{"gene":"FLRT2","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":1999,"finding":"FLRT2 is a type I transmembrane protein containing 10 leucine-rich repeats flanked by cysteine-rich regions, a fibronectin/collagen-like domain, and an intracellular tail; when expressed in SF9 and COS-1 cells it migrates as an ~85-kDa glycoprotein, consistent with a role in cell adhesion and/or receptor signaling.","method":"Heterologous expression in SF9 and COS-1 cells, molecular cloning, glycosylation analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — direct biochemical characterization of recombinant protein, single study","pmids":["10644439"],"is_preprint":false},{"year":2011,"finding":"The shed FLRT2 ectodomain binds specifically to the Unc5D receptor and acts as a repulsive guidance cue for Unc5D-positive neurons; in the developing neocortex, FLRT2/Unc5D signaling delays migration of SVZ-derived neurons toward the cortical plate, as shown by premature migration upon deletion of either FLRT2 or Unc5D and delayed migration upon Unc5D overexpression.","method":"Binding assays (ectodomain-receptor interaction), mouse genetic deletion, overexpression in vivo, neuronal migration assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — reciprocal genetic epistasis (KO + OE), receptor-binding assays, replicated across FLRT2 and FLRT3 family members in same study","pmids":["21673655"],"is_preprint":false},{"year":2011,"finding":"FLRT2 is required in the epicardium for heart morphogenesis; loss of FLRT2 disrupts epicardial sheet integrity and basement membrane organization, leading to mid-gestation cardiac lethality; FLRT2 and FLRT3 are functionally interchangeable in both the epicardium and the AVE, as demonstrated by in vitro and in vivo reconstitution assays.","method":"Gene targeting (conditional KO), in vitro and in vivo reconstitution assays, histological analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 1–2 — gene targeting with defined phenotypic rescue, in vivo reconstitution","pmids":["21350012"],"is_preprint":false},{"year":2011,"finding":"FLRT2 interacts with both the extracellular and intracellular regions of FGFR2; the LRR domain of FLRT2 mediates interaction with the extracellular region of FGFR2, and the C-tail of FLRT2 interacts with the intracellular region of FGFR2; FLRT2 positively regulates FGF signaling (FGFR2 protein/mRNA levels and ERK phosphorylation) in craniofacial tissues.","method":"Co-immunoprecipitation from embryonic craniofacial tissue lysates, GST pulldown, yeast two-hybrid, stable shRNA knockdown and cDNA overexpression with ERK phosphorylation readout","journal":"Journal of dental research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, GST pulldown, Y2H) plus functional downstream readout in same study","pmids":["21765038"],"is_preprint":false},{"year":2011,"finding":"FLRT2 promotes cell proliferation and inhibits cell-cell adhesion (reducing N-cadherin-mediated aggregation) during early chondrogenesis; FLRT2 knockdown slows proliferation and increases PNA-stained cell aggregates, while overexpression accelerates proliferation and reduces aggregation.","method":"Stable knockdown and overexpression in ATDC5 chondroprogenitor cells, proliferation assays, PNA staining, N-cadherin immunostaining, wound-healing migration assay","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD/OE with defined cellular phenotypes, single lab","pmids":["21769912"],"is_preprint":false},{"year":2014,"finding":"FLRT2 interacts with fibronectin in the extracellular matrix of ATDC5 chondroprogenitor cells; FLRT2 co-localizes with fibronectin fibrils, is found in ECM fractions, and co-immunoprecipitates with fibronectin; disruption of fibronectin fibril formation reduces extracellular FLRT2 accumulation; FLRT2 exists in both membrane-bound and shed forms.","method":"Co-immunoprecipitation, immunolocalization, ECM fractionation, fibronectin-coated bead binding, fibronectin-blocking peptide experiments, Western blot with domain-specific antibodies","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple orthogonal methods but all from one lab, no in vitro reconstitution with purified proteins","pmids":["24585683"],"is_preprint":false},{"year":2017,"finding":"FLRT2 expressed on endothelial cells in the placental labyrinth signals through the UNC5B receptor to mediate inter-endothelial repulsion, which is required for proper alignment of endothelial cells and feto-maternal circulation; endothelial-specific deletion of FLRT2 causes aberrant endothelial layering and embryonic lethality.","method":"Endothelial cell-specific conditional KO mouse, phenotypic analysis of placental labyrinth, receptor-ligand interaction with UNC5B","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined cellular phenotype and receptor identification, replicated concept from neuronal FLRT2-UNC5 studies","pmids":["28576770"],"is_preprint":false},{"year":2019,"finding":"FLRT2 regulates osteoclast multinucleation by interfering with Netrin1-Unc5B interaction; FLRT2 deficiency reduces hyper-multinucleation and attenuates RANKL-induced Rac1 activation, effects rescued by Unc5B knockdown; Netrin1 inhibitory effects on multinucleation are abolished in FLRT2-deficient cells.","method":"Genetic KO in osteoclasts, RNAi knockdown of Unc5B, Rac1 activation assay, Netrin1 treatment, osteoclast differentiation assays","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis (FLRT2 KO + Unc5B KD rescue), Rac1 biochemical readout, single study","pmids":["31383250"],"is_preprint":false},{"year":2021,"finding":"FLRT2 and FLRT3 cooperate in a non-cell-autonomous repulsive mechanism to maintain tangential migratory streams of cortical interneurons; double KO of FLRT2/FLRT3 phenocopies double KO of their repulsive receptors Unc5B/Unc5D; FLRT proteins act as chemorepellent ligands for interneurons in vitro, partially dependent on FLRT-Unc5 interaction.","method":"Double conditional KO mice (FLRT2/FLRT3 and Unc5B/Unc5D), in vitro chemorepulsion assay, immunostaining of interneuron streams","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double KO phenocopy, in vitro functional assay, multiple orthogonal approaches","pmids":["34301831"],"is_preprint":false},{"year":2021,"finding":"FLRT2 is localized to pre- and postsynapses in the CA1 region of the adult hippocampus and is upregulated in reactive astrocytes around spinal cord injury lesion sites; its expression is dynamic across postnatal CNS development.","method":"Flrt2-LacZ knock-in reporter mice, immunofluorescence, subcellular fractionation analysis","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization using knock-in reporter and immunostaining, single lab","pmids":["34744626"],"is_preprint":false},{"year":2022,"finding":"FLRT2 forms homophilic (in trans) interendothelial adhesions in tumor vasculature that safeguard endothelial cells against oxidative stress; endothelial-specific Flrt2 deletion selectively prunes abnormalized vessels, induces oxygen-glucose uncoupling, suppresses tumor metastasis, and enhances responses to immune checkpoint