{"gene":"USH1C","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2000,"finding":"USH1C encodes harmonin, a PDZ domain-containing protein expressed exclusively in inner ear sensory hair cells (not in the eye for certain isoforms). Some isoforms contain an additional coiled-coil domain and proline/serine-rich region. Splice-site, frameshift, and VNTR mutations in USH1C cause Usher syndrome type 1C.","method":"Subtracted mouse cDNA library, RT-PCR expression analysis, mutation identification in patients","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — foundational identification paper with multiple orthogonal methods, independently replicated across subsequent studies","pmids":["10973247"],"is_preprint":false},{"year":2002,"finding":"Harmonin-b is an F-actin-bundling protein that binds directly to cadherin 23 and myosin VIIa, forming a functional unit that anchors cadherin 23 to stereocilia microfilaments and shapes the hair bundle. Harmonin b is absent from disorganized hair bundles of myosin VIIa mutant mice, suggesting myosin VIIa conveys harmonin b along the actin core of developing stereocilia.","method":"Co-immunoprecipitation, in vitro binding assays, F-actin bundling assay, immunolocalization in wild-type and myosin VIIa mutant mice","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, actin bundling assay, in vivo localization in mutant mice), independently corroborated by multiple subsequent studies","pmids":["12485990"],"is_preprint":false},{"year":2002,"finding":"Two PDZ domains in harmonin interact with two complementary binding surfaces in the CDH23 cytoplasmic domain, forming a protein complex. CDH23 and harmonin are co-expressed in stereocilia of hair cells. One CDH23 binding surface is disrupted by sequences from an alternatively spliced exon expressed in the ear but not the retina.","method":"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, immunolocalization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding assays with domain mapping, replicated by multiple independent labs","pmids":["12407180"],"is_preprint":false},{"year":2003,"finding":"SANS (USH1G protein) associates with harmonin via its C-terminal class I PDZ-binding motif, placing SANS in the same USH1 protein network as harmonin, myosin VIIa, and cadherin 23.","method":"Co-transfection/co-immunoprecipitation in cell culture","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP experiment, but replicated in subsequent studies on the USH interactome","pmids":["12588794"],"is_preprint":false},{"year":2003,"finding":"Harmonin isoforms are differentially distributed in photoreceptor cell compartments: harmonin b isoforms are restricted to the light-sensitive outer segment, while harmonin a and c isoforms are more ubiquitously distributed. At photoreceptor synaptic terminals, harmonin a and c co-localize with myosin VIIa and cadherin 23.","method":"Western blot of subcellular photoreceptor fractions, immunofluorescence, electron microscopy of retina","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct subcellular fractionation combined with immunolocalization, single lab","pmids":["14578428"],"is_preprint":false},{"year":2005,"finding":"Harmonin (USH1C) acts as a scaffold protein that molecularly links USH1 and USH2 proteins: the PDZ1 domain of harmonin interacts with the PDZ-binding motifs at the C-termini of USH2A, VLGR1 (USH2C), and NBC3. These USH2 proteins are co-expressed with harmonin at synaptic terminals of retinal photoreceptors and inner ear hair cells.","method":"Co-immunoprecipitation, yeast two-hybrid, immunolocalization","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with domain mapping (PDZ1 specificity), single lab","pmids":["16301216"],"is_preprint":false},{"year":2005,"finding":"Protocadherin 15 (PCDH15/USH1F) interacts with harmonin PDZ2 domain. In the retina, PCDH15 co-localizes with harmonin at the photoreceptor synaptic terminal and at the base of the outer segment where new disk membranes form.","method":"GST pulldown, yeast two-hybrid, immunofluorescence, immunoelectron microscopy","journal":"Molecular vision","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal in vitro binding assays plus in situ localization, single lab","pmids":["15928608"],"is_preprint":false},{"year":2006,"finding":"A novel isoform of DOCK4 (DOCK4-Ex49), a guanine nucleotide exchange factor for Rac GTPase, interacts with harmonin and localizes to hair bundle stereocilia in the inner ear, suggesting a Rac-DOCK4-harmonin signaling pathway regulating actin cytoskeleton organization in stereocilia.","method":"Yeast two-hybrid, co-immunoprecipitation, immunostaining of inner ear","journal":"Journal of molecular biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, yeast two-hybrid plus single Co-IP, limited functional follow-up","pmids":["16464467"],"is_preprint":false},{"year":2009,"finding":"Harmonin is a component of the upper tip-link density (UTLD) where CDH23 inserts into the stereociliary membrane. Harmonin domains mediating CDH23 and F-actin interactions control harmonin localization in stereocilia. Mice expressing a harmonin mutant that prevents UTLD formation show reduced sensitivity of hair bundles to mechanical stimulation.","method":"Immunolocalization, transgenic mouse with harmonin domain mutations, hair bundle mechanosensitivity recordings","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo domain-mapping with transgenic mice combined with electrophysiological readout, orthogonal methods","pmids":["19447093"],"is_preprint":false},{"year":2009,"finding":"Harmonin-b, located at the upper tip-link insertion point, is required for normal adaptation of mechanoelectrical transduction. In Ush1c mutant mice defective for harmonin-b, step deflections evoke transduction currents with altered speed and extent of adaptation. Harmonin-b acts as an intracellular link that limits adaptation and engages adaptation motors, consistent with its binding to both actin filaments and cadherin 23.","method":"Electrophysiological recordings of transduction currents in vestibular and cochlear hair cells of Ush1c (dfcr-2J) mutant mice; modeling based on gating spring theory","journal":"Pflugers Archiv : European journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct electrophysiology in KO mice with specific phenotypic readout plus theoretical modeling, corroborated by other studies","pmids":["19756723"],"is_preprint":false},{"year":2009,"finding":"The harmonin N-terminal domain (NTD) adopts an autonomously-folded domain that specifically binds an internal peptide fragment of the cadherin 23 cytoplasmic domain. The harmonin PDZ2 domain separately binds the cadherin 23 C-terminal tail. This multidentate binding mode (NTD + PDZ2) provides the structural basis for stable tip-link complex assembly.","method":"X-ray crystal structures of harmonin N-domain alone and in complex with cadherin 23 internal peptide; crystal structure of harmonin PDZ2 in complex with cadherin 23 C-terminal tail; biochemical binding assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — two crystal structures with functional validation, rigorous biochemical corroboration","pmids":["19297620"],"is_preprint":false},{"year":2010,"finding":"Cadherin 23, harmonin, and myosin VIIa form a ternary complex. The cadherin 23 cytoplasmic region binds harmonin via the harmonin Nter-PDZ1 supramodule with unusually high affinity (not via the cadherin 23 C-terminal PDZ-binding motif). Cadherin 23 also directly binds myosin VIIa tail. Harmonin, cadherin 23, and myosin VIIa all interact with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) on synthetic liposomes, which may