{"gene":"SGO1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2006,"finding":"Human SGO1 directly binds to protein phosphatase 2A (PP2A), and this interaction is required for centromeric localization of SGO1. Bub1 targets PP2A to centromeres in a Bub1-dependent manner, and PP2A at centromeres counteracts Plk1-mediated removal of SGO1 from centromeres.","method":"Co-immunoprecipitation, RNAi knockdown, localization rescue experiments","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with functional rescue, replicated in multiple follow-up studies","pmids":["16580887"],"is_preprint":false},{"year":2005,"finding":"Budding yeast Sgo1 is required for sensing lack of tension at the kinetochore during mitosis (spindle checkpoint tension-sensing component), but not for responding to microtubule depolymerization; Sgo1 degradation upon sister chromatid separation prevents cell cycle arrest in anaphase.","method":"Genetic analysis, spindle checkpoint assays, chromosome segregation assays in budding yeast","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with defined phenotypic readout, foundational paper with 154 citations","pmids":["15637284"],"is_preprint":false},{"year":2012,"finding":"CDK-mediated, mitosis-specific phosphorylation of human SGO1 activates its cohesion-protection function and enables direct binding to cohesin. Phospho-SGO1-bound cohesin contains PP2A, PDS5, and hypophosphorylated sororin but lacks WAPL. SGO1-PP2A dephosphorylates PDS5-bound sororin, protecting centromeric cohesin from WAPL-mediated removal.","method":"In vitro binding assays, phosphorylation-deficient mutants, Co-IP, RNAi rescue experiments","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including in vitro binding, mutagenesis, and functional rescue","pmids":["23242214"],"is_preprint":false},{"year":2008,"finding":"A major splice variant of SGO1, sSgo1, localizes to centrosomes in interphase and spindle poles in mitosis (distinct from full-length Sgo1 at kinetochores). sSgo1 interacts with Plk1 and its spindle pole localization is Plk1-dependent. sSgo1 is required for centriole cohesion, preventing premature centriole separation.","method":"RNAi, GFP localization, Co-immunoprecipitation, dominant-negative expression","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, direct localization with functional consequence, rescue experiments","pmids":["18331714"],"is_preprint":false},{"year":2009,"finding":"In Xenopus egg extracts, Sgo1 plays a role in stabilizing cohesin along chromosome arms, which is antagonized by the mitotic kinases Plk1 and Aurora B; Wapl and Pds5 directly modulate cohesin conformational changes for dissociation during prophase.","method":"In vitro Xenopus egg extract system, immunodepletion, add-back experiments","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro system with biochemical depletion and add-back","pmids":["19696148"],"is_preprint":false},{"year":2005,"finding":"In budding yeast meiosis, Sgo1 localizes to cohesin-associated regions at the centromere and the 50-kb surrounding region, establishing a cohesin-protected domain. This domain requires the 120-bp core centromere, Bub1, and the meiosis-specific factor Spo13. Cohesins and kinetochore proteins Iml3 and Chl4 are necessary for Sgo1 association with pericentric regions.","method":"ChIP, genetic epistasis, meiotic chromosome analysis in budding yeast","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — ChIP mapping combined with genetic epistasis, multiple orthogonal approaches","pmids":["16357219"],"is_preprint":false},{"year":2013,"finding":"In human cells, cohesin and H2A-pT120 specify two distinct pools of Sgo1-PP2A: one at inner centromeres (cohesin-dependent) and one at kinetochores (H2A-pT120-dependent). Kinetochore tension triggers Sgo1 dephosphorylation and redistribution from inner centromeres to kinetochores; incomplete redistribution causes chromosome nondisjunction.","method":"Localization studies, phospho-specific antibodies, RNAi, tension manipulation","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods establishing two distinct functional Sgo1 pools","pmids":["24055156"],"is_preprint":false},{"year":2015,"finding":"Human SGO1 is a direct reader of the Bub1-mediated H2A-pT120 mark at kinetochores. Bub1 also recruits RNA Polymerase II to unattached kinetochores, promoting active transcription that enables kinetochore-bound Sgo1 (recruited by H2A-pT120) to reach cohesin embedded in centromeric chromatin. Sgo1 interacts with Pol II in human cells and with RNA in vitro.","method":"In vitro binding assays, Co-IP, live imaging, Pol II inactivation in mitosis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro binding combined with functional rescue and genetic epistasis","pmids":["26190260"],"is_preprint":false},{"year":2007,"finding":"NEK2A directly binds human Sgo1 in vitro and co-localizes with Sgo1 at the kinetochore. NEK2A phosphorylates Sgo1 at Ser14 and Ser507, and expression of non-phosphorylatable Sgo1 mutants causes chromosome congression defects including syntelic and monotelic attachments.","method":"In vitro kinase assay, 32P incorporation, Co-IP, expression of phosphorylation-deficient mutants","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with site mapping and mutagenesis validation","pmids":["17621308"],"is_preprint":false},{"year":2007,"finding":"In budding yeast, Bub1 kinase domain is required for proper localization of Sgo1 to centromeres, and both Bub1 kinase activity and Sgo1 are required for accurate chromosome biorientation after nocodazole treatment.","method":"Genetic analysis, localization studies, chromosome segregation assays in budding yeast","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with defined phenotypic readouts, multiple chromosome segregation assays","pmids":["18081426"],"is_preprint":false},{"year":2008,"finding":"Human Sgo1 is degraded during mitotic exit via the APC/C-Cdh1 pathway. Sgo1 contains two functional degradation motifs (KEN box and D box); deletion of both is required to stabilize the protein. Bub1 contributes to Sgo1 steady-state protein levels through an APC/C-independent mechanism. Non-degradable Sgo1 does not impair mitotic progression.","method":"In vitro ubiquitination assay, mutagenesis of degrons, overexpression of Cdh1, cell cycle analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro ubiquitination reconstitution with mutagenesis validation","pmids":["19015261"],"is_preprint":false},{"year":2011,"finding":"In human cells, HP1α is recruited to mitotic centromeres by INCENP (CPC subunit), not by Sgo1. Both HP1-INCENP and HP1-Sgo1 interactions require the HP1 chromo shadow domain binding to PXVXL/I motifs. A Sgo1 mutant deficient in HP1 binding is functional in centromeric cohesion protection and localizes normally to centromeres in mitosis, demonstrating that HP1-Sgo1 interaction is dispensable for cohesion protection.","method":"Biochemical pull-down, structural analysis, functional complementation with HP1-binding deficient mutants","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 — structural and biochemical characterization with functional validation by mutagenesis","pmids":["21346195"],"is_preprint":false},{"year":2010,"finding":"Human Sgo1 is first recruited to centromeric heterochromatin in G2 in an HP1-dependent manner, then becomes diffusely localized in early prophase, before returning to centromeres in prophase via Bub1 kinase activity. Centromeric cohesion is maintained even when Bub1 kinase is absent and Sgo1 is absent from mitotic centromeres, because Sgo1 establishes protection in G2.","method":"Live-cell imaging, Bub1 kinase-dead complementation in Bub1-null MEFs, cell cycle-staged localization","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — clean