{"gene":"FAT3","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2011,"finding":"Fat3 is required for amacrine cell (AC) neurite pruning during retinal development; in fat3 mutants, AC precursors fail to reliably retract trailing processes as they migrate through the neuroblastic layer, resulting in a bipolar morphology with two dendritic trees instead of the normal unipolar morphology.","method":"Genetic loss-of-function (fat3 mutant mice), histology, and morphological analysis of retinal amacrine cells","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with specific cellular phenotype (neurite pruning failure) replicated across development; foundational paper with 87 citations","pmids":["21903076"],"is_preprint":false},{"year":2016,"finding":"Fat3 functions cell-autonomously as a cell-surface receptor and directly influences the cytoskeleton through its intracellular domain, which binds and localizes Ena/VASP family actin regulators; altered Ena/VASP distribution alone recapitulates the Fat3 mutant amacrine cell phenotype.","method":"Time-lapse imaging assay of amacrine cell migration/retraction in fat3 mutant mice, cell-autonomous rescue experiments, co-immunoprecipitation/binding assays for Fat3 ICD–Ena/VASP interaction, and Ena/VASP redistribution phenocopy experiment","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assay for ICD–Ena/VASP, live imaging, and phenocopy experiment; multiple orthogonal methods in a single rigorous study","pmids":["27122175"],"is_preprint":false},{"year":2016,"finding":"Fat3 contains a Kinesin/Kif5 Interaction domain (Kif5-ID) in its cytosolic domain that directly binds Kif5B and mediates anterograde transport/distribution of Fat3 in neurons and polarized epithelial cells; alternative splicing of the Kif5-ID modulates this interaction and switches Fat3 distribution between early and later stages of retinal development.","method":"Co-immunoprecipitation of Fat3 ICD constructs with Kif5B, subcellular localization of Fat3 constructs in neurons and MDCK cells, Kif5-ID mutagenesis, and alternative splicing analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with mutagenesis and localization readout, single lab","pmids":["27788242"],"is_preprint":false},{"year":2022,"finding":"The Fat3 intracellular domain (ICD) binds cytoskeletal regulators and synaptic proteins through discrete motifs: separate ICD motifs are required for amacrine cell migration versus neurite retraction. Upon ICD deletion, ectopic neurites form but do not make ectopic synapses, demonstrating that Fat3 independently regulates neurite outgrowth and synapse localization.","method":"Genetic dissection with ICD deletion mice, domain mutagenesis, immunostaining for synaptic markers, pulldown assays for ICD-binding partners","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain-specific mutagenesis combined with clean knockout phenotype and synaptic marker analysis; multiple orthogonal methods","pmids":["35108541"],"is_preprint":false},{"year":2022,"finding":"Fat3 promotes Yap activity in neural progenitor cells of the developing spinal cord by regulating LATS1/2 phosphorylation: Fat3 knockdown increases LATS1/2 phosphorylation, leading to reduced (phosphorylated/inactive) Yap and depletion of proliferating progenitors; Fat3 thus acts upstream of the Hippo pathway kinase cascade.","method":"Fat3 knockdown in chick neural tube (in ovo electroporation), Fat3 knockout mice, western blotting for phospho-LATS1/2 and Yap, and immunostaining for proliferation/neural markers","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in two model systems with defined biochemical readout (LATS1/2 phosphorylation), single lab","pmids":["36042367"],"is_preprint":false},{"year":2025,"finding":"FAT3 binds the synaptic protein PTPσ intracellularly and is required to localize the glutamate receptor GRIK1 to OFF-cone bipolar cell synapses with cone photoreceptors; loss of FAT3 reduces electroretinography and perceptual responses to high-frequency flashes.","method":"Fat3 mutant mice, co-immunoprecipitation of FAT3 with PTPσ, immunostaining for GRIK1 localization at synapses, ERG recordings, and perceptual behavioral assays","journal":"The Journal of general physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP for FAT3–PTPσ interaction plus functional synaptic localization readout (GRIK1) and physiological assay (ERG), multiple orthogonal methods","pmids":["39903280"],"is_preprint":false},{"year":2024,"finding":"FAT3 binds PTPσ intracellularly and is required to localize GRIK1 to OFF-cone bipolar cell synapses (preprint version confirming peer-reviewed finding).","method":"Co-immunoprecipitation, immunostaining, ERG recordings in Fat3 mutant