{"gene":"MON1A","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2010,"finding":"MON1A (and MON1B) are required for phagosome maturation: phagosomes in MON1A-deficient cells recruit RAB5 but fail to progress to the RAB7-positive stage. MON1 interacts with GTP-bound RAB5, identifying MON1 as a RAB5 effector. The MON1-CCZ1 complex (but not either protein alone) binds RAB7 and promotes RAB7 activation, functioning as a critical link in progression from RAB5-positive to RAB7-positive phagosome maturation.","method":"Genetic epistasis (C. elegans sand-1/ccz-1 mutants), mammalian cell knockdown, co-immunoprecipitation with GTP-bound RAB5, RAB7 binding assays, phagosome maturation imaging","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, loss-of-function with defined cellular phenotype, replicated in C. elegans and mammalian cells, highly cited foundational paper","pmids":["20305638"],"is_preprint":false},{"year":2007,"finding":"MON1A is required for trafficking of ferroportin (the major mammalian iron exporter) to the macrophage cell surface, and is also important for trafficking of other cell-surface and secreted molecules, indicating a fundamental role in the mammalian secretory apparatus.","method":"QTL analysis in mice; missense allele co-segregation; cell-based trafficking assays with surface ferroportin measurement; siRNA knockdown","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — forward genetics plus cell-based functional assays, replicated in congenic mouse lines","pmids":["17632513"],"is_preprint":false},{"year":2012,"finding":"MON1A acts in anterograde secretory trafficking: siRNA knockdown delays ER-to-Golgi traffic (shown by Endo H sensitivity of ts045VSVG-GFP), delays Golgi reformation after Brefeldin A treatment, and delays Golgi-to-plasma membrane trafficking. MON1A associates with dynein intermediate chain (identified by immunoprecipitation and mass spectrometry), and both MON1A and dynein reduction alter steady-state Golgi morphology.","method":"siRNA knockdown, Endo H assay, Brefeldin A washout, immunoprecipitation + mass spectrometry, immunofluorescence microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (biochemical trafficking assay, IP-MS, morphological readouts) in a single study","pmids":["22665492"],"is_preprint":false},{"year":2020,"finding":"MON1A/MON1B are components of the trimeric Mon1-Ccz1-C18orf8 (MCC) GEF complex for RAB7. MON1A/B-deficient cells lack RAB7 activation, show severe late endosome morphology defects, impaired endosomal LDL trafficking, and failure of NPC1-dependent lysosomal cholesterol export. Active RAB7 (downstream of MCC GEF activity) interacts with the NPC1 cholesterol transporter to license lysosomal cholesterol export.","method":"Genome-wide CRISPR screen, CRISPR knockout of MON1A/B and C18orf8, RAB7 activation assays, cholesterol reporter, late endosome morphology imaging, LDL trafficking assays, constitutively active RAB7 rescue","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide CRISPR screen plus multiple functional validation assays, constitutively active mutant rescue, defines trimeric complex","pmids":["33144569"],"is_preprint":false},{"year":2020,"finding":"NRBF2 maintains CCZ1-MON1A GEF activity by interacting with the CCZ1-MON1A complex, regulating CCZ1-MON1A interaction with PI3KC3/VPS34 and CCZ1-associated PI3KC3 kinase activity; loss of NRBF2 impairs GTP-RAB7 generation and autophagosome maturation. MON1A also participates in the CCZ1-MON1A-RAB7 module that interacts with APP to facilitate degradation of APP-containing vesicles.","method":"Co-immunoprecipitation, RAB7-GTP pull-down assay, siRNA/KO of NRBF2, autophagosome maturation assay, APP-CTF degradation assay","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 — multiple co-IP and functional assays from a single lab","pmids":["32543313"],"is_preprint":false},{"year":2022,"finding":"MON1A-CCZ1 GEF activity is required for autophagosome maturation in Alzheimer disease models: active RAB7 is selectively decreased in autophagosome fractions from AD models, accompanied by impaired CCZ1-MON1A GEF activity. Overexpressing CCZ1-MON1A increases GTP-RAB7 levels, enhances autophagosome maturation, and promotes degradation of APP-CTFs, Aβ and P-tau in cells and a mouse AD model.","method":"GST-R7BD affinity-isolation assay for GTP-RAB7 in autophagosome fractions, AAV-mediated overexpression/knockdown of MON1A in mouse brain, immunoblotting, autophagosome purification, RNA-seq","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo AAV rescue plus biochemical GEF activity assay, single lab","pmids":["35198070"],"is_preprint":false},{"year":2022,"finding":"The lysosomal V-ATPase a3 subunit interacts with MON1A-CCZ1 complex and recruits it to secretory lysosomes in osteoclasts. The interaction is mediated by the N-terminal half domain of a3 and the longin motifs of MON1A and CCZ1. Loss of a3 abolishes lysosomal localization of endogenous CCZ1, and exogenous expression of MON1A-CCZ1 GEF promotes the a3-RAB7 interaction.","method":"Co-immunoprecipitation in HEK293T cells, domain mapping (longin motif mutants), immunofluorescence