{"gene":"MTMR1","run_date":"2026-06-10T02:59:51","timeline":{"discoveries":[{"year":2002,"finding":"The two main MTMR1 protein muscular isoforms efficiently dephosphorylate phosphatidylinositol 3-phosphate (PI(3)P) in vitro, consistent with phosphatase activity shared with the family founder MTM1.","method":"In vitro phosphatase assay with recombinant MTMR1 muscle isoforms","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro enzymatic assay with recombinant protein, single lab but clear biochemical demonstration","pmids":["12217958"],"is_preprint":false},{"year":2002,"finding":"MTMR1 undergoes muscle-specific alternative splicing during myogenesis; a muscle-specific transcript isoform is induced during differentiation in vitro and in vivo and represents the major isoform in adult skeletal muscle. This splicing is impaired in congenital myotonic dystrophy type 1 (cDM1) muscle cells, where the muscle-specific isoform is reduced and an abnormal transcript appears.","method":"RT-PCR, Northern blot, and in vitro/in vivo differentiation assays in human and mouse muscle cells; analysis of cDM1 patient-derived muscle cells","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (RT-PCR, differentiation assays, patient samples) in single lab","pmids":["12217958"],"is_preprint":false},{"year":2001,"finding":"MTMR1, like other myotubularin family members, dephosphorylates PI(3)P as its physiologic substrate, as demonstrated by direct lipid phosphatase assay with recombinant protein.","method":"In vitro lipid phosphatase assay with recombinant MTMR1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assay replicated across multiple family members in same study, consistent with independent report (PMID:12217958)","pmids":["11733541"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of human MTMR1 was determined at ~2 Å resolution, revealing PH-GRAM and phosphatase (PTP) domains highly similar to MTMR2. Two phosphate molecules are coordinated by conserved residues in the C(X)5R motif of the active site. Biochemical studies confirmed substrate specificity for PI(3)P and PI(3,5)P2 over other phosphatidylinositol phosphates.","method":"X-ray crystallography and in vitro lipid phosphatase assay","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with functional biochemical validation in same study, single lab","pmids":["27018598"],"is_preprint":false},{"year":2000,"finding":"MTMR1 contains a functional PDZ-binding site (C-terminal X-S/T-X-V motif) that mediates interaction with the PDZ domain protein TIP-15/PSD-95, confirmed by co-immunoprecipitation from transfected COS7 cells.","method":"Yeast two-hybrid screen followed by co-immunoprecipitation in COS7 cells","journal":"Molecular biology reports","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single Co-IP confirmation from single lab; physiological relevance not established","pmids":["11455957"],"is_preprint":false},{"year":2005,"finding":"CUG-BP1 overexpression in transgenic mouse skeletal muscle disrupts splicing of MTMR1 pre-mRNA, demonstrating that increased CUG-BP1 activity is sufficient to recapitulate the MTMR1 splicing mis-regulation observed in DM1.","method":"Transgenic mouse overexpressing CUG-BP1 with RT-PCR splicing analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic/transgenic model with defined molecular readout; single lab but in vivo system","pmids":["15843400"],"is_preprint":false},{"year":2005,"finding":"ETR-3 (CELF2/CUGBP2) regulates MTMR1 alternative splicing via UG-rich binding motifs in the pre-mRNA, as demonstrated using SELEX-identified binding sequences and minigene splicing reporters.","method":"SELEX, minigene splicing reporter assays in cell transfection","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SELEX-derived binding motif tested in functional minigene reporter; single lab","pmids":["15657417"],"is_preprint":false},{"year":2018,"finding":"Intramuscular delivery of rAAV encoding MTMR1 failed to rescue the phenotype of Mtm1-deficient knockout mice, whereas rAAV encoding MTMR2 did provide therapeutic benefit, indicating that MTMR1 is not functionally redundant with MTM1 in skeletal muscle.","method":"rAAV intramuscular injection in Mtm1 knockout mice with motor and histological outcome measures","journal":"Journal of neuropathology and experimental neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo gene replacement assay with clear negative result for MTMR1; single lab","pmids":["29408998"],"is_preprint":false},{"year":2023,"finding":"Overexpression of MTMR1 (a PI(3)P