{"gene":"TTBK2","run_date":"2026-04-28T21:43:00","timeline":{"discoveries":[{"year":2007,"finding":"TTBK2 mutations (frameshift/truncating) cause spinocerebellar ataxia type 11 (SCA11), with affected brain tissue showing cerebellar degeneration and tau deposition, implicating TTBK2 in the tau phosphorylation cascade and cerebellar neuronal survival.","method":"Human genetic linkage/mutation analysis, neuropathology","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — foundational human genetics paper, replicated in multiple subsequent studies","pmids":["18037885"],"is_preprint":false},{"year":2011,"finding":"TTBK2 has an unusual substrate specificity with preference for a phosphotyrosine at the +2 position relative to the phosphorylation site; SCA11 truncating mutations promote TTBK2 protein expression, suppress kinase activity, and cause enhanced nuclear localization; homozygous SCA11 knockin mutation causes embryonic lethality at E10.","method":"In vitro kinase assay with peptide library, mutagenesis of putative phosphate-priming groove, knockin mouse model, cell fractionation/immunofluorescence","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis, validated in vivo knockin model with multiple orthogonal methods","pmids":["21548880"],"is_preprint":false},{"year":2014,"finding":"TTBK2 is recruited to the mother centriole via binding to distal appendage protein CEP164 through a proline-rich motif (not via EB1/SxIP motifs); CEP164 binding is essential for TTBK2's function in CP110 removal and ciliogenesis initiation. TTBK2 can phosphorylate CEP164 and CEP97 and inhibits the CEP164–Dishevelled-3 interaction in a kinase-activity-dependent manner.","method":"Reciprocal co-immunoprecipitation, TTBK2 binding-motif mutagenesis, siRNA depletion/rescue, in vitro kinase assay","journal":"Genes to cells","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, mutagenesis, loss-of-function rescue, replicated by subsequent studies","pmids":["25297623"],"is_preprint":false},{"year":2015,"finding":"TTBK2 acts as a microtubule plus-end tracking protein (+TIP) by binding EB1/3, and phosphorylates the MT-depolymerizing kinesin KIF2A at S135 in an EB1/3-dependent manner, inactivating its depolymerizing activity and stabilizing MT plus ends to promote cell migration.","method":"Co-immunoprecipitation, in vitro kinase assay, siRNA depletion, non-phosphorylatable KIF2A mutant expression, live-cell imaging of MT dynamics, cell migration assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with identified phosphosite, mutagenesis, functional rescue, orthogonal phenotypic readouts","pmids":["26323690"],"is_preprint":false},{"year":2018,"finding":"TTBK2 co-expressed with tau in C. elegans synergistically exacerbates behavioral abnormalities, aberrant neuronal architecture, and neuron loss compared to either alone, indicating TTBK2 kinase activity drives tau-dependent neurodegeneration. TTBK2 co-expression with TDP-43 did not exacerbate TDP-43 proteinopathy phenotypes.","method":"Transgenic C. elegans co-expression, behavioral assays, immunofluorescence for phospho-tau and phospho-TDP-43","journal":"Molecular neurodegeneration","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in C. elegans with multiple phenotypic readouts, single lab","pmids":["29409526"],"is_preprint":false},{"year":2018,"finding":"SCA11-associated truncating mutations in TTBK2 act as dominant negative alleles; the truncated protein (TTBK2SCA11) interferes with full-length TTBK2 function in ciliogenesis, reduces cilia number, and disrupts ciliary trafficking of Smoothened (SMO) and Sonic Hedgehog (SHH) signaling components.","method":"Ttbk2 allelic series in mice, quantitative cilia immunofluorescence, SMO/SHH pathway reporter assays, conditional mouse genetics","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — genetic allelic series in vivo, multiple orthogonal functional readouts","pmids":["30532139"],"is_preprint":false},{"year":2019,"finding":"TTBK2 phosphorylates CEP83 at four sites after being recruited to distal appendages by CEP164; TTBK2-dependent CEP83 phosphorylation is required for early ciliogenesis steps including ciliary vesicle docking and CP110 removal. Superresolution microscopy revealed serum starvation causes TTBK2 redistribution from the periphery toward the root of distal appendages.","method":"Superresolution microscopy (STORM/STED), in vitro kinase assay, phosphosite mapping by mass spectrometry, CEP164-dependent TTBK2 recruitment assays, CEP83 phospho-mutant functional analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with phosphosite characterization, structural imaging, functional mutagenesis, multiple orthogonal methods","pmids":["31455668"],"is_preprint":false},{"year":2020,"finding":"Conditional knockout of Ttbk2 in adult mice causes loss of primary cilia throughout the brain, motor coordination deficits, and Purkinje cell degeneration recapitulating SCA11; conditional knockout of the ciliary trafficking gene Ift88 produces nearly identical phenotypes, indicating that disruption of ciliary signaling is a key driver.","method":"Conditional knockout mouse, behavioral assays, immunofluorescence, genetic epistasis (Ttbk2 vs Ift88 conditional KO comparison)","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with conditional KO, multiple phenotypic readouts, direct comparison of Ttbk2 and Ift88 mutants","pmids":["31934864"],"is_preprint":false},{"year":2021,"finding":"Structural and biochemical analysis of the CEP164-TTBK2 complex revealed how CEP164 recruits TTBK2 to centrioles, how two ciliopathic mutations in CEP164 compromise this interaction, and how CEP164 binding coordinates with TTBK2 activities.","method":"X-ray crystallography/NMR structural analysis, biochemical binding assays, functional complementation with ciliopathy mutants","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — structural determination with biochemical and functional validation","pmids":["34499853"],"is_preprint":false},{"year":2022,"finding":"TTBK2 maintains cilium stability after assembly by regulating centriolar satellite composition, maintaining basal body pools of intraflagellar transport (IFT) proteins, and suppressing actin-based cilia disassembly; loss of TTBK2 increases cilia break frequency and reduces axonemal microtubule modifications.","method":"Tamoxifen-inducible Ttbk2 deletion in MEFs, immunofluorescence time-course, actin inhibitor rescue experiments, quantitative microscopy of IFT and satellite proteins","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — inducible KO with mechanistic dissection, multiple pathway inhibitors and