{"gene":"LRIF1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2015,"finding":"LRIF1 mediates chromatin loading of SMCHD1 by interacting with HP1γ at H3K9me3-modified chromatin sites on chromosome arms, establishing LRIF1 as the principal loading factor for SMCHD1 at heterochromatin.","method":"Co-immunoprecipitation, chromatin fractionation, epistasis experiments in mammalian cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction data, multiple orthogonal methods, replicated conceptually across multiple subsequent studies","pmids":["26391951"],"is_preprint":false},{"year":2018,"finding":"LRIF1 directly interacts with HP1α chromoshadow domain via an evolutionarily conserved PXVXL motif in its C-terminus, recruits HP1α to centromeres of mitotic chromosomes, and this interaction is required for Aurora B activity in the inner centromere and accurate chromosome segregation.","method":"Co-immunoprecipitation, direct binding assay, PXVXL motif mutagenesis, live-cell imaging of mitotic chromosomes, chromosome segregation assay","journal":"Journal of molecular cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct binding assay with mutagenesis, functional readout (chromosome segregation defects), multiple orthogonal methods in one study","pmids":["30016453"],"is_preprint":false},{"year":2013,"finding":"LRIF1 is a telomere-associated protein; QTIP (quantitative telomeric chromatin isolation) demonstrated that LRIF1 is enriched at telomeres together with SMCHD1, with higher density at long telomeres.","method":"QTIP (chromatin immunopurification + SILAC mass spectrometry)","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — rigorous quantitative chromatin proteomics method, single study, localization established but functional consequence not directly tested","pmids":["24270157"],"is_preprint":false},{"year":2017,"finding":"LRIF1 is identified as a novel alpha satellite (centromeric alphoid DNA)-associated protein in human cells, placing it among heterochromatin-binding proteins at the centromere.","method":"HyCCAPP (hybridization capture of chromatin-associated proteins) followed by mass spectrometry","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — DNA-centric chromatin pulldown with MS validation, single study, localization only","pmids":["28704058"],"is_preprint":false},{"year":2020,"finding":"LRIF1 (long isoform) binds directly to the D4Z4 repeat and is required for D4Z4 chromatin compaction; loss of the long LRIF1 isoform causes D4Z4 chromatin relaxation and derepression of DUX4 and DUX4 target genes in muscle cells.","method":"Chromatin immunoprecipitation (ChIP) showing LRIF1 binding to D4Z4; siRNA knockdown of LRIF1 long isoform in muscle cells with readout of DUX4 and target gene expression; patient-derived nonsense mutation abolishing long isoform","journal":"Neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP, loss-of-function knockdown, patient mutation with epigenetic readout; convergent evidence across genetic and molecular approaches","pmids":["32467133"],"is_preprint":false},{"year":2023,"finding":"SMCHD1, together with the long isoform of LRIF1, binds to the LRIF1 promoter and represses LRIF1 expression; the interdependency of SMCHD1 and LRIF1 binding differs between the D4Z4 locus and the LRIF1 promoter, and somatic loss-of-function of either SMCHD1 or LRIF1 alone does not result in D4Z4 chromatin changes.","method":"ChIP, loss-of-function experiments (somatic knockdown/knockout), reporter assays, epigenetic analysis of D4Z4 methylation","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (ChIP, KO/KD, methylation analysis), reveals regulatory feedback and context-specific binding","pmids":["37380887"],"is_preprint":false},{"year":2022,"finding":"Lrif1 knockout in zebrafish phenocopies Smchd1 knockout, including precocious/ectopic HOX transcription and vertebrate patterning defects; Lrif1 acts as a direct interacting partner of Smchd1 in mediating maternal epigenetic regulation of HOX loci.","method":"Zebrafish lrif1 knockout, genetic epistasis with smchd1 knockout, molecular phenotyping of HOX expression and DNA methylation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (phenocopy), knockout animals, multiple molecular readouts across two independent organisms","pmids":["35739109"],"is_preprint":false},{"year":2024,"finding":"Upon AAV transduction, SMCHD1 forms a complex with LRIF1 and HP1 to directly bind the AAV genome and maintain a heterochromatin-like state repressing AAV transgene expression; LRIF1 knockdown disrupts this complex and activates AAV transcription.","method":"Genome-wide CRISPR screen, RNAi/CRISPRi knockdown, co-immunoprecipitation demonstrating SMCHD1-LRIF1-HP1 complex, viral transduction assays","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen plus Co-IP plus functional KD assay, single lab, multiple complementary approaches","pmids":["38976714"],"is_preprint":false},{"year":2025,"finding":"LRIF1 is