{"gene":"FRMD4B","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":2001,"finding":"FRMD4B (GRSP1) was identified as a direct binding partner of the ARF guanine nucleotide exchange factor GRP1; the interaction is mediated through coiled-coil domains in both proteins. In Chinese hamster ovary cells co-expressing GRSP1 and GRP1 with the human insulin receptor, both proteins showed diffuse cytoplasmic localization at baseline and acutely co-translocated to plasma membrane ruffles upon insulin stimulation. Immunodepletion experiments demonstrated that virtually all endogenous GRSP1 exists in complex with GRP1 in lung tissue.","method":"Radiolabeled GRP1 probe screen of cDNA expression library; domain-mapping co-immunoprecipitation; co-expression in CHO cells with confocal imaging; immunodepletion from lung lysates","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding mapped to specific domains, localization with functional consequence (insulin-stimulated translocation), immunodepletion confirming endogenous complex; multiple orthogonal methods in one rigorous study","pmids":["11445584"],"is_preprint":false},{"year":2010,"finding":"FRMD4B (GRSP1) forms heterodimeric complexes with GRP1 family ARF exchange factors (GRP1, ARNO, and Cytohesin-1) via heptad-repeat coiled-coil interactions. At low micromolar concentrations, Grsp1 and Cytohesin-1 are monomeric while GRP1 and ARNO are homodimeric; mixing Grsp1 with GRP1 or Cytohesin-1 leads to spontaneous re-equilibration into heterodimers, whereas ~50% of ARNO remains homodimeric. FRET experiments indicate the heterodimers adopt a largely antiparallel orientation. Formation of Grsp1–GRP1 heterodimers does not substantially alter GRP1 binding to PtdIns(3,4,5)P3 or PtdIns(4,5)P2 headgroups, nor does it influence liposome partitioning.","method":"Analytical ultracentrifugation, fluorescence resonance energy transfer (FRET), in vitro reconstitution of complexes, liposome co-sedimentation assay","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple biophysical methods (AUC, FRET, liposome assay), single lab but orthogonal approaches","pmids":["20527794"],"is_preprint":false},{"year":2018,"finding":"A missense variant in FRMD4B (S938P, Tvrm222 allele) suppresses photoreceptor dysplasia (outer nuclear layer rosettes, external limiting membrane fragmentation) in Nr2e3rd7/rd7 and Nrl−/− mouse retinas. In vitro experiments showed that the FRMD4B-S938P variant fails to be efficiently recruited to the cell surface upon insulin stimulation. Tvrm222 retinas displayed reduced AKT phosphorylation and increased levels of cell junction proteins Beta-catenin (Catenin beta 1) and tight junction protein 1 (ZO-1) at the cell membrane, indicating that FRMD4B participates in cell junction remodeling and maintenance of external limiting membrane integrity.","method":"Chemical mutagenesis screen and genetic mapping; Frmd4b missense mutation identification; in vitro cell-surface recruitment assay upon insulin stimulation; Western blot for AKT phosphorylation and junction protein levels; histological analysis of retinal morphology in mouse models","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic epistasis with defined retinal phenotype, in vitro localization assay, and biochemical readouts (pAKT, junction proteins); single lab, multiple orthogonal methods","pmids":["29947801"],"is_preprint":false},{"year":2025,"finding":"CRISPR/Cas9-based knockout of frmd4b in zebrafish (G0 and F2 germline) produced defects in cranial motor neuron/ocular motor development, identifying FRMD4B as a candidate gene for ocular congenital cranial dysinnervation disorders (oCCDDs) with a role in cranial motor neuron development.","method":"G0 CRISPR/Cas9 knockout screen in zebrafish embryos; F2 germline mutant generation; phenotypic analysis of cranial motor development","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — zebrafish loss-of-function with defined cranial motor phenotype, single study with in vivo genetic approach but no molecular mechanism resolved","pmids":["40162949"],"is_preprint":false},{"year":2025,"finding":"Knockdown of Frmd4b in primary cortical neurons and in the N1E-115 neuronal cell line using RNA-targeting CRISPR/Cas13 reduced