexes of worm.
To masculinize the brains of hermaphroditic worms, the researchers activated a gene named fem-3, but only in the nervous system. The fem-3 gene makes the body develop male structures such as a tail, which male worms use for copulation. With the gene active only in the brain, the hermaphrodites still had the same bodies and genitalia, but their brains were male, so they were attracted to other hermaphrodites.
To demonstrate the hermaphrodites produce sexual attractants or pheromones, the researchers washed hermaphrodites, and put some of the wash water on agar, a jelly-like growth medium, in a culture dish. When worms were placed on the dish, males moved toward the hermaphrodite wash water while hermaphrodites moved away.
When the scientists genetically altered hermaphrodites brains to change their sexual orientation, they crawled toward the pheromones of other hermaphrodites.
"People debate whether the brain is influenced by sexual hormones from the gonads or whether the behavior is derived from the brain alone, Jorgensen says. In this case, its clear the brain is sexualized. The surprise was that sensory neurons found in the hermaphrodite brain are involved in sexual attraction in males.
|Contact: Lee Siegel|
University of Utah