required for genome-wide chromatin binding of SMCHD1 by mediating its interaction with H3K9me2/3-modified nucleosomes; SMCHD1 ATPase (ATP hydrolysis) activity is additionally required for selective enrichment at specific chromatin regions including the inactive X chromosome for gene silencing.","method":"Live-cell and single-molecule imaging, engineered ATPase domain mutations, LRIF1-dependent SMCHD1 chromatin-binding assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1–2 / Weak — single-molecule imaging and mutagenesis, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.06.13.659515"],"is_preprint":true},{"year":2025,"finding":"SMCHD1's coiled-coil domain facilitates interaction with LRIF1; SMCHD1 can compact DNA independently and in an ATP-regulated manner, but the LRIF1 interaction domain (coiled-coil) does not affect DNA compaction rate per se.","method":"Biophysical reconstitution assays (DNA compaction), domain deletion analysis, nucleosome array assays","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution but preprint, single lab, and LRIF1 finding is secondary to the main SMCHD1 compaction result","pmids":["bio_10.1101_2025.07.08.663435"],"is_preprint":true},{"year":2024,"finding":"Lrif1 interacts with Trim28 (a known Dux repressor) in mouse embryonic stem cells in a manner independent of Cbx proteins and Smchd1; Lrif1 knockdown leads to decreased Trim28 occupancy at the Dux locus and modest upregulation of 2-cell transcriptional program.","method":"Co-immunoprecipitation, ChIP, siRNA knockdown in mESCs, RNA-seq for transcriptional program analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ChIP plus KD with transcriptional readout; published in two forms (preprint and peer-reviewed PMID:39605603)","pmids":["39605603","bio_10.1101_2024.11.18.624083"],"is_preprint":false},{"year":2025,"finding":"LRIF1 is necessary for epigenetic silencing activity at a defined D4Z4 regulatory fragment; reporter assays show that LRIF1, along with SETDB1, ATF7IP, and SIN3A/B, is required for silencing of a constitutively driven reporter placed adjacent to a D4Z4 fragment.","method":"Reporter gene assay with D4Z4 fragment cloning, loss-of-function of LRIF1 and other silencing factors, epigenetic analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional reporter assay with defined DNA element, genetic requirement established, single lab","pmids":["40627547"],"is_preprint":false},{"year":2024,"finding":"SUMOylation of SMCHD1 (primarily at K1374) impacts LRIF1 promoter activity, suggesting SMCHD1 SUMOylation modulates its regulation of LRIF1 expression in a post-translational manner.","method":"SUMOylation site mapping by MS, SUMO-dependent reporter assay for LRIF1 promoter activity, Co-IP","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, indirect evidence for LRIF1 promoter regulation as secondary finding in a study primarily focused on SMCHD1 SUMOylation","pmids":["bio_10.1101_2024.10.13.618066"],"is_preprint":true}],"current_model":"LRIF1 is a heterochromatin-associated protein that acts as a loading factor for SMCHD1 at H3K9me2/3-modified chromatin by mediating SMCHD1 interaction with HP1 proteins (via a conserved PXVXL motif); it directly binds the D4Z4 macrosatellite repeat to maintain repressive chromatin and silence DUX4/Dux expression, recruits HP1α to mitotic centromeres to ensure accurate chromosome segregation, interacts with TRIM28 to repress the 2-cell transcriptional program in embryonic stem cells, and forms a repressive SMCHD1–LRIF1–HP1 complex at heterochromatin-like genomic regions; loss of LRIF1 function causes D4Z4 chromatin relaxation and aberrant DUX4 expression, resulting in FSHD type 2."},"narrative":{"mechanistic_narrative":"LRIF1 is a heterochromatin-associated protein that serves as the principal chromatin-loading factor for the chromatin compaction protein SMCHD1, bridging it to repressive H3K9me2/3-modified nucleosomes and HP1 proteins to enforce gene silencing at heterochromatin [PMID:26391951, PMID:bio_10.1101_2025.06.13.659515]. LRIF1 binds HP1 directly through an evolutionarily conserved PXVXL motif in its C-terminus that engages the HP1 chromoshadow domain, and this interaction recruits HP1α to mitotic centromeres where it is required for inner-centromere Aurora B activity and accurate chromosome segregation [PMID:30016453]. At the D4Z4 macrosatellite repeat, the long isoform of LRIF1 binds directly to maintain a compacted, repressive chromatin state that silences DUX4 and its target genes; a patient-derived nonsense mutation abolishing the long isoform causes D4Z4 chromatin relaxation and aberrant DUX4 expression, establishing LRIF1 loss of function as a cause of FSHD type 2 [PMID:32467133]. LRIF1 and SMCHD1 operate as an interdependent, context-specific repressive module: in zebrafish, lrif1 knockout phenocopies smchd1 knockout with ectopic HOX transcription, identifying the two as direct partners in maternal epigenetic