![]() ![]() ![]() The major glycoproteins of the egg coat responsible, are known as sperm-binding proteins. Also allows correct embryo development and size. The thick membrane of the zona pellucida functions to only allow species-specific fertilization to prevent polyspermy, and enable the acrosome reaction for the successful adhesion and penetration by the sperm cell. In non-mammals it is called the vitelline membrane or vitelline envelope. Its formation, which depends on a conserved Zona pellucida-like (ZP) module that mediates the polymerization of egg coat components, is critical to successful fertilization. The zona pellucida is a translucent matrix of cross-linked glycoprotein filaments that surrounds the mammalian oocyte and is 6.5–20 μm thick depending on the species. The zona pellucida is essential for oocyte growth and fertilization. In humans, five days after the fertilization, the blastocyst performs zona hatching the zona pellucida degenerates and decomposes, to be replaced by the underlying layer of trophoblastic cells. The exact characterisation of what occurs in other species has become more complicated as further zona proteins have been identified. ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle. In the mouse (the best characterised mammalian system), the zona glycoprotein, ZP3, is responsible for sperm binding, adhering to proteins on the sperm plasma membrane. This structure binds spermatozoa, and is required to initiate the acrosome reaction. The corona is composed of cells that care for the egg when it is emitted from the ovary. The zona pellucida is surrounded by the corona radiata. It is secreted by both the oocyte and the ovarian follicles. The zona pellucida first appears in unilaminar primary oocytes. It is a vital constitutive part of the oocyte. The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a specialized extracellular matrix that surrounds the plasma membrane of mammalian oocytes. ![]()
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