{"gene":"ATXN1","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":1993,"finding":"SCA1 is caused by expansion of an unstable CAG trinucleotide repeat within the coding region of the ATXN1 gene on chromosome 6p, encoding a polyglutamine tract in the protein ataxin-1; repeat size directly correlates with age of onset.","method":"Positional cloning, CAG repeat identification, linkage analysis, mRNA characterization","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 1 — original disease gene identification, foundational study replicated globally, 1518 citations","pmids":["8358429"],"is_preprint":false},{"year":1994,"finding":"The SCA1 gene spans 450 kb, is organized in nine exons (first seven in the 5' UTR with alternative splicing), produces a 10,660-base transcript encoding ataxin-1, and is transcribed from both wild-type and expanded alleles.","method":"cDNA cloning, genomic organization, Northern blot, sequencing","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 1 — foundational characterization of gene structure, widely replicated","pmids":["7951322"],"is_preprint":false},{"year":1995,"finding":"Ataxin-1 protein localizes to the nucleus in all brain regions examined, with cytoplasmic localization also observed in cerebellar Purkinje cells; mutant protein migrates aberrantly by size proportional to CAG repeat length and shows normal stability and distribution.","method":"Immunoblot analysis of patient and normal tissues, immunofluorescence","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — direct protein localization with multiple tissue/cell types, foundational study","pmids":["7647801"],"is_preprint":false},{"year":1997,"finding":"Mutant ataxin-1 with expanded polyglutamine localizes to a single large nuclear inclusion (~2 µm) in Purkinje cells of transgenic mice and SCA1 patients, whereas wild-type ataxin-1 distributes to multiple smaller nuclear structures (~0.5 µm); both forms associate with the nuclear matrix, and mutant ataxin-1 causes redistribution of the PML-containing nuclear matrix-associated domain.","method":"Immunofluorescence in transgenic mice and SCA1 patient neurons, nuclear matrix fractionation, COS-1 cell transfection","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — direct subcellular localization with functional consequence (nuclear matrix reorganization), replicated in multiple model systems","pmids":["9353120"],"is_preprint":false},{"year":1997,"finding":"The leucine-rich acidic nuclear protein LANP interacts with ataxin-1 in a glutamine-length-dependent manner (stronger interaction with expanded polyglutamine); both proteins co-localize in nuclear matrix-associated subnuclear structures, and LANP is expressed predominantly in Purkinje cells — the primary site of SCA1 pathology.","method":"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence colocalization, Western blot","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction validation with glutamine-length dependence, replicated across systems","pmids":["9353121"],"is_preprint":false},{"year":1998,"finding":"Nuclear inclusions of mutant ataxin-1 in SCA1 patient neurons and transgenic mice stain positively for the 20S proteasome and the DnaJ chaperone HDJ-2/HSDJ; overexpression of wild-type HDJ-2/HSDJ in HeLa cells decreases frequency of ataxin-1 aggregation, implying that protein misfolding drives nuclear aggregate formation.","method":"Immunostaining of patient tissue and transgenic mouse brains, HeLa cell transfection, chaperone overexpression assay","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — functional rescue by chaperone overexpression, orthogonal methods across patient tissue and cell models","pmids":["9620770"],"is_preprint":false},{"year":2001,"finding":"Overexpression of inducible HSP70 in SCA1 transgenic mice suppresses neuropathology and improves motor function, indicating that enhancing chaperone activity mitigates polyglutamine-mediated neurodegeneration in a mammalian model.","method":"Crossbreeding of SCA1 transgenic mice with iHSP70-overexpressing mice, rotarod behavioral assay, neuropathological assessment","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic rescue experiment in mammalian model, multiple phenotypic readouts","pmids":["11448943"],"is_preprint":false},{"year":2003,"finding":"Phosphorylation of ataxin-1 at serine 776 (S776) by Akt is critical for SCA1 pathogenesis: S776 phosphorylation is required for binding to 14-3-3 protein, which stabilizes ataxin-1 and slows its degradation; both 14-3-3 and Akt modulate neurodegeneration in a Drosophila SCA1 model.","method":"Phosphorylation site identification, co-immunoprecipitation, Drosophila genetic epistasis, cell-based degradation assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — mechanism validated in multiple systems (cell, fly) with epistasis and biochemical interaction data","pmids":["12757707"],"is_preprint":false},{"year":2003,"finding":"Serine 776 (S776) phosphorylation of ataxin-1 is critical for polyglutamine-induced disease: ataxin-1[82Q]-A776 (S776A mutant) fails to form nuclear inclusions in cell culture and substantially fails to induce cerebellar disease in transgenic mice despite nuclear localization, demonstrating that polyglutamine expansion plus nuclear localization alone are insufficient without S776 phosphorylation.","method":"Mutagenesis, transgenic mouse generation, rotarod assay, neuropathological analysis","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1 — active-site mutagenesis with in vivo phenotypic validation in transgenic mice","pmids":["12741986"],"is_preprint":false},{"year":2004,"finding":"Ataxin-1 interacts with the transcriptional corepressor SMRT and with histone deacetylase 3; ataxin-1 binds chromosomes and mediates transcriptional repression when tethered to DNA; interaction with SMRT-related factors is conserved (ataxin-1 also binds Drosophila SMRTER); mutant ataxin-1 sequesters SMRTER into aggregates, and Smrter mutation enhances, while Smrter duplication suppresses, the neurodegenerative eye phenotype in flies.","method":"Co-immunoprecipitation, tethered transcriptional repression assay, Drosophila genetic epistasis, immunofluorescence","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — biochemical interaction plus genetic epistasis in Drosophila, multiple orthogonal methods","pmids":["15016912"],"is_preprint":false},{"year":2006,"finding":"The majority of both wild-type and expanded ATXN1 assembles into large stable protein complexes containing the transcriptional repressor Capicua (CIC) in mouse cerebellum; ATXN1 directly binds CIC, modulates CIC repressor activity, and loss of ATXN1 decreases CIC steady-state levels; the S776A mutation substantially reduces mutant ATXN1-CIC association in vivo, linking this interaction to neuropathogenesis.","method":"Native protein complex purification from mouse cerebellum, co-immunoprecipitation, Drosophila and mammalian cell reporter assays, Western blot","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — native complex purification, direct binding demonstrated, genetic and biochemical validation across species","pmids":["17190598"],"is_preprint":false},{"year":2006,"finding":"ATXN1 forms a complex with RORalpha (a transcription factor critical for cerebellar development) and the RORalpha coactivator Tip60; mutant ATXN1 destabilizes RORalpha, reducing expression of RORalpha-controlled genes; partial loss of RORalpha enhances mutant ATXN1 pathogenicity, and delayed postnatal expression of mutant ATXN1 substantially reduces disease severity.","method":"Conditional transgenic mouse model, co-immunoprecipitation, gene expression analysis, behavioral assessment","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — complex identification by co-IP, genetic epistasis in vivo, conditional transgenic model","pmids":["17110330"],"is_preprint":false},{"year":2006,"finding":"CHIP (E3 ubiquitin ligase) directly interacts with ataxin-1 (both expanded and unexpanded) and co-localizes in nuclear inclusions; CHIP promotes ubiquitination of ataxin-1 in vitro and in cell culture, augmented by Hsp70; CHIP overexpression in a Drosophila SCA1 model decreases ataxin-1 steady-state levels and suppresses toxicity for polyglutamine in the context of the ataxin-1 backbone.","method":"Co-immunoprecipitation, in vitro ubiquitination assay, Drosophila overexpression, protein level quantification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro ubiquitination assay plus in vivo Drosophila rescue, multiple orthogonal methods","pmids":["16831871"],"is_preprint":false},{"year":2006,"finding":"Protein-protein interaction network screen (yeast two-hybrid) for ataxia-related proteins identified 770 novel interactions involving ATXN1 and other ataxia proteins; 83% of tested pairs verified in mammalian cells by co-IP, revealing shared interacting partners that modify neurodegeneration.","method":"Yeast two-hybrid screen, mammalian cell co-immunoprecipitation verification","journal":"Cell","confidence":"Medium","confidence_rationale":"Tier 3 — large-scale Y2H with mammalian verification, but individual ATXN1 interactions not deeply characterized mechanistically","pmids":["16713569"],"is_preprint":false},{"year":2008,"finding":"Polyglutamine expansion in ATXN1 has opposing effects on distinct endogenous protein complexes: it favors formation of an ATXN1-RBM17 complex (gain-of-function contributing to SCA1 neuropathology) while attenuating formation and function of the ATXN1-Capicua complex (partial loss-of-function); both mechanisms contribute to SCA1 pathogenesis.","method":"Native complex purification, co-immunoprecipitation, Drosophila genetic epistasis, cell-based functional assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — multiple native complexes characterized biochemically with genetic validation in Drosophila, strong mechanistic resolution","pmids":["18337722"],"is_preprint":false},{"year":2008,"finding":"miR-19, miR-101, and miR-130 co-regulate ataxin-1 levels; inhibition of these microRNAs enhanced cytotoxicity of polyglutamine-expanded ATXN1 in human cells, revealing post-transcriptional regulation of ATXN1 dosage.","method":"microRNA inhibitor experiments in human cells, ATXN1 protein level quantification, cytotoxicity assay","journal":"Nature neuroscience","confidence":"Medium","confidence_rationale":"Tier 3 — functional cell-based experiments with defined phenotypic readout, single study","pmids":["18758459"],"is_preprint":false},{"year":2008,"finding":"UbcH6, an E2 ubiquitin-conjugating enzyme, interacts with ataxin-1 via its AXH domain and ubiquitinates ataxin-1 in the absence of an E3 ligase; UbcH6 co-immunoprecipitates and co-localizes with ataxin-1 in the nucleus, and its expression level regulates the rate of ataxin-1 degradation.","method":"Yeast two-hybrid, co-immunoprecipitation, co-localization, in vitro ubiquitination assay, protein degradation assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro ubiquitination assay plus co-IP and degradation assay, single lab study","pmids":["18439907"],"is_preprint":false},{"year":2009,"finding":"Phosphorylation of ATXN1 at S776 in cerebellar Purkinje cells is mediated by cyclic AMP-dependent protein kinase (PKA), not Akt: immunodepletion and inhibition of PKA decreased S776 phosphorylation in a cerebellar extract-based assay and in vivo, while Akt inhibition did not; S776 phosphorylation is associated with ATXN1 stabilization in Purkinje cells.","method":"Cerebellar extract-based phosphorylation assay, kinase inhibition/immunodepletion, in vivo kinase inhibition, Western blot","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 — cell-free biochemical assay plus in vivo validation, identifies specific kinase contradicting prior model","pmids":["19500214"],"is_preprint":false},{"year":2010,"finding":"Loss of function of ATXN1 increases amyloid beta-protein levels (Aβ40 and Aβ42) by potentiating β-secretase (BACE1) processing of APP; knockdown of ATXN1 by RNAi increased Aβ levels, and this was rescued by concurrent ATXN1 overexpression; overexpression of ATXN1 decreased Aβ levels.","method":"RNA interference in human neuronal cell model and mouse primary cortical neurons, ELISA for Aβ levels, ATXN1 overexpression