regulation [PMID:35739109], and the SMCHD1–LRIF1–HP1 complex also represses foreign DNA such as the AAV genome [PMID:38976714]. Beyond the SMCHD1 axis, LRIF1 contributes to repression of the 2-cell transcriptional program through an SMCHD1- and CBX-independent interaction with TRIM28 at the Dux locus [PMID:39605603, PMID:bio_10.1101_2024.11.18.624083].","teleology":[{"year":2013,"claim":"Before its function was known, LRIF1 was placed at a specific genomic compartment, establishing that it is a chromatin-associated protein co-resident with SMCHD1 at telomeres.","evidence":"Quantitative telomeric chromatin isolation (QTIP) with SILAC mass spectrometry in mammalian cells","pmids":["24270157"],"confidence":"Medium","gaps":["Functional consequence at telomeres not tested","Direct vs. indirect telomere association not resolved"]},{"year":2015,"claim":"Identified the core mechanistic role of LRIF1 as the loading factor that delivers SMCHD1 to heterochromatin, answering how SMCHD1 reaches H3K9me3 chromatin.","evidence":"Co-immunoprecipitation, chromatin fractionation, and epistasis in mammalian cells","pmids":["26391951"],"confidence":"High","gaps":["Whether LRIF1 binds nucleosomes directly or via HP1 not fully separated","Genome-wide scope of dependency not mapped at this stage"]},{"year":2017,"claim":"Extended LRIF1's heterochromatin association to centromeric alpha-satellite DNA, broadening its identified chromatin targets.","evidence":"HyCCAPP chromatin pulldown followed by mass spectrometry in human cells","pmids":["28704058"],"confidence":"Medium","gaps":["Localization only; no functional readout","Direct DNA binding versus complex co-capture not distinguished"]},{"year":2018,"claim":"Defined the molecular basis of LRIF1-HP1 binding and revealed a mitotic function, showing the PXVXL motif recruits HP1α to centromeres to support chromosome segregation.","evidence":"Direct binding assays, PXVXL motif mutagenesis, live-cell imaging and chromosome segregation assays","pmids":["30016453"],"confidence":"High","gaps":["Relationship between mitotic HP1 recruitment and SMCHD1 loading not integrated","How the same motif partitions between interphase heterochromatin and mitotic centromeres unclear"]},{"year":2020,"claim":"Connected LRIF1 to human disease by showing the long isoform directly binds D4Z4 and is required for its compaction and DUX4 silencing, with a patient mutation causing FSHD type 2.","evidence":"ChIP, siRNA knockdown in muscle cells, and patient-derived nonsense mutation with DUX4 expression readout","pmids":["32467133"],"confidence":"High","gaps":["Isoform-specific structural basis for D4Z4 binding not defined","Why short isoform cannot substitute not established"]},{"year":2022,"claim":"Established LRIF1 and SMCHD1 as functionally interdependent in vivo through genetic phenocopy at developmental HOX loci.","evidence":"Zebrafish lrif1 knockout, genetic epistasis with smchd1, and HOX expression/methylation phenotyping","pmids":["35739109"],"confidence":"High","gaps":["Maternal vs. zygotic contribution of LRIF1 not fully separated","Conservation of HOX regulation in mammals not directly tested here"]},{"year":2023,"claim":"Revealed context-specific and feedback regulation, showing SMCHD1-LRIF1 binding is interdependent at the LRIF1 promoter but not equivalently at D4Z4, and that single-factor somatic loss is insufficient to relax D4Z4.","evidence":"ChIP, somatic loss-of-function, reporter assays, and D4Z4 methylation analysis","pmids":["37380887"],"confidence":"High","gaps":["Molecular basis of locus-specific interdependency unknown","Threshold of combined loss needed for D4Z4 change not quantified"]},{"year":2024,"claim":"Identified an SMCHD1-independent repressive route, showing LRIF1 interacts with TRIM28 to maintain its occupancy at Dux and restrain the 2-cell program in mESCs.","evidence":"Co-IP, ChIP, and siRNA knockdown with RNA-seq in mouse embryonic stem cells","pmids":["39605603"],"confidence":"Medium","gaps":["Direct vs. bridged LRIF1-TRIM28 contact not resolved","Only modest transcriptional effect; functional importance in development not established"]},{"year":2024,"claim":"Generalized the SMCHD1-LRIF1-HP1 complex to silencing of foreign DNA, demonstrating it heterochromatinizes the AAV genome to repress transgene expression.","evidence":"Genome-wide CRISPR screen, RNAi/CRISPRi knockdown, Co-IP, and viral transduction assays","pmids":["38976714"],"confidence":"Medium","gaps":["Single-lab finding","How the complex recognizes episomal foreign DNA unknown"]},{"year":2025,"claim":"Defined the chromatin-recognition logic, showing LRIF1 is required genome-wide for SMCHD1 binding to H3K9me2/3 nucleosomes while SMCHD1 ATPase activity drives selective regional enrichment.","evidence":"Live-cell and single-molecule imaging with engineered ATPase mutations (preprint)","pmids":["bio_10.1101_2025.06.13.659515"],"confidence":"Medium","gaps":["Preprint, not