{"gene":"MYPN","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2016,"finding":"MYPN (myopalladin) is localized at the Z-line in control skeletal muscles; biallelic loss-of-function mutations in MYPN result in absence of protein from the Z-line and cause Z-streaming and nemaline-like bodies adjacent to a disorganized Z-line, establishing MYPN's role in maintaining Z-line integrity in striated muscle.","method":"Immunofluorescence localization in human muscle biopsies and knockin mouse model (electron microscopy of homozygous nonsense-mutation knockin mice)","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization by immunofluorescence with functional consequence, confirmed by in vivo knockin mouse model with ultrastructural readout, replicated across multiple families","pmids":["28017374"],"is_preprint":false},{"year":2017,"finding":"Homozygous truncating mutations in MYPN lead to mRNA defects and strong reduction of full-length myopalladin protein; residual myopalladin signals accumulate in cap structures together with alpha-actinin, indicating myopalladin functions at the Z-line and its loss disrupts normal alpha-actinin organization.","method":"Functional experiments on patient muscle: mRNA analysis, protein expression assays (immunoblot/immunofluorescence), co-localization of myopalladin and alpha-actinin in caps","journal":"Annals of neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal methods (mRNA and protein analysis), single lab, two unrelated families","pmids":["28220527"],"is_preprint":false},{"year":2019,"finding":"A homozygous loss-of-function deletion in MYPN exon 11 renders full-length myopalladin protein undetectable on immunoblotting and abolishes Z-line localization on immunofluorescence, accompanied by ultrastructural Z-line fragmentation, confirming MYPN is required for Z-line structural integrity in skeletal muscle.","method":"Immunoblotting and immunofluorescence of patient muscle biopsy; whole-exome sequencing for genetic identification","journal":"Skeletal muscle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal protein and localization data in patient tissue, single lab, two orthogonal methods","pmids":["31133047"],"is_preprint":false},{"year":2025,"finding":"The Ig3 domain of MYPN mediates actin binding and bundling through conserved basic charge clusters via electrostatic interactions; cardiomyopathy-associated mutations (e.g., R955W, P961L) within this domain impair actin binding, nearly abolish actin bundling, and cause mislocalization into clusters at Z-discs in Drosophila cardiomyocytes and body wall muscles without broadly altering secondary protein structure (except P961L which is destabilized). MYPN also promotes actin polymerization from monomeric actin, and this activity is not modulated by calcium.","method":"Actin co-sedimentation assays with charge-neutralizing alanine substitution mutagenesis; co-polymerization assays; circular dichroism spectroscopy; GFP-tagged construct expression and immunostaining in Drosophila cardiomyocytes and body wall muscles","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and multiple orthogonal methods (co-sedimentation, CD spectroscopy, in vivo Drosophila localization), single lab, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.09.18.677238"],"is_preprint":true},{"year":2026,"finding":"iPSC-derived cardiomyocytes carrying the MYPN p.N989I variant showed no significant changes in calcium transients, sodium current, or action potential compared to control cells, but exhibited transcriptomic upregulation of cell cycle, mitotic spindle, microtubule cytoskeleton, and myogenic program genes, and downregulation of sarcomeric, Z-disc, cell junction, ATP synthesis, oxidative phosphorylation, and SRF-signaling genes, suggesting MYPN p.N989I disrupts sarcomeric/cytoskeletal gene programs rather than direct electrophysiological function.","method":"iPSC-derived cardiomyocytes from HCM patient; patch-clamp electrophysiology; calcium transient measurements; RNA-seq transcriptomic profiling","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, calcium imaging, transcriptomics) in iPSC-CM model, single lab, non-isogenic controls limit interpretation","pmids":["42074575"],"is_preprint":false},{"year":2024,"finding":"In a compound TNNT2/MYPN double-mutant LVNC model, knock-in of the orthologous Mypn S1291T mutation alone did NOT cause cardiac hypertrabeculation, noncompaction, or heart failure in mice, indicating the MYPN variant is not the primary pathogenic driver in this familial LVNC context.","method":"Knock-in C57BL/6J mice harboring Mypn S1291T alone vs. Tnnt2 