Zona pellucida

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Oocyte and developing zona pellucida in the ovary
Oocyte and developing zona pellucida in the ovary
Human blastocyst "hatching" from the zona pellucida
Human blastocyst "hatching" from the zona pellucida (week 1 Carnegie stage 3)

(Latin, zona pellucida = transparent zone) The zona pellucida (ZP) is a specialized extracellular matrix surrounding the developing oocyte (egg, ovum) within each follicle within the ovary. This thick matrix is thought to be formed by secretions from the oocyte and the follicle granulosa cells and in human oocytes consists of four types of zona pellucida glycoproteins ZP1, ZP2, ZP3 and ZP4 which have different roles in fertilization. Note that mice also have 4 ZP genes, but multiple stop and missense codons in ZP4 means that only three are produced. Polymers of ZP2 and ZP3 organized into extended filaments that are cross-linked by ZP1 homodimers.

Note that depending upon species and type of study, the zona pellucida can also be called the: oolemma, egg coat or vitelline membrane.

The zona pellucid has many different roles including in oocyte development, protection during growth and transport, fertilization, spermatozoa binding, preventing polyspermy, blastocyst development, and preventing premature implantation (ectopic pregnancy).

Human oocyte 11.jpg Early zygote.jpg
Human oocyte contained inside zona pellucida.[1] Early zygote inside zona pellucida

In human development, during the first week of development following fertilization the zona pellucida remains surrounding the blastocyst from which it "hatches" to commence implantation.

Fertilization Links: Fertilization | Oocyte | Spermatozoa | Cell Division - Meiosis | Zona pellucida | Zygote | Lecture - Fertilization | Cell Division - Mitosis | Lecture - Week 1 and 2 | Hydatidiform Mole | Assisted Reproductive Technology | Lecture - Genital Development

Some Recent Findings

Human zygote inside the zone pellucida
Mouse germinal vesicle
Mouse germinal vesicle[2]
  • A single domain of the ZP2 zona pellucida protein mediates gamete recognition in mice and humans[3] "The extracellular zona pellucida surrounds ovulated eggs and mediates gamete recognition that is essential for mammalian fertilization. Zonae matrices contain three (mouse) or four (human) glycoproteins (ZP1-4), but which protein binds sperm remains controversial. ...These observations in transgenic mice document that the ZP2(51-149) sperm-binding domain is necessary for human and mouse gamete recognition and penetration through the zona pellucida."
  • Biosynthesis of hamster zona pellucida is restricted to the oocyte[4] "In the present work, the expression of ZP1, ZP2, ZP3 and ZP4 is carefully analyzed by in situ hybridization (ISH) in hamster ovaries. Our data suggest that the four hamster ZP genes are expressed in a coordinate and oocyte-specific manner during folliculogenesis. Furthermore, this expression is maximal during the first stages of the oocyte development and declines in oocytes from later development stages, particularly within large antral follicles."
  • Zona pellucida birefringence in in vivo and in vitro matured oocytes[5]
  • Zona pellucida glycoprotein-1 binds to spermatozoa and induces acrosomal exocytosis[6] "These studies revealed for the first time that in humans ZP1, in addition to ZP3 and ZP4, binds to capacitated spermatozoa and induces acrosomal exocytosis."
More recent papers
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This table shows an automated computer PubMed search using the listed sub-heading term.
  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
  • References appear in this list based upon the date of the actual page viewing.