genetic null complementation with stage-specific localization analysis","pmids":["20124418"],"is_preprint":false},{"year":2014,"finding":"In budding yeast, Sgo1 together with PP2A-Rts1 ensures localization of condensin to centromeric chromatin; failure to recruit condensin results in abnormal pericentric chromatin conformation. Sgo1 is also required for maintaining Aurora B/Ipl1 localization on kinetochores during metaphase, suggesting a dual role in promoting biorientation.","method":"Genetic epistasis, ChIP, localization studies in budding yeast","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple readouts establishing two distinct functions","pmids":["24945276"],"is_preprint":false},{"year":2011,"finding":"In budding yeast, Sgo1 overexpression partially rescues chromosome segregation defects of bub1Δ cells. Sgo1 is identified as a possible partner of Mps1; Mps1 is required for Sgo1 localization to kinetochores, and Sgo1 overexpression rescues metaphase Mps1 inactivation defects. Bub1, Sgo1, and Mps1 facilitate chromosome biorientation independently of the Aurora B pathway.","method":"High-copy suppressor screen, genetic epistasis, localization studies in budding yeast","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis established, but physical Sgo1-Mps1 interaction not directly demonstrated","pmids":["21389114"],"is_preprint":false},{"year":2012,"finding":"In budding yeast, Bub1 and Sgo1 regulate pericentric chromatin geometry and dynamics in response to altered microtubule dynamics; Bub1-mediated H2A phosphorylation and Sgo1 recruitment soften the chromatin spring, causing radial expansion of pericentric chromatin and cohesin ring.","method":"Live imaging, FRAP, genetic analysis in budding yeast","journal":"Current biology : CB","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with functional consequence via live imaging and genetic perturbation","pmids":["22365852"],"is_preprint":false},{"year":2014,"finding":"In budding yeast, Sgo1 recruits the Rts1 isoform of PP2A to pericentromeric chromatin, and artificial recruitment of Rts1 to a single chromosome is sufficient to perform Sgo1 function on that chromosome. Sgo1 removal from chromosomes before anaphase depends on tension between sister chromatids, not on APC/C-mediated degradation. Sgo1 is an APC/C substrate in budding yeast with an unusual D-box-related sequence motif.","method":"Genetic epistasis, artificial tethering experiments, APC/C degradation assays in budding yeast","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — artificial tethering reconstitutes function, multiple orthogonal methods","pmids":["25236599"],"is_preprint":false},{"year":2016,"finding":"In budding yeast, the Bub1-H2A-Sgo1-PP2A-Rts1 axis prevents premature spindle assembly checkpoint silencing prior to tension generation; Sgo1 mutants with abolished binding to H2A or PP2A-Rts1 show premature SAC silencing, establishing this pathway in tension-sensitive checkpoint maintenance.","method":"Genetic epistasis, checkpoint duration assays, separation-of-function Sgo1 mutants in budding yeast","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with separation-of-function mutants, but single organism system","pmids":["28040741"],"is_preprint":false},{"year":2016,"finding":"In Xenopus egg extract system, Bub1 targeting to centromeres (via CENP-C and CENP-T independently through the KMN network) is sufficient for Sgo1 recruitment in the absence of other kinetochore components. Mps1 is required for this Bub1-dependent Sgo1 recruitment pathway even in the absence of checkpoint signaling.","method":"Xenopus cell-free system, forced targeting experiments, immunodepletion","journal":"Chromosoma","confidence":"High","confidence_rationale":"Tier 1 — reconstituted cell-free system with forced targeting and mechanistic dissection","pmids":["27116032"],"is_preprint":false},{"year":2018,"finding":"In budding yeast, CENP-A (Cse4) interacts with Sgo1 in vivo and in vitro. The N-terminal coiled-coil domain of Sgo1 is sufficient for CENP-A interaction and for association with centromeric (but not pericentromeric) chromatin. Depletion of CENP-A results in loss of Sgo1 from centromeric chromatin.","method":"Co-IP in vivo, in vitro binding assay, domain mapping, ChIP, chromosome segregation assays","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1-2 — in vivo and in vitro binding with domain mapping and functional validation","pmids":["28980861"],"is_preprint":false},{"year":2020,"finding":"In Xenopus egg extracts and biochemical reconstitution, Sgo1 directly interacts with the dimerization domain of Borealin (CPC subunit). Borealin and PP2A can bind simultaneously to the coiled-coil domain of Sgo1. A Borealin mutant disrupting the Sgo1-Borealin interaction causes defects in CPC chromosomal recruitment and Aurora B-dependent spindle assembly but not spindle assembly checkpoint signaling at unattached kinetochores.","method":"Biochemical reconstitution, in vitro binding assays, Xenopus egg extracts, separation-of-function mutants","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution establishing direct molecular interaction with functional validation","pmids":["32697622"],"is_preprint":false},{"year":2022,"finding":"Using an integrative structure-function approach, the Sgo1 N-terminal 'histone H3-like' tail interacts with the Survivin BIR domain as a hotspot for CPC-Sgo1 assembly; downstream Sgo1 residues and Borealin contribute to high-affinity binding. Sgo1 and H3T3ph use the same surface on Survivin to bind CPC, suggesting spatiotemporally restricted interactions. Disrupting Sgo1-Survivin interaction perturbs CPC centromere localization and function.","method":"Structure-function analysis, mutagenesis, biochemical binding assays, functional validation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — integrative structural and functional approach with mutagenesis validation","pmids":["35776132"],"is_preprint":false},{"year":2014,"finding":"Aurora B kinase interacts with and phosphorylates Sgo1 in vitro and in vivo. Aurora B-mediated phosphorylation of Sgo1 regulates the distribution of Sgo1 between centromeres and chromosome arms; expression of Aurora B kinase-dead mutants of Sgo1 causes mislocalization from centromeres to chromosome arms.","method":"Co-IP, in vitro kinase assay, expression of kinase-dead mutants, localization analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro kinase assay with functional mutants, single lab study","pmids":["25451264"],"is_preprint":false},{"year":2019,"finding":"SET, a known PP2A inhibitor, directly binds a domain in Sgo1 adjacent to the cohesin-binding motif and disrupts Sgo1-cohesin binding in a dose-dependent manner in vitro and in cells. SET-binding-deficient Sgo1 mutant fully supports centromeric cohesion protection but delays chromosome segregation, indicating SET promotes timely chromosome segregation by disrupting Sgo1-cohesin interaction.","method":"In vitro binding assay, Co-IP, dose-response experiments, separation-of-function Sgo1 mutants","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of inhibitory mechanism with separation-of-function validation","pmids":["31227592"],"is_preprint":false},{"year":2024,"finding":"Human CENP-A directly interacts with Sgo1 and determines Sgo1 localization to centromeres during mitosis. Lysine and arginine residues in the C-terminal domain of Sgo1 are critical for CENP-A binding. Mutation of these basic residues perturbs localization of both Sgo1 and Aurora B to centromeres, resulting in aberrant chromosome segregation and premature chromatid separation.","method":"Co-IP, biochemical domain mapping, mutational analysis, localization studies","journal":"Journal of molecular cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding with domain mapping and functional validation, single study","pmids":["37777834"],"is_preprint":false},{"year":2014,"finding":"Homozygous founder mutation in SGOL1 (K23E) causes CAID syndrome (Chronic Atrial and Intestinal Dysrhythmia). Patient fibroblasts show accelerated cell cycle progression, higher senescence rate, enhanced TGF-β signaling activation, and karyotypes displaying centromeric cohesion defects (railroad appearance). Morpholino knockdown of sgol1 in zebrafish recapitulates the human abnormalities.","method":"Human genetics, patient fibroblast analysis, zebrafish morpholino knockdown","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — human disease gene identification with cellular and organismal phenotypic validation","pmids":["25282101"],"is_preprint":false},{"year":2006,"finding":"Two major isoforms of human Sgo1 have entirely different subcellular localization patterns: the long isoform localizes to kinetochores during G2 and mitosis, while the short isoform (sSgo1, lacking exon 6) localizes to mitotic spindles and does not associate with kinetochores at any stage.","method":"GFP fusion localization, cell cycle staging","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 3 — direct localization experiment establishing isoform-specific subcellular distribution","pmids":["16582621"],"is_preprint":false}],"current_model":"SGO1 is a centromeric adaptor protein that protects centromeric cohesin from premature removal during mitosis: it is recruited to centromeres via Bub1-mediated phosphorylation of histone H2A-T120 (a mark SGO1 directly reads), CDK-mediated phosphorylation of SGO1 itself enables direct cohesin binding, and the SGO1-PP2A complex dephosphorylates sororin to exclude WAPL from the cohesin complex; SGO1 additionally recruits the chromosomal passenger complex (CPC/Aurora B) to centromeres through direct interactions with Survivin (via its histone H3-like N-terminal tail) and Borealin (via its coiled-coil domain), interacts with CENP-A for centromere localization, is phosphorylated by NEK2A and Aurora B to regulate its kinetochore distribution and microtubule attachment fidelity, is antagonized by SET (which disrupts SGO1-cohesin binding to allow timely chromosome segregation), and is degraded after mitosis by APC/C-Cdh1 via KEN box and D box motifs; a distinct splice variant (sSgo1) localizes to centrosomes in a Plk1-dependent manner to protect centriole cohesion."},"narrative":{"teleology":[{"year":2005,"claim":"The foundational question of what Sgo1 does during chromosome segregation was answered: Sgo1 functions as a tension-sensing component of the spindle checkpoint in budding yeast and protects pericentromeric cohesin in a domain established by Bub1, the core centromere, and kinetochore proteins.","evidence":"Genetic epistasis, spindle checkpoint assays, ChIP mapping of Sgo1-cohesin domains in budding yeast","pmids":["15637284","16357219"],"confidence":"High","gaps":["Mechanism of Sgo1-mediated cohesin protection unknown","Human ortholog function not yet demonstrated","How Bub1 recruits Sgo1 molecularly was undefined"]},{"year":2006,"claim":"The molecular basis of Sgo1 cohesion protection was established: SGO1 directly binds PP2A, and this complex is required for centromeric localization and counteracts Plk1-mediated cohesin removal. Two human isoforms with distinct subcellular localizations were identified.","evidence":"Co-immunoprecipitation, RNAi rescue, GFP-fusion localization in human cells","pmids":["16580887","16582621"],"confidence":"High","gaps":["How PP2A enzymatic activity protects cohesin was unknown","Substrate of SGO1-PP2A at centromeres not identified","Functional significance of the short isoform unclear"]},{"year":2007,"claim":"Phospho-regulation of SGO1 by NEK2A and Bub1 kinase was established: NEK2A directly phosphorylates SGO1 at Ser14/Ser507 to regulate kinetochore distribution and chromosome congression, while Bub1 kinase activity is required for Sgo1 centromeric localization and biorientation.","evidence":"In vitro kinase assays, phospho-mutant expression, genetic epistasis in human cells and budding yeast","pmids":["17621308","18081426"],"confidence":"High","gaps":["Whether NEK2A and Bub1 regulate Sgo1 through the same or parallel pathways was unclear","Direct chromatin mark read by Sgo1 not yet identified"]},{"year":2008,"claim":"The short splice variant sSgo1 was shown to have a distinct centrosomal/centriole cohesion function dependent on Plk1, expanding SGO1 biology beyond chromosome cohesion. Separately, SGO1 degradation at mitotic exit was shown to require APC/C-Cdh1 acting on KEN box and D box motifs.","evidence":"RNAi, GFP localization, Co-IP for sSgo1-Plk1; in vitro ubiquitination and degron mutagenesis for degradation","pmids":["18331714","19015261"],"confidence":"High","gaps":["Centriole cohesion substrates of sSgo1 not identified","Whether non-degradable SGO1 causes long-term cellular consequences was untested"]},{"year":2010,"claim":"The temporal sequence of SGO1 centromere recruitment was resolved: SGO1 first associates with centromeric heterochromatin in G2 via HP1, establishing cohesion protection before mitotic entry, then is re-recruited in prophase by Bub1, although HP1-SGO1 interaction proved dispensable for cohesion protection per se.","evidence":"Live-cell imaging in Bub1-null MEFs with complementation; HP1-binding-deficient Sgo1 mutant functional analysis","pmids":["20124418","21346195"],"confidence":"High","gaps":["What G2-specific SGO1 does mechanistically to 'establish' protection was undefined","How SGO1 transitions between HP1-dependent and Bub1-dependent binding modes was unclear"]},{"year":2012,"claim":"The core biochemical mechanism of cohesion protection was elucidated: CDK phosphorylation activates SGO1 direct binding to cohesin, and the resulting SGO1-PP2A complex dephosphorylates sororin on PDS5, thereby excluding WAPL from the cohesin complex. In yeast, Bub1-H2A phosphorylation and Sgo1 were shown to regulate pericentric chromatin geometry.","evidence":"In vitro binding assays, phospho-mutant rescue, Co-IP of cohesin sub-complexes in human cells; live imaging and FRAP in budding yeast","pmids":["23242214","22365852"],"confidence":"High","gaps":["Structural basis of phospho-SGO1/cohesin interaction unknown","Whether CDK acts directly on SGO1 in vivo required further confirmation"]},{"year":2013,"claim":"Two functionally distinct pools of SGO1-PP2A were identified: a cohesin-dependent inner centromere pool and an H2A-pT120-dependent kinetochore pool, with tension-dependent redistribution between them controlling chromosome segregation fidelity.","evidence":"Phospho-specific antibodies, RNAi, tension manipulation in human cells","pmids":["24055156"],"confidence":"High","gaps":["Phosphatase responsible for tension-dependent SGO1 dephosphorylation unknown","How the two pools coordinate their functions during biorientation unclear"]},{"year":2014,"claim":"Multiple additional functions of Sgo1 were uncovered: Sgo1-PP2A recruits condensin to pericentric chromatin and maintains Aurora B/Ipl1 at kinetochores in yeast; artificial PP2A tethering recapitulates Sgo1 function on individual chromosomes; and Aurora B phosphorylates SGO1 to regulate its centromere-arm distribution. A homozygous K23E mutation in SGOL1 was identified as the cause of CAID syndrome.","evidence":"ChIP and genetic epistasis in yeast; artificial tethering; in vitro kinase assay in human cells; human genetics with patient fibroblast and zebrafish validation","pmids":["24945276","25236599","25451264","25282101"],"confidence":"High","gaps":["How K23E mechanistically disrupts SGO1 function in cardiac and intestinal tissues unknown","Whether condensin recruitment