Essential Fertility Protein Discovered That Binds Sperm With Eggs

An integral component of the fertility process has been discovered by British scientists. Scientists discovered a protein that allows sperm and eggs to bind together, The Guardian reports. 

The molecule, which is named Juno after the Roman goddess of fertility, sits on the egg's surface and binds with sperm on a fertilizing sperm cell. 

Japanese researchers identified the sperm protein in 2005, inspiring the search for its counterpart. 

Researchers said that understanding the way molecules interact during the process can lead to new fertility and contraception developments. 

"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, from the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire.

"Without this essential interaction, fertilization just cannot happen. We may be able to use this discovery to improve fertility treatments and develop new contraceptives."

The Sanger Institute created an artificial version of the sperm protein, which is called Izumo1 after a Japanese marriage shrine. The single protein on the egg, Juno, has been identified as Izumo1's other half. 

Juno's significance was revealed by studying female laboratory mice that were engineered to produce eggs that lacked the molecule. All of the female mice lacking the protein were unable to concieve. 

Researchers discovered that male mice missing Izumo1 were also unable to conceive, which showed the protein's equal significance. 

Research suggests that Juno also plays a role in preventing more sperm from fusing with an egg that's already been fertilized. 

"The Izumo-Juno pairing is the first known essential interaction for sperm-egg recognition in any organism," said co-author Dr Enrica Bianchi, also from the Sanger Institute. "The binding of the two proteins is very weak, which probably explains why this has remained a mystery until now."

After the egg and sperm bind, Juno detaches and is undetectable for 40 minutes. Such a finding may help explain why an egg puts up a barrier once it has been fertilized by one sperm cell. Fertilization of more than one sperm could lead to abnormal embryos with too many chromosomes. 

Scientists are now studying infertile women to see whether they have Juno defects. 

Researchers say it may be possible to do without the natural mating of Juno and Izumo1 by using intracytoplasmic sperm injection (Icsi). The method involves injecting sperm right into the egg. 

Fertility expert Dr. Allan Pacey, senior lecturer in reproduction and developmental medicine at the University of Sheffield, said: "I think this is a very exciting paper. We are still remarkably sketchy about some of the key molecules involved in the early stages of fertilisation when the sperm and egg first interact."

Pacey added, "Yet the information could be immensely useful to help in the diagnosis of infertility but also in the design of new novel contraceptives for both humans and other animal species."