contribute to mechanotransduction adaptation.","method":"Surface plasmon resonance, liposome binding assays, immunolocalization in wild-type and cadherin 23 null mutant mice","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Strong — rigorous quantitative binding (SPR) plus reconstitution of ternary complex, in vivo localization data, multiple orthogonal methods","pmids":["20639393"],"is_preprint":false},{"year":2010,"finding":"When harmonin is co-expressed with CDH23 in LLC-PK1 epithelial cells, a large fraction of harmonin co-localizes with CDH23 in microvilli. The primary interaction between CDH23 and harmonin is between the harmonin N-domain and a 35-residue internal peptide of the CDH23 cytoplasmic tail; the CDH23 C-terminal PDZ-binding motif was not required, and the exon 68 peptide did not modulate harmonin binding levels.","method":"Epithelial cell transfection model (LLC-PK1-CL4 cells), co-localization imaging, in vitro protein binding assays","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based targeting assay plus in vitro binding, single lab; contradicts previous PDZ-binding model but consistent with crystal structure data","pmids":["20505086"],"is_preprint":false},{"year":2010,"finding":"In Ush1c knockout mice, loss of harmonin causes mislocalization of Pcdh15 (concentrated apically rather than at the stereocilia base/cuticular plate) and mislocalization of Sans (shifted toward the base of stereocilia), demonstrating that harmonin is required for correct subcellular positioning of Pcdh15 and Sans within hair cells.","method":"Immunofluorescence on cochlear sections and whole-mount preparations of Ush1c(-/-) knockout mice","journal":"International journal of experimental pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment in conditional KO with specific protein readout, single lab","pmids":["21156003"],"is_preprint":false},{"year":2011,"finding":"Harmonin associates with presynaptic Cav1.3 Ca2+ channels at the mouse inner hair cell synapse and limits channel availability through a ubiquitin-dependent pathway.","method":"Co-immunoprecipitation, immunolocalization at IHC synapse, electrophysiology","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — presynaptic Co-IP plus functional electrophysiology plus mechanistic ubiquitin pathway data, published in high-impact journal","pmids":["21822269"],"is_preprint":false},{"year":2011,"finding":"Harmonin (ush1c) is required in zebrafish Müller glial cells for photoreceptor synaptic development and function. Loss of ush1c function in zebrafish (nonsense mutant and morpholino knockdown) causes specific defects in sensory cell structure, hearing, balance, and visual function from the onset of vision.","method":"Zebrafish genetic model (ush1c nonsense mutant and morpholino knockdown), behavioral assays, histological analysis","journal":"Disease models & mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two independent zebrafish loss-of-function models with histological and functional readouts, single lab","pmids":["21757509"],"is_preprint":false},{"year":2012,"finding":"The three harmonin binding sites on cadherin 23 (the NTD-binding motif, the exon68 peptide, and the C-terminal PDZ-binding motif) do not synergize in binding to harmonin but instead facilitate formation of polymeric cadherin 23/harmonin complexes, providing a stable rootlet structure for anchoring tip links of stereocilia.","method":"In vitro biochemical binding assays, size exclusion chromatography, analytical ultracentrifugation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro reconstitution demonstrating polymer formation, single lab","pmids":["22879593"],"is_preprint":false},{"year":2013,"finding":"Harmonin binding to the distal C-terminus of the Cav1.3 α1 subunit enhances voltage-dependent facilitation (VDF) of Cav1.3 currents in HEK293T cells and in mouse inner hair cells. The dfcr harmonin mutant that does not interact with the Cav1.3 C-terminus does not promote VDF. Harmonin also plays a role in synchronous exocytosis and increases the efficiency of Ca2+ influx for triggering exocytosis in IHCs.","method":"Whole-cell patch clamp of transfected HEK293T cells and mouse IHCs, membrane capacitance recordings in dfcr mutant and control IHCs","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — electrophysiology in both cell line and primary hair cells, domain-mutant controls, multiple functional readouts","pmids":["23613530"],"is_preprint":false},{"year":2004,"finding":"The first PDZ domain of harmonin interacts with HARP (harmonin-interacting, ankyrin repeat-containing protein) via the three C-terminal amino acids of HARP. Harmonin and HARP co-localize in pancreatic duct epithelium and in a pancreatic beta-cell line under native conditions, forming a putative scaffolding complex.","method":"Yeast two-hybrid, overexpression co-immunoprecipitation, confocal microscopy of native tissue","journal":"Genes to cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — yeast two-hybrid plus single Co-IP in overexpression system, limited functional follow-up","pmids":["15461667"],"is_preprint":false},{"year":2017,"finding":"Harmonin-a1 can switch between open and closed conformations through intramolecular binding of its C-terminal PDZ-binding motif to its N-terminal NTD-PDZ1 supramodule, and through a flexible PDZ2-PDZ3 linker. This conformational switch affects interaction with cadherin-related 23.","method":"Biochemical and biophysical analyses (NMR, analytical ultracentrifugation, circular dichroism, surface plasmon resonance)","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biophysical methods demonstrating conformational switching with functional consequence for partner binding, single lab","pmids":["28653419"],"is_preprint":false},{"year":2018,"finding":"Glutathionylation of USH proteins promotes the physical interaction between Ush1c (harmonin) and Ush1ga (Sans), while Grxcr1 prevents this interaction by acting as a deglutathionylating enzyme. Grxcr1 does not affect the assembly of the Ush1c-Cadherin23-Myosin7aa tripartite complex. This identifies a redox-dependent regulatory mechanism for selective USH protein complex formation.","method":"In vitro binding assays with glutathionylated proteins, zebrafish grxcr1 mutant analysis, hair bundle morphology assessment","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro biochemical assay plus in vivo zebrafish model, single lab, two orthogonal approaches","pmids":["30380418"],"is_preprint":false},{"year":2019,"finding":"MYO7A, USH1C (harmonin), and USH1G (SANS) form a tripartite complex that undergoes liquid-liquid phase separation in vitro and in cells, suggesting that stereocilia tip-link densities form via phase separation. Strong multivalent interactions between the three proteins are required. Usher syndrome patient mutations in MYO7A weaken multivalent interactions and impair phase separation of the complex.","method":"In vitro phase separation assays, fluorescence microscopy of condensates in cells, Co-IP, mutational analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro reconstitution of phase separation plus cell-based validation with disease mutations, single lab","pmids":["31644917"],"is_preprint":false},{"year":2022,"finding":"Crystal structure of harmonin PDZ2 and coiled-coil domains in complex with the tail of cadherin-related family member 2 (CDHR2) reveals that Usher syndrome patient mutations in PDZ2 affect domain stability and target binding. The coiled-coil domain can form antiparallel dimers, potentially relevant to harmonin behavior during liquid-liquid phase separation at tip-link densities.","method":"X-ray