{"gene":"TMC2","run_date":"2026-04-28T21:42:59","timeline":{"discoveries":[{"year":2013,"finding":"TMC1 and TMC2 are components of the mechanosensitive ion channel in inner ear hair cells: cells expressing TMC2 alone had high calcium permeability and large single-channel currents; cells with TMC1 and TMC2 together showed a broad range of single-channel currents suggesting heteromeric assemblies; mutant TMC1 reduced calcium permeability and single-channel conductance.","method":"Whole-cell and single-channel patch-clamp recordings from mouse hair cells expressing Tmc1, Tmc2, or mutant Tmc1","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 — direct electrophysiology with single-channel resolution, multiple genotypes, replicated across labs","pmids":["23871232"],"is_preprint":false},{"year":2015,"finding":"TMC1 and TMC2 localize to stereocilia tips (the site of mechanotransduction) in developing hair cells, transitioning from along the full length of immature stereocilia to predominantly tip localization as hair cells mature; both are absent from the tallest stereocilia row where MET activity is undetectable.","method":"Live imaging and immunofluorescence of fluorescently tagged TMC1-mCherry and TMC2-AcGFP knock-in mice; functional rescue of MET currents in Tmc1Δ/Δ;Tmc2Δ/Δ mice confirmed tag functionality","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — direct subcellular localization with functional validation by MET current rescue in double-KO mice","pmids":["26321635"],"is_preprint":false},{"year":2014,"finding":"PCDH15 (tip-link protein protocadherin 15) directly interacts with TMC1 and TMC2; the interaction requires the cytoplasmic CD1 or CD3 domains of PCDH15 and the N-terminal region of TMC2; overexpression of the TMC2a N-terminus in zebrafish hair cells mislocalizes PCDH15 and reduces mechanosensitive responses.","method":"Membrane-based yeast two-hybrid screen, yeast two-hybrid assay, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal two-hybrid plus Co-IP in mouse and zebrafish, functional consequence in vivo","pmids":["25114259"],"is_preprint":false},{"year":2017,"finding":"CIB2 (calcium and integrin-binding protein 2) physically interacts with TMC1 and TMC2, and this interaction is disrupted by deafness-causing CIB2 mutations; CIB2 is required for normal mechanotransducer channel operation in auditory hair cells.","method":"Co-immunoprecipitation; characterization of Cib2 knockout and Cib2 deafness-mutation knock-in mouse lines with MET current recordings","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, KO mouse with MET recording, human deafness mutation disrupts interaction","pmids":["28663585"],"is_preprint":false},{"year":2019,"finding":"TMC2 (budgerigar MuTMC2) is a pore-forming subunit of a mechanosensitive ion channel: purified, liposome-reconstituted MuTMC2 possesses ion channel activity and responds to mechanical pressure applied to proteoliposomes.","method":"Heterologous expression in insect cells, protein purification, liposome reconstitution, electrophysiology of proteoliposomes with applied pressure","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in vitro with mechanosensitivity demonstrated directly","pmids":["31761710"],"is_preprint":false},{"year":2017,"finding":"TMC2 modifies permeation and pharmacology of the MET channel pore in neonatal cochlear outer hair cells: in the presence of TMC2, the channel blocker dihydrostreptomycin has lower affinity both extracellularly and intracellularly, indicating TMC2 contributes to pore-forming properties of the immature MET channel.","method":"MET current recordings from Tmc2 knockout mouse outer hair cells with pharmacological block by dihydrostreptomycin","journal":"Frontiers in molecular neuroscience","confidence":"High","confidence_rationale":"Tier 2 — direct electrophysiology in KO vs. wildtype with pharmacological dissection, functional pore contribution established","pmids":["29093662"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structure of the C. elegans TMC-2 complex reveals it as a homodimer containing two TMC-2 pore-forming subunits, the calcium and integrin binding protein CALM-1, and the transmembrane inner ear protein TMIE; conserved protein-lipid interactions and a π-helical structural motif in pore-forming helices suggest a mechanism for mechanosensory transduction.","method":"Single-particle cryo-electron microscopy of native TMC-2 complex isolated from C. elegans","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — high-resolution cryo-EM structure of native complex with mechanistic interpretation","pmids":["38354260"],"is_preprint":false},{"year":2025,"finding":"Full-length mouse TMC2, when driven to the plasma membrane via a Fyn lipidation tag, functions as a mechanosensitive channel on its own; TMIE robustly stimulates TMC2 channel activity by modulating gating, and TMIE palmitoylation at C76/C77 is required for this stimulation. TMC2+TMIE forms 24 pS single channels with biophysical and