Protein on egg cells may solve infertility

Written by Linzasaur

Researchers at the Wellcome Trust Sanger Institute are one step closer to improved fertility treatments with the discovery of interacting proteins on sperm and egg cells.

Researchers at the Wellcome Trust Sanger Institute are one step closer to improved fertility treatments with the discovery of interacting proteins on sperm and egg cells. Never been found before, the proteins on egg cells are essential to the beginning of life as they allow the sperm and egg to recognise each other and fuse to form an embryo.

It has been known for a long time what happens during fertilization, but the discovery of these proteins answers yet more questions about how life occurs. The Izumo protein, named after a Japanese marriage shrine, is displayed on the sperm and was identified in 2005 by Japanese researchers. However, the corresponding egg protein that pairs with Izumo has remained a mystery until now. The researchers have named it Juno after the Roman Goddess of fertility and marriage.

By creating an artificial version of Izumo, it was discovered that Izumo on the sperm cell interacted with Juno on the surface of the egg to initiate fertilisation.

Some answers, but still some questions

Dr Gavin Write, who took part in the experiments, said: “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 discovery may be incredibly useful in fertilization treatments, as female mice that were developed without the Juno protein on their egg cells were found to be infertile. The same was true of male mice that lacked the Izumo protein. This could well be true of human men and women who have trouble conceiving, and could be invaluable when developing new ways of helping them have children.

Initial experiments had shown that the interaction of the proteins was weak, which made finding the corresponding protein to Izumo difficult. The reason for this is that after just 40 minutes, the Juno protein disappears from the egg surface, making it virtually undetectable.

This could be the answer for why egg cells are not fertilized with more than one sperm, as the egg cannot recognise any more Izumo proteins once it has fused with a sperm cell. More than one sperm fusing with an egg would be very problematic, as the foetus would have twice the correct number of chromosomes from the father, and ultimately die. This makes the loss of Juno after fertilisation an important evolutionary strategy.

The team at Sanger are currently screening women to determine whether defects with Juno proteins are in fact to blame for some problems with conceiving. If it is found to be important, then many women could be saved the expense of fertility treatments that may be futile, and the stress of not knowing whether a treatment is going to work or not could be reduced in many cases.

The options of couples with problems with fertility can be reduced, and people may now have more of an idea about what they can and can’t achieve. In the case of Juno defects, women can be offered intracytoplasmic sperm injections (ICSI), a treatment that consists of the sperm cell of the father being directly injected into the egg cell of the woman which bypasses any need for the surface proteins to bind.

Contraceptive vaccines are also a possibility with this discovery, which target the binging of Juno and Izumo. These could be a remedy for pest species in the wild such as badgers, rather than the culling of innocent animals. Owners of domestic pets could also benefit.

While still being in the research stages, the discovery of Juno and Izumo opens a lot of doors with fertility, contraception and the beginnings of life. It is a breakthrough not just for scientists and academics, but for families too.

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