blockers.","method":"Endothelial-specific conditional KO mouse, tumor implantation models, metabolic analysis, immune checkpoint blockade experiments, mechanistic identification of homophilic binding","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined metabolic and functional phenotypes, homophilic binding mechanism identified, in vivo therapeutic validation","pmids":["35104247"],"is_preprint":false},{"year":2022,"finding":"FLRT2 dimerizes in cis via two Small-X3-Small motifs in its transmembrane helix, which synergize with a third dimerization motif in the extracellular domain to permit cis association and co-diffusion on the cell surface; this cis dimerization may compete with in trans interactions, suggesting a switching mechanism between adhesion states.","method":"Molecular dynamics simulations, single particle tracking (SPT) experiments, transmembrane motif mutagenesis","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — MD simulations validated by single-particle tracking with mutagenesis, multiple orthogonal methods in single study","pmids":["35700726"],"is_preprint":false},{"year":2023,"finding":"FLRT2-UNC5 transcellular signaling mediates rejection of inappropriate synaptic partners in the mouse retina; FLRT2 expressed by direction-selective (DS) circuit neurons binds UNC5C/D on non-DS neurons, causing elimination of misdirected dendrites; loss of FLRT2-UNC5 binding allows mistargeted arbors to persist and acquire synapses from wrong partners, while UNC5 misexpression drives arbors into adjacent sublayers; mechanistically, UNC5s promote dendrite elimination by interfering with FLRT2-mediated adhesion.","method":"In vivo gain- and loss-of-function (conditional KO, misexpression), live imaging, synapse analysis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function in vivo with defined molecular mechanism, single but rigorous study","pmids":["37557174"],"is_preprint":false},{"year":2023,"finding":"FLRT2 elevates ACSL4 expression to increase lipid peroxidation and trigger ferroptosis in bladder cancer cells, thereby suppressing tumor cell growth and migration.","method":"Overexpression and knockdown in bladder cancer cell lines, lipid peroxidation assays, ferroptosis markers, ACSL4 expression analysis","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 3 — KD/OE with mechanistic pathway (ACSL4/lipid peroxidation) but no direct protein-protein interaction assay, single lab","pmids":["37480224"],"is_preprint":false},{"year":2024,"finding":"FLRT2 directly associates with integrin subunit beta 4 (ITGB4) and promotes ITGB4 phosphorylation; this interaction mediates prevention of endothelial cell senescence via the mTORC2/AKT/p53 signaling pathway; FLRT2 silencing in mice promotes vascular aging, and FLRT2 overexpression rescues premature vascular aging.","method":"Co-immunoprecipitation (direct association with ITGB4), ITGB4 inhibition rescue experiments, mTORC2/AKT/p53 pathway analysis, in vivo FLRT2 silencing and overexpression mouse models","journal":"JCI insight","confidence":"High","confidence_rationale":"Tier 2 — direct Co-IP identifying ITGB4 as binding partner, epistasis via ITGB4 inhibitor rescue, in vivo validation, moderate evidence","pmids":["38587072"],"is_preprint":false},{"year":2024,"finding":"NEDD4 (E3 ubiquitin ligase) binds FLRT2, ubiquitinates it, and promotes its proteasomal degradation; NEDD4 overexpression abolishes FLRT2-mediated suppression of NSCLC stem cell proliferation and sphere formation.","method":"Co-immunoprecipitation (NEDD4-FLRT2 binding), ubiquitination assay, overexpression/knockdown in NSCLC cells and xenograft mouse models","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP identifies E3 ligase, functional epistasis shown in vitro and in vivo, single lab","pmids":["39444619"],"is_preprint":false},{"year":2024,"finding":"FLRT2 interacts with VE-cadherin and, together with the endocytic adaptor Numb, modulates adherens junction morphology in retinal and cortical vessels; endothelial FLRT2 deletion in postnatal mice causes defects in retinal vein endothelial cell proliferation, sprouting, and polarity, reduces tip cells, and disrupts blood-brain barrier development by altering crosstalk between adherens and tight junctions.","method":"Endothelial-specific conditional KO, expansion microscopy of VE-cadherin distribution, Co-immunoprecipitation (FLRT2-VE-cadherin), in vivo retinal and cortical vascular phenotyping","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — Co-IP identifies VE-cadherin partner, conditional KO with defined vascular phenotypes, expansion microscopy for mechanistic insight, rigorous study","pmids":["39609404"],"is_preprint":false}],"current_model":"FLRT2 is a shed/transmembrane leucine-rich repeat glycoprotein that functions as a repulsive ligand for Unc5 receptors (Unc5B/D) to guide neuronal migration, axon pathfinding, interneuron stream maintenance, and synaptic partner rejection, while also acting as a homophilic adhesion molecule (including cis-dimerization via TM Small-X3-Small motifs) in endothelial cells where it interacts with VE-cadherin and ITGB4 to regulate vascular morphogenesis and prevent senescence; intracellularly, it positively modulates FGF/FGFR2-ERK signaling and is subject to ubiquitin-mediated degradation by NEDD4."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing the gene product identity: FLRT2 was shown to encode a type I transmembrane glycoprotein with 10 leucine-rich repeats, cysteine-rich flanking domains, and a fibronectin-like domain — a domain architecture suggestive of adhesion/receptor function but with no known ligand or binding partner.","evidence":"Molecular cloning and heterologous expression in SF9/COS-1 cells with glycosylation analysis","pmids":["10644439"],"confidence":"Medium","gaps":["No binding partner or receptor identified","No in vivo functional data","Mechanism of action entirely unknown"]},{"year":2011,"claim":"Four studies simultaneously established FLRT2's core molecular functions: it binds Unc5D to act as a repulsive cue delaying cortical neuron migration, it is essential for epicardial integrity and heart morphogenesis, it interacts with FGFR2 to potentiate FGF-ERK signaling, and it modulates N-cadherin-dependent cell aggregation during chondrogenesis — collectively revealing FLRT2 as a multifunctional regulator of cell positioning and signaling.","evidence":"Binding assays and reciprocal KO/OE in mouse cortex (PMID:21673655); conditional KO with in vivo rescue in epicardium (PMID:21350012); Co-IP/GST-pulldown/Y2H with ERK readout in craniofacial tissue (PMID:21765038); KD/OE in ATDC5 cells with proliferation and aggregation assays (PMID:21769912)","pmids":["21673655","21350012","21765038","21769912"],"confidence":"High","gaps":["Structural basis of FLRT2-Unc5D and FLRT2-FGFR2 interfaces unresolved","Whether FLRT2's adhesive and repulsive functions are context-dependent or simultaneous unclear","Intracellular signaling downstream of FLRT2 in epicardium not defined"]},{"year":2014,"claim":"FLRT2 was found to associate with fibronectin in the extracellular matrix, existing in