A FUNDAMENTAL key to fertility has been discovered by British scientists who have identified an elusive protein that allows eggs and sperm to join together.
The molecule, named Juno after the Roman goddess of fertility, sits on the egg surface and binds with a male partner on a fertilising sperm cell.
Japanese researchers identified the sperm protein in 2005, sparking a hunt for its “mate”.
Understanding the process by which the molecules interact opens the door to new developments in fertility treatment and contraception.
“We have solved a long- standing mystery in biology by identifying the molecules displayed on all sperm and egg that must bind each other at the moment we were conceived,” said lead researcher Dr Gavin Wright, of the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire.
“Without this essential interaction, fertilisation just cannot happen. We may be able to use this discovery to improve fertility treatments and develop new contraceptives.”
The Sanger Institute team first created an artificial version of the sperm protein, called Izumo1 after a Japanese marriage shrine. This was used to search for partners on the surface of the egg. A single protein, Juno, was identified as Izumo1’s “other half”.
Juno’s importance to fertility was revealed by female laboratory mice engineered to produce eggs lacking the molecule. All the animals were infertile. Male mice missing Izumo1 were also unable to conceive.
The research, reported in the journal Nature, also suggests Juno may stop additional sperm fusing with a fertilised egg.
“The Izumo-Juno pairing is the first known essential interaction for sperm-egg recognition in any organism,” said co-author Dr Enrica Bianchi. “The binding of the two proteins is very weak, which probably explains why this has remained a mystery until now.”
After the initial binding of sperm and egg, Juno bows out, becoming virtually undetectable after 40 minutes, it was found.
This may help explain why as soon as an egg is fertilised by one sperm cell, it puts up a barrier against others.
Fertilisation involving more than one sperm would lead to the formation of abnormal and doomed embryos.
The scientists are now screening infertile women to see whether Juno defects underlie their condition. If they do, a simple genetic screening test could help doctors provide the most appropriate treatment quickly.
Fertility expert Dr Allan Pacey, senior lecturer in reproduction and developmental medicine at the University of Sheffield, said: “The identification of the Juno protein opens up many exciting prospects.”