by SGO1 is conserved in vertebrates untested"]},{"year":2015,"claim":"SGO1 was established as a direct reader of H2A-pT120, and a Bub1-driven RNA Polymerase II transcription mechanism at kinetochores was shown to facilitate SGO1 transit from kinetochores to centromeric cohesin.","evidence":"In vitro binding assays, Co-IP of SGO1-Pol II, Pol II inactivation during mitosis in human cells","pmids":["26190260"],"confidence":"High","gaps":["Nature and function of SGO1-RNA interaction not characterized","Whether Pol II transcription at kinetochores is universally required for cohesion protection unclear"]},{"year":2018,"claim":"CENP-A was identified as a direct binding partner that anchors Sgo1 specifically to centromeric chromatin, with the N-terminal coiled-coil of Sgo1 sufficient for this interaction.","evidence":"In vivo Co-IP, in vitro binding, domain mapping, ChIP in budding yeast","pmids":["28980861"],"confidence":"High","gaps":["Whether CENP-A and H2A-pT120 recruit Sgo1 through the same or separate binding events was unclear","Structural basis of Sgo1-CENP-A interaction unknown"]},{"year":2019,"claim":"The mechanism for timely release of cohesin protection was identified: SET directly binds SGO1 adjacent to its cohesin-binding motif and dose-dependently disrupts SGO1-cohesin interaction, promoting chromosome segregation without abolishing cohesion protection.","evidence":"In vitro dose-response binding, Co-IP, separation-of-function SGO1 mutants in human cells","pmids":["31227592"],"confidence":"High","gaps":["How SET activity is temporally regulated relative to anaphase onset unknown","Whether SET acts on both SGO1 pools (inner centromere and kinetochore) untested"]},{"year":2022,"claim":"The molecular basis for CPC recruitment by SGO1 was resolved: the SGO1 N-terminal histone H3-like tail binds the Survivin BIR domain using the same surface as H3T3ph, while the coiled-coil domain binds Borealin, enabling simultaneous CPC and PP2A binding to SGO1.","evidence":"Structure-function analysis, mutagenesis, biochemical reconstitution in Xenopus extracts and human cells","pmids":["35776132","32697622"],"confidence":"High","gaps":["Full structural model of the SGO1-CPC-PP2A ternary complex lacking","How H3T3ph and SGO1 compete or cooperate for CPC binding in vivo not fully resolved"]},{"year":2024,"claim":"Conservation of the CENP-A-SGO1 interaction was extended to human cells, with basic residues in the SGO1 C-terminal domain identified as critical for CENP-A binding and for proper centromeric localization of both SGO1 and Aurora B.","evidence":"Co-IP, domain mapping, mutational analysis, localization studies in human cells","pmids":["37777834"],"confidence":"Medium","gaps":["Whether CENP-A binding and H2A-pT120 reading are sequential or parallel recruitment mechanisms remains unresolved","Structural basis of human CENP-A-SGO1 interaction unknown"]},{"year":null,"claim":"Key open questions include: the structural basis of the multi-valent SGO1 platform integrating cohesin, PP2A, CPC, CENP-A, and H2A-pT120 interactions; how SGO1 dysfunction in non-dividing tissues leads to CAID syndrome cardiac and intestinal pathology; and whether the Pol II-dependent transit mechanism and SET-mediated release are coordinated in vivo to achieve the precise timing of cohesion resolution.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of full-length SGO1 with its partners","Tissue-specific functions of SGO1 in post-mitotic cells mechanistically undefined","In vivo coordination of SGO1 recruitment and release pathways not fully resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,20,21]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[7,19,24]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[5,6,7,12,19,24]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,1,2,6,10,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[25]}],"complexes":["SGO1-PP2A","Chromosomal Passenger Complex (CPC)"],"partners":["PP2A","BUB1","CENP-A","PLK1","BIRC5","CDCA8","SET","NEK2A"],"other_free_text":[]},"mechanistic_narrative":"SGO1 is a centromeric adaptor protein that protects sister chromatid cohesion during cell division and recruits key mitotic regulators to ensure accurate chromosome segregation. SGO1 is targeted to centromeres through direct binding to CENP-A and recognition of the Bub1-phosphorylated H2A-T120 mark; CDK-mediated phosphorylation of SGO1 activates its direct binding to cohesin, whereupon the SGO1-PP2A complex dephosphorylates sororin to exclude WAPL and shield centromeric cohesin from prophase removal [PMID:23242214, PMID:26190260, PMID:37777834]. SGO1 also recruits the chromosomal passenger complex (CPC) to centromeres through its histone H3-like N-terminal tail binding Survivin and its coiled-coil domain binding Borealin, while SET antagonizes SGO1-cohesin interaction to permit timely anaphase onset, and APC/C-Cdh1 degrades SGO1 after mitosis via KEN box and D box motifs [PMID:35776132, PMID:32697622, PMID:31227592, PMID:19015261]. A homozygous K23E mutation in SGOL1 causes Chronic Atrial and Intestinal Dysrhythmia (CAID syndrome), with patient cells exhibiting centromeric cohesion defects and enhanced TGF-β signaling [PMID:25282101]."},"prefetch_data":{"uniprot":{"accession":"Q5FBB7","full_name":"Shugoshin 1","aliases":["Serologically defined breast cancer antigen NY-BR-85","Shugoshin-like 1"],"length_aa":561,"mass_kda":64.2,"function":"Plays a central role in chromosome cohesion during mitosis by preventing premature dissociation of cohesin complex from centromeres after prophase, when most of cohesin complex dissociates from chromosomes arms. May act by preventing phosphorylation of the STAG2 subunit of cohesin complex at the centromere, ensuring cohesin persistence at centromere until cohesin cleavage by ESPL1/separase at anaphase. Essential for proper chromosome segregation during mitosis and this function requires interaction with PPP2R1A. Its phosphorylated form is necessary for chromosome congression and for the proper attachment of spindle microtubule to the kinetochore. Necessary for kinetochore localization of PLK1 and CENPF. May play a role in the tension sensing mechanism of the spindle-assembly checkpoint by regulating PLK1 kinetochore affinity. Isoform 3 plays a role in maintaining centriole cohesion involved in controlling spindle pole integrity. Involved in centromeric enrichment of AUKRB in prometaphase","subcellular_location":"Nucleus; Chromosome, centromere; Chromosome, centromere, kinetochore; Cytoplasm, cytoskeleton, spindle pole; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome; Nucleus speckle","url":"https://www.uniprot.org/uniprotkb/Q5FBB7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SGO1","classification":"Common Essential","n_dependent_lines":1115,"n_total_lines":1208,"dependency_fraction":0.9230132450331126},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PPP2CA","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SGO1","total_profiled":1310},"omim":[{"mim_id":"619247","title":"SPINDLE- AND KINETOCHORE-ASSOCIATED COMPLEX, SUBUNIT 3; SKA3","url":"https://www.omim.org/entry/619247"},{"mim_id":"618311","title":"RIBOSOME BIOGENESIS REGULATOR 1 HOMOLOG; RRS1","url":"https://www.omim.org/entry/618311"},{"mim_id":"614560","title":"MAU2 SISTER CHROMATID COHESION FACTOR; MAU2","url":"https://www.omim.org/entry/614560"},{"mim_id":"612425","title":"SHUGOSHIN-LIKE 2; SGOL2","url":"https://www.omim.org/entry/612425"},{"mim_id":"609374","title":"CELL DIVISION CYCLE-ASSOCIATED PROTEIN 5; CDCA5","url":"https://www.omim.org/entry/609374"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Kinetochore","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"bone marrow","ntpm":8.2},{"tissue":"lymphoid tissue","ntpm":12.1},{"tissue":"testis","ntpm":6.2}],"url":"https://www.proteinatlas.org/search/SGO1"},"hgnc":{"alias_symbol":["NY-BR-85"],"prev_symbol":["SGOL1"]},"alphafold":{"accession":"Q5FBB7","domains":[{"cath_id":"1.10.287","chopping":"528-561","consensus_level":"medium","plddt":76.4503,"start":528,"end":561}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5FBB7","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5FBB7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5FBB7-F1-predicted_aligned_error_v6.png","plddt_mean":55.09},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SGO1","jax_strain_url":"https://www.jax.org/strain/search?query=SGO1"},"sequence":{"accession":"Q5FBB7","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5FBB7.