both membrane-bound and shed forms, suggesting the ECM environment regulates FLRT2 availability and function.","evidence":"Co-IP, immunolocalization, ECM fractionation, and fibronectin-blocking peptide experiments in ATDC5 cells","pmids":["24585683"],"confidence":"Medium","gaps":["No reconstitution with purified proteins to confirm direct fibronectin binding","Shedding protease not identified","Functional consequence of ECM-bound FLRT2 versus shed FLRT2 not distinguished in vivo"]},{"year":2017,"claim":"The FLRT2–Unc5B repulsive axis was extended beyond the nervous system: endothelial FLRT2 signals through Unc5B to mediate inter-endothelial repulsion required for proper vessel alignment in the placental labyrinth, with endothelial-specific deletion causing embryonic lethality.","evidence":"Endothelial-specific conditional KO mouse with phenotypic analysis of placental vasculature","pmids":["28576770"],"confidence":"High","gaps":["Downstream endothelial signaling cascades linking Unc5B activation to cytoskeletal remodeling not defined","Whether shed or membrane-bound FLRT2 drives the endothelial phenotype unknown"]},{"year":2019,"claim":"FLRT2's interaction with the Unc5B pathway was shown to regulate osteoclast multinucleation by modulating Netrin1–Unc5B crosstalk and Rac1 activation, revealing a role in bone biology.","evidence":"FLRT2 KO osteoclasts with Unc5B RNAi rescue, Rac1 activation assay, Netrin1 epistasis","pmids":["31383250"],"confidence":"Medium","gaps":["Whether FLRT2 competes directly with Netrin1 for Unc5B binding or acts allosterically not resolved","In vivo bone phenotype of FLRT2-deficient mice not characterized"]},{"year":2021,"claim":"FLRT2 and FLRT3 were shown to cooperate as non-cell-autonomous chemorepellent ligands maintaining cortical interneuron migratory streams, with double KO phenocopying loss of their receptors Unc5B/Unc5D — establishing genetic epistasis for the FLRT–Unc5 repulsion axis in interneuron guidance.","evidence":"Double conditional KO mice (FLRT2/FLRT3 and Unc5B/Unc5D), in vitro chemorepulsion assay","pmids":["34301831"],"confidence":"High","gaps":["Source cells producing FLRT2 ligand in this context not fully defined","Whether FLRT2 acts as shed or membrane-bound ligand for interneurons not distinguished"]},{"year":2021,"claim":"Subcellular mapping showed FLRT2 is present at both pre- and postsynaptic compartments in the hippocampus and is dynamically expressed through postnatal CNS development, positioning it as a potential synaptic organizer.","evidence":"Flrt2-LacZ knock-in reporter mice with immunofluorescence and subcellular fractionation","pmids":["34744626"],"confidence":"Medium","gaps":["No functional test of synaptic role in hippocampus performed","Synaptic binding partners at these sites not identified","Single reporter approach without independent antibody validation"]},{"year":2022,"claim":"FLRT2 was identified as a homophilic adhesion molecule in tumor endothelium: trans-homophilic FLRT2 interactions safeguard abnormalized vessels against oxidative stress, and endothelial-specific deletion selectively prunes these vessels, suppresses metastasis, and enhances anti-tumor immunity — revealing a druggable vascular maintenance mechanism.","evidence":"Endothelial-specific conditional KO with tumor implantation, metabolic analysis, immune checkpoint blockade, homophilic binding identification","pmids":["35104247"],"confidence":"High","gaps":["Structural basis of homophilic versus Unc5-binding interface not compared","How FLRT2 switches between homophilic adhesion and Unc5-mediated repulsion in endothelium unknown"]},{"year":2022,"claim":"The cis-dimerization mechanism was resolved: FLRT2 dimerizes through two Small-X3-Small motifs in its transmembrane helix that synergize with an extracellular dimerization motif, suggesting cis/trans switching controls adhesion state.","evidence":"Molecular dynamics simulations validated by single-particle tracking and transmembrane motif mutagenesis","pmids":["35700726"],"confidence":"High","gaps":["Functional consequence of cis versus trans states on repulsion/adhesion not tested in vivo","Whether cis dimerization is regulated by ligand binding or post-translational modification unknown"]},{"year":2023,"claim":"FLRT2–Unc5 signaling was shown to mediate synaptic partner rejection in the retina: FLRT2 on direction-selective neurons binds Unc5C/D on non-DS neurons to eliminate misdirected dendrites, establishing FLRT2 as a molecular determinant of synaptic specificity beyond axon guidance.","evidence":"Conditional KO, misexpression, live imaging, and synapse analysis in mouse retina","pmids":["37557174"],"confidence":"High","gaps":["Whether FLRT2 adhesion and Unc5-mediated repulsion are simultaneously active at the same synapse not resolved","Downstream signaling in the eliminated dendrite not characterized"]},{"year":2024,"claim":"Three studies expanded FLRT2's endothelial roles: FLRT2 directly binds ITGB4 to prevent endothelial senescence via mTORC2/AKT/p53, interacts with VE-cadherin/Numb to regulate adherens junction morphology and blood–brain barrier integrity, and is subject to NEDD4-mediated ubiquitination controlling its protein stability.","evidence":"Co-IP identifying ITGB4 and VE-cadherin as partners, ITGB4 inhibitor rescue, expansion microscopy, conditional KO retinal/cortical phenotyping (PMID:38587072, PMID:39609404); NEDD4–FLRT2 ubiquitination assay and NSCLC xenograft epistasis (PMID:39444619)","pmids":["38587072","39609404","39444619"],"confidence":"High","gaps":["How FLRT2 coordinates ITGB4, VE-cadherin, and Unc5B interactions at the endothelial surface not integrated","Whether NEDD4-mediated degradation is regulated by FLRT2 ligand engagement unknown","FLRT2 structural domains mediating VE-cadherin versus ITGB4 binding not mapped"]},{"year":null,"claim":"A central unresolved question is how FLRT2 switches between its repulsive (Unc5-binding) and adhesive (homophilic, VE-cadherin, ITGB4) modes at the molecular level, and whether cis-dimerization state, shedding, or post-translational modifications control this switch in different tissues.