Affinage

FREM2

FRAS1-related extracellular matrix protein 2 · UniProt Q5SZK8

Length
3169 aa
Mass
351.2 kDa
Annotated
2026-06-09
22 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2005 Medium

    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

    PMID:16087869

    Open questions at the time
    • Did not identify the molecular partners of FREM2
    • Mechanism of how FREM2 supports cell migration/rearrangement unresolved
  2. 2006 High

    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

    PMID:16880404

    Open questions at the time
    • Stoichiometry and structural arrangement of the complex not defined
    • Direct binding interfaces not mapped
  3. 2007 Medium

    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

    PMID:17596926

    Open questions at the time
    • Molecular mechanism by which FRAS1 chaperones FREM2 secretion unknown
    • Whether FREM1 contributes to trafficking not addressed
  4. 2007 Medium

    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

    PMID:17462874 PMID:17596926

    Open questions at the time
    • Functional relationship between FREM3 and the Fraser complex not determined
  5. 2018 Medium

    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

    PMID:29688405

    Open questions at the time
    • Quantitative interaction binding affinities not measured
    • In vivo confirmation of variant-specific phenotypes not performed in this study
  6. 2018 Medium

    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

    PMID:29618029

    Open questions at the time
    • Cellular mechanism linking complex loss to mesothelial fold failure unresolved
    • Incomplete penetrance (~8%) not explained
  7. 2019 Medium

    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

    PMID:30802441

    Open questions at the time
    • Role of retinal FREM2 expression not functionally tested
    • Downstream transcriptional changes not mechanistically linked
  8. 2023 Medium

    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

    PMID:37047755

    Open questions at the time
    • Factors that do drive anchoring cord assembly remain unidentified
  9. 2025 Medium

    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

    PMID:41006360

    Open questions at the time
    • Mechanism of renal agenesis at the cellular level not defined
  10. 2025 Medium

    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

    PMID:39982223

    Open questions at the time
    • Functional role of FREM2 in glioblastoma biology not established
    • Mechanism of cytotoxicity not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis of Fraser complex assembly and the molecular mechanism by which FREM2-containing anchoring cords mediate epithelial-mesenchymal adhesion remain undefined.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2 GO:0098631 cell adhesion mediator activity 2
Localization
GO:0031012 extracellular matrix 3 GO:0005886 plasma membrane 2
Pathway
R-HSA-1266738 Developmental Biology 3 R-HSA-1474244 Extracellular matrix organization 2
Partners
FRAS1FREM1
Complex memberships
Fraser complex (FRAS1-FREM1-FREM2)

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 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. Immunofluorescence/immunohistochemistry in multiple mutant mouse models (Frem2, Fras1/GRIP1, Qbrick/Frem1 knockouts); co-immunoprecipitation/complex formation assay in transfected cells Proceedings of the National Academy of Sciences of the United States of America High 16880404
2005 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. ENU mutagenesis screen; genetic mapping and complementation; phenotypic analysis of Frem2 mutant mouse embryos Proceedings of the National Academy of Sciences of the United States of America Medium 16087869
2007 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. Immunofluorescence/immunohistochemistry in Fras1-null mutant mouse embryos Matrix biology : journal of the International Society for Matrix Biology Medium 17596926
2007 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. Immunofluorescence in Fras1-null embryos and blebbing mutant mice; tissue distribution analysis Matrix biology : journal of the International Society for Matrix Biology Medium 17462874 17596926
2018 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. Co-immunoprecipitation/interaction assay comparing wild-type and mutant FREM2 with FREM1; comparison of two missense variants for interaction strength Human molecular genetics Medium 29688405
2018 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. Analysis of Frem2 hypomorphic (ne/ne) mouse model; histological and developmental analysis of diaphragmatic mesothelial fold progression Human molecular genetics Medium 29618029
2019 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. CRISPR/Cas9 knock-in mouse model; immunohistochemistry; RNA-seq of fetal mutant mice Experimental eye research Medium 30802441
2023 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. Generation and characterization of AMACO-knockout mice; immunofluorescence and ultrastructural analysis of basement membrane and anchoring cords International journal of molecular sciences Medium 37047755
2025 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. Constitutive knockout mouse model; histological and phenotypic analysis Scientific reports Medium 41006360
2025 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. Surface plasmon resonance; flow cytometry; immunocytochemistry; transmission electron microscopy; in silico 3D modeling Antibodies (Basel, Switzerland) Medium 39982223

