{"gene":"MTMR8","run_date":"2026-06-10T05:19:51","timeline":{"discoveries":[{"year":2006,"finding":"MTMR8 forms a heteromeric complex with MTMR9, as identified by directed two-hybrid screening and immunoprecipitation of epitope-tagged proteins.","method":"Yeast two-hybrid and co-immunoprecipitation of epitope-tagged proteins","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP and two-hybrid, confirmed across multiple myotubularin pairs in same study, independently replicated in PMID:22647598","pmids":["16787938"],"is_preprint":false},{"year":2012,"finding":"MTMR9 dimerizes with MTMR8 and increases MTMR8 catalytic activity: MTMR9 enhances MTMR8 activity 4-fold toward PtdIns(3)P and 1.4-fold toward PtdIns(3,5)P2, shifting substrate preference of the complex to PtdIns(3)P. In cells, the MTMR8/MTMR9 complex reduces cellular PtdIns(3)P levels and inhibits autophagy.","method":"In vitro phosphatase assays with purified MTMR8/MTMR9 complexes, substrate specificity measurements, cellular PtdIns(3)P quantification, autophagy assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic reconstitution with defined substrates plus cellular functional readouts, multiple orthogonal methods in one rigorous study","pmids":["22647598"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of the MTMR8 phosphatase domain reveals: (1) the protein dimerizes via a novel mode mediated by the phosphatase domain with twofold symmetry; (2) Lys255 interacts with the substrate diacylglycerol moiety (analogous to Lys333 of MTMR2); (3) catalytic activity is inhibited by oxidation and reversibly reactivated by reduction, suggesting an oxidation-protective intermediate other than a disulfide bond because no second cysteine is within disulfide-bond distance of the catalytic Cys338.","method":"X-ray crystallography of the phosphatase domain, mutation studies, redox activity assays","journal":"Acta crystallographica. Section D, Biological crystallography","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis plus enzymatic activity assays in one study, single lab","pmids":["26143924"],"is_preprint":false},{"year":2009,"finding":"In zebrafish, Mtmr8 knockdown causes defects in somitogenesis and disorganization of actin cytoskeleton. The PH/G domain of Mtmr8 is required for its function: PH/G domain deletion alone does not cause phenotype, but combined with PI3K inhibition (LY294002) it does. Mtmr8 loss increases Akt phosphorylation, indicating cooperation with PI3K signaling to regulate actin filament modeling and muscle development. Cell transplantation experiments show Mtmr8 acts non-cell-autonomously in actin modeling.","method":"Morpholino knockdown in zebrafish, domain-deletion analysis, PI3K inhibitor treatment, Akt phosphorylation western blot, cell transplantation","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — morpholino KD with multiple orthogonal readouts (phospho-Akt, actin staining, domain deletion, cell transplantation), single lab","pmids":["19325702"],"is_preprint":false},{"year":2010,"finding":"In zebrafish, Mtmr8 knockdown impairs arterial endothelial marker expression, causes endothelial cell reduction, vasculogenesis defects (retarded intersegmental vessel development, interrupted dorsal aorta), and loss of arterial endothelial cell identity. These defects are rescued by PI3K inhibitor (low concentration), dominant-negative PKA mRNA overexpression, or VEGF mRNA overexpression, indicating Mtmr8 represses PI3K activity to regulate arterial specification through the Hedgehog/PI3K/VEGF signaling cascade.","method":"Morpholino knockdown in zebrafish, rescue experiments with PI3K inhibitor and mRNA overexpression, arterial marker expression analysis","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — morpholino KD with genetic/pharmacological rescue and multiple markers, single lab","pmids":["20815916"],"is_preprint":false},{"year":2020,"finding":"Decreased MTMR8 function in higher animal cells results in autophagic vesicle accumulation and influences endolysosomal homeostasis, establishing MTMR8 as a regulator of autophagic flux.","method":"Loss-of-function studies in cell lines with autophagic vesicle and endolysosomal markers","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD/KO with defined cellular phenotype (vesicle accumulation, endolysosomal changes), corroborated by parallel Drosophila ortholog data in same