{"gene":"MON2","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2005,"finding":"Yeast Mon2 localizes to the trans-Golgi and forms a complex with Dop1 (human DOPEY orthologue); deletion of Mon2 causes mislocalization of Dop1 from the Golgi, demonstrating that Mon2 acts as a scaffold to recruit the Golgi-localized pool of Dop1. Loss of Mon2 also causes defects in endosome-to-Golgi cycling.","method":"Yeast genetics, subcellular localization (fluorescence microscopy), co-immunoprecipitation, deletion mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (localization, pulldown, genetic deletion phenotype) in a foundational study with 34 citations","pmids":["16301316"],"is_preprint":false},{"year":2011,"finding":"Drosophila Mon2 (ortholog) acts downstream of Oskar at the oocyte posterior to remodel cortical actin and anchor germ plasm. Mon2 physically interacts with actin nucleators Cappuccino and Spire, promotes Rho1 accumulation at the posterior, and couples Oskar-induced endocytosis with F-actin projection formation, functioning as a scaffold on vesicles.","method":"Genetic epistasis (Drosophila loss-of-function), co-immunoprecipitation (Mon2 with Capu/Spire), live imaging, subcellular localization","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, genetic epistasis, and live imaging with defined phenotypic readout; 34 citations","pmids":["21610029"],"is_preprint":false},{"year":2011,"finding":"Human MON2 (hMon2) is required for efficient production of infectious HIV-1 virions; depletion of hMon2 in human cells reduces infectious particle production, consistent with its role in protein trafficking to the plasma membrane.","method":"siRNA knockdown in human cells, HIV-1 Gag VLP release assay, yeast genetic screen","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined cellular phenotype but single lab, single method in human cells","pmids":["21450827"],"is_preprint":false},{"year":2012,"finding":"In yeast, MON2 functions as a negative regulator of the GTP-restricted form of the monomeric G protein Arl1, as demonstrated by synthetic lethality and nucleotide-binding allele epistasis experiments.","method":"Yeast genetic epistasis, site-directed mutagenesis of ARL1, synthetic lethality analysis","journal":"FEMS yeast research","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis with defined alleles, but single lab study","pmids":["22594927"],"is_preprint":false},{"year":2018,"finding":"Human MON2 forms an evolutionarily conserved endosome-associated complex with DOPEY2 and the putative aminophospholipid translocase ATP9A; this complex associates with SNX3-retromer to mediate endosome-to-Golgi transport of Wntless. Phospholipid flippase activity of ATP9A contributes to SNX3-retromer-mediated Wntless sorting and Wnt secretion. In vivo suppression of Ce-mon-2, Ce-pad-1 (DOPEY2 orthologue), or Ce-tat-5 (ATP9A orthologue) phenocopies loss of SNX3-retromer function.","method":"Co-immunoprecipitation, in vivo C. elegans RNAi knockdown, ATPase-inhibited mutant (TAT-5 E246Q) overexpression, lysosomal degradation assay, Wnt signaling readout","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, in vivo epistasis in two organisms, ATPase mutant rescue; 69 citations, multiple orthogonal methods","pmids":["30213940"],"is_preprint":false},{"year":2019,"finding":"Dopey1 and Mon2 assemble into a complex that localizes to the Golgi, endolysosome, and ER exit sites. Golgi localization of Mon2 requires binding to phosphatidic acid, while Dopey1 requires phosphatidylinositol-4-phosphate. The N-terminus of Dopey1 interacts with kinesin-1, making the Dopey1-Mon2 complex a dual-lipid-regulated cargo adaptor that recruits kinesin-1 for centrifugally biased bidirectional membrane transport.","method":"Co-immunoprecipitation, lipid-binding assays, subcellular localization (fluorescence microscopy), kinesin-1 pulldown, domain mapping","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (lipid binding, Co-IP, localization, motor recruitment) in a single rigorous study; 28 citations","pmids":["31324769"],"is_preprint":false},{"year":2020,"finding":"MON2 drives separation of recycling endosomes (RE) from early endosomes (EE) and is required for formation of a tubular RE network. MON2 co-localizes with RE marker RAB4B; MON2 knockout impairs segregation of RE from EE and intracellular transferrin receptor recycling. DOPEY2 membrane recruitment depends on MON2 expression, and DOPEY2 binds kinesin and dynein/dynactin motors. MON2 is required for retrograde transport of Wntless through RE before delivery to the Golgi.","method":"MON2/DOPEY2 knockout