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of full-length FLRT2 or its complexes with Unc5 versus homophilic partners","Identity of the shedding protease(s) unknown","Relationship between cis-dimerization state and functional output not tested in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[2,4,10,16]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[1,6,8,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,11,16]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,5,10]},{"term_id":"GO:0031012","term_label":"extracellular matrix","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,2,8,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,14]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[4,10,16]}],"complexes":[],"partners":["UNC5B","UNC5D","FGFR2","CDH5","ITGB4","NEDD4","UNC5C","FN1"],"other_free_text":[]},"mechanistic_narrative":"FLRT2 is a leucine-rich repeat transmembrane glycoprotein that functions as both a repulsive guidance ligand and a homophilic adhesion molecule, directing cell positioning during neural development, vascular morphogenesis, and synapse specificity. As a shed or membrane-bound ligand for Unc5 family receptors (Unc5B, Unc5C, Unc5D), FLRT2 mediates chemorepulsive signaling that controls cortical neuron migration timing, interneuron stream maintenance, endothelial cell alignment in the placental labyrinth, and rejection of inappropriate synaptic partners in the retina [PMID:21673655, PMID:34301831, PMID:28576770, PMID:37557174]. In endothelial cells, FLRT2 forms homophilic trans-adhesions that protect tumor vasculature from oxidative stress, interacts with VE-cadherin and the adaptor Numb to regulate adherens junction morphology and blood–brain barrier integrity, and associates with ITGB4 to prevent endothelial senescence via mTORC2/AKT/p53 signaling [PMID:35104247, PMID:39609404, PMID:38587072]. Intracellularly, FLRT2 binds FGFR2 through both its LRR ectodomain and cytoplasmic tail to potentiate FGF-ERK signaling in craniofacial tissues, and is subject to NEDD4-mediated ubiquitination and proteasomal degradation [PMID:21765038, PMID:39444619]."},"prefetch_data":{"uniprot":{"accession":"O43155","full_name":"Leucine-rich repeat transmembrane protein FLRT2","aliases":["Fibronectin-like domain-containing leucine-rich transmembrane protein 2"],"length_aa":660,"mass_kda":74.0,"function":"Functions in cell-cell adhesion, cell migration and axon guidance. Mediates cell-cell adhesion via its interactions with ADGRL3 and probably also other latrophilins that are expressed at the surface of adjacent cells. May play a role in the migration of cortical neurons during brain development via its interaction with UNC5D. Mediates axon growth cone collapse and plays a repulsive role in neuron guidance via its interaction with UNC5D, and possibly also other UNC-5 family members. Plays a role in fibroblast growth factor-mediated signaling cascades. Required for normal organization of the cardiac basement membrane during embryogenesis, and for normal embryonic epicardium and heart morphogenesis","subcellular_location":"Cell membrane; Endoplasmic reticulum membrane; Cell junction, focal adhesion; Secreted, extracellular space, extracellular matrix; Microsome membrane; Secreted; Synapse, synaptosome","url":"https://www.uniprot.org/uniprotkb/O43155/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FLRT2","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/FLRT2","total_profiled":1310},"omim":[{"mim_id":"616417","title":"ADHESION G PROTEIN-COUPLED RECEPTOR L3; ADGRL3","url":"https://www.omim.org/entry/616417"},{"mim_id":"604808","title":"FIBRONECTIN-LIKE DOMAIN-CONTAINING LEUCINE-RICH TRANSMEMBRANE PROTEIN 3; FLRT3","url":"https://www.omim.org/entry/604808"},{"mim_id":"604807","title":"FIBRONECTIN-LIKE DOMAIN-CONTAINING LEUCINE-RICH TRANSMEMBRANE PROTEIN 2; FLRT2","url":"https://www.omim.org/entry/604807"},{"mim_id":"604806","title":"FIBRONECTIN-LIKE DOMAIN-CONTAINING LEUCINE-RICH TRANSMEMBRANE PROTEIN 1; FLRT1","url":"https://www.omim.org/entry/604806"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"ovary","ntpm":38.6}],"url":"https://www.proteinatlas.org/search/FLRT2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O43155","domains":[{"cath_id":"3.80.10.10","chopping":"36-171","consensus_level":"medium","plddt":96.1697,"start":36,"end":171},{"cath_id":"2.60.40.10","chopping":"426-515","consensus_level":"high","plddt":80.2139,"start":426,"end":515}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O43155","model_url":"https://alphafold.ebi.ac.uk/files/AF-O43155-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O43155-F1-predicted_aligned_error_v6.png","plddt_mean":74.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FLRT2","jax_strain_url":"https://www.jax.org/strain/search?query=FLRT2"},"sequence":{"accession":"O43155","fasta_url":"https://rest.uniprot.org/uniprotkb/O43155.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O43155/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O43155"}},"corpus_meta":[{"pmid":"21673655","id":"PMC_21673655","title":"FLRT2 and FLRT3 act as repulsive guidance cues for Unc5-positive neurons.","date":"2011","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/21673655","citation_count":122,"is_preprint":false},{"pmid":"10644439","id":"PMC_10644439","title":"Identification of FLRT1, FLRT2, and FLRT3: a novel family of transmembrane leucine-rich repeat proteins.","date":"1999","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10644439","citation_count":102,"is_preprint":false},{"pmid":"21350012","id":"PMC_21350012","title":"The fibronectin leucine-rich repeat transmembrane protein Flrt2 is required in the epicardium to promote heart morphogenesis.","date":"2011","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/21350012","citation_count":42,"is_preprint":false},{"pmid":"26890304","id":"PMC_26890304","title":"Methylation profiling identified novel differentially methylated markers including OPCML and FLRT2 in prostate cancer.","date":"2016","source":"Epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/26890304","citation_count":40,"is_preprint":false},{"pmid":"28325946","id":"PMC_28325946","title":"Epigenetically regulated Fibronectin leucine rich transmembrane protein 2 (FLRT2) shows tumor suppressor activity in breast cancer cells.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28325946","citation_count":27,"is_preprint":false},{"pmid":"28576770","id":"PMC_28576770","title":"Placental labyrinth formation in mice requires endothelial FLRT2/UNC5B signaling.","date":"2017","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/28576770","citation_count":27,"is_preprint":false},{"pmid":"19635589","id":"PMC_19635589","title":"Flrt2 and Flrt3 have overlapping and non-overlapping expression during craniofacial development.","date":"2009","source":"Gene expression patterns : GEP","url":"https://pubmed.ncbi.nlm.nih.gov/19635589","citation_count":26,"is_preprint":false},{"pmid":"21765038","id":"PMC_21765038","title":"Mouse FLRT2 interacts with the extracellular and intracellular regions of FGFR2.","date":"2011","source":"Journal of dental research","url":"https://pubmed.ncbi.nlm.nih.gov/21765038","citation_count":22,"is_preprint":false},{"pmid":"35104247","id":"PMC_35104247","title":"Tumor-specific interendothelial adhesion mediated by FLRT2 facilitates cancer aggressiveness.","date":"2022","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/35104247","citation_count":21,"is_preprint":false},{"pmid":"21769912","id":"PMC_21769912","title":"FLRT2 promotes cellular proliferation and inhibits cell adhesion during chondrogenesis.","date":"2011","source":"Journal of cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21769912","citation_count":18,"is_preprint":false},{"pmid":"34301831","id":"PMC_34301831","title":"FLRT2 and FLRT3 Cooperate in Maintaining the Tangential Migratory Streams of Cortical Interneurons during Development.","date":"2021","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/34301831","citation_count":16,"is_preprint":false},{"pmid":"37480224","id":"PMC_37480224","title":"FLRT2 suppresses bladder cancer progression through inducing ferroptosis.","date":"2023","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37480224","citation_count":14,"is_preprint":false},{"pmid":"33193897","id":"PMC_33193897","title":"FLRT2 functions as Tumor Suppressor gene inactivated by promoter methylation in Colorectal Cancer.","date":"2020","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/33193897","citation_count":13,"is_preprint":false},{"pmid":"29487336","id":"PMC_29487336","title":"Enhanced synaptic plasticity and spatial memory in female but not male FLRT2-haplodeficient mice.