peer-reviewed","Stoichiometry of the LRIF1-SMCHD1-nucleosome interaction not resolved"]},{"year":2025,"claim":"Localized the SMCHD1 interaction interface to its coiled-coil domain and dissected its contribution to DNA compaction in vitro.","evidence":"Biophysical DNA-compaction reconstitution and domain-deletion analysis (preprint)","pmids":["bio_10.1101_2025.07.08.663435"],"confidence":"Low","gaps":["Preprint and LRIF1 finding secondary to SMCHD1 result","LRIF1's own role in compaction not directly reconstituted"]},{"year":2025,"claim":"Placed LRIF1 within a defined silencing factor set at a D4Z4 regulatory element, showing it is required alongside SETDB1, ATF7IP, and SIN3A/B for reporter silencing.","evidence":"Reporter assay with cloned D4Z4 fragment and loss-of-function of silencing factors","pmids":["40627547"],"confidence":"Medium","gaps":["Direct physical links among LRIF1 and the other factors not shown","Whether these factors act in one complex or parallel pathways unknown"]},{"year":null,"claim":"The structural basis by which LRIF1 simultaneously engages H3K9me-modified nucleosomes, HP1, and SMCHD1, and how it partitions between SMCHD1-dependent and TRIM28-dependent repression, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of LRIF1 or its complexes","Mechanism selecting between SMCHD1 and TRIM28 partnerships unknown","Isoform-specific functional division not mechanistically explained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,8]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[4,5,11]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,3]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,4]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,4,8]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[4,5,11]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1]}],"complexes":["SMCHD1–LRIF1–HP1 complex"],"partners":["SMCHD1","CBX5","CBX3","TRIM28"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5T3J3","full_name":"Ligand-dependent nuclear receptor-interacting factor 1","aliases":["HP1-binding protein enriched in inactive X chromosome protein 1","HBiX1","Receptor-interacting factor 1"],"length_aa":769,"mass_kda":84.6,"function":"Together with SMCHD1, involved in chromosome X inactivation in females by promoting the compaction of heterochromatin (PubMed:23542155). Also able to repress the ligand-induced transcriptional activity of retinoic acid receptor alpha (RARA), possibly through direct recruitment of histone deacetylases (PubMed:17455211). Also required for silencing of the DUX4 locus in somatic cells (PubMed:32467133)","subcellular_location":"Chromosome; Nucleus matrix","url":"https://www.uniprot.org/uniprotkb/Q5T3J3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LRIF1","classification":"Not Classified","n_dependent_lines":12,"n_total_lines":1208,"dependency_fraction":0.009933774834437087},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"HIST2H2BE","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/LRIF1","total_profiled":1310},"omim":[{"mim_id":"619477","title":"FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY 3, DIGENIC; FSHD3","url":"https://www.omim.org/entry/619477"},{"mim_id":"615354","title":"LIGAND-DEPENDENT NUCLEAR RECEPTOR-INTERACTING FACTOR 1; LRIF1","url":"https://www.omim.org/entry/615354"},{"mim_id":"614066","title":"SPASTIC PARAPLEGIA 47, AUTOSOMAL RECESSIVE; SPG47","url":"https://www.omim.org/entry/614066"},{"mim_id":"607245","title":"ADAPTOR-RELATED PROTEIN COMPLEX 4, BETA-1 SUBUNIT; AP4B1","url":"https://www.omim.org/entry/607245"},{"mim_id":"158900","title":"FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY 1; FSHD1","url":"https://www.omim.org/entry/158900"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Centriolar satellite","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/LRIF1"},"hgnc":{"alias_symbol":["RIF1","FLJ11269"],"prev_symbol":["C1orf103"]},"alphafold":{"accession":"Q5T3J3","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T3J3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T3J3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T3J3-F1-predicted_aligned_error_v6.png","plddt_mean":48.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LRIF1","jax_strain_url":"https://www.jax.org/strain/search?query=LRIF1"},"sequence":{"accession":"Q5T3J3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5T3J3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5T3J3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T3J3"}},"corpus_meta":[{"pmid":"32467133","id":"PMC_32467133","title":"Homozygous nonsense variant in LRIF1 associated with facioscapulohumeral muscular dystrophy.","date":"2020","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/32467133","citation_count":115,"is_preprint":false},{"pmid":"24270157","id":"PMC_24270157","title":"A quantitative telomeric chromatin isolation protocol identifies different telomeric