Alternative titles; symbols
HGNC Approved Gene Symbol: ZP2
Cytogenetic location: 16p12.3-p12.2 Genomic coordinates (GRCh38) : 16:21,197,450-21,214,510 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 16p12.3-p12.2 | Oocyte/zygote/embryo maturation arrest 6 | 618353 | Autosomal recessive | 3 |
Liang et al. (1990) determined that the mouse Zp2 gene is transcribed and processed into a 2,201-nucleotide mRNA with very short 5-prime (30 nucleotide) and 3-prime (32 nucleotide) untranslated regions. Human ZP2 mRNA has a single open reading frame initiated at an ATG that encodes a polypeptide of 713 amino acids with a molecular weight of 80,217 daltons. The first 34 amino acids represent a signal peptide that directs secretion; following cleavage, the resultant core polypeptide is incorporated into the extracellular matrix. The ZP2 amino acid sequence contains 7 potential N-linked glycosylation sites (asn-X-ser/thr) and more than 100 potential O-linked glycosylation sites.
Liang et al. (1990) demonstrated that the mouse Zp2 gene contains 18 exons that range in size from 45 to 190 bp. The gene spans 12.1 kb of DNA.
Gross (2014) mapped the ZP2 gene to chromosome 16p12.2 based on an alignment of the ZP2 sequence (GenBank BC096304) with the genomic sequence (GRCh37).
At fertilization, mouse sperm binds to the zona pellucida, which consists of glycoproteins ZP1 (195000), ZP2, and ZP3 (182889), that surrounds eggs. A ZP2 cleavage model of gamete recognition requires intact ZP2, and a glycan release model postulates that zona glycans are ligands for sperm. Gahlay et al. (2010) tested these 2 models by replacing endogenous protein with ZP2 that cannot be cleaved (Zp2-Mut) or with ZP3 lacking implicated O-glycans (Zp3-Mut). Sperm bound to 2-cell Zp2-Mut embryos despite fertilization and cortical granule exocytosis. Contrary to prediction, sperm fertilized Zp3-Mut eggs. Sperm at the surface of the zona pellucida remained acrosome-intact for more than 2 hours and were displaced by additional sperm. Gahlay et al. (2010) concluded that sperm-egg recognition depends on the cleavage status of ZP2 and that binding at the surface of the zona is not sufficient to induce sperm acrosome exocytosis.
In 2 Chinese sisters and an unrelated woman with primary infertility due to an oocyte maturation defect of the zona pellucida (OZEMA6; 618353), Dai et al. (2019) identified homozygosity for a splice site mutation (182888.0001) and a 4-bp duplication (182888.0002) in the ZP2 gene, respectively. The mutations segregated fully with disease in each family, and neither was found in population-matched controls or in public variant databases. A fertile male in the second family was also homozygous for the ZP2 duplication, indicating that loss of ZP2 does not affect male fertility.
In 2 Chinese sisters with primary infertility due to very thin or absent oocyte zona pellucida, Zhou et al. (2019) identified homozygosity for a missense mutation in the ZP2 gene (C372S; 182888.0003).
Liu et al. (2017) generated mice with a truncated Zp2 protein and observed that fully grown oocytes from heterozygous female mice were surrounded by a zona pellucida (ZP) that was approximately one-half the thickness of the ZP in wildtype females. These heterozygous mutant females were as fertile as wildtype females; however, homozygous Zp2 -/- females were sterile, with oocytes completely lacking a ZP.
ZP2 has been implicated as a secondary sperm receptor that binds sperm only after the induction of the sperm acrosome reaction. Immediately after fertilization, there are 2 major changes that prevent polyspermy: a rapid electrical depolarization of the egg plasma membrane that blocks additional sperm in the perivitelline space from fusing with the egg, and biochemical modifications of the zona pellucida. Both ZP2 and ZP3 are modified by the zona reaction: ZP2 undergoes a proteolytic cleavage and ZP3 loses its ability to induce the acrosome reaction and its sperm receptor activity (summary by Dean, 1992).
In 2 Chinese sisters (family 1, II-3 and II-4) with primary infertility due to a defective oocyte zona pellucida (OZEMA6; 618353), Dai et al. (2019) identified homozygosity for a c.1695-2A-G transition (c.1695-2A-G, NM_003460.2) in intron 15 of the ZP2 gene. Their first-cousin parents and a fertile sister were heterozygous for the mutation, which was not found in 100 population-matched controls or in the Exome Variant Server, 1000 Genomes Project, or ExAC databases. Analysis of ZP2 cDNA from patient oocytes showed that the mutation causes skipping of exons 16 and 17, resulting in a frameshift and a premature termination codon (Cys566HisfsTer5), with loss of a C-terminal ZP-C subdomain, a consensus furin cleavage site, an external hydrophobic patch, and a transmembrane domain. Immunoblot data from transfected CHO cells confirmed a decrease of approximately 20 kD for mutant ZP2 compared to wildtype. Immunofluorescence staining of patient oocytes showed complete absence of ZP2 in the zona pellucida, whereas cytoplasmic staining of ZP2 was stronger than in control oocytes, suggesting that ZP2 was intracellularly sequestrated.
