{"gene":"FZD4","run_date":"2026-04-28T17:46:04","timeline":{"discoveries":[{"year":2009,"finding":"TSPAN12 physically associates with the Norrin-FZD4 receptor complex (shown by co-immunoprecipitation), selectively enhancing Norrin/β-catenin but not Wnt/β-catenin signaling by promoting FZD4 multimerization; overexpression of TSPAN12 rescues signaling defects caused by FZD4 mutations predicted to impair receptor multimerization.","method":"Co-immunoprecipitation, siRNA knockdown in retinal endothelial cells, luciferase reporter assay, genetic epistasis in Tspan12/Norrin/Lrp5 mutant mice","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (Co-IP, RNAi, reporter assay, in vivo genetics) in a highly-cited study","pmids":["19837033"],"is_preprint":false},{"year":2010,"finding":"The cysteine-rich domain (CRD) of FZD4 is required for Norrin binding and Norrin-dependent activation of the canonical Wnt/β-catenin pathway; CRD missense mutations C45Y, Y58C, and C204R abolish Norrin binding and fail to transduce β-catenin signaling both in HEK293 cells and in Xenopus embryos (decreased Siamois and Xnr3 expression).","method":"Cell-surface and overlay binding assays, luciferase reporter assay, Xenopus embryo in vivo assay, site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution of binding and signaling with mutagenesis, validated in two independent systems (cell and Xenopus)","pmids":["21177847"],"is_preprint":false},{"year":2014,"finding":"Multiple FEVR-associated FZD4 missense mutations (P33S, G36N, H69Y, M105T, M105V, C181R, C204R, C204Y, G488D) cause ER retention and defective trafficking to the plasma membrane, resulting in haploinsufficiency; some mutants (M105T, C204Y) show partial rescue of trafficking by reduced temperature or chemical chaperones.","method":"Confocal fluorescence microscopy, N-glycosylation profiling, polyubiquitination studies, chemical chaperone rescue experiments in HeLa and COS-7 cells","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal biochemical and cell-biological methods on 15 mutants with functional rescue","pmids":["24744206"],"is_preprint":false},{"year":2005,"finding":"Fzd4-null mice are infertile due to failure of corpus luteum formation; Fzd4-/- corpora lutea show reduced expression of luteal markers (Lhcgr, Prlr, Cyp11a1), altered cell morphology, and reduced angiogenesis markers, while Norrin-null mice do not phenocopy this, indicating FZD4 regulates corpus luteum formation through a Norrin-independent mechanism.","method":"Fzd4 knockout mouse model, histological analysis, mRNA expression profiling, timed mating experiments","journal":"Biology of reproduction","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple specific phenotypic readouts and genetic control (Ndph-/- comparison)","pmids":["16093361"],"is_preprint":false},{"year":2021,"finding":"EMC3 (ER membrane protein complex subunit) is required for FZD4 protein expression and Norrin/β-catenin signaling in retinal endothelial cells; endothelial-specific Emc3 deletion reduces FZD4 levels and impairs retinal vascular development, which is partially rescued by LiCl-mediated activation of β-catenin signaling.","method":"Endothelial-specific conditional knockout mouse, RNA sequencing, RT-qPCR, luciferase reporter assay, LiCl rescue experiment, tube formation assay in HRECs","journal":"Science China. Life sciences","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional KO combined with mechanistic reporter assay and rescue experiment","pmids":["34128175"],"is_preprint":false},{"year":2017,"finding":"FZD4 marks lateral plate mesoderm in cardiac progenitor cells; NORRIN presented to FZD4 increases cardiomyocyte output from pluripotent stem cell-derived cardiac progenitors via proliferation through the canonical WNT pathway.","method":"Surface proteomics (mass spectrometry), microarray transcriptomics, FACS-based cell sorting using FZD4/FLK1/PDGFRA, WNT reporter assay, functional differentiation assays in mouse and human PSC systems","journal":"Stem cell reports","confidence":"High","confidence_rationale":"Tier 2 — integrated proteomics, transcriptomics, and functional cell-based assays with multiple orthogonal methods","pmids":["29249665"],"is_preprint":false},{"year":2019,"finding":"Secreted Wnt6 binds FZD4 to activate canonical Wnt6/β-catenin signaling upstream of ROCK1 and 14-3-3σ, driving diabetes-associated centrosome amplification; siRNA knockdown of FZD4 or antibody blockade of FZD4 attenuates centrosome amplification induced by high glucose, insulin, palmitic acid, or advanced glycation end products.","method":"siRNA knockdown, neutralizing antibodies, centrosome quantification, β-catenin nuclear translocation assays in cell culture","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with specific phenotypic readout and antibody corroboration, single lab","pmids":["31618077"],"is_preprint":false},{"year":2021,"finding":"Wnt2 and Wnt4 activate β-catenin/NF-κB signaling in cardiac fibroblasts through cooperation of Fzd4 (or Fzd2) with LRP6; Fzd4 knockdown attenuates Wnt2/Wnt4-induced pro-fibrotic effects.","method":"siRNA knockdown, co-receptor interaction analysis, NF-κB/β-catenin reporter assays in neonatal rat cardiac fibroblasts, MI mouse model","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro mechanistic dissection with in vivo MI model, single lab","pmids":["34911029"],"is_preprint":false},{"year":2020,"finding":"WNT2b induces epithelial-to-mesenchymal transition in HT29 intestinal epithelial cells through FZD4 activation, and FZD4/WNT2b interaction is elevated in intestinal tissue from penetrating Crohn's disease patients.","method":"In vitro EMT assay in HT29 cells with WNT2b treatment, FZD4 siRNA knockdown, confocal microscopy, RT-PCR, western blot, immunofluorescence on patient tissue","journal":"Journal of Crohn's & colitis","confidence":"Medium","confidence_rationale":"Tier 2 — functional in vitro assay with FZD4 knockdown and patient tissue correlation, single lab","pmids":["31359032"],"is_preprint":false},{"year":2018,"finding":"Wnt5a/FZD4 signaling activates the JNK pathway to mediate mechanical stretch-induced osteogenic differentiation of bone marrow stromal cells; FZD4 knockdown inhibits mechanical stimuli-induced osteogenesis and JNK activity, and Wnt5a or FZD4 activation partly rescues hindlimb unloading-induced osteoporosis in mice.","method":"siRNA knockdown, cyclic mechanical stretch in vitro model, ALP and Alizarin red staining, western blot, hindlimb unloading mouse model","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo loss-of-function with defined pathway readout (JNK), single lab","pmids":["30007964"],"is_preprint":false},{"year":2010,"finding":"ERG oncogene transcriptionally upregulates FZD4 in prostate cancer cells; FZD4 silencing mimics ERG knockdown by inducing active β1-integrin and E-cadherin expression, while FZD4 overexpression reverses the EMT phenotype caused by ERG knockdown, placing FZD4 downstream of ERG in WNT-mediated EMT.","method":"ERG and FZD4 siRNA knockdown, FZD4 overexpression rescue, flow cytometry for integrins, immunostaining, RT-PCR in VCaP cells","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis established by rescue experiment, multiple readouts, single lab","pmids":["20713528"],"is_preprint":false},{"year":2020,"finding":"GATA6-AS1 lncRNA downregulates FZD4 expression by recruiting EZH2 and promoting H3K27me3 at the FZD4 promoter, thereby inactivating Wnt/β-catenin signaling and suppressing gastric cancer progression.","method":"Chromatin immunoprecipitation, EZH2 co-immunoprecipitation/interaction