Zona pellucida is a glycoprotein layer that surrounds the mammalian oocytes. Zona pellucida is present between the plasma membrane of oocytes and the corona radiata. Zona pellucida plays an important role in successful fertilisation and initiates the acrosome reaction for the entry of sperm into the secondary oocyte.
Structure
Zona pellucida surrounds mammalian oocytes. It is a translucent matrix of glycoproteins.
There are four sperm binding proteins present. They are ZP1, ZP2, ZP3 and ZP4.
ZP1 connects and forms cross-linking between ZP2 and ZP3. The glycoprotein ZP3 is involved in sperm binding that triggers the acrosome reaction. ZP2 mediates further sperm binding.
The zona pellucida layer is known as the vitelline membrane or envelope in insects and other non-mammals.
Functions
Zona pellucida plays an important role in successful fertilisation.
- It is present between oocytes and follicular cells and acts as a link between them at the time of oogenesis.
- It protects oocytes or eggs and embryos during development.
- It initiates the acrosome reaction for the binding and penetration of sperm cells.
- It helps in preventing polyspermy.
- The binding to zona pellucida glycoprotein (ZP3) triggers acrosome reaction.
- It helps in species-specific fertilisation and prevents cross-breeding of different species.
- It regulates the interaction between free-swimming sperms and ovulated eggs or secondary oocytes.
- The sperm binding proteins (ZP1, ZP2, ZP3 and ZP4) are the targets for immunocontraception.
- The female mutants who lack the zona pellucida layer surrounding the egg are infertile.
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