This is how the egg protects itself from fertilization by multiple sperm –

Fertilization in mammals begins with the attachment of the sperm to the envelope surrounding the egg.

Eggshells are made of long chains of proteins called filaments. These are chains of proteins that the sperm must penetrate in order to fuse with the egg.

Now researchers have mapped in detail the structure and function of the protein ZP2, a component of egg envelope filaments that plays an important role in regulating how eggs and sperm interact with each other during fertilization.

The egg shell becomes hard

– It is already known that ZP2 separates after the first sperm enters the egg, says Luca Goffin, professor at the Department of Life Sciences and Nutrition at Karolinska Institutet.

– Now we can show how this event makes the shell of the egg more rigid and impermeable to other sperm. In this way, polyspermy is prevented, that is, the fusion of several sperm into one egg, which is a fatal condition for the fetus.

Crucial for fertility

Changes in eggshells after fertilization are also crucial to a woman's fertility because they protect the growing embryo before it implants in the uterus.

The new knowledge could thus be important for the development of non-hormonal contraceptives that interfere with egg shell formation, according to the researchers. In addition, the study explains infertility in women resulting from changes in the egg shell.

The study also shows that part of ZP2 that was previously thought to function as a receptor, or sperm receptor, is not necessary for sperm to attach to the egg. This raises the question of what the sperm's actual future is on the egg envelope, something the researchers plan to investigate further.

Scientific material:

Cleavage of ZP2 prevents polyspermy by modifying the structure of the egg envelope, cell.

communication:

Luca Goffin, Professor, Department of Life Sciences and Nutrition, Karolinska Institutet
[email protected]