of osteoclasts lacking a3","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP with domain mapping and cellular localization data, single lab","pmids":["35589873"],"is_preprint":false},{"year":2020,"finding":"MON1A (via the CCZ1-MON1A complex) interacts with FYCO1 through the FYCO1 C-terminal GOLD domain, as identified by AP-MS and validated by co-immunoprecipitation; this interaction is required for RAB7A activation and fusion of autophagosomal/endosomal vesicles with lysosomes.","method":"Affinity purification-mass spectrometry (AP-MS) with spin-tip IMAC columns, co-immunoprecipitation validation","journal":"Analytical chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — AP-MS discovery confirmed by co-IP, single lab","pmids":["31992042"],"is_preprint":false},{"year":2023,"finding":"FYCO1 interacts via its C-terminal GOLD domain with the CCZ1-MON1A complex; this interaction is necessary for RAB7A activation and lysosomal delivery of TNFRSF10B/TRAIL-R2. CASP8 cleaves FYCO1 at aspartate 1306, releasing the GOLD domain and inactivating FYCO1 function, thereby preventing further CCZ1-MON1A-dependent vesicle-lysosome fusion and allowing apoptosis to proceed.","method":"Co-immunoprecipitation (two-step), CRISPR KO of FYCO1, apoptosis assays, receptor trafficking/lysosomal degradation assays, caspase cleavage site identification","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple co-IP validations plus CRISPR KO functional assays, single lab","pmids":["37418591"],"is_preprint":false},{"year":2024,"finding":"GORASP2 controls RAB7A activity by modulating its GEF complex MON1A-CCZ1, and this is required for RAB7A interaction with the HOPS complex and autophagosome-lysosome fusion during glucose starvation.","method":"Super-resolution microscopy, siRNA depletion of GORASP2, RAB7A activation assay, co-immunoprecipitation, SNARE complex assembly assay","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional epistasis with biochemical GEF activity assay, single lab","pmids":["39056394"],"is_preprint":false},{"year":2023,"finding":"MON1A is required for maintenance of Golgi ribbon architecture. MON1A interacts with the F-BAR protein FCHO2 (identified by yeast two-hybrid and co-immunoprecipitation). siRNA depletion of MON1A or FCHO2 causes Golgi fragmentation and prevents exchange of resident membrane proteins between Golgi ministacks (shown by FRAP). MON1A-silencing effect on Golgi disruption is cell cycle-independent, whereas FCHO2-silencing effect requires mitosis.","method":"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, immunofluorescence, FRAP analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2–3 — yeast two-hybrid confirmed by co-IP, FRAP functional data, single lab preprint","pmids":["37461455"],"is_preprint":true},{"year":2025,"finding":"MON1A variants cause congenital diarrhea and enteropathy (CODE) in humans. Functional characterization in cell and zebrafish models demonstrated that MON1A loss-of-function results in intestinal disease, establishing MON1A as a novel CODE gene.","method":"Exome/genome sequencing of patient cohort, cell model functional assays, zebrafish loss-of-function models","journal":"The New England journal of medicine","confidence":"Medium","confidence_rationale":"Tier 2 — human genetics plus cell and zebrafish functional validation, single study","pmids":["40174224"],"is_preprint":false}],"current_model":"MON1A forms a complex with CCZ1 (and the third subunit C18orf8/MCFD2) that functions as a guanine nucleotide exchange factor (GEF) for RAB7, acting downstream of GTP-RAB5 (which recruits MON1A) to drive RAB5-to-RAB7 conversion during endosome maturation, phagosome maturation, and autophagosome maturation; additionally, MON1A acts in anterograde secretory trafficking (ER-to-Golgi and Golgi-to-plasma membrane) by associating with dynein, and maintains Golgi ribbon architecture by interacting with the F-BAR protein FCHO2."},"narrative":{"teleology":[{"year":2007,"claim":"Forward genetics in mice revealed that MON1A is required for trafficking of ferroportin and other secreted/surface molecules, establishing the gene as a fundamental component of the mammalian secretory apparatus.","evidence":"QTL mapping in congenic mouse lines, cell-based ferroportin surface assays, siRNA knockdown","pmids":["17632513"],"confidence":"High","gaps":["Mechanism of MON1A action in secretory trafficking was unknown","Whether MON1A functions as part of a complex was not addressed","Relationship to endosomal RAB GTPases not yet explored in mammals"]},{"year":2010,"claim":"The MON1-CCZ1 complex was identified as a RAB5 effector and RAB7 GEF that drives RAB5-to-RAB7 conversion on phagosomes, establishing the central mechanistic paradigm for MON1A function in membrane maturation.","evidence":"C. elegans sand-1/ccz-1 mutants, mammalian knockdown, co-immunoprecipitation with GTP-RAB5, RAB7 binding and activation assays, phagosome imaging","pmids":["20305638"],"confidence":"High","gaps":["Stoichiometry and structure of the GEF complex were undefined","Whether additional subunits exist was unknown","Extension to