{"gene":"SKA1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2009,"finding":"The human Ska1 complex is a three-subunit complex (including Ska1 and Rama1/Ska3) that localizes to the outer kinetochore and spindle microtubules. Reconstituted Ska1 complex possesses two separable biochemical activities: direct microtubule binding through the Ska1 subunit, and microtubule-stimulated oligomerization imparted by the Rama1 subunit. The full complex forms assemblies on microtubules that facilitate processive movement of microspheres along depolymerizing microtubules.","method":"Biochemical reconstitution, microtubule co-sedimentation assay, bead motility assay on depolymerizing microtubules, siRNA depletion with chromosome segregation readout","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of purified complex with functional motility assay, subunit-specific activity mapping, replicated by multiple subsequent studies","pmids":["19289083"],"is_preprint":false},{"year":2006,"finding":"Ska1 and Ska2 form a complex; Ska1 is required for Ska2 stability in vivo. Ska1 associates with kinetochores following microtubule attachment during prometaphase. Depletion of either subunit causes loss of both from kinetochores, increased cold-sensitivity of kinetochore fibres, and a prolonged checkpoint-dependent metaphase-like arrest with Mad2 retention at kinetochores.","method":"siRNA depletion, live-cell imaging, immunofluorescence, cold-stability assay of kinetochore fibres","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction, functional KD phenotype with defined checkpoint readout, replicated by later studies","pmids":["17093495"],"is_preprint":false},{"year":2012,"finding":"The Ska1 complex tracks with depolymerizing microtubule ends and binds both the straight microtubule lattice and curved protofilaments, whereas the Ndc80 complex binds only straight lattice and lacks tracking activity. The Ska1 complex imparts its tracking capability to the Ndc80 complex. A crystal structure of the Ska1 microtubule-binding domain (MTBD) was determined, revealing its interaction with microtubules and its regulation by Aurora B phosphorylation.","method":"Single-molecule TIRF tracking assay, cryo-EM, X-ray crystallography of Ska1 MTBD, Aurora B phosphorylation of MTBD with microtubule binding assay","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure of MTBD plus single-molecule tracking plus Aurora B regulation, multiple orthogonal methods in one study","pmids":["23085020"],"is_preprint":false},{"year":2016,"finding":"Ska3 modulates the microtubule-binding capability of the Ska complex by (i) directly interacting with tubulin monomers and (ii) allosterically interacting with tubulin-contacting regions of Ska1. Perturbing either Ska3-microtubule or Ska3-Ska1 interactions reduces microtubule binding in vitro and delays anaphase onset in cells.","method":"In vitro microtubule binding assay with purified mutant complexes, co-IP of Ska3–Ska1 interaction, time-lapse imaging of anaphase onset","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis plus cellular phenotype readout, single lab with multiple orthogonal methods","pmids":["27667719"],"is_preprint":false},{"year":2016,"finding":"EB1 interacts directly with Ska1 and facilitates Ska1 localization on microtubules in vertebrate cells. EB1 depletion reduces Ska1 recruitment onto microtubules and causes chromosome alignment defects. Together EB1 and Ska1 form extended structures on the microtubule lattice as revealed by structural studies.","method":"Co-IP (EB1–Ska1), EB1 siRNA depletion with Ska1 localization readout, in vitro microtubule co-sedimentation, structural EM of EB1–Ska complexes on microtubules, computational modelling","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — reciprocal interaction, structural evidence, functional KD with localization readout, multiple orthogonal methods single lab","pmids":["27225956"],"is_preprint":false},{"year":2017,"finding":"The Ska1 MTBD autonomously tracks growing microtubule ends in vitro in addition to depolymerizing ends. Multiple distinct surfaces of the Ska1 MTBD interact with diverse tubulin substrates: it binds the microtubule lattice, dolastatin-induced protofilament-like structures, and soluble tubulin heterodimers, and can promote assembly of oligomeric ring-like tubulin structures. Mutations on distinct MTBD surfaces that disrupt soluble tubulin binding without preventing lattice binding compromise microtubule tracking and cause defective chromosome alignment and mitotic progression in cells.","method":"Single-molecule TIRF assay for tip tracking, in vitro microtubule binding with purified mutant Ska1, CRISPR/Cas9 replacement assay in cells with chromosome alignment readout","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with structure-guided mutagenesis plus CRISPR replacement in cells, multiple orthogonal methods","pmids":["29153323"],"is_preprint":false},{"year":2014,"finding":"SKA1 localizes to centrosomes in addition to spindle microtubules and the outer kinetochore. Depletion of Ska1 causes failure of centrosome duplication, while Ska1 over-expression leads to centrosome amplification via induction of centriole over-duplication in human prostate epithelial cells, which is sufficient to convert cells to a tumourigenic state.","method":"siRNA depletion with centrosome duplication readout, Ska1 over-expression with centriole counting, immunofluorescence, transgenic mouse model, xenograft tumourigenicity assay","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by immunofluorescence tied to functional consequence, loss- and gain-of-function with centrosome phenotype, single lab","pmids":["24827423"],"is_preprint":false},{"year":2016,"finding":"Ska1 and DDA3 act as molecular linkers between spindle dynamics and kinetochore composition. DDA3 recruits Kif2a onto the mitotic spindle, and Ska1 subsequently targets Kif2a to the minus-end of spindle microtubules to facilitate spindle dynamics. DDA3 also targets Ska1 to kinetochores to stabilize end-on attachment.","method":"Co-IP (Ska1–DDA3–Kif2a), siRNA depletion, immunofluorescence localization of Kif2a on spindle minus-ends","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2–3 / Weak — co-IP and localization data, single lab, limited in vitro validation","pmids":["26797278"],"is_preprint":false},{"year":2019,"finding":"SKA1 interacts with the DNA-directed RNA polymerase II subunit RPB3. In MTX-sensitive cells, RPB3 binds the FPGS gene promoter and drives FPGS transcription upon MTX treatment; this is blocked in SKA1-overexpressing cells through formation of an inhibitory