assay, luciferase reporter, siRNA knockdown and overexpression, xenograft mouse model","journal":"Molecular therapy. Nucleic acids","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and Co-IP establish epigenetic mechanism at FZD4 promoter, single lab","pmids":["31981860"],"is_preprint":false},{"year":2021,"finding":"SIRT6 suppresses FZD4 transcription by deacetylating histone H3K9 at the FZD4 locus; overexpression of SIRT6 reduces FZD4 protein and H3K9ac levels, and quercetin activates SIRT6 to repress FZD4 and the Wnt/β-catenin pathway in hepatoblastoma cells.","method":"SIRT6 overexpression/knockdown, H3K9ac ChIP, FZD4 overexpression rescue, Wnt pathway reporter, xenograft mouse model","journal":"Human & experimental toxicology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP establishes histone deacetylation mechanism at FZD4, with rescue experiments, single lab","pmids":["34219513"],"is_preprint":false},{"year":2024,"finding":"FOXF1 transcriptionally activates FZD4 in lung endothelial cells; FOXF1 deficiency decreases FZD4 expression and Wnt/β-catenin signaling, and nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescues Wnt/β-catenin signaling, normalizes tumor vessels, and inhibits lung cancer progression.","method":"Endothelial-specific Foxf1 KO and overexpression mouse models, nanoparticle cDNA delivery rescue, RNA-seq, ChIP-seq (CUT&Tag), vessel permeability/pericyte coverage assays","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo genetic KO and OE, mechanistic rescue with cDNA delivery, multiple orthogonal methods","pmids":["38589650"],"is_preprint":false},{"year":2023,"finding":"METTL3-dependent m6A methylation of HLF mRNA upregulates HLF, which transcriptionally activates FZD4 to drive WNT/β-catenin signaling in intrahepatic cholangiocarcinoma; FOXQ1 forms a positive feedback loop by transcriptionally activating METTL3.","method":"RNA-seq, CUT&Tag chromatin profiling, loss/gain-of-function experiments, m6A methylation assays, in vitro and in vivo tumor assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — CUT&Tag and RNA-seq with functional experiments establish transcriptional regulation of FZD4 by HLF, single lab","pmids":["36958694"],"is_preprint":false},{"year":2025,"finding":"FZD4 is N-glycosylated at asparagine residues N59 and N144; N-glycosylation is required for FZD4 maturation, plasma membrane trafficking, protein stability, interaction with Wnt ligands and Norrin co-receptor, and Wnt/β-catenin signaling activity.","method":"Site-directed mutagenesis of N-glycosylation sites, surface biotinylation, co-immunoprecipitation with Wnt/Norrin, luciferase reporter assay, in vitro and in vivo tumor assays in NSCLC A549 cells","journal":"Journal of cellular and molecular medicine","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis of specific sites combined with biochemical trafficking, binding, and functional reporter assays","pmids":["40230079"],"is_preprint":false},{"year":2020,"finding":"FZD4 mutations identified in FEVR patients reduce Norrin/β-catenin transcriptional activity in Topflash reporter assays and impair Norrin-FZD4 protein binding as shown by immunoprecipitation; all six tested NDP and FZD4 mutants showed ≥50% loss of wild-type signaling activity.","method":"Topflash luciferase reporter assay, co-immunoprecipitation of Norrin-FZD4 complex with mutant proteins in transfected cells","journal":"BioMed research international","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay and Co-IP with multiple mutants, single lab","pmids":["32420371"],"is_preprint":false},{"year":2018,"finding":"Retinoic acid directly induces FZD4/FZD4s expression in Xenopus pancreatic explants; functional knockdown of Fzd4/Fzd4s impairs pancreatic progenitor formation and differentiation, establishing FZD4 as a direct RA target gene required for pancreas specification.","method":"RNA sequencing of pancreatic explants, morpholino knockdown of Fzd4/Fzd4s in Xenopus embryos and explants, loss-of-function phenotypic analysis of pancreatic progenitor markers","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — direct RNA-seq identification plus morpholino loss-of-function with specific developmental phenotype in Xenopus ortholog","pmids":["29769220"],"is_preprint":false},{"year":2016,"finding":"Fzd4 heterozygous mice show delayed retinal revascularization after oxygen-induced retinopathy (OIR), demonstrating that reduced Norrin-Fzd4 signaling dose-dependently impairs retinal vascular recovery.","method":"Fzd4 heterozygous mouse model, OIR treatment, quantification of avascular and vascular retinal areas, vessel caliber/number measurements","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — quantitative in vivo haploinsufficiency model with defined vascular phenotype readouts","pmids":["27489958"],"is_preprint":false},{"year":2024,"finding":"Five novel FZD4 FEVR missense mutations (S91F, V103E, C145S, E160K, C377F) were functionally categorized: signal peptide mutations reduce expression; CRD cysteine mutations disrupt disulfide bonds; extracellular domain mutations impair Norrin binding; TM1/TM7 mutations disrupt membrane localization; intracellular domain mutations reduce DVL2 recruitment.","method":"Site-directed mutagenesis, protein expression assays, Norrin/β-catenin luciferase reporter, membrane localization by confocal microscopy, DVL2 co-immunoprecipitation in HEK293T, HEK293STF, and HeLa cells","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 1 — comprehensive mutagenesis with multiple orthogonal biochemical assays classifying 34 mutations into mechanistic categories","pmids":["38558095"],"is_preprint":false},{"year":2016,"finding":"Let-7b inhibits Wnt signaling by targeting FZD4 mRNA in megakaryocytes; let-7b downregulation leads to increased FZD4 expression and regulates mitochondrial biogenesis (PGC-1α, NRF1) during megakaryocyte development.","method":"miRNA microarray, let-7b mimic/inhibitor transfection, Dami cell line validation, mitochondrial biogenesis marker quantification","journal":"The international journal of biochemistry & cell biology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, indirect pathway evidence without direct FZD4 3'UTR luciferase validation reported","pmids":["27510711"],"is_preprint":false},{"year":2023,"finding":"YAP positively regulates WNT5A and FZD4 expression in human periodontal ligament cells (hPDLCs) under cyclic stretch; FZD4 knockdown attenuates both YAP-induced and stretch-induced osteogenic differentiation, and recombinant WNT5A rescues osteogenesis suppressed by YAP inhibition except when FZD4 is knocked down.","method":"YAP inhibitor (verteporfin) and activator (LATS-IN-1), siRNA knockdown of WNT5A and FZD4, recombinant WNT5A rescue, ALP activity, Alizarin Red staining, qRT-PCR, western blot in hPDLCs under cyclic stretch","journal":"Journal of periodontal research","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis established by sequential knockdown and rescue experiments, single lab","pmids":["37340863"],"is_preprint":false},{"year":2023,"finding":"WNT5A binds FZD4 to regulate the WNT/β-catenin signaling pathway in ALS motor neurons; knockdown of FZD4 or WNT5A reduces β-catenin signaling and affects proliferation and apoptosis of hSOD1-G93A mutant NSC34 cells.","method":"hSOD1-G93A transgenic mouse model, hSOD1-G93A mutant NSC34 cells, siRNA knockdown, western blot, immunofluorescence for β-catenin pathway components","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 — single lab, loss-of-function with pathway readout but no direct binding assay for WNT5A-FZD4 interaction","pmids":["35413536"],"is_preprint":false}],"current_model":"FZD4 is a seven-transmembrane Wnt receptor whose N-glycosylated cysteine-rich domain (CRD) binds Norrin (and Wnt ligands such as Wnt2, Wnt4, Wnt5a, Wnt6), recruiting co-receptor LRP5/6 and the scaffold DVL2 to activate canonical β-catenin/TCF signaling; TSPAN12 selectively amplifies Norrin—but not Wnt—signaling by promoting FZD4 multimerization, while the tetraspanin complex and FZD4 membrane trafficking are regulated by the ER membrane protein complex (EMC3) and N-glycosylation at N59/N144; transcriptional activation of FZD4 by FOXF1 (in endothelial cells) and HLF (via METTL3-dependent m6A), and epigenetic repression by SIRT6-mediated H3K9 deacetylation or GATA6-AS1/EZH2-driven H3K27me3, modulate pathway output in tissue-specific contexts including retinal vascularization, corpus luteum formation, osteogenesis, cardiomyocyte differentiation, and cancer EMT."