cells, live imaging, subcellular co-localization, transferrin receptor recycling assay, Wntless transport assay","journal":"Cell structure and function","confidence":"High","confidence_rationale":"Tier 2 — KO with multiple defined phenotypic readouts and live imaging; 13 citations","pmids":["32404555"],"is_preprint":false},{"year":2021,"finding":"Mammalian MON2 physically interacts with GABARAPL2 (mammalian Atg8 orthologue) and this interaction increases autophagic flux in mammalian cells; C. elegans MON-2 similarly activates the GABARAP orthologue LGG-1. Under starvation, MON2 translocates from the Golgi to the endosome and upregulates autophagy.","method":"Co-immunoprecipitation (MON2–GABARAPL2), autophagic flux assays in mammalian cells, C. elegans genetic knockdown, subcellular localization under starvation","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and functional flux assay across two organisms, but single lab","pmids":["34860542"],"is_preprint":false}],"current_model":"MON2 is a trans-Golgi/endosome scaffold protein (distantly related to large Arf-GEFs but lacking a Sec7 catalytic domain) that nucleates a conserved MON2–DOPEY2–ATP9A complex on endosomes; this complex coordinates SNX3-retromer-mediated endosome-to-Golgi retrograde transport (including Wntless recycling) by regulating recycling-endosome biogenesis, recruits kinesin-1 via Dopey1 for bidirectional organelle transport through dual phospholipid (phosphatidic acid/PI4P) sensing, negatively regulates the GTPase Arl1, couples endocytosis to actin remodeling through interactions with Cappuccino and Spire, and promotes autophagy by binding and activating GABARAPL2/LGG-1 upon Golgi-to-endosome translocation under nutrient stress."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing that Mon2 is a trans-Golgi scaffold that recruits Dop1 and is required for endosome-to-Golgi cycling resolved Mon2's core cellular role as a trafficking organizer rather than a catalytic GEF.","evidence":"Yeast deletion mutants, fluorescence localization, and co-immunoprecipitation of Mon2–Dop1","pmids":["16301316"],"confidence":"High","gaps":["Mammalian conservation of the Mon2–Dop1 interaction not yet tested","Mechanism by which Mon2 recruits Dop1 to the Golgi unknown","No identification of specific cargo sorted by Mon2"]},{"year":2011,"claim":"Demonstration that Drosophila Mon2 couples Oskar-triggered endocytosis to actin remodeling via Cappuccino and Spire established that Mon2 scaffolding extends beyond vesicle trafficking to cytoskeletal regulation.","evidence":"Reciprocal co-immunoprecipitation, genetic epistasis, and live imaging in Drosophila oocytes","pmids":["21610029"],"confidence":"High","gaps":["Whether MON2–actin nucleator interaction is conserved in mammals is untested","Structural basis of MON2 interaction with Cappuccino/Spire undefined"]},{"year":2012,"claim":"Genetic evidence that Mon2 negatively regulates the GTPase Arl1 placed Mon2 upstream of a major Golgi-localized GTPase signaling axis.","evidence":"Synthetic lethality and nucleotide-binding allele epistasis in yeast","pmids":["22594927"],"confidence":"Medium","gaps":["No biochemical demonstration of direct Mon2-Arl1 interaction","Whether MON2 acts on Arl1 in mammalian cells is unknown","Single laboratory study"]},{"year":2018,"claim":"Identification of the conserved MON2–DOPEY2–ATP9A complex and its association with SNX3-retromer for Wntless retrieval defined the molecular machinery through which MON2 controls endosome-to-Golgi retrograde sorting and Wnt signaling.","evidence":"Reciprocal co-immunoprecipitation in human cells, C. elegans RNAi phenocopy of SNX3-retromer loss, ATPase-dead mutant rescue","pmids":["30213940"],"confidence":"High","gaps":["How the flippase activity of ATP9A is coordinated with SNX3-retromer tubule formation is unclear","Direct structural interface between MON2 and SNX3-retromer not mapped"]},{"year":2019,"claim":"Showing that MON2 binds phosphatidic acid and partners with PI4P-sensing DOPEY1 to recruit kinesin-1 revealed a dual-lipid-regulated cargo adaptor mechanism coupling membrane identity to motor-driven transport.","evidence":"Lipid-binding assays, co-immunoprecipitation, domain mapping, kinesin-1 pulldown","pmids":["31324769"],"confidence":"High","gaps":["Whether MON2's PA-binding domain is required in vivo for Golgi localization not tested by mutation","Relative contributions of kinesin-1 vs dynein/dynactin to MON2-dependent transport unresolved"]},{"year":2020,"claim":"Demonstrating that MON2 knockout abolishes recycling-endosome biogenesis and impairs both transferrin receptor