process elongation, establishing a role for FRMD4B in neuronal process (neurite) outgrowth. The decreased process elongation was recovered by hesperetin, which stimulated phosphorylation of MAPKs/ERKs, suggesting that FRMD4B supports process elongation through a signaling pathway linked to sustained MAPK/ERK phosphorylation.","method":"CRISPR/Cas13 knockdown of Frmd4b in primary cortical neurons and N1E-115 cells; morphometric analysis of process length; Western blot for MAPK/ERK phosphorylation; pharmacological rescue with hesperetin","journal":"International journal of molecular sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, knockdown with morphological readout and pharmacological rescue; MAPK/ERK pathway linkage is indirect (no direct epistasis experiment)","pmids":["41155374"],"is_preprint":false}],"current_model":"FRMD4B (GRSP1/KIAA1013) is a FERM domain-containing scaffolding protein that forms heterodimeric complexes with ARF-GEF family members (GRP1, Cytohesin-1, ARNO) via antiparallel coiled-coil interactions, co-translocates with GRP1 to plasma membrane ruffles upon insulin/PI3K signaling, participates in cell junction remodeling and maintenance of retinal external limiting membrane integrity through regulation of AKT signaling and junction protein levels, and is required for neuronal process elongation, with loss-of-function in zebrafish implicating it in cranial motor neuron development."},"narrative":{"mechanistic_narrative":"FRMD4B (GRSP1/KIAA1013) is a FERM domain-containing scaffolding protein that couples ARF guanine nucleotide exchange factor signaling to PI3K/insulin inputs and cell junction remodeling [PMID:11445584, PMID:29947801]. It binds GRP1-family ARF-GEFs (GRP1, ARNO, Cytohesin-1) through antiparallel heptad-repeat coiled-coil interactions, re-equilibrating these GEFs from homodimers into Grsp1-containing heterodimers without altering GRP1 phosphoinositide headgroup binding [PMID:11445584, PMID:20527794]. Endogenous GRSP1 exists essentially entirely in complex with GRP1, and the pair co-translocates from cytoplasm to plasma membrane ruffles upon insulin stimulation [PMID:11445584]. Through this membrane recruitment, FRMD4B regulates AKT phosphorylation and the membrane levels of junction proteins beta-catenin and ZO-1, and is required for maintenance of retinal external limiting membrane integrity, where a recruitment-deficient S938P variant suppresses photoreceptor dysplasia [PMID:29947801]. In neurons, FRMD4B supports process elongation in a manner linked to sustained MAPK/ERK phosphorylation, and loss of frmd4b in zebrafish impairs cranial motor neuron development, implicating it as a candidate gene for ocular congenital cranial dysinnervation disorders [PMID:40162949, PMID:41155374].","teleology":[{"year":2001,"claim":"Established FRMD4B/GRSP1 as a dedicated binding partner of the ARF-GEF GRP1 that links GRP1 to insulin signaling, answering whether GRSP1 has a defined molecular partner and where it acts.","evidence":"cDNA expression library screen with radiolabeled GRP1 probe, domain-mapping co-IP, insulin-stimulated co-translocation imaging in CHO cells, and immunodepletion from lung lysates","pmids":["11445584"],"confidence":"High","gaps":["Functional consequence of the GRSP1-GRP1 complex on downstream ARF activation not resolved","Whether membrane recruitment requires GRP1 binding or FRMD4B's own determinants not dissected"]},{"year":2010,"claim":"Defined the biophysical basis and selectivity of FRMD4B-GEF complex formation, answering how Grsp1 assembles with GRP1-family proteins and whether it alters their lipid binding.","evidence":"In vitro reconstitution with analytical ultracentrifugation, FRET orientation analysis, and liposome co-sedimentation","pmids":["20527794"],"confidence":"High","gaps":["Functional output of heterodimerization on GEF catalytic activity not measured","Cellular consequence of antiparallel orientation untested in vivo"]},{"year":2018,"claim":"Connected FRMD4B membrane recruitment to AKT signaling and junction protein turnover, answering whether the insulin-driven translocation has a tissue-level functional role.","evidence":"Chemical mutagenesis screen identifying the S938P (Tvrm222) suppressor