{"gene":"TMEM63B","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":2020,"finding":"TMEM63B functions as an osmosensitive nonselective cation channel (NSCC) activated by hypotonic stress. Genetic deletion of TMEM63B in mice causes necroptosis of outer hair cells (OHCs) and progressive hearing loss. Mechanistically, TMEM63B mediates hypo-osmolarity-induced Ca2+ influx, which activates Ca2+-dependent K+ channels required for maintenance of OHC morphology, establishing TMEM63B as the osmosensor of the mammalian inner ear and the cation channel mediating Ca2+-dependent regulatory volume decrease (RVD).","method":"Electrophysiology, genetic knockout (KO) mouse, Ca2+ imaging, cell volume assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined cellular phenotype, electrophysiology, Ca2+ imaging, and mechanistic pathway placement; replicated in subsequent studies","pmids":["32375046"],"is_preprint":false},{"year":2016,"finding":"Co-expression of all three mouse TMEM63 family members (TMEM63A, TMEM63B, and TMEM63C) together in HEK293 cells confers hyperosmolarity-activated ion currents; expression of any two subtypes alone is insufficient to produce these currents, suggesting all three are required to constitute a functional hyperosmolarity-activated ion channel.","method":"Heterologous expression in HEK293 cells, patch-clamp electrophysiology","journal":"Cell biochemistry and function","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — electrophysiology in heterologous system, single lab, single method; later studies demonstrate TMEM63B can function independently","pmids":["27045885"],"is_preprint":false},{"year":2019,"finding":"TMEM63B localizes to the plasma membrane and associates with F-actin in HEK293T cells. It functions as a Ca2+-permeable channel that mediates Ca2+ influx in response to hyperosmolarity and extracellular Ca2+ concentration. Overexpression of TMEM63B significantly enhances cell migration and wound healing.","method":"Immunofluorescence, Ca2+ imaging, wound healing/migration assays, overexpression in HEK293T cells","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization by immunofluorescence, Ca2+ imaging, and functional migration assay; single lab, multiple orthogonal methods","pmids":["31243992"],"is_preprint":false},{"year":2020,"finding":"TMEM63B pre-mRNA undergoes brain-specific A-to-I RNA editing at exon 20 (Q/R site) catalyzed by ADAR2 (ADARB1), requiring an editing site complementary sequence in intron 20. A brain-specific alternative splicing of exon 4 (~80% of brain mRNAs lack exon 4) is coupled to this editing: the Q/R editing occurs almost exclusively in the exon-4-lacking isoform. The splicing plays the dominant role (exon 4 inclusion suppresses Q/R editing). The two modifications coordinately regulate Ca2+ permeability and osmosensitivity of the channel.","method":"RT-PCR, sequencing, ADAR2 knockout mice, transfection in cerebellar granule neurons, electrophysiology, Ca2+ imaging","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (KO mice, sequencing, electrophysiology, Ca2+ imaging), mechanistic coupling between RNA editing and splicing established","pmids":["33100268"],"is_preprint":false},{"year":2022,"finding":"The exon 4-containing long isoform of TMEM63B contains an RXR-type ER retention signal (RER motif) within the exon 4-encoded sequence that binds COPI retrieval vesicles, causing retrotranslocation to the ER and reduced surface expression. The short isoform (lacking exon 4) exhibits stronger plasma membrane surface expression and enhanced responses to hypoosmotic stimulation. Additionally, long TMEM63B isoforms can form heterodimers with short isoforms and reduce their surface expression.","method":"Mutagenesis screening, surface biotinylation, co-immunoprecipitation, COPI binding assay, electrophysiology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — mutagenesis, co-IP for dimerization, COPI binding, surface expression assay, and functional electrophysiology in a single study with multiple orthogonal methods","pmids":["36496074"],"is_preprint":false},{"year":2023,"finding":"Disease-associated heterozygous missense variants in TMEM63B transmembrane domains (e.g., p.Val44Met, p.Arg433His, p.Thr481Asn, p.Gly580Ser, p.Arg660Thr, p.Phe697Leu) produce inward leak cation currents in isotonic conditions (gain-of-function), while impairing the hypo-osmotic challenge response and reducing Ca2+ transients under hypo-osmotic stimulation. Expression of p.Val44Met and p.Gly580Cys variants in Drosophila causes early death.","method":"Patch-clamp electrophysiology in transfected Neuro2a cells, Ca2+ imaging, Drosophila ectopic expression lethality assay","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — electrophysiology with multiple variants, Ca2+ imaging, and in vivo Drosophila lethality; multiple orthogonal methods, multiple variants tested","pmids":["37421948"],"is_preprint":false},{"year":2024,"finding":"TMEM63A and TMEM63B are mechanosensitive channels predominantly localized at the limiting membrane of the lamellar body (LB) in alveolar type 2 (AT2) cells. Loss of TMEM63A/B results in atelectasis and respiratory failure in mice due to surfactant secretion deficit. Activation of TMEM63A/B during cell stretch facilitates surfactant and ATP release from LBs fused with the plasma membrane; released ATP evokes Ca2+ signaling in AT2 cells, potentiating exocytic fusion of more LBs.","method":"Genetic KO mice, immunofluorescence/confocal localization, electrophysiology, surfactant secretion assays, ATP release assays, Ca2+ imaging","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined respiratory phenotype, organelle localization, mechanistic pathway (stretch→ATP→Ca2+→LB fusion) established with multiple orthogonal methods","pmids":["38127458"],"is_preprint":false},{"year":2024,"finding":"TMEM63B functions as a membrane structure-responsive lipid scramblase localized at the plasma membrane and lysosomes, activating bidirectional lipid translocation in response to changes in membrane curvature and thickness. TMEM63B contains two intracellular loops with palmitoylated cysteine residue clusters essential for its scrambling function. TMEM63B deficiency alters phosphatidylcholine and sphingomyelin distributions in the plasma membrane. The disease variant p.Val44Met confers constitutive scramblase activity, disrupting plasma membrane phospholipid asymmetry. Cryo-EM structures of TMEM63B in open and closed conformations reveal a lipid translocation pathway formed in response to membrane environment changes.","method":"Cryo-EM structure determination, lipid scramblase assay (phosphatidylserine externalization, fluorescent lipid incorporation), mutagenesis of palmitoylation sites, TMEM63B-deficient cells, phospholipid distribution analysis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures of open and closed states combined with mutagenesis and functional scramblase assays in a single rigorous study","pmids":["39424995"],"is_preprint":false},{"year":2025,"finding":"TMEM63B