pharmacological properties matching native MET channels.","method":"Heterologous expression in mammalian cells with Fyn lipidation tag for membrane targeting, patch-clamp electrophysiology, TMIE palmitoylation site mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct functional reconstitution in heterologous cells, mutagenesis of gating modifier, single-channel characterization","pmids":["39999170"],"is_preprint":false},{"year":2018,"finding":"TMC2 can partially substitute for TMC1 in vestibular hair cells (restoring sensory transduction and balance), but cannot fully substitute for TMC1 in mature cochlear hair cells (no auditory rescue), demonstrating distinct functional requirements for TMC1 vs. TMC2 in different hair cell populations.","method":"Cre-inducible Tmc2 knock-in mouse crossed with Tmc1 KO; sensory transduction recordings, auditory brainstem responses, vestibular behavioral assays","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis/rescue experiment with electrophysiology and behavioral readouts in multiple hair cell types","pmids":["30108254","30108230"],"is_preprint":false},{"year":2025,"finding":"TMC1 and TMC2 function as cholesterol-regulated lipid scramblases that facilitate phospholipid translocation across membrane bilayers; this activity modulates plasma membrane asymmetry (phosphatidylserine externalization) in murine auditory hair cells, and deafness-causing TMC1 mutations enhance scramblase activity.","method":"Reconstituted proteoliposomes, molecular dynamics simulations, phosphatidylserine externalization assay in murine auditory hair cells","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 method (reconstitution + MD) but single preprint study, not yet peer-reviewed","pmids":["40631239"],"is_preprint":true},{"year":2024,"finding":"TMC1 and TMC2 act as mechanosensitive scramblases in stereocilia: scramblase activity depends on the MET channel being open, as demonstrated by developmental, genetic, electrophysiological, and pharmacological approaches using a membrane viscosity sensor (BODIPY 1c).","method":"Fluorescent membrane viscosity sensor (BODIPY 1c), pharmacological MET channel blockade, genetic KO of Tmc1/Tmc2, electrophysiology in inner ear hair cells","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 method but preprint, single lab, novel activity not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"TMC2 is a pore-forming subunit of the mechanosensitive mechanotransduction (MET) channel in inner ear hair cells: it forms heteromeric assemblies with TMC1 at stereocilia tips, interacts directly with the tip-link protein PCDH15 and the auxiliary protein CIB2, confers high calcium permeability and large single-channel conductance to the immature MET channel, is potently stimulated by TMIE (which requires palmitoylation), and additionally functions as a cholesterol-regulated lipid scramblase that modulates membrane phospholipid asymmetry in auditory hair cells."},"narrative":{"teleology":[{"year":2013,"claim":"Establishing that TMC proteins are channel components rather than mere trafficking factors resolved the identity of the long-sought hair cell MET channel pore: TMC2-expressing hair cells exhibited high Ca²⁺ permeability and large single-channel conductance, and TMC1/TMC2 co-expression produced a range of conductances consistent with heteromeric assemblies.","evidence":"Whole-cell and single-channel patch-clamp recordings from mouse hair cells of various Tmc genotypes","pmids":["23871232"],"confidence":"High","gaps":["Whether TMC2 directly forms the pore or acts as an obligate accessory subunit was not resolved by cellular electrophysiology alone","Stoichiometry of TMC1–TMC2 heteromeric assemblies remained undefined"]},{"year":2014,"claim":"Identifying a direct physical link between the tip-link protein PCDH15 and TMC2 established the molecular basis for force transmission from the tip link to the channel complex.","evidence":"Yeast two-hybrid, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout","pmids":["25114259"],"confidence":"High","gaps":["Structural details of the PCDH15–TMC2 interface were unknown","Whether PCDH15 binding directly gates TMC2 or simply anchors it remained unclear"]},{"year":2015,"claim":"Demonstrating that TMC2 localizes to stereocilia tips — the precise site of mechanotransduction — provided spatial evidence consistent with a direct channel role and revealed developmental redistribution from shaft to tip.","evidence":"Live imaging and immunofluorescence of TMC2-AcGFP knock-in mice with MET current rescue in Tmc1/Tmc2 double-KO","pmids":["26321635"],"confidence":"High","gaps":["Mechanism controlling TMC2 trafficking to stereocilia tips was not identified","Why TMC2 is excluded from the tallest stereocilia row was unexplained"]},{"year":2017,"claim":"Two advances in 2017 clarified TMC2's pore contribution and its auxiliary protein network: TMC2 altered intracellular and extracellular drug-binding sites in the MET pore, and CIB2 was identified as a