The “switch” that triggers the sudden tail whip that sperm use to penetrate and fertilize an egg has been pinpointed by researchers.

The finding could help identify a possible cause of male infertility. And, the study authors suggested, the switch could be a potential target for new contraceptives that work in both women and men.

The investigators found that the surface of a sperm’s tail has thousands of protein receptors. These receptors respond to the female hormone progesterone, which is released by the egg. When sperm get close to the egg, these receptors react to the progesterone and cause the tail to snap like a whip in an attempt to reach the egg.

“If the receptor protein doesn’t recognize progesterone, you would be infertile,” study first author Melissa Miller, a postdoctoral fellow at the University of California, Berkeley, said in a university news release. “This gives us an understanding of another pathway that is involved in human sperm activity.”

Currently, the cause of nearly 80 percent of cases of male infertility is unknown. Sperm may be the problem in half of all cases of infertile couples, the researchers said.

In addition, the study authors suggested that a drug that deactivates the progesterone receptors on sperm might prove an effective contraceptive for both men and women.

“What’s really cool is that we have an actual target for unisex contraceptive development,” Miller said. “If you can stop progesterone from inducing a power stroke, sperm are not going to be able to reach or penetrate the [egg].”

The study was published online recently in the journal Science.

More information

The American Academy of Family Physicians has more on male infertility.

Source: HealthDay