{"gene":"FREM2","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":2006,"finding":"FREM2, FRAS1, and QBRICK/FREM1 form a ternary complex at the basement membrane and reciprocally stabilize each other's deposition there; loss of any one component (including FREM2) leads to coordinated depletion of all three from the basement membrane zone, as shown in Fraser syndrome model mice and by ternary complex formation in transfected cells.","method":"Immunofluorescence/immunohistochemistry in multiple mutant mouse models (Frem2, Fras1/GRIP1, Qbrick/Frem1 knockouts); co-immunoprecipitation/complex formation assay in transfected cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and multiple genetic KO models across independent Fraser syndrome mouse lines, independently consistent with findings in subsequent papers","pmids":["16880404"],"is_preprint":false},{"year":2005,"finding":"Loss of Frem2 function in mice (myelencephalic blebs mutation myF11) causes defects in morphogenetic events associated with vascular and multi-germ-layer tissue rearrangements, establishing a required role for FREM2 as an extracellular matrix component that supports cell migration and rearrangement during embryogenesis.","method":"ENU mutagenesis screen; genetic mapping and complementation; phenotypic analysis of Frem2 mutant mouse embryos","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean loss-of-function genetic model with defined developmental phenotype, single lab","pmids":["16087869"],"is_preprint":false},{"year":2007,"finding":"In the absence of FRAS1, FREM2 accumulates intracellularly within epithelial cells rather than being secreted to the basement membrane, indicating that FRAS1 is required for proper intracellular trafficking and export of FREM2 from embryonic epithelial cells, in addition to extracellular stabilization via complex formation.","method":"Immunofluorescence/immunohistochemistry in Fras1-null mutant mouse embryos","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence in genetic KO model, single lab","pmids":["17596926"],"is_preprint":false},{"year":2007,"finding":"FREM3 localizes to the sublamina densa basement membrane independently of the FRAS1/FREM1/FREM2 complex; in Fras1-null embryos, FREM3 basement membrane deposition is unaffected while FREM1 and FREM2 are abolished, demonstrating that FREM2 basement membrane localization is part of the interdependent FRAS1/FREM1/FREM2 complex but FREM3 is not.","method":"Immunofluorescence in Fras1-null embryos and blebbing mutant mice; tissue distribution analysis","journal":"Matrix biology : journal of the International Society for Matrix Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization in multiple genetic KO models, single lab, consistent with PMID 16880404","pmids":["17596926","17462874"],"is_preprint":false},{"year":2018,"finding":"A missense mutation p.Arg2167Trp in FREM2 decreases its interaction with FREM1 and impairs the function of the FRAS1–FREM2–FREM1 ternary complex; compared to the Fraser syndrome-associated p.Glu1972Lys mutation, p.Arg2167Trp has a weaker effect on disrupting the FREM2–FREM1 interaction, correlating with a milder (isolated cryptophthalmos) versus severe (Fraser syndrome) phenotype.","method":"Co-immunoprecipitation/interaction assay comparing wild-type and mutant FREM2 with FREM1; comparison of two missense variants for interaction strength","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein interaction assay with mutagenesis, single lab, genotype-phenotype correlation","pmids":["29688405"],"is_preprint":false},{"year":2018,"finding":"Deficiency of FREM2 (Frem2ne/ne mice) results in anterior sac congenital diaphragmatic hernia (CDH) in ~8% of animals, phenocopying FREM1 deficiency, and is preceded by failure of anterior mesothelial fold progression, establishing that the FREM1/FREM2/FRAS1 complex is required for normal diaphragm morphogenesis.","method":"Analysis of Frem2 hypomorphic (ne/ne) mouse model; histological and developmental analysis of diaphragmatic mesothelial fold progression","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean loss-of-function mouse model with defined cellular/developmental phenotype, single lab","pmids":["29618029"],"is_preprint":false},{"year":2019,"finding":"CRISPR/Cas9-generated mice carrying Frem2 compound heterozygous mutations (R725X/R2156W) recapitulate human isolated cryptophthalmos, and FREM2 protein is detected in the outer plexiform layer of the retina in cryptophthalmic eyes, establishing a required role for FREM2 in eyelid and anterior eye segment development.","method":"CRISPR/Cas9 knock-in mouse model; immunohistochemistry; RNA-seq of fetal mutant mice","journal":"Experimental eye research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct genetic model with phenotype and localization data, single