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Wednesday, 10 October, 2001, 23:01 GMT 00:01 UK
Sperm tail protein points to male pill
Sperm under microscope BBC
Genetically altered sperm were less active
The discovery of a key protein which controls the beating of a sperm's tail could eventually lead to male contraceptives with fewer side effects.

And women might also be able to take the pill either just before or just after sex - with potentially fewer side effects than traditional hormonal contraceptives.

The protein appears to be present only in one section of the sperm tail, so any drug aimed at it would probably have only a very localised effect.

The protein, named CatSper by researchers at the Howard Hughes Medical Institute and Harvard Medical School, US, seems to play a central role in fertility.

Sperm need their tails to propel them up the fallopian tubes to meet the egg.

And when they reach the egg, they need a bit more power so they can burst through into its centre and fertilise it.

It might be that this is involved in giving the sperm's tail beating a kind of turbocharge at the last instant

Dr David Clapham, Howard Hughes Institute
To test their theory, researchers took some mice and genetically altered them so they lacked the gene which helps produce the vital protein.

They found that genetically altered mice were completely infertile, and their sperm were considerably less vigorous.

In a separate test, when the outer layer of an egg, called the zona pellucida, was removed, the altered sperm were able to fertilise it normally.

Researcher David Clapham, from the Howard Hughes Institute, said: "The only thing that seems to be wrong in the sperm of these mice is their inability to penetrate the zona pellucida.

"It might be that this channel is involved in giving the sperm's tail beating a kind of turbocharge at the last instant, when it needs a bit more power to penetrate the zona pellucida."

Unisex drug

A drug to block the action of the protein is now a possibility, he believes.

If this can be achieved, it could be safer than traditional hormonal contraceptives for women.

He said: "Hormonal contraceptives have to be taken daily throughout a woman's fertile life.

"Also, they have potential side effects, such as increased risk of blood clotting and cancer."

He said that, in theory, a drug could also be taken by women, either just before or just after sex.

The research is published in the journal Nature.

See also:

11 Jul 01 | Health
Male 'pill' within four years
23 Feb 00 | Health
Most men 'would take the pill'
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