markers","pmids":["36322399"],"is_preprint":false},{"year":2023,"finding":"TTBK2 inhibition by a small molecule (indolyl pyrimidinamine 10) significantly reduces primary cilia formation on human iPSCs, phenocopying TTBK2 knockout and confirming TTBK2 kinase activity is required for ciliogenesis.","method":"Chemical tool compound, iPSC cilia quantification, comparison to genetic TTBK2 KO","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic phenocopy in human iPSCs, single study","pmids":["37059819"],"is_preprint":false},{"year":2023,"finding":"SCA11-associated TTBK2 truncating mutations contain a bona fide peroxisomal targeting signal type 1 (PTS1); their expression reduces peroxisome numbers, disrupts peroxisome fission, and impairs ciliary SMO trafficking upon SHH signaling, revealing a neomorphic function of mutant TTBK2 in peroxisome biology.","method":"Immunofluorescence peroxisome quantification, peroxisome fission pathway analysis, SMO ciliary trafficking assays in RPE1 cells expressing SCA11 variants","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 3 — multiple cellular assays but single lab, preprint, novel neomorphic mechanism","pmids":["36778451"],"is_preprint":true},{"year":2024,"finding":"HUWE1 is an E3 ubiquitin ligase that targets TTBK2 for proteasomal degradation at the centrosome, driving primary cilia disassembly; TTBK2 stabilizes cilia by inhibiting their disassembly, thereby promoting granule neuron progenitor (GNP) proliferation in response to SHH during cerebellar development.","method":"Co-immunoprecipitation, ubiquitination assays, HUWE1 KD/TTBK2 KD in GNPs and medulloblastoma cells, primary cilia dynamics assays, in vivo cerebellar development analysis","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, ubiquitination assay, loss-of-function with mechanistic readout, in vivo validation","pmids":["38879724"],"is_preprint":false},{"year":2016,"finding":"TTBK2 wild-type (but not kinase-dead mutant) decreases GluK2 glutamate receptor abundance at the cell membrane via RAB5-dependent endocytosis, reducing GluK2 currents; truncated SCA11-associated TTBK2(450) lacks this activity, suggesting TTBK2 kinase activity modulates synaptic receptor trafficking.","method":"Xenopus oocyte expression, dual-electrode voltage clamp, confocal microscopy of EGFP-GluK2, dominant-negative RAB5 rescue","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — electrophysiology + imaging + genetic dissection, but single lab and heterologous expression system","pmids":["27607061"],"is_preprint":false},{"year":2025,"finding":"CEP164 forms dynamic condensates with TTBK2 through phase separation driven by multivalent electrostatic interactions via CEP164's intrinsically disordered region; this phase separation is required for efficient TTBK2 recruitment to distal appendages and cilia formation.","method":"In vitro phase separation assays, live-cell condensate imaging, electrostatic interaction mutagenesis, TTBK2 recruitment quantification at distal appendages","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro reconstitution of phase separation plus cell-based functional assays, single study","pmids":["40483689"],"is_preprint":false},{"year":2025,"finding":"CEP164 homodimerization via its central coiled-coil region is necessary for its localization to the mother centriole and subsequent TTBK2 recruitment; TTBK2 kinase activity and its interaction with CEP164 are required for recruitment of IFT-A, IFT-B, and dynein-2 complexes and removal of CP110 from the mother centriole, though CP110 removal is not always coupled with IFT protein recruitment.","method":"CEP164-KO and TTBK2-KO cell lines, reconstitution with chimeric and truncation constructs, immunofluorescence quantification of IFT machinery recruitment","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — KO cells with domain-mapping using chimeric constructs, multiple functional readouts","pmids":["40305080"],"is_preprint":false},{"year":2025,"finding":"A missense variant in the TTBK2 kinase domain (L209F), introduced by CRISPR/Cas9 knock-in, reduces TTBK2 protein levels, impairs kinase activity toward TDP-43, alters cytoskeleton-related protein levels, and dysregulates phosphoproteome pathways including cytoskeletal organization and TGF-β signaling.","method":"CRISPR/Cas9 knock-in cell model, quantitative phosphoproteomics, in-cell kinase activity assay, Western blot","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — CRISPR knock-in with phosphoproteomics and in-cell kinase activity readout in a single comprehensive study","pmids":["41422144"],"is_preprint":false},{"year":2025,"finding":"TTBK2 is expressed in mouse testis and co-localizes with α-tubulin in the manchette during spermiogenesis; TTBK2 knockdown by intratesticular injection increases sperm tail deformity, reduces sperm motility, and disorganizes axonemal microtubule structure, with downregulation of CEP164, CEP83, and IFT88 expression.","method":"Intratesticular siRNA injection, transmission electron microscopy, RT-qPCR, Western blot, immunofluorescence co-localization","journal":"Molecular human reproduction","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo loss-of-function with ultrastructural and molecular readouts, single study","pmids":["40581359"],"is_preprint":false}],"current_model":"TTBK2 is a centriolar serine-threonine kinase recruited to distal appendages of the mother centriole by CEP164 (via phase separation and direct binding), where its kinase activity drives ciliogenesis by phosphorylating CEP83 to enable ciliary vesicle docking and CP110 removal, recruiting IFT-A/B and dynein-2 complexes, and maintaining cilium stability through regulation of centriolar satellites and axonemal microtubule modifications; it also phosphorylates KIF2A (inactivating MT depolymerization to promote cell migration), tau, TDP-43, and GluK2 (modulating synaptic receptor endocytosis), and is subject to regulated degradation by the E3 ligase HUWE1; SCA11-causing truncating mutations act as dominant negatives that mislocalize from centrioles, suppress kinase activity, disrupt ciliogenesis and SHH signaling, and may acquire neomorphic peroxisomal targeting."