mice","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — preprint with reciprocal Co-IP and localization assay, single lab; superseded by peer-reviewed publication (PMID 39903280)","pmids":["37961274"],"is_preprint":true},{"year":2020,"finding":"FAT3 expression is induced in microglial BV2 cells by high-nutrient medium and by the purinergic analog hypoxanthine; elevated FAT3 extends the duration of an elongated microglial morphology, defining a hypoxanthine–FAT3 axis that regulates microglial shape changes.","method":"Microarray identification of FAT3 induction, hypoxanthine treatment of BV2 cells and primary microglia, morphological quantification after FAT3 manipulation","journal":"eNeuro","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, microarray plus morphological readout; no direct mechanistic pathway established beyond induction and morphology correlation","pmids":["32868309"],"is_preprint":false},{"year":2002,"finding":"Rat Fat3 encodes a ~4555 amino acid transmembrane protein with 34 cadherin domains, 4 EGF-like motifs, a laminin A-G motif, and a cytoplasmic domain; its mRNA and protein expression in the brain peaks at embryonic day E15, with robust expression in spinal cord, suggesting a role in axon fasciculation and modulation of extracellular space during embryonic development.","method":"cDNA cloning, domain architecture analysis, Northern blot, immunostaining of developing brain and spinal cord","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — protein identification with multiple expression/localization methods; foundational characterization replicated by subsequent studies","pmids":["11811999"],"is_preprint":false},{"year":2026,"finding":"Reduced fat3 function in vivo (zebrafish or Drosophila models) impairs cranial neural crest cell (CNCC) induction and migration, and fat3 knockdown leads to reduced β-catenin levels, implicating FAT3 in modulation of canonical Wnt/β-catenin signaling during craniofacial development.","method":"fat3 knockdown in animal models, immunostaining for CNCC markers, western blotting for β-catenin","journal":"Human genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo loss-of-function with defined biochemical (β-catenin) readout, single lab, single paper","pmids":["41933378"],"is_preprint":false},{"year":2026,"finding":"FAT3 knockdown in Drosophila results in rough eye phenotype, shortened lifespan, impaired motor function, and defective motor neuron branching; Fat3 knockout and knockin mice display perinatal lethality, sciatic nerve axonal degeneration, and central nervous system abnormalities, establishing FAT3 as required for motor neuron integrity and axonal maintenance.","method":"Drosophila FAT3 knockdown (RNAi), Fat3 knockout and knockin mouse models, histological analysis of sciatic nerve, behavioral motor assays","journal":"Genetics in medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in two model organisms with specific cellular (axonal degeneration) and behavioral readouts; single lab","pmids":["41937739"],"is_preprint":false}],"current_model":"FAT3 is a large transmembrane atypical cadherin that acts as a cell-surface receptor to coordinate polarized cell morphology and circuit assembly: its intracellular domain binds Ena/VASP actin regulators (to control neurite retraction), cytoskeletal regulators and synaptic proteins through discrete motifs (separating migration from neurite retraction functions), Kif5B kinesin (for directed transport via an alternatively spliced Kif5-ID), and the synaptic phosphatase receptor PTPσ (to localize GRIK1 at OFF-cone bipolar cell synapses); it also suppresses LATS1/2 kinase activity to stabilize Yap and maintain neural progenitor proliferation via the Hippo pathway, and in cranial neural crest cells modulates β-catenin to support Wnt signaling during craniofacial development."},"narrative":{"mechanistic_narrative":"FAT3 is a large transmembrane atypical cadherin that functions as a cell-surface receptor coordinating polarized neuronal morphology, circuit assembly, and progenitor proliferation during development [PMID:21903076, PMID:11811999]. Its cytoplasmic domain acts as a signaling and adaptor hub: discrete intracellular motifs separately control amacrine cell migration versus neurite retraction, with the retraction function executed through direct binding and localization of Ena/VASP actin regulators, such that mislocalizing Ena/VASP alone reproduces the Fat3 mutant phenotype [PMID:27122175, PMID:35108541]. Through its intracellular domain FAT3 also engages the synaptic phosphatase receptor PTPσ to localize the glutamate receptor GRIK1 at OFF-cone bipolar cell synapses, a step required for normal high-frequency visual responses, and