By Sean Henahan, Access Excellence

NEW HAVEN, CT- Mutations induced by jumping genes can produce marked changes in the courting behavior in male fruit flies, including bisexual traits, according to a recent collaborative study.

The fruit fly, Drosophila melanogaster, has been a favorite research tool for geneticists since the beginning of the century. For one thing, fruit flies only have four chromosomes. For another thing, they breed like, well, like flies. The female produces hundreds of eggs at a time and a new generation comes along every two weeks or so.

Yale researcher Klemens F. Stoertkuhl and colleagues were able to feminize different areas of the brains of male fruit flies. As a result, the male flies began to display courting behavior to other males. The researchers used genetic fragments that move spontaneously from one location on a chromosome to another, sometimes causing mutations. Called transposons or "jumping genes," these bits of DNA are known to jump short distances within the same chromosome or even to neighboring chromosomes.

In nature, the male fly initiates courtship by approaching the female and touching her with the foremost of his two front pairs of legs in order to sense sexual scents, or pheromones. If he is not rebuffed by a swift kick from the female, the male pursues the female as she walks around the courting area. As he chases her, he produces a high-pitched love song by extending and fluttering one of his wings, Dr. Stoertkuhl said.

"We were able to produce several different genotypes with varying degrees of male courting behavior, showing that the relationship between genotype, brain structure and sexual orientation is complex, even in an organism as relatively simple as Drosophila," said Dr. Stoertkuhl.

The current study is based on an a recent advance in genetic engineering. The first step involved inserting a yeast gene for a gene-activated protein, Ga14, in the flies genome. Different strains of flies express the protein in different tissues. Next, those flies are mated with other flies genetically altered to contain a gene of choice connected to an activator of Ga14. The researchers concentrated their research on flies expressing Ga14 in brain tissues. These flies were then bred to a strain engineered to include a transformer gene linked to Ga14. The transformer gene can switch male cells to a female pattern, a process known as feminization.

The researchers used jumping gene techniques both to mark the brain tissues and to trigger production of the transformer protein in those targeted brain areas to turn male structures into female structures. Males of the special strain remain normal males in all ways, except for the brain areas genetically altered to be female.

"This study shows that the relation between genotype, brain structure and sexual orientation is complex, even in an organism as relatively simple as Drosophila. Subtle differences in human brain structures have been correlated with male homosexuality as have certain genetic markers.

"In spite of the behavioral and phylogenetic gulf that separates our studies, investigations of Drosophila sexual behavior may provide insights into fundamental aspects of the relation between genes, brain structure, and sexual behavior in higher organisms," said Dr. Stoertkuhl.

For the complete data from the bisexual fly research, please see Science, 2/10/95, V.267, pp. 791-92, and 902-905.

Transmitted: 95-04-03 17:46:48 EDT