How, among hundreds of millions, a single sperm achieves its purpose. This is the mystery of life. Well the recognition between the mother’s egg and the chosen sperm is due to two specific proteins, Izumo and Juno. Their recognition is the 1st vital step of fertilization in all mammals.
Everything is in the magic of a meeting. The intimate fusion of a sperm and its female counterpart, the oocyte. Small problem: if the woman offers a single oocyte, the male, not stingy, puts at her disposal, in a few cubic centimeters of sperm, 200 to 300 million spermatozoa, all candidates for the jackpot!
We know that there will be only one chosen one, at most 2 or 3 in multiple pregnancies. Why this particular sperm? Cambridge researchers have published in the journal Nature, the explanation of this mystery. It is due to two proteins: Izumo and Juno.
We start with Izumo, which is named after a famous Japanese shrine dedicated to marriage. It is a protein, discovered in 2005, located in the sperm membrane. Its role is to allow fusion with the membrane of an oocyte.
It is its female counterpart that British researchers have discovered. They named her Juno, after Juno, goddess of marriage and fertility. By creating a synthetic version of Izumo, they were able to observe that the fertilization process begins with the interaction between these two proteins. Izumo of the sperm and Juno located on the surface of the oocyte. Confirmation by experiment: female mice conceived without Juno protein remained infertile like male mice lacking Izumo.
So, without Izumo and Juno, no fertilization …
Why only one victorious sperm?
The mystery is not to know why only one is the chosen one but rather why the others do not enter the ovum? We have the answer: the sperm turn around the egg to tire its membrane. As soon as one of them succeeds in penetrating, because it is authorized by the Juno proteins which are on the surface of the ovum, these stop their recognition process.
What practical applications?
First, it’s always interesting to understand. But researchers immediately thought about the problem of female infertility. Could it be due, in part, to the faults of this Juno receiver? If this is the case, a simple genetic screening would identify the origin of the problem and adapt the treatments accordingly. And then the researchers also evoke another avenue of application of their work: since the Izumo protein is essential for the fusion between spermatozoon and oocyte, it is perhaps the solution to … the development of a chemical contraception for the man ! Absolute parity …
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