this synapse-localization role is genetically separable from its control of neurite outgrowth [PMID:35108541, PMID:39903280]. Beyond morphogenesis, FAT3 acts upstream of the Hippo pathway, restraining LATS1/2 phosphorylation to stabilize active Yap and maintain proliferating neural progenitors [PMID:36042367], and modulates β-catenin to support canonical Wnt signaling during cranial neural crest induction and craniofacial development [PMID:41933378]. FAT3 is broadly required for neuronal integrity, as its loss causes motor neuron branching defects, axonal degeneration, and perinatal lethality in animal models [PMID:41937739].","teleology":[{"year":2002,"claim":"Establishing the molecular identity of FAT3 was the prerequisite for any mechanistic study; cloning defined it as a giant cadherin-superfamily transmembrane protein with developmental expression patterns pointing to a neural role.","evidence":"cDNA cloning, domain analysis, Northern blot, and immunostaining of developing rat brain and spinal cord","pmids":["11811999"],"confidence":"Medium","gaps":["No functional assay linking the architecture to a cellular activity","Ligand and binding partners undefined","Inferred axon fasciculation role not directly tested"]},{"year":2011,"claim":"The first loss-of-function phenotype answered what FAT3 does in vivo, showing it is required for amacrine cells to retract trailing neurites and achieve unipolar morphology during migration.","evidence":"Genetic knockout mice with retinal histology and amacrine cell morphology analysis","pmids":["21903076"],"confidence":"High","gaps":["Molecular effectors of retraction not identified","Whether FAT3 acts cell-autonomously not yet resolved","Signaling downstream of the receptor unknown"]},{"year":2016,"claim":"Two studies defined the mechanistic basis of FAT3 action: cell-autonomous receptor signaling through an intracellular domain that recruits Ena/VASP actin regulators, and a Kif5-ID motif that links FAT3 to kinesin-mediated transport with developmental switching via alternative splicing.","evidence":"Time-lapse imaging, cell-autonomous rescue, ICD–Ena/VASP and ICD–Kif5B Co-IP, mutagenesis, and Ena/VASP redistribution phenocopy in mice and MDCK cells","pmids":["27122175","27788242"],"confidence":"High","gaps":["Structural basis of ICD–Ena/VASP and ICD–Kif5B binding not resolved","Whether transport and actin-regulatory functions are coupled in the same cells unclear","Extracellular ligand driving receptor activation unknown"]},{"year":2022,"claim":"Domain dissection separated FAT3's distinct downstream functions, showing migration and neurite retraction are controlled by different ICD motifs and that neurite outgrowth is regulated independently of synapse formation.","evidence":"ICD-deletion and domain-mutant mice, pulldown assays, and synaptic marker immunostaining","pmids":["35108541"],"confidence":"High","gaps":["Identity of all motif-specific binding partners incomplete","How separate motifs are spatially coordinated unknown"]},{"year":2022,"claim":"FAT3 was placed upstream of the Hippo pathway, answering how it controls progenitor number: it suppresses LATS1/2 phosphorylation to keep Yap active and sustain neural progenitor proliferation.","evidence":"Fat3 knockdown in chick neural tube and knockout mice, with western blots for phospho-LATS1/2 and Yap","pmids":["36042367"],"confidence":"Medium","gaps":["Mechanism by which FAT3 represses LATS1/2 not defined","Single lab","Link between receptor engagement and kinase regulation unmapped"]},{"year":2025,"claim":"The synaptic role of FAT3 was given molecular form: its ICD binds PTPσ to localize the glutamate receptor GRIK1 at OFF-cone bipolar cell synapses, with loss impairing visual physiology and perception.","evidence":"FAT3–PTPσ Co-IP, GRIK1 immunostaining, ERG recordings, and behavioral assays in Fat3 mutant mice (peer-reviewed; preprint #6)","pmids":["39903280","37961274"],"confidence":"High","gaps":["Whether FAT3–PTPσ acts in cis or trans at the synapse unclear","Direct interaction between FAT3 and GRIK1 not established","Generalizability beyond OFF-cone bipolar synapses untested"]},{"year":2026,"claim":"Two 2026 studies broadened FAT3's developmental reach, linking it to Wnt/β-catenin signaling in cranial neural crest and to motor neuron integrity and axonal maintenance across organisms.","evidence":"fat3 knockdown in zebrafish and Drosophila and Fat3 mouse knockout/knockin, with β-catenin western blots, CNCC marker staining, nerve histology, and motor assays","pmids":["41933378","41937739"],"confidence":"Medium","gaps":["Mechanism connecting FAT3 to β-catenin levels undefined","Single lab per finding","Whether axonal degeneration reflects a developmental or maintenance defect unresolved"]},{"year":null,"claim":"The extracellular ligand that activates FAT3 and the structural mechanism coupling receptor engagement to its multiple intracellular outputs (Ena/VASP, Kif5B, PTPσ, Hippo, Wnt) remain unknown.