study","pmids":["32915229"],"is_preprint":false},{"year":2019,"finding":"MTMR9 (inactive phosphatase) localizes to the intermediate compartment and Golgi apparatus and recruits its active partner MTMR8 to these locations. MTMR8 and MTMR9 co-localize with RAB1A and regulate RAB1A localization, linking the MTMR8/MTMR9 complex to ER-to-Golgi trafficking.","method":"Fluorescence co-localization, loss-of-function (MTMR9 knockdown/overexpression), RAB1A localization assays, protein secretion assays","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiments with functional consequence (RAB1A redistribution, secretion defects), single lab, multiple orthogonal methods","pmids":["31704058"],"is_preprint":false}],"current_model":"MTMR8 is an active PtdIns(3)P-preferring lipid 3-phosphatase whose catalytic activity, substrate specificity, and autophagy-inhibitory function are amplified by dimerization with the inactive family member MTMR9; the crystal structure of its phosphatase domain reveals a novel dimerization mode, a Lys255-mediated substrate interaction, and reversible oxidation-dependent inhibition of its catalytic Cys338, while in vivo studies in zebrafish and mammalian cells show it cooperates with PI3K signaling to regulate actin cytoskeleton organization, muscle and vascular development, ER-to-Golgi trafficking (via MTMR9-dependent recruitment to the Golgi and RAB1A regulation), and autophagic flux."},"narrative":{"mechanistic_narrative":"MTMR8 is an active myotubularin-family lipid 3-phosphatase that preferentially dephosphorylates PtdIns(3)P and, together with the catalytically inactive family member MTMR9, controls phosphoinositide pools governing autophagy, membrane trafficking, and actin-dependent development [PMID:22647598, PMID:26143924]. MTMR8 forms a stable heteromeric complex with MTMR9, and this partnership amplifies its catalytic output—enhancing activity ~4-fold toward PtdIns(3)P and shifting the complex's substrate preference toward PtdIns(3)P—so that the complex lowers cellular PtdIns(3)P and inhibits autophagy [PMID:16787938, PMID:22647598]. Consistent with this, loss of MTMR8 function causes autophagic vesicle accumulation and perturbs endolysosomal homeostasis, establishing it as a regulator of autophagic flux [PMID:32915229]. The crystal structure of its phosphatase domain reveals a novel dimerization mode with twofold symmetry, a Lys255 contact with the substrate diacylglycerol moiety, and reversible oxidation-dependent inactivation of the catalytic Cys338 via a non-disulfide oxidation-protective intermediate [PMID:26143924]. Through MTMR9, which localizes to the intermediate compartment and Golgi, MTMR8 is recruited to these compartments where the complex co-localizes with and regulates RAB1A, linking it to ER-to-Golgi trafficking [PMID:31704058]. In zebrafish, Mtmr8 represses PI3K/Akt signaling to organize the actin cytoskeleton during somitogenesis and muscle development, and to specify arterial endothelial identity through a Hedgehog/PI3K/VEGF cascade [PMID:19325702, PMID:20815916].","teleology":[{"year":2006,"claim":"Established that MTMR8 does not act alone but physically partners with another myotubularin, identifying MTMR9 as a heteromeric complex partner and framing MTMR8 function as complex-dependent.","evidence":"Yeast two-hybrid and reciprocal co-immunoprecipitation of epitope-tagged proteins","pmids":["16787938"],"confidence":"High","gaps":["Did not define the catalytic or functional consequence of the interaction","No stoichiometry or interface mapping"]},{"year":2009,"claim":"Provided the first in vivo functional role, showing MTMR8 organizes the actin cytoskeleton and muscle development by restraining PI3K/Akt signaling, with the PH/G domain required for function.","evidence":"Morpholino knockdown in zebrafish with domain-deletion, PI3K inhibitor treatment, phospho-Akt western blot, and cell transplantation","pmids":["19325702"],"confidence":"Medium","gaps":["Morpholino-based; mechanism connecting lipid phosphatase activity to actin not biochemically resolved","Non-cell-autonomous effector unidentified"]},{"year":2010,"claim":"Extended the developmental role to vascular patterning, showing MTMR8 represses PI3K to specify arterial endothelial identity within a Hedgehog/PI3K/VEGF cascade.","evidence":"Morpholino knockdown in zebrafish with pharmacological and mRNA rescue and arterial marker