lab","pmids":["30802441"],"is_preprint":false},{"year":2023,"finding":"The Fraser complex proteins FREM1, FREM2, and FRAS1 form anchoring cords at the dermal-epidermal junction independently of AMACO (VWA2); AMACO-deficient mice show no disruption of Fraser complex basement membrane deposition or anchoring cord formation, indicating AMACO is not required for complex assembly.","method":"Generation and characterization of AMACO-knockout mice; immunofluorescence and ultrastructural analysis of basement membrane and anchoring cords","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with direct localization readout, single lab","pmids":["37047755"],"is_preprint":false},{"year":2025,"finding":"Constitutive Frem2-knockout mice exhibit neonatal lethality primarily due to bilateral renal agenesis, as well as blood-filled blisters, cryptophthalmos, and syndactyly, confirming FREM2's essential role in kidney, skin, and eye development; FREM2 is described as a single-pass membrane protein of 3169 amino acids.","method":"Constitutive knockout mouse model; histological and phenotypic analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — constitutive KO with defined multi-organ phenotype, single lab, consistent with prior Frem2 mutant models","pmids":["41006360"],"is_preprint":false},{"year":2025,"finding":"An anti-FREM2 nanobody (NB3F18) binds the membrane-associated FREM2 protein on glioblastoma stem cells with moderate affinity (confirmed by surface plasmon resonance), localizes to the cell surface and is internalized via the endocytic pathway into multivesicular bodies and lysosomes, and is cytotoxic to glioblastoma stem cells.","method":"Surface plasmon resonance; flow cytometry; immunocytochemistry; transmission electron microscopy; in silico 3D modeling","journal":"Antibodies (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay (SPR) plus cell-based localization and cytotoxicity, single lab, multiple orthogonal methods","pmids":["39982223"],"is_preprint":false}],"current_model":"FREM2 is a single-pass extracellular matrix protein that localizes to the sublamina densa of the basement membrane, where it forms a reciprocally stabilizing ternary complex with FRAS1 and FREM1 (the Fraser complex); FRAS1 is required for FREM2's intracellular trafficking and secretion, and the intact complex is essential for epithelial-mesenchymal adhesion during embryogenesis, with loss of FREM2 causing Fraser syndrome phenotypes including subepidermal blistering, cryptophthalmos, syndactyly, renal agenesis, and diaphragmatic hernia."},"narrative":{"mechanistic_narrative":"FREM2 is an extracellular matrix protein that supports epithelial-mesenchymal adhesion and tissue morphogenesis during embryogenesis [PMID:16087869]. At the sublamina densa of the basement membrane it forms a reciprocally stabilizing ternary complex with FRAS1 and FREM1 (the Fraser complex), such that loss of any one component depletes all three from the basement membrane zone [PMID:16880404]; FRAS1 is additionally required for the intracellular trafficking and secretion of FREM2, which otherwise accumulates within epithelial cells [PMID:17596926]. Within this complex FREM2 contributes anchoring cords at the dermal-epidermal junction that assemble independently of AMACO/VWA2 and of the independently deposited FREM3 [PMID:17596926, PMID:17462874, PMID:37047755]. Disruption of FREM2 in mice causes a graded set of developmental defects—bilateral renal agenesis with neonatal lethality, subepidermal/blood-filled blisters, cryptophthalmos, syndactyly, and anterior congenital diaphragmatic hernia—establishing requirements in kidney, skin, eye, and diaphragm morphogenesis [PMID:41006360, PMID:29618029, PMID:30802441]. Missense variants that weaken the FREM2–FREM1 interaction produce correspondingly graded phenotypes, with stronger disruption causing full Fraser syndrome and weaker disruption causing isolated cryptophthalmos [PMID:29688405]. FREM2 is also displayed on the surface of glioblastoma stem cells, where an internalizing anti-FREM2 nanobody is cytotoxic [PMID:39982223].","teleology":[{"year":2005,"claim":"Establishing what process FREM2 serves, loss-of-function in mice showed it is an extracellular matrix component required for morphogenetic tissue rearrangements during embryogenesis.","evidence":"ENU mutagenesis screen and phenotypic analysis of Frem2 mutant mouse embryos","pmids":["16087869"],"confidence":"Medium","gaps":["Did not identify the molecular partners of FREM2","Mechanism of how FREM2 supports cell migration/rearrangement unresolved"]},{"year":2006,"claim":"Resolving the molecular basis of FREM2 function, FREM2 was shown to form a ternary complex with FRAS1 and FREM1 at the basement membrane in which the three proteins reciprocally stabilize each other's deposition.","evidence":"Co-immunoprecipitation in transfected cells and immunolocalization