Scientists determine how egg and sperm merge

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A discovery by scientists has revealed the finding of a protein which enables sperm to bind to an egg. This could pave the way for new contraception methods and for infertile couples to benefit.

The molecule that was discovered has been named Juno, which is the Roman goddess of fertility. It has been found on the egg’s surface and binds with a protein on the sperm cell which is very similar.

When this occurs, it is the first moment of conception.

Japanese scientists were able to discover how the male part of the process works during 2005, but have not had success with its counterpart, until now.

Dr Gavin Wright, the lead researcher from the Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire, has said that they have managed to solve a biology mystery by the identification of molecules on the egg and sperm that is required for conception. He said that without this interaction, fertilisation is impossible. This opens a path to the development of new contraceptives and an improvement in treatments for fertility.

The researchers believe that the protein on the sperm, known as ‘Isumo’, behaves in the same way as a metal detector searching for ‘Juno’ on the female egg.

They discovered that mice without the ‘Juno’ or ‘Izumo’ molecules were unable to experience the fusion.

The research also indicated that ‘Juno’ has a huge role in the prevention of additional sperm fusing with an egg which has already been fertilised.

Dr Enrica Bianchi, a co-author from the Sanger Institute, said this pairing is the first known interaction of sperm-egg recognition. She stated that the binding of these two proteins is extremely weak and this may be the reason why it has remained a mystery to scientists for so long.

Scientists found that about 40 minutes after the first sperm and egg binding, ‘Juno’ disappears. This stops other sperm from binding. The researchers have claimed that this could be an explanation as to why a barrier is created by an egg as soon as it has been fertilised by one sperm. Fertilisation of an egg by more than one sperm may lead to abnormal embryos which will be doomed.

This discovery has prompted scientists to start a screening process of infertile women to determine if ‘Juno’ defects are causing their condition. If this is the case, a simple genetic test will allow doctors to offer them the most appropriate treatments.

Regular IVF treatment where sperm is randomly used to fertilise eggs in a lab dish would not be successful without ‘Juno.’ However, the natural mating process of the two molecules can be bypassed. This is done by injecting a sperm directly into the egg.

Although ‘Juno’ is said to be critical in the initiation of the sperm and egg binding process, scientists believe that it may be necessary to have other proteins present to initiate the full fusion that ultimately leads to fertilisation.

Fertility experts believe that this identification exposes exciting prospects. They feel that the most obvious application of this discovery is that it could be used as a fertility test.

The second application would be if scientists were able to devise vaccines or drugs that would block the manner in which the protein works, which would lead to a new non-hormonal contraception method for all mammals.

Image credit: Andrea Laurel

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