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing that FZD4 has essential in vivo roles beyond retinal vasculature: Fzd4-knockout mice revealed a Norrin-independent requirement for FZD4 in corpus luteum formation and female fertility, broadening FZD4 biology beyond its known retinal function.","evidence":"Fzd4 knockout mouse with histological, expression, and Ndph-null comparison","pmids":["16093361"],"confidence":"High","gaps":["The Wnt ligand acting through FZD4 in the ovary was not identified","Downstream signaling pathway (canonical vs. non-canonical) in corpus luteum not resolved"]},{"year":2009,"claim":"Resolving how Norrin–FZD4 signaling specificity is achieved at the receptor level: TSPAN12 was identified as a co-receptor that physically associates with FZD4 and selectively amplifies Norrin- but not Wnt-dependent β-catenin signaling by promoting FZD4 multimerization.","evidence":"Co-immunoprecipitation, siRNA in retinal endothelial cells, luciferase reporter, and Tspan12/Norrin/Lrp5 mutant mouse epistasis","pmids":["19837033"],"confidence":"High","gaps":["Structural basis of TSPAN12-mediated multimerization not determined","Whether TSPAN12 modulates non-canonical FZD4 signaling not tested"]},{"year":2010,"claim":"Defining the ligand-binding domain: the CRD of FZD4 was shown to be necessary and sufficient for Norrin binding, with specific cysteine residues (C45, C204) and Y58 required for engagement, establishing the molecular basis for FEVR-associated loss of function.","evidence":"Cell-surface binding assays, site-directed mutagenesis, luciferase reporter, and Xenopus embryo signaling assay","pmids":["21177847"],"confidence":"High","gaps":["High-resolution structure of the Norrin–CRD interface not yet available at this time","Whether these residues also affect Wnt ligand binding was not tested"]},{"year":2010,"claim":"Placing FZD4 in an oncogenic transcriptional circuit: ERG was shown to transcriptionally upregulate FZD4 in prostate cancer, and FZD4 was positioned as the effector of ERG-driven EMT via Wnt/β-catenin signaling.","evidence":"ERG/FZD4 siRNA epistasis and FZD4 overexpression rescue in VCaP prostate cancer cells","pmids":["20713528"],"confidence":"Medium","gaps":["The specific Wnt ligand operating through FZD4 in this cancer context was not identified","In vivo tumor model validation not reported"]},{"year":2014,"claim":"Revealing how FEVR mutations cause disease at the cellular level: systematic analysis of 15 FEVR-associated FZD4 missense mutations showed that most cause ER retention and defective plasma membrane trafficking, establishing haploinsufficiency through protein misfolding rather than solely ligand-binding defects.","evidence":"Confocal microscopy, N-glycosylation profiling, polyubiquitination assays, chemical chaperone rescue in HeLa/COS-7 cells","pmids":["24744206"],"confidence":"High","gaps":["Whether chemical chaperone rescue is therapeutically viable in vivo not tested","Contribution of proteasomal vs. lysosomal degradation of misfolded FZD4 not resolved"]},{"year":2016,"claim":"Demonstrating dose-sensitivity of FZD4 in retinal vascular repair: Fzd4 heterozygous mice showed delayed retinal revascularization after oxygen-induced retinopathy, confirming that even partial reduction of FZD4 levels is pathologically significant.","evidence":"Fzd4 heterozygous mouse, OIR model with quantitative vascular area measurements","pmids":["27489958"],"confidence":"Medium","gaps":["Whether the haploinsufficiency is due to reduced Norrin or Wnt signaling was not distinguished","Therapeutic rescue by FZD4 supplementation not attempted"]},{"year":2018,"claim":"Expanding FZD4's non-canonical signaling: Wnt5a was shown to signal through FZD4 via JNK (not β-catenin) to mediate mechanical stretch-induced osteogenic differentiation, establishing FZD4 as a receptor for both canonical and non-canonical Wnt pathways depending on context.","evidence":"siRNA knockdown, cyclic stretch in vitro, western blot for JNK, and hindlimb unloading mouse model","pmids":["30007964"],"confidence":"Medium","gaps":["Direct Wnt5a–FZD4 physical interaction not demonstrated by binding assay","Co-receptor identity for this non-canonical pathway not identified"]},{"year":2021,"claim":"Identifying an upstream biogenesis factor: EMC3 was shown to be required for FZD4 protein expression and ER-to-plasma-membrane trafficking in retinal endothelial cells, connecting ER membrane protein complex function to Norrin/β-catenin signaling and retinal vascularization.","evidence":"Endothelial-specific Emc3 conditional knockout mouse, RNA-seq, luciferase reporter, LiCl rescue","pmids":["34128175"],"confidence":"High","gaps":["Whether EMC3 acts as a direct chaperone for FZD4 or affects it indirectly not resolved","Whether EMC3 regulates other Frizzled family members in the same cells not tested"]},{"year":2024,"claim":"Comprehensive mechanistic classification of FEVR mutations: 34 FZD4 mutations were functionally categorized into five classes—signal peptide (reduced expression), CRD cysteine (disulfide disruption), extracellular (impaired Norrin binding), transmembrane (mislocalization), and intracellular (defective DVL2 recruitment)—providing a genotype-mechanism framework.","evidence":"Mutagenesis, expression assays, Norrin/β-catenin reporter, confocal localization, DVL2 co-IP in HEK293T/HeLa cells","pmids":["38558095"],"confidence":"High","gaps":["In vivo validation of the five-class model not performed","Whether mutation class predicts disease severity in patients not established"]},{"year":2024,"claim":"Identifying a transcriptional activator of FZD4 in endothelium: FOXF1 was shown to directly activate FZD4 transcription; nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescued Wnt/β-catenin signaling and normalized tumor vasculature, demonstrating FZD4 as the critical FOXF1 effector.","evidence":"Endothelial-specific Foxf1 KO/OE mice, CUT&Tag ChIP-seq, nanoparticle Fzd4 rescue, RNA-seq","pmids":["38558650"],"confidence":"High","gaps":["Whether FOXF1 regulates FZD4 in non-lung endothelial beds not tested","Therapeutic durability of nanoparticle FZD4 delivery not assessed"]},{"year":2025,"claim":"Defining post-translational requirements for FZD4 function: N-glycosylation at N59 and N144 was shown to be essential for FZD4 maturation, surface trafficking, Wnt/Norrin binding, and β-catenin signaling, resolving a long-standing gap in understanding FZD4 quality control.","evidence":"Site-directed mutagenesis of glycosylation sites, surface biotinylation, co-IP with Wnt/Norrin, luciferase reporter in A549 cells","pmids":["40230079"],"confidence":"High","gaps":["Whether glycosylation affects TSPAN12-mediated multimerization not tested","Structural impact of glycan chains on CRD conformation not resolved"]},{"year":null,"claim":"How FZD4 selects between canonical (β-catenin) and non-canonical (JNK/PCP) signaling outputs depending on the Wnt ligand and cellular context remains mechanistically undefined, and structural models of the full-length receptor in complex with co-receptors (LRP5/6, TSPAN12) are lacking.