A Sperm Finds Its Egg

Courtesy of Richard Mooi

For sea urchins, sex is an out-of-body experience. And in external fertilization, species-specific gamete receptors serve as one way to prevent cross-fertilization. The discovery of an egg protein responsible for this specificity ended a 25-year quest for Charles Glabe, molecular biologist at University of California, Irvine.

Glabe and postdoc Noriko Kamei identified the glycoprotein on sea urchin eggs, called egg bindin receptor 1 (EBR1), which is involved in sperm recognition for two sea urchin species.1 A rapidly evolving species-specific domain makes up one-third to one-half of the 350 kDa protein. The technique that facilitated EBR1's discovery, representation difference analysis, is "a quick way to identify rapidly evolving genes in closely related species," says Glabe. Because of their specificity, these proteins prevent hybridization and provide "a reasonable dividing line between one species and another."

Victor Vacquier, Glabe's former doctoral adviser now...

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