},"narrative":{"teleology":[{"year":2007,"claim":"Identifying TTBK2 as the SCA11 disease gene established that this kinase is essential for cerebellar neuronal survival and linked it to tau pathology, but the cellular mechanism was unknown.","evidence":"Linkage analysis and mutation screening in SCA11 families with neuropathological examination of affected brain tissue","pmids":["18037885"],"confidence":"High","gaps":["Whether disease arises from loss of kinase function, dominant-negative effects, or gain-of-function was unresolved","Substrates beyond tau were not identified","No cellular mechanism connecting TTBK2 loss to neurodegeneration was proposed"]},{"year":2011,"claim":"Biochemical characterization revealed TTBK2's unusual substrate preference for phosphotyrosine-primed sites and showed that SCA11 truncations suppress kinase activity while increasing protein expression, establishing the enzymological framework for interpreting disease mutations.","evidence":"In vitro kinase assay with oriented peptide library, mutagenesis of phosphate-priming groove, SCA11 knockin mouse showing embryonic lethality","pmids":["21548880"],"confidence":"High","gaps":["Physiological substrates primed by phosphotyrosine were not identified","How SCA11 truncations cause disease at the cellular level remained unclear"]},{"year":2014,"claim":"Discovery that CEP164 recruits TTBK2 to mother centriole distal appendages via a proline-rich motif, and that this recruitment is essential for CP110 removal and ciliogenesis, reframed TTBK2 as a centriolar kinase controlling cilium initiation.","evidence":"Reciprocal co-immunoprecipitation, TTBK2 binding-motif mutagenesis, siRNA depletion/rescue, in vitro kinase assay for CEP164 and CEP97","pmids":["25297623"],"confidence":"High","gaps":["The direct centriolar substrates of TTBK2 required for ciliogenesis were not mapped","Structural basis of the CEP164–TTBK2 interaction was not determined"]},{"year":2015,"claim":"Demonstration that TTBK2 tracks microtubule plus ends via EB1/3 and phosphorylates KIF2A at S135 to inhibit MT depolymerization established a cilia-independent function in cytoskeletal regulation and cell migration.","evidence":"Co-IP, in vitro kinase assay with phosphosite identification, non-phosphorylatable mutant rescue, live-cell MT imaging, migration assays","pmids":["26323690"],"confidence":"High","gaps":["Whether the EB1-dependent function is separable from the CEP164-dependent ciliogenesis role in vivo was unclear","Upstream signals regulating TTBK2 plus-end tracking were not identified"]},{"year":2016,"claim":"Showing that TTBK2 kinase activity drives RAB5-dependent endocytosis of the GluK2 glutamate receptor extended its functional repertoire to synaptic receptor trafficking, suggesting a direct synaptic role.","evidence":"Xenopus oocyte expression with dual-electrode voltage clamp, confocal imaging, dominant-negative RAB5 rescue","pmids":["27607061"],"confidence":"Medium","gaps":["The direct phosphorylation target mediating GluK2 endocytosis was not identified","Relevance in mammalian neurons was not demonstrated","Heterologous expression system limits physiological interpretation"]},{"year":2018,"claim":"Two studies clarified the disease mechanism: TTBK2 synergizes with tau to cause neurodegeneration in C. elegans, and SCA11 truncating mutations act as dominant negatives that disrupt ciliogenesis and SHH signaling in mice, establishing ciliary dysfunction as a core disease driver.","evidence":"Transgenic C. elegans co-expression with tau; mouse allelic series with quantitative cilia IF and SHH reporter assays","pmids":["29409526","30532139"],"confidence":"High","gaps":["Relative contributions of tau toxicity versus ciliary defects to SCA11 pathogenesis were not dissected","Whether SCA11 truncation retains partial kinase activity in vivo was not resolved"]},{"year":2019,"claim":"Identification of CEP83 as a direct TTBK2 substrate at four phosphosites, required for ciliary vesicle docking and CP110 removal, provided the first detailed mechanism of how TTBK2 kinase activity initiates ciliogenesis at the distal appendage.","evidence":"STORM/STED superresolution microscopy, in vitro kinase assay with mass spectrometry phosphosite mapping, CEP83 phospho-mutant functional analysis","pmids":["31455668"],"confidence":"High","gaps":["Whether additional substrates are required alongside phospho-CEP83 was unknown","How CEP83 phosphorylation connects to CP110 removal machinery was not defined"]},{"year":2020,"claim":"Conditional Ttbk2 knockout in adult mouse brain phenocopied by Ift88 conditional knockout demonstrated that TTBK2's essential role in maintaining primary cilia—not a cilia-independent function—drives Purkinje cell degeneration and motor deficits in SCA11.","evidence":"Adult conditional knockout mice, behavioral assays, cilia quantification, genetic comparison with Ift88 CKO","pmids":["31934864"],"confidence":"High","gaps":["Whether restoring cilia can rescue established degeneration was not tested","Cell-type-specific vulnerability within the cerebellum was not fully dissected"]},{"year":2021,"claim":"Structural determination of the CEP164–TTBK2 complex revealed how ciliopathic CEP164 mutations disrupt TTBK2 recruitment, providing atomic-level understanding of the ciliogenesis-initiating interaction.","evidence":"X-ray crystallography/NMR, biochemical binding assays, functional complementation with ciliopathy mutants","pmids":["34499853"],"confidence":"High","gaps":["Structure of full-length TTBK2 was not solved","How kinase activation relates to binding was not determined"]},{"year":2022,"claim":"Post-assembly cilium maintenance was shown to require TTBK2 for regulating centriolar satellites, IFT protein pools, and suppressing actin-dependent cilia disassembly, extending TTBK2's role beyond initiation to ongoing cilium stability.","evidence":"Tamoxifen-inducible Ttbk2 deletion in MEFs, time-course immunofluorescence, actin inhibitor rescue","pmids":["36322399"],"confidence":"High","gaps":["Direct substrates mediating satellite regulation and actin suppression were not identified","Whether maintenance and assembly functions use identical phosphorylation events was unclear"]},{"year":2023,"claim":"Pharmacological inhibition of TTBK2 phenocopied genetic knockout in human iPSCs, validating kinase activity as druggable and confirming catalytic requirement for ciliogenesis in a human cellular context.","evidence":"Indolyl pyrimidinamine inhibitor treatment with iPSC cilia quantification, comparison to TTBK2 KO","pmids":["37059819"],"confidence":"Medium","gaps":["Inhibitor selectivity among related kinases was not fully profiled","In vivo pharmacological validation was not performed"]},{"year":2024,"claim":"Identification of HUWE1 as the E3 ligase targeting TTBK2 for proteasomal degradation at the centrosome established how TTBK2 protein levels are regulated to control cilia disassembly, linking TTBK2 turnover to SHH-dependent cerebellar development.","evidence":"Co-IP, ubiquitination assays, HUWE1/TTBK2 knockdown in GNPs and medulloblastoma cells, in vivo cerebellar development analysis","pmids":["38879724"],"confidence":"High","gaps":["Signals