rescue","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — bidirectional manipulation (KD and OE) with defined molecular readout, single lab","pmids":["20097758"],"is_preprint":false},{"year":2011,"finding":"ATXN1 and ATAXIN1-Like (ATXN1L) form complexes with the transcriptional repressor Capicua (CIC) that are functionally redundant; loss of ATXN1L destabilizes CIC, leading to derepression of Etv4 (an activator of Mmp genes) and MMP9 overexpression, causing lung alveolarization defects and other developmental phenotypes.","method":"Knockout mouse generation (Atxn1L-/-, Atxn1-/-;Atxn1L-/-), Western blot, gene expression analysis, phenotypic characterization","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — double knockout epistasis with molecular pathway placement, replicated genetic analysis","pmids":["22014525"],"is_preprint":false},{"year":2013,"finding":"HOTAIR lncRNA associates with the E3 ubiquitin ligase Dzip3 and its substrate ataxin-1, facilitating ubiquitination of ataxin-1 by Dzip3 in cells and in vitro, thereby accelerating ataxin-1 degradation; HOTAIR levels are elevated in senescent cells and drive rapid ataxin-1 decay.","method":"RNA immunoprecipitation, co-immunoprecipitation, in vitro ubiquitination assay, protein degradation assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro ubiquitination assay with cell-based validation, single lab study","pmids":["24326307"],"is_preprint":false},{"year":2015,"finding":"The RNA-binding protein PUMILIO1 (PUM1) directly regulates ATXN1 mRNA levels post-transcriptionally; Pum1 haploinsufficiency causes SCA1-like neurodegeneration by increasing Ataxin-1 levels; breeding Pum1+/- mice with Atxn1+/- mice normalized ATAXIN1 levels and largely rescued the Pum1+/- phenotype.","method":"Mouse genetics (haploinsufficiency, crossbreeding, knockin), behavioral assays, protein level quantification, epistasis analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic epistasis with rescue, quantitative molecular readouts, multiple mouse lines","pmids":["25768905"],"is_preprint":false},{"year":2015,"finding":"Soluble ATXN1 oligomers form in vivo and their levels correlate with disease progression in Atxn1(154Q/+) mice; oligomeric toxicity, stabilization, and seeding require interaction with Capicua, which is expressed at higher ratios relative to ATXN1 in the cerebellum than in less vulnerable brain regions, explaining regional vulnerability.","method":"Conformational antibody detection of oligomers, co-immunoprecipitation, disease progression correlation, regional expression analysis","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods linking oligomer formation to CIC interaction and regional vulnerability, single lab","pmids":["25988806"],"is_preprint":false},{"year":2017,"finding":"The ATXN1-CIC complex is essential for forebrain development: conditional loss of ATXN1-CIC causes hyperactivity, impaired learning and memory, and defective maturation of upper-layer cortical neurons; CIC in the hypothalamus and medial amygdala modulates social interactions; five individuals with de novo truncating CIC mutations share intellectual disability, ADHD, and autism features.","method":"Conditional mouse knockouts, behavioral phenotyping, cortical neuron characterization, human genetic analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in multiple brain regions with defined cellular and behavioral phenotypes, confirmed in human patients","pmids":["28288114"],"is_preprint":false},{"year":2002,"finding":"PQBP-1 interacts with mutant ataxin-1 in a polyglutamine-length-dependent manner (both in vitro and in vivo); mutant ataxin-1 enhances PQBP-1 binding to the C-terminal domain of RNA Pol II large subunit, reducing Pol II phosphorylation and transcription; this interaction induces apoptotic cell death.","method":"In vitro and in vivo binding assays, co-immunoprecipitation, cell death assay, transcription assay","journal":"Neuron","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical mechanism defined with multiple assays, single lab study","pmids":["12062018"],"is_preprint":false},{"year":2009,"finding":"p62/SQSTM1 is essential for accumulation of polyubiquitinated proteins in PML nuclear bodies upon inhibition of nuclear protein export; p62 contributes to the assembly of proteasome-containing degradative compartments near nuclear aggregates containing polyglutamine-expanded Ataxin-1[Q84] and to degradation of Ataxin-1[Q84].","method":"RNAi knockdown, immunofluorescence, nuclear fractionation, cell-based degradation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with defined molecular readout involving ATXN1 as substrate, single study","pmids":["20018885"],"is_preprint":false},{"year":2020,"finding":"miR760 binds a conserved site in ATXN1's unusually long 5' UTR to induce RNA degradation and translational inhibition; delivery of AAV-expressing miR760 in the cerebellum reduces ATXN1 levels in vivo and mitigates motor coordination deficits in a SCA1 mouse model.","method":"miRNA target site mapping, reporter assays, AAV delivery in vivo, motor coordination assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — 5' UTR mechanism validated in vitro and with in vivo AAV rescue, multiple methods","pmids":["32763910"],"is_preprint":false},{"year":2020,"finding":"ATXN1 intermediate repeat expansions are significantly associated with ALS; ATXN1 reduces the nucleocytoplasmic ratio of TDP-43 and enhances ALS phenotypes in Drosophila, implicating ATXN1 in TDP-43 mislocalization as a disease mechanism.","method":"Large-scale genetic association (11,700 individuals), Drosophila functional experiments, TDP-43 localization assay","journal":"Brain communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — genetic association supported by functional Drosophila experiments, mechanism partially characterized","pmids":["32954321"],"is_preprint":false},{"year":2022,"finding":"Nuclear localization of mutant ATXN1 is required broadly for SCA1-like phenotypes including motor dysfunction, cognitive deficits, and premature lethality; CRISPR-Cas9 K772T mutation in the nuclear localization sequence of expanded ATXN1 corrected many disease-like phenotypes and normalized transcriptomic profiles in multiple brain regions.","method":"CRISPR-Cas9 knock-in mouse, behavioral testing, RNA sequencing across brain regions","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 — precise CRISPR mutagenesis of NLS with comprehensive phenotypic and transcriptomic rescue validation","pmids":["36577403"],"is_preprint":false},{"year":2022,"finding":"Disrupting the ATXN1-CIC interaction globally normalizes genome-wide CIC binding but only partially corrects transcriptional and behavioral phenotypes; unbiased proteomics identified additional ATXN1-interacting transcription factors RFX1, ZBTB5, and ZKSCAN1 whose target genes show altered expression in SCA1 mice and patient-derived iNeurons.","method":"Knockin mouse with ATXN1-CIC interaction mutation, ChIP-seq, RNA-seq, affinity purification mass spectrometry proteomics, patient-derived neurons","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — multi-omic unbiased approach with human patient validation, multiple orthogonal methods","pmids":["36577402"],"is_preprint":false},{"year":2016,"finding":"Loss of ATXN1 induces early alterations in cerebellar bioenergetics proteins (glycolysis and ATP synthesis enzymes); ATXN1 regulates cerebellar bioenergetics via the GSK3β-mTOR pathway — GSK3β is decreased in Atxn1-KO and increased in SCA1 mice, while mTOR is decreased in SCA1 mice before ataxia onset; pharmacological inhibition of GSK3β and activation of mTOR ameliorated metabolic alterations in a SCA1 cell model.","method":"Proteomics of Atxn1-KO cerebellum, Western blot, pharmacological rescue in SCA1 cell model","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — unbiased proteomics with pathway validation, single lab study","pmids":["27466200"],"is_preprint":false}],"current_model":"ATXN1 is a nuclear protein that functions as a transcriptional regulator, assembling into large native complexes with the transcriptional repressor Capicua (CIC) and other factors (RORalpha/Tip60, RFX1, ZBTB5, ZKSCAN1, SMRT/HDAC3); its activity and stability are controlled by PKA-mediated phosphorylation at S776 (which promotes 14-3-3 binding and protein stabilization), ubiquitination by CHIP and UbcH6, and post-transcriptional regulation by PUMILIO1 and multiple microRNAs (miR-19, miR-101, miR-130, miR760) targeting its unusually long 5' UTR; in SCA1, polyglutamine expansion shifts the balance of ATXN1 complexes — favoring the ATXN1-RBM17 complex (gain-of-function) while impairing the ATXN1-CIC complex (partial loss-of-function) — and nuclear localization plus S776 phosphorylation are both required for neurodegeneration, while chaperones (HSP70, HDJ-2) and the proteasome system attempt to clear misfolded aggregates."},"narrative":{"teleology":[{"year":1993,"claim":"Identification of the causative mutation—an unstable CAG repeat expansion in ATXN1—established the molecular basis of SCA1 and linked polyglutamine tract length to disease severity.","evidence":"Positional cloning and linkage analysis in SCA1 families","pmids":["8358429"],"confidence":"High","gaps":["Why Purkinje cells are selectively vulnerable was not explained","Function of the normal ataxin-1 protein was unknown"]},{"year":1995,"claim":"Demonstrating that ataxin-1 is a nuclear protein—with additional cytoplasmic localization in Purkinje cells—established that its primary site of action is the nucleus, redirecting the field away from cytoplasmic aggregation models.","evidence":"Immunoblot and immunofluorescence of patient and normal human brain tissues","pmids":["7647801"],"confidence":"High","gaps":["Nuclear function remained undefined","Mechanism of nuclear targeting not mapped"]},{"year":1997,"claim":"Discovery that mutant ataxin-1 forms a single large nuclear inclusion that reorganizes the PML-containing nuclear matrix, and that LANP interacts with ataxin-1 in a glutamine-length-dependent manner in Purkinje cells, implicated nuclear matrix disruption and selective protein interactions in pathogenesis.","evidence":"Immunofluorescence and nuclear matrix fractionation in transgenic mice and patient tissue; yeast two-hybrid and co-IP for LANP","pmids":["9353120","9353121"],"confidence":"High","gaps":["Whether nuclear inclusions are toxic or protective was unresolved","LANP's functional role in the ATXN1 pathway was unclear"]},{"year":1998,"claim":"Finding that proteasome subunits and chaperone HDJ-2 colocalize with nuclear inclusions, and that HDJ-2 overexpression reduces aggregation, established that protein quality control machinery engages misfolded ataxin-1.","evidence":"Immunostaining of patient and transgenic mouse brain, chaperone overexpression in HeLa cells","pmids":["9620770"],"confidence":"High","gaps":["Whether chaperone-mediated clearance is sufficient to prevent disease in vivo was untested","Ubiquitination machinery for ataxin-1 was unidentified"]},{"year":2001,"claim":"In vivo demonstration that HSP70 overexpression suppresses SCA1 neuropathology in transgenic mice provided the first mammalian proof that enhancing proteostasis can rescue polyglutamine-mediated neurodegeneration.","evidence":"Crossbreeding SCA1 transgenic with iHSP70-overexpressing mice; rotarod and neuropathology","pmids":["11448943"],"confidence":"High","gaps":["Specific substrates of HSP70 in this context were not defined","Whether clearance versus refolding underlies rescue was unclear"]},{"year":2003,"claim":"Identification of S776 phosphorylation as a disease-critical post-translational modification—required for 14-3-3 binding, protein stabilization, nuclear inclusion formation, and in vivo cerebellar pathology—established that polyglutamine expansion alone is insufficient for neurodegeneration.","evidence":"Phospho-site identification, co-IP with 14-3-3, Drosophila epistasis, S776A transgenic mice with rotarod and neuropathology","pmids":["12757707","12741986"],"confidence":"High","gaps":["The kinase responsible for S776 phosphorylation in Purkinje cells was initially misassigned to Akt","Downstream consequences of 14-3-3 binding beyond stabilization