states.","date":"2013","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/24270157","citation_count":91,"is_preprint":false},{"pmid":"26391951","id":"PMC_26391951","title":"Independent Mechanisms Target SMCHD1 to Trimethylated Histone H3 Lysine 9-Modified Chromatin and the Inactive X Chromosome.","date":"2015","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/26391951","citation_count":61,"is_preprint":false},{"pmid":"36348371","id":"PMC_36348371","title":"Simultaneous measurement of the size and methylation of chromosome 4qA-D4Z4 repeats in facioscapulohumeral muscular dystrophy by long-read sequencing.","date":"2022","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36348371","citation_count":30,"is_preprint":false},{"pmid":"34569420","id":"PMC_34569420","title":"Associations between infant sex and DNA methylation across umbilical cord blood, artery, and placenta samples.","date":"2021","source":"Epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/34569420","citation_count":26,"is_preprint":false},{"pmid":"30016453","id":"PMC_30016453","title":"LRIF1 interacts with HP1α to coordinate accurate chromosome segregation during mitosis.","date":"2018","source":"Journal of molecular cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/30016453","citation_count":18,"is_preprint":false},{"pmid":"34711481","id":"PMC_34711481","title":"Facioscapulohumeral muscular dystrophy type 2: an update on the clinical, genetic, and molecular findings.","date":"2021","source":"Neuromuscular disorders : NMD","url":"https://pubmed.ncbi.nlm.nih.gov/34711481","citation_count":17,"is_preprint":false},{"pmid":"38021397","id":"PMC_38021397","title":"Molecular Diagnosis of Facioscapulohumeral Muscular Dystrophy in Patients Clinically Suspected of FSHD Using Optical Genome Mapping.","date":"2023","source":"Neurology. 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manner","date":"2024-10-13","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.13.618066","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13331,"output_tokens":3162,"usd":0.043712,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10557,"output_tokens":3892,"usd":0.075042,"stage2_stop_reason":"end_turn"},"total_usd":0.118754,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2015,\n      \"finding\": \"LRIF1 mediates chromatin loading of SMCHD1 by interacting with HP1γ at H3K9me3-modified chromatin sites on chromosome arms, establishing LRIF1 as the principal loading factor for SMCHD1 at heterochromatin.\",\n      \"method\": \"Co-immunoprecipitation, chromatin fractionation, epistasis experiments in mammalian cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction data, multiple orthogonal methods, replicated conceptually across multiple subsequent studies\",\n      \"pmids\": [\"26391951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"LRIF1 directly interacts with HP1α chromoshadow domain via an evolutionarily conserved PXVXL motif in its C-terminus, recruits HP1α to centromeres of mitotic chromosomes, and this interaction is required for Aurora B activity in the inner centromere and accurate chromosome segregation.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assay, PXVXL motif mutagenesis, live-cell imaging of mitotic chromosomes, chromosome segregation assay\",\n      \"journal\": \"Journal of molecular cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct binding assay with mutagenesis, functional readout (chromosome segregation defects), multiple orthogonal methods in one study\",\n      \"pmids\": [\"30016453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LRIF1 is a telomere-associated protein; QTIP (quantitative telomeric chromatin isolation) demonstrated that LRIF1 is enriched at telomeres together with SMCHD1, with higher density at long telomeres.\",\n      \"method\": \"QTIP (chromatin immunopurification + SILAC mass spectrometry)\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — rigorous quantitative chromatin proteomics method, single study, localization established but functional consequence not directly tested\",\n      \"pmids\": [\"24270157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"LRIF1 is identified as a novel alpha satellite (centromeric alphoid DNA)-associated protein in human cells, placing it among heterochromatin-binding proteins at the centromere.\",\n      \"method\": \"HyCCAPP (hybridization capture of chromatin-associated proteins) followed by mass spectrometry\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — DNA-centric chromatin pulldown with MS validation, single study, localization only\",\n      \"pmids\": [\"28704058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"LRIF1 (long isoform) binds directly to the D4Z4 repeat and is required for D4Z4 chromatin compaction; loss of the long LRIF1 isoform causes D4Z4 chromatin relaxation and derepression of DUX4 and DUX4 target genes in muscle cells.