Two studies shed light on the movement of sperm cells and how to stop them in their tracks.

Imagine the following scenario from the not-so-far-off future: You’re at a bar, drinking a vodka tonic and minding your own business. A gentleman sidles up to you with a proposition. You, the daughter of two OB-GYNs, are naturally anxious around unknown men after years of having the words “unwanted pregnancy” drilled into your head. But you are agreeable to this guy’s overtures. You’re just waiting for an indication that you can safely move beyond this initial stage of courtship.

Then he disarms you and puts your fears to rest in one sweet turn of phrase: “It’s okay, baby, I’m on the pill.”

The male birth control pill recently took a step towards reality when two studies isolated different functional mechanisms of sperm cells.

A collaborative research effort between Children’s Hospital Boston and the Howard Hughes Medical Institute measured, for the first time, a sperm cell’s electric activity. The feat allowed them to pin down the role of a protein called CatSper, which is central to male fertility. At the same time, researchers at Bar-Ilan University in Israel discovered that, contrary to a long-held belief, protein translation does take place in sperm cells during sex.

Both discoveries could lead to drugs that would effectively slow a sperm cell down before it can penetrate an egg.

David Clapham, Betsy Navarro and Yuriy Kirichok published a paper in the February 9th issue of Nature, proving that a CatSper channel in the sperm cell is triggered to open under certain alkaline conditions.

“Recording electrical activity of the sperm has shown that CatSper is a calcium selective channel which, at particular moments when the sperm is close to the egg, allows calcium to go inside the sperm flagellum, and this hyper-activation of the sperm allows sperm to penetrate through the barriers and fertilize the egg,” said Kirichok.

The exact role of CatSper in the fertilization process was unclear until now. Clapham first discovered CatSper in the tails of mature mice sperm in 2001, further noting that mice lacking the protein were infertile because their sperms’ flagella were too weak to enter an egg.

Hydra Biosciences, a biotech company co-founded by Clapham in Cambridge, MA, is developing a drug that could block CatSper without hindering other calcium channels in the body. The drug could be used by men or women.

The Israeli research, published in the February 15th issue of Genes and Development, pertains to the biochemical processes that take place in sperm cells during their residence in the female reproductive tract. Scientists had assumed that protein translation—the creation of proteins from a DNA blueprint—had no reason to take place in sperm cells.

But Yael Gur and Haim Breitbart found that protein translation does take place in the sperm cells of humans, bulls, rats and mice. They hypothesize that translation is necessary for replacing proteins that are used up during the cell’s relatively long trip through the female reproductive tract and, most importantly, to aid with capacitation, the final enabling process the sperm cell undergoes while preparing to penetrate the egg.

When the protein translation is inhibited, capacitation becomes impaired and fertilization is much less likely.

Breitbart said his team’s findings would primarily be used to develop female contraceptives, though he added, “We might be developing a male contraceptive as well.”

OB-GYNs, better lock up your daughters.

Originally published March 1, 2006

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