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29487336","citation_count":13,"is_preprint":false},{"pmid":"24585683","id":"PMC_24585683","title":"FLRT2 interacts with fibronectin in the ATDC5 chondroprogenitor cells.","date":"2014","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24585683","citation_count":13,"is_preprint":false},{"pmid":"35700726","id":"PMC_35700726","title":"The guidance and adhesion protein FLRT2 dimerizes in cis via dual small-X3-small transmembrane motifs.","date":"2022","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/35700726","citation_count":10,"is_preprint":false},{"pmid":"38587072","id":"PMC_38587072","title":"FLRT2 prevents endothelial cell senescence and vascular aging by regulating the ITGB4/mTORC2/p53 signaling pathway.","date":"2024","source":"JCI insight","url":"https://pubmed.ncbi.nlm.nih.gov/38587072","citation_count":9,"is_preprint":false},{"pmid":"37557174","id":"PMC_37557174","title":"Rejection of inappropriate synaptic partners in mouse retina mediated by transcellular FLRT2-UNC5 signaling.","date":"2023","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/37557174","citation_count":8,"is_preprint":false},{"pmid":"34744626","id":"PMC_34744626","title":"Expression of FLRT2 in Postnatal Central Nervous System Development and After Spinal Cord Injury.","date":"2021","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/34744626","citation_count":8,"is_preprint":false},{"pmid":"31383250","id":"PMC_31383250","title":"Flrt2 is involved in fine-tuning of osteoclast multinucleation.","date":"2019","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/31383250","citation_count":7,"is_preprint":false},{"pmid":"37098630","id":"PMC_37098630","title":"LncRNA ZFAS1 protects chondrocytes from IL-1β-induced apoptosis and extracellular matrix degradation via regulating miR-7-5p/FLRT2 axis.","date":"2023","source":"Journal of orthopaedic surgery and research","url":"https://pubmed.ncbi.nlm.nih.gov/37098630","citation_count":6,"is_preprint":false},{"pmid":"39609404","id":"PMC_39609404","title":"Vascular FLRT2 regulates venous-mediated angiogenic expansion and CNS barriergenesis.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/39609404","citation_count":3,"is_preprint":false},{"pmid":"38584835","id":"PMC_38584835","title":"FLRT2 mediates chondrogenesis of nasal septal cartilage and mandibular condyle cartilage.","date":"2024","source":"Open medicine (Warsaw, Poland)","url":"https://pubmed.ncbi.nlm.nih.gov/38584835","citation_count":3,"is_preprint":false},{"pmid":"37259881","id":"PMC_37259881","title":"Loss of flrt2 gene leads to microphthalmia in zebrafish.","date":"2023","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/37259881","citation_count":2,"is_preprint":false},{"pmid":"39444619","id":"PMC_39444619","title":"The NEDD4/FLRT2 axis regulates NSCLC cell stemness.","date":"2024","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39444619","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.05.06.652098","title":"Single-cell transcriptomic profiling reveals a novel signature of necrotizing granulomatous lesions in the lungs of <i>Mycobacterium tuberculosis</i> -infected C3HeB/FeJ mice","date":"2025-05-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.06.652098","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.08.09.25333350","title":"Multi-organ AI Endophenotypes Chart the Heterogeneity of Pan-disease in the Brain, Eye, and Heart","date":"2025-08-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.09.25333350","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.01.616077","title":"Regulatory T cells crosstalk with tumor and endothelium through lymphotoxin signaling","date":"2024-10-03","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.01.616077","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15170,"output_tokens":4333,"usd":0.055253},"stage2":{"model":"claude-opus-4-6","input_tokens":7772,"output_tokens":3504,"usd":0.18969},"total_usd":0.244943,"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\": 1999,\n      \"finding\": \"FLRT2 is a type I transmembrane protein containing 10 leucine-rich repeats flanked by cysteine-rich regions, a fibronectin/collagen-like domain, and an intracellular tail; when expressed in SF9 and COS-1 cells it migrates as an ~85-kDa glycoprotein, consistent with a role in cell adhesion and/or receptor signaling.\",\n      \"method\": \"Heterologous expression in SF9 and COS-1 cells, molecular cloning, glycosylation analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct biochemical characterization of recombinant protein, single study\",\n      \"pmids\": [\"10644439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The shed FLRT2 ectodomain binds specifically to the Unc5D receptor and acts as a repulsive guidance cue for Unc5D-positive neurons; in the developing neocortex, FLRT2/Unc5D signaling delays migration of SVZ-derived neurons toward the cortical plate, as shown by premature migration upon deletion of either FLRT2 or Unc5D and delayed migration upon Unc5D overexpression.\",\n      \"method\": \"Binding assays (ectodomain-receptor interaction), mouse genetic deletion, overexpression in vivo, neuronal migration assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic epistasis (KO + OE), receptor-binding assays, replicated across FLRT2 and FLRT3 family members in same study\",\n      \"pmids\": [\"21673655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FLRT2 is required in the epicardium for heart morphogenesis; loss of FLRT2 disrupts epicardial sheet integrity and basement membrane organization, leading to mid-gestation cardiac lethality; FLRT2 and FLRT3 are functionally interchangeable in both the epicardium and the AVE, as demonstrated by in vitro and in vivo reconstitution assays.\",\n      \"method\": \"Gene targeting (conditional KO), in vitro and in vivo reconstitution assays, histological analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — gene targeting with defined phenotypic rescue, in vivo reconstitution\",\n      \"pmids\": [\"21350012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FLRT2 interacts with both the extracellular and intracellular regions of FGFR2; the LRR domain of FLRT2 mediates interaction with the extracellular region of FGFR2, and the C-tail of FLRT2 interacts with the intracellular region of FGFR2; FLRT2 positively regulates FGF signaling (FGFR2 protein/mRNA levels and ERK phosphorylation) in craniofacial tissues.