were unexplored"]},{"year":2006,"claim":"Purification of native ATXN1-containing complexes revealed that ataxin-1 functions primarily as a component of large transcriptional regulatory complexes: a CIC-containing repressor complex, an RORα/Tip60 coactivator complex, and a SMRT/HDAC3 corepressor complex, redefining ataxin-1 as a transcriptional regulator rather than merely an aggregation-prone protein.","evidence":"Native complex purification from mouse cerebellum, co-IP, reporter assays, Drosophila genetic epistasis for SMRT and RORα pathways","pmids":["17190598","17110330","15016912"],"confidence":"High","gaps":["How ATXN1 coordinates membership across distinct complexes was unknown","Genome-wide transcriptional targets of these complexes were not mapped"]},{"year":2006,"claim":"Demonstration that CHIP ubiquitin ligase and UbcH6 ubiquitin-conjugating enzyme mediate ataxin-1 ubiquitination and degradation defined the proteolytic pathway controlling ataxin-1 turnover.","evidence":"In vitro ubiquitination assays, co-IP, Drosophila CHIP overexpression rescue","pmids":["16831871","18439907"],"confidence":"High","gaps":["Relative contributions of CHIP versus UbcH6-mediated ubiquitination in vivo were not resolved","Ubiquitin chain type specificity was not determined"]},{"year":2008,"claim":"The finding that polyglutamine expansion shifts the equilibrium between ATXN1 complexes—favoring the pathogenic ATXN1–RBM17 complex while attenuating the ATXN1–CIC complex—established a dual gain-of-function/partial loss-of-function model for SCA1 pathogenesis.","evidence":"Native complex purification, co-IP, Drosophila genetic epistasis","pmids":["18337722"],"confidence":"High","gaps":["Structural basis for differential complex assembly was unknown","Whether therapeutic rebalancing of complexes is achievable was untested"]},{"year":2009,"claim":"Reassignment of the S776 kinase from Akt to PKA in cerebellar Purkinje cells corrected a key mechanistic detail and focused therapeutic kinase-targeting efforts on the cAMP-PKA signaling axis.","evidence":"Cerebellar extract kinase assay with immunodepletion and inhibition, in vivo kinase inhibition","pmids":["19500214"],"confidence":"High","gaps":["Whether other kinases contribute in non-cerebellar cell types was unexplored","Upstream signals regulating PKA-dependent ATXN1 phosphorylation were not defined"]},{"year":2015,"claim":"Discovery that PUMILIO1 post-transcriptionally controls ATXN1 mRNA levels, and that Pum1 haploinsufficiency causes SCA1-like neurodegeneration rescuable by reducing Atxn1 gene dosage, established that ATXN1 protein levels are tightly regulated and that even modest elevation is pathogenic.","evidence":"Mouse genetic epistasis (Pum1+/− × Atxn1+/−), behavioral assays, protein quantification","pmids":["25768905"],"confidence":"High","gaps":["Whether PUM1 acts on the 3′ UTR, 5′ UTR, or coding sequence was not fully resolved","Other RNA-binding proteins regulating ATXN1 mRNA were not systematically identified"]},{"year":2017,"claim":"Conditional knockout studies demonstrated that the ATXN1–CIC complex is essential for forebrain neuron maturation, learning, memory, and social behavior, extending ATXN1 function beyond the cerebellum and linking CIC mutations to intellectual disability and autism in humans.","evidence":"Conditional mouse knockouts, behavioral phenotyping, cortical neuron characterization, human de novo CIC mutation analysis","pmids":["28288114"],"confidence":"High","gaps":["Direct genomic targets of ATXN1–CIC in forebrain were not comprehensively mapped","Whether ATXN1-independent CIC functions contribute to the human phenotype was unclear"]},{"year":2020,"claim":"Identification of miR-760 as a regulator acting through the ATXN1 5′ UTR, with AAV-delivered miR-760 reducing ATXN1 levels and rescuing motor deficits in SCA1 mice, established a therapeutic strategy exploiting post-transcriptional dosage control.","evidence":"miRNA target site mapping, reporter assays, AAV delivery in SCA1 mouse cerebellum, motor coordination assay","pmids":["32763910"],"confidence":"High","gaps":["Long-term safety and off-target effects of miR-760 delivery were not assessed","Whether combining miR-760 with other miRNAs (miR-19, miR-101, miR-130) provides additive benefit was untested"]},{"year":2022,"claim":"CRISPR-based disruption of the ATXN1 nuclear localization signal rescued motor, cognitive, and transcriptomic phenotypes genome-wide, definitively proving that nuclear localization of mutant ATXN1 is required for the full spectrum of SCA1 pathology; meanwhile, disrupting the ATXN1–CIC interaction only partially corrected phenotypes, and proteomics identified RFX1, ZBTB5, and ZKSCAN1 as additional transcription factor partners whose target genes are dysregulated in SCA1.","evidence":"CRISPR-Cas9 NLS knock-in mouse, CIC-interaction mutant knock-in mouse, ChIP-seq, RNA-seq, affinity purification mass spectrometry, patient-derived iNeurons","pmids":["36577403","36577402"],"confidence":"High","gaps":["Relative pathogenic contributions of RFX1, ZBTB5, and ZKSCAN1 complex disruption versus CIC complex disruption are unquantified","Structural basis for ATXN1 interaction with these new partners is unknown"]},{"year":null,"claim":"The full transcription factor interaction landscape of ATXN1, the structural basis for polyglutamine-dependent complex switching, and the therapeutic potential of combined dosage-reduction and complex-rebalancing strategies remain to be determined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of ATXN1 in complex with CIC or RBM17 exists","How ATXN1 intermediate-length repeats contribute to ALS via TDP-43 mislocalization requires mechanistic resolution","Whether pharmacological PKA inhibition or miRNA-based ATXN1 reduction translates to human SCA1 therapy is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[9,10,11,14,29]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[10,14,19]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,3,5,8,16,28]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[3,9,29]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[9,10,11,29]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[3,9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[7,12,16,20]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,17,30]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,8,14,28]}],"complexes":["ATXN1-CIC repressor complex","ATXN1-RBM17 complex","ATXN1-RORα-Tip60 complex","ATXN1-SMRT-HDAC3 complex"],"partners":["CIC","RBM17","RORA","KAT5","NCOR2","STUB1","PUM1","YWHAZ"],"other_free_text":[]},"mechanistic_narrative":"ATXN1 encodes the nuclear transcriptional regulator ataxin-1, which assembles into distinct native protein complexes—most prominently with the transcriptional repressor Capicua (CIC) and with RORα/Tip60—to control gene expression programs essential for cerebellar Purkinje cell maintenance and forebrain development [PMID:17190598, PMID:17110330, PMID:28288114]. ATXN1 stability and function are governed by PKA-mediated phosphorylation at S776 (promoting 14-3-3 binding and protein stabilization), ubiquitin-dependent degradation via CHIP and UbcH6, and post-transcriptional dosage control by PUMILIO1 and multiple microRNAs targeting its extended 5′ UTR [PMID:19500214, PMID:16831871, PMID:25768905, PMID:32763910]. CAG trinucleotide repeat expansion in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), in which polyglutamine-expanded ataxin-1 shifts the balance of endogenous complexes—favoring the pathogenic ATXN1–RBM17 interaction while impairing the ATXN1–CIC complex—with nuclear localization and S776 phosphorylation both required for neurodegeneration [PMID:8358429, PMID:18337722, PMID:12741986, PMID:36577403]. Unbiased proteomics has further identified ATXN1 interactions with transcription factors RFX1, ZBTB5, and ZKSCAN1, whose dysregulation contributes to the broader transcriptional pathology of SCA1 [PMID:36577402]."},"prefetch_data":{"uniprot":{"accession":"P54253","full_name":"Ataxin-1","aliases":["Spinocerebellar ataxia type 1 protein"],"length_aa":815,"mass_kda":86.9,"function":"Chromatin-binding factor that repress Notch signaling in the absence of Notch intracellular domain by acting as a CBF1 corepressor. Binds to the HEY promoter and might assist, along with NCOR2, RBPJ-mediated repression. Binds RNA in vitro. May be involved in RNA metabolism (PubMed:21475249). In concert with CIC and ATXN1L, involved in brain development (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P54253/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATXN1","classification":"Not Classified","n_dependent_lines":8,"n_total_lines":1208,"dependency_fraction":0.006622516556291391},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ATXN1","total_profiled":1310},"omim":[{"mim_id":"620719","title":"NEURODEVELOPMENTAL DISORDER WITH MOTOR ABNORMALITIES, SEIZURES, AND FACIAL DYSMORPHISM; NEDMSF","url":"https://www.omim.org/entry/620719"},{"mim_id":"620098","title":"DEVELOPMENTAL DELAY WITH VARIABLE INTELLECTUAL DISABILITY AND DYSMORPHIC FACIES; DIDDF","url":"https://www.omim.org/entry/620098"},{"mim_id":"617600","title":"INTELLECTUAL DEVELOPMENTAL DISORDER, AUTOSOMAL DOMINANT 45; MRD45","url":"https://www.omim.org/entry/617600"},{"mim_id":"614301","title":"ATAXIN 1-LIKE; ATXN1L","url":"https://www.omim.org/entry/614301"},{"mim_id":"612876","title":"SPINOCEREBELLAR ATAXIA 9; SCA9","url":"https://www.omim.org/entry/612876"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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molecular chaperone HDJ-2/HSDJ, indicating protein misfolding; overexpression of wild-type HDJ-2/HSDJ decreases the frequency of ataxin-1 nuclear aggregation in HeLa cells, suggesting that DnaJ chaperones can promote refolding or ubiquitin-dependent degradation of misfolded ATXN1.\",\n      \"method\": \"Immunostaining of SCA1 patient/transgenic mouse tissue, HeLa cell transfection with mutant ATXN1, colocalization with proteasome and chaperone markers, HDJ-2/HSDJ overexpression to reduce aggregation frequency\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal colocalization plus functional gain-of-function (chaperone OE) with defined phenotypic readout; replicated in patient tissue and mouse models\",\n      \"pmids\": [\"9620770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Overexpression of inducible HSP70 in SCA1 mice suppresses neuropathology and improves motor function, demonstrating that enhanced chaperone activity can mitigate polyglutamine-induced protein misfolding and neurodegeneration caused by mutant ATXN1.\",\n      \"method\": \"Crossbreeding SCA1 transgenic mice with iHSP70 overexpressing mice; rotarod behavioral testing; histopathological analysis of Purkinje cell pathology\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic rescue experiment with multiple orthogonal readouts (behavioral + histopathological)\",\n      \"pmids\": [\"11448943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ATXN1 interacts with the transcriptional corepressor SMRT and with histone deacetylase 3; ATXN1 binds chromosomes and mediates transcriptional repression when tethered to DNA. This interaction is conserved with Drosophila SMRTER, and mutant ATXN1 aggregates sequester SMRTER, implicating disruption of corepressor-dependent transcriptional pathways in SCA1 pathogenesis.\",\n      \"method\": \"Co-immunoprecipitation, reporter gene transcriptional repression assays, Drosophila genetic epistasis (Smrter loss-of-function enhances neurodegeneration; Smrter duplication suppresses it)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, functional transcriptional assay, and in vivo genetic epistasis in Drosophila with multiple orthogonal methods\",\n      \"pmids\": [\"15016912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"RORalpha, a transcription factor critical for cerebellar development, is destabilized in SCA1 mice expressing mutant ATXN1; ATXN1 exists in a complex with RORalpha and the RORalpha coactivator Tip60. Partial loss of RORalpha enhances mutant ATXN1 pathogenicity, and delayed postnatal expression of mutant ATXN1 (after cerebellar development) substantially reduces disease severity in adults.