A team of researchers has identified a sperm protein that is essential for the fusion of the sperm and egg membranes during fertilization, according to a report in this week's Nature. They called the protein "Izumo," after the Japanese shrine dedicated to marriage.

Masaru Okabe of Osaka University and coworkers used the fusion-inhibiting monoclonal antibody OBF13 and gene-cloning techniques to identify an antigen on mice sperm involved in fusion. "The antigen Izumo is a novel protein of the immunoglobulin superfamily," Okabe, the senior author of the study, told The Scientist. Proteins belonging to this family are membrane-anchored, and are usually involved in cell-cell adhesion.

Okabe has been seeking the sperm protein since 1987, when his group reported that OBF13 bound to an unknown molecule on the sperm head. Further studies revealed that the antibody did not prevent sperm binding, but did inhibit fertilization. This gave the researchers a...

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