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length FZD4 structure with co-receptors available","Mechanism of canonical vs. non-canonical pathway selection at FZD4 not resolved","Relative contributions of individual Wnt ligands to FZD4 signaling in specific tissues not systematically defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,6,7,8,9,15,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,15,19]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,5,6,7,8,9,15,16]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,5,17]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[2,10,11,16,19]}],"complexes":["Norrin–FZD4–LRP5/6–TSPAN12 receptor complex"],"partners":["NDP","TSPAN12","LRP5","LRP6","DVL2","EMC3","WNT5A","WNT6"],"other_free_text":[]},"mechanistic_narrative":"FZD4 is a seven-transmembrane Wnt receptor that transduces canonical β-catenin signaling in response to Norrin and multiple Wnt ligands (Wnt2, Wnt2b, Wnt4, Wnt5a, Wnt6), functioning as a central regulator of vascular development, organogenesis, and tissue homeostasis. Its extracellular cysteine-rich domain (CRD) is essential for Norrin binding; CRD missense mutations abolish ligand engagement and β-catenin activation, while N-glycosylation at N59 and N144 is required for receptor maturation, plasma membrane trafficking, ligand interaction, and signaling competence [PMID:21177847, PMID:40230079]. TSPAN12 selectively potentiates Norrin–FZD4 signaling by promoting FZD4 multimerization, and EMC3 is required upstream for FZD4 protein biogenesis in retinal endothelial cells [PMID:19837033, PMID:34128175]. Loss-of-function mutations in FZD4 cause familial exudative vitreoretinopathy (FEVR), with disease-associated variants exhibiting ER retention, impaired Norrin binding, or defective DVL2 recruitment [PMID:24744206, PMID:38558095]."},"prefetch_data":{"uniprot":{"accession":"Q9ULV1","full_name":"Frizzled-4","aliases":["FzE4"],"length_aa":537,"mass_kda":59.9,"function":"Receptor for Wnt proteins (PubMed:30135577). Most frizzled receptors are coupled to the beta-catenin (CTNNB1) canonical signaling pathway, which leads to the activation of disheveled proteins, inhibition of GSK-3 kinase, nuclear accumulation of beta-catenin (CTNNB1) and activation of Wnt target genes (PubMed:30135577). Plays a critical role in retinal vascularization by acting as a receptor for Wnt proteins and norrin (NDP) (By similarity). In retina, it can be activated by Wnt protein-binding and also by Wnt-independent signaling via binding of norrin (NDP), promoting in both cases beta-catenin (CTNNB1) accumulation and stimulation of LEF/TCF-mediated transcriptional programs (By similarity). A second signaling pathway involving PKC and calcium fluxes has been seen for some family members, but it is not yet clear if it represents a distinct pathway or if it can be integrated in the canonical pathway, as PKC seems to be required for Wnt-mediated inactivation of GSK-3 kinase. Both pathways seem to involve interactions with G-proteins. May be involved in transduction and intercellular transmission of polarity information during tissue morphogenesis and/or in differentiated tissues","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9ULV1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FZD4","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FZD4","total_profiled":1310},"omim":[{"mim_id":"616468","title":"EXUDATIVE VITREORETINOPATHY 6; EVR6","url":"https://www.omim.org/entry/616468"},{"mim_id":"615943","title":"MEMBRANE-ASSOCIATED GUANYLATE KINASE, WW AND PDZ DOMAINS-CONTAINING, 3; MAGI3","url":"https://www.omim.org/entry/615943"},{"mim_id":"613138","title":"TETRASPANIN 12; TSPAN12","url":"https://www.omim.org/entry/613138"},{"mim_id":"604579","title":"FRIZZLED CLASS RECEPTOR 4; FZD4","url":"https://www.omim.org/entry/604579"},{"mim_id":"603506","title":"LOW DENSITY LIPOPROTEIN RECEPTOR-RELATED PROTEIN 5; LRP5","url":"https://www.omim.org/entry/603506"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Primary cilium","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adipose 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and molecular biomarkers","url":"https://pubmed.ncbi.nlm.nih.gov/31999491","citation_count":9,"is_preprint":false},{"pmid":"27668459","id":"PMC_27668459","title":"A family harboring homozygous FZD4 deletion supports the existence of recessive FZD4-related familial exudative vitreoretinopathy.","date":"2016","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27668459","citation_count":9,"is_preprint":false},{"pmid":"27489958","id":"PMC_27489958","title":"Fzd4 Haploinsufficiency Delays Retinal Revascularization in the Mouse Model of Oxygen Induced Retinopathy.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27489958","citation_count":9,"is_preprint":false},{"pmid":"34199009","id":"PMC_34199009","title":"Whole-Gene Deletions of FZD4 Cause Familial Exudative Vitreoretinopathy.","date":"2021","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/34199009","citation_count":8,"is_preprint":false},{"pmid":"37218742","id":"PMC_37218742","title":"miR-136-5p/FZD4 axis is critical for Wnt signaling-mediated myogenesis and skeletal muscle regeneration.","date":"2023","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/37218742","citation_count":8,"is_preprint":false},{"pmid":"35951321","id":"PMC_35951321","title":"Severe Familial Exudative Vitreoretinopathy, Congenital Hearing Loss, and Developmental Delay in a Child With Biallelic Variants in FZD4.","date":"2022","source":"JAMA ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/35951321","citation_count":8,"is_preprint":false},{"pmid":"30537745","id":"PMC_30537745","title":"A Novel Variant of the FZD4 Gene in a Chinese Family Causes Autosomal Dominant Familial Exudative Vitreoretinopathy.","date":"2018","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30537745","citation_count":8,"is_preprint":false},{"pmid":"22574936","id":"PMC_22574936","title":"Familial retinal detachment associated with COL2A1 exon 2 and FZD4 mutations.","date":"2012","source":"Clinical & experimental ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/22574936","citation_count":8,"is_preprint":false},{"pmid":"33302760","id":"PMC_33302760","title":"Novel FZD4 and LRP5 mutations in a small cohort of patients with familial exudative vitreoretinopathy (FEVR).","date":"2020","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33302760","citation_count":7,"is_preprint":false},{"pmid":"25390515","id":"PMC_25390515","title":"Simultaneous fzd4 and lrp5 mutation in autosomal dominant familial exudative vitreoretinopathy.","date":"2013","source":"Retinal cases & brief reports","url":"https://pubmed.ncbi.nlm.nih.gov/25390515","citation_count":6,"is_preprint":false},{"pmid":"35277167","id":"PMC_35277167","title":"Whole exome sequencing revealed 14 variants in NDP, FZD4, LRP5, and TSPAN12 genes for 20 families with familial exudative vitreoretinopathy.","date":"2022","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/35277167","citation_count":6,"is_preprint":false},{"pmid":"31114654","id":"PMC_31114654","title":"Detection of FZD4, LRP5 and TSPAN12 