crystallography, biochemical stability assays","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structure with biochemical validation, single lab","pmids":["35747925"],"is_preprint":false},{"year":2023,"finding":"Harmonin binds to β-catenin, the key effector of the canonical Wnt (cWnt) signaling pathway, particularly to stabilized acetylated β-catenin in nuclei. Overexpression of USH1C/harmonin significantly reduces cWnt signaling in HEK293T cells, while the USH1C-R31* mutant form does not. USH1C patient-derived fibroblasts show increased cWnt signaling, which is reverted by Ataluren-induced read-through restoring USH1C expression.","method":"Co-immunoprecipitation, luciferase reporter assays for cWnt signaling, RNAseq of patient fibroblasts, Ataluren rescue experiment","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus functional signaling assay plus patient cell rescue, single lab, multiple orthogonal methods","pmids":["36846582"],"is_preprint":false},{"year":2023,"finding":"In human retina, harmonin_a1 is the most abundant USH1C transcript. Harmonin is expressed in Müller glia cells (MGCs) and retinal neurons, localizing to terminal endfeet and apical microvilli of MGCs, presynaptic region of cones, outer segments of rods, and at adhesive junctions between MGCs and photoreceptors in the outer limiting membrane (OLM). Harmonin interacts with OLM molecules in PRCs and MGCs, and with rhodopsin in PRCs. Primary cilia defects in USH1C patient-derived fibroblasts are reverted by delivery of harmonin_a1 transcript.","method":"RNA-seq, immunoblotting, immunolocalization, co-immunoprecipitation, gene delivery rescue experiment in patient fibroblasts","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods including Co-IP and functional rescue, single lab","pmids":["35997788"],"is_preprint":false},{"year":2020,"finding":"A heterozygous USH1C missense variant (p.Gly223Cys) in the carboxylate-binding loop of harmonin PDZ2 causes ~16-fold reduction in affinity for the CDH23 PDZ-binding motif peptide due to a conformational change in the PDZ2 domain, establishing that disruption of harmonin-CDH23 interaction can cause autosomal dominant nonsyndromic hearing loss.","method":"Biolayer interferometry, circular dichroism, exome sequencing with segregation analysis","journal":"Annals of laboratory medicine","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — quantitative biophysical binding assay with structural explanation, single lab","pmids":["31858762"],"is_preprint":false}],"current_model":"USH1C/harmonin is a multi-PDZ-domain scaffold protein that functions as a master organizer of the Usher interactome in inner ear hair cells and retinal photoreceptors: its NTD-PDZ1 supramodule and PDZ2 domain bind cadherin 23 in a multidentate manner to anchor tip links to the stereocilia F-actin core, harmonin-b bundles actin and limits mechanotransduction adaptation at the upper tip-link density, harmonin interacts with myosin VIIa (which conveys it along developing stereocilia), SANS, PCDH15, and USH2 proteins to form a broader USH interactome network, harmonin regulates presynaptic Cav1.3 Ca²⁺ channels via ubiquitin-dependent degradation and enhances voltage-dependent facilitation to control exocytosis at the inner hair cell synapse, the three-protein MYO7A/USH1C/SANS complex undergoes liquid-liquid phase separation to form tip-link densities, harmonin undergoes intramolecular conformational switching between open and closed states that modulates partner binding, and harmonin suppresses canonical Wnt/β-catenin signaling by direct interaction with β-catenin."},"narrative":{"mechanistic_narrative":"USH1C encodes harmonin, a multi-PDZ-domain scaffold protein that organizes the Usher syndrome (USH) interactome in inner ear hair cells and retinal cells, and its mutation causes Usher syndrome type 1C [PMID:10973247]. Harmonin engages cadherin 23 in a multidentate manner — its N-terminal domain and PDZ1 supramodule bind an internal cytoplasmic peptide of CDH23 with high affinity while PDZ2 binds the CDH23 C-terminal tail — and these non-synergizing sites instead drive formation of polymeric CDH23/harmonin complexes that anchor stereocilia tip links [PMID:19297620, PMID:20639393, PMID:22879593]. Within the upper tip-link density, the F-actin-bundling harmonin-b isoform links CDH23 to the stereociliary actin core and limits the speed and extent of mechanoelectrical transduction adaptation; loss of this localization reduces hair-bundle mechanosensitivity [PMID:12485990, PMID:19447093, PMID:19756723]. Harmonin nucleates a broader USH protein network, binding myosin VIIa, SANS (USH1G), PCDH15 (USH1F), and the USH2 proteins USH2A and VLGR1, and is required for correct subcellular positioning of PCDH15 and SANS in hair cells [PMID:12485990, PMID:12588794, PMID:16301216, PMID:15928608, PMID:21156003]; the MYO7A/USH1C/SANS tripartite complex assembles through multivalent interactions that undergo liquid-liquid phase separation, a process disrupted by USH disease mutations [PMID:31644917]. At the inner hair cell ribbon synapse harmonin associates with presynaptic Cav1.3 Ca²⁺ channels, limiting channel availability via a ubiquitin-dependent pathway and enhancing voltage-dependent facilitation to control synchronous exocytosis [PMID:21822269, PMID:23613530]. Harmonin also suppresses canonical Wnt/β-catenin signaling through direct interaction with β-catenin [PMID:36846582], and its activity is further tuned by an intramolecular open/closed conformational switch and by redox-dependent (glutathionylation) modification that gates partner binding [PMID:28653419, PMID:30380418].","teleology":[{"year":2000,"claim":"Established that USH1C encodes harmonin, a PDZ-domain protein, and that its mutation causes Usher syndrome type 1C, defining the gene's disease relevance and domain architecture.","evidence":"Subtracted cDNA cloning, RT-PCR expression, and patient mutation identification","pmids":["10973247"],"confidence":"High","gaps":["Molecular function of the scaffold not yet defined","Tissue distribution of isoforms only partly resolved"]},{"year":2002,"claim":"Showed harmonin is the physical and functional hub of the hair-bundle anchoring unit by demonstrating direct binding to cadherin 23 and myosin VIIa and actin-bundling activity, explaining how it shapes stereocilia.","evidence":"Co-IP, in vitro binding, F-actin bundling assays, and localization in myosin VIIa mutant mice; yeast two-hybrid and pulldown for CDH23 with domain mapping","pmids":["12485990","12407180"],"confidence":"High","gaps":["Structural basis of the dual CDH23 binding surfaces unresolved at this stage","Functional consequence of disrupting the link in vivo not yet tested"]},{"year":2003,"claim":"Expanded the USH1 network by placing SANS (USH1G) in complex with harmonin and mapping harmonin isoform distribution in photoreceptor compartments, linking ear and retinal roles.","evidence":"Co-transfection/Co-IP and subcellular fractionation with immunolocalization in retina","pmids":["12588794","14578428"],"confidence":"Medium","gaps":["SANS interaction rested on a single Co-IP","Functional significance of isoform compartmentalization in retina untested"]},{"year":2005,"claim":"Defined harmonin as the scaffold bridging USH1 and USH2 protein classes by mapping PDZ1 binding to USH2A, VLGR1, and NBC3, and PDZ2 binding to PCDH15.","evidence":"Co-IP, yeast two-hybrid, GST pulldown, and immunolocalization at synaptic terminals","pmids":["16301216","15928608"],"confidence":"Medium","gaps":["Interactions characterized in vitro or by localization, not in native complexes","In vivo dependence of network assembly on these contacts