Jan. 30, 2008

Seminal fluid can impact female fruit fly's fertility, offering clues into human reproduction

The reproductive biology of the fruit fly may have a lot to teach us about human fertility.

A new Cornell study identifies six so-called accessory-gland proteins in the seminal fluid of fruit flies that affect reproduction by changing the female's post-mating behavior and physiology.

The study, published last month in PloS Genetics, found that one of those proteins is required to fully stimulate egg production in the Drosophila female on the first day after mating. The other five proteins sustain changes in the female caused by mating, such as her increased egg production and her reduced likelihood to mate again. Until now, the ability in insects to maintain these responses had been associated with only a single insect-specific accessory gland protein.

Maintenance of such responses after mating requires the presence of stored sperm. Females of all species that mate internally store sperm in the body, from a few days in most mammals to 20 years in some bees and ants.

"Females have to keep sperm alive and control the release of their eggs," said the paper's senior author Mariana Wolfner, a Cornell professor of molecular biology and genetics. "These five accessory gland proteins were found to control the release of sperm from storage." K. Ravi Ram, a research associate in Wolfner's lab, was the paper's lead author.

These accessory-gland proteins are chemically related to proteins found in seminal fluid across species, from insects to mammals, including humans. Studying Drosophila gives researchers a workable model to pinpoint the functions of such proteins. These insights may then direct studies on the function of these classes of seminal proteins in humans.

In addition to helping to understand some cases of infertility in humans, the research may also aid in developing new strategies to control insects that transmit human diseases. Mosquitoes that transmit dengue fever and West Nile Virus, for example, are "cousins" of fruit flies. Studies of similar proteins in such mosquitoes, initiated by Cornell postdoctoral fellow Laura Sirot, working with Wolfner and with entomology professor Laura Harrington, may help researchers reduce a female mosquito's fertility and thus her ability to spread disease, said Wolfner.

This work was supported by the National Institutes of Health.