\",\n      \"method\": \"Conditional transgenic mouse model with delayed transgene expression; gene expression profiling; co-immunoprecipitation identifying ATXN1-RORalpha-Tip60 complex; genetic interaction with RORalpha haploinsufficiency\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — conditional mouse model, complex identification by Co-IP, genetic epistasis, and gene expression analysis in a single study with multiple orthogonal approaches\",\n      \"pmids\": [\"17110330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"miR-19, miR-101, and miR-130 co-regulate ATXN1 protein levels post-transcriptionally; inhibition of these miRNAs in human cells enhanced cytotoxicity of polyglutamine-expanded ATXN1, establishing that ATXN1 levels are under miRNA-mediated post-transcriptional control.\",\n      \"method\": \"miRNA inhibitor experiments in human cells; ATXN1 protein level measurement; cytotoxicity assays\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional loss-of-function miRNA experiments with defined molecular (protein level) and cellular (cytotoxicity) phenotypic readouts\",\n      \"pmids\": [\"18758459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Phosphorylation of ATXN1 at serine 776 (S776) stabilizes ATXN1 in cerebellar Purkinje cells. Cyclic AMP-dependent protein kinase (PKA), not Akt, is the primary kinase responsible for S776 phosphorylation in the cerebellum, as demonstrated by immunodepletion and inhibition experiments.\",\n      \"method\": \"In vivo PKA and Akt inhibition in mice; cerebellar extract-based phosphorylation assays; immunodepletion; Western blot analysis of ATXN1 stability\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro kinase assay with immunodepletion and in vivo inhibitor experiments, multiple orthogonal methods identifying the kinase\",\n      \"pmids\": [\"19500214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATXN1 and ATXN1L form complexes with the transcriptional repressor Capicua (CIC) and function redundantly to regulate extracellular matrix remodeling during development. Loss of ATXN1L (or combined ATXN1/ATXN1L) destabilizes CIC, leading to derepression of Etv4 and overexpression of MMP9, causing lung alveolarization defects.\",\n      \"method\": \"Atxn1L-/- and Atxn1-/-;Atxn1L-/- mouse knockout; gene expression profiling; CIC protein stability assays; genetic epistasis with Cic knockout\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double knockout with multiple phenotypic readouts and molecular pathway placement (ATXN1/1L→CIC→Etv4→MMP9); multiple orthogonal methods\",\n      \"pmids\": [\"22014525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Knockdown of ATXN1 in human neuronal cells and mouse primary cortical neurons significantly increases Aβ40 and Aβ42 levels by potentiating β-secretase (BACE1) cleavage of APP; overexpression of ATXN1 decreases Aβ levels. This establishes ATXN1 as a regulator of β-secretase processing of APP.\",\n      \"method\": \"RNA interference knockdown of ATXN1 in human neuronal cell model and mouse primary cortical neurons; ELISA for Aβ40/42; rescue with ATXN1 overexpression; mechanistic focus on β-secretase cleavage pathway\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KD and OE with defined molecular mechanism (β-secretase pathway), replicated in two cell systems\",\n      \"pmids\": [\"20097758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In SCA1 transgenic mice expressing ATXN1[82Q], there is a preferential reduction in Purkinje cell responsiveness to climbing fiber (CF) activation (but not parallel fiber activation), accompanied by decreased CF extension on PC dendrites. This deficit requires nuclear entry of ATXN1[82Q] and is ameliorated when mutant transgene expression is prevented during postnatal cerebellar development.\",\n      \"method\": \"Flavoprotein autofluorescence optical imaging; extracellular field potential recordings; immunostaining for VGluT2; comparison across multiple ATXN1 transgenic lines including nuclear localization mutant\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo electrophysiology and imaging with multiple transgenic lines and functional genetic controls, multiple orthogonal methods\",\n      \"pmids\": [\"21900557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Polyglutamine-expanded ATXN1 forms soluble toxic oligomers whose levels correlate with disease progression. Oligomeric toxicity, stabilization, and seeding require interaction with Capicua (CIC), which is expressed at greater ratios with respect to ATXN1 in the cerebellum than in less vulnerable brain regions, explaining regional vulnerability.\",\n      \"method\": \"Conformational antibody detection of oligomers in Atxn1(154Q/+) mice; correlation of oligomer levels with disease progression; functional seeding and toxicity assays; CIC interaction studies\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods demonstrating oligomer formation and CIC-dependent stabilization with in vivo disease correlation\",\n      \"pmids\": [\"25988806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The RNA-binding protein PUMILIO1 (PUM1) directly regulates ATXN1 mRNA/protein levels post-transcriptionally. Loss of Pum1 increases Ataxin-1 levels, causing SCA1-like neurodegeneration; breeding Pum1+/- mice to Atxn1+/- mice normalized Ataxin-1 levels and largely rescued the Pum1+/- phenotype, establishing PUM1 as a direct post-transcriptional regulator of ATXN1.\",\n      \"method\": \"Pum1 heterozygous and homozygous knockout mice; crossbreeding with SCA1 and Atxn1+/- mice; ATXN1 protein level measurements; motor behavior testing; genetic epistasis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple mouse crosses, direct protein level measurements, and behavioral phenotypic rescue; replicated across multiple genetic backgrounds\",\n      \"pmids\": [\"25768905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The ATXN1-CIC transcriptional repressor complex is essential for normal forebrain development; loss of ATXN1-CIC complex causes hyperactivity, impaired learning and memory, and abnormal maturation of upper-layer cortical neurons. CIC activity in the hypothalamus and medial amygdala modulates social interactions.\",\n      \"method\": \"Conditional mouse knockouts of ATXN1-CIC interaction; behavioral testing (hyperactivity, learning/memory, social behavior); cortical neuron maturation analysis; human patient identification with CIC truncating mutations\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional knockout mouse with multiple behavioral and cellular phenotypic readouts, plus human genetic validation\",\n      \"pmids\": [\"28288114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UbcH6, an E2 ubiquitin-conjugating enzyme, interacts with ataxin-1 through its AXH domain, co-localizes with it in the nucleus, and ubiquitinates ataxin-1 in the absence of an E3 ligase. UbcH6 expression level regulates the rate of ataxin-1 degradation.\",\n      \"method\": \"Yeast two-hybrid screen; co-immunoprecipitation; colocalization in nucleus; in vitro ubiquitination assay without E3; pulse-chase degradation assay; domain mapping with AXH domain\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus in vitro ubiquitination assay and functional degradation assay, but single lab study\",\n      \"pmids\": [\"18439907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of ATXN1 in knockout mice induces alterations in glycolytic and bioenergetic proteins and decreases GSK3β activity, while SCA1 mice show decreased mTOR activity; pharmacological inhibition of GSK3β and activation of mTOR in a SCA1 cell model ameliorated metabolic proteome and ATP alterations, indicating that ATXN1 regulates cerebellar bioenergetics through the GSK3β-mTOR pathway.\",\n      \"method\": \"Atxn1-KO mouse cerebellar proteomics; ATP measurement; GSK3β and mTOR activity assays; pharmacological manipulation in SCA1 cell model\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics plus functional pathway manipulation, but single lab study with primarily correlative proteomics supporting the mechanistic claim\",\n      \"pmids\": [\"27466200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Impaired climbing fiber-mediated synaptic transmission diminishes mTORC1 signaling in Purkinje cells of Sca1(154Q/2Q) mice, leading to reduced Homer-3 expression. Ablating mTORC1 in PCs exacerbated and accelerated SCA1 pathology; reinstating Homer-3 expression attenuated cellular dysfunction and improved motor deficits.\",\n      \"method\": \"Proteomic profiling of Sca1(154Q/2Q) Purkinje cells; mTORC1 conditional knockout; pharmacological mTORC1 inhibition; AAV-mediated Homer-3 restoration; behavioral and electrophysiological assessment\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (proteomics, genetic KO, pharmacology, AAV rescue) with defined pathway placement (CF→mTORC1→Homer-3) in a single study\",\n      \"pmids\": [\"26748090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ATXN1 reduces the nucleocytoplasmic ratio of TDP-43; intermediate ATXN1 repeat expansions are significantly associated with ALS. Functional experiments in Drosophila demonstrated that ATXN1 enhances ALS-related phenotypes, linking ATXN1 polyglutamine expansions to TDP-43 mislocalization.\",\n      \"method\": \"Large-scale genetic association study (11,700 individuals); Drosophila functional experiments measuring TDP-43 nucleocytoplasmic ratio; ALS phenotype enhancement assays\",\n      \"journal\": \"Brain communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — genetic association with functional Drosophila validation, but TDP-43 mechanism established only in Drosophila model\",\n      \"pmids\": [\"32954321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR760 binds to a conserved site in ATXN1's unusually long 5' UTR to induce RNA degradation and translational inhibition, negatively regulating ATXN1 expression; AAV-mediated delivery of miR760 to the cerebellum reduces ATXN1 levels in vivo and mitigates motor coordination deficits in a SCA1 mouse model.\",\n      \"method\": \"5' UTR deletion and mutagenesis assays; luciferase reporter assays; RNA degradation and translational inhibition measurements; AAV-miR760 delivery in SCA1 mice; motor behavioral testing\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mechanistic dissection of 5' UTR regulation with mutagenesis, functional reporter assays, and in vivo rescue, multiple orthogonal methods in a single study\",\n      \"pmids\": [\"32763910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Proper nuclear localization of mutant ATXN1 contributes to multiple SCA1 disease phenotypes including motor dysfunction, cognitive deficits, and premature lethality; CRISPR-Cas9 introduction of the K772T amino acid alteration in ATXN1's nuclear localization sequence in the expanded allele substantially corrects these phenotypes and normalizes transcriptomic profiles across multiple brain regions.\",\n      \"method\": \"CRISPR-Cas9 knock-in of K772T mutation in expanded Atxn1 allele; motor and cognitive behavioral testing; RNA sequencing across brain regions; comparison across cerebellar, brainstem, cortical, hippocampal, and striatal transcriptomes\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — precise endogenous gene editing with multiple phenotypic readouts and transcriptomic characterization across brain regions, rigorous in vivo mechanistic study\",\n      \"pmids\": [\"36577403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Disruption of the ATXN1-CIC interaction globally only partially corrects transcriptional and behavioral phenotypes in SCA1 mice; unbiased proteomics identified additional ATXN1-interacting transcription factors RFX1, ZBTB5, and ZKSCAN1, whose target gene expression is altered in SCA1 mice and patient-derived iNeurons, revealing a more complex transcriptional mechanism beyond ATXN1-CIC.