not established"]},{"year":2009,"claim":"Tied harmonin's molecular interactions to mechanotransduction physiology by localizing it to the upper tip-link density and showing harmonin-b limits adaptation, establishing a direct structure-to-function chain.","evidence":"Transgenic mice with harmonin domain mutations, immunolocalization, and electrophysiological transduction-current recordings in Ush1c mutants","pmids":["19447093","19756723"],"confidence":"High","gaps":["Identity of adaptation motors engaged not fully defined","Quantitative contribution of actin vs cadherin binding to adaptation not separated"]},{"year":2010,"claim":"Provided the atomic and biophysical basis for tip-link assembly by showing multidentate (NTD + PDZ2) CDH23 binding, ternary CDH23/harmonin/myosin VIIa complex formation, and PI(4,5)P2 binding.","evidence":"X-ray crystallography of harmonin NTD and PDZ2 with CDH23 peptides, SPR, liposome binding, and cell-based co-localization in LLC-PK1 cells","pmids":["19297620","20639393","20505086"],"confidence":"High","gaps":["Role of the C-terminal PDZ-binding motif reassigned, leaving its physiological function open","Mechanistic contribution of PI(4,5)P2 to adaptation not directly demonstrated in vivo"]},{"year":2010,"claim":"Resolved how the multiple CDH23 binding sites cooperate, showing they drive polymeric rather than synergistic complexes to build a stable tip-link rootlet.","evidence":"In vitro binding, size-exclusion chromatography, and analytical ultracentrifugation","pmids":["22879593"],"confidence":"Medium","gaps":["Polymer architecture demonstrated in vitro only","Stoichiometry within the native tip-link density unknown"]},{"year":2011,"claim":"Demonstrated harmonin is required in vivo for spatial organization of the network and revealed a distinct presynaptic role regulating Cav1.3 channels via ubiquitin-dependent degradation.","evidence":"Immunofluorescence of Pcdh15/Sans in Ush1c knockout cochlea; Co-IP, IHC-synapse localization, and electrophysiology for Cav1.3; zebrafish loss-of-function models","pmids":["21156003","21822269","21757509"],"confidence":"High","gaps":["Ubiquitin ligase mediating Cav1.3 turnover not identified","Müller-glia-specific synaptic requirement mechanism not fully defined"]},{"year":2013,"claim":"Refined the synaptic role by showing harmonin binding to the Cav1.3 C-terminus enhances voltage-dependent facilitation and synchronous exocytosis, with a disease mutant abolishing the effect.","evidence":"Whole-cell patch clamp and capacitance recordings in HEK293T cells and mouse IHCs with dfcr mutant controls","pmids":["23613530"],"confidence":"High","gaps":["Relationship between facilitation and ubiquitin-dependent channel limitation not integrated","Structural basis of harmonin-Cav1.3 C-terminus contact unresolved"]},{"year":2018,"claim":"Identified a redox-dependent gating mechanism for selective USH complex assembly, showing glutathionylation promotes harmonin-SANS binding while Grxcr1 reverses it.","evidence":"In vitro binding with glutathionylated proteins and zebrafish grxcr1 mutant hair-bundle analysis","pmids":["30380418"],"confidence":"Medium","gaps":["Physiological trigger for glutathionylation in hair cells unknown","Selective vs tripartite complex regulation mechanism only partly mapped"]},{"year":2019,"claim":"Reframed tip-link density assembly as a phase-separation phenomenon, showing MYO7A/USH1C/SANS multivalent interactions drive liquid-liquid phase separation that disease mutations impair.","evidence":"In vitro phase separation assays, condensate imaging in cells, Co-IP, and mutational analysis","pmids":["31644917"],"confidence":"Medium","gaps":["In vivo demonstration of condensates at native tip-link densities lacking","Material properties and regulation of the condensate in hair cells undefined"]},{"year":2022,"claim":"Provided structural and conformational insight into harmonin regulation, defining a PDZ2/coiled-coil-CDHR2 structure with disease mutations and an intramolecular open/closed conformational switch controlling partner binding.","evidence":"X-ray crystallography with stability assays; NMR, AUC, CD, and SPR for the conformational switch","pmids":["35747925","28653419"],"confidence":"Medium","gaps":["Trigger that toggles the conformational switch in cells unknown","Coiled-coil dimerization role in phase separation not directly tested"]},{"year":2023,"claim":"Uncovered a signaling role beyond scaffolding, showing harmonin suppresses canonical Wnt/β-catenin signaling and defining its retinal localization and interactions, with patient-cell rescue linking these to USH1C disease.","evidence":"Co-IP, luciferase Wnt reporters, RNA-seq, and Ataluren/transcript-delivery rescue in patient fibroblasts; retinal immunolocalization and rhodopsin Co-IP","pmids":["36846582","35997788"],"confidence":"Medium","gaps":["Connection between Wnt suppression and sensory phenotypes unclear","Whether nuclear β-catenin binding occurs in hair cells/photoreceptors in vivo untested"]},{"year":null,"claim":"How harmonin's distinct activities — tip-link anchoring, phase separation, presynaptic Cav1.3 regulation, redox/conformational gating, and Wnt suppression — are coordinated within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model integrating mechanotransduction and synaptic roles","Upstream signals controlling conformational/redox switching unidentified","In vivo phase-separation behavior at tip links not demonstrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,2,5,10,11]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[1,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[14,17,23]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[11]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,8,9]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[8,11,14]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[23]}],"pathway":[],"complexes":["USH interactome (MYO7A/USH1C/SANS tip-link density complex)","upper tip-link density","CDH23/harmonin/myosin VIIa ternary complex"],"partners":["CDH23","MYO7A","USH1G","PCDH15","USH2A","VLGR1","CACNA1D","CTNNB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y6N9","full_name":"Harmonin","aliases":["Antigen NY-CO-38/NY-CO-37","Autoimmune enteropathy-related antigen AIE-75","Protein PDZ-73","Renal carcinoma antigen NY-REN-3","Usher syndrome type-1C protein"],"length_aa":552,"mass_kda":62.2,"function":"Anchoring/scaffolding protein that is a part of the functional network formed by USH1C, USH1G, CDH23 and MYO7A that mediates mechanotransduction in cochlear hair cells. Required for normal development and maintenance of cochlear hair cell bundles (By similarity). As part of the intermicrovillar adhesion complex/IMAC plays a role in brush border differentiation, controlling microvilli organization and length. Probably plays a central regulatory role in the assembly of the complex, recruiting CDHR2, CDHR5 and MYO7B to the microvilli tips (PubMed:24725409, PubMed:26812018)","subcellular_location":"Cytoplasm, cytosol; Cytoplasm, cytoskeleton; Cell projection, microvillus","url":"https://www.uniprot.org/uniprotkb/Q9Y6N9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/USH1C","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/USH1C","total_profiled":1310},"omim":[{"mim_id":"614945","title":"DEAFNESS, AUTOSOMAL RECESSIVE 18B; DFNB18B","url":"https://www.omim.org/entry/614945"},{"mim_id":"612971","title":"PDZ DOMAIN-CONTAINING 7; PDZD7","url":"https://www.omim.org/entry/612971"},{"mim_id":"611810","title":"USH1C-BINDING PROTEIN 1; USHBP1","url":"https://www.omim.org/entry/611810"},{"mim_id":"609901","title":"ANKYRIN REPEAT AND STERILE ALPHA MOTIF DOMAINS-CONTAINING PROTEIN 4B; ANKS4B","url":"https://www.omim.org/entry/609901"},{"mim_id":"608400","title":"USHERIN; USH2A","url":"https://www.omim.org/entry/608400"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Cytosol","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in 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Some isoforms contain an additional coiled-coil domain and proline/serine-rich region. Splice-site, frameshift, and VNTR mutations in USH1C cause Usher syndrome type 1C.