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No identified extracellular binding partner/ligand","No structural model of the ICD or its multivalent interactions","How a single receptor partitions among migration, retraction, transport, synaptic, and signaling functions is unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,5]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[1]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,3,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,9,10]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[5]}],"complexes":[],"partners":["ENAH","KIF5B","PTPRS","LATS1","LATS2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8TDW7","full_name":"Protocadherin Fat 3","aliases":["Cadherin family member 15","FAT tumor suppressor homolog 3"],"length_aa":4557,"mass_kda":502.0,"function":"May play a role in the interactions between neurites derived from specific subsets of neurons during development","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q8TDW7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FAT3","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":77,"dependency_fraction":0.025974025974025976},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FAT3","total_profiled":1310},"omim":[{"mim_id":"612483","title":"FAT ATYPICAL CADHERIN 3; FAT3","url":"https://www.omim.org/entry/612483"},{"mim_id":"612411","title":"FAT ATYPICAL CADHERIN 4; FAT4","url":"https://www.omim.org/entry/612411"},{"mim_id":"604269","title":"FAT ATYPICAL CADHERIN 2; FAT2","url":"https://www.omim.org/entry/604269"},{"mim_id":"600976","title":"FAT ATYPICAL CADHERIN 1; FAT1","url":"https://www.omim.org/entry/600976"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cell Junctions","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"blood vessel","ntpm":5.3},{"tissue":"brain","ntpm":13.6}],"url":"https://www.proteinatlas.org/search/FAT3"},"hgnc":{"alias_symbol":["KIAA1989","CDHF15","CDHR10"],"prev_symbol":[]},"alphafold":{"accession":"Q8TDW7","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDW7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDW7-2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDW7-2-F1-predicted_aligned_error_v6.png","plddt_mean":81.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FAT3","jax_strain_url":"https://www.jax.org/strain/search?query=FAT3"},"sequence":{"accession":"Q8TDW7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TDW7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TDW7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDW7"}},"corpus_meta":[{"pmid":"21903076","id":"PMC_21903076","title":"Control of neuronal morphology by the atypical cadherin Fat3.","date":"2011","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/21903076","citation_count":87,"is_preprint":false},{"pmid":"16865240","id":"PMC_16865240","title":"Comparative integromics on FAT1, FAT2, FAT3 and FAT4.","date":"2006","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/16865240","citation_count":70,"is_preprint":false},{"pmid":"11811999","id":"PMC_11811999","title":"Mammalian fat3: a large protein that contains multiple cadherin and EGF-like motifs.","date":"2002","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/11811999","citation_count":41,"is_preprint":false},{"pmid":"27122175","id":"PMC_27122175","title":"Fat3 and Ena/VASP proteins influence the emergence of asymmetric cell morphology in the developing retina.","date":"2016","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/27122175","citation_count":34,"is_preprint":false},{"pmid":"35069585","id":"PMC_35069585","title":"Co-Mutation of FAT3 and LRP1B in Lung Adenocarcinoma Defines a Unique Subset Correlated With the Efficacy of Immunotherapy.","date":"2022","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/35069585","citation_count":27,"is_preprint":false},{"pmid":"36840844","id":"PMC_36840844","title":"A Circular RNA Expressed from the FAT3 Locus Regulates Neural Development.","date":"2023","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/36840844","citation_count":17,"is_preprint":false},{"pmid":"35108541","id":"PMC_35108541","title":"Fat3 acts through independent cytoskeletal effectors to coordinate asymmetric cell behaviors during polarized circuit assembly.","date":"2022","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/35108541","citation_count":16,"is_preprint":false},{"pmid":"36042367","id":"PMC_36042367","title":"Fat3 regulates neural progenitor cells by promoting Yap activity during spinal cord development.