\",\n      \"method\": \"Global ATXN1-CIC interaction-disrupting knockin mice; genome-wide CIC ChIP-seq; unbiased Co-IP proteomics; RNA-seq in SCA1 mice and patient iNeurons; behavioral phenotyping\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal approaches (proteomics, ChIP-seq, RNA-seq, behavioral) in a single rigorous study identifying novel ATXN1 interactors\",\n      \"pmids\": [\"36577402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A single antisense oligonucleotide (ASO) treatment targeting Atxn1 mRNA in Atxn1(154Q/2Q) knockin mice at 5 weeks of age rescued motor deficits and premature lethality, and reversed neurochemical abnormalities in the cerebellum and brainstem, demonstrating that reducing ATXN1 RNA levels is sufficient to ameliorate both motor and survival phenotypes in SCA1.\",\n      \"method\": \"Single ASO injection in SCA1 knockin mice; rotarod motor testing; survival analysis; RNA-seq analysis; MRS neurochemical measurements\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo knockdown with multiple phenotypic and molecular readouts demonstrating direct therapeutic efficacy of ATXN1 reduction\",\n      \"pmids\": [\"30385727\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATXN1 is a nuclear protein that functions primarily as a transcriptional regulator through complexes with CIC, RORalpha/Tip60, and SMRT/HDAC3 corepressors; its stability and nuclear activity are regulated by PKA-mediated phosphorylation at Ser776, post-transcriptional regulation by miRNAs (miR-19, miR-101, miR-130, miR760) and the RNA-binding protein PUM1, and ubiquitin-mediated degradation via UbcH6; polyglutamine expansion in ATXN1 causes SCA1 by exaggerating its native transcriptional functions—particularly through the ATXN1-CIC complex—leading to preferential climbing fiber-Purkinje cell circuit dysfunction, mTORC1-Homer-3 signaling impairment, and progressive cerebellar neurodegeneration.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1993,\n      \"finding\": \"SCA1 is caused by expansion of an unstable CAG trinucleotide repeat within the coding region of the ATXN1 gene on chromosome 6p, encoding a polyglutamine tract in the protein ataxin-1; repeat size directly correlates with age of onset.\",\n      \"method\": \"Positional cloning, CAG repeat identification, linkage analysis, mRNA characterization\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original disease gene identification, foundational study replicated globally, 1518 citations\",\n      \"pmids\": [\"8358429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The SCA1 gene spans 450 kb, is organized in nine exons (first seven in the 5' UTR with alternative splicing), produces a 10,660-base transcript encoding ataxin-1, and is transcribed from both wild-type and expanded alleles.\",\n      \"method\": \"cDNA cloning, genomic organization, Northern blot, sequencing\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — foundational characterization of gene structure, widely replicated\",\n      \"pmids\": [\"7951322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Ataxin-1 protein localizes to the nucleus in all brain regions examined, with cytoplasmic localization also observed in cerebellar Purkinje cells; mutant protein migrates aberrantly by size proportional to CAG repeat length and shows normal stability and distribution.\",\n      \"method\": \"Immunoblot analysis of patient and normal tissues, immunofluorescence\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct protein localization with multiple tissue/cell types, foundational study\",\n      \"pmids\": [\"7647801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mutant ataxin-1 with expanded polyglutamine localizes to a single large nuclear inclusion (~2 µm) in Purkinje cells of transgenic mice and SCA1 patients, whereas wild-type ataxin-1 distributes to multiple smaller nuclear structures (~0.5 µm); both forms associate with the nuclear matrix, and mutant ataxin-1 causes redistribution of the PML-containing nuclear matrix-associated domain.\",\n      \"method\": \"Immunofluorescence in transgenic mice and SCA1 patient neurons, nuclear matrix fractionation, COS-1 cell transfection\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization with functional consequence (nuclear matrix reorganization), replicated in multiple model systems\",\n      \"pmids\": [\"9353120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The leucine-rich acidic nuclear protein LANP interacts with ataxin-1 in a glutamine-length-dependent manner (stronger interaction with expanded polyglutamine); both proteins co-localize in nuclear matrix-associated subnuclear structures, and LANP is expressed predominantly in Purkinje cells — the primary site of SCA1 pathology.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence colocalization, Western blot\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction validation with glutamine-length dependence, replicated across systems\",\n      \"pmids\": [\"9353121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Nuclear inclusions of mutant ataxin-1 in SCA1 patient neurons and transgenic mice stain positively for the 20S proteasome and the DnaJ chaperone HDJ-2/HSDJ; overexpression of wild-type HDJ-2/HSDJ in HeLa cells decreases frequency of ataxin-1 aggregation, implying that protein misfolding drives nuclear aggregate formation.\",\n      \"method\": \"Immunostaining of patient tissue and transgenic mouse brains, HeLa cell transfection, chaperone overexpression assay\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional rescue by chaperone overexpression, orthogonal methods across patient tissue and cell models\",\n      \"pmids\": [\"9620770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Overexpression of inducible HSP70 in SCA1 transgenic mice suppresses neuropathology and improves motor function, indicating that enhancing chaperone activity mitigates polyglutamine-mediated neurodegeneration in a mammalian model.\",\n      \"method\": \"Crossbreeding of SCA1 transgenic mice with iHSP70-overexpressing mice, rotarod behavioral assay, neuropathological assessment\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic rescue experiment in mammalian model, multiple phenotypic readouts\",\n      \"pmids\": [\"11448943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Phosphorylation of ataxin-1 at serine 776 (S776) by Akt is critical for SCA1 pathogenesis: S776 phosphorylation is required for binding to 14-3-3 protein, which stabilizes ataxin-1 and slows its degradation; both 14-3-3 and Akt modulate neurodegeneration in a Drosophila SCA1 model.\",\n      \"method\": \"Phosphorylation site identification, co-immunoprecipitation, Drosophila genetic epistasis, cell-based degradation assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mechanism validated in multiple systems (cell, fly) with epistasis and biochemical interaction data\",\n      \"pmids\": [\"12757707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Serine 776 (S776) phosphorylation of ataxin-1 is critical for polyglutamine-induced disease: ataxin-1[82Q]-A776 (S776A mutant) fails to form nuclear inclusions in cell culture and substantially fails to induce cerebellar disease in transgenic mice despite nuclear localization, demonstrating that polyglutamine expansion plus nuclear localization alone are insufficient without S776 phosphorylation.\",\n      \"method\": \"Mutagenesis, transgenic mouse generation, rotarod assay, neuropathological analysis\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — active-site mutagenesis with in vivo phenotypic validation in transgenic mice\",\n      \"pmids\": [\"12741986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Ataxin-1 interacts with the transcriptional corepressor SMRT and with histone deacetylase 3; ataxin-1 binds chromosomes and mediates transcriptional repression when tethered to DNA; interaction with SMRT-related factors is conserved (ataxin-1 also binds Drosophila SMRTER); mutant ataxin-1 sequesters SMRTER into aggregates, and Smrter mutation enhances, while Smrter duplication suppresses, the neurodegenerative eye phenotype in flies.\",\n      \"method\": \"Co-immunoprecipitation, tethered transcriptional repression assay, Drosophila genetic epistasis, immunofluorescence\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical interaction plus genetic epistasis in Drosophila, multiple orthogonal methods\",\n      \"pmids\": [\"15016912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The majority of both wild-type and expanded ATXN1 assembles into large stable protein complexes containing the transcriptional repressor Capicua (CIC) in mouse cerebellum; ATXN1 directly binds CIC, modulates CIC repressor activity, and loss of ATXN1 decreases CIC steady-state levels; the S776A mutation substantially reduces mutant ATXN1-CIC association in vivo, linking this interaction to neuropathogenesis.\",\n      \"method\": \"Native protein complex purification from mouse cerebellum, co-immunoprecipitation, Drosophila and mammalian cell reporter assays, Western blot\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — native complex purification, direct binding demonstrated, genetic and biochemical validation across species\",\n      \"pmids\": [\"17190598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ATXN1 forms a complex with RORalpha (a transcription factor critical for cerebellar development) and the RORalpha coactivator Tip60; mutant ATXN1 destabilizes RORalpha, reducing expression of RORalpha-controlled genes; partial loss of RORalpha enhances mutant ATXN1 pathogenicity, and delayed postnatal expression of mutant ATXN1 substantially reduces disease severity.\",\n      \"method\": \"Conditional transgenic mouse model, co-immunoprecipitation, gene expression analysis, behavioral assessment\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — complex identification by co-IP, genetic epistasis in vivo, conditional transgenic model\",\n      \"pmids\": [\"17110330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CHIP (E3 ubiquitin ligase) directly interacts with ataxin-1 (both expanded and unexpanded) and co-localizes in nuclear inclusions; CHIP promotes ubiquitination of ataxin-1 in vitro and in cell culture, augmented by Hsp70; CHIP overexpression in a Drosophila SCA1 model decreases ataxin-1 steady-state levels and suppresses toxicity for polyglutamine in the context of the ataxin-1 backbone.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination assay, Drosophila overexpression, protein level quantification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro ubiquitination assay plus in vivo Drosophila rescue, multiple orthogonal methods\",\n      \"pmids\": [\"16831871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Protein-protein interaction network screen (yeast two-hybrid) for ataxia-related proteins identified 770 novel interactions involving ATXN1 and other ataxia proteins; 83% of tested pairs verified in mammalian cells by co-IP, revealing shared interacting partners that modify neurodegeneration.\",\n      \"method\": \"Yeast two-hybrid screen, mammalian cell co-immunoprecipitation verification\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — large-scale Y2H with mammalian verification, but individual ATXN1 interactions not deeply characterized mechanistically\",\n      \"pmids\": [\"16713569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Polyglutamine expansion in ATXN1 has opposing effects on distinct endogenous protein complexes: it favors formation of an ATXN1-RBM17 complex (gain-of-function contributing to SCA1 neuropathology) while attenuating formation and function of the ATXN1-Capicua complex (partial loss-of-function); both mechanisms contribute to SCA1 pathogenesis.\",\n      \"method\": \"Native complex purification, co-immunoprecipitation, Drosophila genetic epistasis, cell-based functional assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple native complexes characterized biochemically with genetic validation in Drosophila, strong mechanistic resolution\",\n      \"pmids\": [\"18337722\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"miR-19, miR-101, and miR-130 co-regulate ataxin-1 levels; inhibition of these microRNAs enhanced cytotoxicity of polyglutamine-expanded ATXN1 in human cells, revealing post-transcriptional regulation of ATXN1 dosage.