analysis","pmids":["20815916"],"confidence":"Medium","gaps":["Morpholino-based; direct phosphoinositide substrate in endothelium not measured","Epistatic placement within Hedgehog/PI3K/VEGF inferred from rescue, not direct interaction"]},{"year":2012,"claim":"Resolved the biochemical basis of the MTMR8–MTMR9 partnership, demonstrating MTMR9 dimerization boosts MTMR8 phosphatase activity, biases the complex toward PtdIns(3)P, and lowers cellular PtdIns(3)P to inhibit autophagy.","evidence":"In vitro phosphatase assays with purified MTMR8/MTMR9 complexes, substrate specificity measurements, cellular PtdIns(3)P quantification, and autophagy assays","pmids":["22647598"],"confidence":"High","gaps":["Structural basis of activation not defined here","In vivo substrate site in cells not directly identified"]},{"year":2015,"claim":"Defined the structural and regulatory architecture of the catalytic domain, revealing a novel dimerization mode, a Lys255 substrate contact, and reversible redox control of the catalytic Cys338.","evidence":"X-ray crystallography of the phosphatase domain with mutagenesis and redox activity assays","pmids":["26143924"],"confidence":"High","gaps":["Structure of the MTMR8–MTMR9 heterocomplex not solved","Identity of the oxidation-protective intermediate at Cys338 unresolved","Physiological trigger of redox regulation unknown"]},{"year":2019,"claim":"Connected the complex to a new membrane-trafficking arena, showing MTMR9 recruits MTMR8 to the intermediate compartment/Golgi where the complex regulates RAB1A and ER-to-Golgi transport.","evidence":"Fluorescence co-localization, MTMR9 loss/gain-of-function, RAB1A localization assays, and secretion assays","pmids":["31704058"],"confidence":"Medium","gaps":["Whether RAB1A regulation depends on MTMR8 catalytic activity not established","Single lab; mechanism linking PtdIns(3)P turnover to RAB1A localization unclear"]},{"year":2020,"claim":"Consolidated the autophagy role in higher-animal cells, showing reduced MTMR8 function drives autophagic vesicle accumulation and disrupts endolysosomal homeostasis, marking it a regulator of autophagic flux.","evidence":"Loss-of-function studies in cell lines with autophagic and endolysosomal markers, corroborated by Drosophila ortholog data","pmids":["32915229"],"confidence":"Medium","gaps":["Step in the autophagy pathway directly controlled not pinpointed","Dependence on MTMR9 partnership in this context not tested"]},{"year":null,"claim":"How MTMR8's catalytic regulation, trafficking, and developmental signaling roles are mechanistically unified—and whether redox control of Cys338 operates physiologically—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the active MTMR8–MTMR9 heterocomplex","Direct effector linking PtdIns(3)P turnover to actin and arterial specification not identified","Physiological context of redox inactivation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[1,2]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4]}],"complexes":["MTMR8–MTMR9 heterodimer"],"partners":["MTMR9","RAB1A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96EF0","full_name":"Phosphatidylinositol-3,5-bisphosphate 3-phosphatase MTMR8","aliases":["Myotubularin-related protein 8","Phosphatidylinositol-3-phosphate phosphatase"],"length_aa":704,"mass_kda":78.9,"function":"Lipid phosphatase that specifically dephosphorylates the D-3 position of phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate, generating phosphatidylinositol and phosphatidylinositol 5-phosphate (PubMed:22647598, PubMed:26143924). In complex with MTMR9, negatively regulates autophagy (PubMed:22647598)","subcellular_location":"Nucleus envelope","url":"https://www.uniprot.org/uniprotkb/Q96EF0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MTMR8","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MTMR8","total_profiled":1310},"omim":[{"mim_id":"606260","title":"MYOTUBULARIN-RELATED PROTEIN 9; MTMR9","url":"https://www.omim.org/entry/606260"},{"mim_id":"603561","title":"MYOTUBULARIN-RELATED PROTEIN 6; MTMR6","url":"https://www.omim.org/entry/603561"},{"mim_id":"301061","title":"MYOTUBULARIN-RELATED PROTEIN 8; MTMR8","url":"https://www.omim.org/entry/301061"},{"mim_id":"300415","title":"MYOTUBULARIN; MTM1","url":"https://www.omim.org/entry/300415"},{"mim_id":"148370","title":"KERATOLYTIC WINTER ERYTHEMA; KWE","url":"https://www.omim.org/entry/148370"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in