\",\n      \"method\": \"Co-immunoprecipitation from embryonic craniofacial tissue lysates, GST pulldown, yeast two-hybrid, stable shRNA knockdown and cDNA overexpression with ERK phosphorylation readout\",\n      \"journal\": \"Journal of dental research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, GST pulldown, Y2H) plus functional downstream readout in same study\",\n      \"pmids\": [\"21765038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FLRT2 promotes cell proliferation and inhibits cell-cell adhesion (reducing N-cadherin-mediated aggregation) during early chondrogenesis; FLRT2 knockdown slows proliferation and increases PNA-stained cell aggregates, while overexpression accelerates proliferation and reduces aggregation.\",\n      \"method\": \"Stable knockdown and overexpression in ATDC5 chondroprogenitor cells, proliferation assays, PNA staining, N-cadherin immunostaining, wound-healing migration assay\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD/OE with defined cellular phenotypes, single lab\",\n      \"pmids\": [\"21769912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"FLRT2 interacts with fibronectin in the extracellular matrix of ATDC5 chondroprogenitor cells; FLRT2 co-localizes with fibronectin fibrils, is found in ECM fractions, and co-immunoprecipitates with fibronectin; disruption of fibronectin fibril formation reduces extracellular FLRT2 accumulation; FLRT2 exists in both membrane-bound and shed forms.\",\n      \"method\": \"Co-immunoprecipitation, immunolocalization, ECM fractionation, fibronectin-coated bead binding, fibronectin-blocking peptide experiments, Western blot with domain-specific antibodies\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple orthogonal methods but all from one lab, no in vitro reconstitution with purified proteins\",\n      \"pmids\": [\"24585683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FLRT2 expressed on endothelial cells in the placental labyrinth signals through the UNC5B receptor to mediate inter-endothelial repulsion, which is required for proper alignment of endothelial cells and feto-maternal circulation; endothelial-specific deletion of FLRT2 causes aberrant endothelial layering and embryonic lethality.\",\n      \"method\": \"Endothelial cell-specific conditional KO mouse, phenotypic analysis of placental labyrinth, receptor-ligand interaction with UNC5B\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined cellular phenotype and receptor identification, replicated concept from neuronal FLRT2-UNC5 studies\",\n      \"pmids\": [\"28576770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FLRT2 regulates osteoclast multinucleation by interfering with Netrin1-Unc5B interaction; FLRT2 deficiency reduces hyper-multinucleation and attenuates RANKL-induced Rac1 activation, effects rescued by Unc5B knockdown; Netrin1 inhibitory effects on multinucleation are abolished in FLRT2-deficient cells.\",\n      \"method\": \"Genetic KO in osteoclasts, RNAi knockdown of Unc5B, Rac1 activation assay, Netrin1 treatment, osteoclast differentiation assays\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (FLRT2 KO + Unc5B KD rescue), Rac1 biochemical readout, single study\",\n      \"pmids\": [\"31383250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FLRT2 and FLRT3 cooperate in a non-cell-autonomous repulsive mechanism to maintain tangential migratory streams of cortical interneurons; double KO of FLRT2/FLRT3 phenocopies double KO of their repulsive receptors Unc5B/Unc5D; FLRT proteins act as chemorepellent ligands for interneurons in vitro, partially dependent on FLRT-Unc5 interaction.\",\n      \"method\": \"Double conditional KO mice (FLRT2/FLRT3 and Unc5B/Unc5D), in vitro chemorepulsion assay, immunostaining of interneuron streams\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double KO phenocopy, in vitro functional assay, multiple orthogonal approaches\",\n      \"pmids\": [\"34301831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FLRT2 is localized to pre- and postsynapses in the CA1 region of the adult hippocampus and is upregulated in reactive astrocytes around spinal cord injury lesion sites; its expression is dynamic across postnatal CNS development.\",\n      \"method\": \"Flrt2-LacZ knock-in reporter mice, immunofluorescence, subcellular fractionation analysis\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization using knock-in reporter and immunostaining, single lab\",\n      \"pmids\": [\"34744626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FLRT2 forms homophilic (in trans) interendothelial adhesions in tumor vasculature that safeguard endothelial cells against oxidative stress; endothelial-specific Flrt2 deletion selectively prunes abnormalized vessels, induces oxygen-glucose uncoupling, suppresses tumor metastasis, and enhances responses to immune checkpoint blockers.\",\n      \"method\": \"Endothelial-specific conditional KO mouse, tumor implantation models, metabolic analysis, immune checkpoint blockade experiments, mechanistic identification of homophilic binding\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined metabolic and functional phenotypes, homophilic binding mechanism identified, in vivo therapeutic validation\",\n      \"pmids\": [\"35104247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FLRT2 dimerizes in cis via two Small-X3-Small motifs in its transmembrane helix, which synergize with a third dimerization motif in the extracellular domain to permit cis association and co-diffusion on the cell surface; this cis dimerization may compete with in trans interactions, suggesting a switching mechanism between adhesion states.\",\n      \"method\": \"Molecular dynamics simulations, single particle tracking (SPT) experiments, transmembrane motif mutagenesis\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — MD simulations validated by single-particle tracking with mutagenesis, multiple orthogonal methods in single study\",\n      \"pmids\": [\"35700726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FLRT2-UNC5 transcellular signaling mediates rejection of inappropriate synaptic partners in the mouse retina; FLRT2 expressed by direction-selective (DS) circuit neurons binds UNC5C/D on non-DS neurons, causing elimination of misdirected dendrites; loss of FLRT2-UNC5 binding allows mistargeted arbors to persist and acquire synapses from wrong partners, while UNC5 misexpression drives arbors into adjacent sublayers; mechanistically, UNC5s promote dendrite elimination by interfering with FLRT2-mediated adhesion.\",\n      \"method\": \"In vivo gain- and loss-of-function (conditional KO, misexpression), live imaging, synapse analysis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function in vivo with defined molecular mechanism, single but rigorous study\",\n      \"pmids\": [\"37557174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FLRT2 elevates ACSL4 expression to increase lipid peroxidation and trigger ferroptosis in bladder cancer cells, thereby suppressing tumor cell growth and migration.