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/36042367","citation_count":12,"is_preprint":false},{"pmid":"21308896","id":"PMC_21308896","title":"Trans fat diet causes decreased brood size and shortened lifespan in Caenorhabditis elegans delta-6-desaturase mutant fat-3.","date":"2011","source":"Journal of biochemical and molecular toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/21308896","citation_count":12,"is_preprint":false},{"pmid":"32868309","id":"PMC_32868309","title":"Atypical Cadherin FAT3 Is a Novel Mediator for Morphological Changes of Microglia.","date":"2020","source":"eNeuro","url":"https://pubmed.ncbi.nlm.nih.gov/32868309","citation_count":9,"is_preprint":false},{"pmid":"27788242","id":"PMC_27788242","title":"Disparate Regulatory Mechanisms Control Fat3 and P75NTR Protein Transport through a Conserved Kif5-Interaction Domain.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27788242","citation_count":9,"is_preprint":false},{"pmid":"39903280","id":"PMC_39903280","title":"ERG responses to high-frequency flickers require FAT3 signaling in mouse retinal bipolar cells.","date":"2025","source":"The Journal of general physiology","url":"https://pubmed.ncbi.nlm.nih.gov/39903280","citation_count":5,"is_preprint":false},{"pmid":"39380691","id":"PMC_39380691","title":"Aggressive high-grade NF2 mutant meningiomas downregulate oncogenic YAP signaling via the upregulation of VGLL4 and FAT3/4.","date":"2024","source":"Neuro-oncology advances","url":"https://pubmed.ncbi.nlm.nih.gov/39380691","citation_count":5,"is_preprint":false},{"pmid":"35853984","id":"PMC_35853984","title":"Identification of FAT3 as a new candidate gene for adolescent idiopathic scoliosis.","date":"2022","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/35853984","citation_count":4,"is_preprint":false},{"pmid":"32961767","id":"PMC_32961767","title":"Juniperonic Acid Biosynthesis is Essential in Caenorhabditis Elegans Lacking Δ6 Desaturase (fat-3) and Generates New ω-3 Endocannabinoids.","date":"2020","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/32961767","citation_count":4,"is_preprint":false},{"pmid":"38973948","id":"PMC_38973948","title":"Tumor mutation burden and FAT3 mutation influence long-term survival in surgically resected small cell lung cancer.","date":"2024","source":"Translational lung cancer 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/37961274","citation_count":0,"is_preprint":false},{"pmid":"40941328","id":"PMC_40941328","title":"Genetic Polymorphism Reveals FAT3 Gene Associations with Wool Traits in Subo Merino Sheep.","date":"2025","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/40941328","citation_count":0,"is_preprint":false},{"pmid":"41933378","id":"PMC_41933378","title":"Rare variants in FAT3 as possible contributors to non-syndromic orofacial cleft risk.","date":"2026","source":"Human genomics","url":"https://pubmed.ncbi.nlm.nih.gov/41933378","citation_count":0,"is_preprint":false},{"pmid":"41975421","id":"PMC_41975421","title":"DNA-based characterization of primary hepatic MALT lymphoma reveals a rare FAT3 missense variant and Hippo pathway activation: a case report and literature review.","date":"2026","source":"World journal of surgical 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     \"finding\": \"Fat3 is required for amacrine cell (AC) neurite pruning during retinal development; in fat3 mutants, AC precursors fail to reliably retract trailing processes as they migrate through the neuroblastic layer, resulting in a bipolar morphology with two dendritic trees instead of the normal unipolar morphology.\",\n      \"method\": \"Genetic loss-of-function (fat3 mutant mice), histology, and morphological analysis of retinal amacrine cells\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with specific cellular phenotype (neurite pruning failure) replicated across development; foundational paper with 87 citations\",\n      \"pmids\": [\"21903076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fat3 functions cell-autonomously as a cell-surface receptor and directly influences the cytoskeleton through its intracellular domain, which binds and localizes Ena/VASP family actin regulators; altered Ena/VASP distribution alone recapitulates the Fat3 mutant amacrine cell phenotype.