allele, in vitro cell-surface recruitment assay, Western blot for pAKT and junction proteins, and retinal histology in mouse models","pmids":["29947801"],"confidence":"Medium","gaps":["Direct mechanism linking FRMD4B to AKT phosphorylation not established","Whether junction protein changes are cause or consequence of altered AKT signaling unresolved","Role of GRP1/ARF activity in the retinal phenotype not tested"]},{"year":2025,"claim":"Demonstrated an in vivo developmental requirement for FRMD4B in cranial motor neuron formation, answering whether the gene contributes to neuronal patterning relevant to human disease.","evidence":"G0 and F2 germline CRISPR/Cas9 frmd4b knockout in zebrafish with phenotypic analysis of cranial motor development","pmids":["40162949"],"confidence":"Medium","gaps":["No molecular mechanism for the cranial motor phenotype resolved","Causal human variant in oCCDD patients not demonstrated"]},{"year":2025,"claim":"Implicated FRMD4B in neuronal process elongation via a MAPK/ERK-linked pathway, addressing a cell-autonomous neuronal function.","evidence":"CRISPR/Cas13 knockdown in primary cortical neurons and N1E-115 cells with morphometric analysis, MAPK/ERK Western blot, and hesperetin pharmacological rescue","pmids":["41155374"],"confidence":"Low","gaps":["MAPK/ERK linkage is indirect with no direct epistasis experiment","Whether the GRP1/ARF or AKT pathways mediate this effect not tested","Pharmacological rescue does not establish FRMD4B acts directly upstream of ERK"]},{"year":null,"claim":"How the FRMD4B-ARF-GEF complex mechanistically couples membrane recruitment to AKT, MAPK/ERK, and junction remodeling across retinal and neuronal contexts remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of the FERM domain in function","No demonstrated effect of FRMD4B on ARF GTPase loading in cells","Unifying mechanism across retina and neurons not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2]}],"complexes":[],"partners":["GRP1","ARNO","CYTH1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y2L6","full_name":"FERM domain-containing protein 4B","aliases":["GRP1-binding protein GRSP1"],"length_aa":1034,"mass_kda":118.0,"function":"Member of GRP1 signaling complexes that are acutely recruited to plasma membrane ruffles in response to insulin receptor signaling. May function as a scaffolding protein that regulates epithelial cell polarity by connecting ARF6 activation with the PAR3 complex. Plays a redundant role with FRMD4A in epithelial polarization","subcellular_location":"Cytoplasm, cytoskeleton; Cell junction, tight junction; Cell junction, adherens junction","url":"https://www.uniprot.org/uniprotkb/Q9Y2L6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FRMD4B","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FRMD4B","total_profiled":1310},"omim":[{"mim_id":"617467","title":"FERM DOMAIN-CONTAINING PROTEIN 4B; FRMD4B","url":"https://www.omim.org/entry/617467"},{"mim_id":"616305","title":"FERM DOMAIN-CONTAINING PROTEIN 4A; FRMD4A","url":"https://www.omim.org/entry/616305"},{"mim_id":"182115","title":"CYTOHESIN 1; CYTH1","url":"https://www.omim.org/entry/182115"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Centriolar satellite","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/FRMD4B"},"hgnc":{"alias_symbol":["KIAA1013","GRSP1"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y2L6","domains":[{"cath_id":"1.20.80.10","chopping":"60-320_330-384","consensus_level":"medium","plddt":91.0467,"start":60,"end":384},{"cath_id":"1.10.287","chopping":"2-47","consensus_level":"high","plddt":64.193,"start":2,"end":47},{"cath_id":"1.20.58","chopping":"499-560","consensus_level":"high","plddt":87.7805,"start":499,"end":560}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y2L6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y2L6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y2L6-F1-predicted_aligned_error_v6.png","plddt_mean":62.