Sex-Specific Genes Identified

DURHAM, N.C. – Researchers at Duke have identified several sex-specific genes that have male or female specific roles in the physiology of the adult fruit fly Drosophila melanogaster. The study, which was carried out by Sinsuke Fujji and Hubert Amrein in the Department of Molecular Genetics and Microbiology and was published in the most recent issue of EMBO Journal, sought to identify genes with roles in sex-specific behaviors, such as male courtship and female rejection and egg laying behavior.

The authors applied a molecular genomics approach known as Serial Analysis of Gene Expression (SAGE), a method championed at Duke by Gregory Riggins, Department of Pathology, to find differences in the make up of genes expressed in either the male or female head of the fly.

A major surprise of their investigations is the observation that all four genes are mainly expressed in the fat cells of the head, a group of cells that is poorly understood. “Most everyone would have expected that head- and sex-specific genes with defined roles in the adult are going to be expressed in the brain/” Dr. Fujii comments on their findings.

Many sex-specific genes are known, but almost all these genes have functions in the differentiation of germ cells (gametogenesis), and are expressed in eggs or sperm of female and male, respectively. Three of the four genes that the Duke researchers found are virtually only expressed in the head, implying a role unrelated to gametogenesis, but suggesting a role in other sex-specific differences of adult flies. Since the fat cells in the head completely surround the brain, an attractive role for these genes might be to modulate brain function in either males or females. Indeed, three of the four genes encode proteins with biochemical properties that could account for the production of small, diffusible molecules and peptides. “We don’t know yet what the target tissue of these proteins are. We do suspect, though, that their functions are very specific for and restricted to one sex or the other and — based on their predicted biological activity -– that they will modulate brain function, thereby affecting some aspects of behavior. Of course, the first such behavior that comes to mind is courtship behavior, which is very distinct in males and females,” the senior author of the study, Dr. Amrein says. He points out, however, that caution is in place, since other behaviors, specifically circadian activity, might have sex-specific components.

The authors are now investigating the specific roles of these genes using RNA interference (RNAi) and over- expression studies. Fujii is very encouraged by the first experiments he carried out over the last month. “We do see that over-expression of a male-specific gene in females causes a subtle change in their receptivity, i.e. their willingness to copulate.” However, both authors believe that RNAi will be more informative, since such experiments address specifically what goes wrong in the absence of a protein. For example, they suspect that the very pronounced male courtship behavior will be disrupted in males that lack a male-specific protein, should such a protein indeed play a role in this process.