direct TMC2 interactor required for MET channel function, with deafness mutations disrupting the interaction.","evidence":"MET recordings from Tmc2 KO vs. WT with dihydrostreptomycin block; co-immunoprecipitation and Cib2 KO/knock-in mice with MET recordings","pmids":["29093662","28663585"],"confidence":"High","gaps":["How CIB2 modulates TMC2 gating at a structural level was unknown","Whether CIB2's role is Ca²⁺-dependent regulation or structural assembly was not resolved"]},{"year":2018,"claim":"Genetic rescue experiments revealed that TMC2 can substitute for TMC1 in vestibular but not cochlear hair cells, demonstrating that TMC1 and TMC2 fulfill non-redundant roles across sensory epithelia.","evidence":"Cre-inducible Tmc2 knock-in in Tmc1 KO mice with ABR, VsEP, and MET recordings","pmids":["30108254","30108230"],"confidence":"High","gaps":["Molecular basis for cochlear-specific TMC1 requirement (e.g., conductance, tonotopic tuning) was not determined","Whether TMC2 is actively silenced in mature cochlear hair cells or simply down-regulated was unclear"]},{"year":2019,"claim":"Reconstitution of purified budgerigar TMC2 into liposomes provided definitive proof that TMC2 itself is a mechanosensitive pore-forming protein, independent of other hair cell components.","evidence":"Heterologous expression in insect cells, purification, liposome reconstitution, electrophysiology under applied pressure","pmids":["31761710"],"confidence":"High","gaps":["Reconstituted channel properties differed from native MET channels, suggesting missing auxiliary subunits","Lipid requirements for mechanosensitivity were not systematically explored"]},{"year":2024,"claim":"The cryo-EM structure of the C. elegans TMC-2 complex revealed a homodimeric architecture with two TMC-2 pore subunits, CALM-1 (CIB2 ortholog), and TMIE, providing the first atomic-level view of the assembled mechanotransduction complex and identifying conserved protein–lipid interactions and a π-helical motif in pore helices.","evidence":"Single-particle cryo-EM of native TMC-2 complex from C. elegans","pmids":["38354260"],"confidence":"High","gaps":["Structure was captured in a closed/resting state; an open-state structure is needed to understand gating conformational changes","Whether mammalian TMC2 adopts the same dimeric stoichiometry was not verified"]},{"year":2025,"claim":"Heterologous reconstitution of mouse TMC2 with TMIE in mammalian cells showed that TMIE is the key gating stimulator of TMC2, requiring palmitoylation at C76/C77, and that the TMC2+TMIE channel recapitulates native MET biophysics (24 pS conductance).","evidence":"Patch-clamp of Fyn-tagged TMC2 ± TMIE in HEK cells, palmitoylation-site mutagenesis","pmids":["39999170"],"confidence":"High","gaps":["Whether PCDH15 further modulates TMC2+TMIE gating was not tested in this system","Role of CIB2 in the heterologous reconstitution was not assessed"]},{"year":2025,"claim":"Beyond ion conduction, TMC2 was shown to function as a cholesterol-regulated lipid scramblase that modulates phospholipid asymmetry in hair cell membranes, linking channel activity to membrane remodeling.","evidence":"Reconstituted proteoliposome scramblase assays, molecular dynamics simulations, phosphatidylserine externalization in murine hair cells (preprint)","pmids":["40631239"],"confidence":"Medium","gaps":["Preprint findings have not been peer-reviewed or independently replicated","Physiological significance of scramblase activity for hearing or hair cell survival is undefined","Whether scramblase and ion channel activities occur through the same pore path is unknown"]},{"year":null,"claim":"Key unresolved questions include the open-state structure of the mammalian TMC2 channel complex, the molecular basis for cochlear-specific TMC1 dependence versus vestibular TMC2 sufficiency, and whether TMC2 scramblase activity has physiological relevance for hair cell function and survival.","evidence":"","pmids":[],"confidence":"High","gaps":["No open-state structural model for mammalian TMC2","Mechanism of tonotopic or epithelium-specific TMC1 versus TMC2 functional divergence is undefined","Physiological role of TMC2 scramblase activity in vivo is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,4,5,7]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[4,7]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,7]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[0,5,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,4,7]}],"complexes":["TMC MET channel complex (TMC2-TMIE-CIB2/CALM-1)"],"partners":["TMC1","PCDH15","CIB2","TMIE"],"other_free_text":[]},"mechanistic_narrative":"TMC2 is a pore-forming subunit of the mechanotransduction (MET) channel in inner ear hair cells, where it localizes to stereocilia tips and confers high calcium permeability, large single-channel conductance, and altered pharmacological sensitivity to the immature channel complex [PMID:23871232, PMID:26321635, PMID:29093662]. Purified TMC2 reconstituted into proteoliposomes forms a mechanosensitive ion channel, and in heterologous cells TMC2 paired with the auxiliary subunit TMIE (whose palmitoylation is required for gating stimulation) recapitulates native MET channel biophysics [PMID:31761710, PMID:39999170]. TMC2 assembles as a homodimer in complex with CALM-1/CIB2 and TMIE, and interacts directly with the tip-link protein PCDH15 via its N-terminal domain, coupling mechanical force to channel gating [PMID:38354260, PMID:25114259, PMID:28663585]. TMC2 can rescue vestibular but not auditory mechanotransduction in the absence of TMC1, indicating non-redundant roles across hair cell populations [PMID:30108254]."