References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches

Search term: Zona pellucida Development

Juan Li, Alejandra I Olvera, Omar S Akbari, Annie Moradian, Michael J Sweredoski, Sonja Hess, Bruce A Hay Vectored antibody gene delivery mediates long-term contraception. Curr. Biol.: 2015, 25(19);R820-R822 PubMed 26439332

Rong Li, Ying Liu, Hanne Skovsgaard Pedersen, Henrik Callesen Cytoplasmic membrane activities during first cleavage of zona-free porcine embryos: description and consequences. Reprod. Fertil. Dev.: 2015; PubMed 26391407

Julian Marcos, Sonia Pérez-Albalá, Amparo Mifsud, Marta Molla, Jose Landeras, Marcos Meseguer Collapse of blastocysts is strongly related to lower implantation success: a time-lapse study. Hum. Reprod.: 2015; PubMed 26355116

Bing He, Cheng Junping, Huang Li, Tan Weihong, Xue Lintao, Wang Shikai Effects of human menopausal gonadotropin on zona pellucida and pregnancy outcomes of ovarian stimulation protocols. Iran J Reprod Med: 2015, 13(6);337-44 PubMed 26330847

Jin Young Joo, Jonghwan Lee, Hae Young Ko, Yong Seung Lee, Hyejung Heo, Ha-Na Gu, Sujeong Cho, Soonhag Kim VisuFect-mediated siRNA delivery into zygotes. Colloids Surf B Biointerfaces: 2015, 135;646-651 PubMed 26322479

Three-dimensional Structure

Mouse zona pellucida[7]

Electron microscopic studies have shown a variety of appearances from a porous, net-like structure to a nearly smooth and compact structure.

An scanning electron microscopic review[7] of both human and mouse zona pellucida structures at ovulation show:

  • spongy ZP appearance well correlates with mature oocytes.
  • a delicate meshwork of thin interconnected filaments
  • a regular alternating pattern of wide and tight meshes.
  • wide meshes correspond to "pores" of the "spongy" ZP.
    • tight meshes correspond to the compact parts of the ZP surrounding the pores.

Human Zona Pellucida

An immunochemistry study[8] of human ZP proteins expression during folliculogenesis within the ovary primordial follicle identified the presence of ZP1 and ZP3 in most follicles (93% and 95%, respectively), with ZP2 only in 32% of these follicles. The ZP proteins were also detected in the cytoplasm of cuboidal granulosa cells. This localization suggested to the authors that these proteins had been present since oogenesis.

Mouse Zona Pellucida

Mouse zona pellucida

Mouse zona pellucida development.[7]

In the mouse ovarian oocytes, and not granulosa cells, are the only source for mouse ZP glycoproteins.[9]

Zona Pellucida Glycoprotein Features

Human oocyte contained inside zona pellucida
Human oocyte contained inside zona pellucida.[1]
  1. A "ZP domain", which is a signature domain comprised of approximately 260 amino acid (aa) residues.
  2. An N-terminal hydrophobic signal peptide sequence.
  3. A potential N- and O-linked glycosylation sites.
  4. A C-terminal hydrophobic transmembrane-like domain (TMD)
  5. A potential consensus proprotein convertase (furin) cleavage site (CFCS) upstream of transmembrane-like domain (TMD).

Zona Pellucida glycoprotein 1

(ZP1) A 638 amino acid glycoprotein located in the zona pellucida, synthesized by and surrounding the oocyte.

Links: OMIM - ZP1

Zona Pellucida glycoprotein 2

Model of gamete recognition zona pellucida
=Model of gamete recognition zona pellucida[10]

(ZP2) A 745 amino acid glycoprotein located in the zona pellucida, synthesized by and surrounding the oocyte. The protein acts as a secondary sperm receptor that binds sperm only after the induction of the sperm acrosome reaction. Before fertilization ZP2 binds spermatozoa. After fertilization ZP2 is proteolytically cleaved as an initial block to polyspermy.

Links: OMIM - ZP2

Zona Pellucida glycoprotein 3

(ZP3) A 424 amino acid glycoprotein located in the zona pellucida, synthesized by and surrounding the oocyte required for initial zona matrix formation and during fertilization for species-specific sperm binding. Now thought to exist in 2 isoforms ZP3A and ZP3B (a second polymorphic allele).

Links: OMIM - ZP3

Zona Pellucida glycoprotein 4

(ZP4) A 540 amino acid glycoprotein located in the zona pellucida, synthesized by and surrounding the oocyte required for initial zona matrix formation and along with ZP3 during fertilization for inducing the acrosome reaction and inhibited the binding of spermatozoa to zona pellucida in a time- and dose-dependent reaction. Associated with several mammalian species (human, rat, hamster and rabbit) but not all mammalian species.