\",\n      \"method\": \"microRNA inhibitor experiments in human cells, ATXN1 protein level quantification, cytotoxicity assay\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — functional cell-based experiments with defined phenotypic readout, single study\",\n      \"pmids\": [\"18758459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UbcH6, an E2 ubiquitin-conjugating enzyme, interacts with ataxin-1 via its AXH domain and ubiquitinates ataxin-1 in the absence of an E3 ligase; UbcH6 co-immunoprecipitates and co-localizes with ataxin-1 in the nucleus, and its expression level regulates the rate of ataxin-1 degradation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, co-localization, in vitro ubiquitination assay, protein degradation assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro ubiquitination assay plus co-IP and degradation assay, single lab study\",\n      \"pmids\": [\"18439907\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Phosphorylation of ATXN1 at S776 in cerebellar Purkinje cells is mediated by cyclic AMP-dependent protein kinase (PKA), not Akt: immunodepletion and inhibition of PKA decreased S776 phosphorylation in a cerebellar extract-based assay and in vivo, while Akt inhibition did not; S776 phosphorylation is associated with ATXN1 stabilization in Purkinje cells.\",\n      \"method\": \"Cerebellar extract-based phosphorylation assay, kinase inhibition/immunodepletion, in vivo kinase inhibition, Western blot\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-free biochemical assay plus in vivo validation, identifies specific kinase contradicting prior model\",\n      \"pmids\": [\"19500214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Loss of function of ATXN1 increases amyloid beta-protein levels (Aβ40 and Aβ42) by potentiating β-secretase (BACE1) processing of APP; knockdown of ATXN1 by RNAi increased Aβ levels, and this was rescued by concurrent ATXN1 overexpression; overexpression of ATXN1 decreased Aβ levels.\",\n      \"method\": \"RNA interference in human neuronal cell model and mouse primary cortical neurons, ELISA for Aβ levels, ATXN1 overexpression rescue\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional manipulation (KD and OE) with defined molecular readout, single lab\",\n      \"pmids\": [\"20097758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATXN1 and ATAXIN1-Like (ATXN1L) form complexes with the transcriptional repressor Capicua (CIC) that are functionally redundant; loss of ATXN1L destabilizes CIC, leading to derepression of Etv4 (an activator of Mmp genes) and MMP9 overexpression, causing lung alveolarization defects and other developmental phenotypes.\",\n      \"method\": \"Knockout mouse generation (Atxn1L-/-, Atxn1-/-;Atxn1L-/-), Western blot, gene expression analysis, phenotypic characterization\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double knockout epistasis with molecular pathway placement, replicated genetic analysis\",\n      \"pmids\": [\"22014525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HOTAIR lncRNA associates with the E3 ubiquitin ligase Dzip3 and its substrate ataxin-1, facilitating ubiquitination of ataxin-1 by Dzip3 in cells and in vitro, thereby accelerating ataxin-1 degradation; HOTAIR levels are elevated in senescent cells and drive rapid ataxin-1 decay.\",\n      \"method\": \"RNA immunoprecipitation, co-immunoprecipitation, in vitro ubiquitination assay, protein degradation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro ubiquitination assay with cell-based validation, single lab study\",\n      \"pmids\": [\"24326307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The RNA-binding protein PUMILIO1 (PUM1) directly regulates ATXN1 mRNA levels post-transcriptionally; Pum1 haploinsufficiency causes SCA1-like neurodegeneration by increasing Ataxin-1 levels; breeding Pum1+/- mice with Atxn1+/- mice normalized ATAXIN1 levels and largely rescued the Pum1+/- phenotype.\",\n      \"method\": \"Mouse genetics (haploinsufficiency, crossbreeding, knockin), behavioral assays, protein level quantification, epistasis analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic epistasis with rescue, quantitative molecular readouts, multiple mouse lines\",\n      \"pmids\": [\"25768905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Soluble ATXN1 oligomers form in vivo and their levels correlate with disease progression in Atxn1(154Q/+) mice; oligomeric toxicity, stabilization, and seeding require interaction with Capicua, which is expressed at higher ratios relative to ATXN1 in the cerebellum than in less vulnerable brain regions, explaining regional vulnerability.\",\n      \"method\": \"Conformational antibody detection of oligomers, co-immunoprecipitation, disease progression correlation, regional expression analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods linking oligomer formation to CIC interaction and regional vulnerability, single lab\",\n      \"pmids\": [\"25988806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The ATXN1-CIC complex is essential for forebrain development: conditional loss of ATXN1-CIC causes hyperactivity, impaired learning and memory, and defective maturation of upper-layer cortical neurons; CIC in the hypothalamus and medial amygdala modulates social interactions; five individuals with de novo truncating CIC mutations share intellectual disability, ADHD, and autism features.\",\n      \"method\": \"Conditional mouse knockouts, behavioral phenotyping, cortical neuron characterization, human genetic analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in multiple brain regions with defined cellular and behavioral phenotypes, confirmed in human patients\",\n      \"pmids\": [\"28288114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PQBP-1 interacts with mutant ataxin-1 in a polyglutamine-length-dependent manner (both in vitro and in vivo); mutant ataxin-1 enhances PQBP-1 binding to the C-terminal domain of RNA Pol II large subunit, reducing Pol II phosphorylation and transcription; this interaction induces apoptotic cell death.\",\n      \"method\": \"In vitro and in vivo binding assays, co-immunoprecipitation, cell death assay, transcription assay\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical mechanism defined with multiple assays, single lab study\",\n      \"pmids\": [\"12062018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"p62/SQSTM1 is essential for accumulation of polyubiquitinated proteins in PML nuclear bodies upon inhibition of nuclear protein export; p62 contributes to the assembly of proteasome-containing degradative compartments near nuclear aggregates containing polyglutamine-expanded Ataxin-1[Q84] and to degradation of Ataxin-1[Q84].\",\n      \"method\": \"RNAi knockdown, immunofluorescence, nuclear fractionation, cell-based degradation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined molecular readout involving ATXN1 as substrate, single study\",\n      \"pmids\": [\"20018885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"miR760 binds a conserved site in ATXN1's unusually long 5' UTR to induce RNA degradation and translational inhibition; delivery of AAV-expressing miR760 in the cerebellum reduces ATXN1 levels in vivo and mitigates motor coordination deficits in a SCA1 mouse model.\",\n      \"method\": \"miRNA target site mapping, reporter assays, AAV delivery in vivo, motor coordination assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — 5' UTR mechanism validated in vitro and with in vivo AAV rescue, multiple methods\",\n      \"pmids\": [\"32763910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ATXN1 intermediate repeat expansions are significantly associated with ALS; ATXN1 reduces the nucleocytoplasmic ratio of TDP-43 and enhances ALS phenotypes in Drosophila, implicating ATXN1 in TDP-43 mislocalization as a disease mechanism.\",\n      \"method\": \"Large-scale genetic association (11,700 individuals), Drosophila functional experiments, TDP-43 localization assay\",\n      \"journal\": \"Brain communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — genetic association supported by functional Drosophila experiments, mechanism partially characterized\",\n      \"pmids\": [\"32954321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Nuclear localization of mutant ATXN1 is required broadly for SCA1-like phenotypes including motor dysfunction, cognitive deficits, and premature lethality; CRISPR-Cas9 K772T mutation in the nuclear localization sequence of expanded ATXN1 corrected many disease-like phenotypes and normalized transcriptomic profiles in multiple brain regions.\",\n      \"method\": \"CRISPR-Cas9 knock-in mouse, behavioral testing, RNA sequencing across brain regions\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — precise CRISPR mutagenesis of NLS with comprehensive phenotypic and transcriptomic rescue validation\",\n      \"pmids\": [\"36577403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Disrupting the ATXN1-CIC interaction globally normalizes genome-wide CIC binding but only partially corrects transcriptional and behavioral phenotypes; unbiased proteomics identified additional ATXN1-interacting transcription factors RFX1, ZBTB5, and ZKSCAN1 whose target genes show altered expression in SCA1 mice and patient-derived iNeurons.\",\n      \"method\": \"Knockin mouse with ATXN1-CIC interaction mutation, ChIP-seq, RNA-seq, affinity purification mass spectrometry proteomics, patient-derived neurons\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multi-omic unbiased approach with human patient validation, multiple orthogonal methods\",\n      \"pmids\": [\"36577402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of ATXN1 induces early alterations in cerebellar bioenergetics proteins (glycolysis and ATP synthesis enzymes); ATXN1 regulates cerebellar bioenergetics via the GSK3β-mTOR pathway — GSK3β is decreased in Atxn1-KO and increased in SCA1 mice, while mTOR is decreased in SCA1 mice before ataxia onset; pharmacological inhibition of GSK3β and activation of mTOR ameliorated metabolic alterations in a SCA1 cell model.\",\n      \"method\": \"Proteomics of Atxn1-KO cerebellum, Western blot, pharmacological rescue in SCA1 cell model\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — unbiased proteomics with pathway validation, single lab study\",\n      \"pmids\": [\"27466200\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATXN1 is a nuclear protein that functions as a transcriptional regulator, assembling into large native complexes with the transcriptional repressor Capicua (CIC) and other factors (RORalpha/Tip60, RFX1, ZBTB5, ZKSCAN1, SMRT/HDAC3); its activity and stability are controlled by PKA-mediated phosphorylation at S776 (which promotes 14-3-3 binding and protein stabilization), ubiquitination by CHIP and UbcH6, and post-transcriptional regulation by PUMILIO1 and multiple microRNAs (miR-19, miR-101, miR-130, miR760) targeting its unusually long 5' UTR; in SCA1, polyglutamine expansion shifts the balance of ATXN1 complexes — favoring the ATXN1-RBM17 complex (gain-of-function) while impairing the ATXN1-CIC complex (partial loss-of-function) — and nuclear localization plus S776 phosphorylation are both required for neurodegeneration, while chaperones (HSP70, HDJ-2) and the proteasome system attempt to clear misfolded aggregates.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ATXN1 is a nuclear transcriptional regulator whose polyglutamine expansion causes spinocerebellar ataxia type 1 (SCA1). ATXN1 forms transcriptional repressor complexes with Capicua (CIC), SMRT/HDAC3, and RORα/Tip60, and together with its paralog ATXN1L stabilizes CIC to repress target genes such as Etv4 in developmental contexts including forebrain neuron maturation and lung alveolarization [PMID:15016912, PMID:17110330, PMID:22014525, PMID:28288114]. ATXN1 protein levels are tightly controlled by PKA-mediated Ser776 phosphorylation, UbcH6-dependent ubiquitination, and post-transcriptional regulation via PUM1 and multiple miRNAs (miR-19, miR-101, miR-130, miR-760) [PMID:19500214, PMID:18758459, PMID:25768905, PMID:32763910]. In SCA1, nuclear polyglutamine-expanded ATXN1 exaggerates its native transcriptional repressor functions through CIC-dependent and CIC-independent mechanisms—including interactions with RFX1, ZBTB5, and ZKSCAN1—leading to climbing fiber–Purkinje cell circuit dysfunction, impaired mTORC1–Homer-3 signaling, and progressive cerebellar neurodegeneration that is reversible by antisense oligonucleotide-mediated ATXN1 reduction [PMID:36577402, PMID:26748090, PMID:36577403, PMID:30385727].