},"prefetch_data":{"uniprot":{"accession":"Q8TDI7","full_name":"Transmembrane channel-like protein 2","aliases":["Transmembrane cochlear-expressed protein 2"],"length_aa":906,"mass_kda":102.6,"function":"Pore-forming subunit of the mechanotransducer (MET) non-selective cation channel complex located at the tips of stereocilia of cochlear hair cells and that mediates sensory transduction in the auditory system (PubMed:11850618). The MET complex is composed of two dimeric pore-forming ion-conducting transmembrane TMC (TMC1 or TMC2) subunits, and aided by several auxiliary proteins including LHFPL5, TMIE, CIB2/3 and TOMT, and the tip-link PCDH15. MET channel is activated by tension in the tip-link extending from the side wall of one stereocilium to the tip of the adjacent shorter stereocilium, where the channel is located (By similarity). TMC2 MET channel is highly permeable to calcium and likely transports monovalent cations. Also involved in vestibular hair cell transduction current of the mammalian inner ear (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8TDI7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TMC2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TMC2","total_profiled":1310},"omim":[{"mim_id":"617198","title":"TRANSMEMBRANE CHANNEL-LIKE PROTEIN 7; TMC7","url":"https://www.omim.org/entry/617198"},{"mim_id":"617197","title":"TRANSMEMBRANE CHANNEL-LIKE PROTEIN 5; TMC5","url":"https://www.omim.org/entry/617197"},{"mim_id":"617196","title":"TRANSMEMBRANE CHANNEL-LIKE PROTEIN 3; TMC3","url":"https://www.omim.org/entry/617196"},{"mim_id":"617181","title":"TRANSMEMBRANE CHANNEL-LIKE PROTEIN 4; TMC4","url":"https://www.omim.org/entry/617181"},{"mim_id":"606707","title":"TRANSMEMBRANE CHANNEL-LIKE PROTEIN 2; TMC2","url":"https://www.omim.org/entry/606707"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":2.7}],"url":"https://www.proteinatlas.org/search/TMC2"},"hgnc":{"alias_symbol":["dJ686C3.3"],"prev_symbol":["C20orf145"]},"alphafold":{"accession":"Q8TDI7","domains":[{"cath_id":"-","chopping":"236-283_326-544_574-720","consensus_level":"medium","plddt":81.0164,"start":236,"end":720},{"cath_id":"1.20.5","chopping":"776-807","consensus_level":"medium","plddt":76.7606,"start":776,"end":807}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDI7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDI7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDI7-F1-predicted_aligned_error_v6.png","plddt_mean":67.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TMC2","jax_strain_url":"https://www.jax.org/strain/search?query=TMC2"},"sequence":{"accession":"Q8TDI7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TDI7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TDI7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDI7"}},"corpus_meta":[{"pmid":"23871232","id":"PMC_23871232","title":"TMC1 and TMC2 are components of the mechanotransduction channel in hair cells of the mammalian inner ear.","date":"2013","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/23871232","citation_count":340,"is_preprint":false},{"pmid":"26321635","id":"PMC_26321635","title":"TMC1 and TMC2 Localize at the Site of Mechanotransduction in Mammalian Inner Ear Hair Cell Stereocilia.","date":"2015","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/26321635","citation_count":154,"is_preprint":false},{"pmid":"28663585","id":"PMC_28663585","title":"CIB2 interacts with TMC1 and TMC2 and is essential for mechanotransduction in auditory hair cells.","date":"2017","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/28663585","citation_count":146,"is_preprint":false},{"pmid":"25114259","id":"PMC_25114259","title":"Tip-link protein protocadherin 15 interacts with transmembrane channel-like proteins TMC1 and TMC2.","date":"2014","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/25114259","citation_count":137,"is_preprint":false},{"pmid":"31761710","id":"PMC_31761710","title":"TMC1 and TMC2 Proteins Are Pore-Forming Subunits of Mechanosensitive Ion Channels.","date":"2019","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/31761710","citation_count":128,"is_preprint":false},{"pmid":"18259073","id":"PMC_18259073","title":"TMC1 but not TMC2 is responsible for autosomal recessive nonsyndromic hearing impairment in Tunisian families.","date":"2008","source":"Audiology & neuro-otology","url":"https://pubmed.ncbi.nlm.nih.gov/18259073","citation_count":52,"is_preprint":false},{"pmid":"29093662","id":"PMC_29093662","title":"TMC2 Modifies Permeation Properties of the Mechanoelectrical Transducer Channel in Early Postnatal Mouse Cochlear Outer Hair Cells.","date":"2017","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/29093662","citation_count":30,"is_preprint":false},{"pmid":"38354260","id":"PMC_38354260","title":"The structure of the Caenorhabditis elegans TMC-2 complex suggests roles of lipid-mediated subunit contacts in mechanosensory transduction.","date":"2024","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/38354260","citation_count":27,"is_preprint":false},{"pmid":"30108254","id":"PMC_30108254","title":"Transgenic Tmc2 expression preserves inner ear hair cells and vestibular function in mice lacking Tmc1.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30108254","citation_count":23,"is_preprint":false},{"pmid":"30108230","id":"PMC_30108230","title":"Tmc2 expression partially restores auditory function in a mouse model of DFNB7/B11 deafness caused by loss of Tmc1 function.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30108230","citation_count":23,"is_preprint":false},{"pmid":"39999170","id":"PMC_39999170","title":"Ectopic mouse TMC1 and TMC2 alone form mechanosensitive channels that are potently modulated by TMIE.","date":"2025","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/39999170","citation_count":6,"is_preprint":false},{"pmid":"40280017","id":"PMC_40280017","title":"TMC1 and TMC2 function as the mechano-electrical transduction ion channel in hearing.","date":"2025","source":"Current opinion in neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/40280017","citation_count":4,"is_preprint":false},{"pmid":"37645790","id":"PMC_37645790","title":"Structure of C. elegans TMC-2 complex suggests roles of lipid-mediated subunit contacts in mechanosensory transduction.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37645790","citation_count":3,"is_preprint":false},{"pmid":"40631239","id":"PMC_40631239","title":"TMC1 and TMC2 are cholesterol-dependent scramblases that regulate membrane homeostasis in auditory hair cells.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40631239","citation_count":1,"is_preprint":false},{"pmid":"36568409","id":"PMC_36568409","title":"Functional consequences of Genetics variant in TMC1 and TMC2 within a United Arab Emirates family with Pre-lingual hearing loss.","date":"2022","source":"Saudi journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36568409","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.09.27.615395","title":"Dynamic modulation of auditory hair cell stereocilia membrane mechanics by the scrambling mechanotransduction complex","date":"2024-09-30","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.27.615395","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.05.24.595729","title":"Molecular Specializations Underlying Phenotypic Differences in Inner Ear Hair Cells of Zebrafish and Mice","date":"2024-05-26","source":"bioRxiv","url":"https://doi.org/10.1101/2024.05.24.595729","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9571,"output_tokens":2686,"usd":0.034501},"stage2":{"model":"claude-opus-4-6","input_tokens":6007,"output_tokens":2695,"usd":0.146115},"total_usd":0.180616,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"TMC1 and TMC2 are components of the mechanosensitive ion channel in inner ear hair cells: cells expressing TMC2 alone had high calcium permeability and large single-channel currents; cells with TMC1 and TMC2 together showed a broad range of single-channel currents suggesting heteromeric assemblies; mutant TMC1 reduced calcium permeability and single-channel conductance.\",\n      \"method\": \"Whole-cell and single-channel patch-clamp recordings from mouse hair cells expressing Tmc1, Tmc2, or mutant Tmc1\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct electrophysiology with single-channel resolution, multiple genotypes, replicated across labs\",\n      \"pmids\": [\"23871232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TMC1 and TMC2 localize to stereocilia tips (the site of mechanotransduction) in developing hair cells, transitioning from along the full length of immature stereocilia to predominantly tip localization as hair cells mature; both are absent from the tallest stereocilia row where MET activity is undetectable.\",\n      \"method\": \"Live imaging and immunofluorescence of fluorescently tagged TMC1-mCherry and TMC2-AcGFP knock-in mice; functional rescue of MET currents in Tmc1Δ/Δ;Tmc2Δ/Δ mice confirmed tag functionality\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization with functional validation by MET current rescue in double-KO mice\",\n      \"pmids\": [\"26321635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PCDH15 (tip-link protein protocadherin 15) directly interacts with TMC1 and TMC2; the interaction requires the cytoplasmic CD1 or CD3 domains of PCDH15 and the N-terminal region of TMC2; overexpression of the TMC2a N-terminus in zebrafish hair cells mislocalizes PCDH15 and reduces mechanosensitive responses.