is a stretch-activated cation channel (SAC) expressed in pancreatic β-cells. Deletion of TMEM63B impairs insulin secretion in response to high glucose. Mechanistically, glucose metabolism induces cell swelling, which activates TMEM63B, leading to Ca2+ influx, β-cell depolarization, and insulin secretion. TMEM63B deletion eliminates the increased Ca2+ influx and firing frequency normally induced by high glucose.","method":"Conditional KO mice, patch-clamp electrophysiology, Ca2+ imaging, insulin secretion assays","journal":"Science China. Life sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO mouse with defined secretory phenotype, electrophysiology, Ca2+ imaging, mechanistic pathway established with multiple orthogonal methods","pmids":["39985646"],"is_preprint":false},{"year":2026,"finding":"TMEM63B functions as the primary mechanosensor on the plasma membrane of alveolar type II (AT2) cells. Stretch induces significant currents in AT2 cells that are abolished by TMEM63B deletion. TMEM63B activation causes Ca2+ influx, lamellar body (LB) fusion, and pulmonary surfactant secretion. ATP-induced Ca2+ influx and LB fusion are unaffected by TMEM63B deletion, indicating TMEM63B specifically senses mechanical stretch rather than ATP signaling in this context.","method":"Conditional KO (Tmem63bHA-fl/HA-fl mice), patch-clamp electrophysiology in AT2 cells, Ca2+ imaging, LB fusion assay, surfactant secretion assay","journal":"Journal of genetics and genomics","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined stretch-activated current abolition, Ca2+ imaging, LB fusion and surfactant secretion assays; multiple orthogonal methods in AT2 cells","pmids":["42067058"],"is_preprint":false},{"year":2026,"finding":"TMEM63B modulates nucleocytoplasmic transport (NCT) by stabilizing NCT components. Loss of TMEM63B compromises Ran protein expression and the Ran-XPO1 complex, impairing nuclear export of CDKN1A/p21, leading to defective trophoblast proliferation, placental dysfunction, and perinatal lethality in mice.","method":"Genetic KO mice, co-immunoprecipitation (Ran-XPO1 complex), immunofluorescence (nuclear shuttling), western blot (Ran levels, p21 localization), trophoblast proliferation assays","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KO mouse with defined perinatal lethal phenotype and mechanistic pathway (Ran/XPO1/p21), co-IP, localization; single lab","pmids":["42259794"],"is_preprint":false},{"year":2026,"finding":"The C-terminal tail of TMEM63B contains an autoinhibitory AQVLQD motif (residues 773-778). Deletion of the adjacent LQD motif (Δ776-778) or substitution of Leu776 with alanine induces constitutive lipid scrambling (phosphatidylserine externalization and enhanced phosphatidylcholine incorporation), while substitutions at Gln777 or Asp778 have minimal effects. Cryo-EM structural analysis positions the AQVLQD motif adjacent to conserved intracellular helices in the open conformation, with Leu776 near hydrophobic residues, suggesting the C-terminal tail maintains TMEM63B in an inactive state through interactions with intracellular helices.","method":"Mutagenesis (chimeric constructs, truncations, internal deletions), lipid scramblase functional assays (phosphatidylserine externalization, fluorescent phosphatidylcholine incorporation), cryo-EM structural analysis, antibody epitope mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with functional scramblase assays and cryo-EM structural analysis; single lab with multiple orthogonal methods","pmids":["42248451"],"is_preprint":false},{"year":2026,"finding":"Bi-allelic loss-of-function variants in TMEM63B cause a syndromic surfactant dysfunction disorder in humans with early-onset respiratory distress. Functional evaluation of splice donor and nonsense variants confirmed loss-of-function mechanism. The pulmonary phenotype parallels Tmem63b-knockout mice with neonatal respiratory failure due to impaired surfactant secretion.","method":"Functional variant evaluation (splice/nonsense variant testing), clinical genotype-phenotype correlation, parallel KO mouse comparison","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional variant evaluation supports loss-of-function; single study, limited functional detail in abstract","pmids":["42259295"],"is_preprint":false},{"year":2025,"finding":"TMEM63B is expressed in the urothelium of the bladder and dorsal root ganglia sensory neurons innervating the bladder. However, conditional deletion of TMEM63B in urothelium or sensory neurons does not produce a demonstrable voiding phenotype, even under cyclophosphamide-induced stress (negative result for bladder mechanosensory function).","method":"Conditional KO mice, void-spot screening assay, immunofluorescence","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with systematic behavioral assay in two tissue-specific lines; negative result well-controlled","pmids":["41348674"],"is_preprint":false}],"current_model":"TMEM63B is a mechanosensitive and osmosensitive cation channel and lipid scramblase that is activated by membrane stretch, hypo-osmotic stress, or changes in membrane physical properties; it localizes to the plasma membrane, lysosomes, and organelle-limiting membranes, where it mediates Ca2+ influx to drive diverse downstream processes including Ca2+-dependent K+ channel activation in cochlear hair cells, lamellar body fusion and surfactant secretion in alveolar type II cells, insulin secretion in β-cells, and trophoblast cell cycle control via nucleocytoplasmic transport; its activity is regulated post-transcriptionally by brain-specific exon 4 splicing (controlling surface expression via an ER retention/COPI signal) coupled to ADAR2-dependent A-to-I RNA editing, and is autoinhibited at rest by its C-terminal AQVLQD motif that interacts with intracellular helices, as revealed by cryo-EM structures of open and closed conformations."},"narrative":{"mechanistic_narrative":"TMEM63B is a mechanosensitive and osmosensitive nonselective cation channel that converts membrane physical stimuli — hypo-osmotic swelling and membrane stretch — into Ca2+ influx to drive tissue-specific physiological responses [PMID:32375046, PMID:39985646, PMID:42067058]. In cochlear outer hair cells it serves as the inner-ear osmosensor, mediating hypo-osmolarity-induced Ca2+ entry that activates Ca2+-dependent K+ channels for regulatory volume decrease; its loss causes outer hair cell necroptosis and progressive hearing loss [PMID:32375046]. The same channel activity underlies stretch-evoked Ca2+ influx that triggers lamellar body fusion and pulmonary surfactant secretion in alveolar type II cells [PMID:38127458, PMID:42067058], glucose-swelling-induced depolarization and insulin secretion in pancreatic β-cells [PMID:39985646], and it additionally stabilizes nucleocytoplasmic transport machinery (the Ran-XPO1 complex) to permit p21 nuclear export and trophoblast proliferation [PMID:42259794]. Beyond ion conduction, TMEM63B is a membrane-structure-responsive lipid scramblase