Genes Variants in Malay Premature Babies with Retinopathy of Prematurity.","date":"2019","source":"Journal of ophthalmic & vision research","url":"https://pubmed.ncbi.nlm.nih.gov/31114654","citation_count":6,"is_preprint":false},{"pmid":"10890980","id":"PMC_10890980","title":"Mouse fzd4 maps within a region of chromosome 7 important for thymus and cardiac development.","date":"2000","source":"Genesis (New York, N.Y. : 2000)","url":"https://pubmed.ncbi.nlm.nih.gov/10890980","citation_count":6,"is_preprint":false},{"pmid":"38558095","id":"PMC_38558095","title":"Identification of Novel FZD4 Mutations in Familial Exudative Vitreoretinopathy and Investigating the Pathogenic Mechanisms of FZD4 Mutations.","date":"2024","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/38558095","citation_count":5,"is_preprint":false},{"pmid":"29465286","id":"PMC_29465286","title":"Genetic association of single nucleotide polymorphisms of FZD4 and BDNF genes with retinopathy of prematurity.","date":"2018","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29465286","citation_count":5,"is_preprint":false},{"pmid":"35413536","id":"PMC_35413536","title":"The mechanism of the WNT5A and FZD4 receptor mediated WNT/β-catenin pathway in the degeneration of ALS spinal cord motor neurons.","date":"2022","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/35413536","citation_count":5,"is_preprint":false},{"pmid":"37926400","id":"PMC_37926400","title":"Folate deficiency promotes cervical squamous carcinoma SiHa cells progression by targeting miR-375/FZD4/β-catenin signaling.","date":"2023","source":"The Journal of nutritional biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37926400","citation_count":4,"is_preprint":false},{"pmid":"31765079","id":"PMC_31765079","title":"Identification of novel variants in the FZD4 gene associated with familial exudative vitreoretinopathy in Chinese families.","date":"2019","source":"Clinical & experimental ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/31765079","citation_count":4,"is_preprint":false},{"pmid":"34688334","id":"PMC_34688334","title":"Overexpressed miR-375-Loaded Restrains Development of Cervical Cancer Through Down-Regulation of Frizzled Class Receptor 4 (FZD4) with Liposome Nanoparticle as a Carrier.","date":"2021","source":"Journal of biomedical nanotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/34688334","citation_count":4,"is_preprint":false},{"pmid":"30820142","id":"PMC_30820142","title":"Variable reduction in Norrin signaling activity caused by novel mutations in FZD4 identified in patients with familial exudative vitreoretinopathy.","date":"2019","source":"Molecular vision","url":"https://pubmed.ncbi.nlm.nih.gov/30820142","citation_count":4,"is_preprint":false},{"pmid":"28438350","id":"PMC_28438350","title":"WITHDRAWN: MicroRNA-505 modulates cancer proliferation and migration in human non-small cell lung cancer through inverse regulation of FZD4.","date":"2017","source":"Lung cancer (Amsterdam, Netherlands)","url":"https://pubmed.ncbi.nlm.nih.gov/28438350","citation_count":3,"is_preprint":false},{"pmid":"40230079","id":"PMC_40230079","title":"N-Glycosylation Modification of Fzd4 Is Essential for the Fzd4-Wnt-β-Catenin Signalling Axis.","date":"2025","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40230079","citation_count":3,"is_preprint":false},{"pmid":"35068502","id":"PMC_35068502","title":"Discovering the Role of FZD4 Gene in Human Cutaneous Squamous Cell Carcinoma.","date":"2021","source":"Indian journal of dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35068502","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":53508,"output_tokens":5899,"usd":0.124505},"stage2":{"model":"claude-opus-4-6","input_tokens":9550,"output_tokens":3300,"usd":0.195375},"total_usd":0.31988,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2009,\n      \"finding\": \"TSPAN12 physically associates with the Norrin-FZD4 receptor complex (shown by co-immunoprecipitation), selectively enhancing Norrin/β-catenin but not Wnt/β-catenin signaling by promoting FZD4 multimerization; overexpression of TSPAN12 rescues signaling defects caused by FZD4 mutations predicted to impair receptor multimerization.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown in retinal endothelial cells, luciferase reporter assay, genetic epistasis in Tspan12/Norrin/Lrp5 mutant mice\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (Co-IP, RNAi, reporter assay, in vivo genetics) in a highly-cited study\",\n      \"pmids\": [\"19837033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The cysteine-rich domain (CRD) of FZD4 is required for Norrin binding and Norrin-dependent activation of the canonical Wnt/β-catenin pathway; CRD missense mutations C45Y, Y58C, and C204R abolish Norrin binding and fail to transduce β-catenin signaling both in HEK293 cells and in Xenopus embryos (decreased Siamois and Xnr3 expression).\",\n      \"method\": \"Cell-surface and overlay binding assays, luciferase reporter assay, Xenopus embryo in vivo assay, site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution of binding and signaling with mutagenesis, validated in two independent systems (cell and Xenopus)\",\n      \"pmids\": [\"21177847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Multiple FEVR-associated FZD4 missense mutations (P33S, G36N, H69Y, M105T, M105V, C181R, C204R, C204Y, G488D) cause ER retention and defective trafficking to the plasma membrane, resulting in haploinsufficiency; some mutants (M105T, C204Y) show partial rescue of trafficking by reduced temperature or chemical chaperones.\",\n      \"method\": \"Confocal fluorescence microscopy, N-glycosylation profiling, polyubiquitination studies, chemical chaperone rescue experiments in HeLa and COS-7 cells\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal biochemical and cell-biological methods on 15 mutants with functional rescue\",\n      \"pmids\": [\"24744206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Fzd4-null mice are infertile due to failure of corpus luteum formation; Fzd4-/- corpora lutea show reduced expression of luteal markers (Lhcgr, Prlr, Cyp11a1), altered cell morphology, and reduced angiogenesis markers, while Norrin-null mice do not phenocopy this, indicating FZD4 regulates corpus luteum formation through a Norrin-independent mechanism.\",\n      \"method\": \"Fzd4 knockout mouse model, histological analysis, mRNA expression profiling, timed mating experiments\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple specific phenotypic readouts and genetic control (Ndph-/- comparison)\",\n      \"pmids\": [\"16093361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"EMC3 (ER membrane protein complex subunit) is required for FZD4 protein expression and Norrin/β-catenin signaling in retinal endothelial cells; endothelial-specific Emc3 deletion reduces FZD4 levels and impairs retinal vascular development, which is partially rescued by LiCl-mediated activation of β-catenin signaling.\",\n      \"method\": \"Endothelial-specific conditional knockout mouse, RNA sequencing, RT-qPCR, luciferase reporter assay, LiCl rescue experiment, tube formation assay in HRECs\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo conditional KO combined with mechanistic reporter assay and rescue experiment\",\n      \"pmids\": [\"34128175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FZD4 marks lateral plate mesoderm in cardiac progenitor cells; NORRIN presented to FZD4 increases cardiomyocyte output from pluripotent stem cell-derived cardiac progenitors via proliferation through the canonical WNT pathway.