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Zona pellucida

From Wikipedia, the free encyclopedia

Thezona pellucida(Latin meaning "transparent zone" ) is the specialized area surroundingmammalianoocytes(eggs). It is also known as an egg coat. The zona pellucida is essential for oocyte growth andfertilization.

Zona pellucida
Humanovum:The zona pellucida is seen as a thick clear girdle surrounded by the cells of thecorona radiata.
Identifiers
MeSHD015044
FMA18674
Anatomical terminology

The zona pellucida is anextracellular matrixthat surrounds theplasma membraneof the egg cell. It helps protect the egg, and has an essential role in fertilization by sperm. It is surrounded by thecorona radiata.The corona is composed of cells that care for the egg when it is emitted from the ovary.[1]

Structure

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The zona pellucida is a translucent matrix of cross-linkedglycoproteinfilaments that surrounds the mammalianoocyteand is 6.5–20 μm thick depending on the species. Its formation, which depends on a conservedzona pellucida-like(ZP) module that mediates the polymerization of egg coat components,[2]is critical to successful fertilization.[3]In non-mammals, it is called thevitelline membraneor vitelline envelope.[4]

Function

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The thick membrane of the zona pellucida functions to only allow species-specific fertilization; to preventpolyspermy,and enable theacrosome reactionfor the successful adhesion and penetration by thesperm cell.It also allows correctembryo developmentand size. The major glycoproteins of the egg coat responsible, are known assperm-binding proteins.[5]

The zona pellucida bindsspermatozoa,and is required to initiate theacrosome reaction.In mice, the zona glycoprotein (ZP3) is responsible for sperm binding, adhering toproteinson the sperm plasma membrane. During the acrosome reaction, a sperm cell releases the DNA contained in theacrosomal vesicleinto the egg. In other species, the process is slightly different and more complicated. Several more zona proteins have been identified.[6][7]

The four major sperm-binding proteins, or sperm-receptors, areZP1,ZP2,ZP3,andZP4.They bind tocapacitated spermatozoaand induce theacrosome reaction.Successfulfertilizationdepends on the ability of sperm to penetrate theextracellular matrixof the zona pellucida that surrounds the egg.[citation needed] In the mouse:

  • ZP3allows species-specific sperm binding
  • ZP2mediates subsequent sperm binding
  • ZP1cross-links ZP2 and ZP3.

In humans, five days after fertilization, theblastocystperformszona hatching;the zona pellucida degenerates and decomposes, to be replaced by the underlying layer oftrophoblasticcells.[citation needed]

Immunocontraception

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Main article:Immunocontraception

ZP module-containing glycoproteinsZP1,ZP2,ZP3andZP4are targets forimmunocontraceptionin mammals.[citation needed]

In non-mammals, the zona pellucida is called thevitelline membraneor envelope, and thevitelline envelopeininsects,and plays an important role in preventing cross-breeding of different species, especially in species such asfishthat fertilize outside of the body.[citation needed]

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 toimmune response.This effect can be temporary or permanent, depending on the method used. InNew Jersey,immunocontraception usingporcine zona pellucidahas been trialled for the control ofdeer.[8]

Additional images

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  • First stages of segmentation of a mammalian ovum
    First stages of segmentation of a mammalianovum
  • Section of vesicular ovarian follicle of a cat, x 50
    Section of vesicular ovarian follicle of a cat, x 50
  • The initial stages of human embryogenesis
    The initial stages ofhuman embryogenesis

References

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  1. ^Gilbert, Scott (2013).Developmental Biology.Sinauer Associates Inc. p. 123.ISBN9781605351926.
  2. ^Jovine L, Qi H, Williams Z, Litscher E, de Sanctis D, Wassarman PM (2002). "The ZP domain is a conserved module for polymerization of extracellular proteins".Nat. Cell Biol.4(6): 457–461.doi:10.1038/ncb802.PMID12021773.S2CID11575790.
  3. ^Gupta, SK; et al. (September 2012). "Mammalian zona pellucida glycoproteins: structure and function during fertilization".Cell and Tissue Research.349(3): 665–78.doi:10.1007/s00441-011-1319-y.PMID22298023.S2CID16174953.
  4. ^Monné, M; Jovine, L (October 2011)."A structural view of egg coat architecture and function in fertilization".Biology of Reproduction.85(4): 661–9.doi:10.1095/biolreprod.111.092098.hdl:11563/21648.PMID21715714.
  5. ^Gupta, SK; Bansal, P; Ganguly, A; Bhandari, B; Chakrabarti, K (December 2009)."Human zona pellucida glycoproteins: functional relevance during fertilization".Journal of Reproductive Immunology.83(1–2): 50–5.doi:10.1016/j.jri.2009.07.008.PMID19850354.
  6. ^Conner, SJ; Hughes, DC (2003)."Analysis of fish ZP1/ZPB homologous genes--evidence for both genome duplication and species-specific amplification models of evolution".Reproduction.126(3): 347–52.doi:10.1530/rep.0.1260347.PMID12968942.
  7. ^Conner, S.J.; Lefièvre, L; Hughes, DC; Barratt, CL (2005)."Cracking the egg: Increased complexity in the zona pellucida".Human Reproduction.20(5): 1148–52.doi:10.1093/humrep/deh835.PMID15760956.
  8. ^"Community-Based Deer Management".New Jersey Department of Environmental Protection. 24 September 2014.Retrieved8 July2015.

Further reading

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