\",\n      \"method\": \"Time-lapse imaging assay of amacrine cell migration/retraction in fat3 mutant mice, cell-autonomous rescue experiments, co-immunoprecipitation/binding assays for Fat3 ICD–Ena/VASP interaction, and Ena/VASP redistribution phenocopy experiment\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assay for ICD–Ena/VASP, live imaging, and phenocopy experiment; multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"27122175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Fat3 contains a Kinesin/Kif5 Interaction domain (Kif5-ID) in its cytosolic domain that directly binds Kif5B and mediates anterograde transport/distribution of Fat3 in neurons and polarized epithelial cells; alternative splicing of the Kif5-ID modulates this interaction and switches Fat3 distribution between early and later stages of retinal development.\",\n      \"method\": \"Co-immunoprecipitation of Fat3 ICD constructs with Kif5B, subcellular localization of Fat3 constructs in neurons and MDCK cells, Kif5-ID mutagenesis, and alternative splicing analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with mutagenesis and localization readout, single lab\",\n      \"pmids\": [\"27788242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The Fat3 intracellular domain (ICD) binds cytoskeletal regulators and synaptic proteins through discrete motifs: separate ICD motifs are required for amacrine cell migration versus neurite retraction. Upon ICD deletion, ectopic neurites form but do not make ectopic synapses, demonstrating that Fat3 independently regulates neurite outgrowth and synapse localization.\",\n      \"method\": \"Genetic dissection with ICD deletion mice, domain mutagenesis, immunostaining for synaptic markers, pulldown assays for ICD-binding partners\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain-specific mutagenesis combined with clean knockout phenotype and synaptic marker analysis; multiple orthogonal methods\",\n      \"pmids\": [\"35108541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Fat3 promotes Yap activity in neural progenitor cells of the developing spinal cord by regulating LATS1/2 phosphorylation: Fat3 knockdown increases LATS1/2 phosphorylation, leading to reduced (phosphorylated/inactive) Yap and depletion of proliferating progenitors; Fat3 thus acts upstream of the Hippo pathway kinase cascade.\",\n      \"method\": \"Fat3 knockdown in chick neural tube (in ovo electroporation), Fat3 knockout mice, western blotting for phospho-LATS1/2 and Yap, and immunostaining for proliferation/neural markers\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in two model systems with defined biochemical readout (LATS1/2 phosphorylation), single lab\",\n      \"pmids\": [\"36042367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FAT3 binds the synaptic protein PTPσ intracellularly and is required to localize the glutamate receptor GRIK1 to OFF-cone bipolar cell synapses with cone photoreceptors; loss of FAT3 reduces electroretinography and perceptual responses to high-frequency flashes.\",\n      \"method\": \"Fat3 mutant mice, co-immunoprecipitation of FAT3 with PTPσ, immunostaining for GRIK1 localization at synapses, ERG recordings, and perceptual behavioral assays\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP for FAT3–PTPσ interaction plus functional synaptic localization readout (GRIK1) and physiological assay (ERG), multiple orthogonal methods\",\n      \"pmids\": [\"39903280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FAT3 binds PTPσ intracellularly and is required to localize GRIK1 to OFF-cone bipolar cell synapses (preprint version confirming peer-reviewed finding).\",\n      \"method\": \"Co-immunoprecipitation, immunostaining, ERG recordings in Fat3 mutant mice\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — preprint with reciprocal Co-IP and localization assay, single lab; superseded by peer-reviewed publication (PMID 39903280)\",\n      \"pmids\": [\"37961274\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"FAT3 expression is induced in microglial BV2 cells by high-nutrient medium and by the purinergic analog hypoxanthine; elevated FAT3 extends the duration of an elongated microglial morphology, defining a hypoxanthine–FAT3 axis that regulates microglial shape changes.\",\n      \"method\": \"Microarray identification of FAT3 induction, hypoxanthine treatment of BV2 cells and primary microglia, morphological quantification after FAT3 manipulation\",\n      \"journal\": \"eNeuro\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, microarray plus morphological readout; no direct mechanistic pathway established beyond induction and morphology correlation\",\n      \"pmids\": [\"32868309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rat Fat3 encodes a ~4555 amino acid transmembrane protein with 34 cadherin domains, 4 EGF-like motifs, a laminin A-G motif, and a cytoplasmic domain; its mRNA and protein expression in the brain peaks at embryonic day E15, with robust expression in spinal cord, suggesting a role in axon fasciculation and modulation of extracellular space during embryonic development.