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FRMD4B","jax_strain_url":"https://www.jax.org/strain/search?query=FRMD4B"},"sequence":{"accession":"Q9Y2L6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y2L6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y2L6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y2L6"}},"corpus_meta":[{"pmid":"20124441","id":"PMC_20124441","title":"Common variants in HSPB7 and FRMD4B associated with advanced heart failure.","date":"2010","source":"Circulation. Cardiovascular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20124441","citation_count":107,"is_preprint":false},{"pmid":"29313708","id":"PMC_29313708","title":"Human Lung DNA Methylation Quantitative Trait Loci Colocalize with Chronic Obstructive Pulmonary Disease Genome-Wide Association Loci.","date":"2018","source":"American journal of respiratory and critical care medicine","url":"https://pubmed.ncbi.nlm.nih.gov/29313708","citation_count":91,"is_preprint":false},{"pmid":"25380588","id":"PMC_25380588","title":"Integrated whole transcriptome and DNA methylation analysis identifies gene networks specific to late-onset Alzheimer's disease.","date":"2015","source":"Journal of Alzheimer's disease : JAD","url":"https://pubmed.ncbi.nlm.nih.gov/25380588","citation_count":63,"is_preprint":false},{"pmid":"11445584","id":"PMC_11445584","title":"Signaling complexes of the FERM domain-containing protein GRSP1 bound to ARF exchange factor GRP1.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11445584","citation_count":41,"is_preprint":false},{"pmid":"24624911","id":"PMC_24624911","title":"Thiopurine pharmacogenomics: association of SNPs with clinical response and functional validation of candidate genes.","date":"2014","source":"Pharmacogenomics","url":"https://pubmed.ncbi.nlm.nih.gov/24624911","citation_count":38,"is_preprint":false},{"pmid":"32428537","id":"PMC_32428537","title":"Genome-Wide Association Study in Asians Identifies Novel Loci for High Myopia and Highlights a Nervous System Role in Its Pathogenesis.","date":"2020","source":"Ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/32428537","citation_count":31,"is_preprint":false},{"pmid":"32699239","id":"PMC_32699239","title":"Genome-wide association study of cognitive function in diverse Hispanics/Latinos: results from the Hispanic Community Health Study/Study of Latinos.","date":"2020","source":"Translational 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In Chinese hamster ovary cells co-expressing GRSP1 and GRP1 with the human insulin receptor, both proteins showed diffuse cytoplasmic localization at baseline and acutely co-translocated to plasma membrane ruffles upon insulin stimulation. Immunodepletion experiments demonstrated that virtually all endogenous GRSP1 exists in complex with GRP1 in lung tissue.\",\n      \"method\": \"Radiolabeled GRP1 probe screen of cDNA expression library; domain-mapping co-immunoprecipitation; co-expression in CHO cells with confocal imaging; immunodepletion from lung lysates\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding mapped to specific domains, localization with functional consequence (insulin-stimulated translocation), immunodepletion confirming endogenous complex; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"11445584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"FRMD4B (GRSP1) forms heterodimeric complexes with GRP1 family ARF exchange factors (GRP1, ARNO, and Cytohesin-1) via heptad-repeat coiled-coil interactions. At low micromolar concentrations, Grsp1 and Cytohesin-1 are monomeric while GRP1 and ARNO are homodimeric; mixing Grsp1 with GRP1 or Cytohesin-1 leads to spontaneous re-equilibration into heterodimers, whereas ~50% of ARNO remains homodimeric. FRET experiments indicate the heterodimers adopt a largely antiparallel orientation. Formation of Grsp1–GRP1 heterodimers does not substantially alter GRP1 binding to PtdIns(3,4,5)P3 or PtdIns(4,5)P2 headgroups, nor does it influence liposome partitioning.\",\n      \"method\": \"Analytical ultracentrifugation, fluorescence resonance energy transfer (FRET), in vitro reconstitution of complexes, liposome co-sedimentation assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple biophysical methods (AUC, FRET, liposome assay), single lab but orthogonal approaches\",\n      \"pmids\": [\"20527794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A missense variant in FRMD4B (S938P, Tvrm222 allele) suppresses photoreceptor dysplasia (outer nuclear layer rosettes, external limiting membrane fragmentation) in Nr2e3rd7/rd7 and Nrl−/− mouse retinas. In vitro experiments showed that the FRMD4B-S938P variant fails to be efficiently recruited to the cell surface upon insulin stimulation. Tvrm222 retinas displayed reduced AKT phosphorylation and increased levels of cell junction proteins Beta-catenin (Catenin beta 1) and tight junction protein 1 (ZO-1) at the cell membrane, indicating that FRMD4B participates in cell junction remodeling and maintenance of external limiting membrane integrity.