Saturday, January 27, 2007

Forth, Spermatazoa!

Small Wonders: Understanding the Way of the Warrior Sperm: A Conversation with David E. Clapham by Claudia Dreifus ran in Tuesday's New York Times Science Section. Clapham and his associates published an article last February in Nature announcing their work on the CatSper gene, an ion-channel found in the tail of mature sperm. Ion channels are "molecular gates on the membranes of our cells" that allow ions to flow through them when they open and close. Under alkaline conditions found near an egg in the uterus, the ion channel opens to release calcium into the tail of the sperm. According to Clapham, the discovery of CatSper is the "key to one of the great mysteries of reproduction: how sperm penetrate eggs." Says Clapham:
As you know, a human sperm needs to swim through the female reproductive tract for something like 15 minutes to get to the egg. They have a kind of built-in motor that permits them to do that. When sperm get to the egg, they need to crash through the ovum’s membrane to deposit their DNA there.
The way that happens is that at the end of its run, this ion channel brings the sperm calcium, which changes the shape of its tail and turns it into a kind of whip. The sperm is then propelled into hyper drive — pushing it into the egg with 20 times the force of normal swimming.

According to Clapham, whose specialty is ion channels, not the study of sperm,
I’m fascinated by how determined they are. Sperm — each one seems an individual in the way they move. When they change from one motion to another, it’s fascinating.
Moreover, they have the ability to do much more than most other human cells: they crawl long distances in a short period of time, they can sense their surroundings. In fact, they have molecules that are much the same as olfactory receptors in our noses.
As you watch them under a microscope, you get the sense that they are going somewhere, or at least “think” they are. They surround an egg and vigorously try to fuse with it. They don’t give up until they run out of energy. . . . The social behavior of sperm is somewhat like the social behavior of humans. Sperm cluster around an egg. Sperm get more vigorous when they’re around an egg. (Laughs) It remind us of what males are like around females.
Clapham is not alone in his fantasy of fertilization. Last May the Philadelphia Inquirer reported on Clapham's work in an article entitled Scientists Find Sperm's Sex Potion: Sperm like it warm and perfumed--with a spcial (sic) turn-on.
Or, as Silvershoes remarks in her precis of Clapham's work, Every Sperm is Great, sperm are "great at karaoke."
Compare Clapham's description of fertilization to this one from The Agressive Egg, published in Discover Magazine in 1992 by David Freedman:
First, a wastefully huge swarm of sperm weakly flops along, its members bumping into walls and flailing aimlessly through thick strands of mucus. Eventually, through sheer odds of pinball-like bouncing more than anything else, a few sperm end up close to an egg. As they mill around, the egg selects one and reels it in, pinning it down in spite of its efforts to escape. It’s no contest, really. The gigantic, hardy egg yanks this tiny sperm inside, distills out the chromosomes, and sets out to become an embryo.

Freedman's account is based on the research of Emily Martin who in 1987 published The Woman in the Body, reissued with a new preface in 2001.
Martin did her ethnographic work among biologists studying fertilization. In Freedman's words, these biologists:
had started the year before with a simple experiment--measuring human sperm’s ability to escape and swim away from a tiny suction pipet placed against the side of the sperm cell’s head. To the team’s great surprise, the sperm turned out to be feeble swimmers; their heads thrashed from side to side ten times more vigorously than their bodies pushed forward. The team went on to determine that the sperm tries to pull its getaway act even on the egg itself, but is held down against its struggles by molecules on the surface of the egg that hook together with counterparts on the sperm’s surface, fastening the sperm until the egg can absorb it.

Clapham describes this process as "going somewhere" propelled by a "motor" kicked into "overdrive" when it "senses" the presence of an egg so it can "crash into" the egg to "penetrate" it. Remarkably, so did the researchers Martin studied, for years after their own research had shown the inaccuracy of this account. Freedman reports:
Martin concedes that she herself was slow to recognize the disparity between the discoveries at Johns Hopkins and the way the findings were written up. It didn’t strike me for a few years, she says. But innocent or not, she adds, the cultural conditioning these biologists had absorbed early in their careers influenced more than their writing: it skewed their research. I believe, and my husband believes, and the lab believes, that they would have seen these results sooner if they hadn’t had these male-oriented images of sperm. In fact, biologists could have figured out a hundred years ago that sperm are weak forward-propulsion units, but it’s hard for men to accept the idea that sperm are best at escaping. The imagery you employ guides you to ask certain questions and to not ask certain others.

This obfuscation is not, of course, harmless, as it impedes the research needed to develop new contraceptives for men--or, at least, contraceptives with fewer side effects for women. Not that such research needs any additional impediments. As Sara at f-words points out, work on new contraceptives is languishing for lack of interest, while Clapham reports that large pharmaceutical firms are not interested in his work because "[t]here’s a general feeling throughout the industry that reproduction is just too risky in terms of potential liability and in terms of controversy. They feel that the estrogen-based birth control pill works fine. As far as they are concerned, the problem is solved."
Martin points out other reasons to be concerned about the persistence of sex-stereotyped imagery of fertilization:
When we anthropomorphize the egg and sperm, when we turn them into a miniature bride and groom complete with personalities, what effect does this have on abortion legislation?
Martin also observes,
that it’s been known since the 1960s that women exposed to toxic chemicals bear children who run a higher risk of serious medical problems. Those findings reinforced the cultural notion that women should be sheltered . . . But only in the past few years have comparable studies shown that men exposed to high levels of lead, vinyl chloride, and about a dozen other chemicals also have children who are at higher risk. It’s the notion of invulnerable sperm, she claims, that made it take so long for scientists and the public to accept the male role in birth defects and infertility.

I can't help thinking that male-dominated science's reluctance to interfere with the heroic mission of the valiant sperm has discouraged insight into male contraception. Maybe reimagining fertilization as the greedy, grasping egg seizing and devouring the hapless, helpless sperm would stimulate more researchers to ride out to the rescue of their threatened brothers?

See also Rethinking the ova, the Sperm and the Metaphors of Reproduction (August 2006), Seed Magazine: Slowing Sperm Down, and The Thoughts of a Frumpy Professor The Deep Thrust.

1 comment:

Sara E Anderson said...

I thought the anthropomorphization stuff was really weird too, though the guy does seem perfectly willing to cripple sperm.