that catalyzes bidirectional phospholipid translocation in response to changes in membrane curvature and thickness, a function requiring palmitoylated intracellular cysteine clusters and resolved by cryo-EM structures capturing open and closed states with a defined lipid translocation pathway [PMID:39424995]. The channel is autoinhibited at rest by a C-terminal AQVLQD motif whose Leu776 packs against intracellular helices; disrupting this motif yields constitutive scrambling [PMID:42248451]. Activity is further tuned post-transcriptionally by brain-specific exon 4 alternative splicing — the exon-4 isoform carries an RXR-type COPI-dependent ER retention signal limiting surface expression — coupled to ADAR2-dependent Q/R A-to-I editing that occurs almost exclusively in the exon-4-lacking isoform [PMID:33100268, PMID:36496074]. Heterozygous transmembrane missense variants act as gain-of-function alleles producing isotonic leak currents [PMID:37421948], whereas bi-allelic loss-of-function variants cause a syndromic surfactant dysfunction disorder with neonatal respiratory failure paralleling the knockout mouse [PMID:42259295].","teleology":[{"year":2016,"claim":"Established the TMEM63 family as candidate osmolarity-activated channels, raising the question of whether subunits act independently or cooperatively.","evidence":"Heterologous co-expression of TMEM63A/B/C in HEK293 cells with patch-clamp","pmids":["27045885"],"confidence":"Medium","gaps":["Inferred obligate three-subunit requirement was contradicted by later evidence that TMEM63B functions independently","No native tissue context tested"]},{"year":2019,"claim":"Showed TMEM63B is a plasma-membrane Ca2+-permeable channel responsive to hyperosmolarity and capable of promoting cell migration, defining it as an independent functional unit.","evidence":"Immunofluorescence, Ca2+ imaging, and wound-healing assays with overexpression in HEK293T cells","pmids":["31243992"],"confidence":"Medium","gaps":["Single overexpression system without endogenous validation","Mechanism linking channel activity to migration not resolved"]},{"year":2020,"claim":"Defined the physiological role of TMEM63B as the inner-ear osmosensor, answering what process its channel activity serves in vivo.","evidence":"Knockout mouse, electrophysiology, Ca2+ imaging, and volume assays in outer hair cells","pmids":["32375046"],"confidence":"High","gaps":["Selectivity filter and gating residues not mapped","Link from Ca2+ influx to necroptosis not mechanistically detailed"]},{"year":2020,"claim":"Revealed that channel properties are post-transcriptionally tuned, answering how Ca2+ permeability and osmosensitivity are regulated in a tissue-specific manner.","evidence":"RT-PCR/sequencing, ADAR2 knockout mice, and electrophysiology in cerebellar granule neurons","pmids":["33100268"],"confidence":"High","gaps":["Functional consequence in intact neural circuits not established","Structural basis of Q/R-site effect on permeation unknown at the time"]},{"year":2022,"claim":"Explained how alternative splicing controls surface availability, linking exon 4 to a COPI-dependent ER retention signal and to heterodimer-mediated suppression.","evidence":"Mutagenesis, surface biotinylation, co-IP, COPI binding assays, and electrophysiology","pmids":["36496074"],"confidence":"High","gaps":["In vivo significance of isoform ratios per tissue not quantified","Stoichiometry of long/short heterodimers undefined"]},{"year":2023,"claim":"Connected TMEM63B to human neurodevelopmental disease through gain-of-function transmembrane variants producing isotonic leak currents.","evidence":"Patch-clamp and Ca2+ imaging in Neuro2a cells plus Drosophila lethality assay","pmids":["37421948"],"confidence":"High","gaps":["Channel-pore residues underlying leak not structurally localized in this study","Genotype-phenotype correlation across variant positions incomplete"]},{"year":2024,"claim":"Identified an organelle-membrane role: TMEM63B as a stretch sensor on lamellar body membranes driving surfactant and ATP release in the lung.","evidence":"Knockout mice, confocal localization, electrophysiology, surfactant/ATP release and Ca2+ imaging in AT2 cells","pmids":["38127458"],"confidence":"High","gaps":["Relative contribution of TMEM63A vs TMEM63B not separated","Direct gating by membrane tension at the LB membrane not reconstituted"]},{"year":2024,"claim":"Expanded the molecular function beyond ion conduction by demonstrating lipid scramblase activity and providing open/closed cryo-EM structures.","evidence":"Cryo-EM, scramblase assays, palmitoylation-site mutagenesis, and phospholipid distribution analysis in deficient cells","pmids":["39424995"],"confidence":"High","gaps":["Relationship between ion conduction and lipid scrambling pathways not fully resolved","Physiological readout of scrambling in native tissues limited"]},{"year":2025,"claim":"Extended the stretch-channel role to metabolism, showing glucose-induced swelling activates TMEM63B to promote β-cell depolarization and insulin secretion.","evidence":"Conditional knockout mice, patch-clamp, Ca2+ imaging, and insulin secretion assays","pmids":["39985646"],"confidence":"High","gaps":["Coupling between swelling and channel gating in β-cells not directly measured","Contribution relative to canonical KATP-dependent secretion unclear"]},{"year":2025,"claim":"Tested whether TMEM63B contributes to bladder mechanosensation, returning a well-controlled negative result that bounds its functional scope.","evidence":"Tissue-specific conditional knockouts with void-spot assays under cyclophosphamide stress","pmids":["41348674"],"confidence":"Medium","gaps":["Possible redundancy with other mechanosensors not excluded","Subthreshold or compensatory roles not assayed"]},{"year":2026,"claim":"Confirmed TMEM63B as the primary stretch sensor on the AT2 plasma membrane and dissociated mechanical sensing from downstream ATP signaling.","evidence":"Conditional knockout, patch-clamp, Ca2+ imaging, and LB fusion/surfactant assays in AT2 cells","pmids":["42067058"],"confidence":"High","gaps":["Molecular force-transduction mechanism not defined","Integration with the earlier LB-membrane localization model not fully reconciled"]},{"year":2026,"claim":"Uncovered a non-channel role in nucleocytoplasmic transport, linking TMEM63B loss to Ran/XPO1 destabilization and impaired p21 export in trophoblasts.","evidence":"Knockout mice, co-IP of Ran-XPO1, immunofluorescence shuttling, and trophoblast proliferation assays","pmids":["42259794"],"confidence":"Medium","gaps":["Mechanism by which a membrane channel stabilizes Ran is unresolved","Single lab; direct physical interaction not established"]},{"year":2026,"claim":"Defined the autoinhibitory switch, showing the C-terminal AQVLQD motif (Leu776) holds TMEM63B inactive via intracellular helix contacts.","evidence":"Mutagenesis/truncations, scramblase assays, and cryo-EM structural analysis","pmids":["42248451"],"confidence":"High","gaps":["How physiological stimuli relieve