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Zona pellucida

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The zona pellucida (Latin meaning "transparent zone") is the specialized area surrounding mammalian oocytes (eggs). It is also known as an egg coat. The zona pellucida is essential for oocyte growth and fertilization.

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

The zona pellucida is an extracellular matrix that surrounds the plasma membrane of the egg cell. It helps protect the egg, and has an essential role in fertilization by sperm. It is surrounded by the corona 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-linked glycoprotein filaments that surrounds the mammalian oocyte and is 6.5–20 μm thick depending on the species. Its formation, which depends on a conserved zona 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 the vitelline membrane or vitelline envelope.[4]

Function

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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. It also allows correct embryo development and size. The major glycoproteins of the egg coat responsible, are known as sperm-binding proteins.[5]

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

There are two key mechanisms of interaction to prevent polyspermy (fertilization of an egg by more than one sperm). The first one is an immediate and transient early block and after a while a permamnent block.

The four major sperm-binding proteins, or sperm-receptors, are ZP1, ZP2, ZP3, and ZP4. They bind to capacitated spermatozoa and induce the acrosome reaction. Successful fertilization depends on the ability of sperm to penetrate the extracellular matrix of the zona pellucida that surrounds the egg.[citation needed]

  • ZP3 allows species-specific[citation needed] sperm binding. It's sufficient and necessary for sperm-binding in mice in vitro,[8] but is insufficient for fertilization in vivo.[9] It promotes the acrosome reaction in human sperm.[10]
  • ZP2 selectively activates sperm of the correct species, and it also appears necessary for sperm binding in vivo, for both humans and mice. In addition, it's cleaved by ovastacin post-fertilization, which turns the ZP into a form that prevents further sperm binding.[9]
  • ZP1 cross-links ZP2 and ZP3 to form the ZP filaments.[11] It promotes the acrosome reaction in human sperm. Notably, it is absent in pigs, cows, and dogs.[10]
  • ZP4 is absent in mice. It promotes the acrosome reaction in human sperm.[10]

In humans, five days after fertilization, the blastocyst performs zona hatching; the zona pellucida degenerates and decomposes, to be replaced by the underlying layer of trophoblastic cells.[citation needed]

Immunocontraception

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Main article: Immunocontraception

ZP module-containing glycoproteins ZP1, ZP2, ZP3 and ZP4 are targets for immunocontraception in mammals.[citation needed]

In non-mammals, the zona pellucida is called the vitelline membrane or envelope, and the vitelline envelope in insects, and plays an important role in preventing cross-breeding of different species, especially in species such as fish that 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 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.[12]

Additional images

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  • First stages of segmentation of a mammalian ovum
    First stages of segmentation of a mammalian ovum
  • 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 of human embryogenesis

References

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  1. ^ Gilbert, Scott (2013). Developmental Biology. Sinauer Associates Inc. p. 123. ISBN 9781605351926.
  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. PMID 12021773. S2CID 11575790.
  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. PMID 22298023. S2CID 16174953.
  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. PMID 21715714.
  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. PMID 19850354.
  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. PMID 12968942.
  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. PMID 15760956.
  8. ^ Litscher, E. S.; Williams, Z.; Wassarman, P. M. (2009). "Zona pellucida glycoprotein ZP3 and fertilization in mammals". Molecular Reproduction and Development. 76 (10): 933–941. doi:10.1002/mrd.21046. PMID 19504560. S2CID 21186053.
  9. ^ a b Avella MA, Baibakov B, Dean J (2014). "A single domain of the ZP2 zona pellucida protein mediates gamete recognition in mice and humans". J Cell Biol. 205 (6): 801–809. doi:10.1083/jcb.201404025. PMC 4068139. PMID 24934154. Female mice that form a zona pellucida lacking ZP2 are sterile
  10. ^ a b c Gupta, SK; Bhandari, B (January 2011). "Acrosome reaction: relevance of zona pellucida glycoproteins". Asian Journal of Andrology. 13 (1): 97–105. doi:10.1038/aja.2010.72. PMC 3739397. PMID 21042299.
  11. ^ Familiari, G; Relucenti, M; Heyn, R; Micara, G; Correr, S (June 2006). "Three-dimensional structure of the zona pellucida at ovulation". Microscopy Research and Technique. 69 (6): 415–26. doi:10.1002/jemt.20301. PMID 16703610.
  12. ^ "Community-Based Deer Management". New Jersey Department of Environmental Protection. 24 September 2014. Retrieved 8 July 2015.

Further reading

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