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"The initial question of how expanded ATXN1 causes cellular pathology was addressed by showing that polyglutamine-expanded ATXN1 accumulates in ubiquitin-positive nuclear inclusions with proteasomes and chaperones, establishing protein misfolding and impaired proteostasis as early pathogenic events.\",\n      \"evidence\": \"Immunostaining of SCA1 patient/mouse tissue and HeLa transfection with mutant ATXN1; chaperone overexpression reduced aggregation\",\n      \"pmids\": [\"9620770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether aggregates themselves are toxic or protective was not resolved\", \"The E3 ligase(s) responsible for aggregate ubiquitination were not identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Whether enhancing protein quality control could rescue SCA1 in vivo was answered by demonstrating that inducible HSP70 overexpression suppressed Purkinje cell pathology and improved motor function in SCA1 mice, validating the chaperone-mediated misfolding model.\",\n      \"evidence\": \"Crossbreeding SCA1 transgenic mice with iHSP70-overexpressing mice; rotarod and histopathology\",\n      \"pmids\": [\"11448943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous chaperone levels decline during disease was not tested\", \"Mechanism of HSP70 rescue (refolding vs. degradation) was not distinguished\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The question of whether ATXN1 has a normal nuclear function was resolved by identifying ATXN1 as a transcriptional repressor that interacts with SMRT and HDAC3, and demonstrating that mutant ATXN1 aggregates sequester these corepressors, shifting the disease model from pure proteotoxicity to transcriptional dysregulation.\",\n      \"evidence\": \"Co-IP, reporter-based transcriptional repression assays, Drosophila genetic epistasis with SMRTER\",\n      \"pmids\": [\"15016912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct genomic targets of ATXN1-SMRT repression were not defined\", \"Whether SMRT sequestration is rate-limiting for pathology was unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The basis for cerebellar-selective vulnerability in SCA1 was advanced by discovering that ATXN1 forms a complex with RORα and Tip60, and that mutant ATXN1 destabilizes RORα—a transcription factor essential for cerebellar development—with developmental timing of mutant expression critically modulating disease severity.\",\n      \"evidence\": \"Conditional transgenic mice with delayed expression; Co-IP of ATXN1-RORα-Tip60; RORα haploinsufficiency enhancement\",\n      \"pmids\": [\"17110330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RORα destabilization occurs through proteasomal degradation or other mechanism was not resolved\", \"Direct downstream genes of the ATXN1-RORα-Tip60 complex were not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"How ATXN1 protein levels are regulated was addressed by two discoveries: miR-19, miR-101, and miR-130 post-transcriptionally repress ATXN1, and UbcH6 ubiquitinates ATXN1 via its AXH domain to promote degradation, establishing both RNA-level and protein-level control mechanisms.\",\n      \"evidence\": \"miRNA inhibitor experiments with protein level and cytotoxicity readouts; yeast two-hybrid, Co-IP, in vitro ubiquitination, and pulse-chase degradation assays for UbcH6\",\n      \"pmids\": [\"18758459\", \"18439907\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The E3 ligase cooperating with UbcH6 was not identified\", \"Whether miRNA-mediated regulation is altered during disease progression was not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The kinase responsible for the key stabilizing phosphorylation of ATXN1 at Ser776 was identified as PKA rather than Akt in the cerebellum, establishing PKA as a critical upstream regulator of ATXN1 protein stability.\",\n      \"evidence\": \"In vivo PKA/Akt inhibition in mice; cerebellar extract phosphorylation assays with immunodepletion\",\n      \"pmids\": [\"19500214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase(s) that dephosphorylate S776 were not identified\", \"Whether PKA-S776 regulation differs between normal and expanded ATXN1 was not fully resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Beyond cerebellar function, ATXN1 was shown to regulate β-secretase (BACE1) processing of APP, with ATXN1 loss increasing Aβ40/42 levels, linking ATXN1 to amyloid metabolism.\",\n      \"evidence\": \"RNAi knockdown and overexpression in human neuronal cells and mouse primary cortical neurons; ELISA for Aβ peptides\",\n      \"pmids\": [\"20097758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ATXN1 directly interacts with BACE1 or acts indirectly was not determined\", \"In vivo relevance for Alzheimer's disease pathology was not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The ATXN1-CIC complex was established as a central functional unit: ATXN1 and ATXN1L redundantly stabilize CIC to repress developmental target genes (Etv4/MMP9), while in SCA1 mice mutant ATXN1 causes preferential climbing fiber–Purkinje cell circuit dysfunction that requires nuclear localization.\",\n      \"evidence\": \"Atxn1/Atxn1L double-KO mice with lung phenotype and CIC destabilization; in vivo electrophysiology and imaging across multiple ATXN1 transgenic lines\",\n      \"pmids\": [\"22014525\", \"21900557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CIC gain-of-function versus loss-of-function predominates in SCA1 cerebellum was unresolved\", \"How nuclear ATXN1 specifically impairs CF but not PF circuits was not mechanistically explained\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The toxic species in SCA1 was identified as CIC-dependent soluble oligomers of expanded ATXN1 whose levels correlate with disease progression, and the higher CIC:ATXN1 ratio in cerebellum was proposed to explain regional vulnerability; separately, PUM1 was established as a direct post-transcriptional regulator of ATXN1 whose haploinsufficiency causes SCA1-like neurodegeneration through ATXN1 upregulation.\",\n      \"evidence\": \"Conformational antibody-based oligomer detection in Atxn1(154Q/+) mice with CIC interaction studies; Pum1-KO and Pum1+/-;Atxn1+/- genetic epistasis with behavioral and molecular readouts\",\n      \"pmids\": [\"25988806\", \"25768905\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural characterization of ATXN1 oligomers was lacking\", \"Whether PUM1 regulation is altered in SCA1 patient cerebellum was not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The downstream signaling consequences of mutant ATXN1 in Purkinje cells were delineated: impaired climbing fiber input diminishes mTORC1 signaling, reducing Homer-3 expression; Homer-3 restoration rescues cellular dysfunction, while ATXN1 also regulates cerebellar bioenergetics through a GSK3β-mTOR pathway.\",\n      \"evidence\": \"Proteomics of SCA1 Purkinje cells; mTORC1 conditional KO; AAV-Homer-3 rescue; pharmacological mTORC1/GSK3β manipulation in SCA1 cells\",\n      \"pmids\": [\"26748090\", \"27466200\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mTORC1-Homer-3 impairment is specific to Purkinje cells or generalizable was unknown\", \"Direct mechanistic link between ATXN1 and GSK3β activity was not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The ATXN1-CIC complex was shown to be essential for normal forebrain development: its disruption causes hyperactivity, impaired learning/memory, and abnormal cortical neuron maturation, extending ATXN1's transcriptional role beyond the cerebellum.\",\n      \"evidence\": \"Conditional ATXN1-CIC interaction-disrupting KO mice; behavioral testing; cortical neuron maturation analysis; human CIC mutation identification\",\n      \"pmids\": [\"28288114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific CIC target genes mediating forebrain phenotypes were not fully characterized\", \"Whether ATXN1-CIC disruption contributes to cognitive deficits in SCA1 patients was not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The therapeutic reversibility of SCA1 was demonstrated by showing that a single antisense oligonucleotide injection reducing ATXN1 mRNA rescued motor deficits, premature lethality, and neurochemical abnormalities in SCA1 knockin mice.\",\n      \"evidence\": \"ASO injection in Atxn1(154Q/2Q) mice; rotarod, survival, RNA-seq, and MRS readouts\",\n      \"pmids\": [\"30385727\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Optimal therapeutic window and durability of ASO effects were not fully defined\", \"Whether complete ATXN1 loss causes adverse effects in adults was not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"A novel post-transcriptional regulatory axis was identified: miR-760 targets a conserved site in ATXN1's unusually long 5' UTR to induce RNA degradation and translational inhibition, and AAV-miR-760 delivery mitigates SCA1 motor deficits in vivo; separately, intermediate ATXN1 repeat expansions were linked to ALS through TDP-43 mislocalization.\",\n      \"evidence\": \"5' UTR mutagenesis/reporter assays and AAV-miR-760 in SCA1 mice; genetic association in 11,700 individuals with Drosophila TDP-43 functional validation\",\n      \"pmids\": [\"32763910\", \"32954321\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether miR-760 levels change during SCA1 progression was not tested\", \"TDP-43 mislocalization mechanism was only validated in Drosophila, not mammalian models\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The mechanistic model was refined in two ways: nuclear localization of expanded ATXN1 was confirmed as necessary for multi-system SCA1 phenotypes via precise K772T NLS editing, and CIC-independent ATXN1 interactors (RFX1, ZBTB5, ZKSCAN1) were identified, revealing that SCA1 transcriptional pathology extends beyond the ATXN1-CIC axis.\",\n      \"evidence\": \"CRISPR-Cas9 K772T knockin with behavioral/transcriptomic characterization; unbiased Co-IP proteomics, CIC ChIP-seq, and RNA-seq in SCA1 mice and patient iNeurons\",\n      \"pmids\": [\"36577403\", \"36577402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct genomic targets of RFX1/ZBTB5/ZKSCAN1 disrupted by expanded ATXN1 were not mapped\", \"Relative contributions of CIC-dependent vs. CIC-independent pathways to specific disease phenotypes remain unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of ATXN1 oligomerization and CIC-dependent toxicity; the identity of E3 ligases that mediate ATXN1 degradation; how nuclear ATXN1 selectively impairs climbing fiber versus parallel fiber circuits; and whether CIC-independent transcriptional partners (RFX1, ZBTB5, ZKSCAN1) represent therapeutically tractable disease axes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of ATXN1 or its oligomeric forms exists\", \"E3 ligase(s) for ATXN1 ubiquitination remain unidentified\", \"Relative therapeutic value of targeting CIC-dependent vs. CIC-independent pathways is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [2, 3, 6, 11, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2, 8, 12, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 3, 6, 11, 18]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 6, 11]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [8, 14]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 9, 17, 19]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 13, 14]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 12]}\n    ],\n    \"complexes\": [\n      \"ATXN1-CIC complex\",\n      \"ATXN1-RORα-Tip60 complex\",\n      \"ATXN1-SMRT-HDAC3 complex\"\n    ],\n    \"partners\": [\n      \"CIC\",\n      \"ATXN1L\",\n      \"RORA\",\n      \"KAT5\",\n      \"NCOR2\",\n      \"HDAC3\",\n      \"RFX1\",\n      \"PUM1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"ATXN1 encodes the nuclear transcriptional regulator ataxin-1, which assembles into distinct native protein complexes—most prominently with the transcriptional repressor Capicua (CIC) and with RORα/Tip60—to control gene expression programs essential for cerebellar Purkinje cell maintenance and forebrain development [PMID:17190598, PMID:17110330, PMID:28288114]. ATXN1 stability and function are governed by PKA-mediated phosphorylation at S776 (promoting 14-3-3 binding and protein stabilization), ubiquitin-dependent degradation via CHIP and UbcH6, and post-transcriptional dosage control by PUMILIO1 and multiple microRNAs targeting its extended 5′ UTR [PMID:19500214, PMID:16831871, PMID:25768905, PMID:32763910]. CAG trinucleotide repeat expansion in ATXN1 causes spinocerebellar ataxia type 1 (SCA1), in which polyglutamine-expanded ataxin-1 shifts the balance of endogenous complexes—favoring the pathogenic ATXN1–RBM17 interaction while impairing the ATXN1–CIC complex—with nuclear localization and S776 phosphorylation both required for neurodegeneration [PMID:8358429, PMID:18337722, PMID:12741986, PMID:36577403]. Unbiased proteomics has further identified ATXN1 interactions with transcription factors RFX1, ZBTB5, and ZKSCAN1, whose dysregulation contributes to the broader transcriptional pathology of SCA1 [PMID:36577402].