ZPBP2

ZPBP2 functions both as an acrosomal structural protein essential for spermiogenesis and as a cis-regulatory locus that controls chromatin architecture and gene expression at the 17q21 asthma-susceptibility region. In the testis, ZPBP2 is required for proper acrosome biogenesis and sperm morphogenesis; Zpbp2-null male mice are subfertile with dysmorphic sperm and impaired zona pellucida penetration, and ZPBP2 interacts with the serine protease PRSS54 within the acrosomal granule (PMID:17664285, PMID:35863763). In immune and airway cells, disease-associated SNPs within ZPBP2 alter CTCF binding and chromatin looping, placing distal cis-regulatory elements in contact with the ORMDL3 promoter in CD4+ T cells and modulating domain-wide expression of ORMDL3 and GSDMB in an allele-, sex-, and methylation-dependent manner (PMID:27848966, PMID:19732864, PMID:23546690). Zpbp2 deletion in mice attenuates airway hyperresponsiveness in a sex-specific fashion and alters lung sphingolipid/ceramide profiles, establishing a functional link between the ZPBP2-ORMDL3 regulatory axis and asthma-related phenotypes (PMID:29536159, PMID:32273303).

1. 2007 High

   Establishing that ZPBP2 is not merely a zona-binding accessory protein but an essential structural factor for acrosome biogenesis resolved the gene's primary reproductive function and explained male subfertility when it is absent.

   Evidence Targeted Zpbp2 knockout in mice with ultrastructural electron microscopy, fertility assays, and zona penetration tests

   PMID:17664285

   Open questions at the time

   • Molecular mechanism by which ZPBP2 organizes acrosomal membranes is unknown
   • Whether ZPBP2 structural role requires enzymatic activity or is purely scaffolding is unresolved
2. 2009 High

   Demonstrating that asthma-associated SNPs within ZPBP2 alter nucleosome positioning and CTCF binding established that ZPBP2 harbors cis-regulatory elements controlling domain-wide chromatin organization at 17q21, connecting a testis gene to immune disease genetics.

   Evidence High-throughput resequencing, allele-specific nucleosome mapping, CTCF ChIP, luciferase reporter assays, and family-based association in three independent cohorts

   PMID:19732864

   Open questions at the time

   • Which cell types are most affected by altered CTCF binding was not resolved
   • Downstream gene targets beyond ORMDL3 were not fully characterized
3. 2011 Medium

   Identification of ZPBP2 on the mature sperm surface within a CCT-containing complex extended its function beyond acrosome biogenesis to a potential role in zona pellucida recognition on ejaculated sperm.

   Evidence Blue native PAGE, mass spectrometry, and antibody inhibition of sperm–zona binding

   PMID:21672535

   Open questions at the time

   • Whether ZPBP2 directly contacts zona glycoproteins or acts through the CCT complex is unresolved
   • No reciprocal interaction validation was performed
4. 2013 Medium

   Showing that DNA methylation at a ZPBP2 intragenic region varies by sex and age, overlapping functional SNPs, revealed an epigenetic layer modifying genetic risk for asthma at this locus.

   Evidence Bisulfite sequencing with sex- and age-stratified genetic association analysis

   PMID:23546690

   Open questions at the time

   • Causal direction between methylation changes and disease risk was not established
   • Cell-type-specific methylation patterns were not resolved
5. 2016 High

   4C-Seq chromatin conformation capture in genotype-stratified primary CD4+ T cells proved that asthma risk alleles at ZPBP2 CTCF sites create a chromatin loop bringing upstream enhancers into contact with the ORMDL3 promoter, providing the direct mechanistic link between ZPBP2 regulatory variation and ORMDL3 overexpression.

   Evidence Allele-specific CTCF ChIP-seq and 4C-Seq in primary human CD4+ T cells stratified by genotype

   PMID:27848966

   Open questions at the time

   • Whether the same loop operates in airway epithelial cells is unknown
   • Contribution of GSDMB upregulation via the same loop was not dissected
6. 2017 Medium

   Pharmacological demethylation of the ZPBP2 promoter upregulated its expression in airway epithelial cells in an allele-differential manner, directly demonstrating epigenetic transcriptional control of ZPBP2 itself.

   Evidence 5-aza-dC treatment of NuLi-1 cells with bisulfite sequencing and allelic expression analysis

   PMID:28241063

   Open questions at the time

   • In vivo relevance of demethylation-induced ZPBP2 upregulation in airway disease is untested
   • Whether ZPBP2 protein is produced in airway cells or only the regulatory element is active remains unclear
7. 2018 Medium

   Zpbp2 knockout mice showed attenuated airway hyperresponsiveness and altered lung ceramide profiles exclusively in females, establishing a sex-specific in vivo link between the ZPBP2 locus and sphingolipid metabolism relevant to asthma.

   Evidence Zpbp2 KO mice, methacholine AHR challenge, lipidomic profiling of sphingolipids and ceramides

   PMID:29536159

   Open questions at the time

   • Whether the AHR phenotype is mediated by ZPBP2 protein loss or by altered ORMDL3 expression was not resolved
   • Mechanism connecting ZPBP2 deletion to ceramide pathway changes is unknown
8. 2019 Medium

   Demonstrating that Zpbp2 deletion alters diurnal expression of the clock gene Nr1d1 and tissue-specific Ormdl3 levels revealed an unexpected circadian dimension to the cis-regulatory activity of the ZPBP2 locus.

   Evidence Time-series qRT-PCR across tissues in Zpbp2 KO and WT mice

   PMID:31560728

   Open questions at the time

   • Whether circadian disruption contributes to the asthma phenotype is untested
   • Mechanism linking ZPBP2 locus to Nr1d1 regulation is unknown
9. 2020 Medium

   In an allergic asthma model, Zpbp2 KO mice with reduced Ormdl3 showed lower AHR but unaffected inflammation and ceramide imbalance, placing the ZPBP2-ORMDL3 axis specifically upstream of bronchial hyperresponsiveness rather than the full allergic inflammatory cascade.

   Evidence House dust mite allergic challenge in Zpbp2 KO mice with AHR, lipidomics, qRT-PCR, and IgE measurement

   PMID:32273303

   Open questions at the time

   • Whether ORMDL3 reduction is the sole mediator of AHR attenuation is not confirmed
   • Therapeutic relevance of targeting ZPBP2-dependent CTCF sites in human asthma is unexplored
10. 2022 Medium

    Identification of PRSS54 as a direct interactor that controls ZPBP2 distribution in the acrosome placed ZPBP2 downstream of protease-dependent processing during acrosome maturation.

    Evidence Co-immunoprecipitation, immunofluorescence, and Prss54 KO mouse analysis

    PMID:35863763

    Open questions at the time

    • Whether PRSS54 cleaves ZPBP2 or only scaffolds it is unknown
    • No reciprocal rescue experiment was performed

• It remains unresolved whether ZPBP2 protein has any functional role in non-testicular tissues or whether its disease relevance is entirely mediated through cis-regulatory control of neighboring genes; the structural basis of ZPBP2's acrosomal function and its putative hyaluronic acid binding also lack direct biochemical characterization.
• No crystal structure or direct binding assay for ZPBP2
• Whether ZPBP2 protein is expressed in immune or airway cells is unresolved
• Direct HA-binding activity has not been validated by reconstitution