Whence Life? Receptors Responsible For Fertilization Found

Scientists believe they have found the receptors that allow sperm and egg cells to hook up and create life.

A fertilized human egg

Wellcome Images

Where do babies come from? If your kids ever ask, just tell them the story of Izumo and Juno, receptors found on the surface of sperm and egg cells, respectively. In a study on mice published today in the journal Nature, researchers found that these two proteins allow the sperm and egg to recognize one another, leading to fertilization--and life as we know it. These receptors are found in many mammals, including humans.

It previously wasn't known how sperm and egg recognized each other. Researchers have dubbed the egg's receptor Juno (previously known as folate receptor 4, which definitely doesn't have the same ring), in honor of the ancient Roman goddess of fertility and marriage, Reuters noted. The term Izumo derives from the word for a Japanese marriage shrine.

The Verge explains the study:

To validate their findings, researchers bred mice that didn't produce Juno on eggs or Izumo on sperm. In both cases, these mice were unable to reproduce. Moreover, researchers realized that the Juno disappears from the surface of the egg moments after fertilization — an event they think reveals why eggs aren't usually fertilized by more than one sperm cell at a time. "This explains a 50-year-old mystery as to how eggs fuse with one — and only one — sperm so that there aren't too many chromosome contributed by the male which would result in a nonviable embryo," said [study co-author Gavin] Wright.

The study results could help infertile (human) couples have kids. The scientists are already screening infertile women to see if they have problems with their Juno receptors. If that is the case, these women may be able to undergo a procedure called intracytoplasmic sperm injection, which involves injecting the sperm into the egg and then re-implanting it. "It is remarkable that about 20 percent of infertility cases have an unexplained cause," co-author Enrica Bianchi of the Sanger Institute, told Reuters. "We are now asking whether Juno is involved in these cases of unexplained infertility."