\",\n      \"method\": \"Chemical mutagenesis screen and genetic mapping; Frmd4b missense mutation identification; in vitro cell-surface recruitment assay upon insulin stimulation; Western blot for AKT phosphorylation and junction protein levels; histological analysis of retinal morphology in mouse models\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic epistasis with defined retinal phenotype, in vitro localization assay, and biochemical readouts (pAKT, junction proteins); single lab, multiple orthogonal methods\",\n      \"pmids\": [\"29947801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CRISPR/Cas9-based knockout of frmd4b in zebrafish (G0 and F2 germline) produced defects in cranial motor neuron/ocular motor development, identifying FRMD4B as a candidate gene for ocular congenital cranial dysinnervation disorders (oCCDDs) with a role in cranial motor neuron development.\",\n      \"method\": \"G0 CRISPR/Cas9 knockout screen in zebrafish embryos; F2 germline mutant generation; phenotypic analysis of cranial motor development\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — zebrafish loss-of-function with defined cranial motor phenotype, single study with in vivo genetic approach but no molecular mechanism resolved\",\n      \"pmids\": [\"40162949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Knockdown of Frmd4b in primary cortical neurons and in the N1E-115 neuronal cell line using RNA-targeting CRISPR/Cas13 reduced process elongation, establishing a role for FRMD4B in neuronal process (neurite) outgrowth. The decreased process elongation was recovered by hesperetin, which stimulated phosphorylation of MAPKs/ERKs, suggesting that FRMD4B supports process elongation through a signaling pathway linked to sustained MAPK/ERK phosphorylation.\",\n      \"method\": \"CRISPR/Cas13 knockdown of Frmd4b in primary cortical neurons and N1E-115 cells; morphometric analysis of process length; Western blot for MAPK/ERK phosphorylation; pharmacological rescue with hesperetin\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, knockdown with morphological readout and pharmacological rescue; MAPK/ERK pathway linkage is indirect (no direct epistasis experiment)\",\n      \"pmids\": [\"41155374\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FRMD4B (GRSP1/KIAA1013) is a FERM domain-containing scaffolding protein that forms heterodimeric complexes with ARF-GEF family members (GRP1, Cytohesin-1, ARNO) via antiparallel coiled-coil interactions, co-translocates with GRP1 to plasma membrane ruffles upon insulin/PI3K signaling, participates in cell junction remodeling and maintenance of retinal external limiting membrane integrity through regulation of AKT signaling and junction protein levels, and is required for neuronal process elongation, with loss-of-function in zebrafish implicating it in cranial motor neuron development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FRMD4B (GRSP1/KIAA1013) is a FERM domain-containing scaffolding protein that couples ARF guanine nucleotide exchange factor signaling to PI3K/insulin inputs and cell junction remodeling [#0, #2]. It binds GRP1-family ARF-GEFs (GRP1, ARNO, Cytohesin-1) through antiparallel heptad-repeat coiled-coil interactions, re-equilibrating these GEFs from homodimers into Grsp1-containing heterodimers without altering GRP1 phosphoinositide headgroup binding [#0, #1]. Endogenous GRSP1 exists essentially entirely in complex with GRP1, and the pair co-translocates from cytoplasm to plasma membrane ruffles upon insulin stimulation [#0]. Through this membrane recruitment, FRMD4B regulates AKT phosphorylation and the membrane levels of junction proteins beta-catenin and ZO-1, and is required