SKA1–RPB3 complex, causing downregulation of FPGS and de novo MTX resistance. ChIP confirmed RPB3 binding to the FPGS promoter.","method":"Co-IP (SKA1–RPB3), ChIP of RPB3 on FPGS promoter, siRNA knockdown of SKA1 to restore MTX sensitivity, Western blot for FPGS","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus ChIP plus functional rescue, single lab","pmids":["30851225"],"is_preprint":false},{"year":2019,"finding":"PPARγ directly binds to a predicted response element in the SKA1 gene promoter and transcriptionally upregulates SKA1 expression. Under diabetogenic conditions (high glucose, palmitic acid, insulin), PPARγ-driven SKA1 expression promotes centrosome amplification; knockdown of PPARγ blocks the treatment-induced increase in SKA1, while knockdown of SKA1 does not affect PPARγ levels.","method":"ChIP (PPARγ binding to SKA1 promoter), PPARγ inhibitor/siRNA with SKA1 mRNA and protein readout, centrosome amplification assay","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus pharmacological and siRNA epistasis, single lab, multiple methods","pmids":["30989671"],"is_preprint":false},{"year":2020,"finding":"SKA1 enhances pancreatic cancer cell migration by activating Cdc42 to remodel the actin cytoskeleton. iTRAQ proteomics identified downstream proteins of SKA1, and Cdc42 inhibition (ZCL278) or actin perturbation (cytochalasin B) reversed SKA1-induced morphology and migration changes.","method":"iTRAQ quantitative proteomics, Cdc42 inhibitor (ZCL278), cytochalasin B treatment, immunoblotting and immunofluorescence, in vivo xenograft","journal":"Cell proliferation","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — mass spectrometry-based target identification plus pharmacological validation, single lab","pmids":["32232899"],"is_preprint":false},{"year":2022,"finding":"Ska1 interacts with EB1 through a conserved motif in its N-terminal disordered loop region; Ska1 binds the C-terminal region of the EB1 dimer. Disruption of this interaction (deletion or mutation of the motif) abolishes Ska complex recruitment to kinetochores and induces chromosome alignment defects without affecting Ska complex assembly. NMR showed the Ska1 motif binds EB1 residues that are shared binding sites for other plus-end targeting proteins.","method":"NMR spectroscopy (Ska1 motif–EB1 interaction), atomic-force microscopy imaging, site-directed mutagenesis with kinetochore localization readout, chromosome alignment assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural data plus mutagenesis plus cellular functional readout, multiple orthogonal methods, single lab","pmids":["36592928"],"is_preprint":false},{"year":2022,"finding":"SKA1 interacts specifically with scaffold attachment factor B (SAFB), and this interaction mediates transcriptional repression of DUSP6, promoting ccRCC metastasis. SKA1 knockdown reduces cancer cell motility in vitro and in vivo.","method":"Co-IP (SKA1–SAFB), SKA1 knockdown with motility/invasion assay, in vivo metastasis model","journal":"Aging","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP without reciprocal validation, single lab, limited mechanistic follow-up on SAFB–DUSP6 link","pmids":["36462498"],"is_preprint":false},{"year":2023,"finding":"Cdt1 (DNA replication licensing factor) directly interacts with the Ska1 complex, and this interaction is required for recruiting Cdt1 to kinetochores and spindle microtubules. Cdk1 phosphorylation of Cdt1 is critical for Ska1 binding, kinetochore-microtubule attachments, and mitotic progression. Cdt1 synergizes with Ndc80 and Ska1 to form a diffusive, tripartite Ndc80–Cdt1–Ska1 complex that processively tracks dynamic microtubule plus-ends in vitro.","method":"Auxin-inducible degron for conditional Cdt1 depletion, co-IP (Cdt1–Ska1), in vitro microtubule binding with reconstituted tripartite complex, single-molecule tip-tracking assay, Cdk1 phosphorylation assay with phospho-mimetic/dead mutants","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of tripartite complex with single-molecule tracking, kinase phosphorylation with mutagenesis, conditional degron system, multiple orthogonal methods","pmids":["37265445"],"is_preprint":false},{"year":2023,"finding":"lncRNA MRVI1-AS1 recruits RNA-binding protein CELF2 to bind and stabilize SKA1 mRNA, increasing SKA1 protein expression in HCC cells. RIP assay confirmed direct interactions between CELF2 and both MRVI1-AS1 and SKA1 mRNA. MRVI1-AS1 expression is induced by hypoxia through a HIF-1-dependent pathway.","method":"RNA immunoprecipitation (RIP), actinomycin D mRNA stability assay, microarray mRNA expression analysis, dual luciferase assay, rescue experiments","journal":"World journal of surgical oncology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — RIP assay confirms CELF2–SKA1 mRNA interaction, mRNA stability assay, rescue experiments, single lab","pmids":["36973749"],"is_preprint":false},{"year":2025,"finding":"Oligomeric assemblies of Ska and Ndc80 complexes stabilize microtubule ends against shortening by strengthening lateral contacts between tubulin protofilaments at microtubule plus-ends, as visualized by cryoET. A point mutation in the Ska1 MTBD that does not affect individual Ska1–microtubule binding but abolishes Ska–Ska interactions disrupts stable kinetochore–microtubule attachments both in vitro and in vivo, demonstrating that cooperative Ska oligomerization with Ndc80 is required for stable attachments.","method":"Cryo-electron tomography (cryoET), site-directed mutagenesis of Ska1 MTBD, in vitro microtubule attachment assay, cellular assay of kinetochore-microtubule attachments","journal":"bioRxiv","confidence":"High","confidence_rationale":"Tier 1 / Moderate — cryoET structural data plus structure-guided mutagenesis plus in vitro and in vivo functional validation, novel mechanistic finding not covered by peer-reviewed work","pmids":["bio_10.1101_2025.07.06.663352"],"is_preprint":true}],"current_model":"SKA1 is the microtubule-binding subunit of the trimeric Ska1 complex (with Ska2 and Ska3) at the outer kinetochore; its microtubule-binding domain (MTBD) engages both straight and curved tubulin protofilaments, autonomously tracks growing and shrinking microtubule plus-ends, and—in cooperative oligomeric assemblies with the Ndc80 complex and aided by Cdt1 (phosphorylated by Cdk1) and EB1—stabilizes lateral protofilament contacts at microtubule plus-ends to sustain load-bearing kinetochore-microtubule attachments and silence the spindle checkpoint, while Aurora B phosphorylation of the MTBD down-regulates these interactions; outside its kinetochore role, SKA1 also localizes to centrosomes where its overexpression drives centriole over-duplication and centrosome amplification, and in non-mitotic contexts it can interact with RNA Pol II subunit RPB3 to repress FPGS transcription and with SAFB to suppress DUSP6 transcription."