Links: OMIM - ZP4

Zona Pellucida Binding Protein

(ZPBP) Not a zona pellucida protein, but a spermatozoa protein found located on the acrosome surface and one of several proteins that participate in secondary binding between acrosome-reacted sperm and the zona pellucida.

Links: OMIM - ZPBP

Zona Pellucida Birefringence

(ZPB) Optical property of the zona pellucida using polarization imaging when viewed microscopically. This property has been used to qualitatively predict the developmental potential of a in vitro matured metaphase-II (MII) oocytes.

High birefringence, compared to low, has been associated with oocytes contributing to conception cycles when compared with those of nonconception cycles and higher implantation, pregnancy, and live birth rates from transferred oocytes.[11][5] This work follows on from the earlier discovery of an increased birefringence in the meiotic spindle an early indicator of oocyte activation[12]

Oocyte zona birefringence intensity is associated with embryonic implantation potential in ICSI cycles[11]

"Using zona birefringence as the only selection criterion, two fertilized oocytes, preferably derived from high birefringence (HZB) oocytes, were selected for further culture and transfer. The required criteria were met by 135 ICSI cycles (124 patients; 34.9 ± 4.1 years of age). Embryos for transfer were used in 20 cycles derived from HZB/HZB oocytes, in 50 cycles from HZB/LZB oocytes and in 65 from LZB/LZB oocytes. The corresponding implantation (P < 0.025), pregnancy (P < 0.005) and live birth (P < 0.025) rates were significantly different between HZB/HZB and HZB/LZB versus LZB/LZB group. Embryo development was superior in embryos derived from HZB oocytes."

Zona pellucida birefringence in in vivo and in vitro matured oocytes[5]

The percentage of high birefringence oocytes was higher in immature than in mature oocytes (40.1 vs. 23.6%). Among immature oocytes, an increased percentage of HB in prophase-I stage oocytes compared to metaphase I stage oocytes was also observed (50.7 vs. 25.0%). However, the percentage of HB oocytes did not change when comparing oocytes before and after in vitro maturation for both prophase I and metaphase I oocytes. No influence of ZPB was observed on the spontaneous in vitro maturation potential. Exclusively for metaphase II retrieved oocytes, a positive influence of ZPB on fertilization (odds ratio [OR], 1.78; 95% confidence interval [CI], 1.27-2.49) and embryo quality (OR, 2.28; 95% CI, 1.04-4.99) was noted.

Birefringence - Defined as the double refraction of light in a transparent, molecularly ordered material, which is manifested by the existence of orientation-dependent differences in refractive index.

Links: Olympus - Optical Birefringence


  • acrosome reaction - The chemical change within the spermatozoa following binding to the zona pellucida, that leads to the release of acrosomal enzymatic contents. These enzymes degrade the zona pellucida and allow a spermatozoa to penetrate an oocyte.
  • granulosa cell - A specific cell type that proliferates in association with the oocyte within the developing follicles of the ovary. These cells form the follicle stratum granulosa and are also given specific names based upon their position within the follicle. In the antral follicle, membrana granulosa sits on the follicular basal lamina and lines the antrum as a stratified epithelium. The cumulus oophorus is a column of granulosa cells that attaches the oocyte to the follicle wall. The corona radiata are the granulosa cells that directly surround the oocyte, and are released along with it at ovulation. Following ovulation the corona radiata provide physical protection to the oocyte and granulosa cells within the ovulating follicle contribute to corpus luteum.