\",\n      \"method\": \"Membrane-based yeast two-hybrid screen, yeast two-hybrid assay, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal two-hybrid plus Co-IP in mouse and zebrafish, functional consequence in vivo\",\n      \"pmids\": [\"25114259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CIB2 (calcium and integrin-binding protein 2) physically interacts with TMC1 and TMC2, and this interaction is disrupted by deafness-causing CIB2 mutations; CIB2 is required for normal mechanotransducer channel operation in auditory hair cells.\",\n      \"method\": \"Co-immunoprecipitation; characterization of Cib2 knockout and Cib2 deafness-mutation knock-in mouse lines with MET current recordings\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, KO mouse with MET recording, human deafness mutation disrupts interaction\",\n      \"pmids\": [\"28663585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TMC2 (budgerigar MuTMC2) is a pore-forming subunit of a mechanosensitive ion channel: purified, liposome-reconstituted MuTMC2 possesses ion channel activity and responds to mechanical pressure applied to proteoliposomes.\",\n      \"method\": \"Heterologous expression in insect cells, protein purification, liposome reconstitution, electrophysiology of proteoliposomes with applied pressure\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in vitro with mechanosensitivity demonstrated directly\",\n      \"pmids\": [\"31761710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"TMC2 modifies permeation and pharmacology of the MET channel pore in neonatal cochlear outer hair cells: in the presence of TMC2, the channel blocker dihydrostreptomycin has lower affinity both extracellularly and intracellularly, indicating TMC2 contributes to pore-forming properties of the immature MET channel.\",\n      \"method\": \"MET current recordings from Tmc2 knockout mouse outer hair cells with pharmacological block by dihydrostreptomycin\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct electrophysiology in KO vs. wildtype with pharmacological dissection, functional pore contribution established\",\n      \"pmids\": [\"29093662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structure of the C. elegans TMC-2 complex reveals it as a homodimer containing two TMC-2 pore-forming subunits, the calcium and integrin binding protein CALM-1, and the transmembrane inner ear protein TMIE; conserved protein-lipid interactions and a π-helical structural motif in pore-forming helices suggest a mechanism for mechanosensory transduction.\",\n      \"method\": \"Single-particle cryo-electron microscopy of native TMC-2 complex isolated from C. elegans\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution cryo-EM structure of native complex with mechanistic interpretation\",\n      \"pmids\": [\"38354260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Full-length mouse TMC2, when driven to the plasma membrane via a Fyn lipidation tag, functions as a mechanosensitive channel on its own; TMIE robustly stimulates TMC2 channel activity by modulating gating, and TMIE palmitoylation at C76/C77 is required for this stimulation. TMC2+TMIE forms 24 pS single channels with biophysical and pharmacological properties matching native MET channels.\",\n      \"method\": \"Heterologous expression in mammalian cells with Fyn lipidation tag for membrane targeting, patch-clamp electrophysiology, TMIE palmitoylation site mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct functional reconstitution in heterologous cells, mutagenesis of gating modifier, single-channel characterization\",\n      \"pmids\": [\"39999170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TMC2 can partially substitute for TMC1 in vestibular hair cells (restoring sensory transduction and balance), but cannot fully substitute for TMC1 in mature cochlear hair cells (no auditory rescue), demonstrating distinct functional requirements for TMC1 vs. TMC2 in different hair cell populations.\",\n      \"method\": \"Cre-inducible Tmc2 knock-in mouse crossed with Tmc1 KO; sensory transduction recordings, auditory brainstem responses, vestibular behavioral assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis/rescue experiment with electrophysiology and behavioral readouts in multiple hair cell types\",\n      \"pmids\": [\"30108254\", \"30108230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TMC1 and TMC2 function as cholesterol-regulated lipid scramblases that facilitate phospholipid translocation across membrane bilayers; this activity modulates plasma membrane asymmetry (phosphatidylserine externalization) in murine auditory hair cells, and deafness-causing TMC1 mutations enhance scramblase activity.