autoinhibition not shown","Effect of the motif on ion conduction versus scrambling not separated"]},{"year":2026,"claim":"Established a recessive human disease link, showing bi-allelic loss-of-function variants cause syndromic surfactant dysfunction matching the knockout phenotype.","evidence":"Functional splice/nonsense variant evaluation and clinical genotype-phenotype correlation with KO mouse comparison","pmids":["42259295"],"confidence":"Medium","gaps":["Limited functional detail beyond loss-of-function confirmation","Spectrum of biallelic phenotypes not fully delineated"]},{"year":null,"claim":"How a single protein partitions between ion conduction, lipid scrambling, and a non-channel role in nucleocytoplasmic transport — and how stimulus-specific relief of C-terminal autoinhibition selects among these outputs — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model coupling mechanosensing to choice of ion vs lipid output","Mechanism connecting a membrane channel to Ran/XPO1 stability unknown","Stimulus-to-gating transduction not reconstituted in vitro"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2,8,9]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,6,8,9]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[7,11]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,7,9]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[7]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[6]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[0,8,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,8]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,12]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[10]}],"complexes":[],"partners":["ADAR2","RAN","XPO1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5T3F8","full_name":"Mechanosensitive cation channel TMEM63B","aliases":["Transmembrane protein 63B","hTMEM63B"],"length_aa":832,"mass_kda":95.0,"function":"Mechanosensitive cation channel with low conductance and high activation threshold (PubMed:37543036, PubMed:38127458). Osmosensitive cation channel preferentially activated by hypotonic stress (PubMed:37543036, PubMed:38127458). Also acts as a phospholipid scramblase in response to changes in membrane structure: upon changes in membrane curvature and thickness, alters its conformation and translocates phospholipids, such as phosphatidylcholine and sphingomyelin, thereby controlling plasma membrane lipid distribution (PubMed:39217145, PubMed:39424995, PubMed:39716028). Forms a heterodimer with SLC19A2, which mediates phospholipid scramblase activity following Ca(2+) stimulation (By similarity). Expressed in excitatory neurons of the subfornical organ and functions as a thirst receptor that mediates neuronal response to hyperosmolality to drive thirst and drinking behavior (By similarity). Facilitates intestinal motility by promoting proliferation of intestinal stem cells (By similarity). Essential for the baby's first breath and respiration throughout life (PubMed:38127458). Upon lung inflation conducts cation currents in alveolar type 1 and 2 cells triggering lamellar body exocytosis and surfactant secretion into airspace (PubMed:38127458). Acts as an osmosensor in cochlear outer hair cells (OHCs) where it mediates calcium influx and regulatory volume decrease response (By similarity). Required for the maintenance of OHC morphology, OHC survival and normal hearing (By similarity)","subcellular_location":"Cell membrane; Endoplasmic reticulum membrane; Lysosome membrane; Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q5T3F8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TMEM63B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000137216","cell_line_id":"CID001831","localizations":[{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"RBM25","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001831","total_profiled":1310},"omim":[{"mim_id":"621250","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 118; DEE118","url":"https://www.omim.org/entry/621250"},{"mim_id":"619953","title":"TRANSMEMBRANE PROTEIN 63C; TMEM63C","url":"https://www.omim.org/entry/619953"},{"mim_id":"619952","title":"TRANSMEMBRANE PROTEIN 63B; TMEM63B","url":"https://www.omim.org/entry/619952"},{"mim_id":"618685","title":"TRANSMEMBRANE PROTEIN 63A; TMEM63A","url":"https://www.omim.org/entry/618685"},{"mim_id":"308350","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 1; DEE1","url":"https://www.omim.org/entry/308350"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Plasma membrane","reliability":"Enhanced"},{"location":"Actin filaments","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TMEM63B"},"hgnc":{"alias_symbol":["DKFZp434P0531","dJ421H19.2"],"prev_symbol":["C6orf110"]},"alphafold":{"accession":"Q5T3F8","domains":[{"cath_id":"-","chopping":"40-95_129-235_561-704","consensus_level":"medium","plddt":81.8796,"start":40,"end":704},{"cath_id":"-","chopping":"236-410","consensus_level":"medium","plddt":82.6065,"start":236,"end":410},{"cath_id":"-","chopping":"425-505","consensus_level":"medium","plddt":75.522,"start":425,"end":505}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T3F8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T3F8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T3F8-F1-predicted_aligned_error_v6.png","plddt_mean":72.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TMEM63B","jax_strain_url":"https://www.jax.org/strain/search?query=TMEM63B"},"sequence":{"accession":"Q5T3F8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5T3F8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5T3F8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T3F8"}},"corpus_meta":[{"pmid":"32375046","id":"PMC_32375046","title":"The Cation Channel TMEM63B Is an Osmosensor Required for Hearing.","date":"2020","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/32375046","citation_count":72,"is_preprint":false},{"pmid":"37421948","id":"PMC_37421948","title":"Stretch-activated ion channel TMEM63B associates with developmental and epileptic encephalopathies and progressive neurodegeneration.","date":"2023","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37421948","citation_count":39,"is_preprint":false},{"pmid":"38127458","id":"PMC_38127458","title":"Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation-induced surfactant secretion.","date":"2024","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/38127458","citation_count":38,"is_preprint":false},{"pmid":"27045885","id":"PMC_27045885","title":"Co-expression of mouse TMEM63A, TMEM63B and TMEM63C confers hyperosmolarity activated ion currents in HEK293 cells.","date":"2016","source":"Cell biochemistry and function","url":"https://pubmed.ncbi.nlm.nih.gov/27045885","citation_count":31,"is_preprint":false},{"pmid":"39424995","id":"PMC_39424995","title":"Membrane structure-responsive lipid scrambling by TMEM63B to control plasma membrane lipid distribution.","date":"2024","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/39424995","citation_count":23,"is_preprint":false},{"pmid":"33100268","id":"PMC_33100268","title":"Distant coupling between RNA editing and alternative splicing of the osmosensitive cation channel Tmem63b.