How among hundreds of millions of sperm does one get its way? Here is the mystery. 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 ONE oocytes, 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!
Izumo and Juno.
Why a specific sperm? L’explanation of this mystery. It is due to two proteins: Izumo and Juno.
We start with, Izumo, which bears the name of 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.
British researchers discovered its female counterpart and named it Juno, in reference to 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. Sperm Izumo 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.
Only one elected, maximum 2 or 3 in multiple pregnancies.
The mystery is not to know why only one is chosen but rather why the others do not return. We have the answer. The sperm cycle around the egg to strain 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.
Practical applications
Researchers immediately thought about the problem of female fertility. Could it be due, in part, to 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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