recycling and Wntless retrograde transport established MON2 as an essential determinant of RE–EE segregation.","evidence":"MON2/DOPEY2 knockout cells, live imaging, transferrin recycling and Wntless transport assays","pmids":["32404555"],"confidence":"High","gaps":["Molecular mechanism by which MON2 initiates RE tubule formation is undefined","Whether MON2 directly remodels membrane or acts through effectors is unknown"]},{"year":2021,"claim":"Discovery that MON2 translocates from Golgi to endosomes under starvation and activates GABARAPL2/LGG-1 to promote autophagy expanded MON2's role from constitutive trafficking to stress-responsive autophagy regulation.","evidence":"Co-immunoprecipitation of MON2–GABARAPL2, autophagic flux assays in mammalian cells, C. elegans genetic knockdown","pmids":["34860542"],"confidence":"Medium","gaps":["Single laboratory study; independent confirmation needed","Signal triggering MON2 Golgi-to-endosome translocation under starvation is unidentified","Whether MON2-dependent autophagy is mechanistically linked to its recycling-endosome function is untested"]},{"year":null,"claim":"How MON2 coordinates its dual roles in recycling-endosome biogenesis and autophagy, and whether its membrane-remodeling function is intrinsic or mediated entirely through ATP9A flippase activity and motor recruitment, remain major open questions.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of MON2 or the MON2–DOPEY2–ATP9A complex","Physiological cargo repertoire beyond Wntless and transferrin receptor largely uncharacterized","In vivo roles of MON2 in mammalian development or disease not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,4,5,6]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[4,6,7]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,6]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,4,5,6]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4]}],"complexes":["MON2–DOPEY2–ATP9A","MON2–DOPEY1–kinesin-1"],"partners":["DOPEY2","ATP9A","DOPEY1","GABARAPL2","KIF5B","ARL1"],"other_free_text":[]},"mechanistic_narrative":"MON2 is a large scaffold protein that operates at the trans-Golgi network and endosomes to coordinate retrograde membrane trafficking, recycling-endosome biogenesis, and autophagy. MON2 nucleates a conserved complex with DOPEY1/DOPEY2 and the aminophospholipid translocase ATP9A on endosomal membranes; this complex associates with SNX3-retromer to mediate endosome-to-Golgi retrieval of cargo such as Wntless, thereby regulating Wnt secretion, and drives the physical separation of recycling endosomes from early endosomes required for transferrin receptor recycling [PMID:30213940, PMID:32404555]. MON2 senses phosphatidic acid for its Golgi targeting and, together with DOPEY1 (which binds PI4P), recruits kinesin-1 and dynein/dynactin motors to enable bidirectional organelle transport; it also couples endocytosis to actin remodeling through interactions with the nucleators Cappuccino and Spire [PMID:31324769, PMID:21610029]. Under nutrient stress, MON2 translocates from the Golgi to endosomes, binds and activates GABARAPL2/LGG-1, and promotes autophagic flux [PMID:34860542]."},"prefetch_data":{"uniprot":{"accession":"Q7Z3U7","full_name":"Protein MON2 homolog","aliases":["Protein SF21"],"length_aa":1717,"mass_kda":190.4,"function":"Plays a role in regulating membrane trafficking of cargo proteins. Together with ATP9A and DOP1B, regulates SNX3 retromer-mediated endosomal sorting of WLS away from lysosomal degradation","subcellular_location":"Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q7Z3U7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MON2","classification":"Not Classified","n_dependent_lines":178,"n_total_lines":1208,"dependency_fraction":0.14735099337748345},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SPTLC1","stoichiometry":0.2},{"gene":"TAF12","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MON2","total_profiled":1310},"omim":[{"mim_id":"617574","title":"ICHTHYOSIS, CONGENITAL, AUTOSOMAL RECESSIVE 13; ARCI13","url":"https://www.omim.org/entry/617574"},{"mim_id":"616823","title":"DOP1 LEUCINE ZIPPER-LIKE PROTEIN A; DOP1A","url":"https://www.omim.org/entry/616823"},{"mim_id":"616822","title":"MON2, REGULATOR OF ENDOSOME-TO-GOLGI TRAFFICKING; MON2","url":"https://www.omim.org/entry/616822"},{"mim_id":"615627","title":"BRI3-BINDING PROTEIN; BRI3BP","url":"https://www.omim.org/entry/615627"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nucleoli fibrillar