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) showing LRIF1 binding to D4Z4; siRNA knockdown of LRIF1 long isoform in muscle cells with readout of DUX4 and target gene expression; patient-derived nonsense mutation abolishing long isoform\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP, loss-of-function knockdown, patient mutation with epigenetic readout; convergent evidence across genetic and molecular approaches\",\n      \"pmids\": [\"32467133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SMCHD1, together with the long isoform of LRIF1, binds to the LRIF1 promoter and represses LRIF1 expression; the interdependency of SMCHD1 and LRIF1 binding differs between the D4Z4 locus and the LRIF1 promoter, and somatic loss-of-function of either SMCHD1 or LRIF1 alone does not result in D4Z4 chromatin changes.\",\n      \"method\": \"ChIP, loss-of-function experiments (somatic knockdown/knockout), reporter assays, epigenetic analysis of D4Z4 methylation\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (ChIP, KO/KD, methylation analysis), reveals regulatory feedback and context-specific binding\",\n      \"pmids\": [\"37380887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Lrif1 knockout in zebrafish phenocopies Smchd1 knockout, including precocious/ectopic HOX transcription and vertebrate patterning defects; Lrif1 acts as a direct interacting partner of Smchd1 in mediating maternal epigenetic regulation of HOX loci.\",\n      \"method\": \"Zebrafish lrif1 knockout, genetic epistasis with smchd1 knockout, molecular phenotyping of HOX expression and DNA methylation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (phenocopy), knockout animals, multiple molecular readouts across two independent organisms\",\n      \"pmids\": [\"35739109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Upon AAV transduction, SMCHD1 forms a complex with LRIF1 and HP1 to directly bind the AAV genome and maintain a heterochromatin-like state repressing AAV transgene expression; LRIF1 knockdown disrupts this complex and activates AAV transcription.\",\n      \"method\": \"Genome-wide CRISPR screen, RNAi/CRISPRi knockdown, co-immunoprecipitation demonstrating SMCHD1-LRIF1-HP1 complex, viral transduction assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen plus Co-IP plus functional KD assay, single lab, multiple complementary approaches\",\n      \"pmids\": [\"38976714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LRIF1 is required for genome-wide chromatin binding of SMCHD1 by mediating its interaction with H3K9me2/3-modified nucleosomes; SMCHD1 ATPase (ATP hydrolysis) activity is additionally required for selective enrichment at specific chromatin regions including the inactive X chromosome for gene silencing.\",\n      \"method\": \"Live-cell and single-molecule imaging, engineered ATPase domain mutations, LRIF1-dependent SMCHD1 chromatin-binding assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Weak — single-molecule imaging and mutagenesis, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.13.659515\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMCHD1's coiled-coil domain facilitates interaction with LRIF1; SMCHD1 can compact DNA independently and in an ATP-regulated manner, but the LRIF1 interaction domain (coiled-coil) does not affect DNA compaction rate per se.\",\n      \"method\": \"Biophysical reconstitution assays (DNA compaction), domain deletion analysis, nucleosome array assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution but preprint, single lab, and LRIF1 finding is secondary to the main SMCHD1 compaction result\",\n      \"pmids\": [\"bio_10.1101_2025.07.08.663435\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Lrif1 interacts with Trim28 (a known Dux repressor) in mouse embryonic stem cells in a manner independent of Cbx proteins and Smchd1; Lrif1 knockdown leads to decreased Trim28 occupancy at the Dux locus and modest upregulation of 2-cell transcriptional program.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, siRNA knockdown in mESCs, RNA-seq for transcriptional program analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ChIP plus KD with transcriptional readout; published in two forms (preprint and peer-reviewed PMID:39605603)\",\n      \"pmids\": [\"39605603\", \"bio_10.1101_2024.11.18.624083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LRIF1 is necessary for epigenetic silencing activity at a defined D4Z4 regulatory fragment; reporter assays show that LRIF1, along with SETDB1, ATF7IP, and SIN3A/B, is required for silencing of a constitutively driven reporter placed adjacent to a D4Z4 fragment.\",\n      \"method\": \"Reporter gene assay with D4Z4 fragment cloning, loss-of-function of LRIF1 and other silencing factors, epigenetic analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional reporter assay with defined DNA element, genetic requirement established, single lab\",\n      \"pmids\": [\"40627547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SUMOylation of SMCHD1 (primarily at K1374) impacts LRIF1 promoter activity, suggesting SMCHD1 SUMOylation modulates its regulation of LRIF1 expression in a post-translational manner.