some","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MTMR8"},"hgnc":{"alias_symbol":["FLJ20126"],"prev_symbol":[]},"alphafold":{"accession":"Q96EF0","domains":[{"cath_id":"2.30.29.30","chopping":"9-105","consensus_level":"high","plddt":89.4792,"start":9,"end":105},{"cath_id":"-","chopping":"131-506","consensus_level":"medium","plddt":95.3684,"start":131,"end":506},{"cath_id":"1.10.287","chopping":"515-543_588-623","consensus_level":"medium","plddt":59.6705,"start":515,"end":623}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96EF0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96EF0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96EF0-F1-predicted_aligned_error_v6.png","plddt_mean":81.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MTMR8","jax_strain_url":"https://www.jax.org/strain/search?query=MTMR8"},"sequence":{"accession":"Q96EF0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96EF0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96EF0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96EF0"}},"corpus_meta":[{"pmid":"16787938","id":"PMC_16787938","title":"Systematic analysis of myotubularins: heteromeric interactions, subcellular localisation and endosome related functions.","date":"2006","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/16787938","citation_count":76,"is_preprint":false},{"pmid":"22647598","id":"PMC_22647598","title":"Myotubularin-related protein (MTMR) 9 determines the enzymatic activity, substrate specificity, and role in autophagy of MTMR8.","date":"2012","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/22647598","citation_count":55,"is_preprint":false},{"pmid":"25502460","id":"PMC_25502460","title":"Chromosomal Instability and Phosphoinositide Pathway Gene Signatures in Glioblastoma Multiforme.","date":"2014","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/25502460","citation_count":31,"is_preprint":false},{"pmid":"19325702","id":"PMC_19325702","title":"Cooperation of Mtmr8 with PI3K regulates actin filament modeling and muscle development in zebrafish.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19325702","citation_count":26,"is_preprint":false},{"pmid":"22670894","id":"PMC_22670894","title":"Osteopathia striata congenita with cranial sclerosis and intellectual disability due to contiguous gene deletions involving the WTX locus.","date":"2012","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22670894","citation_count":24,"is_preprint":false},{"pmid":"32915229","id":"PMC_32915229","title":"A conserved myotubularin-related phosphatase regulates autophagy by maintaining autophagic flux.","date":"2020","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/32915229","citation_count":22,"is_preprint":false},{"pmid":"11896452","id":"PMC_11896452","title":"Physical and transcriptional map of the critical region for keratolytic winter erythema (KWE) on chromosome 8p22-p23 between D8S550 and D8S1759.","date":"2002","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/11896452","citation_count":14,"is_preprint":false},{"pmid":"33779490","id":"PMC_33779490","title":"Condition-dependent functional shift of two Drosophila Mtmr lipid phosphatases in autophagy control.","date":"2021","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/33779490","citation_count":10,"is_preprint":false},{"pmid":"11472061","id":"PMC_11472061","title":"Identification and localization of a new human myotubularin-related protein gene, mtmr8, on 8p22-p23.","date":"2001","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/11472061","citation_count":8,"is_preprint":false},{"pmid":"20815916","id":"PMC_20815916","title":"Mtmr8 is essential for vasculature development in zebrafish embryos.","date":"2010","source":"BMC developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/20815916","citation_count":8,"is_preprint":false},{"pmid":"35905688","id":"PMC_35905688","title":"X-linked genetic risk factors that promote autoimmunity and dampen remyelination are associated with multiple sclerosis susceptibility.","date":"2022","source":"Multiple sclerosis and related disorders","url":"https://pubmed.ncbi.nlm.nih.gov/35905688","citation_count":8,"is_preprint":false},{"pmid":"26143924","id":"PMC_26143924","title":"Structure of the catalytic phosphatase domain of MTMR8: implications for dimerization, membrane association and reversible oxidation.","date":"2015","source":"Acta crystallographica. Section D, Biological crystallography","url":"https://pubmed.ncbi.nlm.nih.gov/26143924","citation_count":7,"is_preprint":false},{"pmid":"31704058","id":"PMC_31704058","title":"Human myotubularin-related protein 9 regulates ER-to-Golgi trafficking and modulates WNT3A secretion.","date":"2019","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/31704058","citation_count":4,"is_preprint":false},{"pmid":"24282552","id":"PMC_24282552","title":"X-linked MTMR8 diversity and evolutionary history of sub-Saharan populations.