},"narrative":{"mechanistic_narrative":"SKA1 is the microtubule-binding subunit of the trimeric Ska complex (with Ska2 and Ska3) that localizes to the outer kinetochore and spindle microtubules and stabilizes load-bearing kinetochore-microtubule attachments during mitosis [PMID:19289083, PMID:17093495]. Within the reconstituted complex, SKA1 provides direct microtubule binding while Ska3 modulates this activity both by contacting tubulin directly and by allosterically engaging the tubulin-contacting regions of SKA1 [PMID:19289083, PMID:27667719]. The SKA1 microtubule-binding domain (MTBD) engages both the straight lattice and curved protofilaments and autonomously tracks growing and shrinking microtubule plus-ends, conferring tip-tracking capacity onto the Ndc80 complex, which alone binds only straight lattice [PMID:23085020, PMID:29153323]. Distinct MTBD surfaces recognize soluble tubulin heterodimers, protofilament-like structures, and the lattice, and mutations that selectively disrupt soluble-tubulin binding compromise tracking and chromosome alignment [PMID:29153323]. SKA1 is recruited to microtubules and kinetochores through a conserved N-terminal motif that binds the C-terminal region of the EB1 dimer at sites shared by other plus-end-targeting proteins, and through the replication licensing factor Cdt1, whose Cdk1 phosphorylation drives formation of a processive tripartite Ndc80-Cdt1-Ska1 tip-tracking complex [PMID:27225956, PMID:36592928, PMID:37265445]. Cooperative oligomerization of Ska with Ndc80 strengthens lateral protofilament contacts at plus-ends to sustain stable attachments [PMID:bio_10.1101_2025.07.06.663352], whereas Aurora B phosphorylation of the MTBD down-regulates microtubule binding [PMID:23085020]. Loss of SKA1 destabilizes kinetochore fibres and triggers a Mad2-dependent checkpoint arrest [PMID:17093495]. Beyond mitosis, SKA1 localizes to centrosomes, where its overexpression drives centriole over-duplication and centrosome amplification [PMID:24827423], and it acts in cancer contexts through transcriptional interactions: it binds RNA Pol II subunit RPB3 to repress FPGS and confer methotrexate resistance [PMID:30851225] and activates Cdc42-driven actin remodeling to promote cell migration [PMID:32232899].","teleology":[{"year":2006,"claim":"Established SKA1 as a kinetochore-associated factor required for stable attachments by showing it forms a complex with Ska2 and is needed for cold-stable kinetochore fibres and checkpoint silencing.","evidence":"siRNA depletion, live-cell imaging, and cold-stability assays of kinetochore fibres in human cells","pmids":["17093495"],"confidence":"High","gaps":["Did not establish the biochemical basis of microtubule binding","Mechanism of post-attachment kinetochore recruitment unresolved"]},{"year":2009,"claim":"Defined the Ska complex as a three-subunit machine and mapped its separable activities, showing SKA1 carries direct microtubule binding while Ska3 imparts microtubule-stimulated oligomerization enabling movement along depolymerizing ends.","evidence":"Biochemical reconstitution, co-sedimentation, and bead motility assays on depolymerizing microtubules","pmids":["19289083"],"confidence":"High","gaps":["Structural basis of the SKA1-microtubule interface not defined","How tracking integrates with Ndc80 at kinetochores unknown"]},{"year":2012,"claim":"Provided the structural and mechanistic basis for SKA1 microtubule binding and its regulation, showing the MTBD binds straight and curved tubulin, tracks depolymerizing ends, confers tracking onto Ndc80, and is regulated by Aurora B.","evidence":"Single-molecule TIRF, cryo-EM, X-ray crystallography of the MTBD, and Aurora B phosphorylation binding assays","pmids":["23085020"],"confidence":"High","gaps":["In vivo consequences of Aurora B sites not fully dissected","Recruitment pathway to kinetochores not addressed"]},{"year":2016,"claim":"Resolved how SKA1 is delivered to microtubules and how Ska3 fine-tunes binding, identifying EB1 as a direct partner facilitating SKA1 lattice localization and showing Ska3 acts allosterically on SKA1 tubulin contacts.","evidence":"Co-IP, EB1 siRNA with SKA1 localization readout, structural EM, and in vitro binding with mutant complexes","pmids":["27225956","27667719"],"confidence":"High","gaps":["Precise EB1-binding motif on SKA1 not yet mapped at this stage","Quantitative contribution of Ska3 vs EB1 to recruitment unclear"]},{"year":2017,"claim":"Demonstrated that the SKA1 MTBD autonomously tracks both growing and shrinking ends through multiple tubulin-engaging surfaces, with soluble-tubulin binding being essential for tracking and chromosome alignment.","evidence":"Single-molecule TIRF tip-tracking and CRISPR/Cas9 replacement with structure-guided MTBD mutants","pmids":["29153323"],"confidence":"High","gaps":["How distinct surfaces are coordinated during dynamic tracking unresolved","Interplay with Ndc80 oligomers not addressed here"]},{"year":2022,"claim":"Pinpointed the molecular determinant of SKA1 kinetochore recruitment, identifying a conserved N-terminal motif binding the EB1 C-terminus at sites shared with other +TIPs, whose disruption abolishes kinetochore targeting.","evidence":"NMR, atomic-force microscopy, and site-directed mutagenesis with kinetochore localization and chromosome alignment readouts","pmids":["36592928"],"confidence":"High","gaps":["Competition among +TIPs for the shared EB1 surface not quantified","Cell-cycle timing of EB1-mediated recruitment unresolved"]},{"year":2023,"claim":"Identified Cdt1 as a phosphorylation-gated component of the tip-tracking machinery, showing Cdk1-phosphorylated Cdt1 binds the Ska complex to form a processive Ndc80-Cdt1-Ska1 tripartite complex required for attachment and mitotic progression.","evidence":"Auxin-inducible Cdt1 degron, co-IP, reconstituted tripartite complex with single-molecule tracking, and Cdk1 phospho-mutant assays","pmids":["37265445"],"confidence":"High","gaps":["Stoichiometry and architecture of the tripartite complex at kinetochores undefined","How phosphoregulation is temporally coordinated with Aurora B unknown"]},{"year":2025,"claim":"Provided the structural mechanism of attachment stabilization, showing cooperative Ska-Ndc80 oligomers strengthen lateral contacts between tubulin protofilaments at plus-ends, with a Ska-Ska interaction mutant that abolishes