Abbildung 1a: Zona pellucida
Role of the zona pellucida (ZP) in fertilisation and oocyte maturation. A: Schematic drawing of sperm-ZP interaction (modified from [11]). The capacitated sperm attaches and then tightly binds to the ZP (a, b). These interactions are mediated by ZP3 which serves as a primary receptor for sperm. The acrosome reaction in the bound sperm is induced which is essential for sperm penetration of ZP (c). ZP2 maintains acrosomereacted sperm in the ZP during penetration (d). Following fusion of egg and sperm, cortical granules disintegrate to induce the zona reaction that prevents polyspermy (e, f). Proteolytic cleavage of ZP2 and ZP3 is involved in the zona reaction. After fertilisation ZP still remains to protect the fertilised eggs.