across multiple Fraser-syndrome mutant mouse lines","pmids":["16880404"],"confidence":"High","gaps":["Stoichiometry and structural arrangement of the complex not defined","Direct binding interfaces not mapped"]},{"year":2007,"claim":"Distinguishing trafficking from extracellular stabilization, FRAS1 was found to be required for the intracellular export of FREM2, which accumulates inside epithelial cells when FRAS1 is absent.","evidence":"Immunolocalization in Fras1-null mouse embryos","pmids":["17596926"],"confidence":"Medium","gaps":["Molecular mechanism by which FRAS1 chaperones FREM2 secretion unknown","Whether FREM1 contributes to trafficking not addressed"]},{"year":2007,"claim":"Defining the boundaries of the complex, FREM3 was shown to localize to the same sublamina densa independently of FRAS1/FREM1/FREM2, confirming FREM2 deposition is specifically part of the interdependent Fraser complex.","evidence":"Immunofluorescence in Fras1-null and blebbing mutant mice","pmids":["17596926","17462874"],"confidence":"Medium","gaps":["Functional relationship between FREM3 and the Fraser complex not determined"]},{"year":2018,"claim":"Connecting interaction strength to disease severity, a missense variant (p.Arg2167Trp) that only weakly disrupts the FREM2–FREM1 interaction was shown to cause a milder phenotype than the strongly disrupting p.Glu1972Lys variant.","evidence":"Co-immunoprecipitation interaction assays comparing wild-type and mutant FREM2 variants","pmids":["29688405"],"confidence":"Medium","gaps":["Quantitative interaction binding affinities not measured","In vivo confirmation of variant-specific phenotypes not performed in this study"]},{"year":2018,"claim":"Extending the organ requirements of the complex, Frem2 hypomorphic mice were shown to develop anterior congenital diaphragmatic hernia preceded by failed mesothelial fold progression, phenocopying FREM1 loss.","evidence":"Histological and developmental analysis of Frem2ne/ne hypomorphic mice","pmids":["29618029"],"confidence":"Medium","gaps":["Cellular mechanism linking complex loss to mesothelial fold failure unresolved","Incomplete penetrance (~8%) not explained"]},{"year":2019,"claim":"Establishing the eye-development requirement, compound heterozygous Frem2 mice recapitulated isolated cryptophthalmos and showed FREM2 protein in the retinal outer plexiform layer.","evidence":"CRISPR/Cas9 knock-in mouse model with immunohistochemistry and RNA-seq","pmids":["30802441"],"confidence":"Medium","gaps":["Role of retinal FREM2 expression not functionally tested","Downstream transcriptional changes not mechanistically linked"]},{"year":2023,"claim":"Refining complex assembly requirements, AMACO/VWA2 was shown to be dispensable, as Fraser-complex basement membrane deposition and anchoring cords formed normally in AMACO-knockout mice.","evidence":"AMACO-knockout mice with immunofluorescence and ultrastructural analysis","pmids":["37047755"],"confidence":"Medium","gaps":["Factors that do drive anchoring cord assembly remain unidentified"]},{"year":2025,"claim":"Consolidating the multi-organ requirement, a constitutive Frem2 knockout showed neonatal lethality from bilateral renal agenesis alongside skin, eye, and limb defects.","evidence":"Constitutive knockout mouse with histological and phenotypic analysis","pmids":["41006360"],"confidence":"Medium","gaps":["Mechanism of renal agenesis at the cellular level not defined"]},{"year":2025,"claim":"Opening a translational direction, an internalizing anti-FREM2 nanobody was shown to bind surface FREM2 on glioblastoma stem cells, traffic to lysosomes, and exert cytotoxicity.","evidence":"Surface plasmon resonance, flow cytometry, electron microscopy, and cytotoxicity assays on glioblastoma stem cells","pmids":["39982223"],"confidence":"Medium","gaps":["Functional role of FREM2 in glioblastoma biology not established","Mechanism of cytotoxicity not defined"]},{"year":null,"claim":"The structural basis of Fraser complex assembly and the molecular mechanism by which FREM2-containing anchoring cords mediate epithelial-mesenchymal adhesion remain undefined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the FRAS1–FREM1–FREM2 complex","Direct binding interfaces and stoichiometry unmapped","Signaling or adhesion mechanism downstream of anchoring cords unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,7]}],"localization":[{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[0,3,7]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[8,9]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[0,7]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,5,8]}],"complexes":["Fraser complex (FRAS1-FREM1-FREM2)"],"partners":["FRAS1","FREM1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5SZK8","full_name":"FRAS1-related extracellular matrix protein 2","aliases":["ECM3 