stable attachments without affecting individual binding.","evidence":"Cryo-electron tomography with structure-guided MTBD mutagenesis and in vitro and cellular attachment assays (preprint)","pmids":["bio_10.1101_2025.07.06.663352"],"confidence":"High","gaps":["Preprint not yet peer-reviewed","How oligomer assembly is regulated in cells unresolved"]},{"year":2014,"claim":"Extended SKA1 function beyond the kinetochore, showing it localizes to centrosomes and that its dysregulation perturbs centriole duplication and can drive tumourigenic transformation.","evidence":"siRNA and overexpression with centrosome/centriole counting, immunofluorescence, transgenic mouse, and xenograft assays","pmids":["24827423"],"confidence":"Medium","gaps":["Molecular mechanism linking SKA1 to centriole duplication not defined","Whether centrosome role depends on microtubule binding unknown"]},{"year":2019,"claim":"Revealed a non-mitotic transcriptional activity, showing SKA1 binds RNA Pol II subunit RPB3 to repress FPGS transcription and confer methotrexate resistance.","evidence":"Co-IP, ChIP of RPB3 on the FPGS promoter, and SKA1 knockdown rescue of drug sensitivity","pmids":["30851225"],"confidence":"Medium","gaps":["How a kinetochore protein engages transcriptional machinery mechanistically unclear","Single-lab finding without reciprocal structural validation"]},{"year":2020,"claim":"Linked SKA1 to cytoskeletal signaling in cancer, showing it activates Cdc42 to remodel actin and promote migration.","evidence":"iTRAQ proteomics, Cdc42 inhibitor and cytochalasin B treatment, and xenograft assay","pmids":["32232899"],"confidence":"Medium","gaps":["Direct vs indirect SKA1-Cdc42 link not established","Relationship to mitotic function unknown"]},{"year":2022,"claim":"Proposed an additional transcriptional repression axis in which SKA1 interacts with SAFB to suppress DUSP6 and promote metastasis.","evidence":"Co-IP and SKA1 knockdown with motility/invasion and in vivo metastasis assays","pmids":["36462498"],"confidence":"Low","gaps":["Single Co-IP without reciprocal validation","SAFB-DUSP6 mechanistic link not dissected"]},{"year":2023,"claim":"Identified an upstream post-transcriptional control, showing lncRNA MRVI1-AS1 recruits CELF2 to stabilize SKA1 mRNA under HIF-1-dependent hypoxia.","evidence":"RIP, actinomycin D mRNA stability assay, microarray, luciferase, and rescue experiments in HCC cells","pmids":["36973749"],"confidence":"Medium","gaps":["Whether elevated SKA1 acts via its mitotic or transcriptional roles in HCC unresolved","Single-lab finding"]},{"year":null,"claim":"How SKA1's distinct cellular activities—kinetochore tip-tracking, centrosome regulation, and transcriptional repression—are partitioned and regulated within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model reconciling mitotic and transcriptional functions","Structural basis of non-kinetochore interactions undefined","In vivo physiological significance of centrosome and transcriptional roles unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,2,5]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[8]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,1,13]}],"complexes":["Ska complex","kinetochore","Ndc80-Cdt1-Ska1 tip-tracking complex"],"partners":["SKA2","SKA3","NDC80","EB1","CDT1","RPB3","SAFB","DDA3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96BD8","full_name":"SKA complex subunit 1","aliases":["Spindle and kinetochore-associated protein 1"],"length_aa":255,"mass_kda":29.5,"function":"Component of the SKA complex, a microtubule plus end-binding complex of the outer kinetochore that stabilizes spindle microtubule-kinetochore attachments, promotes alignment of chromosomes at the mitotic spindle equator (chromosome congression) and assists suppression of the spindle assembly checkpoint (PubMed:17093495, PubMed:19289083, PubMed:22371557, PubMed:22483620, PubMed:23085020, PubMed:26981768, PubMed:27697923, PubMed:29487209, PubMed:31804178). Kinetochores, consisting of a centromere-associated inner segment and a microtubule-contacting outer segment, play a crucial role in chromosome segregation by mediating the physical connection between centromeric DNA and spindle microtubules (PubMed:19289083, PubMed:22483620, PubMed:23085020, PubMed:28479321, PubMed:29487209). The outer kinetochore is made up of the ten-subunit KMN network complex, comprising the MIS12, NDC80 and KNL1 complexes, and auxiliary microtubule-associated components such as the SKA complex; together they connect the outer kinetochore with the inner kinetochore, bind microtubules, and mediate interactions with mitotic checkpoint proteins that delay anaphase until chromosomes are bioriented on the spindle (PubMed:17093495, PubMed:19289083, PubMed:23085020, PubMed:28479321, PubMed:29487209). The SKA complex is loaded onto bioriented kinetochores and it facilitates chromosome congression by stabilizing microtubules together with MAPRE1, and end-on attachment of the NDC80 complex to depolymerizing spindle microtubules, thereby assisting the poleward-moving kinetochore in withstanding microtubule pulling forces (PubMed:19289083, PubMed:22371557, PubMed:22454517, PubMed:23085020, PubMed:24413531, PubMed:27697923, PubMed:28479321, PubMed:28495837, PubMed:29487209). The complex associates with dynamic microtubule plus-ends and can track both depolymerizing and elongating microtubules (PubMed:23085020, PubMed:29153323). The complex recruits protein phosphatase 1 (PP1) to the kinetochore in prometaphase and metaphase, to oppose spindle assembly checkpoint signaling and promote the onset of anaphase (PubMed:26981768). In the complex, it mediates interactions with microtubules (PubMed:19289083, PubMed:22483620, PubMed:23085020, PubMed:24413531, PubMed:27667719, PubMed:29153323, PubMed:36592928). It also stimulates AURKB/Aurora B catalytic activity (PubMed:27697923). During meiosis the SKA complex stabilizes the meiotic spindle and is required for its migration to the cortex (By similarity)","subcellular_location":"Cytoplasm, cytoskeleton, spindle; Chromosome, centromere, kinetochore; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/Q96BD8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SKA1","classification":"Common Essential","n_dependent_lines":719,"n_total_lines":1208,"dependency_fraction":0.5951986754966887},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SKA1","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":"616674","title":"SPINDLE- AND KINETOCHORE-ASSOCIATED COMPLEX, SUBUNIT 2; SKA2","url":"https://www.omim.org/entry/616674"},{"mim_id":"616673","title":"SPINDLE- AND KINETOCHORE-ASSOCIATED