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24282552","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9048,"output_tokens":2005,"usd":0.028609,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8897,"output_tokens":2825,"usd":0.057555,"stage2_stop_reason":"end_turn"},"total_usd":0.086164,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"MTMR8 forms a heteromeric complex with MTMR9, as identified by directed two-hybrid screening and immunoprecipitation of epitope-tagged proteins.\",\n      \"method\": \"Yeast two-hybrid and co-immunoprecipitation of epitope-tagged proteins\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP and two-hybrid, confirmed across multiple myotubularin pairs in same study, independently replicated in PMID:22647598\",\n      \"pmids\": [\"16787938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"MTMR9 dimerizes with MTMR8 and increases MTMR8 catalytic activity: MTMR9 enhances MTMR8 activity 4-fold toward PtdIns(3)P and 1.4-fold toward PtdIns(3,5)P2, shifting substrate preference of the complex to PtdIns(3)P. In cells, the MTMR8/MTMR9 complex reduces cellular PtdIns(3)P levels and inhibits autophagy.\",\n      \"method\": \"In vitro phosphatase assays with purified MTMR8/MTMR9 complexes, substrate specificity measurements, cellular PtdIns(3)P quantification, autophagy assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic reconstitution with defined substrates plus cellular functional readouts, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"22647598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of the MTMR8 phosphatase domain reveals: (1) the protein dimerizes via a novel mode mediated by the phosphatase domain with twofold symmetry; (2) Lys255 interacts with the substrate diacylglycerol moiety (analogous to Lys333 of MTMR2); (3) catalytic activity is inhibited by oxidation and reversibly reactivated by reduction, suggesting an oxidation-protective intermediate other than a disulfide bond because no second cysteine is within disulfide-bond distance of the catalytic Cys338.\",\n      \"method\": \"X-ray crystallography of the phosphatase domain, mutation studies, redox activity assays\",\n      \"journal\": \"Acta crystallographica. Section D, Biological crystallography\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis plus enzymatic activity assays in one study, single lab\",\n      \"pmids\": [\"26143924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In zebrafish, Mtmr8 knockdown causes defects in somitogenesis and disorganization of actin cytoskeleton. The PH/G domain of Mtmr8 is required for its function: PH/G domain deletion alone does not cause phenotype, but combined with PI3K inhibition (LY294002) it does. Mtmr8 loss increases Akt phosphorylation, indicating cooperation with PI3K signaling to regulate actin filament modeling and muscle development. Cell transplantation experiments show Mtmr8 acts non-cell-autonomously in actin modeling.\",\n      \"method\": \"Morpholino knockdown in zebrafish, domain-deletion analysis, PI3K inhibitor treatment, Akt phosphorylation western blot, cell transplantation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — morpholino KD with multiple orthogonal readouts (phospho-Akt, actin staining, domain deletion, cell transplantation), single lab\",\n      \"pmids\": [\"19325702\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In zebrafish, Mtmr8 knockdown impairs arterial endothelial marker expression, causes endothelial cell reduction, vasculogenesis defects (retarded intersegmental vessel development, interrupted dorsal aorta), and loss of arterial endothelial cell identity. These defects are rescued by PI3K inhibitor (low concentration), dominant-negative PKA mRNA overexpression, or VEGF mRNA overexpression, indicating Mtmr8 represses PI3K activity to regulate arterial specification through the Hedgehog/PI3K/VEGF signaling cascade.