center","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MON2"},"hgnc":{"alias_symbol":["KIAA1040"],"prev_symbol":[]},"alphafold":{"accession":"Q7Z3U7","domains":[{"cath_id":"-","chopping":"2-136","consensus_level":"medium","plddt":84.0097,"start":2,"end":136},{"cath_id":"-","chopping":"140-186_210-285","consensus_level":"medium","plddt":86.9802,"start":140,"end":285},{"cath_id":"-","chopping":"286-291_305-405_447-492","consensus_level":"medium","plddt":83.9852,"start":286,"end":492},{"cath_id":"-","chopping":"621-626_655-850","consensus_level":"medium","plddt":84.0013,"start":621,"end":850},{"cath_id":"1.20.58","chopping":"1061-1087_1108-1175","consensus_level":"medium","plddt":87.0753,"start":1061,"end":1175},{"cath_id":"1.25.40","chopping":"1236-1257_1267-1383_1402-1425","consensus_level":"medium","plddt":83.1127,"start":1236,"end":1425}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7Z3U7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q7Z3U7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q7Z3U7-F1-predicted_aligned_error_v6.png","plddt_mean":77.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MON2","jax_strain_url":"https://www.jax.org/strain/search?query=MON2"},"sequence":{"accession":"Q7Z3U7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q7Z3U7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q7Z3U7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7Z3U7"}},"corpus_meta":[{"pmid":"30213940","id":"PMC_30213940","title":"SNX3-retromer requires an evolutionary conserved MON2:DOPEY2:ATP9A complex to mediate Wntless sorting and Wnt secretion.","date":"2018","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/30213940","citation_count":69,"is_preprint":false},{"pmid":"16301316","id":"PMC_16301316","title":"Mon2, a relative of large Arf exchange factors, recruits Dop1 to the Golgi apparatus.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16301316","citation_count":34,"is_preprint":false},{"pmid":"21610029","id":"PMC_21610029","title":"Drosophila Mon2 couples Oskar-induced endocytosis with actin remodeling for cortical anchorage of the germ plasm.","date":"2011","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/21610029","citation_count":34,"is_preprint":false},{"pmid":"31324769","id":"PMC_31324769","title":"Dopey1-Mon2 complex binds to dual-lipids and recruits kinesin-1 for membrane trafficking.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31324769","citation_count":28,"is_preprint":false},{"pmid":"21450827","id":"PMC_21450827","title":"The cellular factors Vps18 and Mon2 are required for efficient production of infectious HIV-1 particles.","date":"2011","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/21450827","citation_count":17,"is_preprint":false},{"pmid":"34860542","id":"PMC_34860542","title":"MON-2, a Golgi protein, mediates autophagy-dependent longevity in Caenorhabditis elegans.","date":"2021","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/34860542","citation_count":16,"is_preprint":false},{"pmid":"32404555","id":"PMC_32404555","title":"MON2 Guides Wntless Transport to the Golgi through Recycling Endosomes.","date":"2020","source":"Cell structure and function","url":"https://pubmed.ncbi.nlm.nih.gov/32404555","citation_count":13,"is_preprint":false},{"pmid":"32413468","id":"PMC_32413468","title":"Mon2-monocytes and increased CD-11b expression before transcatheter aortic valve implantation are associated with earlier death.","date":"2020","source":"International journal of cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/32413468","citation_count":12,"is_preprint":false},{"pmid":"22594927","id":"PMC_22594927","title":"Mon2 is a negative regulator of the monomeric G protein, Arl1.","date":"2012","source":"FEMS yeast research","url":"https://pubmed.ncbi.nlm.nih.gov/22594927","citation_count":5,"is_preprint":false},{"pmid":"32572912","id":"PMC_32572912","title":"MicroRNA-133a-5p inhibiting metastatic capacity of renal clear cell carcinoma through regulating MON2.","date":"2020","source":"European review for medical and pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32572912","citation_count":4,"is_preprint":false},{"pmid":"35188063","id":"PMC_35188063","title":"MON-2, a Golgi protein, promotes longevity by upregulating autophagy through mediating inter-organelle communications.","date":"2022","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/35188063","citation_count":4,"is_preprint":false},{"pmid":"34236108","id":"PMC_34236108","title":"Novel MLL/KMT2A-MON2 fusion in a child with therapy-related acute myeloid leukemia after treatment for acute promyelocytic leukemia.","date":"2021","source":"Molecular carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/34236108","citation_count":3,"is_preprint":false},{"pmid":"39628352","id":"PMC_39628352","title":"Targeted RNA sequencing in diagnostically challenging head and neck carcinomas identifies novel MON2::STAT6, NFATC2::NUTM2B, POC5::RAF1, and NSD3::NCOA2 gene fusions.","date":"2024","source":"Histopathology","url":"https://pubmed.ncbi.nlm.nih.gov/39628352","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7209,"output_tokens":2248,"usd":0.027674},"stage2":{"model":"claude-opus-4-6","input_tokens":5529,"output_tokens":2278,"usd":0.126892},"total_usd":0.154566,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"Yeast Mon2 localizes to the trans-Golgi and forms a complex with Dop1 (human DOPEY orthologue); deletion of Mon2 causes mislocalization of Dop1 from the Golgi, demonstrating that Mon2 acts as a scaffold to recruit the Golgi-localized pool of Dop1. Loss of Mon2 also causes defects in endosome-to-Golgi cycling.\",\n      \"method\": \"Yeast genetics, subcellular localization (fluorescence microscopy), co-immunoprecipitation, deletion mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (localization, pulldown, genetic deletion phenotype) in a foundational study with 34 citations\",\n      \"pmids\": [\"16301316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Drosophila Mon2 (ortholog) acts downstream of Oskar at the oocyte posterior to remodel cortical actin and anchor germ plasm. Mon2 physically interacts with actin nucleators Cappuccino and Spire, promotes Rho1 accumulation at the posterior, and couples Oskar-induced endocytosis with F-actin projection formation, functioning as a scaffold on vesicles.\",\n      \"method\": \"Genetic epistasis (Drosophila loss-of-function), co-immunoprecipitation (Mon2 with Capu/Spire), live imaging, subcellular localization\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, genetic epistasis, and live imaging with defined phenotypic readout; 34 citations\",\n      \"pmids\": [\"21610029\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Human MON2 (hMon2) is required for efficient production of infectious HIV-1 virions; depletion of hMon2 in human cells reduces infectious particle production, consistent with its role in protein trafficking to the plasma membrane.\",\n      \"method\": \"siRNA knockdown in human cells, HIV-1 Gag VLP release assay, yeast genetic screen\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotype but single lab, single method in human cells\",\n      \"pmids\": [\"21450827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In yeast, MON2 functions as a negative regulator of the GTP-restricted form of the monomeric G protein Arl1, as demonstrated by synthetic lethality and nucleotide-binding allele epistasis experiments.\",\n      \"method\": \"Yeast genetic epistasis, site-directed mutagenesis of ARL1, synthetic lethality analysis\",\n      \"journal\": \"FEMS yeast research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with defined alleles, but single lab study\",\n      \"pmids\": [\"22594927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Human MON2 forms an evolutionarily conserved endosome-associated complex with DOPEY2 and the putative aminophospholipid translocase ATP9A; this complex associates with SNX3-retromer to mediate endosome-to-Golgi transport of Wntless. Phospholipid flippase activity of ATP9A contributes to SNX3-retromer-mediated Wntless sorting and Wnt secretion. In vivo suppression of Ce-mon-2, Ce-pad-1 (DOPEY2 orthologue), or Ce-tat-5 (ATP9A orthologue) phenocopies loss of SNX3-retromer function.\",\n      \"method\": \"Co-immunoprecipitation, in vivo C. elegans RNAi knockdown, ATPase-inhibited mutant (TAT-5 E246Q) overexpression, lysosomal degradation assay, Wnt signaling readout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, in vivo epistasis in two organisms, ATPase mutant rescue; 69 citations, multiple orthogonal methods\",\n      \"pmids\": [\"30213940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Dopey1 and Mon2 assemble into a complex that localizes to the Golgi, endolysosome, and ER exit sites. Golgi localization of Mon2 requires binding to phosphatidic acid, while Dopey1 requires phosphatidylinositol-4-phosphate. The N-terminus of Dopey1 interacts with kinesin-1, making the Dopey1-Mon2 complex a dual-lipid-regulated cargo adaptor that recruits kinesin-1 for centrifugally biased bidirectional membrane transport.