phosphatase) significantly reduces Arc capsid secretion in mammalian cells, demonstrating that PI(3)P availability at endosomes is required for Arc capsid assembly and secretion through the MVB pathway.","method":"MTMR1 overexpression in mammalian cells with Arc capsid secretion assay","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single overexpression experiment in a preprint, indirect readout, no mechanistic follow-up specific to MTMR1","pmids":["38187623"],"is_preprint":true}],"current_model":"MTMR1 is a PI(3)P and PI(3,5)P2-specific lipid phosphatase whose crystal structure reveals a PH-GRAM domain and a PTP catalytic domain with a C(X)5R active-site motif; it undergoes muscle-specific alternative splicing driven by CELF-family splicing regulators (CUG-BP1, ETR-3), this splicing is disrupted in myotonic dystrophy type 1, and the protein interacts with the PDZ domain protein TIP-15 via a C-terminal PDZ-binding motif, though it cannot functionally substitute for MTM1 in skeletal muscle."},"narrative":{"mechanistic_narrative":"MTMR1 is a myotubularin-family phosphoinositide phosphatase that dephosphorylates PI(3)P, and with extended specificity also PI(3,5)P2, as its physiologic lipid substrates [PMID:11733541, PMID:12217958, PMID:27018598]. Its crystal structure organizes a membrane-targeting PH-GRAM domain together with a PTP catalytic domain whose conserved C(X)5R active-site motif coordinates the substrate phosphate, an architecture closely matching MTMR2 [PMID:27018598]. Through a C-terminal PDZ-binding motif MTMR1 engages the PDZ-domain protein TIP-15/PSD-95 [PMID:11455957]. A defining feature of MTMR1 is its muscle-specific alternative splicing: a muscle-restricted isoform is induced during myogenic differentiation and predominates in adult skeletal muscle, and this splicing is controlled by CELF-family regulators — CUG-BP1 and ETR-3/CELF2 acting through UG-rich pre-mRNA elements [PMID:12217958, PMID:15843400, PMID:15657417]. This splicing program is disrupted in myotonic dystrophy type 1, where elevated CUG-BP1 activity is sufficient to recapitulate the aberrant MTMR1 splicing seen in patient muscle [PMID:12217958, PMID:15843400]. Despite shared PI(3)P phosphatase activity, MTMR1 cannot functionally substitute for MTM1 in skeletal muscle, since MTMR1 gene delivery fails to rescue Mtm1-deficient mice [PMID:29408998].","teleology":[{"year":2000,"claim":"Before any functional partner was known, identifying a C-terminal PDZ-binding motif placed MTMR1 in a potential scaffolded protein assembly.","evidence":"Yeast two-hybrid screen with Co-IP confirmation of TIP-15/PSD-95 interaction in COS7 cells","pmids":["11455957"],"confidence":"Medium","gaps":["single Co-IP without reciprocal validation","physiological relevance of the TIP-15 interaction not established","no link drawn between the interaction and phosphatase function"]},{"year":2001,"claim":"The catalytic identity of MTMR1 was established by demonstrating direct PI(3)P dephosphorylation, defining it as a myotubularin lipid phosphatase rather than an inactive pseudophosphatase.","evidence":"In vitro lipid phosphatase assay with recombinant MTMR1 alongside other family members","pmids":["11733541"],"confidence":"High","gaps":["substrate specificity beyond PI(3)P not resolved in this study","cellular site of action unknown"]},{"year":2002,"claim":"Linking MTMR1 to muscle biology, its main muscle isoforms were shown to retain PI(3)P phosphatase activity and to arise through myogenesis-coupled alternative splicing that is impaired in congenital myotonic dystrophy type 1.","evidence":"In vitro phosphatase assays of muscle isoforms plus RT-PCR/Northern and differentiation assays in human/mouse muscle and cDM1 patient cells","pmids":["12217958"],"confidence":"High","gaps":["functional consequence of isoform switch on muscle physiology not defined","downstream PI(3)P-dependent process in muscle not identified"]},{"year":2005,"claim":"The regulatory logic of MTMR1 splicing was assigned to CELF-family factors, showing CUG-BP1 and ETR-3/CELF2 directly control isoform selection through UG-rich pre-mRNA elements.","evidence":"Transgenic CUG-BP1 overexpression mouse with RT-PCR; SELEX-defined motifs tested in minigene splicing reporters for ETR-3","pmids":["15843400","15657417"],"confidence":"Medium","gaps":["whether the splicing change alters MTMR1 enzymatic output in vivo not addressed","contribution of MTMR1 mis-splicing to DM1 muscle pathology not quantified"]},{"year":2016,"claim":"A high-resolution structure