\",\n      \"method\": \"SUMOylation site mapping by MS, SUMO-dependent reporter assay for LRIF1 promoter activity, Co-IP\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, indirect evidence for LRIF1 promoter regulation as secondary finding in a study primarily focused on SMCHD1 SUMOylation\",\n      \"pmids\": [\"bio_10.1101_2024.10.13.618066\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"LRIF1 is a heterochromatin-associated protein that acts as a loading factor for SMCHD1 at H3K9me2/3-modified chromatin by mediating SMCHD1 interaction with HP1 proteins (via a conserved PXVXL motif); it directly binds the D4Z4 macrosatellite repeat to maintain repressive chromatin and silence DUX4/Dux expression, recruits HP1α to mitotic centromeres to ensure accurate chromosome segregation, interacts with TRIM28 to repress the 2-cell transcriptional program in embryonic stem cells, and forms a repressive SMCHD1–LRIF1–HP1 complex at heterochromatin-like genomic regions; loss of LRIF1 function causes D4Z4 chromatin relaxation and aberrant DUX4 expression, resulting in FSHD type 2.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LRIF1 is a heterochromatin-associated protein that serves as the principal chromatin-loading factor for the chromatin compaction protein SMCHD1, bridging it to repressive H3K9me2/3-modified nucleosomes and HP1 proteins to enforce gene silencing at heterochromatin [#0, #8]. LRIF1 binds HP1 directly through an evolutionarily conserved PXVXL motif in its C-terminus that engages the HP1 chromoshadow domain, and this interaction recruits HP1\\u03b1 to mitotic centromeres where it is required for inner-centromere Aurora B activity and accurate chromosome segregation [#1]. At the D4Z4 macrosatellite repeat, the long isoform of LRIF1 binds directly to maintain a compacted, repressive chromatin state that silences DUX4 and its target genes; a patient-derived nonsense mutation abolishing the long isoform causes D4Z4 chromatin relaxation and aberrant DUX4 expression, establishing LRIF1 loss of function as a cause of FSHD type 2 [#4]. LRIF1 and SMCHD1 operate as an interdependent, context-specific repressive module: in zebrafish, lrif1 knockout phenocopies smchd1 knockout with ectopic HOX transcription, identifying the two as direct partners in maternal epigenetic regulation [#6], and the SMCHD1\\u2013LRIF1\\u2013HP1 complex also represses foreign DNA such as the AAV genome [#7]. Beyond the SMCHD1 axis, LRIF1 contributes to repression of the 2-cell transcriptional program through an SMCHD1- and CBX-independent interaction with TRIM28 at the Dux locus [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Before its function was known, LRIF1 was placed at a specific genomic compartment, establishing that it is a chromatin-associated protein co-resident with SMCHD1 at telomeres.\",\n      \"evidence\": \"Quantitative telomeric chromatin isolation (QTIP) with SILAC mass spectrometry in mammalian cells\",\n      \"pmids\": [\"24270157\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence at telomeres not tested\", \"Direct vs. indirect telomere association not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified the core mechanistic role of LRIF1 as the loading factor that delivers SMCHD1 to heterochromatin, answering how SMCHD1 reaches H3K9me3 chromatin.\",\n      \"evidence\": \"Co-immunoprecipitation, chromatin fractionation, and epistasis in mammalian cells\",\n      \"pmids\": [\"26391951\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether LRIF1 binds nucleosomes directly or via HP1 not fully separated\", \"Genome-wide scope of dependency not mapped at this stage\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended LRIF1's heterochromatin association to centromeric alpha-satellite DNA, broadening its identified chromatin targets.\",\n      \"evidence\": \"HyCCAPP chromatin pulldown followed by mass spectrometry in human cells\",\n      \"pmids\": [\"28704058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localization only; no functional readout\", \"Direct DNA binding versus complex co-capture not distinguished\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the molecular basis of LRIF1-HP1 binding and revealed a mitotic function, showing the PXVXL motif recruits HP1\\u03b1 to centromeres to support chromosome segregation.\",\n      \"evidence\": \"Direct binding assays, PXVXL motif mutagenesis, live-cell imaging and chromosome segregation assays\",\n      \"pmids\": [\"30016453\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between mitotic HP1 recruitment and SMCHD1 loading not integrated\", \"How the same motif partitions between interphase heterochromatin and mitotic centromeres unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected LRIF1 to human disease by showing the long isoform directly binds D4Z4 and is required for its compaction and DUX4 silencing, with a patient mutation causing FSHD type 2.