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New protein could help male subfertility

The discovery of a new protein may deepen understanding of male subfertility and lead to improvements in in vitro fertilisation techniques. One in six British couples cannot conceive after two years of trying, and male subfertility--which affects more than a fifth of men--is the commonest single cause. A letter to Nature (25 January, p 364) outlines evidence that the new protein, oscillin, named after the oscillations that it induces in mammalian ova, is a key component in activating the process of fertilisation.

This is important news for scientists trying to perfect the in vitro fertilisation techniques of intra-cytoplasmic sperm injection and round spermatid nuclear injection, which inject sperm directly into the egg, bypassing the need for sperm to be motile. A knowledge of the protein and its actions may help researchers find out why these techniques don't always work.

The protein has been shown in the sperm cytoplasm of many mammals including man, and its arrival into the cytoplasm of the egg is thought to cause direct release of calcium stores, setting in train the chain of events that leads to embryo formation. The prevailing belief is that the sperm binds to a receptor on the egg's surface, activating secondary messengers within the egg, before it releases its DNA.

"It is biological commonsense that the sperm should wait until its DNA is safely within the egg before it activates the process of fertilisation," argues Dr Karl Swann, a lecturer in the department of anatomy, University College London, "but the receptor site theorists threw down a gauntlet and challenged me to demonstrate the mechanism. Well, here it is."

Clinicians still face a wait for a practical application of the work, much of which has been done on hamster sperm. Preliminary results on a few such men suggest that oscillin may sometimes be deficient.--DOUGLAS CARNALL, editorial registrar, BMJ

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