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/33100268","citation_count":23,"is_preprint":false},{"pmid":"23037145","id":"PMC_23037145","title":"Association of genes on chromosome 6, GRIK2 , TMEM217 and TMEM63B (linked to MRPL14 ) with diabetic retinopathy.","date":"2012","source":"Ophthalmologica. Journal international d'ophtalmologie. International journal of ophthalmology. Zeitschrift fur Augenheilkunde","url":"https://pubmed.ncbi.nlm.nih.gov/23037145","citation_count":19,"is_preprint":false},{"pmid":"31243992","id":"PMC_31243992","title":"Overexpression of Osmosensitive Ca2+-Permeable Channel TMEM63B Promotes Migration in HEK293T Cells.","date":"2019","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31243992","citation_count":13,"is_preprint":false},{"pmid":"36496074","id":"PMC_36496074","title":"A splicing-dependent ER retention signal regulates surface expression of the mechanosensitive TMEM63B cation channel.","date":"2022","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/36496074","citation_count":12,"is_preprint":false},{"pmid":"39985646","id":"PMC_39985646","title":"Osmosensor TMEM63B facilitates insulin secretion in pancreatic β-cells.","date":"2025","source":"Science China. Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/39985646","citation_count":6,"is_preprint":false},{"pmid":"38724885","id":"PMC_38724885","title":"Expression and localization of the mechanosensitive/osmosensitive ion channel TMEM63B in the mouse urinary tract.","date":"2024","source":"Physiological reports","url":"https://pubmed.ncbi.nlm.nih.gov/38724885","citation_count":4,"is_preprint":false},{"pmid":"41176617","id":"PMC_41176617","title":"Targeting Tmem63b and Piezo2 in C-fiber low-threshold mechanoreceptors: Limitation of Vglut3-IRES-Cre.","date":"2025","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/41176617","citation_count":1,"is_preprint":false},{"pmid":"41348674","id":"PMC_41348674","title":"Conditional deletion of Tmem63b does not impact mouse voiding behavior.","date":"2025","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41348674","citation_count":0,"is_preprint":false},{"pmid":"40766537","id":"PMC_40766537","title":"Targeting Tmem63b and Piezo2 in C-fiber low threshold mechanoreceptor: limitation of Vglut3-IRES-Cre.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40766537","citation_count":0,"is_preprint":false},{"pmid":"42259794","id":"PMC_42259794","title":"TMEM63B regulates nucleocytoplasmic transport and placental development.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/42259794","citation_count":0,"is_preprint":false},{"pmid":"42067058","id":"PMC_42067058","title":"TMEM63B channel is the mechanosensor in alveolar epithelial type II cells.","date":"2026","source":"Journal of genetics and genomics = Yi chuan xue bao","url":"https://pubmed.ncbi.nlm.nih.gov/42067058","citation_count":0,"is_preprint":false},{"pmid":"42259295","id":"PMC_42259295","title":"Bi-allelic loss-of-function variants in TMEM63B cause syndromic surfactant dysfunction disorder.","date":"2026","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/42259295","citation_count":0,"is_preprint":false},{"pmid":"42248451","id":"PMC_42248451","title":"Autoinhibition of the mechanosensitive lipid scramblase TMEM63B by its C-terminal tail.","date":"2026","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/42248451","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.26.666969","title":"Targeting  <i>Tmem63b</i>  and  <i>Piezo2</i>  in C-fiber low threshold mechanoreceptor: limitation of  <i>Vglut3</i>  -IRES-  <i>Cre</i>","date":"2025-07-31","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.26.666969","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.07.647591","title":"Conditional deletion of  <i>Tmem63b</i>  does not impact mouse voiding behavior","date":"2025-04-11","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.07.647591","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11759,"output_tokens":4161,"usd":0.048846,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12137,"output_tokens":4503,"usd":0.08663,"stage2_stop_reason":"end_turn"},"total_usd":0.135476,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2020,\n      \"finding\": \"TMEM63B functions as an osmosensitive nonselective cation channel (NSCC) activated by hypotonic stress. Genetic deletion of TMEM63B in mice causes necroptosis of outer hair cells (OHCs) and progressive hearing loss. Mechanistically, TMEM63B mediates hypo-osmolarity-induced Ca2+ influx, which activates Ca2+-dependent K+ channels required for maintenance of OHC morphology, establishing TMEM63B as the osmosensor of the mammalian inner ear and the cation channel mediating Ca2+-dependent regulatory volume decrease (RVD).\",\n      \"method\": \"Electrophysiology, genetic knockout (KO) mouse, Ca2+ imaging, cell volume assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined cellular phenotype, electrophysiology, Ca2+ imaging, and mechanistic pathway placement; replicated in subsequent studies\",\n      \"pmids\": [\"32375046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Co-expression of all three mouse TMEM63 family members (TMEM63A, TMEM63B, and TMEM63C) together in HEK293 cells confers hyperosmolarity-activated ion currents; expression of any two subtypes alone is insufficient to produce these currents, suggesting all three are required to constitute a functional hyperosmolarity-activated ion channel.\",\n      \"method\": \"Heterologous expression in HEK293 cells, patch-clamp electrophysiology\",\n      \"journal\": \"Cell biochemistry and function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — electrophysiology in heterologous system, single lab, single method; later studies demonstrate TMEM63B can function independently\",\n      \"pmids\": [\"27045885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TMEM63B localizes to the plasma membrane and associates with F-actin in HEK293T cells. It functions as a Ca2+-permeable channel that mediates Ca2+ influx in response to hyperosmolarity and extracellular Ca2+ concentration. Overexpression of TMEM63B significantly enhances cell migration and wound healing.\",\n      \"method\": \"Immunofluorescence, Ca2+ imaging, wound healing/migration assays, overexpression in HEK293T cells\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — localization by immunofluorescence, Ca2+ imaging, and functional migration assay; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31243992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TMEM63B pre-mRNA undergoes brain-specific A-to-I RNA editing at exon 20 (Q/R site) catalyzed by ADAR2 (ADARB1), requiring an editing site complementary sequence in intron 20. A brain-specific alternative splicing of exon 4 (~80% of brain mRNAs lack exon 4) is coupled to this editing: the Q/R editing occurs almost exclusively in the exon-4-lacking isoform. The splicing plays the dominant role (exon 4 inclusion suppresses Q/R editing). The two modifications coordinately regulate Ca2+ permeability and osmosensitivity of the channel.