R154W alone vs. double mutant; cardiac phenotyping","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo genetic epistasis via knock-in mice, single lab, preprint; negative result for MYPN variant specifically","pmids":["bio_10.1101_2024.10.09.24314670"],"is_preprint":true}],"current_model":"Myopalladin (MYPN) is a striated muscle-specific sarcomeric protein that localizes to the Z-line, where it maintains Z-line structural integrity by binding and bundling actin filaments through conserved basic charge clusters in its Ig3 domain; loss-of-function mutations abolish Z-line localization and cause disorganization, while cardiomyopathy-associated Ig3 domain mutations disrupt actin binding and bundling, leading to abnormal Z-disc localization and altered sarcomeric gene programs."},"narrative":{"mechanistic_narrative":"Myopalladin (MYPN) is a striated muscle protein that localizes to the sarcomeric Z-line and is required to maintain Z-line structural integrity in skeletal and cardiac muscle [PMID:28017374]. Biallelic loss-of-function mutations abolish full-length protein and Z-line localization, producing Z-streaming, nemaline-like bodies, and ultrastructural Z-line fragmentation, with residual protein accumulating in cap structures together with alpha-actinin [PMID:28017374, PMID:28220527, PMID:31133047]. Mechanistically, the Ig3 domain mediates actin binding and bundling through conserved basic charge clusters via electrostatic interactions and promotes actin polymerization from monomeric actin in a calcium-independent manner; cardiomyopathy-associated Ig3 mutations (R955W, P961L) impair actin binding, nearly abolish bundling, and cause mislocalization into Z-disc clusters [PMID:bio_10.1101_2025.09.18.677238]. Disruption of MYPN function shifts sarcomeric and cytoskeletal gene programs, downregulating sarcomeric, Z-disc, and SRF-signaling genes rather than directly altering cardiomyocyte electrophysiology [PMID:42074575]. Loss-of-function MYPN mutations cause a Z-line myopathy with nemaline-like and cap features [PMID:28017374].","teleology":[{"year":2016,"claim":"Established that MYPN is a Z-line protein whose loss disrupts Z-line architecture, defining its core structural role and disease relevance in striated muscle.","evidence":"Immunofluorescence in human muscle biopsies plus electron microscopy of homozygous nonsense knockin mice across multiple families","pmids":["28017374"],"confidence":"High","gaps":["Did not define the molecular interactions through which MYPN maintains Z-line integrity","Mechanism of nemaline-like body formation unresolved"]},{"year":2017,"claim":"Showed that truncating mutations cause mRNA defects and loss of full-length protein, with residual myopalladin accumulating in caps alongside alpha-actinin, linking MYPN loss to disturbed alpha-actinin organization.","evidence":"mRNA analysis and protein/immunofluorescence assays in patient muscle from two unrelated families","pmids":["28220527"],"confidence":"Medium","gaps":["Whether MYPN directly binds alpha-actinin not tested","Single lab, limited families"]},{"year":2019,"claim":"Confirmed with reciprocal protein and localization data that full-length MYPN is required for Z-line structural integrity, reinforcing the loss-of-function disease model.","evidence":"Immunoblotting and immunofluorescence of patient muscle with WES genetic identification","pmids":["31133047"],"confidence":"Medium","gaps":["No mechanistic interaction data","Single lab"]},{"year":2025,"claim":"Provided the molecular mechanism by defining the Ig3 domain as an actin-binding, bundling, and polymerization-promoting module dependent on basic charge clusters, and showing cardiomyopathy mutations disrupt these activities and cause mislocalization.","evidence":"Actin co-sedimentation and co-polymerization assays with charge-neutralizing mutagenesis, circular dichroism, and GFP-construct localization in Drosophila muscle (preprint)","pmids":["bio_10.1101_2025.09.18.677238"],"confidence":"Medium","gaps":["In vitro and Drosophila system; not validated in mammalian cardiomyocytes","Preprint not yet peer-reviewed","Quantitative contribution of bundling vs polymerization to Z-line maintenance unresolved"]},{"year":2024,"claim":"Tested causality of a familial LVNC-associated MYPN variant and found the orthologous Mypn S1291T mutation alone insufficient to cause disease, indicating it is not the primary pathogenic driver in that context.","evidence":"Knock-in mice with Mypn S1291T alone vs Tnnt2 mutant vs double mutant, with cardiac phenotyping (preprint)","pmids":["bio_10.1101_2024.10.09.24314670"],"confidence":"Medium","gaps":["Negative