Fertilization: How does the egg recognize the sperm? 2026

Getting there is the first step, but there is still something more missing: the egg must recognize the sperm and “let it pass.” Until recently, scientists intuited how the end of this incredible journey that culminates with fertilization would unfold, and the results of the latest research published in Nature reveal new details.

The mechanism by which an egg recognizes a sperm and clears its path of entry follows a system very similar to that of keys and locks. The “key” was already known: a protein located on the outer layer of the sperm that was discovered by a team of Japanese researchers and called Izumo, in reference to a Shinto shrine linked to marriage.

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Years later, scientists from the Wellcome Trust Sanger Institute (United Kingdom) began searching for the receptor, that molecular “lock” capable of recognizing, through the Izumo key, the sperm, opening the way for it to cause fusion with the egg and then closing that door to other male gametes.

Since they had several candidate molecules, the researchers developed an artificial version of Izumo and paired it with all of them, until they found the one that interacted with Izumo in those initial stages of fertilization. The next step was to develop mice in which this protein had been removed from the surface of the egg. Bingo! These mice were infertile and their eggs had lost the ability to fuse with sperm.

The protein is actually a folate 4 receptor, but scientists have named it Juno after the Roman goddess of fertility. Now that we know that Juno and Izumo have a lot to say in the fertilization process, the next step will be to verify that they are also a key piece in the case of humans.

“We have solved one of the mysteries that remained hidden for the longest time in biology by identifying the molecules of the egg and sperm that must associate at the moment we are conceived,” explains Gavin Wright, lead author of the work.

Applications in assisted reproduction

Although it is true that many treatments with in vitro fertilization consist of directly injecting the sperm into an egg, thus avoiding possible anomalies in this key-lock system, this work can be very useful to understand, for example, the origin of some cases of infertility.

Furthermore, the authors think that it could also be used to develop new contraceptive systems by blocking the Juno receptor, because, as the researcher explains, "without this essential interaction, fertilization does not occur."

Source:Wellcome Trust Sanger Institute