In a 32-year-old Chinese woman (family 2, II-1) with primary infertility due to a defective oocyte zona pellucida (OZEMA6; 618353), Dai et al. (2019) identified homozygosity for a 4-bp duplication (c.1691_1694dupATGG, NM_003460.2) in exon 15 of the ZP2 gene, predicted to cause a frameshift resulting in a premature termination codon (Cys566TrpfsTer5), with loss of a C-terminal ZP-C subdomain, a consensus furin cleavage site, an external hydrophobic patch, and a transmembrane domain. Immunoblot data from transfected CHO cells confirmed a decrease of approximately 20 kD for the mutant ZP2 compared to wildtype. The patient's first-cousin parents were heterozygous for the duplication, which was not found in 100 population-matched controls or in the Exome Variant Server, 1000 Genomes Project, or ExAC databases. A fertile brother was also homozygous for the duplication, indicating that loss of ZP2 does not affected male fertility. Immunofluorescence staining of patient oocytes showed complete absence of ZP2 in the zona pellucida, whereas cytoplasmic staining of ZP2 was stronger than in control oocytes, suggesting that ZP2 was intracellularly sequestrated. These findings were confirmed by confocal fluorescence microscopy and flow cytometry in transfected CHO cells. The authors observed that although wildtype ZP2 appeared to traffic independently of other ZP proteins, mutant ZP2 colocalized with the other ZP proteins and appeared to cause their partial retention as well.
In 2 Chinese sisters (family 5) with primary infertility due to very thin or absent oocyte zona pellucida (OZEMA6; 618353), Zhou et al. (2019) identified homozygosity for a c.1115G-C transversion (chr16:21,213,597) in exon 12 of the ZP2 gene, resulting in a cys372-to-ser (C372S) substitution at a conserved residue within the ZP domain. Their fertile sister was heterozygous for the mutation; DNA was unavailable from their unaffected consanguineous parents. Analysis of transfected CHO cells showed that C372S was not secreted into cell culture media, suggesting possible secretory obstruction and subsequent failed assembly of the zona pellucida in vivo.
Dai, C., Hu, L., Gong, F., Tan, Y., Cai, S., Zhang, S., Dai, J., Lu, C., Chen, J., Chen, Y., Lu, G., Du, J., Lin, G. ZP2 pathogenic variants cause in vitro fertilization failure and female infertility. Genet. Med. 21: 431-440, 2019. [PubMed: 29895852] [Full Text: https://doi.org/10.1038/s41436-018-0064-y]
Dean, J. Biology of mammalian fertilization: role of the zona pellucida. J. Clin. Invest. 89: 1055-1059, 1992. [PubMed: 1556174] [Full Text: https://doi.org/10.1172/JCI115684]
Gahlay, G., Gauthier, L., Baibakov, B., Epifano, O., Dean, J. Gamete recognition in mice depends on the cleavage status of an egg's zona pellucida protein. Science 329: 216-219, 2010. [PubMed: 20616279] [Full Text: https://doi.org/10.1126/science.1188178]
Gross, M. B. Personal Communication. Baltimore, Md. 6/24/2014.
Liang, L.-F., Chamow, S. M., Dean, J. Oocyte-specific expression of mouse Zp-2: developmental regulation of the zona pellucida genes. Molec. Cell. Biol. 10: 1507-1515, 1990. [PubMed: 1690843] [Full Text: https://doi.org/10.1128/mcb.10.4.1507-1515.1990]
Liu, W., Li, K., Bai, D., Yin, J., Tang, Y., Chi, F., Zhang, L., Wang, Y., Pan, J., Liang, S., Guo, Y., Ruan, J., Kou, X., Zhao, Y., Wang, H., Chen, J., Teng, X., Gao, S. Dosage effects of ZP2 and ZP3 heterozygous mutations cause human infertility. Hum. Genet. 136: 975-985, 2017. [PubMed: 28646452] [Full Text: https://doi.org/10.1007/s00439-017-1822-7]
Zhou, Z., Ni, C., Wu, L., Chen, B., Xu, Y., Zhang, Z., Mu, J., Li, B., Yan, Z., Fu, J., Wang, W., Zhao, L., Dong, J., Sun, X., Kuang, Y., Sang, Q., Wang, L. Novel mutations in ZP1, ZP2, and ZP3 cause female infertility due to abnormal zona pellucida formation. Hum. Genet. 138: 327-337, 2019. [PubMed: 30810869] [Full Text: https://doi.org/10.1007/s00439-019-01990-1]