Sperm, Egg, Genes: New Research Reveals Unexpected Post-mating Gene Expression In Model Lab Insect

Now, evolutionary and developmental biologists at the University of Georgia and the Hebrew University of Jerusalem have uncovered evidence that after fruit flies mate, the presence of sperm and male proteins in the female's reproductive tract sets off an amazing cascade of heretofore undescribed gene activity. Understanding how this works will give scientists new insights into reproduction, but it could also provide methods to safely control the spread of insect pests by interfering with their reproduction.

"We have been able to define a large number of mating-responsive genes that are activated in Drosophila," said Michael Bender, a developmental biologist in the department of genetics at UGA. "There is a lot of potential in this work for uncovering basic aspects of reproductive biology that will be useful in pest-control approaches."

The research was just published in the online edition of the Proceedings of the National Academy of Sciences. The work resulted from a collaboration between Bender, Paul Mack, a postdoctoral fellow in the Bender lab at UGA, Yael Heifetz of Hebrew University and Anat Kapelnikov, a graduate student in the Heifetz lab. A number of undergraduates at UGA also worked on the research.

Drosophila has been used as a model animal for nearly a century. It is easy to manipulate in a lab, lives only a few weeks and begins mating soon after hatching. Its entire genetic map or genome has also been sequenced, giving researchers a powerful tool in understanding intricate biological processes and the genes that direct them.

Bender's team, using both the established genomic background of Drosophila and studies of mating insects, showed that the sperm and proteins transferred from males to females during mating have "profound effects" on female gene expression. Most surprising is that gene activity rapidly escalates about six hours after mating--something previously unknown.

"We looked at the reproductive tracts of females at three, six and 24 hours post-mating," said Mack. "Just getting enough material through dissection is extremely difficult and time-consuming, but this kind of time-based evaluation of post-mating gene expression in Drosophila had never been done."

Perhaps surprisingly, very little is known about how gene expression in female reproductive tissues changes in response to the presence of sperm and male molecules. The study compared 3-day-old mated and unmated females and discovered the presence in mated females of a startling 539 genes whose activity changes after mating.

"One novel feature of this research was Paul's decision to look at what happens over time," said Bender. "That's how we found out that the activity hits a peak six hours after mating. This indicates quite a large genetic response in the female tract to male-derived molecules and sperm."

Though considerable research has been done on male Drosophila over the years, relatively little had focused on females. Just why the array of gene expression peaks at 6 hours is not yet clear, but revealing this timing could help in controlling insect pests. That is one reason the research was funded by the Binational Agricultural Research and Development (BARD) Fund, a joint program between the United States and Israel. Since 1979, BARD has funded nearly 900 research projects in almost all 50 states. Support for the research also came from The National Institutes of Health.

The Bender and Heifetz teams weren't operating in the dark, since earlier studies had examined some post-mating gene expression in Drosophila, but that earlier work did not examine expression over a set time period and involved examining the whole bodies of mated insects, not just their reproductive tracts.

The researchers' double approach using genomics and proteomics--the study of proteins and the products they turn on--was especially productive because it allowed them to identify genes they would not have found using a single approach.

"The next step will be to choose a few of the most promising genes and to explore their function in females," said Bender.

Once the gene functions are known, then scientists can begin to examine how to manipulate them--both to study the biology involved and to find potential targets for pest control.