\",\n      \"method\": \"Co-immunoprecipitation, lipid-binding assays, subcellular localization (fluorescence microscopy), kinesin-1 pulldown, domain mapping\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (lipid binding, Co-IP, localization, motor recruitment) in a single rigorous study; 28 citations\",\n      \"pmids\": [\"31324769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MON2 drives separation of recycling endosomes (RE) from early endosomes (EE) and is required for formation of a tubular RE network. MON2 co-localizes with RE marker RAB4B; MON2 knockout impairs segregation of RE from EE and intracellular transferrin receptor recycling. DOPEY2 membrane recruitment depends on MON2 expression, and DOPEY2 binds kinesin and dynein/dynactin motors. MON2 is required for retrograde transport of Wntless through RE before delivery to the Golgi.\",\n      \"method\": \"MON2/DOPEY2 knockout cells, live imaging, subcellular co-localization, transferrin receptor recycling assay, Wntless transport assay\",\n      \"journal\": \"Cell structure and function\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with multiple defined phenotypic readouts and live imaging; 13 citations\",\n      \"pmids\": [\"32404555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Mammalian MON2 physically interacts with GABARAPL2 (mammalian Atg8 orthologue) and this interaction increases autophagic flux in mammalian cells; C. elegans MON-2 similarly activates the GABARAP orthologue LGG-1. Under starvation, MON2 translocates from the Golgi to the endosome and upregulates autophagy.\",\n      \"method\": \"Co-immunoprecipitation (MON2–GABARAPL2), autophagic flux assays in mammalian cells, C. elegans genetic knockdown, subcellular localization under starvation\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and functional flux assay across two organisms, but single lab\",\n      \"pmids\": [\"34860542\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MON2 is a trans-Golgi/endosome scaffold protein (distantly related to large Arf-GEFs but lacking a Sec7 catalytic domain) that nucleates a conserved MON2–DOPEY2–ATP9A complex on endosomes; this complex coordinates SNX3-retromer-mediated endosome-to-Golgi retrograde transport (including Wntless recycling) by regulating recycling-endosome biogenesis, recruits kinesin-1 via Dopey1 for bidirectional organelle transport through dual phospholipid (phosphatidic acid/PI4P) sensing, negatively regulates the GTPase Arl1, couples endocytosis to actin remodeling through interactions with Cappuccino and Spire, and promotes autophagy by binding and activating GABARAPL2/LGG-1 upon Golgi-to-endosome translocation under nutrient stress.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MON2 is a large scaffold protein that operates at the trans-Golgi network and endosomes to coordinate retrograde membrane trafficking, recycling-endosome biogenesis, and autophagy. MON2 nucleates a conserved complex with DOPEY1/DOPEY2 and the aminophospholipid translocase ATP9A on endosomal membranes; this complex associates with SNX3-retromer to mediate endosome-to-Golgi retrieval of cargo such as Wntless, thereby regulating Wnt secretion, and drives the physical separation of recycling endosomes from early endosomes required for transferrin receptor recycling [PMID:30213940, PMID:32404555]. MON2 senses phosphatidic acid for its Golgi targeting and, together with DOPEY1 (which binds PI4P), recruits kinesin-1 and dynein/dynactin motors to enable bidirectional organelle transport; it also couples endocytosis to actin remodeling through interactions with the nucleators Cappuccino and Spire [PMID:31324769, PMID:21610029]. Under nutrient stress, MON2 translocates from the Golgi to endosomes, binds and activates GABARAPL2/LGG-1, and promotes autophagic flux [PMID:34860542].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that Mon2 is a trans-Golgi scaffold that recruits Dop1 and is required for endosome-to-Golgi cycling resolved Mon2's core cellular role as a trafficking organizer rather than a catalytic GEF.\",\n      \"evidence\": \"Yeast deletion mutants, fluorescence localization, and co-immunoprecipitation of Mon2–Dop1\",\n      \"pmids\": [\"16301316\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mammalian conservation of the Mon2–Dop1 interaction not yet tested\",\n        \"Mechanism by which Mon2 recruits Dop1 to the Golgi unknown\",\n        \"No identification of specific cargo sorted by Mon2\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstration that Drosophila Mon2 couples Oskar-triggered endocytosis to actin remodeling via Cappuccino and Spire established that Mon2 scaffolding extends beyond vesicle trafficking to cytoskeletal regulation.