triggering HUWE1-mediated TTBK2 degradation were not defined","Whether HUWE1 regulation of TTBK2 is relevant outside of cerebellar development was not tested"]},{"year":2025,"claim":"Three 2025 studies refined the recruitment mechanism and expanded functional scope: CEP164 forms phase-separated condensates with TTBK2 required for efficient recruitment; TTBK2 kinase activity recruits IFT-A/B and dynein-2 complexes independently of CP110 removal; a kinase-domain missense variant dysregulates cytoskeletal and TGF-β phosphoproteome pathways; and TTBK2 is required for sperm axoneme integrity during spermiogenesis.","evidence":"In vitro phase separation reconstitution plus live-cell imaging; KO/chimeric reconstitution with IFT quantification; CRISPR knock-in phosphoproteomics; intratesticular siRNA with TEM ultrastructure","pmids":["40483689","40305080","41422144","40581359"],"confidence":"High","gaps":["Whether phase separation is regulated by upstream signals is unknown","The full complement of TTBK2 substrates at distal appendages remains unmapped","Whether the TGF-β phosphoproteome changes are direct or indirect is unclear"]},{"year":null,"claim":"A comprehensive substrate map for TTBK2 at the centriole, the structural basis for its activation upon CEP164 binding, and the relative contributions of ciliary versus non-ciliary (tau, cytoskeletal) functions to SCA11 pathogenesis remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Full-length TTBK2 structure and activation mechanism not determined","Systematic identification of all centriolar substrates not completed","Whether tau phosphorylation contributes to SCA11 independently of ciliary defects is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2,3,6,10,16]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,3,6,16]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[2,6,8,12,14,15]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,17]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[5,7,9]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[2,6,7,9,10,15]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,7,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[12]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,4,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,5,7]}],"complexes":[],"partners":["CEP164","CEP83","KIF2A","EB1","EB3","HUWE1","CP110","CEP97"],"other_free_text":[]},"mechanistic_narrative":"TTBK2 is a serine-threonine kinase that functions as a master regulator of primary cilium assembly, maintenance, and ciliary signaling, with additional roles in microtubule dynamics, synaptic receptor trafficking, and tau phosphorylation. It is recruited to the distal appendages of the mother centriole by CEP164—via direct binding and phase-separation-driven condensation—where it phosphorylates CEP83 to enable ciliary vesicle docking, triggers CP110 removal, and recruits IFT-A, IFT-B, and dynein-2 complexes required for ciliogenesis; after assembly, it maintains cilium stability by regulating centriolar satellites, IFT protein pools, and axonemal microtubule modifications, with its steady-state levels controlled by HUWE1-mediated proteasomal degradation [PMID:25297623, PMID:31455668, PMID:36322399, PMID:40305080, PMID:38879724, PMID:40483689]. Beyond cilia, TTBK2 tracks microtubule plus ends via EB1/3 and phosphorylates KIF2A to inhibit microtubule depolymerization, promoting cell migration, and it modulates GluK2 glutamate receptor surface abundance through RAB5-dependent endocytosis [PMID:26323690, PMID:27607061]. Truncating mutations in TTBK2 cause spinocerebellar ataxia type 11 (SCA11) by acting as dominant negatives that suppress kinase activity, impair ciliogenesis, and disrupt Sonic Hedgehog signaling, with conditional loss of TTBK2 in adult mice recapitulating cerebellar Purkinje cell degeneration [PMID:18037885, PMID:30532139, PMID:31934864]."},"prefetch_data":{"uniprot":{"accession":"Q6IQ55","full_name":"Tau-tubulin kinase 2","aliases":[],"length_aa":1244,"mass_kda":137.4,"function":"Serine/threonine kinase that acts as a key regulator of ciliogenesis: controls the initiation of ciliogenesis by binding to the distal end of the basal body and promoting the removal of CCP110, which caps the mother centriole, leading to the recruitment of IFT proteins, which build the ciliary axoneme. Has some substrate preference for proteins that are already phosphorylated on a Tyr residue at the +2 position relative to the phosphorylation site. Able to phosphorylate tau on serines in vitro (PubMed:23141541). Phosphorylates MPHOSPH9 which promotes its ubiquitination and proteasomal degradation, loss of MPHOSPH9 facilitates the removal of the CP110-CEP97 complex (a negative regulator of ciliogenesis) from the mother centrioles, promoting the initiation of ciliogenesis (PubMed:30375385). Required for recruitment of CPLANE2 and INTU to the mother centriole (By similarity)","subcellular_location":"Cell projection, cilium; Cytoplasm, cytoskeleton, cilium basal body; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome, centriole; Cytoplasm, cytosol; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q6IQ55/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TTBK2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TTBK2","total_profiled":1310},"omim":[{"mim_id":"620487","title":"CILIOGENESIS AND PLANAR POLARITY EFFECTOR COMPLEX, SUBUNIT 2; CPLANE2","url":"https://www.omim.org/entry/620487"},{"mim_id":"619415","title":"TAU TUBULIN KINASE 1; TTBK1","url":"https://www.omim.org/entry/619415"},{"mim_id":"615944","title":"C2 CALCIUM-DEPENDENT DOMAIN-CONTAINING PROTEIN 3; C2CD3","url":"https://www.omim.org/entry/615944"},{"mim_id":"614848","title":"CENTROSOMAL PROTEIN, 164-KD; CEP164","url":"https://www.omim.org/entry/614848"},{"mim_id":"611695","title":"TAU TUBULIN KINASE 2; TTBK2","url":"https://www.omim.org/entry/611695"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Microtubules","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Primary cilium transition zone","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"testis","ntpm":28.3}],"url":"https://www.proteinatlas.org/search/TTBK2"},"hgnc":{"alias_symbol":["KIAA0847"],"prev_symbol":["SCA11"]},"alphafold":{"accession":"Q6IQ55","domains":[{"cath_id":"3.30.200.20","chopping":"47-97","consensus_level":"medium","plddt":96.0006,"start":47,"end":97},{"cath_id":"1.10.510.10","chopping":"100-305","consensus_level":"high","plddt":96.0733,"start":100,"end":305}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6IQ55","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6IQ55-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6IQ55-F1-predicted_aligned_error_v6.png","plddt_mean":48.84},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TTBK2","jax_strain_url":"https://www.jax.org/strain/search?query=TTBK2"},"sequence":{"accession":"Q6IQ55","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6IQ55.