autophagosome maturation was not tested"]},{"year":2012,"claim":"MON1A was shown to function in anterograde ER-to-Golgi and Golgi-to-PM trafficking and to associate with dynein, revealing a role distinct from its endosomal RAB7-GEF activity.","evidence":"siRNA knockdown, Endo H assay for ER-to-Golgi traffic, BFA washout, IP-mass spectrometry identifying dynein intermediate chain, immunofluorescence","pmids":["22665492"],"confidence":"High","gaps":["Whether the secretory-trafficking function requires CCZ1 or RAB7 activation was not resolved","Direct role of dynein association in MON1A-dependent trafficking was not reconstituted","Relationship between Golgi morphology changes and trafficking delays was unclear"]},{"year":2020,"claim":"A genome-wide CRISPR screen defined MON1A/B as part of a trimeric MCC (MON1-CCZ1-C18orf8) GEF complex whose RAB7 activation is required for NPC1-dependent lysosomal cholesterol export and LDL trafficking, broadening the physiological scope of MON1A's GEF activity.","evidence":"CRISPR screen and knockout of MON1A/B and C18orf8, RAB7-GTP pull-downs, cholesterol reporters, LDL trafficking assays, constitutively active RAB7 rescue","pmids":["33144569"],"confidence":"High","gaps":["Structural basis for trimeric complex assembly was not determined","Tissue-specific contributions of MON1A versus MON1B were unclear","Whether C18orf8 has catalytic versus scaffolding roles was not resolved"]},{"year":2020,"claim":"The MON1A-CCZ1 GEF was placed in the autophagosome maturation pathway through two independent studies: NRBF2 was found to maintain CCZ1-MON1A activity and regulate PI3KC3-dependent RAB7 activation, and FYCO1 was identified as a physical interactor that mediates CCZ1-MON1A-dependent vesicle–lysosome fusion.","evidence":"Co-immunoprecipitation, RAB7-GTP pull-downs, siRNA/KO of NRBF2, APP-CTF degradation assay; AP-MS identifying FYCO1-GOLD domain interaction with MON1A, co-IP validation","pmids":["32543313","31992042"],"confidence":"Medium","gaps":["Whether NRBF2 acts directly on the MON1A-CCZ1 complex or via PI3KC3 was not fully separated","Structural details of the FYCO1-GOLD domain–MON1A interface were unknown","In vivo validation in animal models was lacking"]},{"year":2022,"claim":"MON1A-CCZ1 GEF activity was shown to be diminished in Alzheimer disease models, with restored overexpression rescuing RAB7 activation, autophagosome maturation, and clearance of Aβ and phospho-tau in vivo, linking the GEF to neurodegeneration-relevant proteostasis.","evidence":"GST-R7BD affinity isolation for GTP-RAB7 in autophagosome fractions, AAV-mediated MON1A expression in mouse brain, immunoblotting","pmids":["35198070"],"confidence":"Medium","gaps":["Mechanism of GEF activity decline in AD was not identified","Whether effects are MON1A-specific or reflect general endolysosomal dysfunction was unclear","Independent replication in a second AD model was not reported"]},{"year":2022,"claim":"The lysosomal V-ATPase a3 subunit was identified as a membrane receptor that recruits MON1A-CCZ1 to secretory lysosomes in osteoclasts, with the interaction mapped to MON1A longin motifs, revealing a mechanism for GEF targeting to specific organelles.","evidence":"Co-immunoprecipitation in HEK293T, longin-motif domain mapping, immunofluorescence in a3-deficient osteoclasts","pmids":["35589873"],"confidence":"Medium","gaps":["Whether a3-mediated recruitment is required for RAB7 activation in osteoclasts was not directly tested by GEF assay","Generality of V-ATPase subunit-dependent GEF recruitment to other cell types was unknown","Structural resolution of the longin–a3 interface was lacking"]},{"year":2023,"claim":"CASP8 cleavage of the FYCO1 GOLD domain was shown to sever the FYCO1–CCZ1-MON1A interaction, blocking RAB7A activation and lysosomal delivery of TRAIL-R2, thereby linking MON1A-dependent vesicle maturation to apoptotic signaling.","evidence":"Two-step co-immunoprecipitation, CRISPR KO of FYCO1, caspase cleavage site mapping, receptor trafficking and apoptosis assays","pmids":["37418591"],"confidence":"Medium","gaps":["Whether CASP8 cleavage of FYCO1 is the dominant mechanism shutting down MON1A-CCZ1 during apoptosis was not established","In vivo relevance of FYCO1-MON1A axis in TRAIL signaling was not tested"]},{"year":2023,"claim":"MON1A was found to maintain Golgi ribbon architecture through a physical interaction with the F-BAR protein FCHO2, establishing a GEF-independent structural role at the Golgi. (preprint)","evidence":"(preprint) Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, FRAP of Golgi residents","pmids":["37461455"],"confidence":"Medium","gaps":["Awaits peer review and independent replication","Whether this Golgi role requires CCZ1 or RAB7 was not resolved","Molecular mechanism by which MON1A-FCHO2 maintains ribbon continuity is unknown"]},{"year":2025,"claim":"Human loss-of-function variants in MON1A were identified as the cause of congenital diarrhea and enteropathy (CODE), establishing MON1A as a disease gene and demonstrating its essential role in intestinal epithelial function.","evidence":"Exome/genome sequencing of patient cohort, cell model functional assays, zebrafish loss-of-function models","pmids":["40174224"],"confidence":"Medium","gaps":["Specific intestinal cellular pathway disrupted by MON1A loss (endosomal vs. secretory) was not delineated","Whether MON1B compensates in non-intestinal tissues remains unknown","Only a single study; independent cohort replication pending"]},{"year":null,"claim":"Key unresolved questions include the structural basis of trimeric MCC complex assembly and substrate specificity, whether MON1A's secretory/Golgi functions are mechanistically independent of RAB7 GEF activity, and the tissue-specific division of labor between MON1A and MON1B.