\",\n      \"method\": \"Reconstituted proteoliposomes, molecular dynamics simulations, phosphatidylserine externalization assay in murine auditory hair cells\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 method (reconstitution + MD) but single preprint study, not yet peer-reviewed\",\n      \"pmids\": [\"40631239\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TMC1 and TMC2 act as mechanosensitive scramblases in stereocilia: scramblase activity depends on the MET channel being open, as demonstrated by developmental, genetic, electrophysiological, and pharmacological approaches using a membrane viscosity sensor (BODIPY 1c).\",\n      \"method\": \"Fluorescent membrane viscosity sensor (BODIPY 1c), pharmacological MET channel blockade, genetic KO of Tmc1/Tmc2, electrophysiology in inner ear hair cells\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 method but preprint, single lab, novel activity not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TMC2 is a pore-forming subunit of the mechanosensitive mechanotransduction (MET) channel in inner ear hair cells: it forms heteromeric assemblies with TMC1 at stereocilia tips, interacts directly with the tip-link protein PCDH15 and the auxiliary protein CIB2, confers high calcium permeability and large single-channel conductance to the immature MET channel, is potently stimulated by TMIE (which requires palmitoylation), and additionally functions as a cholesterol-regulated lipid scramblase that modulates membrane phospholipid asymmetry in auditory hair cells.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TMC2 is a pore-forming subunit of the mechanotransduction (MET) channel in inner ear hair cells, where it localizes to stereocilia tips and confers high calcium permeability, large single-channel conductance, and altered pharmacological sensitivity to the immature channel complex [PMID:23871232, PMID:26321635, PMID:29093662]. Purified TMC2 reconstituted into proteoliposomes forms a mechanosensitive ion channel, and in heterologous cells TMC2 paired with the auxiliary subunit TMIE (whose palmitoylation is required for gating stimulation) recapitulates native MET channel biophysics [PMID:31761710, PMID:39999170]. TMC2 assembles as a homodimer in complex with CALM-1/CIB2 and TMIE, and interacts directly with the tip-link protein PCDH15 via its N-terminal domain, coupling mechanical force to channel gating [PMID:38354260, PMID:25114259, PMID:28663585]. TMC2 can rescue vestibular but not auditory mechanotransduction in the absence of TMC1, indicating non-redundant roles across hair cell populations [PMID:30108254].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Establishing that TMC proteins are channel components rather than mere trafficking factors resolved the identity of the long-sought hair cell MET channel pore: TMC2-expressing hair cells exhibited high Ca²⁺ permeability and large single-channel conductance, and TMC1/TMC2 co-expression produced a range of conductances consistent with heteromeric assemblies.\",\n      \"evidence\": \"Whole-cell and single-channel patch-clamp recordings from mouse hair cells of various Tmc genotypes\",\n      \"pmids\": [\"23871232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether TMC2 directly forms the pore or acts as an obligate accessory subunit was not resolved by cellular electrophysiology alone\",\n        \"Stoichiometry of TMC1–TMC2 heteromeric assemblies remained undefined\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying a direct physical link between the tip-link protein PCDH15 and TMC2 established the molecular basis for force transmission from the tip link to the channel complex.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout\",\n      \"pmids\": [\"25114259\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural details of the PCDH15–TMC2 interface were unknown\",\n        \"Whether PCDH15 binding directly gates TMC2 or simply anchors it remained unclear\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrating that TMC2 localizes to stereocilia tips — the precise site of mechanotransduction — provided spatial evidence consistent with a direct channel role and revealed developmental redistribution from shaft to tip.\",\n      \"evidence\": \"Live imaging and immunofluorescence of TMC2-AcGFP knock-in mice with MET current rescue in Tmc1/Tmc2 double-KO\",\n      \"pmids\": [\"26321635\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism controlling TMC2 trafficking to stereocilia tips was not identified\",\n        \"Why TMC2 is excluded from the tallest stereocilia row was unexplained\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Two advances in 2017 clarified TMC2's pore contribution and its auxiliary protein network: TMC2 altered intracellular and extracellular drug-binding sites in the MET pore, and CIB2 was identified as a direct TMC2 interactor required for MET channel function, with deafness mutations disrupting the interaction.