\",\n      \"method\": \"Morpholino knockdown in zebrafish, rescue experiments with PI3K inhibitor and mRNA overexpression, arterial marker expression analysis\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — morpholino KD with genetic/pharmacological rescue and multiple markers, single lab\",\n      \"pmids\": [\"20815916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Decreased MTMR8 function in higher animal cells results in autophagic vesicle accumulation and influences endolysosomal homeostasis, establishing MTMR8 as a regulator of autophagic flux.\",\n      \"method\": \"Loss-of-function studies in cell lines with autophagic vesicle and endolysosomal markers\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD/KO with defined cellular phenotype (vesicle accumulation, endolysosomal changes), corroborated by parallel Drosophila ortholog data in same study\",\n      \"pmids\": [\"32915229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MTMR9 (inactive phosphatase) localizes to the intermediate compartment and Golgi apparatus and recruits its active partner MTMR8 to these locations. MTMR8 and MTMR9 co-localize with RAB1A and regulate RAB1A localization, linking the MTMR8/MTMR9 complex to ER-to-Golgi trafficking.\",\n      \"method\": \"Fluorescence co-localization, loss-of-function (MTMR9 knockdown/overexpression), RAB1A localization assays, protein secretion assays\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiments with functional consequence (RAB1A redistribution, secretion defects), single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31704058\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MTMR8 is an active PtdIns(3)P-preferring lipid 3-phosphatase whose catalytic activity, substrate specificity, and autophagy-inhibitory function are amplified by dimerization with the inactive family member MTMR9; the crystal structure of its phosphatase domain reveals a novel dimerization mode, a Lys255-mediated substrate interaction, and reversible oxidation-dependent inhibition of its catalytic Cys338, while in vivo studies in zebrafish and mammalian cells show it cooperates with PI3K signaling to regulate actin cytoskeleton organization, muscle and vascular development, ER-to-Golgi trafficking (via MTMR9-dependent recruitment to the Golgi and RAB1A regulation), and autophagic flux.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MTMR8 is an active myotubularin-family lipid 3-phosphatase that preferentially dephosphorylates PtdIns(3)P and, together with the catalytically inactive family member MTMR9, controls phosphoinositide pools governing autophagy, membrane trafficking, and actin-dependent development [#1, #2]. MTMR8 forms a stable heteromeric complex with MTMR9, and this partnership amplifies its catalytic output—enhancing activity ~4-fold toward PtdIns(3)P and shifting the complex's substrate preference toward PtdIns(3)P—so that the complex lowers cellular PtdIns(3)P and inhibits autophagy [#0, #1]. Consistent with this, loss of MTMR8 function causes autophagic vesicle accumulation and perturbs endolysosomal homeostasis, establishing it as a regulator of autophagic flux [#5]. The crystal structure of its phosphatase domain reveals a novel dimerization mode with twofold symmetry, a Lys255 contact with the substrate diacylglycerol moiety, and reversible oxidation-dependent inactivation of the catalytic Cys338 via a non-disulfide oxidation-protective intermediate [#2]. Through MTMR9, which localizes to the intermediate compartment and Golgi, MTMR8 is recruited to these compartments where the complex co-localizes with and regulates RAB1A, linking it to ER-to-Golgi trafficking [#6]. In zebrafish, Mtmr8 represses PI3K/Akt signaling to organize the actin cytoskeleton during somitogenesis and muscle development, and to specify arterial endothelial identity through a Hedgehog/PI3K/VEGF cascade [#3, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that MTMR8 does not act alone but physically partners with another myotubularin, identifying MTMR9 as a heteromeric complex partner and framing MTMR8 function as complex-dependent.