Zona pellucida

Zona pellucida
Human ovum: The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata.
Identifiers
MeSH	A05.360.490.690.950
Dorlands /Elsevier	z_01/12869767
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terminology [[[d:|edit on Wikidata]]]

The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. The zona pellucida first appears in unilaminar primary oocytes. It is secreted by both the oocyte and the follicular cells. The zona pellucida is surrounded by the cumulus oophorus. The cumulus is composed of cells that care for the egg when it is emitted from the ovary.

This structure binds spermatozoa, and is required to initiate the acrosome reaction. 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 (GalT). ZP3 is then involved in the induction of the acrosome reaction, whereby a spermatozoon releases the contents of the acrosomal vesicle. The exact characterisation of what occurs in other species has become more complicated as further zona proteins have been identified.

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 zona pellucida is essential for oocyte death and fertilization.

In some older texts, it has also been called zona striata and stratum lucidum (not to be confused with the stratum lucidum of the skin).

Immunocontraception

Glycoproteins in ZP1, 2, 3 and 4 are targets for immunocontraception in mammals.

In non-mammalian animals, the zona pellucida (called vitelline layer) plays an important role in preventing cross-breeding of different species, especially in species that fertilize outside of the body (e.g. fish).

The zona pellucida is commonly used to control wildlife population problems by immunocontraception. When the zona pellucida of one animal species is injected into the bloodstream of another, it results in sterility of the second species due to immune response. This effect can be temporary or permanent, depending on the method used. In New Jersey, immunocontraception using porcine zona pellucida has been trialled for the control of deer populations, for example using the products "SpayVac" and "GonaCon".

Zona pellucida glycoproteins

There are four major zona pellucida glycoproteins, termed ZP1-4. ZP1, ZP3 and ZP4 bind to capacitated spermatozoa and induce the acrosome reaction. Successful fertilization depends on the ability of sperm to penetrate the extracellular matrix that surrounds the egg. In the mouse:

• ZP3 allows species-specific sperm binding
• ZP2 mediates subsequent sperm binding
• ZP1 cross-links ZP2 and ZP3.

Data with native human protein are not currently available.

Additional images

• 

  First stages of segmentation of a mammalian ovum

• 

  Section of vesicular ovarian follicle of cat, x 50

• 

  The initial stages of human embryogenesis

See also

• Maternal influence on sex determination

Further reading

• Bagnell C (2005). "Animal Reproduction". Rutgers University Department of Animal Sciences.

External links

• Histology image: 18404loa – Histology Learning System at Boston University - "Female Reproductive System: ovary, cumulus oophorus "
• Histology image: 14805loa – Histology Learning System at Boston University - "Female Reproductive System: ovary, multilaminar primary follicle"
• Anatomy photo: Reproductive/mammal/ovary2/ovary7 - Comparative Organology at University of California, Davis - "Mammal, canine ovary (LM, High)"
• Image at um.edu.mt
• Image at um.edu.mt