Fertilization takes place when the female egg and the male sperm fuse and create an embryo. That’s elementary.
But the how the egg and the sperm recognize one another in the first place is a more complicated question. Only in 2005 did researchers in Japan identify a protein on the sperm that performed the function of recognizing the egg.
They named the receptor protein “Izumo,” after a Japanese marriage shrine. Until now, however, its mate on the egg has been missing.
In the latest edition of the journal Nature, researchers report identifying the corresponding receptor protein on the egg: They named it “Juno,” after the Roman goddess of fertility.
Izumo, meet Juno.
A team of four from the Wellcome Trust Sanger Institute in Britain, led by Gavin Wright and Enrica Bianchi, made the discovery.
In a summary of their findings on the Wellcome Trust Sanger Institute Web site, the researchers reported that they developed mice that “lacked the Juno protein on the surface of their eggs,” and found them to be infertile: their eggs did not fuse with normal sperm.
“In the same way, male mice lacking the Izumo protein are also infertile, highlighting its essential role in male fertility,” according to the Web site.
An accompanying comment in Nature said the discovery makes the Juno-Izumo partnership “the first discovered in any organism to be essential to reproduction.”
The finding is not academic. It has the potential to aid in a big way couples attempting in vitro fertilization (IVF), Wright explained in a video (above).
Currently, IVF can be a series of progressively complicated and costly steps starting with an attempt to join egg and sperm in a lab. If that fails, it sometimes becomes necessary to inject sperm through an egg’s shell so that it does not need to penetrate on its own.
The team reported that it is “screening infertile women to understand whether defects in the Juno receptor are a cause of infertility. If it is, then a simple genetic screening test could help inform the appropriate treatment for women struggling to conceive naturally by reducing the expense and stress often involved in assisted fertility treatments.”
“What we can do is perform a very simple genetic screening test that isn’t invasive,” Wright said in the video. “This would then allow us to guide the fertility treatment so that women [who lack Juno] can proceed directly” to the sperm injection “rather than going through the previous rounds” of IVF treatment.
“That saves an enormous expense,” he said.
Juno performs an additional crucial chivalrous task, according to the findings: It blocks other sperm cells from joining to an egg once it has been fertilized.
“After one sperm cell joined to the egg, Juno disappeared from the egg surface within 30-45 minutes,” according to Nature.