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6IQ55/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6IQ55"}},"corpus_meta":[{"pmid":"28219405","id":"PMC_28219405","title":"TTBK2 circular RNA promotes glioma malignancy by regulating miR-217/HNF1β/Derlin-1 pathway.","date":"2017","source":"Journal of hematology & oncology","url":"https://pubmed.ncbi.nlm.nih.gov/28219405","citation_count":189,"is_preprint":false},{"pmid":"18037885","id":"PMC_18037885","title":"Mutations in TTBK2, encoding a kinase implicated in tau phosphorylation, segregate with spinocerebellar ataxia type 11.","date":"2007","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/18037885","citation_count":142,"is_preprint":false},{"pmid":"32196629","id":"PMC_32196629","title":"Circular RNA TTBK2 regulates cell proliferation, invasion and ferroptosis via miR-761/ITGB8 axis in glioma.","date":"2020","source":"European review for medical and pharmacological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/32196629","citation_count":87,"is_preprint":false},{"pmid":"29409526","id":"PMC_29409526","title":"Pathological phosphorylation of tau and TDP-43 by TTBK1 and TTBK2 drives neurodegeneration.","date":"2018","source":"Molecular neurodegeneration","url":"https://pubmed.ncbi.nlm.nih.gov/29409526","citation_count":77,"is_preprint":false},{"pmid":"31455668","id":"PMC_31455668","title":"Phosphorylation of CEP83 by TTBK2 is necessary for cilia initiation.","date":"2019","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/31455668","citation_count":67,"is_preprint":false},{"pmid":"31934864","id":"PMC_31934864","title":"TTBK2 and primary cilia are essential for the connectivity and survival of cerebellar Purkinje neurons.","date":"2020","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/31934864","citation_count":64,"is_preprint":false},{"pmid":"25297623","id":"PMC_25297623","title":"Binding to Cep164, but not EB1, is essential for centriolar localization of TTBK2 and its function in ciliogenesis.","date":"2014","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/25297623","citation_count":55,"is_preprint":false},{"pmid":"22020623","id":"PMC_22020623","title":"PRKX, TTBK2 and RSK4 expression causes Sunitinib resistance in kidney carcinoma- and melanoma-cell lines.","date":"2012","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/22020623","citation_count":52,"is_preprint":false},{"pmid":"26323690","id":"PMC_26323690","title":"TTBK2 with EB1/3 regulates microtubule dynamics in migrating cells through KIF2A phosphorylation.","date":"2015","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/26323690","citation_count":47,"is_preprint":false},{"pmid":"30532139","id":"PMC_30532139","title":"Spinocerebellar ataxia type 11-associated alleles of Ttbk2 dominantly interfere with ciliogenesis and cilium stability.","date":"2018","source":"PLoS 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pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"TTBK2 mutations (frameshift/truncating) cause spinocerebellar ataxia type 11 (SCA11), with affected brain tissue showing cerebellar degeneration and tau deposition, implicating TTBK2 in the tau phosphorylation cascade and cerebellar neuronal survival.\",\n      \"method\": \"Human genetic linkage/mutation analysis, neuropathology\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — foundational human genetics paper, replicated in multiple subsequent studies\",\n      \"pmids\": [\"18037885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TTBK2 has an unusual substrate specificity with preference for a phosphotyrosine at the +2 position relative to the phosphorylation site; SCA11 truncating mutations promote TTBK2 protein expression, suppress kinase activity, and cause enhanced nuclear localization; homozygous SCA11 knockin mutation causes embryonic lethality at E10.\",\n      \"method\": \"In vitro kinase assay with peptide library, mutagenesis of putative phosphate-priming groove, knockin mouse model, cell fractionation/immunofluorescence\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis, validated in vivo knockin model with multiple orthogonal methods\",\n      \"pmids\": [\"21548880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TTBK2 is recruited to the mother centriole via binding to distal appendage protein CEP164 through a proline-rich motif (not via EB1/SxIP motifs); CEP164 binding is essential for TTBK2's function in CP110 removal and ciliogenesis initiation. TTBK2 can phosphorylate CEP164 and CEP97 and inhibits the CEP164–Dishevelled-3 interaction in a kinase-activity-dependent manner.\",\n      \"method\": \"Reciprocal co-immunoprecipitation, TTBK2 binding-motif mutagenesis, siRNA depletion/rescue, in vitro kinase assay\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, mutagenesis, loss-of-function rescue, replicated by subsequent studies\",\n      \"pmids\": [\"25297623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TTBK2 acts as a microtubule plus-end tracking protein (+TIP) by binding EB1/3, and phosphorylates the MT-depolymerizing kinesin KIF2A at S135 in an EB1/3-dependent manner, inactivating its depolymerizing activity and stabilizing MT plus ends to promote cell migration.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, siRNA depletion, non-phosphorylatable KIF2A mutant expression, live-cell imaging of MT dynamics, cell migration assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with identified phosphosite, mutagenesis, functional rescue, orthogonal phenotypic readouts\",\n      \"pmids\": [\"26323690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TTBK2 co-expressed with tau in C. elegans synergistically exacerbates behavioral abnormalities, aberrant neuronal architecture, and neuron loss compared to either alone, indicating TTBK2 kinase activity drives tau-dependent neurodegeneration. TTBK2 co-expression with TDP-43 did not exacerbate TDP-43 proteinopathy phenotypes.\",\n      \"method\": \"Transgenic C. elegans co-expression, behavioral assays, immunofluorescence for phospho-tau and phospho-TDP-43\",\n      \"journal\": \"Molecular neurodegeneration\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in C. elegans with multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"29409526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SCA11-associated truncating mutations in TTBK2 act as dominant negative alleles; the truncated protein (TTBK2SCA11) interferes with full-length TTBK2 function in ciliogenesis, reduces cilia number, and disrupts ciliary trafficking of Smoothened (SMO) and Sonic Hedgehog (SHH) signaling components.