for maintenance of retinal external limiting membrane integrity, where a recruitment-deficient S938P variant suppresses photoreceptor dysplasia [#2]. In neurons, FRMD4B supports process elongation in a manner linked to sustained MAPK/ERK phosphorylation, and loss of frmd4b in zebrafish impairs cranial motor neuron development, implicating it as a candidate gene for ocular congenital cranial dysinnervation disorders [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established FRMD4B/GRSP1 as a dedicated binding partner of the ARF-GEF GRP1 that links GRP1 to insulin signaling, answering whether GRSP1 has a defined molecular partner and where it acts.\",\n      \"evidence\": \"cDNA expression library screen with radiolabeled GRP1 probe, domain-mapping co-IP, insulin-stimulated co-translocation imaging in CHO cells, and immunodepletion from lung lysates\",\n      \"pmids\": [\"11445584\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the GRSP1-GRP1 complex on downstream ARF activation not resolved\", \"Whether membrane recruitment requires GRP1 binding or FRMD4B's own determinants not dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the biophysical basis and selectivity of FRMD4B-GEF complex formation, answering how Grsp1 assembles with GRP1-family proteins and whether it alters their lipid binding.\",\n      \"evidence\": \"In vitro reconstitution with analytical ultracentrifugation, FRET orientation analysis, and liposome co-sedimentation\",\n      \"pmids\": [\"20527794\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional output of heterodimerization on GEF catalytic activity not measured\", \"Cellular consequence of antiparallel orientation untested in vivo\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected FRMD4B membrane recruitment to AKT signaling and junction protein turnover, answering whether the insulin-driven translocation has a tissue-level functional role.\",\n      \"evidence\": \"Chemical mutagenesis screen identifying the S938P (Tvrm222) suppressor allele, in vitro cell-surface recruitment assay, Western blot for pAKT and junction proteins, and retinal histology in mouse models\",\n      \"pmids\": [\"29947801\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism linking FRMD4B to AKT phosphorylation not established\", \"Whether junction protein changes are cause or consequence of altered AKT signaling unresolved\", \"Role of GRP1/ARF activity in the retinal phenotype not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstrated an in vivo developmental requirement for FRMD4B in cranial motor neuron formation, answering whether the gene contributes to neuronal patterning relevant to human disease.\",\n      \"evidence\": \"G0 and F2 germline CRISPR/Cas9 frmd4b knockout in zebrafish with phenotypic analysis of cranial motor development\",\n      \"pmids\": [\"40162949\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular mechanism for the cranial motor phenotype resolved\", \"Causal human variant in oCCDD patients not demonstrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated FRMD4B in neuronal process elongation via a MAPK/ERK-linked pathway, addressing a cell-autonomous neuronal function.\",\n      \"evidence\": \"CRISPR/Cas13 knockdown in primary cortical neurons and N1E-115 cells with morphometric analysis, MAPK/ERK Western blot, and hesperetin pharmacological rescue\",\n      \"pmids\": [\"41155374\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"MAPK/ERK linkage is indirect with no direct epistasis experiment\", \"Whether the GRP1/ARF or AKT pathways mediate this effect not tested\", \"Pharmacological rescue does not establish FRMD4B acts directly upstream of ERK\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the FRMD4B-ARF-GEF complex mechanistically couples membrane recruitment to AKT, MAPK/ERK, and junction remodeling across retinal and neuronal contexts remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of the FERM domain in function\", \"No demonstrated effect of FRMD4B on ARF GTPase loading in cells\", \"Unifying mechanism across retina and neurons not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GRP1\", \"ARNO\", \"CYTH1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}