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5FBB7/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5FBB7"}},"corpus_meta":[{"pmid":"16580887","id":"PMC_16580887","title":"PP2A 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Bub1 targets PP2A to centromeres in a Bub1-dependent manner, and PP2A at centromeres counteracts Plk1-mediated removal of SGO1 from centromeres.\",\n      \"method\": \"Co-immunoprecipitation, RNAi knockdown, localization rescue experiments\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with functional rescue, replicated in multiple follow-up studies\",\n      \"pmids\": [\"16580887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Budding yeast Sgo1 is required for sensing lack of tension at the kinetochore during mitosis (spindle checkpoint tension-sensing component), but not for responding to microtubule depolymerization; Sgo1 degradation upon sister chromatid separation prevents cell cycle arrest in anaphase.\",\n      \"method\": \"Genetic analysis, spindle checkpoint assays, chromosome segregation assays in budding yeast\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with defined phenotypic readout, foundational paper with 154 citations\",\n      \"pmids\": [\"15637284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CDK-mediated, mitosis-specific phosphorylation of human SGO1 activates its cohesion-protection function and enables direct binding to cohesin. Phospho-SGO1-bound cohesin contains PP2A, PDS5, and hypophosphorylated sororin but lacks WAPL. SGO1-PP2A dephosphorylates PDS5-bound sororin, protecting centromeric cohesin from WAPL-mediated removal.\",\n      \"method\": \"In vitro binding assays, phosphorylation-deficient mutants, Co-IP, RNAi rescue experiments\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including in vitro binding, mutagenesis, and functional rescue\",\n      \"pmids\": [\"23242214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A major splice variant of SGO1, sSgo1, localizes to centrosomes in interphase and spindle poles in mitosis (distinct from full-length Sgo1 at kinetochores). sSgo1 interacts with Plk1 and its spindle pole localization is Plk1-dependent. sSgo1 is required for centriole cohesion, preventing premature centriole separation.\",\n      \"method\": \"RNAi, GFP localization, Co-immunoprecipitation, dominant-negative expression\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, direct localization with functional consequence, rescue experiments\",\n      \"pmids\": [\"18331714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Xenopus egg extracts, Sgo1 plays a role in stabilizing cohesin along chromosome arms, which is antagonized by the mitotic kinases Plk1 and Aurora B; Wapl and Pds5 directly modulate cohesin conformational changes for dissociation during prophase.\",\n      \"method\": \"In vitro Xenopus egg extract system, immunodepletion, add-back experiments\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro system with biochemical depletion and add-back\",\n      \"pmids\": [\"19696148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In budding yeast meiosis, Sgo1 localizes to cohesin-associated regions at the centromere and the 50-kb surrounding region, establishing a cohesin-protected domain. This domain requires the 120-bp core centromere, Bub1, and the meiosis-specific factor Spo13. Cohesins and kinetochore proteins Iml3 and Chl4 are necessary for Sgo1 association with pericentric regions.\",\n      \"method\": \"ChIP, genetic epistasis, meiotic chromosome analysis in budding yeast\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP mapping combined with genetic epistasis, multiple orthogonal approaches\",\n      \"pmids\": [\"16357219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In human cells, cohesin and H2A-pT120 specify two distinct pools of Sgo1-PP2A: one at inner centromeres (cohesin-dependent) and one at kinetochores (H2A-pT120-dependent). Kinetochore tension triggers Sgo1 dephosphorylation and redistribution from inner centromeres to kinetochores; incomplete redistribution causes chromosome nondisjunction.\",\n      \"method\": \"Localization studies, phospho-specific antibodies, RNAi, tension manipulation\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods establishing two distinct functional Sgo1 pools\",\n      \"pmids\": [\"24055156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human SGO1 is a direct reader of the Bub1-mediated H2A-pT120 mark at kinetochores. Bub1 also recruits RNA Polymerase II to unattached kinetochores, promoting active transcription that enables kinetochore-bound Sgo1 (recruited by H2A-pT120) to reach cohesin embedded in centromeric chromatin. Sgo1 interacts with Pol II in human cells and with RNA in vitro.\",\n      \"method\": \"In vitro binding assays, Co-IP, live imaging, Pol II inactivation in mitosis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro binding combined with functional rescue and genetic epistasis\",\n      \"pmids\": [\"26190260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NEK2A directly binds human Sgo1 in vitro and co-localizes with Sgo1 at the kinetochore. NEK2A phosphorylates Sgo1 at Ser14 and Ser507, and expression of non-phosphorylatable Sgo1 mutants causes chromosome congression defects including syntelic and monotelic attachments.\",\n      \"method\": \"In vitro kinase assay, 32P incorporation, Co-IP, expression of phosphorylation-deficient mutants\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with site mapping and mutagenesis validation\",\n      \"pmids\": [\"17621308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In budding yeast, Bub1 kinase domain is required for proper localization of Sgo1 to centromeres, and both Bub1 kinase activity and Sgo1 are required for accurate chromosome biorientation after nocodazole treatment.\",\n      \"method\": \"Genetic analysis, localization studies, chromosome segregation assays in budding yeast\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with defined phenotypic readouts, multiple chromosome segregation assays\",\n      \"pmids\": [\"18081426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human Sgo1 is degraded during mitotic exit via the APC/C-Cdh1 pathway. Sgo1 contains two functional degradation motifs (KEN box and D box); deletion of both is required to stabilize the protein. Bub1 contributes to Sgo1 steady-state protein levels through an APC/C-independent mechanism. Non-degradable Sgo1 does not impair mitotic progression.\",\n      \"method\": \"In vitro ubiquitination assay, mutagenesis of degrons, overexpression of Cdh1, cell cycle analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro ubiquitination reconstitution with mutagenesis validation\",\n      \"pmids\": [\"19015261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In human cells, HP1α is recruited to mitotic centromeres by INCENP (CPC subunit), not by Sgo1. Both HP1-INCENP and HP1-Sgo1 interactions require the HP1 chromo shadow domain binding to PXVXL/I motifs. A Sgo1 mutant deficient in HP1 binding is functional in centromeric cohesion protection and localizes normally to centromeres in mitosis, demonstrating that HP1-Sgo1 interaction is dispensable for cohesion protection.