\",\n      \"method\": \"Subtracted mouse cDNA library, RT-PCR expression analysis, mutation identification in patients\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — foundational identification paper with multiple orthogonal methods, independently replicated across subsequent studies\",\n      \"pmids\": [\"10973247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Harmonin-b is an F-actin-bundling protein that binds directly to cadherin 23 and myosin VIIa, forming a functional unit that anchors cadherin 23 to stereocilia microfilaments and shapes the hair bundle. Harmonin b is absent from disorganized hair bundles of myosin VIIa mutant mice, suggesting myosin VIIa conveys harmonin b along the actin core of developing stereocilia.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding assays, F-actin bundling assay, immunolocalization in wild-type and myosin VIIa mutant mice\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, actin bundling assay, in vivo localization in mutant mice), independently corroborated by multiple subsequent studies\",\n      \"pmids\": [\"12485990\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Two PDZ domains in harmonin interact with two complementary binding surfaces in the CDH23 cytoplasmic domain, forming a protein complex. CDH23 and harmonin are co-expressed in stereocilia of hair cells. One CDH23 binding surface is disrupted by sequences from an alternatively spliced exon expressed in the ear but not the retina.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, immunolocalization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding assays with domain mapping, replicated by multiple independent labs\",\n      \"pmids\": [\"12407180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SANS (USH1G protein) associates with harmonin via its C-terminal class I PDZ-binding motif, placing SANS in the same USH1 protein network as harmonin, myosin VIIa, and cadherin 23.\",\n      \"method\": \"Co-transfection/co-immunoprecipitation in cell culture\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP experiment, but replicated in subsequent studies on the USH interactome\",\n      \"pmids\": [\"12588794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Harmonin isoforms are differentially distributed in photoreceptor cell compartments: harmonin b isoforms are restricted to the light-sensitive outer segment, while harmonin a and c isoforms are more ubiquitously distributed. At photoreceptor synaptic terminals, harmonin a and c co-localize with myosin VIIa and cadherin 23.\",\n      \"method\": \"Western blot of subcellular photoreceptor fractions, immunofluorescence, electron microscopy of retina\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct subcellular fractionation combined with immunolocalization, single lab\",\n      \"pmids\": [\"14578428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Harmonin (USH1C) acts as a scaffold protein that molecularly links USH1 and USH2 proteins: the PDZ1 domain of harmonin interacts with the PDZ-binding motifs at the C-termini of USH2A, VLGR1 (USH2C), and NBC3. These USH2 proteins are co-expressed with harmonin at synaptic terminals of retinal photoreceptors and inner ear hair cells.\",\n      \"method\": \"Co-immunoprecipitation, yeast two-hybrid, immunolocalization\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with domain mapping (PDZ1 specificity), single lab\",\n      \"pmids\": [\"16301216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Protocadherin 15 (PCDH15/USH1F) interacts with harmonin PDZ2 domain. In the retina, PCDH15 co-localizes with harmonin at the photoreceptor synaptic terminal and at the base of the outer segment where new disk membranes form.\",\n      \"method\": \"GST pulldown, yeast two-hybrid, immunofluorescence, immunoelectron microscopy\",\n      \"journal\": \"Molecular vision\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal in vitro binding assays plus in situ localization, single lab\",\n      \"pmids\": [\"15928608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A novel isoform of DOCK4 (DOCK4-Ex49), a guanine nucleotide exchange factor for Rac GTPase, interacts with harmonin and localizes to hair bundle stereocilia in the inner ear, suggesting a Rac-DOCK4-harmonin signaling pathway regulating actin cytoskeleton organization in stereocilia.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, immunostaining of inner ear\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, yeast two-hybrid plus single Co-IP, limited functional follow-up\",\n      \"pmids\": [\"16464467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Harmonin is a component of the upper tip-link density (UTLD) where CDH23 inserts into the stereociliary membrane. Harmonin domains mediating CDH23 and F-actin interactions control harmonin localization in stereocilia. Mice expressing a harmonin mutant that prevents UTLD formation show reduced sensitivity of hair bundles to mechanical stimulation.\",\n      \"method\": \"Immunolocalization, transgenic mouse with harmonin domain mutations, hair bundle mechanosensitivity recordings\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo domain-mapping with transgenic mice combined with electrophysiological readout, orthogonal methods\",\n      \"pmids\": [\"19447093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Harmonin-b, located at the upper tip-link insertion point, is required for normal adaptation of mechanoelectrical transduction. In Ush1c mutant mice defective for harmonin-b, step deflections evoke transduction currents with altered speed and extent of adaptation. Harmonin-b acts as an intracellular link that limits adaptation and engages adaptation motors, consistent with its binding to both actin filaments and cadherin 23.\",\n      \"method\": \"Electrophysiological recordings of transduction currents in vestibular and cochlear hair cells of Ush1c (dfcr-2J) mutant mice; modeling based on gating spring theory\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct electrophysiology in KO mice with specific phenotypic readout plus theoretical modeling, corroborated by other studies\",\n      \"pmids\": [\"19756723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The harmonin N-terminal domain (NTD) adopts an autonomously-folded domain that specifically binds an internal peptide fragment of the cadherin 23 cytoplasmic domain. The harmonin PDZ2 domain separately binds the cadherin 23 C-terminal tail. This multidentate binding mode (NTD + PDZ2) provides the structural basis for stable tip-link complex assembly.\",\n      \"method\": \"X-ray crystal structures of harmonin N-domain alone and in complex with cadherin 23 internal peptide; crystal structure of harmonin PDZ2 in complex with cadherin 23 C-terminal tail; biochemical binding assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two crystal structures with functional validation, rigorous biochemical corroboration\",\n      \"pmids\": [\"19297620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Cadherin 23, harmonin, and myosin VIIa form a ternary complex. The cadherin 23 cytoplasmic region binds harmonin via the harmonin Nter-PDZ1 supramodule with unusually high affinity (not via the cadherin 23 C-terminal PDZ-binding motif). Cadherin 23 also directly binds myosin VIIa tail. Harmonin, cadherin 23, and myosin VIIa all interact with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) on synthetic liposomes, which may contribute to mechanotransduction adaptation.