Sperm protein needed for fertilization is found

Japanese scientists said on Wednesday they have discovered a protein on sperm that is essential to fertilize eggs.

The protein, which they named Izumo after a Japanese shrine dedicated to marriage, could lead to improvements in contraceptives and fertility techniques.

"The finding not only provides insight into the enigmatic fusion mechanism but also promises benefits in the clinical treatment of infertility and the potential development of new contraceptive strategies," said Masaru Okabe of Osaka University in Japan in the science journal Nature.

Before sperm can fertilize a female egg it must pass through an outer layer of the egg, then interact with the inner coat surrounding it and bind to its plasma membrane.

The scientists bred genetically engineered mice that did not produce the protein and found the animals could not complete fertilization.

The mice were healthy and produced sperm but they were sterile.

The search for Izumo began 18 years ago when the scientists found an antibody that recognized a molecule on sperm and inhibited fertilization.

Human sperm also contains a counterpart of Izumo. When the scientists used the antibody in laboratory experiments, they found that it blocked frozen human sperm from fusing with hamster eggs - a test for male fertility.

Richard Schultz and Carmen Williams at the University of Pennsylvania in the United States described the research in a commentary as compelling.

"These findings raise the exciting possibility that, because Izumo is sperm-specific and extracellular, this protein and its interacting partners could be new targets for non-hormonal contraception," they wrote.