homolog"],"length_aa":3169,"mass_kda":351.2,"function":"Extracellular matrix protein required for maintenance of the integrity of the skin epithelium and for maintenance of renal epithelia (PubMed:15838507). Required for epidermal adhesion (PubMed:15838507). Involved in the development of eyelids and the anterior segment of the eyeballs (PubMed:29688405, PubMed:30802441)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q5SZK8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FREM2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FREM2","total_profiled":1310},"omim":[{"mim_id":"617667","title":"FRASER SYNDROME 3; FRASRS3","url":"https://www.omim.org/entry/617667"},{"mim_id":"617666","title":"FRASER SYNDROME 2; FRASRS2","url":"https://www.omim.org/entry/617666"},{"mim_id":"608980","title":"BIFID NOSE WITH OR WITHOUT ANORECTAL AND RENAL ANOMALIES; BNAR","url":"https://www.omim.org/entry/608980"},{"mim_id":"608945","title":"FRAS1-RELATED EXTRACELLULAR MATRIX PROTEIN 2; FREM2","url":"https://www.omim.org/entry/608945"},{"mim_id":"608944","title":"FRAS1-RELATED EXTRACELLULAR MATRIX PROTEIN 1; FREM1","url":"https://www.omim.org/entry/608944"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"kidney","ntpm":7.2},{"tissue":"thyroid gland","ntpm":4.6}],"url":"https://www.proteinatlas.org/search/FREM2"},"hgnc":{"alias_symbol":["DKFZp686J0811"],"prev_symbol":[]},"alphafold":{"accession":"Q5SZK8","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5SZK8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5SZK8-2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5SZK8-2-F1-predicted_aligned_error_v6.png","plddt_mean":72.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FREM2","jax_strain_url":"https://www.jax.org/strain/search?query=FREM2"},"sequence":{"accession":"Q5SZK8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5SZK8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5SZK8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5SZK8"}},"corpus_meta":[{"pmid":"16880404","id":"PMC_16880404","title":"Breakdown of the reciprocal stabilization of QBRICK/Frem1, Fras1, and Frem2 at the basement membrane provokes Fraser syndrome-like defects.","date":"2006","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16880404","citation_count":110,"is_preprint":false},{"pmid":"16087869","id":"PMC_16087869","title":"Tissue morphogenesis and vascular stability require the Frem2 protein, product of the mouse myelencephalic blebs gene.","date":"2005","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16087869","citation_count":56,"is_preprint":false},{"pmid":"22538188","id":"PMC_22538188","title":"Amplification of the STOML3, FREM2, and LHFP genes is associated with mesenchymal differentiation in gliosarcoma.","date":"2012","source":"The American journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/22538188","citation_count":29,"is_preprint":false},{"pmid":"17596926","id":"PMC_17596926","title":"Basement membrane localization of Frem3 is independent of the Fras1/Frem1/Frem2 protein complex within the sublamina densa.","date":"2007","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/17596926","citation_count":25,"is_preprint":false},{"pmid":"17462874","id":"PMC_17462874","title":"Frem3, a member of the 12 CSPG repeats-containing extracellular matrix protein family, is a basement membrane protein with tissue distribution patterns distinct from those of Fras1, Frem2, and QBRICK/Frem1.","date":"2007","source":"Matrix biology : journal of the International Society for Matrix Biology","url":"https://pubmed.ncbi.nlm.nih.gov/17462874","citation_count":21,"is_preprint":false},{"pmid":"29618029","id":"PMC_29618029","title":"The role of FREM2 and FRAS1 in the development of congenital diaphragmatic hernia.","date":"2018","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29618029","citation_count":19,"is_preprint":false},{"pmid":"30802441","id":"PMC_30802441","title":"Loss-of-function mutations in FREM2 disrupt eye morphogenesis.","date":"2019","source":"Experimental eye research","url":"https://pubmed.ncbi.nlm.nih.gov/30802441","citation_count":18,"is_preprint":false},{"pmid":"34439271","id":"PMC_34439271","title":"Algorithmically Deduced FREM2 Molecular Pathway Is a Potent Grade and Survival Biomarker of Human Gliomas.","date":"2021","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/34439271","citation_count":14,"is_preprint":false},{"pmid":"29688405","id":"PMC_29688405","title":"A homozygous mutation p.Arg2167Trp in FREM2 causes isolated cryptophthalmos.","date":"2018","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/29688405","citation_count":13,"is_preprint":false},{"pmid":"29734672","id":"PMC_29734672","title":"Meta-Analysis and Experimental Validation Identified FREM2 and SPRY1 as New Glioblastoma Marker