\",\n      \"method\": \"Surface plasmon resonance, liposome binding assays, immunolocalization in wild-type and cadherin 23 null mutant mice\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — rigorous quantitative binding (SPR) plus reconstitution of ternary complex, in vivo localization data, multiple orthogonal methods\",\n      \"pmids\": [\"20639393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"When harmonin is co-expressed with CDH23 in LLC-PK1 epithelial cells, a large fraction of harmonin co-localizes with CDH23 in microvilli. The primary interaction between CDH23 and harmonin is between the harmonin N-domain and a 35-residue internal peptide of the CDH23 cytoplasmic tail; the CDH23 C-terminal PDZ-binding motif was not required, and the exon 68 peptide did not modulate harmonin binding levels.\",\n      \"method\": \"Epithelial cell transfection model (LLC-PK1-CL4 cells), co-localization imaging, in vitro protein binding assays\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based targeting assay plus in vitro binding, single lab; contradicts previous PDZ-binding model but consistent with crystal structure data\",\n      \"pmids\": [\"20505086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In Ush1c knockout mice, loss of harmonin causes mislocalization of Pcdh15 (concentrated apically rather than at the stereocilia base/cuticular plate) and mislocalization of Sans (shifted toward the base of stereocilia), demonstrating that harmonin is required for correct subcellular positioning of Pcdh15 and Sans within hair cells.\",\n      \"method\": \"Immunofluorescence on cochlear sections and whole-mount preparations of Ush1c(-/-) knockout mice\",\n      \"journal\": \"International journal of experimental pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment in conditional KO with specific protein readout, single lab\",\n      \"pmids\": [\"21156003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Harmonin associates with presynaptic Cav1.3 Ca2+ channels at the mouse inner hair cell synapse and limits channel availability through a ubiquitin-dependent pathway.\",\n      \"method\": \"Co-immunoprecipitation, immunolocalization at IHC synapse, electrophysiology\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — presynaptic Co-IP plus functional electrophysiology plus mechanistic ubiquitin pathway data, published in high-impact journal\",\n      \"pmids\": [\"21822269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Harmonin (ush1c) is required in zebrafish Müller glial cells for photoreceptor synaptic development and function. Loss of ush1c function in zebrafish (nonsense mutant and morpholino knockdown) causes specific defects in sensory cell structure, hearing, balance, and visual function from the onset of vision.\",\n      \"method\": \"Zebrafish genetic model (ush1c nonsense mutant and morpholino knockdown), behavioral assays, histological analysis\",\n      \"journal\": \"Disease models & mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two independent zebrafish loss-of-function models with histological and functional readouts, single lab\",\n      \"pmids\": [\"21757509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The three harmonin binding sites on cadherin 23 (the NTD-binding motif, the exon68 peptide, and the C-terminal PDZ-binding motif) do not synergize in binding to harmonin but instead facilitate formation of polymeric cadherin 23/harmonin complexes, providing a stable rootlet structure for anchoring tip links of stereocilia.\",\n      \"method\": \"In vitro biochemical binding assays, size exclusion chromatography, analytical ultracentrifugation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro reconstitution demonstrating polymer formation, single lab\",\n      \"pmids\": [\"22879593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Harmonin binding to the distal C-terminus of the Cav1.3 α1 subunit enhances voltage-dependent facilitation (VDF) of Cav1.3 currents in HEK293T cells and in mouse inner hair cells. The dfcr harmonin mutant that does not interact with the Cav1.3 C-terminus does not promote VDF. Harmonin also plays a role in synchronous exocytosis and increases the efficiency of Ca2+ influx for triggering exocytosis in IHCs.\",\n      \"method\": \"Whole-cell patch clamp of transfected HEK293T cells and mouse IHCs, membrane capacitance recordings in dfcr mutant and control IHCs\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — electrophysiology in both cell line and primary hair cells, domain-mutant controls, multiple functional readouts\",\n      \"pmids\": [\"23613530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The first PDZ domain of harmonin interacts with HARP (harmonin-interacting, ankyrin repeat-containing protein) via the three C-terminal amino acids of HARP. Harmonin and HARP co-localize in pancreatic duct epithelium and in a pancreatic beta-cell line under native conditions, forming a putative scaffolding complex.\",\n      \"method\": \"Yeast two-hybrid, overexpression co-immunoprecipitation, confocal microscopy of native tissue\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — yeast two-hybrid plus single Co-IP in overexpression system, limited functional follow-up\",\n      \"pmids\": [\"15461667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Harmonin-a1 can switch between open and closed conformations through intramolecular binding of its C-terminal PDZ-binding motif to its N-terminal NTD-PDZ1 supramodule, and through a flexible PDZ2-PDZ3 linker. This conformational switch affects interaction with cadherin-related 23.\",\n      \"method\": \"Biochemical and biophysical analyses (NMR, analytical ultracentrifugation, circular dichroism, surface plasmon resonance)\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biophysical methods demonstrating conformational switching with functional consequence for partner binding, single lab\",\n      \"pmids\": [\"28653419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Glutathionylation of USH proteins promotes the physical interaction between Ush1c (harmonin) and Ush1ga (Sans), while Grxcr1 prevents this interaction by acting as a deglutathionylating enzyme. Grxcr1 does not affect the assembly of the Ush1c-Cadherin23-Myosin7aa tripartite complex. This identifies a redox-dependent regulatory mechanism for selective USH protein complex formation.\",\n      \"method\": \"In vitro binding assays with glutathionylated proteins, zebrafish grxcr1 mutant analysis, hair bundle morphology assessment\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro biochemical assay plus in vivo zebrafish model, single lab, two orthogonal approaches\",\n      \"pmids\": [\"30380418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MYO7A, USH1C (harmonin), and USH1G (SANS) form a tripartite complex that undergoes liquid-liquid phase separation in vitro and in cells, suggesting that stereocilia tip-link densities form via phase separation. Strong multivalent interactions between the three proteins are required. Usher syndrome patient mutations in MYO7A weaken multivalent interactions and impair phase separation of the complex.