During human (or any mammalian) fertilization, if more than one sperm manages to get inside an egg, there are typically no survivors. A violent competition between the two sperm brings the whole kit and caboodle to a tragic end.
It's called polyspermy. And how human eggs avoid it has been pretty much a mystery until now. Scientists have discovered an enzyme called ovastacin fights off would-be fertilizers when there's already one in the mix.
Polyspermy is a problem because it presents an extra set of chromosomes. So would-be embryos with more than one sperm typically die spontaneously. But if everything is working properly, researchers at the National Institutes of Health have found—using mice as a model—that ovastacin kicks out the extra sperm intruder before sudden death has to happen.
The scientists publish their work in the most recent issue of the Journal of Cell Biology. It's the kind of thing that makes you realize how much there still is to discover about our own biology, let alone the rest of the universe. [Journal of Cell Biology]
Image: Burkart, A.D., et al.