clarified the catalytic mechanism and substrate range, showing a PH-GRAM/PTP architecture with phosphate coordination at the C(X)5R motif and specificity for PI(3)P and PI(3,5)P2.","evidence":"X-ray crystallography at ~2 Å with in vitro lipid phosphatase assays","pmids":["27018598"],"confidence":"High","gaps":["membrane-bound conformation and lipid engagement not captured","structural basis for muscle-isoform functional differences not addressed"]},{"year":2018,"claim":"A gene-replacement test resolved whether MTMR1 is redundant with MTM1, demonstrating it cannot substitute for MTM1 in skeletal muscle despite shared substrate.","evidence":"rAAV intramuscular delivery of MTMR1 vs MTMR2 in Mtm1-knockout mice with motor and histological outcomes","pmids":["29408998"],"confidence":"Medium","gaps":["molecular basis for the lack of redundancy unknown","MTMR1 expression level/localization from the vector not benchmarked against MTM1"]},{"year":2023,"claim":"An emerging cellular role tied MTMR1 phosphatase activity to endosomal PI(3)P-dependent vesicular processes, where its overexpression suppressed Arc capsid secretion.","evidence":"MTMR1 overexpression in mammalian cells with an Arc capsid secretion readout (preprint)","pmids":["38187623"],"confidence":"Low","gaps":["single overexpression experiment in a preprint, not independently confirmed","indirect readout with no MTMR1-specific mechanistic follow-up","endogenous MTMR1 contribution at endosomes not tested"]},{"year":null,"claim":"The endogenous physiological function of MTMR1 — the cellular membrane compartments it regulates and why its muscle-specific isoform matters — remains undefined.","evidence":"","pmids":[],"confidence":"Low","gaps":["no loss-of-function phenotype for MTMR1 itself characterized","subcellular localization of endogenous MTMR1 not established in the corpus","connection between PI(3)P phosphatase activity and muscle differentiation function unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,2,3]}],"localization":[],"pathway":[],"complexes":[],"partners":["DLG4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q13613","full_name":"Phosphatidylinositol-3-phosphate phosphatase MTMR1","aliases":["Myotubularin-related protein 1","Phosphatidylinositol-3,5-bisphosphate 3-phosphatase"],"length_aa":665,"mass_kda":74.7,"function":"Lipid phosphatase that specifically dephosphorylates the D-3 position of phosphatidylinositol 3-phosphate, generating phosphatidylinositol (PubMed:11733541, PubMed:27018598). Could also dephosphorylate phosphatidylinositol 3,5-bisphosphate to produce phosphatidylinositol 5-phosphate (PubMed:27018598)","subcellular_location":"Cell membrane; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q13613/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MTMR1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000063601","cell_line_id":"CID000144","localizations":[{"compartment":"cell_contact","grade":3},{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3},{"compartment":"membrane","grade":2}],"interactors":[{"gene":"GMNN","stoichiometry":4.0},{"gene":"CSNK2A1","stoichiometry":0.2},{"gene":"CSNK2A2","stoichiometry":0.2},{"gene":"SBF2","stoichiometry":0.2},{"gene":"MTMR2","stoichiometry":0.2},{"gene":"VPRBP","stoichiometry":0.2},{"gene":"USP9X","stoichiometry":0.2},{"gene":"NDUFB10","stoichiometry":0.2},{"gene":"BPNT1","stoichiometry":0.2},{"gene":"NADK","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000144","total_profiled":1310},"omim":[{"mim_id":"606260","title":"MYOTUBULARIN-RELATED PROTEIN 9; MTMR9","url":"https://www.omim.org/entry/606260"},{"mim_id":"603557","title":"MYOTUBULARIN-RELATED PROTEIN 2; MTMR2","url":"https://www.omim.org/entry/603557"},{"mim_id":"601278","title":"FSHD REGION GENE 1; FRG1","url":"https://www.omim.org/entry/601278"},{"mim_id":"310400","title":"MYOPATHY, CENTRONUCLEAR, X-LINKED; CNMX","url":"https://www.omim.org/entry/310400"},{"mim_id":"300846","title":"CD99 ANTIGEN-LIKE 2; CD99L2","url":"https://www.omim.org/entry/300846"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MTMR1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q13613","domains":[{"cath_id":"2.30.29.30","chopping":"101-206","consensus_level":"medium","plddt":86.7456,"start":101,"end":206},{"cath_id":"-","chopping":"227-619","consensus_level":"medium","plddt":96.8632,"start":227,"end":619}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13613","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q13613-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q13613-F1-predicted_aligned_error_v6.png","plddt_mean":84.