Candidates.","date":"2018","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/29734672","citation_count":12,"is_preprint":false},{"pmid":"34408272","id":"PMC_34408272","title":"Cryptophthalmos, dental anomalies, oral vestibule defect, and a novel FREM2 mutation.","date":"2021","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34408272","citation_count":8,"is_preprint":false},{"pmid":"26519041","id":"PMC_26519041","title":"Mesenchymal expression of the FRAS1/FREM2 gene unit is decreased in the developing fetal diaphragm of nitrofen-induced congenital diaphragmatic hernia.","date":"2015","source":"Pediatric surgery international","url":"https://pubmed.ncbi.nlm.nih.gov/26519041","citation_count":6,"is_preprint":false},{"pmid":"37047755","id":"PMC_37047755","title":"The Fraser Complex Proteins (Frem1, Frem2, and Fras1) Can Form Anchoring Cords in the Absence of AMACO at the Dermal-Epidermal Junction of Mouse Skin.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37047755","citation_count":5,"is_preprint":false},{"pmid":"33490088","id":"PMC_33490088","title":"The Metabolic Reprogramming of Frem2 Mutant Mice Embryos in Cryptophthalmos Development.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/33490088","citation_count":4,"is_preprint":false},{"pmid":"41006360","id":"PMC_41006360","title":"Frem2 knockout mice exhibit Fraser syndrome phenotypes and neonatal lethality due to bilateral renal agenesis.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/41006360","citation_count":2,"is_preprint":false},{"pmid":"39554083","id":"PMC_39554083","title":"Frem2 Knockout Mice Exhibit Fraser Syndrome Phenotypes and Neonatal Lethality Due to Bilateral Renal Agenesis.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/39554083","citation_count":2,"is_preprint":false},{"pmid":"34837691","id":"PMC_34837691","title":"Excluding embryos with two novel mutations in FREM2 gene by the next-generation sequencing-based single nucleotide polymorphism haplotyping.","date":"2021","source":"Aging","url":"https://pubmed.ncbi.nlm.nih.gov/34837691","citation_count":2,"is_preprint":false},{"pmid":"39982223","id":"PMC_39982223","title":"In Vitro Functional Validation of an Anti-FREM2 Nanobody for Glioblastoma Cell Targeting.","date":"2025","source":"Antibodies (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39982223","citation_count":2,"is_preprint":false},{"pmid":"35640836","id":"PMC_35640836","title":"Targeted resequencing of the 13q13 spondyloarthritis-linked locus identifies a rare variant in FREM2 possibly associated with familial spondyloarthritis.","date":"2022","source":"Joint bone spine","url":"https://pubmed.ncbi.nlm.nih.gov/35640836","citation_count":1,"is_preprint":false},{"pmid":"38684310","id":"PMC_38684310","title":"[Genetic analysis of a fetus with cryptophthalmos due to variants of FREM2 gene].","date":"2024","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38684310","citation_count":1,"is_preprint":false},{"pmid":"41950885","id":"PMC_41950885","title":"FREM2 as a candidate gene for posterior urethral valves: Evidence from a case-parent cohort.","date":"2026","source":"Journal of pediatric urology","url":"https://pubmed.ncbi.nlm.nih.gov/41950885","citation_count":0,"is_preprint":false},{"pmid":"41426592","id":"PMC_41426592","title":"Case Report: A case of Fraser syndrome 2 in a Chinese fetus caused by novel compound heterozygous variants in the FREM2 gene.","date":"2025","source":"Frontiers in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41426592","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.10.28.620501","title":"<i>Frem2</i>  Knockout Mice Exhibit Fraser Syndrome Phenotypes and Neonatal Lethality Due to Bilateral Renal Agenesis","date":"2024-10-28","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.28.620501","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.02.05.636623","title":"Treatment of human oocytes with extracellular vesicles from follicular fluid during rescue in vitro maturation enhances maturation rates and modulates oocyte proteome and ultrastructure","date":"2025-02-05","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.05.636623","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15827,"output_tokens":2498,"usd":0.042475,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9716,"output_tokens":3210,"usd":0.064415,"stage2_stop_reason":"end_turn"},"total_usd":0.10689,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"FREM2, FRAS1, and QBRICK/FREM1 form a ternary complex at the basement membrane and reciprocally stabilize each other's deposition there; loss of any one component (including FREM2) leads to coordinated depletion of all three from the basement membrane zone, as shown in Fraser syndrome model mice and by ternary complex formation in transfected cells.