\",\n      \"method\": \"Ttbk2 allelic series in mice, quantitative cilia immunofluorescence, SMO/SHH pathway reporter assays, conditional mouse genetics\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic allelic series in vivo, multiple orthogonal functional readouts\",\n      \"pmids\": [\"30532139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TTBK2 phosphorylates CEP83 at four sites after being recruited to distal appendages by CEP164; TTBK2-dependent CEP83 phosphorylation is required for early ciliogenesis steps including ciliary vesicle docking and CP110 removal. Superresolution microscopy revealed serum starvation causes TTBK2 redistribution from the periphery toward the root of distal appendages.\",\n      \"method\": \"Superresolution microscopy (STORM/STED), in vitro kinase assay, phosphosite mapping by mass spectrometry, CEP164-dependent TTBK2 recruitment assays, CEP83 phospho-mutant functional analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with phosphosite characterization, structural imaging, functional mutagenesis, multiple orthogonal methods\",\n      \"pmids\": [\"31455668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Conditional knockout of Ttbk2 in adult mice causes loss of primary cilia throughout the brain, motor coordination deficits, and Purkinje cell degeneration recapitulating SCA11; conditional knockout of the ciliary trafficking gene Ift88 produces nearly identical phenotypes, indicating that disruption of ciliary signaling is a key driver.\",\n      \"method\": \"Conditional knockout mouse, behavioral assays, immunofluorescence, genetic epistasis (Ttbk2 vs Ift88 conditional KO comparison)\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with conditional KO, multiple phenotypic readouts, direct comparison of Ttbk2 and Ift88 mutants\",\n      \"pmids\": [\"31934864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Structural and biochemical analysis of the CEP164-TTBK2 complex revealed how CEP164 recruits TTBK2 to centrioles, how two ciliopathic mutations in CEP164 compromise this interaction, and how CEP164 binding coordinates with TTBK2 activities.\",\n      \"method\": \"X-ray crystallography/NMR structural analysis, biochemical binding assays, functional complementation with ciliopathy mutants\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural determination with biochemical and functional validation\",\n      \"pmids\": [\"34499853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TTBK2 maintains cilium stability after assembly by regulating centriolar satellite composition, maintaining basal body pools of intraflagellar transport (IFT) proteins, and suppressing actin-based cilia disassembly; loss of TTBK2 increases cilia break frequency and reduces axonemal microtubule modifications.\",\n      \"method\": \"Tamoxifen-inducible Ttbk2 deletion in MEFs, immunofluorescence time-course, actin inhibitor rescue experiments, quantitative microscopy of IFT and satellite proteins\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — inducible KO with mechanistic dissection, multiple pathway inhibitors and markers\",\n      \"pmids\": [\"36322399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TTBK2 inhibition by a small molecule (indolyl pyrimidinamine 10) significantly reduces primary cilia formation on human iPSCs, phenocopying TTBK2 knockout and confirming TTBK2 kinase activity is required for ciliogenesis.\",\n      \"method\": \"Chemical tool compound, iPSC cilia quantification, comparison to genetic TTBK2 KO\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic phenocopy in human iPSCs, single study\",\n      \"pmids\": [\"37059819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SCA11-associated TTBK2 truncating mutations contain a bona fide peroxisomal targeting signal type 1 (PTS1); their expression reduces peroxisome numbers, disrupts peroxisome fission, and impairs ciliary SMO trafficking upon SHH signaling, revealing a neomorphic function of mutant TTBK2 in peroxisome biology.\",\n      \"method\": \"Immunofluorescence peroxisome quantification, peroxisome fission pathway analysis, SMO ciliary trafficking assays in RPE1 cells expressing SCA11 variants\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — multiple cellular assays but single lab, preprint, novel neomorphic mechanism\",\n      \"pmids\": [\"36778451\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HUWE1 is an E3 ubiquitin ligase that targets TTBK2 for proteasomal degradation at the centrosome, driving primary cilia disassembly; TTBK2 stabilizes cilia by inhibiting their disassembly, thereby promoting granule neuron progenitor (GNP) proliferation in response to SHH during cerebellar development.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays, HUWE1 KD/TTBK2 KD in GNPs and medulloblastoma cells, primary cilia dynamics assays, in vivo cerebellar development analysis\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, ubiquitination assay, loss-of-function with mechanistic readout, in vivo validation\",\n      \"pmids\": [\"38879724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TTBK2 wild-type (but not kinase-dead mutant) decreases GluK2 glutamate receptor abundance at the cell membrane via RAB5-dependent endocytosis, reducing GluK2 currents; truncated SCA11-associated TTBK2(450) lacks this activity, suggesting TTBK2 kinase activity modulates synaptic receptor trafficking.\",\n      \"method\": \"Xenopus oocyte expression, dual-electrode voltage clamp, confocal microscopy of EGFP-GluK2, dominant-negative RAB5 rescue\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — electrophysiology + imaging + genetic dissection, but single lab and heterologous expression system\",\n      \"pmids\": [\"27607061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CEP164 forms dynamic condensates with TTBK2 through phase separation driven by multivalent electrostatic interactions via CEP164's intrinsically disordered region; this phase separation is required for efficient TTBK2 recruitment to distal appendages and cilia formation.