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MTMR1","jax_strain_url":"https://www.jax.org/strain/search?query=MTMR1"},"sequence":{"accession":"Q13613","fasta_url":"https://rest.uniprot.org/uniprotkb/Q13613.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q13613/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q13613"}},"corpus_meta":[{"pmid":"15843400","id":"PMC_15843400","title":"Transgenic mice expressing CUG-BP1 reproduce splicing mis-regulation observed in myotonic dystrophy.","date":"2005","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/15843400","citation_count":195,"is_preprint":false},{"pmid":"10790201","id":"PMC_10790201","title":"MTM1 mutations in X-linked myotubular myopathy.","date":"2000","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/10790201","citation_count":161,"is_preprint":false},{"pmid":"12217958","id":"PMC_12217958","title":"Muscle-specific alternative splicing of myotubularin-related 1 gene is impaired in DM1 muscle cells.","date":"2002","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/12217958","citation_count":104,"is_preprint":false},{"pmid":"11733541","id":"PMC_11733541","title":"Myotubularin and MTMR2, phosphatidylinositol 3-phosphatases mutated in myotubular myopathy and type 4B Charcot-Marie-Tooth disease.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11733541","citation_count":101,"is_preprint":false},{"pmid":"15657417","id":"PMC_15657417","title":"Identification of putative new splicing targets for ETR-3 using sequences identified by systematic evolution of ligands by exponential enrichment.","date":"2005","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15657417","citation_count":81,"is_preprint":false},{"pmid":"15725586","id":"PMC_15725586","title":"Characterization of MTM1 mutations in 31 Japanese families with myotubular myopathy, including a patient carrying 240 kb deletion in Xq28 without male hypogenitalism.","date":"2005","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/15725586","citation_count":36,"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":"9828128","id":"PMC_9828128","title":"Genomic organization of a 225-kb region in Xq28 containing the gene for X-linked myotubular myopathy (MTM1) and a related gene (MTMR1).","date":"1998","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/9828128","citation_count":22,"is_preprint":false},{"pmid":"11455957","id":"PMC_11455957","title":"Identification of functional PDZ domain binding sites in several human proteins.","date":"2000","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/11455957","citation_count":22,"is_preprint":false},{"pmid":"29392408","id":"PMC_29392408","title":"Genome-wide DNA methylation analysis in jejunum of Sus scrofa with intrauterine growth restriction.","date":"2018","source":"Molecular genetics and genomics : MGG","url":"https://pubmed.ncbi.nlm.nih.gov/29392408","citation_count":17,"is_preprint":false},{"pmid":"29408998","id":"PMC_29408998","title":"Intravenous Administration of a MTMR2-Encoding AAV Vector Ameliorates the Phenotype of Myotubular Myopathy in Mice.","date":"2018","source":"Journal of neuropathology and experimental neurology","url":"https://pubmed.ncbi.nlm.nih.gov/29408998","citation_count":15,"is_preprint":false},{"pmid":"34371182","id":"PMC_34371182","title":"Comprehensive transcriptome-wide analysis of spliceopathy correction of myotonic dystrophy using CRISPR-Cas9 in iPSCs-derived cardiomyocytes.","date":"2021","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/34371182","citation_count":14,"is_preprint":false},{"pmid":"20685272","id":"PMC_20685272","title":"Analysis of MTMR1 expression and correlation with muscle pathological features in juvenile/adult onset myotonic dystrophy type 1 (DM1) and in myotonic dystrophy type 2 (DM2).","date":"2010","source":"Experimental and molecular pathology","url":"https://pubmed.ncbi.nlm.nih.gov/20685272","citation_count":13,"is_preprint":false},{"pmid":"27018598","id":"PMC_27018598","title":"Crystal Structure of Human Myotubularin-Related Protein 1 Provides Insight into the Structural Basis of Substrate Specificity.