\",\n      \"method\": \"Overexpression and knockdown in bladder cancer cell lines, lipid peroxidation assays, ferroptosis markers, ACSL4 expression analysis\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — KD/OE with mechanistic pathway (ACSL4/lipid peroxidation) but no direct protein-protein interaction assay, single lab\",\n      \"pmids\": [\"37480224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FLRT2 directly associates with integrin subunit beta 4 (ITGB4) and promotes ITGB4 phosphorylation; this interaction mediates prevention of endothelial cell senescence via the mTORC2/AKT/p53 signaling pathway; FLRT2 silencing in mice promotes vascular aging, and FLRT2 overexpression rescues premature vascular aging.\",\n      \"method\": \"Co-immunoprecipitation (direct association with ITGB4), ITGB4 inhibition rescue experiments, mTORC2/AKT/p53 pathway analysis, in vivo FLRT2 silencing and overexpression mouse models\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct Co-IP identifying ITGB4 as binding partner, epistasis via ITGB4 inhibitor rescue, in vivo validation, moderate evidence\",\n      \"pmids\": [\"38587072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NEDD4 (E3 ubiquitin ligase) binds FLRT2, ubiquitinates it, and promotes its proteasomal degradation; NEDD4 overexpression abolishes FLRT2-mediated suppression of NSCLC stem cell proliferation and sphere formation.\",\n      \"method\": \"Co-immunoprecipitation (NEDD4-FLRT2 binding), ubiquitination assay, overexpression/knockdown in NSCLC cells and xenograft mouse models\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP identifies E3 ligase, functional epistasis shown in vitro and in vivo, single lab\",\n      \"pmids\": [\"39444619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FLRT2 interacts with VE-cadherin and, together with the endocytic adaptor Numb, modulates adherens junction morphology in retinal and cortical vessels; endothelial FLRT2 deletion in postnatal mice causes defects in retinal vein endothelial cell proliferation, sprouting, and polarity, reduces tip cells, and disrupts blood-brain barrier development by altering crosstalk between adherens and tight junctions.\",\n      \"method\": \"Endothelial-specific conditional KO, expansion microscopy of VE-cadherin distribution, Co-immunoprecipitation (FLRT2-VE-cadherin), in vivo retinal and cortical vascular phenotyping\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP identifies VE-cadherin partner, conditional KO with defined vascular phenotypes, expansion microscopy for mechanistic insight, rigorous study\",\n      \"pmids\": [\"39609404\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FLRT2 is a shed/transmembrane leucine-rich repeat glycoprotein that functions as a repulsive ligand for Unc5 receptors (Unc5B/D) to guide neuronal migration, axon pathfinding, interneuron stream maintenance, and synaptic partner rejection, while also acting as a homophilic adhesion molecule (including cis-dimerization via TM Small-X3-Small motifs) in endothelial cells where it interacts with VE-cadherin and ITGB4 to regulate vascular morphogenesis and prevent senescence; intracellularly, it positively modulates FGF/FGFR2-ERK signaling and is subject to ubiquitin-mediated degradation by NEDD4.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"FLRT2 is a leucine-rich repeat transmembrane glycoprotein that functions as both a repulsive guidance ligand and a homophilic adhesion molecule, directing cell positioning during neural development, vascular morphogenesis, and synapse specificity. As a shed or membrane-bound ligand for Unc5 family receptors (Unc5B, Unc5C, Unc5D), FLRT2 mediates chemorepulsive signaling that controls cortical neuron migration timing, interneuron stream maintenance, endothelial cell alignment in the placental labyrinth, and rejection of inappropriate synaptic partners in the retina [PMID:21673655, PMID:34301831, PMID:28576770, PMID:37557174]. In endothelial cells, FLRT2 forms homophilic trans-adhesions that protect tumor vasculature from oxidative stress, interacts with VE-cadherin and the adaptor Numb to regulate adherens junction morphology and blood–brain barrier integrity, and associates with ITGB4 to prevent endothelial senescence via mTORC2/AKT/p53 signaling [PMID:35104247, PMID:39609404, PMID:38587072]. Intracellularly, FLRT2 binds FGFR2 through both its LRR ectodomain and cytoplasmic tail to potentiate FGF-ERK signaling in craniofacial tissues, and is subject to NEDD4-mediated ubiquitination and proteasomal degradation [PMID:21765038, PMID:39444619].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing the gene product identity: FLRT2 was shown to encode a type I transmembrane glycoprotein with 10 leucine-rich repeats, cysteine-rich flanking domains, and a fibronectin-like domain — a domain architecture suggestive of adhesion/receptor function but with no known ligand or binding partner.\",\n      \"evidence\": \"Molecular cloning and heterologous expression in SF9/COS-1 cells with glycosylation analysis\",\n      \"pmids\": [\"10644439\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No binding partner or receptor identified\", \"No in vivo functional data\", \"Mechanism of action entirely unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Four studies simultaneously established FLRT2's core molecular functions: it binds Unc5D to act as a repulsive cue delaying cortical neuron migration, it is essential for epicardial integrity and heart morphogenesis, it interacts with FGFR2 to potentiate FGF-ERK signaling, and it modulates N-cadherin-dependent cell aggregation during chondrogenesis — collectively revealing FLRT2 as a multifunctional regulator of cell positioning and signaling.\",\n      \"evidence\": \"Binding assays and reciprocal KO/OE in mouse cortex (PMID:21673655); conditional KO with in vivo rescue in epicardium (PMID:21350012); Co-IP/GST-pulldown/Y2H with ERK readout in craniofacial tissue (PMID:21765038); KD/OE in ATDC5 cells with proliferation and aggregation assays (PMID:21769912)\",\n      \"pmids\": [\"21673655\", \"21350012\", \"21765038\", \"21769912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FLRT2-Unc5D and FLRT2-FGFR2 interfaces unresolved\", \"Whether FLRT2's adhesive and repulsive functions are context-dependent or simultaneous unclear\", \"Intracellular signaling downstream of FLRT2 in epicardium not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"FLRT2 was found to associate with fibronectin in the extracellular matrix, existing in both membrane-bound and shed forms, suggesting the ECM environment regulates FLRT2 availability and function.\",\n      \"evidence\": \"Co-IP, immunolocalization, ECM fractionation, and fibronectin-blocking peptide experiments in ATDC5 cells\",\n      \"pmids\": [\"24585683\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No reconstitution with purified proteins to confirm direct fibronectin binding\", \"Shedding protease not identified\", \"Functional consequence of ECM-bound FLRT2 versus shed FLRT2 not distinguished in vivo\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The FLRT2–Unc5B repulsive axis was extended beyond the nervous system: endothelial FLRT2 signals through Unc5B to mediate inter-endothelial repulsion required for proper vessel alignment in the placental labyrinth, with endothelial-specific deletion causing embryonic lethality.