\",\n      \"method\": \"In vitro phase separation assays, live-cell condensate imaging, electrostatic interaction mutagenesis, TTBK2 recruitment quantification at distal appendages\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro reconstitution of phase separation plus cell-based functional assays, single study\",\n      \"pmids\": [\"40483689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CEP164 homodimerization via its central coiled-coil region is necessary for its localization to the mother centriole and subsequent TTBK2 recruitment; TTBK2 kinase activity and its interaction with CEP164 are required for recruitment of IFT-A, IFT-B, and dynein-2 complexes and removal of CP110 from the mother centriole, though CP110 removal is not always coupled with IFT protein recruitment.\",\n      \"method\": \"CEP164-KO and TTBK2-KO cell lines, reconstitution with chimeric and truncation constructs, immunofluorescence quantification of IFT machinery recruitment\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO cells with domain-mapping using chimeric constructs, multiple functional readouts\",\n      \"pmids\": [\"40305080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A missense variant in the TTBK2 kinase domain (L209F), introduced by CRISPR/Cas9 knock-in, reduces TTBK2 protein levels, impairs kinase activity toward TDP-43, alters cytoskeleton-related protein levels, and dysregulates phosphoproteome pathways including cytoskeletal organization and TGF-β signaling.\",\n      \"method\": \"CRISPR/Cas9 knock-in cell model, quantitative phosphoproteomics, in-cell kinase activity assay, Western blot\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — CRISPR knock-in with phosphoproteomics and in-cell kinase activity readout in a single comprehensive study\",\n      \"pmids\": [\"41422144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TTBK2 is expressed in mouse testis and co-localizes with α-tubulin in the manchette during spermiogenesis; TTBK2 knockdown by intratesticular injection increases sperm tail deformity, reduces sperm motility, and disorganizes axonemal microtubule structure, with downregulation of CEP164, CEP83, and IFT88 expression.\",\n      \"method\": \"Intratesticular siRNA injection, transmission electron microscopy, RT-qPCR, Western blot, immunofluorescence co-localization\",\n      \"journal\": \"Molecular human reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function with ultrastructural and molecular readouts, single study\",\n      \"pmids\": [\"40581359\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TTBK2 is a centriolar serine-threonine kinase recruited to distal appendages of the mother centriole by CEP164 (via phase separation and direct binding), where its kinase activity drives ciliogenesis by phosphorylating CEP83 to enable ciliary vesicle docking and CP110 removal, recruiting IFT-A/B and dynein-2 complexes, and maintaining cilium stability through regulation of centriolar satellites and axonemal microtubule modifications; it also phosphorylates KIF2A (inactivating MT depolymerization to promote cell migration), tau, TDP-43, and GluK2 (modulating synaptic receptor endocytosis), and is subject to regulated degradation by the E3 ligase HUWE1; SCA11-causing truncating mutations act as dominant negatives that mislocalize from centrioles, suppress kinase activity, disrupt ciliogenesis and SHH signaling, and may acquire neomorphic peroxisomal targeting.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TTBK2 is a serine-threonine kinase that functions as a master regulator of primary cilium assembly, maintenance, and ciliary signaling, with additional roles in microtubule dynamics, synaptic receptor trafficking, and tau phosphorylation. It is recruited to the distal appendages of the mother centriole by CEP164—via direct binding and phase-separation-driven condensation—where it phosphorylates CEP83 to enable ciliary vesicle docking, triggers CP110 removal, and recruits IFT-A, IFT-B, and dynein-2 complexes required for ciliogenesis; after assembly, it maintains cilium stability by regulating centriolar satellites, IFT protein pools, and axonemal microtubule modifications, with its steady-state levels controlled by HUWE1-mediated proteasomal degradation [PMID:25297623, PMID:31455668, PMID:36322399, PMID:40305080, PMID:38879724, PMID:40483689]. Beyond cilia, TTBK2 tracks microtubule plus ends via EB1/3 and phosphorylates KIF2A to inhibit microtubule depolymerization, promoting cell migration, and it modulates GluK2 glutamate receptor surface abundance through RAB5-dependent endocytosis [PMID:26323690, PMID:27607061]. Truncating mutations in TTBK2 cause spinocerebellar ataxia type 11 (SCA11) by acting as dominant negatives that suppress kinase activity, impair ciliogenesis, and disrupt Sonic Hedgehog signaling, with conditional loss of TTBK2 in adult mice recapitulating cerebellar Purkinje cell degeneration [PMID:18037885, PMID:30532139, PMID:31934864].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying TTBK2 as the SCA11 disease gene established that this kinase is essential for cerebellar neuronal survival and linked it to tau pathology, but the cellular mechanism was unknown.\",\n      \"evidence\": \"Linkage analysis and mutation screening in SCA11 families with neuropathological examination of affected brain tissue\",\n      \"pmids\": [\"18037885\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether disease arises from loss of kinase function, dominant-negative effects, or gain-of-function was unresolved\", \"Substrates beyond tau were not identified\", \"No cellular mechanism connecting TTBK2 loss to neurodegeneration was proposed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Biochemical characterization revealed TTBK2's unusual substrate preference for phosphotyrosine-primed sites and showed that SCA11 truncations suppress kinase activity while increasing protein expression, establishing the enzymological framework for interpreting disease mutations.\",\n      \"evidence\": \"In vitro kinase assay with oriented peptide library, mutagenesis of phosphate-priming groove, SCA11 knockin mouse showing embryonic lethality\",\n      \"pmids\": [\"21548880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates primed by phosphotyrosine were not identified\", \"How SCA11 truncations cause disease at the cellular level remained unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that CEP164 recruits TTBK2 to mother centriole distal appendages via a proline-rich motif, and that this recruitment is essential for CP110 removal and ciliogenesis, reframed TTBK2 as a centriolar kinase controlling cilium initiation.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, TTBK2 binding-motif mutagenesis, siRNA depletion/rescue, in vitro kinase assay for CEP164 and CEP97\",\n      \"pmids\": [\"25297623\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The direct centriolar substrates of TTBK2 required for ciliogenesis were not mapped\", \"Structural basis of the CEP164–TTBK2 interaction was not determined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstration that TTBK2 tracks microtubule plus ends via EB1/3 and phosphorylates KIF2A at S135 to inhibit MT depolymerization established a cilia-independent function in cytoskeletal regulation and cell migration.