\",\n      \"evidence\": \"ChIP, siRNA knockdown in muscle cells, and patient-derived nonsense mutation with DUX4 expression readout\",\n      \"pmids\": [\"32467133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Isoform-specific structural basis for D4Z4 binding not defined\", \"Why short isoform cannot substitute not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established LRIF1 and SMCHD1 as functionally interdependent in vivo through genetic phenocopy at developmental HOX loci.\",\n      \"evidence\": \"Zebrafish lrif1 knockout, genetic epistasis with smchd1, and HOX expression/methylation phenotyping\",\n      \"pmids\": [\"35739109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Maternal vs. zygotic contribution of LRIF1 not fully separated\", \"Conservation of HOX regulation in mammals not directly tested here\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed context-specific and feedback regulation, showing SMCHD1-LRIF1 binding is interdependent at the LRIF1 promoter but not equivalently at D4Z4, and that single-factor somatic loss is insufficient to relax D4Z4.\",\n      \"evidence\": \"ChIP, somatic loss-of-function, reporter assays, and D4Z4 methylation analysis\",\n      \"pmids\": [\"37380887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of locus-specific interdependency unknown\", \"Threshold of combined loss needed for D4Z4 change not quantified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified an SMCHD1-independent repressive route, showing LRIF1 interacts with TRIM28 to maintain its occupancy at Dux and restrain the 2-cell program in mESCs.\",\n      \"evidence\": \"Co-IP, ChIP, and siRNA knockdown with RNA-seq in mouse embryonic stem cells\",\n      \"pmids\": [\"39605603\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs. bridged LRIF1-TRIM28 contact not resolved\", \"Only modest transcriptional effect; functional importance in development not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Generalized the SMCHD1-LRIF1-HP1 complex to silencing of foreign DNA, demonstrating it heterochromatinizes the AAV genome to repress transgene expression.\",\n      \"evidence\": \"Genome-wide CRISPR screen, RNAi/CRISPRi knockdown, Co-IP, and viral transduction assays\",\n      \"pmids\": [\"38976714\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"How the complex recognizes episomal foreign DNA unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined the chromatin-recognition logic, showing LRIF1 is required genome-wide for SMCHD1 binding to H3K9me2/3 nucleosomes while SMCHD1 ATPase activity drives selective regional enrichment.\",\n      \"evidence\": \"Live-cell and single-molecule imaging with engineered ATPase mutations (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.06.13.659515\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not peer-reviewed\", \"Stoichiometry of the LRIF1-SMCHD1-nucleosome interaction not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Localized the SMCHD1 interaction interface to its coiled-coil domain and dissected its contribution to DNA compaction in vitro.\",\n      \"evidence\": \"Biophysical DNA-compaction reconstitution and domain-deletion analysis (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.07.08.663435\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Preprint and LRIF1 finding secondary to SMCHD1 result\", \"LRIF1's own role in compaction not directly reconstituted\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed LRIF1 within a defined silencing factor set at a D4Z4 regulatory element, showing it is required alongside SETDB1, ATF7IP, and SIN3A/B for reporter silencing.\",\n      \"evidence\": \"Reporter assay with cloned D4Z4 fragment and loss-of-function of silencing factors\",\n      \"pmids\": [\"40627547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical links among LRIF1 and the other factors not shown\", \"Whether these factors act in one complex or parallel pathways unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis by which LRIF1 simultaneously engages H3K9me-modified nucleosomes, HP1, and SMCHD1, and how it partitions between SMCHD1-dependent and TRIM28-dependent repression, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of LRIF1 or its complexes\", \"Mechanism selecting between SMCHD1 and TRIM28 partnerships unknown\", \"Isoform-specific functional division not mechanistically explained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4, 5, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 4, 8]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [4, 5, 11]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [\"SMCHD1\\u2013LRIF1\\u2013HP1 complex\"],\n    \"partners\": [\"SMCHD1\", \"CBX5\", \"CBX3\", \"TRIM28\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}