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of the human MCC-RAB7 complex exists","The GEF-independent versus GEF-dependent functions of MON1A have not been genetically separated","Tissue-specific redundancy between MON1A and MON1B is not systematically characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,4,5]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[3,6]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2,10]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,5]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,3,7,8]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4,5,9]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[3]}],"complexes":["MON1-CCZ1-C18orf8 (MCC) trimeric RAB7 GEF complex"],"partners":["CCZ1","C18ORF8","RAB5","RAB7A","FYCO1","FCHO2","NRBF2","DYNC1I2"],"other_free_text":[]},"mechanistic_narrative":"MON1A is a core subunit of the trimeric MON1-CCZ1-C18orf8 guanine nucleotide exchange factor (GEF) complex that activates RAB7, serving as the master switch for RAB5-to-RAB7 conversion on endosomes, phagosomes, and autophagosomes [PMID:20305638, PMID:33144569]. MON1A is recruited to membranes as an effector of GTP-bound RAB5, and the assembled MON1-CCZ1 complex then catalyzes RAB7 GTP loading, which is essential for late-endosomal cholesterol export via NPC1, LDL trafficking, autophagosome–lysosome fusion, and APP-CTF/Aβ degradation [PMID:33144569, PMID:35198070, PMID:37418591]. Beyond the endolysosomal system, MON1A functions in anterograde secretory trafficking—including ER-to-Golgi and Golgi-to-plasma-membrane transport of cargoes such as ferroportin—by associating with dynein, and maintains Golgi ribbon integrity through interaction with the F-BAR protein FCHO2 [PMID:17632513, PMID:22665492, PMID:37461455]. Loss-of-function variants in MON1A cause congenital diarrhea and enteropathy in humans [PMID:40174224]."},"prefetch_data":{"uniprot":{"accession":"Q86VX9","full_name":"Vacuolar fusion protein MON1 homolog A","aliases":[],"length_aa":652,"mass_kda":72.9,"function":"Plays an important role in membrane trafficking through the secretory apparatus. Not involved in endocytic trafficking to lysosomes (By similarity). Acts in concert with CCZ1, as a guanine exchange factor (GEF) for RAB7, promotes the exchange of GDP to GTP, converting it from an inactive GDP-bound form into an active GTP-bound form (PubMed:23084991)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q86VX9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MON1A","classification":"Not Classified","n_dependent_lines":8,"n_total_lines":383,"dependency_fraction":0.020887728459530026},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MON1A","total_profiled":1310},"omim":[{"mim_id":"620660","title":"CCZ1 HOMOLOG, VACUOLAR PROTEIN TRAFFICKING- AND BIOGENESIS-ASSOCIATED PROTEIN; CCZ1","url":"https://www.omim.org/entry/620660"},{"mim_id":"611464","title":"MON1 HOMOLOG A, SECRETORY TRAFFICKING-ASSOCIATED; MON1A","url":"https://www.omim.org/entry/611464"},{"mim_id":"608954","title":"MON1 HOMOLOG B, SECRETORY TRAFFICKING-ASSOCIATED; MON1B","url":"https://www.omim.org/entry/608954"},{"mim_id":"601126","title":"TATA ELEMENT MODULATORY FACTOR 1; TMF1","url":"https://www.omim.org/entry/601126"},{"mim_id":"214700","title":"DIARRHEA 1, SECRETORY CHLORIDE, CONGENITAL; DIAR1","url":"https://www.omim.org/entry/214700"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MON1A"},"hgnc":{"alias_symbol":["MGC13272","SAND1"],"prev_symbol":[]},"alphafold":{"accession":"Q86VX9","domains":[{"cath_id":"3.30.450.70","chopping":"252-374","consensus_level":"high","plddt":93.7794,"start":252,"end":374},{"cath_id":"3.30.450.30","chopping":"391-529","consensus_level":"high","plddt":94.7392,"start":391,"end":529},{"cath_id":"3.40.1840.10","chopping":"535-645","consensus_level":"high","plddt":93.7948,"start":535,"end":645}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86VX9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q86VX9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q86VX9-F1-predicted_aligned_error_v6.png","plddt_mean":72.