\",\n      \"method\": \"Biochemical pull-down, structural analysis, functional complementation with HP1-binding deficient mutants\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structural and biochemical characterization with functional validation by mutagenesis\",\n      \"pmids\": [\"21346195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human Sgo1 is first recruited to centromeric heterochromatin in G2 in an HP1-dependent manner, then becomes diffusely localized in early prophase, before returning to centromeres in prophase via Bub1 kinase activity. Centromeric cohesion is maintained even when Bub1 kinase is absent and Sgo1 is absent from mitotic centromeres, because Sgo1 establishes protection in G2.\",\n      \"method\": \"Live-cell imaging, Bub1 kinase-dead complementation in Bub1-null MEFs, cell cycle-staged localization\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic null complementation with stage-specific localization analysis\",\n      \"pmids\": [\"20124418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In budding yeast, Sgo1 together with PP2A-Rts1 ensures localization of condensin to centromeric chromatin; failure to recruit condensin results in abnormal pericentric chromatin conformation. Sgo1 is also required for maintaining Aurora B/Ipl1 localization on kinetochores during metaphase, suggesting a dual role in promoting biorientation.\",\n      \"method\": \"Genetic epistasis, ChIP, localization studies in budding yeast\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple readouts establishing two distinct functions\",\n      \"pmids\": [\"24945276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In budding yeast, Sgo1 overexpression partially rescues chromosome segregation defects of bub1Δ cells. Sgo1 is identified as a possible partner of Mps1; Mps1 is required for Sgo1 localization to kinetochores, and Sgo1 overexpression rescues metaphase Mps1 inactivation defects. Bub1, Sgo1, and Mps1 facilitate chromosome biorientation independently of the Aurora B pathway.\",\n      \"method\": \"High-copy suppressor screen, genetic epistasis, localization studies in budding yeast\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis established, but physical Sgo1-Mps1 interaction not directly demonstrated\",\n      \"pmids\": [\"21389114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In budding yeast, Bub1 and Sgo1 regulate pericentric chromatin geometry and dynamics in response to altered microtubule dynamics; Bub1-mediated H2A phosphorylation and Sgo1 recruitment soften the chromatin spring, causing radial expansion of pericentric chromatin and cohesin ring.\",\n      \"method\": \"Live imaging, FRAP, genetic analysis in budding yeast\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence via live imaging and genetic perturbation\",\n      \"pmids\": [\"22365852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In budding yeast, Sgo1 recruits the Rts1 isoform of PP2A to pericentromeric chromatin, and artificial recruitment of Rts1 to a single chromosome is sufficient to perform Sgo1 function on that chromosome. Sgo1 removal from chromosomes before anaphase depends on tension between sister chromatids, not on APC/C-mediated degradation. Sgo1 is an APC/C substrate in budding yeast with an unusual D-box-related sequence motif.\",\n      \"method\": \"Genetic epistasis, artificial tethering experiments, APC/C degradation assays in budding yeast\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — artificial tethering reconstitutes function, multiple orthogonal methods\",\n      \"pmids\": [\"25236599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In budding yeast, the Bub1-H2A-Sgo1-PP2A-Rts1 axis prevents premature spindle assembly checkpoint silencing prior to tension generation; Sgo1 mutants with abolished binding to H2A or PP2A-Rts1 show premature SAC silencing, establishing this pathway in tension-sensitive checkpoint maintenance.\",\n      \"method\": \"Genetic epistasis, checkpoint duration assays, separation-of-function Sgo1 mutants in budding yeast\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with separation-of-function mutants, but single organism system\",\n      \"pmids\": [\"28040741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In Xenopus egg extract system, Bub1 targeting to centromeres (via CENP-C and CENP-T independently through the KMN network) is sufficient for Sgo1 recruitment in the absence of other kinetochore components. Mps1 is required for this Bub1-dependent Sgo1 recruitment pathway even in the absence of checkpoint signaling.\",\n      \"method\": \"Xenopus cell-free system, forced targeting experiments, immunodepletion\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted cell-free system with forced targeting and mechanistic dissection\",\n      \"pmids\": [\"27116032\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In budding yeast, CENP-A (Cse4) interacts with Sgo1 in vivo and in vitro. The N-terminal coiled-coil domain of Sgo1 is sufficient for CENP-A interaction and for association with centromeric (but not pericentromeric) chromatin. Depletion of CENP-A results in loss of Sgo1 from centromeric chromatin.\",\n      \"method\": \"Co-IP in vivo, in vitro binding assay, domain mapping, ChIP, chromosome segregation assays\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vivo and in vitro binding with domain mapping and functional validation\",\n      \"pmids\": [\"28980861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In Xenopus egg extracts and biochemical reconstitution, Sgo1 directly interacts with the dimerization domain of Borealin (CPC subunit). Borealin and PP2A can bind simultaneously to the coiled-coil domain of Sgo1. A Borealin mutant disrupting the Sgo1-Borealin interaction causes defects in CPC chromosomal recruitment and Aurora B-dependent spindle assembly but not spindle assembly checkpoint signaling at unattached kinetochores.\",\n      \"method\": \"Biochemical reconstitution, in vitro binding assays, Xenopus egg extracts, separation-of-function mutants\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution establishing direct molecular interaction with functional validation\",\n      \"pmids\": [\"32697622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Using an integrative structure-function approach, the Sgo1 N-terminal 'histone H3-like' tail interacts with the Survivin BIR domain as a hotspot for CPC-Sgo1 assembly; downstream Sgo1 residues and Borealin contribute to high-affinity binding. Sgo1 and H3T3ph use the same surface on Survivin to bind CPC, suggesting spatiotemporally restricted interactions. Disrupting Sgo1-Survivin interaction perturbs CPC centromere localization and function.\",\n      \"method\": \"Structure-function analysis, mutagenesis, biochemical binding assays, functional validation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — integrative structural and functional approach with mutagenesis validation\",\n      \"pmids\": [\"35776132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Aurora B kinase interacts with and phosphorylates Sgo1 in vitro and in vivo. Aurora B-mediated phosphorylation of Sgo1 regulates the distribution of Sgo1 between centromeres and chromosome arms; expression of Aurora B kinase-dead mutants of Sgo1 causes mislocalization from centromeres to chromosome arms.