\",\n      \"method\": \"In vitro phase separation assays, fluorescence microscopy of condensates in cells, Co-IP, mutational analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro reconstitution of phase separation plus cell-based validation with disease mutations, single lab\",\n      \"pmids\": [\"31644917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure of harmonin PDZ2 and coiled-coil domains in complex with the tail of cadherin-related family member 2 (CDHR2) reveals that Usher syndrome patient mutations in PDZ2 affect domain stability and target binding. The coiled-coil domain can form antiparallel dimers, potentially relevant to harmonin behavior during liquid-liquid phase separation at tip-link densities.\",\n      \"method\": \"X-ray crystallography, biochemical stability assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with biochemical validation, single lab\",\n      \"pmids\": [\"35747925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Harmonin binds to β-catenin, the key effector of the canonical Wnt (cWnt) signaling pathway, particularly to stabilized acetylated β-catenin in nuclei. Overexpression of USH1C/harmonin significantly reduces cWnt signaling in HEK293T cells, while the USH1C-R31* mutant form does not. USH1C patient-derived fibroblasts show increased cWnt signaling, which is reverted by Ataluren-induced read-through restoring USH1C expression.\",\n      \"method\": \"Co-immunoprecipitation, luciferase reporter assays for cWnt signaling, RNAseq of patient fibroblasts, Ataluren rescue experiment\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus functional signaling assay plus patient cell rescue, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"36846582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In human retina, harmonin_a1 is the most abundant USH1C transcript. Harmonin is expressed in Müller glia cells (MGCs) and retinal neurons, localizing to terminal endfeet and apical microvilli of MGCs, presynaptic region of cones, outer segments of rods, and at adhesive junctions between MGCs and photoreceptors in the outer limiting membrane (OLM). Harmonin interacts with OLM molecules in PRCs and MGCs, and with rhodopsin in PRCs. Primary cilia defects in USH1C patient-derived fibroblasts are reverted by delivery of harmonin_a1 transcript.\",\n      \"method\": \"RNA-seq, immunoblotting, immunolocalization, co-immunoprecipitation, gene delivery rescue experiment in patient fibroblasts\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods including Co-IP and functional rescue, single lab\",\n      \"pmids\": [\"35997788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A heterozygous USH1C missense variant (p.Gly223Cys) in the carboxylate-binding loop of harmonin PDZ2 causes ~16-fold reduction in affinity for the CDH23 PDZ-binding motif peptide due to a conformational change in the PDZ2 domain, establishing that disruption of harmonin-CDH23 interaction can cause autosomal dominant nonsyndromic hearing loss.\",\n      \"method\": \"Biolayer interferometry, circular dichroism, exome sequencing with segregation analysis\",\n      \"journal\": \"Annals of laboratory medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — quantitative biophysical binding assay with structural explanation, single lab\",\n      \"pmids\": [\"31858762\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"USH1C/harmonin is a multi-PDZ-domain scaffold protein that functions as a master organizer of the Usher interactome in inner ear hair cells and retinal photoreceptors: its NTD-PDZ1 supramodule and PDZ2 domain bind cadherin 23 in a multidentate manner to anchor tip links to the stereocilia F-actin core, harmonin-b bundles actin and limits mechanotransduction adaptation at the upper tip-link density, harmonin interacts with myosin VIIa (which conveys it along developing stereocilia), SANS, PCDH15, and USH2 proteins to form a broader USH interactome network, harmonin regulates presynaptic Cav1.3 Ca²⁺ channels via ubiquitin-dependent degradation and enhances voltage-dependent facilitation to control exocytosis at the inner hair cell synapse, the three-protein MYO7A/USH1C/SANS complex undergoes liquid-liquid phase separation to form tip-link densities, harmonin undergoes intramolecular conformational switching between open and closed states that modulates partner binding, and harmonin suppresses canonical Wnt/β-catenin signaling by direct interaction with β-catenin.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"USH1C encodes harmonin, a multi-PDZ-domain scaffold protein that organizes the Usher syndrome (USH) interactome in inner ear hair cells and retinal cells, and its mutation causes Usher syndrome type 1C [#0]. Harmonin engages cadherin 23 in a multidentate manner — its N-terminal domain and PDZ1 supramodule bind an internal cytoplasmic peptide of CDH23 with high affinity while PDZ2 binds the CDH23 C-terminal tail — and these non-synergizing sites instead drive formation of polymeric CDH23/harmonin complexes that anchor stereocilia tip links [#10, #11, #16]. Within the upper tip-link density, the F-actin-bundling harmonin-b isoform links CDH23 to the stereociliary actin core and limits the speed and extent of mechanoelectrical transduction adaptation; loss of this localization reduces hair-bundle mechanosensitivity [#1, #8, #9]. Harmonin nucleates a broader USH protein network, binding myosin VIIa, SANS (USH1G), PCDH15 (USH1F), and the USH2 proteins USH2A and VLGR1, and is required for correct subcellular positioning of PCDH15 and SANS in hair cells [#1, #3, #5, #6, #13]; the MYO7A/USH1C/SANS tripartite complex assembles through multivalent interactions that undergo liquid-liquid phase separation, a process disrupted by USH disease mutations [#21]. At the inner hair cell ribbon synapse harmonin associates with presynaptic Cav1.3 Ca²⁺ channels, limiting channel availability via a ubiquitin-dependent pathway and enhancing voltage-dependent facilitation to control synchronous exocytosis [#14, #17]. Harmonin also suppresses canonical Wnt/β-catenin signaling through direct interaction with β-catenin [#23], and its activity is further tuned by an intramolecular open/closed conformational switch and by redox-dependent (glutathionylation) modification that gates partner binding [#19, #20].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that USH1C encodes harmonin, a PDZ-domain protein, and that its mutation causes Usher syndrome type 1C, defining the gene's disease relevance and domain architecture.\",\n      \"evidence\": \"Subtracted cDNA cloning, RT-PCR expression, and patient mutation identification\",\n      \"pmids\": [\"10973247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular function of the scaffold not yet defined\", \"Tissue distribution of isoforms only partly resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showed harmonin is the physical and functional hub of the hair-bundle anchoring unit by demonstrating direct binding to cadherin 23 and myosin VIIa and actin-bundling activity, explaining how it shapes stereocilia.\",\n      \"evidence\": \"Co-IP, in vitro binding, F-actin bundling assays, and localization in myosin VIIa mutant mice; yeast two-hybrid and pulldown for CDH23 with domain mapping\",\n      \"pmids\": [\"12485990\", \"12407180\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the dual CDH23 binding surfaces unresolved at this stage\", \"Functional consequence of disrupting the link in vivo not yet tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Expanded the USH1 network by placing SANS (USH1G) in complex with harmonin and mapping harmonin isoform distribution in photoreceptor compartments, linking ear and retinal roles.