\",\n      \"method\": \"RT-PCR, sequencing, ADAR2 knockout mice, transfection in cerebellar granule neurons, electrophysiology, Ca2+ imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (KO mice, sequencing, electrophysiology, Ca2+ imaging), mechanistic coupling between RNA editing and splicing established\",\n      \"pmids\": [\"33100268\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The exon 4-containing long isoform of TMEM63B contains an RXR-type ER retention signal (RER motif) within the exon 4-encoded sequence that binds COPI retrieval vesicles, causing retrotranslocation to the ER and reduced surface expression. The short isoform (lacking exon 4) exhibits stronger plasma membrane surface expression and enhanced responses to hypoosmotic stimulation. Additionally, long TMEM63B isoforms can form heterodimers with short isoforms and reduce their surface expression.\",\n      \"method\": \"Mutagenesis screening, surface biotinylation, co-immunoprecipitation, COPI binding assay, electrophysiology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mutagenesis, co-IP for dimerization, COPI binding, surface expression assay, and functional electrophysiology in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"36496074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Disease-associated heterozygous missense variants in TMEM63B transmembrane domains (e.g., p.Val44Met, p.Arg433His, p.Thr481Asn, p.Gly580Ser, p.Arg660Thr, p.Phe697Leu) produce inward leak cation currents in isotonic conditions (gain-of-function), while impairing the hypo-osmotic challenge response and reducing Ca2+ transients under hypo-osmotic stimulation. Expression of p.Val44Met and p.Gly580Cys variants in Drosophila causes early death.\",\n      \"method\": \"Patch-clamp electrophysiology in transfected Neuro2a cells, Ca2+ imaging, Drosophila ectopic expression lethality assay\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — electrophysiology with multiple variants, Ca2+ imaging, and in vivo Drosophila lethality; multiple orthogonal methods, multiple variants tested\",\n      \"pmids\": [\"37421948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TMEM63A and TMEM63B are mechanosensitive channels predominantly localized at the limiting membrane of the lamellar body (LB) in alveolar type 2 (AT2) cells. Loss of TMEM63A/B results in atelectasis and respiratory failure in mice due to surfactant secretion deficit. Activation of TMEM63A/B during cell stretch facilitates surfactant and ATP release from LBs fused with the plasma membrane; released ATP evokes Ca2+ signaling in AT2 cells, potentiating exocytic fusion of more LBs.\",\n      \"method\": \"Genetic KO mice, immunofluorescence/confocal localization, electrophysiology, surfactant secretion assays, ATP release assays, Ca2+ imaging\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined respiratory phenotype, organelle localization, mechanistic pathway (stretch→ATP→Ca2+→LB fusion) established with multiple orthogonal methods\",\n      \"pmids\": [\"38127458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TMEM63B functions as a membrane structure-responsive lipid scramblase localized at the plasma membrane and lysosomes, activating bidirectional lipid translocation in response to changes in membrane curvature and thickness. TMEM63B contains two intracellular loops with palmitoylated cysteine residue clusters essential for its scrambling function. TMEM63B deficiency alters phosphatidylcholine and sphingomyelin distributions in the plasma membrane. The disease variant p.Val44Met confers constitutive scramblase activity, disrupting plasma membrane phospholipid asymmetry. Cryo-EM structures of TMEM63B in open and closed conformations reveal a lipid translocation pathway formed in response to membrane environment changes.\",\n      \"method\": \"Cryo-EM structure determination, lipid scramblase assay (phosphatidylserine externalization, fluorescent lipid incorporation), mutagenesis of palmitoylation sites, TMEM63B-deficient cells, phospholipid distribution analysis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures of open and closed states combined with mutagenesis and functional scramblase assays in a single rigorous study\",\n      \"pmids\": [\"39424995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TMEM63B is a stretch-activated cation channel (SAC) expressed in pancreatic β-cells. Deletion of TMEM63B impairs insulin secretion in response to high glucose. Mechanistically, glucose metabolism induces cell swelling, which activates TMEM63B, leading to Ca2+ influx, β-cell depolarization, and insulin secretion. TMEM63B deletion eliminates the increased Ca2+ influx and firing frequency normally induced by high glucose.\",\n      \"method\": \"Conditional KO mice, patch-clamp electrophysiology, Ca2+ imaging, insulin secretion assays\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO mouse with defined secretory phenotype, electrophysiology, Ca2+ imaging, mechanistic pathway established with multiple orthogonal methods\",\n      \"pmids\": [\"39985646\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TMEM63B functions as the primary mechanosensor on the plasma membrane of alveolar type II (AT2) cells. Stretch induces significant currents in AT2 cells that are abolished by TMEM63B deletion. TMEM63B activation causes Ca2+ influx, lamellar body (LB) fusion, and pulmonary surfactant secretion. ATP-induced Ca2+ influx and LB fusion are unaffected by TMEM63B deletion, indicating TMEM63B specifically senses mechanical stretch rather than ATP signaling in this context.\",\n      \"method\": \"Conditional KO (Tmem63bHA-fl/HA-fl mice), patch-clamp electrophysiology in AT2 cells, Ca2+ imaging, LB fusion assay, surfactant secretion assay\",\n      \"journal\": \"Journal of genetics and genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined stretch-activated current abolition, Ca2+ imaging, LB fusion and surfactant secretion assays; multiple orthogonal methods in AT2 cells\",\n      \"pmids\": [\"42067058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TMEM63B modulates nucleocytoplasmic transport (NCT) by stabilizing NCT components. Loss of TMEM63B compromises Ran protein expression and the Ran-XPO1 complex, impairing nuclear export of CDKN1A/p21, leading to defective trophoblast proliferation, placental dysfunction, and perinatal lethality in mice.