\",\n      \"method\": \"Co-IP, in vitro kinase assay, expression of kinase-dead mutants, localization analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro kinase assay with functional mutants, single lab study\",\n      \"pmids\": [\"25451264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SET, a known PP2A inhibitor, directly binds a domain in Sgo1 adjacent to the cohesin-binding motif and disrupts Sgo1-cohesin binding in a dose-dependent manner in vitro and in cells. SET-binding-deficient Sgo1 mutant fully supports centromeric cohesion protection but delays chromosome segregation, indicating SET promotes timely chromosome segregation by disrupting Sgo1-cohesin interaction.\",\n      \"method\": \"In vitro binding assay, Co-IP, dose-response experiments, separation-of-function Sgo1 mutants\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of inhibitory mechanism with separation-of-function validation\",\n      \"pmids\": [\"31227592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Human CENP-A directly interacts with Sgo1 and determines Sgo1 localization to centromeres during mitosis. Lysine and arginine residues in the C-terminal domain of Sgo1 are critical for CENP-A binding. Mutation of these basic residues perturbs localization of both Sgo1 and Aurora B to centromeres, resulting in aberrant chromosome segregation and premature chromatid separation.\",\n      \"method\": \"Co-IP, biochemical domain mapping, mutational analysis, localization studies\",\n      \"journal\": \"Journal of molecular cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding with domain mapping and functional validation, single study\",\n      \"pmids\": [\"37777834\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Homozygous founder mutation in SGOL1 (K23E) causes CAID syndrome (Chronic Atrial and Intestinal Dysrhythmia). Patient fibroblasts show accelerated cell cycle progression, higher senescence rate, enhanced TGF-β signaling activation, and karyotypes displaying centromeric cohesion defects (railroad appearance). Morpholino knockdown of sgol1 in zebrafish recapitulates the human abnormalities.\",\n      \"method\": \"Human genetics, patient fibroblast analysis, zebrafish morpholino knockdown\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — human disease gene identification with cellular and organismal phenotypic validation\",\n      \"pmids\": [\"25282101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Two major isoforms of human Sgo1 have entirely different subcellular localization patterns: the long isoform localizes to kinetochores during G2 and mitosis, while the short isoform (sSgo1, lacking exon 6) localizes to mitotic spindles and does not associate with kinetochores at any stage.\",\n      \"method\": \"GFP fusion localization, cell cycle staging\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — direct localization experiment establishing isoform-specific subcellular distribution\",\n      \"pmids\": [\"16582621\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SGO1 is a centromeric adaptor protein that protects centromeric cohesin from premature removal during mitosis: it is recruited to centromeres via Bub1-mediated phosphorylation of histone H2A-T120 (a mark SGO1 directly reads), CDK-mediated phosphorylation of SGO1 itself enables direct cohesin binding, and the SGO1-PP2A complex dephosphorylates sororin to exclude WAPL from the cohesin complex; SGO1 additionally recruits the chromosomal passenger complex (CPC/Aurora B) to centromeres through direct interactions with Survivin (via its histone H3-like N-terminal tail) and Borealin (via its coiled-coil domain), interacts with CENP-A for centromere localization, is phosphorylated by NEK2A and Aurora B to regulate its kinetochore distribution and microtubule attachment fidelity, is antagonized by SET (which disrupts SGO1-cohesin binding to allow timely chromosome segregation), and is degraded after mitosis by APC/C-Cdh1 via KEN box and D box motifs; a distinct splice variant (sSgo1) localizes to centrosomes in a Plk1-dependent manner to protect centriole cohesion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SGO1 is a centromeric adaptor protein that protects sister chromatid cohesion during cell division and recruits key mitotic regulators to ensure accurate chromosome segregation. SGO1 is targeted to centromeres through direct binding to CENP-A and recognition of the Bub1-phosphorylated H2A-T120 mark; CDK-mediated phosphorylation of SGO1 activates its direct binding to cohesin, whereupon the SGO1-PP2A complex dephosphorylates sororin to exclude WAPL and shield centromeric cohesin from prophase removal [PMID:23242214, PMID:26190260, PMID:37777834]. SGO1 also recruits the chromosomal passenger complex (CPC) to centromeres through its histone H3-like N-terminal tail binding Survivin and its coiled-coil domain binding Borealin, while SET antagonizes SGO1-cohesin interaction to permit timely anaphase onset, and APC/C-Cdh1 degrades SGO1 after mitosis via KEN box and D box motifs [PMID:35776132, PMID:32697622, PMID:31227592, PMID:19015261]. A homozygous K23E mutation in SGOL1 causes Chronic Atrial and Intestinal Dysrhythmia (CAID syndrome), with patient cells exhibiting centromeric cohesion defects and enhanced TGF-β signaling [PMID:25282101].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"The foundational question of what Sgo1 does during chromosome segregation was answered: Sgo1 functions as a tension-sensing component of the spindle checkpoint in budding yeast and protects pericentromeric cohesin in a domain established by Bub1, the core centromere, and kinetochore proteins.\",\n      \"evidence\": \"Genetic epistasis, spindle checkpoint assays, ChIP mapping of Sgo1-cohesin domains in budding yeast\",\n      \"pmids\": [\"15637284\", \"16357219\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of Sgo1-mediated cohesin protection unknown\", \"Human ortholog function not yet demonstrated\", \"How Bub1 recruits Sgo1 molecularly was undefined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"The molecular basis of Sgo1 cohesion protection was established: SGO1 directly binds PP2A, and this complex is required for centromeric localization and counteracts Plk1-mediated cohesin removal. Two human isoforms with distinct subcellular localizations were identified.\",\n      \"evidence\": \"Co-immunoprecipitation, RNAi rescue, GFP-fusion localization in human cells\",\n      \"pmids\": [\"16580887\", \"16582621\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PP2A enzymatic activity protects cohesin was unknown\", \"Substrate of SGO1-PP2A at centromeres not identified\", \"Functional significance of the short isoform unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Phospho-regulation of SGO1 by NEK2A and Bub1 kinase was established: NEK2A directly phosphorylates SGO1 at Ser14/Ser507 to regulate kinetochore distribution and chromosome congression, while Bub1 kinase activity is required for Sgo1 centromeric localization and biorientation.\",\n      \"evidence\": \"In vitro kinase assays, phospho-mutant expression, genetic epistasis in human cells and budding yeast\",\n      \"pmids\": [\"17621308\", \"18081426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NEK2A and Bub1 regulate Sgo1 through the same or parallel pathways was unclear\", \"Direct chromatin mark read by Sgo1 not yet identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The short splice variant sSgo1 was shown to have a distinct centrosomal/centriole cohesion function dependent on Plk1, expanding SGO1 biology beyond chromosome cohesion. Separately, SGO1 degradation at mitotic exit was shown to require APC/C-Cdh1 acting on KEN box and D box motifs.