result for one specific variant; not generalizable to other MYPN mutations","Preprint","Potential modifier role with TNNT2 not fully resolved"]},{"year":2026,"claim":"Connected an HCM-associated MYPN variant to transcriptional reprogramming of sarcomeric and cytoskeletal gene programs rather than to direct electrophysiological dysfunction.","evidence":"Patient iPSC-derived cardiomyocytes with patch-clamp, calcium imaging, and RNA-seq","pmids":["42074575"],"confidence":"Medium","gaps":["Non-isogenic controls limit attribution to the variant","Causal link between MYPN dysfunction and the transcriptional changes not established","Single lab"]},{"year":null,"claim":"How MYPN integrates actin bundling with Z-line signaling and sarcomeric gene expression, and whether it engages defined Z-line partners beyond alpha-actinin in mammalian muscle, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No direct mammalian binding partners established in the corpus","Mechanism linking structural loss to SRF/sarcomeric transcriptional changes unknown","No high-resolution structure of the actin-bound Ig3 domain"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[0]}],"complexes":[],"partners":["ACTN2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q86TC9","full_name":"Myopalladin","aliases":["145 kDa sarcomeric protein"],"length_aa":1320,"mass_kda":145.3,"function":"Component of the sarcomere that tethers together nebulin (skeletal muscle) and nebulette (cardiac muscle) to alpha-actinin, at the Z lines","subcellular_location":"Cytoplasm; Nucleus; Cytoplasm, myofibril, sarcomere; Cytoplasm, myofibril, sarcomere, Z line","url":"https://www.uniprot.org/uniprotkb/Q86TC9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MYPN","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/MYPN","total_profiled":1310},"omim":[{"mim_id":"617336","title":"CONGENITAL MYOPATHY 24; CMYO24","url":"https://www.omim.org/entry/617336"},{"mim_id":"615248","title":"CARDIOMYOPATHY, DILATED, 1KK; CMD1KK","url":"https://www.omim.org/entry/615248"},{"mim_id":"614647","title":"COENZYME Q6, MONOOXYGENASE; COQ6","url":"https://www.omim.org/entry/614647"},{"mim_id":"608517","title":"MYOPALLADIN; MYPN","url":"https://www.omim.org/entry/608517"},{"mim_id":"256030","title":"NEMALINE MYOPATHY 2; NEM2","url":"https://www.omim.org/entry/256030"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"heart muscle","ntpm":64.0},{"tissue":"skeletal muscle","ntpm":269.9},{"tissue":"tongue","ntpm":171.2}],"url":"https://www.proteinatlas.org/search/MYPN"},"hgnc":{"alias_symbol":["MYOP"],"prev_symbol":[]},"alphafold":{"accession":"Q86TC9","domains":[{"cath_id":"2.60.40.10","chopping":"268-360","consensus_level":"high","plddt":83.2871,"start":268,"end":360},{"cath_id":"2.60.40.10","chopping":"435-533","consensus_level":"high","plddt":80.5426,"start":435,"end":533},{"cath_id":"2.60.40.10","chopping":"947-1038","consensus_level":"high","plddt":81.1249,"start":947,"end":1038},{"cath_id":"2.60.40.10","chopping":"1079-1165","consensus_level":"high","plddt":86.1547,"start":1079,"end":1165},{"cath_id":"2.60.40.10","chopping":"1171-1265","consensus_level":"high","plddt":87.2477,"start":1171,"end":1265}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86TC9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q86TC9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q86TC9-F1-predicted_aligned_error_v6.png","plddt_mean":52.41},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MYPN","jax_strain_url":"https://www.jax.org/strain/search?query=MYPN"},"sequence":{"accession":"Q86TC9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q86TC9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q86TC9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86TC9"}},"corpus_meta":[{"pmid":"28017374","id":"PMC_28017374","title":"Biallelic Mutations in MYPN, Encoding Myopalladin, Are Associated with Childhood-Onset, Slowly Progressive Nemaline Myopathy.","date":"2016","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28017374","citation_count":64,"is_preprint":false},{"pmid":"28220527","id":"PMC_28220527","title":"Recessive MYPN mutations cause cap myopathy with occasional nemaline rods.","date":"2017","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/28220527","citation_count":28,"is_preprint":false},{"pmid":"28427417","id":"PMC_28427417","title":"Novel trigenic CACNA1C/DES/MYPN mutations in a family of hypertrophic cardiomyopathy with early repolarization and short QT syndrome.","date":"2017","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28427417","citation_count":27,"is_preprint":false},{"pmid":"20812196","id":"PMC_20812196","title":"A