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MON1A","jax_strain_url":"https://www.jax.org/strain/search?query=MON1A"},"sequence":{"accession":"Q86VX9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q86VX9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q86VX9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86VX9"}},"corpus_meta":[{"pmid":"20305638","id":"PMC_20305638","title":"Identification 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Enteropathy.","date":"2025","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40174224","citation_count":6,"is_preprint":false},{"pmid":"39056394","id":"PMC_39056394","title":"GORASP2 promotes phagophore closure and autophagosome maturation into autolysosomes.","date":"2024","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/39056394","citation_count":6,"is_preprint":false},{"pmid":"19785692","id":"PMC_19785692","title":"Forward genetics used to identify new gene Mon1a with critical role in controlling macrophage iron metabolism and iron recycling from erythrocytes.","date":"2009","source":"Nutrition reviews","url":"https://pubmed.ncbi.nlm.nih.gov/19785692","citation_count":5,"is_preprint":false},{"pmid":"41265446","id":"PMC_41265446","title":"Genetic architecture of the murine red blood cell proteome reveals central role of hemoglobin beta cysteine 93 in maintaining redox balance.","date":"2025","source":"Cell 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the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40093052","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16683,"output_tokens":3240,"usd":0.049325},"stage2":{"model":"claude-opus-4-6","input_tokens":6596,"output_tokens":3304,"usd":0.17337},"total_usd":0.222695,"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\": 2010,\n      \"finding\": \"MON1A (and MON1B) are required for phagosome maturation: phagosomes in MON1A-deficient cells recruit RAB5 but fail to progress to the RAB7-positive stage. MON1 interacts with GTP-bound RAB5, identifying MON1 as a RAB5 effector. The MON1-CCZ1 complex (but not either protein alone) binds RAB7 and promotes RAB7 activation, functioning as a critical link in progression from RAB5-positive to RAB7-positive phagosome maturation.\",\n      \"method\": \"Genetic epistasis (C. elegans sand-1/ccz-1 mutants), mammalian cell knockdown, co-immunoprecipitation with GTP-bound RAB5, RAB7 binding assays, phagosome maturation imaging\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, loss-of-function with defined cellular phenotype, replicated in C. elegans and mammalian cells, highly cited foundational paper\",\n      \"pmids\": [\"20305638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MON1A is required for trafficking of ferroportin (the major mammalian iron exporter) to the macrophage cell surface, and is also important for trafficking of other cell-surface and secreted molecules, indicating a fundamental role in the mammalian secretory apparatus.\",\n      \"method\": \"QTL analysis in mice; missense allele co-segregation; cell-based trafficking assays with surface ferroportin measurement; siRNA knockdown\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — forward genetics plus cell-based functional assays, replicated in congenic mouse lines\",\n      \"pmids\": [\"17632513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MON1A acts in anterograde secretory trafficking: siRNA knockdown delays ER-to-Golgi traffic (shown by Endo H sensitivity of ts045VSVG-GFP), delays Golgi reformation after Brefeldin A treatment, and delays Golgi-to-plasma membrane trafficking. MON1A associates with dynein intermediate chain (identified by immunoprecipitation and mass spectrometry), and both MON1A and dynein reduction alter steady-state Golgi morphology.\",\n      \"method\": \"siRNA knockdown, Endo H assay, Brefeldin A washout, immunoprecipitation + mass spectrometry, immunofluorescence microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (biochemical trafficking assay, IP-MS, morphological readouts) in a single study\",\n      \"pmids\": [\"22665492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MON1A/MON1B are components of the trimeric Mon1-Ccz1-C18orf8 (MCC) GEF complex for RAB7. MON1A/B-deficient cells lack RAB7 activation, show severe late endosome morphology defects, impaired endosomal LDL trafficking, and failure of NPC1-dependent lysosomal cholesterol export. Active RAB7 (downstream of MCC GEF activity) interacts with the NPC1 cholesterol transporter to license lysosomal cholesterol export.\",\n      \"method\": \"Genome-wide CRISPR screen, CRISPR knockout of MON1A/B and C18orf8, RAB7 activation assays, cholesterol reporter, late endosome morphology imaging, LDL trafficking assays, constitutively active RAB7 rescue\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide CRISPR screen plus multiple functional validation assays, constitutively active mutant rescue, defines trimeric complex\",\n      \"pmids\": [\"33144569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NRBF2 maintains CCZ1-MON1A GEF activity by interacting with the CCZ1-MON1A complex, regulating CCZ1-MON1A interaction with PI3KC3/VPS34 and CCZ1-associated PI3KC3 kinase activity; loss of NRBF2 impairs GTP-RAB7 generation and autophagosome maturation. MON1A also participates in the CCZ1-MON1A-RAB7 module that interacts with APP to facilitate degradation of APP-containing vesicles.