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 Breakdown of the reciprocal stabilization of QBRICK/Frem1, Fras1, and Frem2 at the basement membrane provokes Fraser syndrome-like defects. Proceedings of the National Academy of Sciences of the United States of America 110 16880404
2005 Tissue morphogenesis and vascular stability require the Frem2 protein, product of the mouse myelencephalic blebs gene. Proceedings of the National Academy of Sciences of the United States of America 56 16087869
2012 Amplification of the STOML3, FREM2, and LHFP genes is associated with mesenchymal differentiation in gliosarcoma. The American journal of pathology 29 22538188
2007 Basement membrane localization of Frem3 is independent of the Fras1/Frem1/Frem2 protein complex within the sublamina densa. Matrix biology : journal of the International Society for Matrix Biology 25 17596926
2007 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. Matrix biology : journal of the International Society for Matrix Biology 21 17462874
2018 The role of FREM2 and FRAS1 in the development of congenital diaphragmatic hernia. Human molecular genetics 19 29618029
2019 Loss-of-function mutations in FREM2 disrupt eye morphogenesis. Experimental eye research 18 30802441
2021 Algorithmically Deduced FREM2 Molecular Pathway Is a Potent Grade and Survival Biomarker of Human Gliomas. Cancers 14 34439271
2018 A homozygous mutation p.Arg2167Trp in FREM2 causes isolated cryptophthalmos. Human molecular genetics 13 29688405
2018 Meta-Analysis and Experimental Validation Identified FREM2 and SPRY1 as New Glioblastoma Marker Candidates. International journal of molecular sciences 12 29734672
2021 Cryptophthalmos, dental anomalies, oral vestibule defect, and a novel FREM2 mutation. Journal of human genetics 8 34408272
2015 Mesenchymal expression of the FRAS1/FREM2 gene unit is decreased in the developing fetal diaphragm of nitrofen-induced congenital diaphragmatic hernia. Pediatric surgery international 6 26519041
2023 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. International journal of molecular sciences 5 37047755
2021 The Metabolic Reprogramming of Frem2 Mutant Mice Embryos in Cryptophthalmos Development. Frontiers in cell and developmental biology 4 33490088
2025 Frem2 Knockout Mice Exhibit Fraser Syndrome Phenotypes and Neonatal Lethality Due to Bilateral Renal Agenesis. bioRxiv : the preprint server for biology 2 39554083
2025 In Vitro Functional Validation of an Anti-FREM2 Nanobody for Glioblastoma Cell Targeting. Antibodies (Basel, Switzerland) 2 39982223
2025 Frem2 knockout mice exhibit Fraser syndrome phenotypes and neonatal lethality due to bilateral renal agenesis. Scientific reports 2 41006360
2021 Excluding embryos with two novel mutations in FREM2 gene by the next-generation sequencing-based single nucleotide polymorphism haplotyping. Aging 2 34837691
2024 [Genetic analysis of a fetus with cryptophthalmos due to variants of FREM2 gene]. Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics 1 38684310
2022 Targeted resequencing of the 13q13 spondyloarthritis-linked locus identifies a rare variant in FREM2 possibly associated with familial spondyloarthritis. Joint bone spine 1 35640836
2026 FREM2 as a candidate gene for posterior urethral valves: Evidence from a case-parent cohort. Journal of pediatric urology 0 41950885
2025 Case Report: A case of Fraser syndrome 2 in a Chinese fetus caused by novel compound heterozygous variants in the FREM2 gene. Frontiers in medicine 0 41426592

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