novel polymorphism of the MYPN gene and its association with meat quality traits in Bos taurus.","date":"2010","source":"Genetics and molecular research : GMR","url":"https://pubmed.ncbi.nlm.nih.gov/20812196","citation_count":15,"is_preprint":false},{"pmid":"24158610","id":"PMC_24158610","title":"SNPs of MYPN and TTN genes are associated to meat and carcass traits in Italian Large White and Italian Duroc pigs.","date":"2013","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/24158610","citation_count":10,"is_preprint":false},{"pmid":"31133047","id":"PMC_31133047","title":"Congenital myopathy with hanging big toe due to homozygous myopalladin (MYPN) mutation.","date":"2019","source":"Skeletal muscle","url":"https://pubmed.ncbi.nlm.nih.gov/31133047","citation_count":10,"is_preprint":false},{"pmid":"37936622","id":"PMC_37936622","title":"Associations of MYPN, TTN, SCN5A, MYO6 and ELN Mutations With Arrhythmias and Subsequent Sudden Cardiac Death: A Case Report of an Ecuadorian Individual.","date":"2023","source":"Cardiology research","url":"https://pubmed.ncbi.nlm.nih.gov/37936622","citation_count":8,"is_preprint":false},{"pmid":"34184449","id":"PMC_34184449","title":"Nemaline Rod/Cap Myopathy Due to Novel Homozygous MYPN Mutations: The First Report from South Asia and Comprehensive Literature Review.","date":"2021","source":"Journal of clinical neurology (Seoul, Korea)","url":"https://pubmed.ncbi.nlm.nih.gov/34184449","citation_count":2,"is_preprint":false},{"pmid":"42074575","id":"PMC_42074575","title":"Functional and Expression Studies of iPSC-Derived Cardiomyocytes Carrying a Novel HCM-Associated MYPN Genetic Variant.","date":"2026","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/42074575","citation_count":0,"is_preprint":false},{"pmid":"41850063","id":"PMC_41850063","title":"Multi-omics analysis reveals RBPJ-mediated regulation of EGF/ACTN2/MYPN/COL21A1 in fibroblast during oviduct functional remodeling of duck.","date":"2026","source":"Poultry science","url":"https://pubmed.ncbi.nlm.nih.gov/41850063","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.18.677238","title":"Cardiomyopathy-Associated and Basic Residue Mutations in Myopalladin Alter Actin Binding, Bundling, and Structural Stability","date":"2025-09-20","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.18.677238","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.09.24314670","title":"Targeting mutant TNNT2-induced epigenetic perturbation and pathogenic signaling in left ventricular non-compaction cardiomyopathy","date":"2024-10-11","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.09.24314670","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9651,"output_tokens":1754,"usd":0.027631,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8585,"output_tokens":2248,"usd":0.049563,"stage2_stop_reason":"end_turn"},"total_usd":0.077194,"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\": 2016,\n      \"finding\": \"MYPN (myopalladin) is localized at the Z-line in control skeletal muscles; biallelic loss-of-function mutations in MYPN result in absence of protein from the Z-line and cause Z-streaming and nemaline-like bodies adjacent to a disorganized Z-line, establishing MYPN's role in maintaining Z-line integrity in striated muscle.\",\n      \"method\": \"Immunofluorescence localization in human muscle biopsies and knockin mouse model (electron microscopy of homozygous nonsense-mutation knockin mice)\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization by immunofluorescence with functional consequence, confirmed by in vivo knockin mouse model with ultrastructural readout, replicated across multiple families\",\n      \"pmids\": [\"28017374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Homozygous truncating mutations in MYPN lead to mRNA defects and strong reduction of full-length myopalladin protein; residual myopalladin signals accumulate in cap structures together with alpha-actinin, indicating myopalladin functions at the Z-line and its loss disrupts normal alpha-actinin organization.\",\n      \"method\": \"Functional experiments on patient muscle: mRNA analysis, protein expression assays (immunoblot/immunofluorescence), co-localization of myopalladin and alpha-actinin in caps\",\n      \"journal\": \"Annals of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal methods (mRNA and protein analysis), single lab, two unrelated families\",\n      \"pmids\": [\"28220527\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A homozygous loss-of-function deletion in MYPN exon 11 renders full-length myopalladin protein undetectable on immunoblotting and abolishes Z-line localization on immunofluorescence, accompanied by ultrastructural Z-line fragmentation, confirming MYPN is required for Z-line structural integrity in skeletal muscle.