\",\n      \"method\": \"cDNA cloning, domain architecture analysis, Northern blot, immunostaining of developing brain and spinal cord\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — protein identification with multiple expression/localization methods; foundational characterization replicated by subsequent studies\",\n      \"pmids\": [\"11811999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Reduced fat3 function in vivo (zebrafish or Drosophila models) impairs cranial neural crest cell (CNCC) induction and migration, and fat3 knockdown leads to reduced β-catenin levels, implicating FAT3 in modulation of canonical Wnt/β-catenin signaling during craniofacial development.\",\n      \"method\": \"fat3 knockdown in animal models, immunostaining for CNCC markers, western blotting for β-catenin\",\n      \"journal\": \"Human genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo loss-of-function with defined biochemical (β-catenin) readout, single lab, single paper\",\n      \"pmids\": [\"41933378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"FAT3 knockdown in Drosophila results in rough eye phenotype, shortened lifespan, impaired motor function, and defective motor neuron branching; Fat3 knockout and knockin mice display perinatal lethality, sciatic nerve axonal degeneration, and central nervous system abnormalities, establishing FAT3 as required for motor neuron integrity and axonal maintenance.\",\n      \"method\": \"Drosophila FAT3 knockdown (RNAi), Fat3 knockout and knockin mouse models, histological analysis of sciatic nerve, behavioral motor assays\",\n      \"journal\": \"Genetics in medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in two model organisms with specific cellular (axonal degeneration) and behavioral readouts; single lab\",\n      \"pmids\": [\"41937739\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FAT3 is a large transmembrane atypical cadherin that acts as a cell-surface receptor to coordinate polarized cell morphology and circuit assembly: its intracellular domain binds Ena/VASP actin regulators (to control neurite retraction), cytoskeletal regulators and synaptic proteins through discrete motifs (separating migration from neurite retraction functions), Kif5B kinesin (for directed transport via an alternatively spliced Kif5-ID), and the synaptic phosphatase receptor PTPσ (to localize GRIK1 at OFF-cone bipolar cell synapses); it also suppresses LATS1/2 kinase activity to stabilize Yap and maintain neural progenitor proliferation via the Hippo pathway, and in cranial neural crest cells modulates β-catenin to support Wnt signaling during craniofacial development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FAT3 is a large transmembrane atypical cadherin that functions as a cell-surface receptor coordinating polarized neuronal morphology, circuit assembly, and progenitor proliferation during development [#0, #8]. Its cytoplasmic domain acts as a signaling and adaptor hub: discrete intracellular motifs separately control amacrine cell migration versus neurite retraction, with the retraction function executed through direct binding and localization of Ena/VASP actin regulators, such that mislocalizing Ena/VASP alone reproduces the Fat3 mutant phenotype [#1, #3]. Through its intracellular domain FAT3 also engages the synaptic phosphatase receptor PTPσ to localize the glutamate receptor GRIK1 at OFF-cone bipolar cell synapses, a step required for normal high-frequency visual responses, and this synapse-localization role is genetically separable from its control of neurite outgrowth [#3, #5]. Beyond morphogenesis, FAT3 acts upstream of the Hippo pathway, restraining LATS1/2 phosphorylation to stabilize active Yap and maintain proliferating neural progenitors [#4], and modulates β-catenin to support canonical Wnt signaling during cranial neural crest induction and craniofacial development [#9]. FAT3 is broadly required for neuronal integrity, as its loss causes motor neuron branching defects, axonal degeneration, and perinatal lethality in animal models [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing the molecular identity of FAT3 was the prerequisite for any mechanistic study; cloning defined it as a giant cadherin-superfamily transmembrane protein with developmental expression patterns pointing to a neural role.\",\n      \"evidence\": \"cDNA cloning, domain analysis, Northern blot, and immunostaining of developing rat brain and spinal cord\",\n      \"pmids\": [\"11811999\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional assay linking the architecture to a cellular activity\", \"Ligand and binding partners undefined\", \"Inferred axon fasciculation role not directly tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The first loss-of-function phenotype answered what FAT3 does in vivo, showing it is required for amacrine cells to retract trailing neurites and achieve unipolar morphology during migration.