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27018598","citation_count":11,"is_preprint":false},{"pmid":"36005579","id":"PMC_36005579","title":"Co-Expression Network and Integrative Analysis of Metabolome and Transcriptome Uncovers Biological Pathways for Fertility in Beef Heifers.","date":"2022","source":"Metabolites","url":"https://pubmed.ncbi.nlm.nih.gov/36005579","citation_count":10,"is_preprint":false},{"pmid":"19160676","id":"PMC_19160676","title":"Detection of myotubularin phosphatases activity on phosphoinositides in vitro and ex vivo.","date":"2009","source":"Methods in molecular biology (Clifton, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/19160676","citation_count":5,"is_preprint":false},{"pmid":"33618039","id":"PMC_33618039","title":"Symptomatic heterozygous X-Linked myotubular myopathy female patient with a large deletion at Xq28 and decrease expression of normal allele.","date":"2021","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33618039","citation_count":5,"is_preprint":false},{"pmid":"38187623","id":"PMC_38187623","title":"Phosphatidylinositol 3-phosphate mediates Arc capsids secretion through the multivesicular body pathway.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38187623","citation_count":3,"is_preprint":false},{"pmid":"38459823","id":"PMC_38459823","title":"Genomic analysis of an aggressive hepatic leiomyosarcoma case following treatment for hepatocellular carcinoma.","date":"2024","source":"Hepatology research : the official journal of the Japan Society of Hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/38459823","citation_count":2,"is_preprint":false},{"pmid":"25760698","id":"PMC_25760698","title":"Crystallization and preliminary X-ray crystallographic analysis of human myotubularin-related protein 1.","date":"2015","source":"Acta crystallographica. Section F, Structural biology communications","url":"https://pubmed.ncbi.nlm.nih.gov/25760698","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12169,"output_tokens":2006,"usd":0.033299,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8938,"output_tokens":2630,"usd":0.05522,"stage2_stop_reason":"end_turn"},"total_usd":0.088519,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"The two main MTMR1 protein muscular isoforms efficiently dephosphorylate phosphatidylinositol 3-phosphate (PI(3)P) in vitro, consistent with phosphatase activity shared with the family founder MTM1.\",\n      \"method\": \"In vitro phosphatase assay with recombinant MTMR1 muscle isoforms\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro enzymatic assay with recombinant protein, single lab but clear biochemical demonstration\",\n      \"pmids\": [\"12217958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MTMR1 undergoes muscle-specific alternative splicing during myogenesis; a muscle-specific transcript isoform is induced during differentiation in vitro and in vivo and represents the major isoform in adult skeletal muscle. This splicing is impaired in congenital myotonic dystrophy type 1 (cDM1) muscle cells, where the muscle-specific isoform is reduced and an abnormal transcript appears.\",\n      \"method\": \"RT-PCR, Northern blot, and in vitro/in vivo differentiation assays in human and mouse muscle cells; analysis of cDM1 patient-derived muscle cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (RT-PCR, differentiation assays, patient samples) in single lab\",\n      \"pmids\": [\"12217958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MTMR1, like other myotubularin family members, dephosphorylates PI(3)P as its physiologic substrate, as demonstrated by direct lipid phosphatase assay with recombinant protein.\",\n      \"method\": \"In vitro lipid phosphatase assay with recombinant MTMR1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assay replicated across multiple family members in same study, consistent with independent report (PMID:12217958)\",\n      \"pmids\": [\"11733541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of human MTMR1 was determined at ~2 Å resolution, revealing PH-GRAM and phosphatase (PTP) domains highly similar to MTMR2. Two phosphate molecules are coordinated by conserved residues in the C(X)5R motif of the active site. Biochemical studies confirmed substrate specificity for PI(3)P and PI(3,5)P2 over other phosphatidylinositol phosphates.\",\n      \"method\": \"X-ray crystallography and in vitro lipid phosphatase assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with functional biochemical validation in same study, single lab\",\n      \"pmids\": [\"27018598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MTMR1 contains a functional PDZ-binding site (C-terminal X-S/T-X-V motif) that mediates interaction with the PDZ domain protein TIP-15/PSD-95, confirmed by co-immunoprecipitation from transfected COS7 cells.