\",\n      \"evidence\": \"Yeast two-hybrid and reciprocal co-immunoprecipitation of epitope-tagged proteins\",\n      \"pmids\": [\"16787938\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the catalytic or functional consequence of the interaction\", \"No stoichiometry or interface mapping\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Provided the first in vivo functional role, showing MTMR8 organizes the actin cytoskeleton and muscle development by restraining PI3K/Akt signaling, with the PH/G domain required for function.\",\n      \"evidence\": \"Morpholino knockdown in zebrafish with domain-deletion, PI3K inhibitor treatment, phospho-Akt western blot, and cell transplantation\",\n      \"pmids\": [\"19325702\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Morpholino-based; mechanism connecting lipid phosphatase activity to actin not biochemically resolved\", \"Non-cell-autonomous effector unidentified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended the developmental role to vascular patterning, showing MTMR8 represses PI3K to specify arterial endothelial identity within a Hedgehog/PI3K/VEGF cascade.\",\n      \"evidence\": \"Morpholino knockdown in zebrafish with pharmacological and mRNA rescue and arterial marker analysis\",\n      \"pmids\": [\"20815916\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Morpholino-based; direct phosphoinositide substrate in endothelium not measured\", \"Epistatic placement within Hedgehog/PI3K/VEGF inferred from rescue, not direct interaction\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolved the biochemical basis of the MTMR8–MTMR9 partnership, demonstrating MTMR9 dimerization boosts MTMR8 phosphatase activity, biases the complex toward PtdIns(3)P, and lowers cellular PtdIns(3)P to inhibit autophagy.\",\n      \"evidence\": \"In vitro phosphatase assays with purified MTMR8/MTMR9 complexes, substrate specificity measurements, cellular PtdIns(3)P quantification, and autophagy assays\",\n      \"pmids\": [\"22647598\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of activation not defined here\", \"In vivo substrate site in cells not directly identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the structural and regulatory architecture of the catalytic domain, revealing a novel dimerization mode, a Lys255 substrate contact, and reversible redox control of the catalytic Cys338.\",\n      \"evidence\": \"X-ray crystallography of the phosphatase domain with mutagenesis and redox activity assays\",\n      \"pmids\": [\"26143924\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of the MTMR8–MTMR9 heterocomplex not solved\", \"Identity of the oxidation-protective intermediate at Cys338 unresolved\", \"Physiological trigger of redox regulation unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected the complex to a new membrane-trafficking arena, showing MTMR9 recruits MTMR8 to the intermediate compartment/Golgi where the complex regulates RAB1A and ER-to-Golgi transport.\",\n      \"evidence\": \"Fluorescence co-localization, MTMR9 loss/gain-of-function, RAB1A localization assays, and secretion assays\",\n      \"pmids\": [\"31704058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether RAB1A regulation depends on MTMR8 catalytic activity not established\", \"Single lab; mechanism linking PtdIns(3)P turnover to RAB1A localization unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Consolidated the autophagy role in higher-animal cells, showing reduced MTMR8 function drives autophagic vesicle accumulation and disrupts endolysosomal homeostasis, marking it a regulator of autophagic flux.\",\n      \"evidence\": \"Loss-of-function studies in cell lines with autophagic and endolysosomal markers, corroborated by Drosophila ortholog data\",\n      \"pmids\": [\"32915229\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Step in the autophagy pathway directly controlled not pinpointed\", \"Dependence on MTMR9 partnership in this context not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MTMR8's catalytic regulation, trafficking, and developmental signaling roles are mechanistically unified—and whether redox control of Cys338 operates physiologically—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the active MTMR8–MTMR9 heterocomplex\", \"Direct effector linking PtdIns(3)P turnover to actin and arterial specification not identified\", \"Physiological context of redox inactivation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [\"MTMR8–MTMR9 heterodimer\"],\n    \"partners\": [\"MTMR9\", \"RAB1A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}