Biologists at the University of California at Berkeley believe they have discovered the chemical interaction that gives sperm the kick they need to penetrate and fertilize a human egg. The discovery has the potential to be used to create a contraceptive that could work for both men and women, and treat male infertility.

The researchers found that the key is a type of protein receptor that sits on a sperm's tail and responds to the female sex hormone progesterone. When progesterone is released by the egg, or oocyte, it triggers chemical changes to the protein that then makes the sperm's tail start moving. That motion powers the sperm into (and potentially through) the cells protecting the egg.

If the progesterone can't trigger the sperm's tail to move, then the sperm won't be able to reach or even penetrate the egg. The researchers involved in the project believe a drug that can inactivate the protein receptor on the sperm's tail could have the potential for becoming a unisex contraceptive.

An eventual unisex contraceptive could have the potential for not only making a female birth control obsolete, but would also make moot ongoing attempts to create a male-only birth control pill.

The discovery of the protein receptor may have also started to shed some new light on male infertility, a problem that still remains largely unsolved due to how little is still known about the molecular steps involved in the production of sperm and how it interacts with the egg. Researchers in the US have been further stymied by the fact that the government has made it illegal to use federal funds for research that combines eggs and sperm in the same dish.

So the researchers involved in this project developed an ingenious way of observing what governs sperm behavior absent a human egg, by attaching electrodes on a sperm's tail and recording how it reacted to different hormones, including progesterone.

"If the receptor protein doesn't recognize progesterone, you would be infertile," said Melissa Miller, a postdoctoral fellow at both UC Berkeley and UC San Francisco and the first author of a paper reporting the discovery. "This gives us an understanding of another pathway that is involved in human sperm activity."

The results of the discovery were published in the March 17 issue of Science.

Source: UC Berkeley