Vitality

Discovery of Sperm's 'Power Kick' Could Lead To Unisex Contraceptives And Explain Cause Of Male Infertility

sperm
Discovery of "the switch" that causes sperm to penetrate and fertilize a human egg could lead to the development of a contraceptive that works in both men and women. Pixabay, Public Domain

We’re familiar with the scientific “fairy tale ” of human fertilization — sperm meets egg and together they form a one-celled zygote that will eventually grow and develop into a baby. These steps are well known, but up until now scientists were still unsure of what  triggers the sperm to penetrate and fertilize a human egg.  Biologists at the University of California at Berkeley recently discovered receptors on the sperm tail that are activated once it nears the egg. The new findings uncover another possible source of male infertility, and could also lead to the development of a unisex contraceptive, that works in both men and women.

New research published in the journal Science reveals that as the sperm move closer to the egg the egg releases the female sex hormone  progesterone which  helps trigger the “power kick” sperm need to make the final push to fertilize the egg. When the sperm nears the egg, progesterone released by the egg activates ABHD2, the protein receptors located on the surface of the sperm’s tail. This “ triggers a cascade of changes” that cause the tail to pick up speed; this motion of snapping back and forth like a whip helps power the sperm through the cells protecting the egg, researchers wrote..

The switch that triggers the sperm’s power kick is its protein receptors responding to progesterone released from the egg. However, if the sperm’s receptors don’t react to the progesterone, it can signal something more serious. "If the receptor protein doesn't recognize progesterone, you would be infertile," said researcher Melissa Miller. "This gives us an understanding of another pathway that is involved in human sperm activity."

Little research has been done on how the egg and sperm interact with each other. Researchers cite the U.S. government’s refusal to fund research that brings eggs and sperm together in the same dish. To navigate this roadblock, senior author Polina Lishko and her colleague Yuriy Kirichok developed techniques over the past five years that would allow  them to “stick electrodes on a sperm's tail and record its reactions to hormones, key to probing the molecular cascades that govern sperm behavior,” researchers wrote.

Unisex Contraceptive

This newly discovered receptor also inspired an idea for a contraceptive. Researchers say creating a drug that inactivates the sperm’s receptor could be an effective form of birth control -- one that could be used by either partner.

"What's really cool is that we have an actual target for unisex contraceptive development," Miller explained. "If you can stop progesterone from inducing a power stroke, sperm are not going to be able to reach or penetrate the oocyte."

Previous efforts on creating birth control for men -- who only have three forms of contraception compared to the many options available to women -- have focused on testosterone levels, but researchers are focusing a birth control option that can be used by both men and women. Preventing progestosterone from triggering sperm’s power kick “is one of the better options we have for a unisex contraceptive," Miller said.

The next step for researchers is to see if progesterone, a hormone found in many other tissues, including the brain, the lungs, and smooth muscle, works in a similar manner to trigger major changes in tissues.

Souce: Miller M, Lishko P, Kirichok Y. Unconventional Endocannabinoid Signaling Governs Sperm Activation via Sex Hormone Progesterone. Science. 2016.

Loading...