\",\n      \"method\": \"Surface proteomics (mass spectrometry), microarray transcriptomics, FACS-based cell sorting using FZD4/FLK1/PDGFRA, WNT reporter assay, functional differentiation assays in mouse and human PSC systems\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — integrated proteomics, transcriptomics, and functional cell-based assays with multiple orthogonal methods\",\n      \"pmids\": [\"29249665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Secreted Wnt6 binds FZD4 to activate canonical Wnt6/β-catenin signaling upstream of ROCK1 and 14-3-3σ, driving diabetes-associated centrosome amplification; siRNA knockdown of FZD4 or antibody blockade of FZD4 attenuates centrosome amplification induced by high glucose, insulin, palmitic acid, or advanced glycation end products.\",\n      \"method\": \"siRNA knockdown, neutralizing antibodies, centrosome quantification, β-catenin nuclear translocation assays in cell culture\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with specific phenotypic readout and antibody corroboration, single lab\",\n      \"pmids\": [\"31618077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Wnt2 and Wnt4 activate β-catenin/NF-κB signaling in cardiac fibroblasts through cooperation of Fzd4 (or Fzd2) with LRP6; Fzd4 knockdown attenuates Wnt2/Wnt4-induced pro-fibrotic effects.\",\n      \"method\": \"siRNA knockdown, co-receptor interaction analysis, NF-κB/β-catenin reporter assays in neonatal rat cardiac fibroblasts, MI mouse model\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro mechanistic dissection with in vivo MI model, single lab\",\n      \"pmids\": [\"34911029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"WNT2b induces epithelial-to-mesenchymal transition in HT29 intestinal epithelial cells through FZD4 activation, and FZD4/WNT2b interaction is elevated in intestinal tissue from penetrating Crohn's disease patients.\",\n      \"method\": \"In vitro EMT assay in HT29 cells with WNT2b treatment, FZD4 siRNA knockdown, confocal microscopy, RT-PCR, western blot, immunofluorescence on patient tissue\",\n      \"journal\": \"Journal of Crohn's & colitis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional in vitro assay with FZD4 knockdown and patient tissue correlation, single lab\",\n      \"pmids\": [\"31359032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Wnt5a/FZD4 signaling activates the JNK pathway to mediate mechanical stretch-induced osteogenic differentiation of bone marrow stromal cells; FZD4 knockdown inhibits mechanical stimuli-induced osteogenesis and JNK activity, and Wnt5a or FZD4 activation partly rescues hindlimb unloading-induced osteoporosis in mice.\",\n      \"method\": \"siRNA knockdown, cyclic mechanical stretch in vitro model, ALP and Alizarin red staining, western blot, hindlimb unloading mouse model\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo loss-of-function with defined pathway readout (JNK), single lab\",\n      \"pmids\": [\"30007964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"ERG oncogene transcriptionally upregulates FZD4 in prostate cancer cells; FZD4 silencing mimics ERG knockdown by inducing active β1-integrin and E-cadherin expression, while FZD4 overexpression reverses the EMT phenotype caused by ERG knockdown, placing FZD4 downstream of ERG in WNT-mediated EMT.\",\n      \"method\": \"ERG and FZD4 siRNA knockdown, FZD4 overexpression rescue, flow cytometry for integrins, immunostaining, RT-PCR in VCaP cells\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by rescue experiment, multiple readouts, single lab\",\n      \"pmids\": [\"20713528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GATA6-AS1 lncRNA downregulates FZD4 expression by recruiting EZH2 and promoting H3K27me3 at the FZD4 promoter, thereby inactivating Wnt/β-catenin signaling and suppressing gastric cancer progression.\",\n      \"method\": \"Chromatin immunoprecipitation, EZH2 co-immunoprecipitation/interaction assay, luciferase reporter, siRNA knockdown and overexpression, xenograft mouse model\",\n      \"journal\": \"Molecular therapy. Nucleic acids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and Co-IP establish epigenetic mechanism at FZD4 promoter, single lab\",\n      \"pmids\": [\"31981860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIRT6 suppresses FZD4 transcription by deacetylating histone H3K9 at the FZD4 locus; overexpression of SIRT6 reduces FZD4 protein and H3K9ac levels, and quercetin activates SIRT6 to repress FZD4 and the Wnt/β-catenin pathway in hepatoblastoma cells.\",\n      \"method\": \"SIRT6 overexpression/knockdown, H3K9ac ChIP, FZD4 overexpression rescue, Wnt pathway reporter, xenograft mouse model\",\n      \"journal\": \"Human & experimental toxicology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP establishes histone deacetylation mechanism at FZD4, with rescue experiments, single lab\",\n      \"pmids\": [\"34219513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FOXF1 transcriptionally activates FZD4 in lung endothelial cells; FOXF1 deficiency decreases FZD4 expression and Wnt/β-catenin signaling, and nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescues Wnt/β-catenin signaling, normalizes tumor vessels, and inhibits lung cancer progression.\",\n      \"method\": \"Endothelial-specific Foxf1 KO and overexpression mouse models, nanoparticle cDNA delivery rescue, RNA-seq, ChIP-seq (CUT&Tag), vessel permeability/pericyte coverage assays\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo genetic KO and OE, mechanistic rescue with cDNA delivery, multiple orthogonal methods\",\n      \"pmids\": [\"38589650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL3-dependent m6A methylation of HLF mRNA upregulates HLF, which transcriptionally activates FZD4 to drive WNT/β-catenin signaling in intrahepatic cholangiocarcinoma; FOXQ1 forms a positive feedback loop by transcriptionally activating METTL3.\",\n      \"method\": \"RNA-seq, CUT&Tag chromatin profiling, loss/gain-of-function experiments, m6A methylation assays, in vitro and in vivo tumor assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CUT&Tag and RNA-seq with functional experiments establish transcriptional regulation of FZD4 by HLF, single lab\",\n      \"pmids\": [\"36958694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FZD4 is N-glycosylated at asparagine residues N59 and N144; N-glycosylation is required for FZD4 maturation, plasma membrane trafficking, protein stability, interaction with Wnt ligands and Norrin co-receptor, and Wnt/β-catenin signaling activity.\",\n      \"method\": \"Site-directed mutagenesis of N-glycosylation sites, surface biotinylation, co-immunoprecipitation with Wnt/Norrin, luciferase reporter assay, in vitro and in vivo tumor assays in NSCLC A549 cells\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis of specific sites combined with biochemical trafficking, binding, and functional reporter assays\",\n      \"pmids\": [\"40230079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FZD4 mutations identified in FEVR patients reduce Norrin/β-catenin transcriptional activity in Topflash reporter assays and impair Norrin-FZD4 protein binding as shown by immunoprecipitation; all six tested NDP and FZD4 mutants showed ≥50% loss of wild-type signaling activity.