COMPLEX, SUBUNIT 1; SKA1","url":"https://www.omim.org/entry/616673"},{"mim_id":"609753","title":"CELIAC DISEASE, SUSCEPTIBILITY TO, 4; CELIAC4","url":"https://www.omim.org/entry/609753"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Microtubules","reliability":"Supported"},{"location":"Primary cilium","reliability":"Supported"},{"location":"Cytokinetic bridge","reliability":"Additional"},{"location":"Centriolar satellite","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"bone marrow","ntpm":11.2},{"tissue":"lymphoid tissue","ntpm":4.5}],"url":"https://www.proteinatlas.org/search/SKA1"},"hgnc":{"alias_symbol":["MGC10200"],"prev_symbol":["C18orf24"]},"alphafold":{"accession":"Q96BD8","domains":[{"cath_id":"-","chopping":"4-82","consensus_level":"medium","plddt":95.8795,"start":4,"end":82},{"cath_id":"1.10.10.1890","chopping":"141-253","consensus_level":"high","plddt":92.7624,"start":141,"end":253}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96BD8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96BD8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96BD8-F1-predicted_aligned_error_v6.png","plddt_mean":85.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SKA1","jax_strain_url":"https://www.jax.org/strain/search?query=SKA1"},"sequence":{"accession":"Q96BD8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96BD8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96BD8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96BD8"}},"corpus_meta":[{"pmid":"19289083","id":"PMC_19289083","title":"The human kinetochore Ska1 complex facilitates microtubule depolymerization-coupled motility.","date":"2009","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/19289083","citation_count":214,"is_preprint":false},{"pmid":"17093495","id":"PMC_17093495","title":"Timely anaphase onset requires a novel spindle and kinetochore complex comprising Ska1 and Ska2.","date":"2006","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/17093495","citation_count":207,"is_preprint":false},{"pmid":"23085020","id":"PMC_23085020","title":"The kinetochore-bound Ska1 complex tracks depolymerizing microtubules and binds to curved protofilaments.","date":"2012","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/23085020","citation_count":170,"is_preprint":false},{"pmid":"34288822","id":"PMC_34288822","title":"Circular RNA FAT atypical cadherin 1 (circFAT1)/microRNA-525-5p/spindle and kinetochore-associated complex subunit 1 (SKA1) axis regulates oxaliplatin 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Reconstituted Ska1 complex possesses two separable biochemical activities: direct microtubule binding through the Ska1 subunit, and microtubule-stimulated oligomerization imparted by the Rama1 subunit. The full complex forms assemblies on microtubules that facilitate processive movement of microspheres along depolymerizing microtubules.\",\n      \"method\": \"Biochemical reconstitution, microtubule co-sedimentation assay, bead motility assay on depolymerizing microtubules, siRNA depletion with chromosome segregation readout\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of purified complex with functional motility assay, subunit-specific activity mapping, replicated by multiple subsequent studies\",\n      \"pmids\": [\"19289083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ska1 and Ska2 form a complex; Ska1 is required for Ska2 stability in vivo. Ska1 associates with kinetochores following microtubule attachment during prometaphase. Depletion of either subunit causes loss of both from kinetochores, increased cold-sensitivity of kinetochore fibres, and a prolonged checkpoint-dependent metaphase-like arrest with Mad2 retention at kinetochores.\",\n      \"method\": \"siRNA depletion, live-cell imaging, immunofluorescence, cold-stability assay of kinetochore fibres\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction, functional KD phenotype with defined checkpoint readout, replicated by later studies\",\n      \"pmids\": [\"17093495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Ska1 complex tracks with depolymerizing microtubule ends and binds both the straight microtubule lattice and curved protofilaments, whereas the Ndc80 complex binds only straight lattice and lacks tracking activity. The Ska1 complex imparts its tracking capability to the Ndc80 complex. A crystal structure of the Ska1 microtubule-binding domain (MTBD) was determined, revealing its interaction with microtubules and its regulation by Aurora B phosphorylation.\",\n      \"method\": \"Single-molecule TIRF tracking assay, cryo-EM, X-ray crystallography of Ska1 MTBD, Aurora B phosphorylation of MTBD with microtubule binding assay\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure of MTBD plus single-molecule tracking plus Aurora B regulation, multiple orthogonal methods in one study\",\n      \"pmids\": [\"23085020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ska3 modulates the microtubule-binding capability of the Ska complex by (i) directly interacting with tubulin monomers and (ii) allosterically interacting with tubulin-contacting regions of Ska1. Perturbing either Ska3-microtubule or Ska3-Ska1 interactions reduces microtubule binding in vitro and delays anaphase onset in cells.\",\n      \"method\": \"In vitro microtubule binding assay with purified mutant complexes, co-IP of Ska3–Ska1 interaction, time-lapse imaging of anaphase onset\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis plus cellular phenotype readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27667719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"EB1 interacts directly with Ska1 and facilitates Ska1 localization on microtubules in vertebrate cells. EB1 depletion reduces Ska1 recruitment onto microtubules and causes chromosome alignment defects. Together EB1 and Ska1 form extended structures on the microtubule lattice as revealed by structural studies.\",\n      \"method\": \"Co-IP (EB1–Ska1), EB1 siRNA depletion with Ska1 localization readout, in vitro microtubule co-sedimentation, structural EM of EB1–Ska complexes on microtubules, computational modelling\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — reciprocal interaction, structural evidence, functional KD with localization readout, multiple orthogonal methods single lab\",\n      \"pmids\": [\"27225956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The Ska1 MTBD autonomously tracks growing microtubule ends in vitro in addition to depolymerizing ends. Multiple distinct surfaces of the Ska1 MTBD interact with diverse tubulin substrates: it binds the microtubule lattice, dolastatin-induced protofilament-like structures, and soluble tubulin heterodimers, and can promote assembly of oligomeric ring-like tubulin structures. Mutations on distinct MTBD surfaces that disrupt soluble tubulin binding without preventing lattice binding compromise microtubule tracking and cause defective chromosome alignment and mitotic progression in cells.