\",\n      \"method\": \"Immunofluorescence/immunohistochemistry in multiple mutant mouse models (Frem2, Fras1/GRIP1, Qbrick/Frem1 knockouts); co-immunoprecipitation/complex formation assay in transfected cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and multiple genetic KO models across independent Fraser syndrome mouse lines, independently consistent with findings in subsequent papers\",\n      \"pmids\": [\"16880404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Loss of Frem2 function in mice (myelencephalic blebs mutation myF11) causes defects in morphogenetic events associated with vascular and multi-germ-layer tissue rearrangements, establishing a required role for FREM2 as an extracellular matrix component that supports cell migration and rearrangement during embryogenesis.\",\n      \"method\": \"ENU mutagenesis screen; genetic mapping and complementation; phenotypic analysis of Frem2 mutant mouse embryos\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean loss-of-function genetic model with defined developmental phenotype, single lab\",\n      \"pmids\": [\"16087869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In the absence of FRAS1, FREM2 accumulates intracellularly within epithelial cells rather than being secreted to the basement membrane, indicating that FRAS1 is required for proper intracellular trafficking and export of FREM2 from embryonic epithelial cells, in addition to extracellular stabilization via complex formation.\",\n      \"method\": \"Immunofluorescence/immunohistochemistry in Fras1-null mutant mouse embryos\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence in genetic KO model, single lab\",\n      \"pmids\": [\"17596926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"FREM3 localizes to the sublamina densa basement membrane independently of the FRAS1/FREM1/FREM2 complex; in Fras1-null embryos, FREM3 basement membrane deposition is unaffected while FREM1 and FREM2 are abolished, demonstrating that FREM2 basement membrane localization is part of the interdependent FRAS1/FREM1/FREM2 complex but FREM3 is not.\",\n      \"method\": \"Immunofluorescence in Fras1-null embryos and blebbing mutant mice; tissue distribution analysis\",\n      \"journal\": \"Matrix biology : journal of the International Society for Matrix Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization in multiple genetic KO models, single lab, consistent with PMID 16880404\",\n      \"pmids\": [\"17596926\", \"17462874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A missense mutation p.Arg2167Trp in FREM2 decreases its interaction with FREM1 and impairs the function of the FRAS1–FREM2–FREM1 ternary complex; compared to the Fraser syndrome-associated p.Glu1972Lys mutation, p.Arg2167Trp has a weaker effect on disrupting the FREM2–FREM1 interaction, correlating with a milder (isolated cryptophthalmos) versus severe (Fraser syndrome) phenotype.\",\n      \"method\": \"Co-immunoprecipitation/interaction assay comparing wild-type and mutant FREM2 with FREM1; comparison of two missense variants for interaction strength\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein interaction assay with mutagenesis, single lab, genotype-phenotype correlation\",\n      \"pmids\": [\"29688405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Deficiency of FREM2 (Frem2ne/ne mice) results in anterior sac congenital diaphragmatic hernia (CDH) in ~8% of animals, phenocopying FREM1 deficiency, and is preceded by failure of anterior mesothelial fold progression, establishing that the FREM1/FREM2/FRAS1 complex is required for normal diaphragm morphogenesis.\",\n      \"method\": \"Analysis of Frem2 hypomorphic (ne/ne) mouse model; histological and developmental analysis of diaphragmatic mesothelial fold progression\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean loss-of-function mouse model with defined cellular/developmental phenotype, single lab\",\n      \"pmids\": [\"29618029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CRISPR/Cas9-generated mice carrying Frem2 compound heterozygous mutations (R725X/R2156W) recapitulate human isolated cryptophthalmos, and FREM2 protein is detected in the outer plexiform layer of the retina in cryptophthalmic eyes, establishing a required role for FREM2 in eyelid and anterior eye segment development.\",\n      \"method\": \"CRISPR/Cas9 knock-in mouse model; immunohistochemistry; RNA-seq of fetal mutant mice\",\n      \"journal\": \"Experimental eye research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct genetic model with phenotype and localization data, single lab\",\n      \"pmids\": [\"30802441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The Fraser complex proteins FREM1, FREM2, and FRAS1 form anchoring cords at the dermal-epidermal junction independently of AMACO (VWA2); AMACO-deficient mice show no disruption of Fraser complex basement membrane deposition or anchoring cord formation, indicating AMACO is not required for complex assembly.