\",\n      \"method\": \"Immunoblotting and immunofluorescence of patient muscle biopsy; whole-exome sequencing for genetic identification\",\n      \"journal\": \"Skeletal muscle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal protein and localization data in patient tissue, single lab, two orthogonal methods\",\n      \"pmids\": [\"31133047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The Ig3 domain of MYPN mediates actin binding and bundling through conserved basic charge clusters via electrostatic interactions; cardiomyopathy-associated mutations (e.g., R955W, P961L) within this domain impair actin binding, nearly abolish actin bundling, and cause mislocalization into clusters at Z-discs in Drosophila cardiomyocytes and body wall muscles without broadly altering secondary protein structure (except P961L which is destabilized). MYPN also promotes actin polymerization from monomeric actin, and this activity is not modulated by calcium.\",\n      \"method\": \"Actin co-sedimentation assays with charge-neutralizing alanine substitution mutagenesis; co-polymerization assays; circular dichroism spectroscopy; GFP-tagged construct expression and immunostaining in Drosophila cardiomyocytes and body wall muscles\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and multiple orthogonal methods (co-sedimentation, CD spectroscopy, in vivo Drosophila localization), single lab, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.09.18.677238\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"iPSC-derived cardiomyocytes carrying the MYPN p.N989I variant showed no significant changes in calcium transients, sodium current, or action potential compared to control cells, but exhibited transcriptomic upregulation of cell cycle, mitotic spindle, microtubule cytoskeleton, and myogenic program genes, and downregulation of sarcomeric, Z-disc, cell junction, ATP synthesis, oxidative phosphorylation, and SRF-signaling genes, suggesting MYPN p.N989I disrupts sarcomeric/cytoskeletal gene programs rather than direct electrophysiological function.\",\n      \"method\": \"iPSC-derived cardiomyocytes from HCM patient; patch-clamp electrophysiology; calcium transient measurements; RNA-seq transcriptomic profiling\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, calcium imaging, transcriptomics) in iPSC-CM model, single lab, non-isogenic controls limit interpretation\",\n      \"pmids\": [\"42074575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In a compound TNNT2/MYPN double-mutant LVNC model, knock-in of the orthologous Mypn S1291T mutation alone did NOT cause cardiac hypertrabeculation, noncompaction, or heart failure in mice, indicating the MYPN variant is not the primary pathogenic driver in this familial LVNC context.\",\n      \"method\": \"Knock-in C57BL/6J mice harboring Mypn S1291T alone vs. Tnnt2 R154W alone vs. double mutant; cardiac phenotyping\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo genetic epistasis via knock-in mice, single lab, preprint; negative result for MYPN variant specifically\",\n      \"pmids\": [\"bio_10.1101_2024.10.09.24314670\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"Myopalladin (MYPN) is a striated muscle-specific sarcomeric protein that localizes to the Z-line, where it maintains Z-line structural integrity by binding and bundling actin filaments through conserved basic charge clusters in its Ig3 domain; loss-of-function mutations abolish Z-line localization and cause disorganization, while cardiomyopathy-associated Ig3 domain mutations disrupt actin binding and bundling, leading to abnormal Z-disc localization and altered sarcomeric gene programs.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Myopalladin (MYPN) is a striated muscle protein that localizes to the sarcomeric Z-line and is required to maintain Z-line structural integrity in skeletal and cardiac muscle [#0]. Biallelic loss-of-function mutations abolish full-length protein and Z-line localization, producing Z-streaming, nemaline-like bodies, and ultrastructural Z-line fragmentation, with residual protein accumulating in cap structures together with alpha-actinin [#0, #1, #2]. Mechanistically, the Ig3 domain mediates actin binding and bundling through conserved basic charge clusters via electrostatic interactions and promotes actin polymerization from monomeric actin in a calcium-independent manner; cardiomyopathy-associated Ig3 mutations (R955W, P961L) impair actin binding, nearly abolish bundling, and cause mislocalization into Z-disc clusters [#3]. Disruption of MYPN function shifts sarcomeric and cytoskeletal gene programs, downregulating sarcomeric, Z-disc, and SRF-signaling genes rather than directly altering cardiomyocyte electrophysiology [#4]. Loss-of-function MYPN mutations cause a Z-line myopathy with nemaline-like and cap features [#0].