\",\n      \"method\": \"Genetic KO mice, co-immunoprecipitation (Ran-XPO1 complex), immunofluorescence (nuclear shuttling), western blot (Ran levels, p21 localization), trophoblast proliferation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KO mouse with defined perinatal lethal phenotype and mechanistic pathway (Ran/XPO1/p21), co-IP, localization; single lab\",\n      \"pmids\": [\"42259794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The C-terminal tail of TMEM63B contains an autoinhibitory AQVLQD motif (residues 773-778). Deletion of the adjacent LQD motif (Δ776-778) or substitution of Leu776 with alanine induces constitutive lipid scrambling (phosphatidylserine externalization and enhanced phosphatidylcholine incorporation), while substitutions at Gln777 or Asp778 have minimal effects. Cryo-EM structural analysis positions the AQVLQD motif adjacent to conserved intracellular helices in the open conformation, with Leu776 near hydrophobic residues, suggesting the C-terminal tail maintains TMEM63B in an inactive state through interactions with intracellular helices.\",\n      \"method\": \"Mutagenesis (chimeric constructs, truncations, internal deletions), lipid scramblase functional assays (phosphatidylserine externalization, fluorescent phosphatidylcholine incorporation), cryo-EM structural analysis, antibody epitope mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with functional scramblase assays and cryo-EM structural analysis; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"42248451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Bi-allelic loss-of-function variants in TMEM63B cause a syndromic surfactant dysfunction disorder in humans with early-onset respiratory distress. Functional evaluation of splice donor and nonsense variants confirmed loss-of-function mechanism. The pulmonary phenotype parallels Tmem63b-knockout mice with neonatal respiratory failure due to impaired surfactant secretion.\",\n      \"method\": \"Functional variant evaluation (splice/nonsense variant testing), clinical genotype-phenotype correlation, parallel KO mouse comparison\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional variant evaluation supports loss-of-function; single study, limited functional detail in abstract\",\n      \"pmids\": [\"42259295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TMEM63B is expressed in the urothelium of the bladder and dorsal root ganglia sensory neurons innervating the bladder. However, conditional deletion of TMEM63B in urothelium or sensory neurons does not produce a demonstrable voiding phenotype, even under cyclophosphamide-induced stress (negative result for bladder mechanosensory function).\",\n      \"method\": \"Conditional KO mice, void-spot screening assay, immunofluorescence\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with systematic behavioral assay in two tissue-specific lines; negative result well-controlled\",\n      \"pmids\": [\"41348674\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TMEM63B is a mechanosensitive and osmosensitive cation channel and lipid scramblase that is activated by membrane stretch, hypo-osmotic stress, or changes in membrane physical properties; it localizes to the plasma membrane, lysosomes, and organelle-limiting membranes, where it mediates Ca2+ influx to drive diverse downstream processes including Ca2+-dependent K+ channel activation in cochlear hair cells, lamellar body fusion and surfactant secretion in alveolar type II cells, insulin secretion in β-cells, and trophoblast cell cycle control via nucleocytoplasmic transport; its activity is regulated post-transcriptionally by brain-specific exon 4 splicing (controlling surface expression via an ER retention/COPI signal) coupled to ADAR2-dependent A-to-I RNA editing, and is autoinhibited at rest by its C-terminal AQVLQD motif that interacts with intracellular helices, as revealed by cryo-EM structures of open and closed conformations.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TMEM63B is a mechanosensitive and osmosensitive nonselective cation channel that converts membrane physical stimuli — hypo-osmotic swelling and membrane stretch — into Ca2+ influx to drive tissue-specific physiological responses [#0, #8, #9]. In cochlear outer hair cells it serves as the inner-ear osmosensor, mediating hypo-osmolarity-induced Ca2+ entry that activates Ca2+-dependent K+ channels for regulatory volume decrease; its loss causes outer hair cell necroptosis and progressive hearing loss [#0]. The same channel activity underlies stretch-evoked Ca2+ influx that triggers lamellar body fusion and pulmonary surfactant secretion in alveolar type II cells [#6, #9], glucose-swelling-induced depolarization and insulin secretion in pancreatic β-cells [#8], and it additionally stabilizes nucleocytoplasmic transport machinery (the Ran-XPO1 complex) to permit p21 nuclear export and trophoblast proliferation [#10]. Beyond ion conduction, TMEM63B is a membrane-structure-responsive lipid scramblase that catalyzes bidirectional phospholipid translocation in response to changes in membrane curvature and thickness, a function requiring palmitoylated intracellular cysteine clusters and resolved by cryo-EM structures capturing open and closed states with a defined lipid translocation pathway [#7]. The channel is autoinhibited at rest by a C-terminal AQVLQD motif whose Leu776 packs against intracellular helices; disrupting this motif yields constitutive scrambling [#11]. Activity is further tuned post-transcriptionally by brain-specific exon 4 alternative splicing — the exon-4 isoform carries an RXR-type COPI-dependent ER retention signal limiting surface expression — coupled to ADAR2-dependent Q/R A-to-I editing that occurs almost exclusively in the exon-4-lacking isoform [#3, #4]. Heterozygous transmembrane missense variants act as gain-of-function alleles producing isotonic leak currents [#5], whereas bi-allelic loss-of-function variants cause a syndromic surfactant dysfunction disorder with neonatal respiratory failure paralleling the knockout mouse [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 2016,\n      \"claim\": \"Established the TMEM63 family as candidate osmolarity-activated channels, raising the question of whether subunits act independently or cooperatively.\",\n      \"evidence\": \"Heterologous co-expression of TMEM63A/B/C in HEK293 cells with patch-clamp\",\n      \"pmids\": [\"27045885\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inferred obligate three-subunit requirement was contradicted by later evidence that TMEM63B functions independently\", \"No native tissue context tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed TMEM63B is a plasma-membrane Ca2+-permeable channel responsive to hyperosmolarity and capable of promoting cell migration, defining it as an independent functional unit.\",\n      \"evidence\": \"Immunofluorescence, Ca2+ imaging, and wound-healing assays with overexpression in HEK293T cells\",\n      \"pmids\": [\"31243992\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single overexpression system without endogenous validation\", \"Mechanism linking channel activity to migration not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined the physiological role of TMEM63B as the inner-ear osmosensor, answering what process its channel activity serves in vivo.