\",\n      \"evidence\": \"Co-transfection/Co-IP and subcellular fractionation with immunolocalization in retina\",\n      \"pmids\": [\"12588794\", \"14578428\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SANS interaction rested on a single Co-IP\", \"Functional significance of isoform compartmentalization in retina untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined harmonin as the scaffold bridging USH1 and USH2 protein classes by mapping PDZ1 binding to USH2A, VLGR1, and NBC3, and PDZ2 binding to PCDH15.\",\n      \"evidence\": \"Co-IP, yeast two-hybrid, GST pulldown, and immunolocalization at synaptic terminals\",\n      \"pmids\": [\"16301216\", \"15928608\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interactions characterized in vitro or by localization, not in native complexes\", \"In vivo dependence of network assembly on these contacts not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Tied harmonin's molecular interactions to mechanotransduction physiology by localizing it to the upper tip-link density and showing harmonin-b limits adaptation, establishing a direct structure-to-function chain.\",\n      \"evidence\": \"Transgenic mice with harmonin domain mutations, immunolocalization, and electrophysiological transduction-current recordings in Ush1c mutants\",\n      \"pmids\": [\"19447093\", \"19756723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of adaptation motors engaged not fully defined\", \"Quantitative contribution of actin vs cadherin binding to adaptation not separated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided the atomic and biophysical basis for tip-link assembly by showing multidentate (NTD + PDZ2) CDH23 binding, ternary CDH23/harmonin/myosin VIIa complex formation, and PI(4,5)P2 binding.\",\n      \"evidence\": \"X-ray crystallography of harmonin NTD and PDZ2 with CDH23 peptides, SPR, liposome binding, and cell-based co-localization in LLC-PK1 cells\",\n      \"pmids\": [\"19297620\", \"20639393\", \"20505086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of the C-terminal PDZ-binding motif reassigned, leaving its physiological function open\", \"Mechanistic contribution of PI(4,5)P2 to adaptation not directly demonstrated in vivo\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved how the multiple CDH23 binding sites cooperate, showing they drive polymeric rather than synergistic complexes to build a stable tip-link rootlet.\",\n      \"evidence\": \"In vitro binding, size-exclusion chromatography, and analytical ultracentrifugation\",\n      \"pmids\": [\"22879593\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Polymer architecture demonstrated in vitro only\", \"Stoichiometry within the native tip-link density unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated harmonin is required in vivo for spatial organization of the network and revealed a distinct presynaptic role regulating Cav1.3 channels via ubiquitin-dependent degradation.\",\n      \"evidence\": \"Immunofluorescence of Pcdh15/Sans in Ush1c knockout cochlea; Co-IP, IHC-synapse localization, and electrophysiology for Cav1.3; zebrafish loss-of-function models\",\n      \"pmids\": [\"21156003\", \"21822269\", \"21757509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitin ligase mediating Cav1.3 turnover not identified\", \"Müller-glia-specific synaptic requirement mechanism not fully defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Refined the synaptic role by showing harmonin binding to the Cav1.3 C-terminus enhances voltage-dependent facilitation and synchronous exocytosis, with a disease mutant abolishing the effect.\",\n      \"evidence\": \"Whole-cell patch clamp and capacitance recordings in HEK293T cells and mouse IHCs with dfcr mutant controls\",\n      \"pmids\": [\"23613530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between facilitation and ubiquitin-dependent channel limitation not integrated\", \"Structural basis of harmonin-Cav1.3 C-terminus contact unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a redox-dependent gating mechanism for selective USH complex assembly, showing glutathionylation promotes harmonin-SANS binding while Grxcr1 reverses it.\",\n      \"evidence\": \"In vitro binding with glutathionylated proteins and zebrafish grxcr1 mutant hair-bundle analysis\",\n      \"pmids\": [\"30380418\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological trigger for glutathionylation in hair cells unknown\", \"Selective vs tripartite complex regulation mechanism only partly mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Reframed tip-link density assembly as a phase-separation phenomenon, showing MYO7A/USH1C/SANS multivalent interactions drive liquid-liquid phase separation that disease mutations impair.\",\n      \"evidence\": \"In vitro phase separation assays, condensate imaging in cells, Co-IP, and mutational analysis\",\n      \"pmids\": [\"31644917\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo demonstration of condensates at native tip-link densities lacking\", \"Material properties and regulation of the condensate in hair cells undefined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided structural and conformational insight into harmonin regulation, defining a PDZ2/coiled-coil-CDHR2 structure with disease mutations and an intramolecular open/closed conformational switch controlling partner binding.\",\n      \"evidence\": \"X-ray crystallography with stability assays; NMR, AUC, CD, and SPR for the conformational switch\",\n      \"pmids\": [\"35747925\", \"28653419\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trigger that toggles the conformational switch in cells unknown\", \"Coiled-coil dimerization role in phase separation not directly tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Uncovered a signaling role beyond scaffolding, showing harmonin suppresses canonical Wnt/β-catenin signaling and defining its retinal localization and interactions, with patient-cell rescue linking these to USH1C disease.\",\n      \"evidence\": \"Co-IP, luciferase Wnt reporters, RNA-seq, and Ataluren/transcript-delivery rescue in patient fibroblasts; retinal immunolocalization and rhodopsin Co-IP\",\n      \"pmids\": [\"36846582\", \"35997788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Connection between Wnt suppression and sensory phenotypes unclear\", \"Whether nuclear β-catenin binding occurs in hair cells/photoreceptors in vivo untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How harmonin's distinct activities — tip-link anchoring, phase separation, presynaptic Cav1.3 regulation, redox/conformational gating, and Wnt suppression — are coordinated within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model integrating mechanotransduction and synaptic roles\", \"Upstream signals controlling conformational/redox switching unidentified\", \"In vivo phase-separation behavior at tip links not demonstrated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 2, 5, 10, 11]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [14, 17, 23]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 8, 9]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [8, 11, 14]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0007605\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"complexes\": [\n      \"USH interactome (MYO7A/USH1C/SANS tip-link density complex)\",\n      \"upper tip-link density\",\n      \"CDH23/harmonin/myosin VIIa ternary complex\"\n    ],\n    \"partners\": [\n      \"CDH23\",\n      \"MYO7A\",\n      \"USH1G\",\n      \"PCDH15\",\n      \"USH2A\",\n      \"VLGR1\",\n      \"CACNA1D\",\n      \"CTNNB1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}