\",\n      \"method\": \"Co-immunoprecipitation, RAB7-GTP pull-down assay, siRNA/KO of NRBF2, autophagosome maturation assay, APP-CTF degradation assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple co-IP and functional assays from a single lab\",\n      \"pmids\": [\"32543313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MON1A-CCZ1 GEF activity is required for autophagosome maturation in Alzheimer disease models: active RAB7 is selectively decreased in autophagosome fractions from AD models, accompanied by impaired CCZ1-MON1A GEF activity. Overexpressing CCZ1-MON1A increases GTP-RAB7 levels, enhances autophagosome maturation, and promotes degradation of APP-CTFs, Aβ and P-tau in cells and a mouse AD model.\",\n      \"method\": \"GST-R7BD affinity-isolation assay for GTP-RAB7 in autophagosome fractions, AAV-mediated overexpression/knockdown of MON1A in mouse brain, immunoblotting, autophagosome purification, RNA-seq\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo AAV rescue plus biochemical GEF activity assay, single lab\",\n      \"pmids\": [\"35198070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The lysosomal V-ATPase a3 subunit interacts with MON1A-CCZ1 complex and recruits it to secretory lysosomes in osteoclasts. The interaction is mediated by the N-terminal half domain of a3 and the longin motifs of MON1A and CCZ1. Loss of a3 abolishes lysosomal localization of endogenous CCZ1, and exogenous expression of MON1A-CCZ1 GEF promotes the a3-RAB7 interaction.\",\n      \"method\": \"Co-immunoprecipitation in HEK293T cells, domain mapping (longin motif mutants), immunofluorescence of osteoclasts lacking a3\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP with domain mapping and cellular localization data, single lab\",\n      \"pmids\": [\"35589873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MON1A (via the CCZ1-MON1A complex) interacts with FYCO1 through the FYCO1 C-terminal GOLD domain, as identified by AP-MS and validated by co-immunoprecipitation; this interaction is required for RAB7A activation and fusion of autophagosomal/endosomal vesicles with lysosomes.\",\n      \"method\": \"Affinity purification-mass spectrometry (AP-MS) with spin-tip IMAC columns, co-immunoprecipitation validation\",\n      \"journal\": \"Analytical chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — AP-MS discovery confirmed by co-IP, single lab\",\n      \"pmids\": [\"31992042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FYCO1 interacts via its C-terminal GOLD domain with the CCZ1-MON1A complex; this interaction is necessary for RAB7A activation and lysosomal delivery of TNFRSF10B/TRAIL-R2. CASP8 cleaves FYCO1 at aspartate 1306, releasing the GOLD domain and inactivating FYCO1 function, thereby preventing further CCZ1-MON1A-dependent vesicle-lysosome fusion and allowing apoptosis to proceed.\",\n      \"method\": \"Co-immunoprecipitation (two-step), CRISPR KO of FYCO1, apoptosis assays, receptor trafficking/lysosomal degradation assays, caspase cleavage site identification\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple co-IP validations plus CRISPR KO functional assays, single lab\",\n      \"pmids\": [\"37418591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GORASP2 controls RAB7A activity by modulating its GEF complex MON1A-CCZ1, and this is required for RAB7A interaction with the HOPS complex and autophagosome-lysosome fusion during glucose starvation.\",\n      \"method\": \"Super-resolution microscopy, siRNA depletion of GORASP2, RAB7A activation assay, co-immunoprecipitation, SNARE complex assembly assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional epistasis with biochemical GEF activity assay, single lab\",\n      \"pmids\": [\"39056394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MON1A is required for maintenance of Golgi ribbon architecture. MON1A interacts with the F-BAR protein FCHO2 (identified by yeast two-hybrid and co-immunoprecipitation). siRNA depletion of MON1A or FCHO2 causes Golgi fragmentation and prevents exchange of resident membrane proteins between Golgi ministacks (shown by FRAP). MON1A-silencing effect on Golgi disruption is cell cycle-independent, whereas FCHO2-silencing effect requires mitosis.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, immunofluorescence, FRAP analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — yeast two-hybrid confirmed by co-IP, FRAP functional data, single lab preprint\",\n      \"pmids\": [\"37461455\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MON1A variants cause congenital diarrhea and enteropathy (CODE) in humans. Functional characterization in cell and zebrafish models demonstrated that MON1A loss-of-function results in intestinal disease, establishing MON1A as a novel CODE gene.