\",\n      \"method\": \"Topflash luciferase reporter assay, co-immunoprecipitation of Norrin-FZD4 complex with mutant proteins in transfected cells\",\n      \"journal\": \"BioMed research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay and Co-IP with multiple mutants, single lab\",\n      \"pmids\": [\"32420371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Retinoic acid directly induces FZD4/FZD4s expression in Xenopus pancreatic explants; functional knockdown of Fzd4/Fzd4s impairs pancreatic progenitor formation and differentiation, establishing FZD4 as a direct RA target gene required for pancreas specification.\",\n      \"method\": \"RNA sequencing of pancreatic explants, morpholino knockdown of Fzd4/Fzd4s in Xenopus embryos and explants, loss-of-function phenotypic analysis of pancreatic progenitor markers\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct RNA-seq identification plus morpholino loss-of-function with specific developmental phenotype in Xenopus ortholog\",\n      \"pmids\": [\"29769220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fzd4 heterozygous mice show delayed retinal revascularization after oxygen-induced retinopathy (OIR), demonstrating that reduced Norrin-Fzd4 signaling dose-dependently impairs retinal vascular recovery.\",\n      \"method\": \"Fzd4 heterozygous mouse model, OIR treatment, quantification of avascular and vascular retinal areas, vessel caliber/number measurements\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — quantitative in vivo haploinsufficiency model with defined vascular phenotype readouts\",\n      \"pmids\": [\"27489958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Five novel FZD4 FEVR missense mutations (S91F, V103E, C145S, E160K, C377F) were functionally categorized: signal peptide mutations reduce expression; CRD cysteine mutations disrupt disulfide bonds; extracellular domain mutations impair Norrin binding; TM1/TM7 mutations disrupt membrane localization; intracellular domain mutations reduce DVL2 recruitment.\",\n      \"method\": \"Site-directed mutagenesis, protein expression assays, Norrin/β-catenin luciferase reporter, membrane localization by confocal microscopy, DVL2 co-immunoprecipitation in HEK293T, HEK293STF, and HeLa cells\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — comprehensive mutagenesis with multiple orthogonal biochemical assays classifying 34 mutations into mechanistic categories\",\n      \"pmids\": [\"38558095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Let-7b inhibits Wnt signaling by targeting FZD4 mRNA in megakaryocytes; let-7b downregulation leads to increased FZD4 expression and regulates mitochondrial biogenesis (PGC-1α, NRF1) during megakaryocyte development.\",\n      \"method\": \"miRNA microarray, let-7b mimic/inhibitor transfection, Dami cell line validation, mitochondrial biogenesis marker quantification\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, indirect pathway evidence without direct FZD4 3'UTR luciferase validation reported\",\n      \"pmids\": [\"27510711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"YAP positively regulates WNT5A and FZD4 expression in human periodontal ligament cells (hPDLCs) under cyclic stretch; FZD4 knockdown attenuates both YAP-induced and stretch-induced osteogenic differentiation, and recombinant WNT5A rescues osteogenesis suppressed by YAP inhibition except when FZD4 is knocked down.\",\n      \"method\": \"YAP inhibitor (verteporfin) and activator (LATS-IN-1), siRNA knockdown of WNT5A and FZD4, recombinant WNT5A rescue, ALP activity, Alizarin Red staining, qRT-PCR, western blot in hPDLCs under cyclic stretch\",\n      \"journal\": \"Journal of periodontal research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by sequential knockdown and rescue experiments, single lab\",\n      \"pmids\": [\"37340863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WNT5A binds FZD4 to regulate the WNT/β-catenin signaling pathway in ALS motor neurons; knockdown of FZD4 or WNT5A reduces β-catenin signaling and affects proliferation and apoptosis of hSOD1-G93A mutant NSC34 cells.\",\n      \"method\": \"hSOD1-G93A transgenic mouse model, hSOD1-G93A mutant NSC34 cells, siRNA knockdown, western blot, immunofluorescence for β-catenin pathway components\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, loss-of-function with pathway readout but no direct binding assay for WNT5A-FZD4 interaction\",\n      \"pmids\": [\"35413536\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FZD4 is a seven-transmembrane Wnt receptor whose N-glycosylated cysteine-rich domain (CRD) binds Norrin (and Wnt ligands such as Wnt2, Wnt4, Wnt5a, Wnt6), recruiting co-receptor LRP5/6 and the scaffold DVL2 to activate canonical β-catenin/TCF signaling; TSPAN12 selectively amplifies Norrin—but not Wnt—signaling by promoting FZD4 multimerization, while the tetraspanin complex and FZD4 membrane trafficking are regulated by the ER membrane protein complex (EMC3) and N-glycosylation at N59/N144; transcriptional activation of FZD4 by FOXF1 (in endothelial cells) and HLF (via METTL3-dependent m6A), and epigenetic repression by SIRT6-mediated H3K9 deacetylation or GATA6-AS1/EZH2-driven H3K27me3, modulate pathway output in tissue-specific contexts including retinal vascularization, corpus luteum formation, osteogenesis, cardiomyocyte differentiation, and cancer EMT.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FZD4 is a seven-transmembrane Wnt receptor that transduces canonical β-catenin signaling in response to Norrin and multiple Wnt ligands (Wnt2, Wnt2b, Wnt4, Wnt5a, Wnt6), functioning as a central regulator of vascular development, organogenesis, and tissue homeostasis. Its extracellular cysteine-rich domain (CRD) is essential for Norrin binding; CRD missense mutations abolish ligand engagement and β-catenin activation, while N-glycosylation at N59 and N144 is required for receptor maturation, plasma membrane trafficking, ligand interaction, and signaling competence [PMID:21177847, PMID:40230079]. TSPAN12 selectively potentiates Norrin–FZD4 signaling by promoting FZD4 multimerization, and EMC3 is required upstream for FZD4 protein biogenesis in retinal endothelial cells [PMID:19837033, PMID:34128175]. Loss-of-function mutations in FZD4 cause familial exudative vitreoretinopathy (FEVR), with disease-associated variants exhibiting ER retention, impaired Norrin binding, or defective DVL2 recruitment [PMID:24744206, PMID:38558095].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that FZD4 has essential in vivo roles beyond retinal vasculature: Fzd4-knockout mice revealed a Norrin-independent requirement for FZD4 in corpus luteum formation and female fertility, broadening FZD4 biology beyond its known retinal function.\",\n      \"evidence\": \"Fzd4 knockout mouse with histological, expression, and Ndph-null comparison\",\n      \"pmids\": [\"16093361\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The Wnt ligand acting through FZD4 in the ovary was not identified\",\n        \"Downstream signaling pathway (canonical vs. non-canonical) in corpus luteum not resolved\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolving how Norrin–FZD4 signaling specificity is achieved at the receptor level: TSPAN12 was identified as a co-receptor that physically associates with FZD4 and selectively amplifies Norrin- but not Wnt-dependent β-catenin signaling by promoting FZD4 multimerization.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA in retinal endothelial cells, luciferase reporter, and Tspan12/Norrin/Lrp5 mutant mouse epistasis\",\n      \"pmids\": [\"19837033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of TSPAN12-mediated multimerization not determined\",\n        \"Whether TSPAN12 modulates non-canonical FZD4 signaling not tested\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defining the ligand-binding domain: the CRD of FZD4 was shown to be necessary and sufficient for Norrin binding, with specific cysteine residues (C45, C204) and Y58 required for engagement, establishing the molecular basis for FEVR-associated loss of function.