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, genetic epistasis, and live imaging in Drosophila oocytes\",\n      \"pmids\": [\"21610029\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether MON2–actin nucleator interaction is conserved in mammals is untested\",\n        \"Structural basis of MON2 interaction with Cappuccino/Spire undefined\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Genetic evidence that Mon2 negatively regulates the GTPase Arl1 placed Mon2 upstream of a major Golgi-localized GTPase signaling axis.\",\n      \"evidence\": \"Synthetic lethality and nucleotide-binding allele epistasis in yeast\",\n      \"pmids\": [\"22594927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No biochemical demonstration of direct Mon2-Arl1 interaction\",\n        \"Whether MON2 acts on Arl1 in mammalian cells is unknown\",\n        \"Single laboratory study\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of the conserved MON2–DOPEY2–ATP9A complex and its association with SNX3-retromer for Wntless retrieval defined the molecular machinery through which MON2 controls endosome-to-Golgi retrograde sorting and Wnt signaling.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation in human cells, C. elegans RNAi phenocopy of SNX3-retromer loss, ATPase-dead mutant rescue\",\n      \"pmids\": [\"30213940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How the flippase activity of ATP9A is coordinated with SNX3-retromer tubule formation is unclear\",\n        \"Direct structural interface between MON2 and SNX3-retromer not mapped\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showing that MON2 binds phosphatidic acid and partners with PI4P-sensing DOPEY1 to recruit kinesin-1 revealed a dual-lipid-regulated cargo adaptor mechanism coupling membrane identity to motor-driven transport.\",\n      \"evidence\": \"Lipid-binding assays, co-immunoprecipitation, domain mapping, kinesin-1 pulldown\",\n      \"pmids\": [\"31324769\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether MON2's PA-binding domain is required in vivo for Golgi localization not tested by mutation\",\n        \"Relative contributions of kinesin-1 vs dynein/dynactin to MON2-dependent transport unresolved\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating that MON2 knockout abolishes recycling-endosome biogenesis and impairs both transferrin receptor recycling and Wntless retrograde transport established MON2 as an essential determinant of RE–EE segregation.\",\n      \"evidence\": \"MON2/DOPEY2 knockout cells, live imaging, transferrin recycling and Wntless transport assays\",\n      \"pmids\": [\"32404555\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism by which MON2 initiates RE tubule formation is undefined\",\n        \"Whether MON2 directly remodels membrane or acts through effectors is unknown\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that MON2 translocates from Golgi to endosomes under starvation and activates GABARAPL2/LGG-1 to promote autophagy expanded MON2's role from constitutive trafficking to stress-responsive autophagy regulation.\",\n      \"evidence\": \"Co-immunoprecipitation of MON2–GABARAPL2, autophagic flux assays in mammalian cells, C. elegans genetic knockdown\",\n      \"pmids\": [\"34860542\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single laboratory study; independent confirmation needed\",\n        \"Signal triggering MON2 Golgi-to-endosome translocation under starvation is unidentified\",\n        \"Whether MON2-dependent autophagy is mechanistically linked to its recycling-endosome function is untested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MON2 coordinates its dual roles in recycling-endosome biogenesis and autophagy, and whether its membrane-remodeling function is intrinsic or mediated entirely through ATP9A flippase activity and motor recruitment, remain major open questions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of MON2 or the MON2–DOPEY2–ATP9A complex\",\n        \"Physiological cargo repertoire beyond Wntless and transferrin receptor largely uncharacterized\",\n        \"In vivo roles of MON2 in mammalian development or disease not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 4, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [4, 6, 7]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 4, 5, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\n      \"MON2–DOPEY2–ATP9A\",\n      \"MON2–DOPEY1–kinesin-1\"\n    ],\n    \"partners\": [\n      \"DOPEY2\",\n      \"ATP9A\",\n      \"DOPEY1\",\n      \"GABARAPL2\",\n      \"KIF5B\",\n      \"ARL1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}