Zona pellucida

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]

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]

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]}

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]

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

• Bork, Peer; Sander, Chris (1992). "A large domain common to sperm receptors (Zp2 and Zp3) and TGF-β type III receptor". FEBS Letters. 300 (3): 237–40. doi:10.1016/0014-5793(92)80853-9. PMID 1313375.
• Oehninger, Sergio (2003). "Biochemical and functional characterization of the human zona pellucida". Reproductive BioMedicine Online. 7 (6): 641–8. doi:10.1016/S1472-6483(10)62086-X. PMID 14748962.
• Boja, E. S.; Hoodbhoy, T; Fales, HM; Dean, J (2003). "Structural Characterization of Native Mouse Zona Pellucida Proteins Using Mass Spectrometry". Journal of Biological Chemistry. 278 (36): 34189–202. doi:10.1074/jbc.M304026200. PMID 12799386.
• Bagnell C (2005). "Animal Reproduction". Rutgers University Department of Animal Sciences.^{[verification needed]}
• Jovine, Luca; Darie, Costel C.; Litscher, Eveline S.; Wassarman, Paul M. (2005). "Zona Pellucida Domain Proteins". Annual Review of Biochemistry. 74: 83–114. doi:10.1146/annurev.biochem.74.082803.133039. PMID 15952882.
• Monné, Magnus; Han, Ling; Jovine, Luca (2006). "Tracking Down the ZP Domain: From the Mammalian Zona Pellucida to the Molluscan Vitelline Envelope". Seminars in Reproductive Medicine. 24 (4): 204–16. doi:10.1055/s-2006-948550. hdl:11563/8929. PMID 16944418.
• Wassarman, P. M. (2008). "Zona Pellucida Glycoproteins". Journal of Biological Chemistry. 283 (36): 24285–9. doi:10.1074/jbc.R800027200. PMC 2528931. PMID 18539589.
• Wassarman, Paul M.; Litscher, Eveline S. (2008). "Mammalian fertilization:the eggs multifunctional zona pellucida". The International Journal of Developmental Biology. 52 (5–6): 665–76. doi:10.1387/ijdb.072524pw. PMID 18649280.
• Monné, Magnus; Han, Ling; Schwend, Thomas; Burendahl, Sofia; Jovine, Luca (2008). "Crystal structure of the ZP-N domain of ZP3 reveals the core fold of animal egg coats". Nature. 456 (7222): 653–7. Bibcode:2008Natur.456..653M. doi:10.1038/nature07599. hdl:11563/8930. PMID 19052627. S2CID 4430083.
• Han, Ling; Monné, Magnus; Okumura, Hiroki; Schwend, Thomas; Cherry, Amy L.; Flot, David; Matsuda, Tsukasa; Jovine, Luca (2010). "Insights into Egg Coat Assembly and Egg-Sperm Interaction from the X-Ray Structure of Full-Length ZP3". Cell. 143 (3): 404–15. doi:10.1016/j.cell.2010.09.041. hdl:11563/8931. PMID 20970175. S2CID 18583237.

• 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