\",\n      \"method\": \"Yeast two-hybrid screen followed by co-immunoprecipitation in COS7 cells\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP confirmation from single lab; physiological relevance not established\",\n      \"pmids\": [\"11455957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CUG-BP1 overexpression in transgenic mouse skeletal muscle disrupts splicing of MTMR1 pre-mRNA, demonstrating that increased CUG-BP1 activity is sufficient to recapitulate the MTMR1 splicing mis-regulation observed in DM1.\",\n      \"method\": \"Transgenic mouse overexpressing CUG-BP1 with RT-PCR splicing analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic/transgenic model with defined molecular readout; single lab but in vivo system\",\n      \"pmids\": [\"15843400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ETR-3 (CELF2/CUGBP2) regulates MTMR1 alternative splicing via UG-rich binding motifs in the pre-mRNA, as demonstrated using SELEX-identified binding sequences and minigene splicing reporters.\",\n      \"method\": \"SELEX, minigene splicing reporter assays in cell transfection\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SELEX-derived binding motif tested in functional minigene reporter; single lab\",\n      \"pmids\": [\"15657417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Intramuscular delivery of rAAV encoding MTMR1 failed to rescue the phenotype of Mtm1-deficient knockout mice, whereas rAAV encoding MTMR2 did provide therapeutic benefit, indicating that MTMR1 is not functionally redundant with MTM1 in skeletal muscle.\",\n      \"method\": \"rAAV intramuscular injection in Mtm1 knockout mice with motor and histological outcome measures\",\n      \"journal\": \"Journal of neuropathology and experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo gene replacement assay with clear negative result for MTMR1; single lab\",\n      \"pmids\": [\"29408998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Overexpression of MTMR1 (a PI(3)P phosphatase) significantly reduces Arc capsid secretion in mammalian cells, demonstrating that PI(3)P availability at endosomes is required for Arc capsid assembly and secretion through the MVB pathway.\",\n      \"method\": \"MTMR1 overexpression in mammalian cells with Arc capsid secretion assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single overexpression experiment in a preprint, indirect readout, no mechanistic follow-up specific to MTMR1\",\n      \"pmids\": [\"38187623\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MTMR1 is a PI(3)P and PI(3,5)P2-specific lipid phosphatase whose crystal structure reveals a PH-GRAM domain and a PTP catalytic domain with a C(X)5R active-site motif; it undergoes muscle-specific alternative splicing driven by CELF-family splicing regulators (CUG-BP1, ETR-3), this splicing is disrupted in myotonic dystrophy type 1, and the protein interacts with the PDZ domain protein TIP-15 via a C-terminal PDZ-binding motif, though it cannot functionally substitute for MTM1 in skeletal muscle.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MTMR1 is a myotubularin-family phosphoinositide phosphatase that dephosphorylates PI(3)P, and with extended specificity also PI(3,5)P2, as its physiologic lipid substrates [#2, #0, #3]. Its crystal structure organizes a membrane-targeting PH-GRAM domain together with a PTP catalytic domain whose conserved C(X)5R active-site motif coordinates the substrate phosphate, an architecture closely matching MTMR2 [#3]. Through a C-terminal PDZ-binding motif MTMR1 engages the PDZ-domain protein TIP-15/PSD-95 [#4]. A defining feature of MTMR1 is its muscle-specific alternative splicing: a muscle-restricted isoform is induced during myogenic differentiation and predominates in adult skeletal muscle, and this splicing is controlled by CELF-family regulators — CUG-BP1 and ETR-3/CELF2 acting through UG-rich pre-mRNA elements [#1, #5, #6]. This splicing program is disrupted in myotonic dystrophy type 1, where elevated CUG-BP1 activity is sufficient to recapitulate the aberrant MTMR1 splicing seen in patient muscle [#1, #5]. Despite shared PI(3)P phosphatase activity, MTMR1 cannot functionally substitute for MTM1 in skeletal muscle, since MTMR1 gene delivery fails to rescue Mtm1-deficient mice [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Before any functional partner was known, identifying a C-terminal PDZ-binding motif placed MTMR1 in a potential scaffolded protein assembly.