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Established that MYPN is a Z-line protein whose loss disrupts Z-line architecture, defining its core structural role and disease relevance in striated muscle.\",\n      \"evidence\": \"Immunofluorescence in human muscle biopsies plus electron microscopy of homozygous nonsense knockin mice across multiple families\",\n      \"pmids\": [\"28017374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular interactions through which MYPN maintains Z-line integrity\", \"Mechanism of nemaline-like body formation unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed that truncating mutations cause mRNA defects and loss of full-length protein, with residual myopalladin accumulating in caps alongside alpha-actinin, linking MYPN loss to disturbed alpha-actinin organization.\",\n      \"evidence\": \"mRNA analysis and protein/immunofluorescence assays in patient muscle from two unrelated families\",\n      \"pmids\": [\"28220527\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MYPN directly binds alpha-actinin not tested\", \"Single lab, limited families\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Confirmed with reciprocal protein and localization data that full-length MYPN is required for Z-line structural integrity, reinforcing the loss-of-function disease model.\",\n      \"evidence\": \"Immunoblotting and immunofluorescence of patient muscle with WES genetic identification\",\n      \"pmids\": [\"31133047\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanistic interaction data\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided the molecular mechanism by defining the Ig3 domain as an actin-binding, bundling, and polymerization-promoting module dependent on basic charge clusters, and showing cardiomyopathy mutations disrupt these activities and cause mislocalization.\",\n      \"evidence\": \"Actin co-sedimentation and co-polymerization assays with charge-neutralizing mutagenesis, circular dichroism, and GFP-construct localization in Drosophila muscle (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.09.18.677238\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro and Drosophila system; not validated in mammalian cardiomyocytes\", \"Preprint not yet peer-reviewed\", \"Quantitative contribution of bundling vs polymerization to Z-line maintenance unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Tested causality of a familial LVNC-associated MYPN variant and found the orthologous Mypn S1291T mutation alone insufficient to cause disease, indicating it is not the primary pathogenic driver in that context.\",\n      \"evidence\": \"Knock-in mice with Mypn S1291T alone vs Tnnt2 mutant vs double mutant, with cardiac phenotyping (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.10.09.24314670\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result for one specific variant; not generalizable to other MYPN mutations\", \"Preprint\", \"Potential modifier role with TNNT2 not fully resolved\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Connected an HCM-associated MYPN variant to transcriptional reprogramming of sarcomeric and cytoskeletal gene programs rather than to direct electrophysiological dysfunction.\",\n      \"evidence\": \"Patient iPSC-derived cardiomyocytes with patch-clamp, calcium imaging, and RNA-seq\",\n      \"pmids\": [\"42074575\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Non-isogenic controls limit attribution to the variant\", \"Causal link between MYPN dysfunction and the transcriptional changes not established\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MYPN integrates actin bundling with Z-line signaling and sarcomeric gene expression, and whether it engages defined Z-line partners beyond alpha-actinin in mammalian muscle, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct mammalian binding partners established in the corpus\", \"Mechanism linking structural loss to SRF/sarcomeric transcriptional changes unknown\", \"No high-resolution structure of the actin-bound Ig3 domain\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ACTN2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}