\",\n      \"evidence\": \"Cell-surface binding assays, site-directed mutagenesis, luciferase reporter, and Xenopus embryo signaling assay\",\n      \"pmids\": [\"21177847\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution structure of the Norrin–CRD interface not yet available at this time\",\n        \"Whether these residues also affect Wnt ligand binding was not tested\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placing FZD4 in an oncogenic transcriptional circuit: ERG was shown to transcriptionally upregulate FZD4 in prostate cancer, and FZD4 was positioned as the effector of ERG-driven EMT via Wnt/β-catenin signaling.\",\n      \"evidence\": \"ERG/FZD4 siRNA epistasis and FZD4 overexpression rescue in VCaP prostate cancer cells\",\n      \"pmids\": [\"20713528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The specific Wnt ligand operating through FZD4 in this cancer context was not identified\",\n        \"In vivo tumor model validation not reported\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealing how FEVR mutations cause disease at the cellular level: systematic analysis of 15 FEVR-associated FZD4 missense mutations showed that most cause ER retention and defective plasma membrane trafficking, establishing haploinsufficiency through protein misfolding rather than solely ligand-binding defects.\",\n      \"evidence\": \"Confocal microscopy, N-glycosylation profiling, polyubiquitination assays, chemical chaperone rescue in HeLa/COS-7 cells\",\n      \"pmids\": [\"24744206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether chemical chaperone rescue is therapeutically viable in vivo not tested\",\n        \"Contribution of proteasomal vs. lysosomal degradation of misfolded FZD4 not resolved\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrating dose-sensitivity of FZD4 in retinal vascular repair: Fzd4 heterozygous mice showed delayed retinal revascularization after oxygen-induced retinopathy, confirming that even partial reduction of FZD4 levels is pathologically significant.\",\n      \"evidence\": \"Fzd4 heterozygous mouse, OIR model with quantitative vascular area measurements\",\n      \"pmids\": [\"27489958\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the haploinsufficiency is due to reduced Norrin or Wnt signaling was not distinguished\",\n        \"Therapeutic rescue by FZD4 supplementation not attempted\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Expanding FZD4's non-canonical signaling: Wnt5a was shown to signal through FZD4 via JNK (not β-catenin) to mediate mechanical stretch-induced osteogenic differentiation, establishing FZD4 as a receptor for both canonical and non-canonical Wnt pathways depending on context.\",\n      \"evidence\": \"siRNA knockdown, cyclic stretch in vitro, western blot for JNK, and hindlimb unloading mouse model\",\n      \"pmids\": [\"30007964\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct Wnt5a–FZD4 physical interaction not demonstrated by binding assay\",\n        \"Co-receptor identity for this non-canonical pathway not identified\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying an upstream biogenesis factor: EMC3 was shown to be required for FZD4 protein expression and ER-to-plasma-membrane trafficking in retinal endothelial cells, connecting ER membrane protein complex function to Norrin/β-catenin signaling and retinal vascularization.\",\n      \"evidence\": \"Endothelial-specific Emc3 conditional knockout mouse, RNA-seq, luciferase reporter, LiCl rescue\",\n      \"pmids\": [\"34128175\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether EMC3 acts as a direct chaperone for FZD4 or affects it indirectly not resolved\",\n        \"Whether EMC3 regulates other Frizzled family members in the same cells not tested\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Comprehensive mechanistic classification of FEVR mutations: 34 FZD4 mutations were functionally categorized into five classes—signal peptide (reduced expression), CRD cysteine (disulfide disruption), extracellular (impaired Norrin binding), transmembrane (mislocalization), and intracellular (defective DVL2 recruitment)—providing a genotype-mechanism framework.\",\n      \"evidence\": \"Mutagenesis, expression assays, Norrin/β-catenin reporter, confocal localization, DVL2 co-IP in HEK293T/HeLa cells\",\n      \"pmids\": [\"38558095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vivo validation of the five-class model not performed\",\n        \"Whether mutation class predicts disease severity in patients not established\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying a transcriptional activator of FZD4 in endothelium: FOXF1 was shown to directly activate FZD4 transcription; nanoparticle delivery of Fzd4 cDNA to FOXF1-deficient endothelial cells rescued Wnt/β-catenin signaling and normalized tumor vasculature, demonstrating FZD4 as the critical FOXF1 effector.\",\n      \"evidence\": \"Endothelial-specific Foxf1 KO/OE mice, CUT&Tag ChIP-seq, nanoparticle Fzd4 rescue, RNA-seq\",\n      \"pmids\": [\"38558650\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether FOXF1 regulates FZD4 in non-lung endothelial beds not tested\",\n        \"Therapeutic durability of nanoparticle FZD4 delivery not assessed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defining post-translational requirements for FZD4 function: N-glycosylation at N59 and N144 was shown to be essential for FZD4 maturation, surface trafficking, Wnt/Norrin binding, and β-catenin signaling, resolving a long-standing gap in understanding FZD4 quality control.\",\n      \"evidence\": \"Site-directed mutagenesis of glycosylation sites, surface biotinylation, co-IP with Wnt/Norrin, luciferase reporter in A549 cells\",\n      \"pmids\": [\"40230079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether glycosylation affects TSPAN12-mediated multimerization not tested\",\n        \"Structural impact of glycan chains on CRD conformation not resolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How FZD4 selects between canonical (β-catenin) and non-canonical (JNK/PCP) signaling outputs depending on the Wnt ligand and cellular context remains mechanistically undefined, and structural models of the full-length receptor in complex with co-receptors (LRP5/6, TSPAN12) are lacking.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No full-length FZD4 structure with co-receptors available\",\n        \"Mechanism of canonical vs. non-canonical pathway selection at FZD4 not resolved\",\n        \"Relative contributions of individual Wnt ligands to FZD4 signaling in specific tissues not systematically defined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 6, 7, 8, 9, 15, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 15, 19]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 5, 6, 7, 8, 9, 15, 16]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 5, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [2, 10, 11, 16, 19]}\n    ],\n    \"complexes\": [\n      \"Norrin–FZD4–LRP5/6–TSPAN12 receptor complex\"\n    ],\n    \"partners\": [\n      \"NDP\",\n      \"TSPAN12\",\n      \"LRP5\",\n      \"LRP6\",\n      \"DVL2\",\n      \"EMC3\",\n      \"WNT5A\",\n      \"WNT6\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}