\",\n      \"method\": \"Single-molecule TIRF assay for tip tracking, in vitro microtubule binding with purified mutant Ska1, CRISPR/Cas9 replacement assay in cells with chromosome alignment readout\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with structure-guided mutagenesis plus CRISPR replacement in cells, multiple orthogonal methods\",\n      \"pmids\": [\"29153323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SKA1 localizes to centrosomes in addition to spindle microtubules and the outer kinetochore. Depletion of Ska1 causes failure of centrosome duplication, while Ska1 over-expression leads to centrosome amplification via induction of centriole over-duplication in human prostate epithelial cells, which is sufficient to convert cells to a tumourigenic state.\",\n      \"method\": \"siRNA depletion with centrosome duplication readout, Ska1 over-expression with centriole counting, immunofluorescence, transgenic mouse model, xenograft tumourigenicity assay\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by immunofluorescence tied to functional consequence, loss- and gain-of-function with centrosome phenotype, single lab\",\n      \"pmids\": [\"24827423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ska1 and DDA3 act as molecular linkers between spindle dynamics and kinetochore composition. DDA3 recruits Kif2a onto the mitotic spindle, and Ska1 subsequently targets Kif2a to the minus-end of spindle microtubules to facilitate spindle dynamics. DDA3 also targets Ska1 to kinetochores to stabilize end-on attachment.\",\n      \"method\": \"Co-IP (Ska1–DDA3–Kif2a), siRNA depletion, immunofluorescence localization of Kif2a on spindle minus-ends\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Weak — co-IP and localization data, single lab, limited in vitro validation\",\n      \"pmids\": [\"26797278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SKA1 interacts with the DNA-directed RNA polymerase II subunit RPB3. In MTX-sensitive cells, RPB3 binds the FPGS gene promoter and drives FPGS transcription upon MTX treatment; this is blocked in SKA1-overexpressing cells through formation of an inhibitory SKA1–RPB3 complex, causing downregulation of FPGS and de novo MTX resistance. ChIP confirmed RPB3 binding to the FPGS promoter.\",\n      \"method\": \"Co-IP (SKA1–RPB3), ChIP of RPB3 on FPGS promoter, siRNA knockdown of SKA1 to restore MTX sensitivity, Western blot for FPGS\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus ChIP plus functional rescue, single lab\",\n      \"pmids\": [\"30851225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PPARγ directly binds to a predicted response element in the SKA1 gene promoter and transcriptionally upregulates SKA1 expression. Under diabetogenic conditions (high glucose, palmitic acid, insulin), PPARγ-driven SKA1 expression promotes centrosome amplification; knockdown of PPARγ blocks the treatment-induced increase in SKA1, while knockdown of SKA1 does not affect PPARγ levels.\",\n      \"method\": \"ChIP (PPARγ binding to SKA1 promoter), PPARγ inhibitor/siRNA with SKA1 mRNA and protein readout, centrosome amplification assay\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus pharmacological and siRNA epistasis, single lab, multiple methods\",\n      \"pmids\": [\"30989671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SKA1 enhances pancreatic cancer cell migration by activating Cdc42 to remodel the actin cytoskeleton. iTRAQ proteomics identified downstream proteins of SKA1, and Cdc42 inhibition (ZCL278) or actin perturbation (cytochalasin B) reversed SKA1-induced morphology and migration changes.\",\n      \"method\": \"iTRAQ quantitative proteomics, Cdc42 inhibitor (ZCL278), cytochalasin B treatment, immunoblotting and immunofluorescence, in vivo xenograft\",\n      \"journal\": \"Cell proliferation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — mass spectrometry-based target identification plus pharmacological validation, single lab\",\n      \"pmids\": [\"32232899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Ska1 interacts with EB1 through a conserved motif in its N-terminal disordered loop region; Ska1 binds the C-terminal region of the EB1 dimer. Disruption of this interaction (deletion or mutation of the motif) abolishes Ska complex recruitment to kinetochores and induces chromosome alignment defects without affecting Ska complex assembly. NMR showed the Ska1 motif binds EB1 residues that are shared binding sites for other plus-end targeting proteins.\",\n      \"method\": \"NMR spectroscopy (Ska1 motif–EB1 interaction), atomic-force microscopy imaging, site-directed mutagenesis with kinetochore localization readout, chromosome alignment assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural data plus mutagenesis plus cellular functional readout, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"36592928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SKA1 interacts specifically with scaffold attachment factor B (SAFB), and this interaction mediates transcriptional repression of DUSP6, promoting ccRCC metastasis. SKA1 knockdown reduces cancer cell motility in vitro and in vivo.\",\n      \"method\": \"Co-IP (SKA1–SAFB), SKA1 knockdown with motility/invasion assay, in vivo metastasis model\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP without reciprocal validation, single lab, limited mechanistic follow-up on SAFB–DUSP6 link\",\n      \"pmids\": [\"36462498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cdt1 (DNA replication licensing factor) directly interacts with the Ska1 complex, and this interaction is required for recruiting Cdt1 to kinetochores and spindle microtubules. Cdk1 phosphorylation of Cdt1 is critical for Ska1 binding, kinetochore-microtubule attachments, and mitotic progression. Cdt1 synergizes with Ndc80 and Ska1 to form a diffusive, tripartite Ndc80–Cdt1–Ska1 complex that processively tracks dynamic microtubule plus-ends in vitro.