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For years, people have known that conception occurs when a sperm fertilizes an egg. Despite knowing this, researchers have not been able to discover why the pairing had to be between one sperm and one egg. Now, according to a new British study, researchers found that egg cells have a specific receptor that only allows a sperm cell to attach to it and subsequently fertilize it.

For this study, Gavin Wright, group leader of the Cell Surface Signaling Laboratory at the Wellcome Trust Sanger Institute, a genome research institute in the United Kingdom, and colleagues based their research on a 2005 study conducted by Japanese researchers. In that study, the researchers had identified a special protein receptor on the surface of sperm cells that allowed fertilization to occur. The researchers called that receptor Izumo1.

Wright's team created an artificial version of the Izumo1 protein. They then examined how the protein binds with the surface of egg cells taken from mice models. The researchers discovered a similar protein that exists on the surface of the egg cell that allows fertilization to occur. They named this protein Juno after the Roman goddess of fertility and marriage.

"We believe this is one of the ways in which eggs ensure that they fuse with one and only one sperm," Wright said. "That is, once the first sperm has fertilized the egg, the egg shuts down its ability to recognize additional sperm, ensuring that the fertilized egg doesn't contain too many chromosomes, which would result in a non-viable embryo."

Roughly one in every eight couples from America deal with infertility. In some of these cases, fertility treatments are still not effective. The researchers hope that this study's findings would be able to help develop better treatments for infertility.

"The finding that the interaction between Izumo and Juno is essential for fertilization was, in a way, surprising," said Wright according to WebMD. "One might have expected that something as fundamental as fertilization would not rely on a single critical interaction; if there's anything wrong with Izumo in males, or Juno in females, then infertility results."

The study was published in Nature.