\",\n      \"method\": \"Generation and characterization of AMACO-knockout mice; immunofluorescence and ultrastructural analysis of basement membrane and anchoring cords\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with direct localization readout, single lab\",\n      \"pmids\": [\"37047755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Constitutive Frem2-knockout mice exhibit neonatal lethality primarily due to bilateral renal agenesis, as well as blood-filled blisters, cryptophthalmos, and syndactyly, confirming FREM2's essential role in kidney, skin, and eye development; FREM2 is described as a single-pass membrane protein of 3169 amino acids.\",\n      \"method\": \"Constitutive knockout mouse model; histological and phenotypic analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — constitutive KO with defined multi-organ phenotype, single lab, consistent with prior Frem2 mutant models\",\n      \"pmids\": [\"41006360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"An anti-FREM2 nanobody (NB3F18) binds the membrane-associated FREM2 protein on glioblastoma stem cells with moderate affinity (confirmed by surface plasmon resonance), localizes to the cell surface and is internalized via the endocytic pathway into multivesicular bodies and lysosomes, and is cytotoxic to glioblastoma stem cells.\",\n      \"method\": \"Surface plasmon resonance; flow cytometry; immunocytochemistry; transmission electron microscopy; in silico 3D modeling\",\n      \"journal\": \"Antibodies (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay (SPR) plus cell-based localization and cytotoxicity, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"39982223\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FREM2 is a single-pass extracellular matrix protein that localizes to the sublamina densa of the basement membrane, where it forms a reciprocally stabilizing ternary complex with FRAS1 and FREM1 (the Fraser complex); FRAS1 is required for FREM2's intracellular trafficking and secretion, and the intact complex is essential for epithelial-mesenchymal adhesion during embryogenesis, with loss of FREM2 causing Fraser syndrome phenotypes including subepidermal blistering, cryptophthalmos, syndactyly, renal agenesis, and diaphragmatic hernia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FREM2 is an extracellular matrix protein that supports epithelial-mesenchymal adhesion and tissue morphogenesis during embryogenesis [#1]. At the sublamina densa of the basement membrane it forms a reciprocally stabilizing ternary complex with FRAS1 and FREM1 (the Fraser complex), such that loss of any one component depletes all three from the basement membrane zone [#0]; FRAS1 is additionally required for the intracellular trafficking and secretion of FREM2, which otherwise accumulates within epithelial cells [#2]. Within this complex FREM2 contributes anchoring cords at the dermal-epidermal junction that assemble independently of AMACO/VWA2 and of the independently deposited FREM3 [#3, #7]. Disruption of FREM2 in mice causes a graded set of developmental defects—bilateral renal agenesis with neonatal lethality, subepidermal/blood-filled blisters, cryptophthalmos, syndactyly, and anterior congenital diaphragmatic hernia—establishing requirements in kidney, skin, eye, and diaphragm morphogenesis [#8, #5, #6]. Missense variants that weaken the FREM2–FREM1 interaction produce correspondingly graded phenotypes, with stronger disruption causing full Fraser syndrome and weaker disruption causing isolated cryptophthalmos [#4]. FREM2 is also displayed on the surface of glioblastoma stem cells, where an internalizing anti-FREM2 nanobody is cytotoxic [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing what process FREM2 serves, loss-of-function in mice showed it is an extracellular matrix component required for morphogenetic tissue rearrangements during embryogenesis.\",\n      \"evidence\": \"ENU mutagenesis screen and phenotypic analysis of Frem2 mutant mouse embryos\",\n      \"pmids\": [\"16087869\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the molecular partners of FREM2\", \"Mechanism of how FREM2 supports cell migration/rearrangement unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolving the molecular basis of FREM2 function, FREM2 was shown to form a ternary complex with FRAS1 and FREM1 at the basement membrane in which the three proteins reciprocally stabilize each other's deposition.\",\n      \"evidence\": \"Co-immunoprecipitation in transfected cells and immunolocalization across multiple Fraser-syndrome mutant mouse lines\",\n      \"pmids\": [\"16880404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structural arrangement of the complex not defined\", \"Direct binding interfaces not mapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Distinguishing trafficking from extracellular stabilization, FRAS1 was found to be required for the intracellular export of FREM2, which accumulates inside epithelial cells when FRAS1 is absent.