\",\n      \"evidence\": \"MET recordings from Tmc2 KO vs. WT with dihydrostreptomycin block; co-immunoprecipitation and Cib2 KO/knock-in mice with MET recordings\",\n      \"pmids\": [\"29093662\", \"28663585\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How CIB2 modulates TMC2 gating at a structural level was unknown\",\n        \"Whether CIB2's role is Ca²⁺-dependent regulation or structural assembly was not resolved\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Genetic rescue experiments revealed that TMC2 can substitute for TMC1 in vestibular but not cochlear hair cells, demonstrating that TMC1 and TMC2 fulfill non-redundant roles across sensory epithelia.\",\n      \"evidence\": \"Cre-inducible Tmc2 knock-in in Tmc1 KO mice with ABR, VsEP, and MET recordings\",\n      \"pmids\": [\"30108254\", \"30108230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular basis for cochlear-specific TMC1 requirement (e.g., conductance, tonotopic tuning) was not determined\",\n        \"Whether TMC2 is actively silenced in mature cochlear hair cells or simply down-regulated was unclear\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Reconstitution of purified budgerigar TMC2 into liposomes provided definitive proof that TMC2 itself is a mechanosensitive pore-forming protein, independent of other hair cell components.\",\n      \"evidence\": \"Heterologous expression in insect cells, purification, liposome reconstitution, electrophysiology under applied pressure\",\n      \"pmids\": [\"31761710\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Reconstituted channel properties differed from native MET channels, suggesting missing auxiliary subunits\",\n        \"Lipid requirements for mechanosensitivity were not systematically explored\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The cryo-EM structure of the C. elegans TMC-2 complex revealed a homodimeric architecture with two TMC-2 pore subunits, CALM-1 (CIB2 ortholog), and TMIE, providing the first atomic-level view of the assembled mechanotransduction complex and identifying conserved protein–lipid interactions and a π-helical motif in pore helices.\",\n      \"evidence\": \"Single-particle cryo-EM of native TMC-2 complex from C. elegans\",\n      \"pmids\": [\"38354260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure was captured in a closed/resting state; an open-state structure is needed to understand gating conformational changes\",\n        \"Whether mammalian TMC2 adopts the same dimeric stoichiometry was not verified\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Heterologous reconstitution of mouse TMC2 with TMIE in mammalian cells showed that TMIE is the key gating stimulator of TMC2, requiring palmitoylation at C76/C77, and that the TMC2+TMIE channel recapitulates native MET biophysics (24 pS conductance).\",\n      \"evidence\": \"Patch-clamp of Fyn-tagged TMC2 ± TMIE in HEK cells, palmitoylation-site mutagenesis\",\n      \"pmids\": [\"39999170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether PCDH15 further modulates TMC2+TMIE gating was not tested in this system\",\n        \"Role of CIB2 in the heterologous reconstitution was not assessed\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Beyond ion conduction, TMC2 was shown to function as a cholesterol-regulated lipid scramblase that modulates phospholipid asymmetry in hair cell membranes, linking channel activity to membrane remodeling.\",\n      \"evidence\": \"Reconstituted proteoliposome scramblase assays, molecular dynamics simulations, phosphatidylserine externalization in murine hair cells (preprint)\",\n      \"pmids\": [\"40631239\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint findings have not been peer-reviewed or independently replicated\",\n        \"Physiological significance of scramblase activity for hearing or hair cell survival is undefined\",\n        \"Whether scramblase and ion channel activities occur through the same pore path is unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the open-state structure of the mammalian TMC2 channel complex, the molecular basis for cochlear-specific TMC1 dependence versus vestibular TMC2 sufficiency, and whether TMC2 scramblase activity has physiological relevance for hair cell function and survival.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No open-state structural model for mammalian TMC2\",\n        \"Mechanism of tonotopic or epithelium-specific TMC1 versus TMC2 functional divergence is undefined\",\n        \"Physiological role of TMC2 scramblase activity in vivo is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 4, 5, 7]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [4, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 7]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [0, 5, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 4, 7]}\n    ],\n    \"complexes\": [\n      \"TMC MET channel complex (TMC2-TMIE-CIB2/CALM-1)\"\n    ],\n    \"partners\": [\n      \"TMC1\",\n      \"PCDH15\",\n      \"CIB2\",\n      \"TMIE\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}