\",\n      \"evidence\": \"RNAi, GFP localization, Co-IP for sSgo1-Plk1; in vitro ubiquitination and degron mutagenesis for degradation\",\n      \"pmids\": [\"18331714\", \"19015261\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Centriole cohesion substrates of sSgo1 not identified\", \"Whether non-degradable SGO1 causes long-term cellular consequences was untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The temporal sequence of SGO1 centromere recruitment was resolved: SGO1 first associates with centromeric heterochromatin in G2 via HP1, establishing cohesion protection before mitotic entry, then is re-recruited in prophase by Bub1, although HP1-SGO1 interaction proved dispensable for cohesion protection per se.\",\n      \"evidence\": \"Live-cell imaging in Bub1-null MEFs with complementation; HP1-binding-deficient Sgo1 mutant functional analysis\",\n      \"pmids\": [\"20124418\", \"21346195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What G2-specific SGO1 does mechanistically to 'establish' protection was undefined\", \"How SGO1 transitions between HP1-dependent and Bub1-dependent binding modes was unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The core biochemical mechanism of cohesion protection was elucidated: CDK phosphorylation activates SGO1 direct binding to cohesin, and the resulting SGO1-PP2A complex dephosphorylates sororin on PDS5, thereby excluding WAPL from the cohesin complex. In yeast, Bub1-H2A phosphorylation and Sgo1 were shown to regulate pericentric chromatin geometry.\",\n      \"evidence\": \"In vitro binding assays, phospho-mutant rescue, Co-IP of cohesin sub-complexes in human cells; live imaging and FRAP in budding yeast\",\n      \"pmids\": [\"23242214\", \"22365852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of phospho-SGO1/cohesin interaction unknown\", \"Whether CDK acts directly on SGO1 in vivo required further confirmation\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Two functionally distinct pools of SGO1-PP2A were identified: a cohesin-dependent inner centromere pool and an H2A-pT120-dependent kinetochore pool, with tension-dependent redistribution between them controlling chromosome segregation fidelity.\",\n      \"evidence\": \"Phospho-specific antibodies, RNAi, tension manipulation in human cells\",\n      \"pmids\": [\"24055156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase responsible for tension-dependent SGO1 dephosphorylation unknown\", \"How the two pools coordinate their functions during biorientation unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Multiple additional functions of Sgo1 were uncovered: Sgo1-PP2A recruits condensin to pericentric chromatin and maintains Aurora B/Ipl1 at kinetochores in yeast; artificial PP2A tethering recapitulates Sgo1 function on individual chromosomes; and Aurora B phosphorylates SGO1 to regulate its centromere-arm distribution. A homozygous K23E mutation in SGOL1 was identified as the cause of CAID syndrome.\",\n      \"evidence\": \"ChIP and genetic epistasis in yeast; artificial tethering; in vitro kinase assay in human cells; human genetics with patient fibroblast and zebrafish validation\",\n      \"pmids\": [\"24945276\", \"25236599\", \"25451264\", \"25282101\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How K23E mechanistically disrupts SGO1 function in cardiac and intestinal tissues unknown\", \"Whether condensin recruitment by SGO1 is conserved in vertebrates untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"SGO1 was established as a direct reader of H2A-pT120, and a Bub1-driven RNA Polymerase II transcription mechanism at kinetochores was shown to facilitate SGO1 transit from kinetochores to centromeric cohesin.\",\n      \"evidence\": \"In vitro binding assays, Co-IP of SGO1-Pol II, Pol II inactivation during mitosis in human cells\",\n      \"pmids\": [\"26190260\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nature and function of SGO1-RNA interaction not characterized\", \"Whether Pol II transcription at kinetochores is universally required for cohesion protection unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"CENP-A was identified as a direct binding partner that anchors Sgo1 specifically to centromeric chromatin, with the N-terminal coiled-coil of Sgo1 sufficient for this interaction.\",\n      \"evidence\": \"In vivo Co-IP, in vitro binding, domain mapping, ChIP in budding yeast\",\n      \"pmids\": [\"28980861\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CENP-A and H2A-pT120 recruit Sgo1 through the same or separate binding events was unclear\", \"Structural basis of Sgo1-CENP-A interaction unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The mechanism for timely release of cohesin protection was identified: SET directly binds SGO1 adjacent to its cohesin-binding motif and dose-dependently disrupts SGO1-cohesin interaction, promoting chromosome segregation without abolishing cohesion protection.\",\n      \"evidence\": \"In vitro dose-response binding, Co-IP, separation-of-function SGO1 mutants in human cells\",\n      \"pmids\": [\"31227592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SET activity is temporally regulated relative to anaphase onset unknown\", \"Whether SET acts on both SGO1 pools (inner centromere and kinetochore) untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The molecular basis for CPC recruitment by SGO1 was resolved: the SGO1 N-terminal histone H3-like tail binds the Survivin BIR domain using the same surface as H3T3ph, while the coiled-coil domain binds Borealin, enabling simultaneous CPC and PP2A binding to SGO1.\",\n      \"evidence\": \"Structure-function analysis, mutagenesis, biochemical reconstitution in Xenopus extracts and human cells\",\n      \"pmids\": [\"35776132\", \"32697622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full structural model of the SGO1-CPC-PP2A ternary complex lacking\", \"How H3T3ph and SGO1 compete or cooperate for CPC binding in vivo not fully resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Conservation of the CENP-A-SGO1 interaction was extended to human cells, with basic residues in the SGO1 C-terminal domain identified as critical for CENP-A binding and for proper centromeric localization of both SGO1 and Aurora B.\",\n      \"evidence\": \"Co-IP, domain mapping, mutational analysis, localization studies in human cells\",\n      \"pmids\": [\"37777834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CENP-A binding and H2A-pT120 reading are sequential or parallel recruitment mechanisms remains unresolved\", \"Structural basis of human CENP-A-SGO1 interaction unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include: the structural basis of the multi-valent SGO1 platform integrating cohesin, PP2A, CPC, CENP-A, and H2A-pT120 interactions; how SGO1 dysfunction in non-dividing tissues leads to CAID syndrome cardiac and intestinal pathology; and whether the Pol II-dependent transit mechanism and SET-mediated release are coordinated in vivo to achieve the precise timing of cohesion resolution.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of full-length SGO1 with its partners\", \"Tissue-specific functions of SGO1 in post-mitotic cells mechanistically undefined\", \"In vivo coordination of SGO1 recruitment and release pathways not fully resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 20, 21]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [7, 19, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [5, 6, 7, 12, 19, 24]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 1, 2, 6, 10, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [25]}\n    ],\n    \"complexes\": [\n      \"SGO1-PP2A\",\n      \"Chromosomal Passenger Complex (CPC)\"\n    ],\n    \"partners\": [\n      \"PP2A\",\n      \"BUB1\",\n      \"CENP-A\",\n      \"PLK1\",\n      \"BIRC5\",\n      \"CDCA8\",\n      \"SET\",\n      \"NEK2A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}