\",\n      \"method\": \"Exome/genome sequencing of patient cohort, cell model functional assays, zebrafish loss-of-function models\",\n      \"journal\": \"The New England journal of medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — human genetics plus cell and zebrafish functional validation, single study\",\n      \"pmids\": [\"40174224\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MON1A forms a complex with CCZ1 (and the third subunit C18orf8/MCFD2) that functions as a guanine nucleotide exchange factor (GEF) for RAB7, acting downstream of GTP-RAB5 (which recruits MON1A) to drive RAB5-to-RAB7 conversion during endosome maturation, phagosome maturation, and autophagosome maturation; additionally, MON1A acts in anterograde secretory trafficking (ER-to-Golgi and Golgi-to-plasma membrane) by associating with dynein, and maintains Golgi ribbon architecture by interacting with the F-BAR protein FCHO2.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MON1A is a core subunit of the trimeric MON1-CCZ1-C18orf8 guanine nucleotide exchange factor (GEF) complex that activates RAB7, serving as the master switch for RAB5-to-RAB7 conversion on endosomes, phagosomes, and autophagosomes [PMID:20305638, PMID:33144569]. MON1A is recruited to membranes as an effector of GTP-bound RAB5, and the assembled MON1-CCZ1 complex then catalyzes RAB7 GTP loading, which is essential for late-endosomal cholesterol export via NPC1, LDL trafficking, autophagosome–lysosome fusion, and APP-CTF/Aβ degradation [PMID:33144569, PMID:35198070, PMID:37418591]. Beyond the endolysosomal system, MON1A functions in anterograde secretory trafficking—including ER-to-Golgi and Golgi-to-plasma-membrane transport of cargoes such as ferroportin—by associating with dynein, and maintains Golgi ribbon integrity through interaction with the F-BAR protein FCHO2 [PMID:17632513, PMID:22665492, PMID:37461455]. Loss-of-function variants in MON1A cause congenital diarrhea and enteropathy in humans [PMID:40174224].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Forward genetics in mice revealed that MON1A is required for trafficking of ferroportin and other secreted/surface molecules, establishing the gene as a fundamental component of the mammalian secretory apparatus.\",\n      \"evidence\": \"QTL mapping in congenic mouse lines, cell-based ferroportin surface assays, siRNA knockdown\",\n      \"pmids\": [\"17632513\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism of MON1A action in secretory trafficking was unknown\",\n        \"Whether MON1A functions as part of a complex was not addressed\",\n        \"Relationship to endosomal RAB GTPases not yet explored in mammals\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The MON1-CCZ1 complex was identified as a RAB5 effector and RAB7 GEF that drives RAB5-to-RAB7 conversion on phagosomes, establishing the central mechanistic paradigm for MON1A function in membrane maturation.\",\n      \"evidence\": \"C. elegans sand-1/ccz-1 mutants, mammalian knockdown, co-immunoprecipitation with GTP-RAB5, RAB7 binding and activation assays, phagosome imaging\",\n      \"pmids\": [\"20305638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Stoichiometry and structure of the GEF complex were undefined\",\n        \"Whether additional subunits exist was unknown\",\n        \"Extension to autophagosome maturation was not tested\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"MON1A was shown to function in anterograde ER-to-Golgi and Golgi-to-PM trafficking and to associate with dynein, revealing a role distinct from its endosomal RAB7-GEF activity.\",\n      \"evidence\": \"siRNA knockdown, Endo H assay for ER-to-Golgi traffic, BFA washout, IP-mass spectrometry identifying dynein intermediate chain, immunofluorescence\",\n      \"pmids\": [\"22665492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the secretory-trafficking function requires CCZ1 or RAB7 activation was not resolved\",\n        \"Direct role of dynein association in MON1A-dependent trafficking was not reconstituted\",\n        \"Relationship between Golgi morphology changes and trafficking delays was unclear\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A genome-wide CRISPR screen defined MON1A/B as part of a trimeric MCC (MON1-CCZ1-C18orf8) GEF complex whose RAB7 activation is required for NPC1-dependent lysosomal cholesterol export and LDL trafficking, broadening the physiological scope of MON1A's GEF activity.\",\n      \"evidence\": \"CRISPR screen and knockout of MON1A/B and C18orf8, RAB7-GTP pull-downs, cholesterol reporters, LDL trafficking assays, constitutively active RAB7 rescue\",\n      \"pmids\": [\"33144569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for trimeric complex assembly was not determined\",\n        \"Tissue-specific contributions of MON1A versus MON1B were unclear\",\n        \"Whether C18orf8 has catalytic versus scaffolding roles was not resolved\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The MON1A-CCZ1 GEF was placed in the autophagosome maturation pathway through two independent studies: NRBF2 was found to maintain CCZ1-MON1A activity and regulate PI3KC3-dependent RAB7 activation, and FYCO1 was identified as a physical interactor that mediates CCZ1-MON1A-dependent vesicle–lysosome fusion.