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Identification of the causative mutation—an unstable CAG repeat expansion in ATXN1—established the molecular basis of SCA1 and linked polyglutamine tract length to disease severity.\",\n      \"evidence\": \"Positional cloning and linkage analysis in SCA1 families\",\n      \"pmids\": [\"8358429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why Purkinje cells are selectively vulnerable was not explained\", \"Function of the normal ataxin-1 protein was unknown\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrating that ataxin-1 is a nuclear protein—with additional cytoplasmic localization in Purkinje cells—established that its primary site of action is the nucleus, redirecting the field away from cytoplasmic aggregation models.\",\n      \"evidence\": \"Immunoblot and immunofluorescence of patient and normal human brain tissues\",\n      \"pmids\": [\"7647801\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear function remained undefined\", \"Mechanism of nuclear targeting not mapped\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Discovery that mutant ataxin-1 forms a single large nuclear inclusion that reorganizes the PML-containing nuclear matrix, and that LANP interacts with ataxin-1 in a glutamine-length-dependent manner in Purkinje cells, implicated nuclear matrix disruption and selective protein interactions in pathogenesis.\",\n      \"evidence\": \"Immunofluorescence and nuclear matrix fractionation in transgenic mice and patient tissue; yeast two-hybrid and co-IP for LANP\",\n      \"pmids\": [\"9353120\", \"9353121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether nuclear inclusions are toxic or protective was unresolved\", \"LANP's functional role in the ATXN1 pathway was unclear\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Finding that proteasome subunits and chaperone HDJ-2 colocalize with nuclear inclusions, and that HDJ-2 overexpression reduces aggregation, established that protein quality control machinery engages misfolded ataxin-1.\",\n      \"evidence\": \"Immunostaining of patient and transgenic mouse brain, chaperone overexpression in HeLa cells\",\n      \"pmids\": [\"9620770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether chaperone-mediated clearance is sufficient to prevent disease in vivo was untested\", \"Ubiquitination machinery for ataxin-1 was unidentified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"In vivo demonstration that HSP70 overexpression suppresses SCA1 neuropathology in transgenic mice provided the first mammalian proof that enhancing proteostasis can rescue polyglutamine-mediated neurodegeneration.\",\n      \"evidence\": \"Crossbreeding SCA1 transgenic with iHSP70-overexpressing mice; rotarod and neuropathology\",\n      \"pmids\": [\"11448943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific substrates of HSP70 in this context were not defined\", \"Whether clearance versus refolding underlies rescue was unclear\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of S776 phosphorylation as a disease-critical post-translational modification—required for 14-3-3 binding, protein stabilization, nuclear inclusion formation, and in vivo cerebellar pathology—established that polyglutamine expansion alone is insufficient for neurodegeneration.\",\n      \"evidence\": \"Phospho-site identification, co-IP with 14-3-3, Drosophila epistasis, S776A transgenic mice with rotarod and neuropathology\",\n      \"pmids\": [\"12757707\", \"12741986\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The kinase responsible for S776 phosphorylation in Purkinje cells was initially misassigned to Akt\", \"Downstream consequences of 14-3-3 binding beyond stabilization were unexplored\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Purification of native ATXN1-containing complexes revealed that ataxin-1 functions primarily as a component of large transcriptional regulatory complexes: a CIC-containing repressor complex, an RORα/Tip60 coactivator complex, and a SMRT/HDAC3 corepressor complex, redefining ataxin-1 as a transcriptional regulator rather than merely an aggregation-prone protein.\",\n      \"evidence\": \"Native complex purification from mouse cerebellum, co-IP, reporter assays, Drosophila genetic epistasis for SMRT and RORα pathways\",\n      \"pmids\": [\"17190598\", \"17110330\", \"15016912\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ATXN1 coordinates membership across distinct complexes was unknown\", \"Genome-wide transcriptional targets of these complexes were not mapped\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstration that CHIP ubiquitin ligase and UbcH6 ubiquitin-conjugating enzyme mediate ataxin-1 ubiquitination and degradation defined the proteolytic pathway controlling ataxin-1 turnover.\",\n      \"evidence\": \"In vitro ubiquitination assays, co-IP, Drosophila CHIP overexpression rescue\",\n      \"pmids\": [\"16831871\", \"18439907\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of CHIP versus UbcH6-mediated ubiquitination in vivo were not resolved\", \"Ubiquitin chain type specificity was not determined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The finding that polyglutamine expansion shifts the equilibrium between ATXN1 complexes—favoring the pathogenic ATXN1–RBM17 complex while attenuating the ATXN1–CIC complex—established a dual gain-of-function/partial loss-of-function model for SCA1 pathogenesis.\",\n      \"evidence\": \"Native complex purification, co-IP, Drosophila genetic epistasis\",\n      \"pmids\": [\"18337722\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for differential complex assembly was unknown\", \"Whether therapeutic rebalancing of complexes is achievable was untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reassignment of the S776 kinase from Akt to PKA in cerebellar Purkinje cells corrected a key mechanistic detail and focused therapeutic kinase-targeting efforts on the cAMP-PKA signaling axis.\",\n      \"evidence\": \"Cerebellar extract kinase assay with immunodepletion and inhibition, in vivo kinase inhibition\",\n      \"pmids\": [\"19500214\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other kinases contribute in non-cerebellar cell types was unexplored\", \"Upstream signals regulating PKA-dependent ATXN1 phosphorylation were not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that PUMILIO1 post-transcriptionally controls ATXN1 mRNA levels, and that Pum1 haploinsufficiency causes SCA1-like neurodegeneration rescuable by reducing Atxn1 gene dosage, established that ATXN1 protein levels are tightly regulated and that even modest elevation is pathogenic.\",\n      \"evidence\": \"Mouse genetic epistasis (Pum1+/− × Atxn1+/−), behavioral assays, protein quantification\",\n      \"pmids\": [\"25768905\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PUM1 acts on the 3′ UTR, 5′ UTR, or coding sequence was not fully resolved\", \"Other RNA-binding proteins regulating ATXN1 mRNA were not systematically identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Conditional knockout studies demonstrated that the ATXN1–CIC complex is essential for forebrain neuron maturation, learning, memory, and social behavior, extending ATXN1 function beyond the cerebellum and linking CIC mutations to intellectual disability and autism in humans.\",\n      \"evidence\": \"Conditional mouse knockouts, behavioral phenotyping, cortical neuron characterization, human de novo CIC mutation analysis\",\n      \"pmids\": [\"28288114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct genomic targets of ATXN1–CIC in forebrain were not comprehensively mapped\", \"Whether ATXN1-independent CIC functions contribute to the human phenotype was unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of miR-760 as a regulator acting through the ATXN1 5′ UTR, with AAV-delivered miR-760 reducing ATXN1 levels and rescuing motor deficits in SCA1 mice, established a therapeutic strategy exploiting post-transcriptional dosage control.\",\n      \"evidence\": \"miRNA target site mapping, reporter assays, AAV delivery in SCA1 mouse cerebellum, motor coordination assay\",\n      \"pmids\": [\"32763910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term safety and off-target effects of miR-760 delivery were not assessed\", \"Whether combining miR-760 with other miRNAs (miR-19, miR-101, miR-130) provides additive benefit was untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"CRISPR-based disruption of the ATXN1 nuclear localization signal rescued motor, cognitive, and transcriptomic phenotypes genome-wide, definitively proving that nuclear localization of mutant ATXN1 is required for the full spectrum of SCA1 pathology; meanwhile, disrupting the ATXN1–CIC interaction only partially corrected phenotypes, and proteomics identified RFX1, ZBTB5, and ZKSCAN1 as additional transcription factor partners whose target genes are dysregulated in SCA1.\",\n      \"evidence\": \"CRISPR-Cas9 NLS knock-in mouse, CIC-interaction mutant knock-in mouse, ChIP-seq, RNA-seq, affinity purification mass spectrometry, patient-derived iNeurons\",\n      \"pmids\": [\"36577403\", \"36577402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative pathogenic contributions of RFX1, ZBTB5, and ZKSCAN1 complex disruption versus CIC complex disruption are unquantified\", \"Structural basis for ATXN1 interaction with these new partners is unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full transcription factor interaction landscape of ATXN1, the structural basis for polyglutamine-dependent complex switching, and the therapeutic potential of combined dosage-reduction and complex-rebalancing strategies remain to be determined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of ATXN1 in complex with CIC or RBM17 exists\", \"How ATXN1 intermediate-length repeats contribute to ALS via TDP-43 mislocalization requires mechanistic resolution\", \"Whether pharmacological PKA inhibition or miRNA-based ATXN1 reduction translates to human SCA1 therapy is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [9, 10, 11, 14, 29]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 14, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 3, 5, 8, 16, 28]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [3, 9, 29]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [9, 10, 11, 29]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [3, 9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [7, 12, 16, 20]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 17, 30]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 8, 14, 28]}\n    ],\n    \"complexes\": [\n      \"ATXN1-CIC repressor complex\",\n      \"ATXN1-RBM17 complex\",\n      \"ATXN1-RORα-Tip60 complex\",\n      \"ATXN1-SMRT-HDAC3 complex\"\n    ],\n    \"partners\": [\n      \"CIC\",\n      \"RBM17\",\n      \"RORA\",\n      \"KAT5\",\n      \"NCOR2\",\n      \"STUB1\",\n      \"PUM1\",\n      \"YWHAZ\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}