\",\n      \"evidence\": \"Knockout mouse, electrophysiology, Ca2+ imaging, and volume assays in outer hair cells\",\n      \"pmids\": [\"32375046\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Selectivity filter and gating residues not mapped\", \"Link from Ca2+ influx to necroptosis not mechanistically detailed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed that channel properties are post-transcriptionally tuned, answering how Ca2+ permeability and osmosensitivity are regulated in a tissue-specific manner.\",\n      \"evidence\": \"RT-PCR/sequencing, ADAR2 knockout mice, and electrophysiology in cerebellar granule neurons\",\n      \"pmids\": [\"33100268\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence in intact neural circuits not established\", \"Structural basis of Q/R-site effect on permeation unknown at the time\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Explained how alternative splicing controls surface availability, linking exon 4 to a COPI-dependent ER retention signal and to heterodimer-mediated suppression.\",\n      \"evidence\": \"Mutagenesis, surface biotinylation, co-IP, COPI binding assays, and electrophysiology\",\n      \"pmids\": [\"36496074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of isoform ratios per tissue not quantified\", \"Stoichiometry of long/short heterodimers undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected TMEM63B to human neurodevelopmental disease through gain-of-function transmembrane variants producing isotonic leak currents.\",\n      \"evidence\": \"Patch-clamp and Ca2+ imaging in Neuro2a cells plus Drosophila lethality assay\",\n      \"pmids\": [\"37421948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Channel-pore residues underlying leak not structurally localized in this study\", \"Genotype-phenotype correlation across variant positions incomplete\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified an organelle-membrane role: TMEM63B as a stretch sensor on lamellar body membranes driving surfactant and ATP release in the lung.\",\n      \"evidence\": \"Knockout mice, confocal localization, electrophysiology, surfactant/ATP release and Ca2+ imaging in AT2 cells\",\n      \"pmids\": [\"38127458\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of TMEM63A vs TMEM63B not separated\", \"Direct gating by membrane tension at the LB membrane not reconstituted\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Expanded the molecular function beyond ion conduction by demonstrating lipid scramblase activity and providing open/closed cryo-EM structures.\",\n      \"evidence\": \"Cryo-EM, scramblase assays, palmitoylation-site mutagenesis, and phospholipid distribution analysis in deficient cells\",\n      \"pmids\": [\"39424995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between ion conduction and lipid scrambling pathways not fully resolved\", \"Physiological readout of scrambling in native tissues limited\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the stretch-channel role to metabolism, showing glucose-induced swelling activates TMEM63B to promote β-cell depolarization and insulin secretion.\",\n      \"evidence\": \"Conditional knockout mice, patch-clamp, Ca2+ imaging, and insulin secretion assays\",\n      \"pmids\": [\"39985646\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coupling between swelling and channel gating in β-cells not directly measured\", \"Contribution relative to canonical KATP-dependent secretion unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Tested whether TMEM63B contributes to bladder mechanosensation, returning a well-controlled negative result that bounds its functional scope.\",\n      \"evidence\": \"Tissue-specific conditional knockouts with void-spot assays under cyclophosphamide stress\",\n      \"pmids\": [\"41348674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Possible redundancy with other mechanosensors not excluded\", \"Subthreshold or compensatory roles not assayed\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Confirmed TMEM63B as the primary stretch sensor on the AT2 plasma membrane and dissociated mechanical sensing from downstream ATP signaling.\",\n      \"evidence\": \"Conditional knockout, patch-clamp, Ca2+ imaging, and LB fusion/surfactant assays in AT2 cells\",\n      \"pmids\": [\"42067058\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular force-transduction mechanism not defined\", \"Integration with the earlier LB-membrane localization model not fully reconciled\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Uncovered a non-channel role in nucleocytoplasmic transport, linking TMEM63B loss to Ran/XPO1 destabilization and impaired p21 export in trophoblasts.\",\n      \"evidence\": \"Knockout mice, co-IP of Ran-XPO1, immunofluorescence shuttling, and trophoblast proliferation assays\",\n      \"pmids\": [\"42259794\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which a membrane channel stabilizes Ran is unresolved\", \"Single lab; direct physical interaction not established\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined the autoinhibitory switch, showing the C-terminal AQVLQD motif (Leu776) holds TMEM63B inactive via intracellular helix contacts.\",\n      \"evidence\": \"Mutagenesis/truncations, scramblase assays, and cryo-EM structural analysis\",\n      \"pmids\": [\"42248451\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How physiological stimuli relieve autoinhibition not shown\", \"Effect of the motif on ion conduction versus scrambling not separated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Established a recessive human disease link, showing bi-allelic loss-of-function variants cause syndromic surfactant dysfunction matching the knockout phenotype.\",\n      \"evidence\": \"Functional splice/nonsense variant evaluation and clinical genotype-phenotype correlation with KO mouse comparison\",\n      \"pmids\": [\"42259295\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Limited functional detail beyond loss-of-function confirmation\", \"Spectrum of biallelic phenotypes not fully delineated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single protein partitions between ion conduction, lipid scrambling, and a non-channel role in nucleocytoplasmic transport — and how stimulus-specific relief of C-terminal autoinhibition selects among these outputs — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model coupling mechanosensing to choice of ion vs lipid output\", \"Mechanism connecting a membrane channel to Ran/XPO1 stability unknown\", \"Stimulus-to-gating transduction not reconstituted in vitro\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2, 8, 9]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 6, 8, 9]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [7, 11]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 7, 9]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 8]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 12]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ADAR2\", \"Ran\", \"XPO1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}