\",\n      \"evidence\": \"Yeast two-hybrid screen with Co-IP confirmation of TIP-15/PSD-95 interaction in COS7 cells\",\n      \"pmids\": [\"11455957\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"single Co-IP without reciprocal validation\", \"physiological relevance of the TIP-15 interaction not established\", \"no link drawn between the interaction and phosphatase function\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The catalytic identity of MTMR1 was established by demonstrating direct PI(3)P dephosphorylation, defining it as a myotubularin lipid phosphatase rather than an inactive pseudophosphatase.\",\n      \"evidence\": \"In vitro lipid phosphatase assay with recombinant MTMR1 alongside other family members\",\n      \"pmids\": [\"11733541\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"substrate specificity beyond PI(3)P not resolved in this study\", \"cellular site of action unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linking MTMR1 to muscle biology, its main muscle isoforms were shown to retain PI(3)P phosphatase activity and to arise through myogenesis-coupled alternative splicing that is impaired in congenital myotonic dystrophy type 1.\",\n      \"evidence\": \"In vitro phosphatase assays of muscle isoforms plus RT-PCR/Northern and differentiation assays in human/mouse muscle and cDM1 patient cells\",\n      \"pmids\": [\"12217958\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"functional consequence of isoform switch on muscle physiology not defined\", \"downstream PI(3)P-dependent process in muscle not identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The regulatory logic of MTMR1 splicing was assigned to CELF-family factors, showing CUG-BP1 and ETR-3/CELF2 directly control isoform selection through UG-rich pre-mRNA elements.\",\n      \"evidence\": \"Transgenic CUG-BP1 overexpression mouse with RT-PCR; SELEX-defined motifs tested in minigene splicing reporters for ETR-3\",\n      \"pmids\": [\"15843400\", \"15657417\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"whether the splicing change alters MTMR1 enzymatic output in vivo not addressed\", \"contribution of MTMR1 mis-splicing to DM1 muscle pathology not quantified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A high-resolution structure clarified the catalytic mechanism and substrate range, showing a PH-GRAM/PTP architecture with phosphate coordination at the C(X)5R motif and specificity for PI(3)P and PI(3,5)P2.\",\n      \"evidence\": \"X-ray crystallography at ~2 Å with in vitro lipid phosphatase assays\",\n      \"pmids\": [\"27018598\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"membrane-bound conformation and lipid engagement not captured\", \"structural basis for muscle-isoform functional differences not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"A gene-replacement test resolved whether MTMR1 is redundant with MTM1, demonstrating it cannot substitute for MTM1 in skeletal muscle despite shared substrate.\",\n      \"evidence\": \"rAAV intramuscular delivery of MTMR1 vs MTMR2 in Mtm1-knockout mice with motor and histological outcomes\",\n      \"pmids\": [\"29408998\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"molecular basis for the lack of redundancy unknown\", \"MTMR1 expression level/localization from the vector not benchmarked against MTM1\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"An emerging cellular role tied MTMR1 phosphatase activity to endosomal PI(3)P-dependent vesicular processes, where its overexpression suppressed Arc capsid secretion.\",\n      \"evidence\": \"MTMR1 overexpression in mammalian cells with an Arc capsid secretion readout (preprint)\",\n      \"pmids\": [\"38187623\"],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"single overexpression experiment in a preprint, not independently confirmed\", \"indirect readout with no MTMR1-specific mechanistic follow-up\", \"endogenous MTMR1 contribution at endosomes not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous physiological function of MTMR1 — the cellular membrane compartments it regulates and why its muscle-specific isoform matters — remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"no loss-of-function phenotype for MTMR1 itself characterized\", \"subcellular localization of endogenous MTMR1 not established in the corpus\", \"connection between PI(3)P phosphatase activity and muscle differentiation function unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 2, 3]}\n    ],\n    \"localization\": [],\n    \"pathway\": [],\n    \"complexes\": [],\n    \"partners\": [\"DLG4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}