  1. 1.0 1.1 Wei Shi, Bo Xu, Li-Min Wu, Ren-Tao Jin, Hong-Bing Luan, Li-Hua Luo, Qing Zhu, Lars Johansson, Yu-Sheng Liu, Xian-Hong Tong Oocytes with a dark zona pellucida demonstrate lower fertilization, implantation and clinical pregnancy rates in IVF/ICSI cycles. PLoS ONE: 2014, 9(2);e89409 PubMed 24586757 | PMC3933533 | PLoS One
  2. Hong-Xia Zhou, Yu-Zhen Ma, Ying-Lei Liu, Ying Chen, Cheng-Jie Zhou, Sha-Na Wu, Jiang-Peng Shen, Cheng-Guang Liang Assessment of mouse germinal vesicle stage oocyte quality by evaluating the cumulus layer, zona pellucida, and perivitelline space. PLoS ONE: 2014, 9(8);e105812 PubMed 25144310 | PLoS One.
  3. M J Izquierdo-Rico, L Gimeno, C Jiménez-Cervantes, J Ballesta, M Avilés Biosynthesis of hamster zona pellucida is restricted to the oocyte. Theriogenology: 2011, 75(3);463-72 PubMed 21074836
  4. M J Izquierdo-Rico, L Gimeno, C Jiménez-Cervantes, J Ballesta, M Avilés Biosynthesis of hamster zona pellucida is restricted to the oocyte. Theriogenology: 2011, 75(3);463-72 PubMed 21074836
  5. 5.0 5.1 5.2 Daniela Paes de Almeida Ferreira Braga, Rita de Cássia Savio Figueira, Priscila Queiroz, Camila Madaschi, Assumpto Iaconelli, Edson Borges Zona pellucida birefringence in in vivo and in vitro matured oocytes. Fertil. Steril.: 2010, 94(6);2050-3 PubMed 20079896
  6. Anasua Ganguly, Antonin Bukovsky, Raj K Sharma, Pankaj Bansal, Beena Bhandari, Satish K Gupta In humans, zona pellucida glycoprotein-1 binds to spermatozoa and induces acrosomal exocytosis. Hum. Reprod.: 2010, 25(7);1643-56 PubMed 20504872
  7. 7.0 7.1 7.2 Giuseppe Familiari, Michela Relucenti, Rosemarie Heyn, Giulietta Micara, Silvia Correr Three-dimensional structure of the zona pellucida at ovulation. Microsc. Res. Tech.: 2006, 69(6);415-26 PubMed 16703610
  8. Debra A Gook, D H Edgar, J Borg, M Martic Detection of zona pellucida proteins during human folliculogenesis. Hum. Reprod.: 2008, 23(2);394-402 PubMed 18033806
  9. Majid El-Mestrah, Philip E Castle, Girum Borossa, Frederick W K Kan Subcellular distribution of ZP1, ZP2, and ZP3 glycoproteins during folliculogenesis and demonstration of their topographical disposition within the zona matrix of mouse ovarian oocytes. Biol. Reprod.: 2002, 66(4);866-76 PubMed 11906903
  10. Matteo A Avella, Boris Baibakov, Jurrien Dean A single domain of the ZP2 zona pellucida protein mediates gamete recognition in mice and humans. J. Cell Biol.: 2014, 205(6);801-9 PubMed 24934154
  11. 11.0 11.1 M Montag, T Schimming, M Köster, C Zhou, C Dorn, B Rösing, H van der Ven, K Ven der Ven Oocyte zona birefringence intensity is associated with embryonic implantation potential in ICSI cycles. Reprod. Biomed. Online: 2008, 16(2);239-44 PubMed 18284880
  12. L Liu, J R Trimarchi, R Oldenbourg, D L Keefe Increased birefringence in the meiotic spindle provides a new marker for the onset of activation in living oocytes. Biol. Reprod.: 2000, 63(1);251-8 PubMed 10859266


Paul M Wassarman Zona pellucida glycoproteins. J. Biol. Chem.: 2008, 283(36);24285-9 PubMed 18539589



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Cite this page: Hill, M.A. (2015) Embryology Zona pellucida. Retrieved October 7, 2015, from https://embryology.med.unsw.edu.au/embryology/index.php/Zona_pellucida

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