\",\n      \"method\": \"Auxin-inducible degron for conditional Cdt1 depletion, co-IP (Cdt1–Ska1), in vitro microtubule binding with reconstituted tripartite complex, single-molecule tip-tracking assay, Cdk1 phosphorylation assay with phospho-mimetic/dead mutants\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of tripartite complex with single-molecule tracking, kinase phosphorylation with mutagenesis, conditional degron system, multiple orthogonal methods\",\n      \"pmids\": [\"37265445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"lncRNA MRVI1-AS1 recruits RNA-binding protein CELF2 to bind and stabilize SKA1 mRNA, increasing SKA1 protein expression in HCC cells. RIP assay confirmed direct interactions between CELF2 and both MRVI1-AS1 and SKA1 mRNA. MRVI1-AS1 expression is induced by hypoxia through a HIF-1-dependent pathway.\",\n      \"method\": \"RNA immunoprecipitation (RIP), actinomycin D mRNA stability assay, microarray mRNA expression analysis, dual luciferase assay, rescue experiments\",\n      \"journal\": \"World journal of surgical oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — RIP assay confirms CELF2–SKA1 mRNA interaction, mRNA stability assay, rescue experiments, single lab\",\n      \"pmids\": [\"36973749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Oligomeric assemblies of Ska and Ndc80 complexes stabilize microtubule ends against shortening by strengthening lateral contacts between tubulin protofilaments at microtubule plus-ends, as visualized by cryoET. A point mutation in the Ska1 MTBD that does not affect individual Ska1–microtubule binding but abolishes Ska–Ska interactions disrupts stable kinetochore–microtubule attachments both in vitro and in vivo, demonstrating that cooperative Ska oligomerization with Ndc80 is required for stable attachments.\",\n      \"method\": \"Cryo-electron tomography (cryoET), site-directed mutagenesis of Ska1 MTBD, in vitro microtubule attachment assay, cellular assay of kinetochore-microtubule attachments\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — cryoET structural data plus structure-guided mutagenesis plus in vitro and in vivo functional validation, novel mechanistic finding not covered by peer-reviewed work\",\n      \"pmids\": [\"bio_10.1101_2025.07.06.663352\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SKA1 is the microtubule-binding subunit of the trimeric Ska1 complex (with Ska2 and Ska3) at the outer kinetochore; its microtubule-binding domain (MTBD) engages both straight and curved tubulin protofilaments, autonomously tracks growing and shrinking microtubule plus-ends, and—in cooperative oligomeric assemblies with the Ndc80 complex and aided by Cdt1 (phosphorylated by Cdk1) and EB1—stabilizes lateral protofilament contacts at microtubule plus-ends to sustain load-bearing kinetochore-microtubule attachments and silence the spindle checkpoint, while Aurora B phosphorylation of the MTBD down-regulates these interactions; outside its kinetochore role, SKA1 also localizes to centrosomes where its overexpression drives centriole over-duplication and centrosome amplification, and in non-mitotic contexts it can interact with RNA Pol II subunit RPB3 to repress FPGS transcription and with SAFB to suppress DUSP6 transcription.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SKA1 is the microtubule-binding subunit of the trimeric Ska complex (with Ska2 and Ska3) that localizes to the outer kinetochore and spindle microtubules and stabilizes load-bearing kinetochore-microtubule attachments during mitosis [#0, #1]. Within the reconstituted complex, SKA1 provides direct microtubule binding while Ska3 modulates this activity both by contacting tubulin directly and by allosterically engaging the tubulin-contacting regions of SKA1 [#0, #3]. The SKA1 microtubule-binding domain (MTBD) engages both the straight lattice and curved protofilaments and autonomously tracks growing and shrinking microtubule plus-ends, conferring tip-tracking capacity onto the Ndc80 complex, which alone binds only straight lattice [#2, #5]. Distinct MTBD surfaces recognize soluble tubulin heterodimers, protofilament-like structures, and the lattice, and mutations that selectively disrupt soluble-tubulin binding compromise tracking and chromosome alignment [#5]. SKA1 is recruited to microtubules and kinetochores through a conserved N-terminal motif that binds the C-terminal region of the EB1 dimer at sites shared by other plus-end-targeting proteins, and through the replication licensing factor Cdt1, whose Cdk1 phosphorylation drives formation of a processive tripartite Ndc80-Cdt1-Ska1 tip-tracking complex [#4, #11, #13]. Cooperative oligomerization of Ska with Ndc80 strengthens lateral protofilament contacts at plus-ends to sustain stable attachments [#15], whereas Aurora B phosphorylation of the MTBD down-regulates microtubule binding [#2]. Loss of SKA1 destabilizes kinetochore fibres and triggers a Mad2-dependent checkpoint arrest [#1]. Beyond mitosis, SKA1 localizes to centrosomes, where its overexpression drives centriole over-duplication and centrosome amplification [#6], and it acts in cancer contexts through transcriptional interactions: it binds RNA Pol II subunit RPB3 to repress FPGS and confer methotrexate resistance [#8] and activates Cdc42-driven actin remodeling to promote cell migration [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established SKA1 as a kinetochore-associated factor required for stable attachments by showing it forms a complex with Ska2 and is needed for cold-stable kinetochore fibres and checkpoint silencing.\",\n      \"evidence\": \"siRNA depletion, live-cell imaging, and cold-stability assays of kinetochore fibres in human cells\",\n      \"pmids\": [\"17093495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the biochemical basis of microtubule binding\", \"Mechanism of post-attachment kinetochore recruitment unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the Ska complex as a three-subunit machine and mapped its separable activities, showing SKA1 carries direct microtubule binding while Ska3 imparts microtubule-stimulated oligomerization enabling movement along depolymerizing ends.\",\n      \"evidence\": \"Biochemical reconstitution, co-sedimentation, and bead motility assays on depolymerizing microtubules\",\n      \"pmids\": [\"19289083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the SKA1-microtubule interface not defined\", \"How tracking integrates with Ndc80 at kinetochores unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Provided the structural and mechanistic basis for SKA1 microtubule binding and its regulation, showing the MTBD binds straight and curved tubulin, tracks depolymerizing ends, confers tracking onto Ndc80, and is regulated by Aurora B.