\",\n      \"evidence\": \"Endothelial-specific conditional KO mouse with phenotypic analysis of placental vasculature\",\n      \"pmids\": [\"28576770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream endothelial signaling cascades linking Unc5B activation to cytoskeletal remodeling not defined\", \"Whether shed or membrane-bound FLRT2 drives the endothelial phenotype unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"FLRT2's interaction with the Unc5B pathway was shown to regulate osteoclast multinucleation by modulating Netrin1–Unc5B crosstalk and Rac1 activation, revealing a role in bone biology.\",\n      \"evidence\": \"FLRT2 KO osteoclasts with Unc5B RNAi rescue, Rac1 activation assay, Netrin1 epistasis\",\n      \"pmids\": [\"31383250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether FLRT2 competes directly with Netrin1 for Unc5B binding or acts allosterically not resolved\", \"In vivo bone phenotype of FLRT2-deficient mice not characterized\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"FLRT2 and FLRT3 were shown to cooperate as non-cell-autonomous chemorepellent ligands maintaining cortical interneuron migratory streams, with double KO phenocopying loss of their receptors Unc5B/Unc5D — establishing genetic epistasis for the FLRT–Unc5 repulsion axis in interneuron guidance.\",\n      \"evidence\": \"Double conditional KO mice (FLRT2/FLRT3 and Unc5B/Unc5D), in vitro chemorepulsion assay\",\n      \"pmids\": [\"34301831\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source cells producing FLRT2 ligand in this context not fully defined\", \"Whether FLRT2 acts as shed or membrane-bound ligand for interneurons not distinguished\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Subcellular mapping showed FLRT2 is present at both pre- and postsynaptic compartments in the hippocampus and is dynamically expressed through postnatal CNS development, positioning it as a potential synaptic organizer.\",\n      \"evidence\": \"Flrt2-LacZ knock-in reporter mice with immunofluorescence and subcellular fractionation\",\n      \"pmids\": [\"34744626\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional test of synaptic role in hippocampus performed\", \"Synaptic binding partners at these sites not identified\", \"Single reporter approach without independent antibody validation\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"FLRT2 was identified as a homophilic adhesion molecule in tumor endothelium: trans-homophilic FLRT2 interactions safeguard abnormalized vessels against oxidative stress, and endothelial-specific deletion selectively prunes these vessels, suppresses metastasis, and enhances anti-tumor immunity — revealing a druggable vascular maintenance mechanism.\",\n      \"evidence\": \"Endothelial-specific conditional KO with tumor implantation, metabolic analysis, immune checkpoint blockade, homophilic binding identification\",\n      \"pmids\": [\"35104247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of homophilic versus Unc5-binding interface not compared\", \"How FLRT2 switches between homophilic adhesion and Unc5-mediated repulsion in endothelium unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The cis-dimerization mechanism was resolved: FLRT2 dimerizes through two Small-X3-Small motifs in its transmembrane helix that synergize with an extracellular dimerization motif, suggesting cis/trans switching controls adhesion state.\",\n      \"evidence\": \"Molecular dynamics simulations validated by single-particle tracking and transmembrane motif mutagenesis\",\n      \"pmids\": [\"35700726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of cis versus trans states on repulsion/adhesion not tested in vivo\", \"Whether cis dimerization is regulated by ligand binding or post-translational modification unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"FLRT2–Unc5 signaling was shown to mediate synaptic partner rejection in the retina: FLRT2 on direction-selective neurons binds Unc5C/D on non-DS neurons to eliminate misdirected dendrites, establishing FLRT2 as a molecular determinant of synaptic specificity beyond axon guidance.\",\n      \"evidence\": \"Conditional KO, misexpression, live imaging, and synapse analysis in mouse retina\",\n      \"pmids\": [\"37557174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FLRT2 adhesion and Unc5-mediated repulsion are simultaneously active at the same synapse not resolved\", \"Downstream signaling in the eliminated dendrite not characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Three studies expanded FLRT2's endothelial roles: FLRT2 directly binds ITGB4 to prevent endothelial senescence via mTORC2/AKT/p53, interacts with VE-cadherin/Numb to regulate adherens junction morphology and blood–brain barrier integrity, and is subject to NEDD4-mediated ubiquitination controlling its protein stability.\",\n      \"evidence\": \"Co-IP identifying ITGB4 and VE-cadherin as partners, ITGB4 inhibitor rescue, expansion microscopy, conditional KO retinal/cortical phenotyping (PMID:38587072, PMID:39609404); NEDD4–FLRT2 ubiquitination assay and NSCLC xenograft epistasis (PMID:39444619)\",\n      \"pmids\": [\"38587072\", \"39609404\", \"39444619\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How FLRT2 coordinates ITGB4, VE-cadherin, and Unc5B interactions at the endothelial surface not integrated\", \"Whether NEDD4-mediated degradation is regulated by FLRT2 ligand engagement unknown\", \"FLRT2 structural domains mediating VE-cadherin versus ITGB4 binding not mapped\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A central unresolved question is how FLRT2 switches between its repulsive (Unc5-binding) and adhesive (homophilic, VE-cadherin, ITGB4) modes at the molecular level, and whether cis-dimerization state, shedding, or post-translational modifications control this switch in different tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of full-length FLRT2 or its complexes with Unc5 versus homophilic partners\", \"Identity of the shedding protease(s) unknown\", \"Relationship between cis-dimerization state and functional output not tested in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [2, 4, 10, 16]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1, 6, 8, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 11, 16]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 5, 10]},\n      {\"term_id\": \"GO:0031012\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 2, 8, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 14]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [4, 10, 16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"UNC5B\",\n      \"UNC5D\",\n      \"FGFR2\",\n      \"CDH5\",\n      \"ITGB4\",\n      \"NEDD4\",\n      \"UNC5C\",\n      \"FN1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}