"Biologists have discovered the switch that triggers the power kick sperm use to penetrate and fertilize a human egg, uncovering not only a possible source of male infertility but also a potential target for contraceptives that work in both men and women.
The switch is a protein receptor that responds to the female sex hormone progesterone, which is released by the egg or oocyte, the ultimate goal toward which sperm swim.
Thousands of these receptors sit on the surface of a sperm’s tail and when the sperm gets close to the egg, the hormone activates the receptor and triggers a cascade of changes that make the tail snap like a whip, powering the sperm into and hopefully through the cells protecting the egg.
“If the receptor protein doesn’t recognize progesterone, you would be infertile,” says Melissa Miller, a postdoctoral fellow at University of California, Berkeley, and University of California, 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.”
A drug that inactivates this newly discovered receptor, however, might make a good “unisex” contraceptive—one that could be used by either sexual partner..."
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