\",\n      \"evidence\": \"Co-immunoprecipitation, RAB7-GTP pull-downs, siRNA/KO of NRBF2, APP-CTF degradation assay; AP-MS identifying FYCO1-GOLD domain interaction with MON1A, co-IP validation\",\n      \"pmids\": [\"32543313\", \"31992042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether NRBF2 acts directly on the MON1A-CCZ1 complex or via PI3KC3 was not fully separated\",\n        \"Structural details of the FYCO1-GOLD domain–MON1A interface were unknown\",\n        \"In vivo validation in animal models was lacking\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"MON1A-CCZ1 GEF activity was shown to be diminished in Alzheimer disease models, with restored overexpression rescuing RAB7 activation, autophagosome maturation, and clearance of Aβ and phospho-tau in vivo, linking the GEF to neurodegeneration-relevant proteostasis.\",\n      \"evidence\": \"GST-R7BD affinity isolation for GTP-RAB7 in autophagosome fractions, AAV-mediated MON1A expression in mouse brain, immunoblotting\",\n      \"pmids\": [\"35198070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism of GEF activity decline in AD was not identified\",\n        \"Whether effects are MON1A-specific or reflect general endolysosomal dysfunction was unclear\",\n        \"Independent replication in a second AD model was not reported\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The lysosomal V-ATPase a3 subunit was identified as a membrane receptor that recruits MON1A-CCZ1 to secretory lysosomes in osteoclasts, with the interaction mapped to MON1A longin motifs, revealing a mechanism for GEF targeting to specific organelles.\",\n      \"evidence\": \"Co-immunoprecipitation in HEK293T, longin-motif domain mapping, immunofluorescence in a3-deficient osteoclasts\",\n      \"pmids\": [\"35589873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether a3-mediated recruitment is required for RAB7 activation in osteoclasts was not directly tested by GEF assay\",\n        \"Generality of V-ATPase subunit-dependent GEF recruitment to other cell types was unknown\",\n        \"Structural resolution of the longin–a3 interface was lacking\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"CASP8 cleavage of the FYCO1 GOLD domain was shown to sever the FYCO1–CCZ1-MON1A interaction, blocking RAB7A activation and lysosomal delivery of TRAIL-R2, thereby linking MON1A-dependent vesicle maturation to apoptotic signaling.\",\n      \"evidence\": \"Two-step co-immunoprecipitation, CRISPR KO of FYCO1, caspase cleavage site mapping, receptor trafficking and apoptosis assays\",\n      \"pmids\": [\"37418591\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether CASP8 cleavage of FYCO1 is the dominant mechanism shutting down MON1A-CCZ1 during apoptosis was not established\",\n        \"In vivo relevance of FYCO1-MON1A axis in TRAIL signaling was not tested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"MON1A was found to maintain Golgi ribbon architecture through a physical interaction with the F-BAR protein FCHO2, establishing a GEF-independent structural role at the Golgi. (preprint)\",\n      \"evidence\": \"(preprint) Yeast two-hybrid, co-immunoprecipitation, siRNA knockdown, FRAP of Golgi residents\",\n      \"pmids\": [\"37461455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Awaits peer review and independent replication\",\n        \"Whether this Golgi role requires CCZ1 or RAB7 was not resolved\",\n        \"Molecular mechanism by which MON1A-FCHO2 maintains ribbon continuity is unknown\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Human loss-of-function variants in MON1A were identified as the cause of congenital diarrhea and enteropathy (CODE), establishing MON1A as a disease gene and demonstrating its essential role in intestinal epithelial function.\",\n      \"evidence\": \"Exome/genome sequencing of patient cohort, cell model functional assays, zebrafish loss-of-function models\",\n      \"pmids\": [\"40174224\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Specific intestinal cellular pathway disrupted by MON1A loss (endosomal vs. secretory) was not delineated\",\n        \"Whether MON1B compensates in non-intestinal tissues remains unknown\",\n        \"Only a single study; independent cohort replication pending\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of trimeric MCC complex assembly and substrate specificity, whether MON1A's secretory/Golgi functions are mechanistically independent of RAB7 GEF activity, and the tissue-specific division of labor between MON1A and MON1B.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of the human MCC-RAB7 complex exists\",\n        \"The GEF-independent versus GEF-dependent functions of MON1A have not been genetically separated\",\n        \"Tissue-specific redundancy between MON1A and MON1B is not systematically characterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2, 10]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 3, 7, 8]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4, 5, 9]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [\n      \"MON1-CCZ1-C18orf8 (MCC) trimeric RAB7 GEF complex\"\n    ],\n    \"partners\": [\n      \"CCZ1\",\n      \"C18orf8\",\n      \"RAB5\",\n      \"RAB7A\",\n      \"FYCO1\",\n      \"FCHO2\",\n      \"NRBF2\",\n      \"DYNC1I2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}