\",\n      \"evidence\": \"Immunolocalization in Fras1-null mouse embryos\",\n      \"pmids\": [\"17596926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism by which FRAS1 chaperones FREM2 secretion unknown\", \"Whether FREM1 contributes to trafficking not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defining the boundaries of the complex, FREM3 was shown to localize to the same sublamina densa independently of FRAS1/FREM1/FREM2, confirming FREM2 deposition is specifically part of the interdependent Fraser complex.\",\n      \"evidence\": \"Immunofluorescence in Fras1-null and blebbing mutant mice\",\n      \"pmids\": [\"17596926\", \"17462874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional relationship between FREM3 and the Fraser complex not determined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connecting interaction strength to disease severity, a missense variant (p.Arg2167Trp) that only weakly disrupts the FREM2–FREM1 interaction was shown to cause a milder phenotype than the strongly disrupting p.Glu1972Lys variant.\",\n      \"evidence\": \"Co-immunoprecipitation interaction assays comparing wild-type and mutant FREM2 variants\",\n      \"pmids\": [\"29688405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quantitative interaction binding affinities not measured\", \"In vivo confirmation of variant-specific phenotypes not performed in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extending the organ requirements of the complex, Frem2 hypomorphic mice were shown to develop anterior congenital diaphragmatic hernia preceded by failed mesothelial fold progression, phenocopying FREM1 loss.\",\n      \"evidence\": \"Histological and developmental analysis of Frem2ne/ne hypomorphic mice\",\n      \"pmids\": [\"29618029\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cellular mechanism linking complex loss to mesothelial fold failure unresolved\", \"Incomplete penetrance (~8%) not explained\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Establishing the eye-development requirement, compound heterozygous Frem2 mice recapitulated isolated cryptophthalmos and showed FREM2 protein in the retinal outer plexiform layer.\",\n      \"evidence\": \"CRISPR/Cas9 knock-in mouse model with immunohistochemistry and RNA-seq\",\n      \"pmids\": [\"30802441\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Role of retinal FREM2 expression not functionally tested\", \"Downstream transcriptional changes not mechanistically linked\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Refining complex assembly requirements, AMACO/VWA2 was shown to be dispensable, as Fraser-complex basement membrane deposition and anchoring cords formed normally in AMACO-knockout mice.\",\n      \"evidence\": \"AMACO-knockout mice with immunofluorescence and ultrastructural analysis\",\n      \"pmids\": [\"37047755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Factors that do drive anchoring cord assembly remain unidentified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Consolidating the multi-organ requirement, a constitutive Frem2 knockout showed neonatal lethality from bilateral renal agenesis alongside skin, eye, and limb defects.\",\n      \"evidence\": \"Constitutive knockout mouse with histological and phenotypic analysis\",\n      \"pmids\": [\"41006360\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of renal agenesis at the cellular level not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Opening a translational direction, an internalizing anti-FREM2 nanobody was shown to bind surface FREM2 on glioblastoma stem cells, traffic to lysosomes, and exert cytotoxicity.\",\n      \"evidence\": \"Surface plasmon resonance, flow cytometry, electron microscopy, and cytotoxicity assays on glioblastoma stem cells\",\n      \"pmids\": [\"39982223\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of FREM2 in glioblastoma biology not established\", \"Mechanism of cytotoxicity not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of Fraser complex assembly and the molecular mechanism by which FREM2-containing anchoring cords mediate epithelial-mesenchymal adhesion remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the FRAS1–FREM1–FREM2 complex\", \"Direct binding interfaces and stoichiometry unmapped\", \"Signaling or adhesion mechanism downstream of anchoring cords unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [0, 3, 7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 5, 8]}\n    ],\n    \"complexes\": [\"Fraser complex (FRAS1-FREM1-FREM2)\"],\n    \"partners\": [\"FRAS1\", \"FREM1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}