\",\n      \"evidence\": \"Single-molecule TIRF, cryo-EM, X-ray crystallography of the MTBD, and Aurora B phosphorylation binding assays\",\n      \"pmids\": [\"23085020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo consequences of Aurora B sites not fully dissected\", \"Recruitment pathway to kinetochores not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved how SKA1 is delivered to microtubules and how Ska3 fine-tunes binding, identifying EB1 as a direct partner facilitating SKA1 lattice localization and showing Ska3 acts allosterically on SKA1 tubulin contacts.\",\n      \"evidence\": \"Co-IP, EB1 siRNA with SKA1 localization readout, structural EM, and in vitro binding with mutant complexes\",\n      \"pmids\": [\"27225956\", \"27667719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise EB1-binding motif on SKA1 not yet mapped at this stage\", \"Quantitative contribution of Ska3 vs EB1 to recruitment unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that the SKA1 MTBD autonomously tracks both growing and shrinking ends through multiple tubulin-engaging surfaces, with soluble-tubulin binding being essential for tracking and chromosome alignment.\",\n      \"evidence\": \"Single-molecule TIRF tip-tracking and CRISPR/Cas9 replacement with structure-guided MTBD mutants\",\n      \"pmids\": [\"29153323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How distinct surfaces are coordinated during dynamic tracking unresolved\", \"Interplay with Ndc80 oligomers not addressed here\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Pinpointed the molecular determinant of SKA1 kinetochore recruitment, identifying a conserved N-terminal motif binding the EB1 C-terminus at sites shared with other +TIPs, whose disruption abolishes kinetochore targeting.\",\n      \"evidence\": \"NMR, atomic-force microscopy, and site-directed mutagenesis with kinetochore localization and chromosome alignment readouts\",\n      \"pmids\": [\"36592928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Competition among +TIPs for the shared EB1 surface not quantified\", \"Cell-cycle timing of EB1-mediated recruitment unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified Cdt1 as a phosphorylation-gated component of the tip-tracking machinery, showing Cdk1-phosphorylated Cdt1 binds the Ska complex to form a processive Ndc80-Cdt1-Ska1 tripartite complex required for attachment and mitotic progression.\",\n      \"evidence\": \"Auxin-inducible Cdt1 degron, co-IP, reconstituted tripartite complex with single-molecule tracking, and Cdk1 phospho-mutant assays\",\n      \"pmids\": [\"37265445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and architecture of the tripartite complex at kinetochores undefined\", \"How phosphoregulation is temporally coordinated with Aurora B unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided the structural mechanism of attachment stabilization, showing cooperative Ska-Ndc80 oligomers strengthen lateral contacts between tubulin protofilaments at plus-ends, with a Ska-Ska interaction mutant that abolishes stable attachments without affecting individual binding.\",\n      \"evidence\": \"Cryo-electron tomography with structure-guided MTBD mutagenesis and in vitro and cellular attachment assays (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.07.06.663352\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Preprint not yet peer-reviewed\", \"How oligomer assembly is regulated in cells unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended SKA1 function beyond the kinetochore, showing it localizes to centrosomes and that its dysregulation perturbs centriole duplication and can drive tumourigenic transformation.\",\n      \"evidence\": \"siRNA and overexpression with centrosome/centriole counting, immunofluorescence, transgenic mouse, and xenograft assays\",\n      \"pmids\": [\"24827423\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism linking SKA1 to centriole duplication not defined\", \"Whether centrosome role depends on microtubule binding unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a non-mitotic transcriptional activity, showing SKA1 binds RNA Pol II subunit RPB3 to repress FPGS transcription and confer methotrexate resistance.\",\n      \"evidence\": \"Co-IP, ChIP of RPB3 on the FPGS promoter, and SKA1 knockdown rescue of drug sensitivity\",\n      \"pmids\": [\"30851225\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a kinetochore protein engages transcriptional machinery mechanistically unclear\", \"Single-lab finding without reciprocal structural validation\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linked SKA1 to cytoskeletal signaling in cancer, showing it activates Cdc42 to remodel actin and promote migration.\",\n      \"evidence\": \"iTRAQ proteomics, Cdc42 inhibitor and cytochalasin B treatment, and xenograft assay\",\n      \"pmids\": [\"32232899\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect SKA1-Cdc42 link not established\", \"Relationship to mitotic function unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Proposed an additional transcriptional repression axis in which SKA1 interacts with SAFB to suppress DUSP6 and promote metastasis.\",\n      \"evidence\": \"Co-IP and SKA1 knockdown with motility/invasion and in vivo metastasis assays\",\n      \"pmids\": [\"36462498\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Co-IP without reciprocal validation\", \"SAFB-DUSP6 mechanistic link not dissected\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified an upstream post-transcriptional control, showing lncRNA MRVI1-AS1 recruits CELF2 to stabilize SKA1 mRNA under HIF-1-dependent hypoxia.\",\n      \"evidence\": \"RIP, actinomycin D mRNA stability assay, microarray, luciferase, and rescue experiments in HCC cells\",\n      \"pmids\": [\"36973749\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether elevated SKA1 acts via its mitotic or transcriptional roles in HCC unresolved\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SKA1's distinct cellular activities—kinetochore tip-tracking, centrosome regulation, and transcriptional repression—are partitioned and regulated within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model reconciling mitotic and transcriptional functions\", \"Structural basis of non-kinetochore interactions undefined\", \"In vivo physiological significance of centrosome and transcriptional roles unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 1, 13]}\n    ],\n    \"complexes\": [\"Ska complex\", \"kinetochore\", \"Ndc80-Cdt1-Ska1 tip-tracking complex\"],\n    \"partners\": [\"SKA2\", \"SKA3\", \"NDC80\", \"EB1\", \"CDT1\", \"RPB3\", \"SAFB\", \"DDA3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}