\",\n      \"evidence\": \"Genetic knockout mice with retinal histology and amacrine cell morphology analysis\",\n      \"pmids\": [\"21903076\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular effectors of retraction not identified\", \"Whether FAT3 acts cell-autonomously not yet resolved\", \"Signaling downstream of the receptor unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Two studies defined the mechanistic basis of FAT3 action: cell-autonomous receptor signaling through an intracellular domain that recruits Ena/VASP actin regulators, and a Kif5-ID motif that links FAT3 to kinesin-mediated transport with developmental switching via alternative splicing.\",\n      \"evidence\": \"Time-lapse imaging, cell-autonomous rescue, ICD–Ena/VASP and ICD–Kif5B Co-IP, mutagenesis, and Ena/VASP redistribution phenocopy in mice and MDCK cells\",\n      \"pmids\": [\"27122175\", \"27788242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ICD–Ena/VASP and ICD–Kif5B binding not resolved\", \"Whether transport and actin-regulatory functions are coupled in the same cells unclear\", \"Extracellular ligand driving receptor activation unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Domain dissection separated FAT3's distinct downstream functions, showing migration and neurite retraction are controlled by different ICD motifs and that neurite outgrowth is regulated independently of synapse formation.\",\n      \"evidence\": \"ICD-deletion and domain-mutant mice, pulldown assays, and synaptic marker immunostaining\",\n      \"pmids\": [\"35108541\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of all motif-specific binding partners incomplete\", \"How separate motifs are spatially coordinated unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"FAT3 was placed upstream of the Hippo pathway, answering how it controls progenitor number: it suppresses LATS1/2 phosphorylation to keep Yap active and sustain neural progenitor proliferation.\",\n      \"evidence\": \"Fat3 knockdown in chick neural tube and knockout mice, with western blots for phospho-LATS1/2 and Yap\",\n      \"pmids\": [\"36042367\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which FAT3 represses LATS1/2 not defined\", \"Single lab\", \"Link between receptor engagement and kinase regulation unmapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The synaptic role of FAT3 was given molecular form: its ICD binds PTPσ to localize the glutamate receptor GRIK1 at OFF-cone bipolar cell synapses, with loss impairing visual physiology and perception.\",\n      \"evidence\": \"FAT3–PTPσ Co-IP, GRIK1 immunostaining, ERG recordings, and behavioral assays in Fat3 mutant mice (peer-reviewed; preprint #6)\",\n      \"pmids\": [\"39903280\", \"37961274\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FAT3–PTPσ acts in cis or trans at the synapse unclear\", \"Direct interaction between FAT3 and GRIK1 not established\", \"Generalizability beyond OFF-cone bipolar synapses untested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Two 2026 studies broadened FAT3's developmental reach, linking it to Wnt/β-catenin signaling in cranial neural crest and to motor neuron integrity and axonal maintenance across organisms.\",\n      \"evidence\": \"fat3 knockdown in zebrafish and Drosophila and Fat3 mouse knockout/knockin, with β-catenin western blots, CNCC marker staining, nerve histology, and motor assays\",\n      \"pmids\": [\"41933378\", \"41937739\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism connecting FAT3 to β-catenin levels undefined\", \"Single lab per finding\", \"Whether axonal degeneration reflects a developmental or maintenance defect unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The extracellular ligand that activates FAT3 and the structural mechanism coupling receptor engagement to its multiple intracellular outputs (Ena/VASP, Kif5B, PTPσ, Hippo, Wnt) remain unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified extracellular binding partner/ligand\", \"No structural model of the ICD or its multivalent interactions\", \"How a single receptor partitions among migration, retraction, transport, synaptic, and signaling functions is unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 9, 10]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ENAH\", \"KIF5B\", \"PTPRS\", \"LATS1\", \"LATS2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}