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay with phosphosite identification, non-phosphorylatable mutant rescue, live-cell MT imaging, migration assays\",\n      \"pmids\": [\"26323690\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the EB1-dependent function is separable from the CEP164-dependent ciliogenesis role in vivo was unclear\", \"Upstream signals regulating TTBK2 plus-end tracking were not identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showing that TTBK2 kinase activity drives RAB5-dependent endocytosis of the GluK2 glutamate receptor extended its functional repertoire to synaptic receptor trafficking, suggesting a direct synaptic role.\",\n      \"evidence\": \"Xenopus oocyte expression with dual-electrode voltage clamp, confocal imaging, dominant-negative RAB5 rescue\",\n      \"pmids\": [\"27607061\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The direct phosphorylation target mediating GluK2 endocytosis was not identified\", \"Relevance in mammalian neurons was not demonstrated\", \"Heterologous expression system limits physiological interpretation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Two studies clarified the disease mechanism: TTBK2 synergizes with tau to cause neurodegeneration in C. elegans, and SCA11 truncating mutations act as dominant negatives that disrupt ciliogenesis and SHH signaling in mice, establishing ciliary dysfunction as a core disease driver.\",\n      \"evidence\": \"Transgenic C. elegans co-expression with tau; mouse allelic series with quantitative cilia IF and SHH reporter assays\",\n      \"pmids\": [\"29409526\", \"30532139\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of tau toxicity versus ciliary defects to SCA11 pathogenesis were not dissected\", \"Whether SCA11 truncation retains partial kinase activity in vivo was not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of CEP83 as a direct TTBK2 substrate at four phosphosites, required for ciliary vesicle docking and CP110 removal, provided the first detailed mechanism of how TTBK2 kinase activity initiates ciliogenesis at the distal appendage.\",\n      \"evidence\": \"STORM/STED superresolution microscopy, in vitro kinase assay with mass spectrometry phosphosite mapping, CEP83 phospho-mutant functional analysis\",\n      \"pmids\": [\"31455668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether additional substrates are required alongside phospho-CEP83 was unknown\", \"How CEP83 phosphorylation connects to CP110 removal machinery was not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Conditional Ttbk2 knockout in adult mouse brain phenocopied by Ift88 conditional knockout demonstrated that TTBK2's essential role in maintaining primary cilia—not a cilia-independent function—drives Purkinje cell degeneration and motor deficits in SCA11.\",\n      \"evidence\": \"Adult conditional knockout mice, behavioral assays, cilia quantification, genetic comparison with Ift88 CKO\",\n      \"pmids\": [\"31934864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether restoring cilia can rescue established degeneration was not tested\", \"Cell-type-specific vulnerability within the cerebellum was not fully dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Structural determination of the CEP164–TTBK2 complex revealed how ciliopathic CEP164 mutations disrupt TTBK2 recruitment, providing atomic-level understanding of the ciliogenesis-initiating interaction.\",\n      \"evidence\": \"X-ray crystallography/NMR, biochemical binding assays, functional complementation with ciliopathy mutants\",\n      \"pmids\": [\"34499853\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length TTBK2 was not solved\", \"How kinase activation relates to binding was not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Post-assembly cilium maintenance was shown to require TTBK2 for regulating centriolar satellites, IFT protein pools, and suppressing actin-dependent cilia disassembly, extending TTBK2's role beyond initiation to ongoing cilium stability.\",\n      \"evidence\": \"Tamoxifen-inducible Ttbk2 deletion in MEFs, time-course immunofluorescence, actin inhibitor rescue\",\n      \"pmids\": [\"36322399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrates mediating satellite regulation and actin suppression were not identified\", \"Whether maintenance and assembly functions use identical phosphorylation events was unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Pharmacological inhibition of TTBK2 phenocopied genetic knockout in human iPSCs, validating kinase activity as druggable and confirming catalytic requirement for ciliogenesis in a human cellular context.\",\n      \"evidence\": \"Indolyl pyrimidinamine inhibitor treatment with iPSC cilia quantification, comparison to TTBK2 KO\",\n      \"pmids\": [\"37059819\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inhibitor selectivity among related kinases was not fully profiled\", \"In vivo pharmacological validation was not performed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of HUWE1 as the E3 ligase targeting TTBK2 for proteasomal degradation at the centrosome established how TTBK2 protein levels are regulated to control cilia disassembly, linking TTBK2 turnover to SHH-dependent cerebellar development.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, HUWE1/TTBK2 knockdown in GNPs and medulloblastoma cells, in vivo cerebellar development analysis\",\n      \"pmids\": [\"38879724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals triggering HUWE1-mediated TTBK2 degradation were not defined\", \"Whether HUWE1 regulation of TTBK2 is relevant outside of cerebellar development was not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Three 2025 studies refined the recruitment mechanism and expanded functional scope: CEP164 forms phase-separated condensates with TTBK2 required for efficient recruitment; TTBK2 kinase activity recruits IFT-A/B and dynein-2 complexes independently of CP110 removal; a kinase-domain missense variant dysregulates cytoskeletal and TGF-β phosphoproteome pathways; and TTBK2 is required for sperm axoneme integrity during spermiogenesis.\",\n      \"evidence\": \"In vitro phase separation reconstitution plus live-cell imaging; KO/chimeric reconstitution with IFT quantification; CRISPR knock-in phosphoproteomics; intratesticular siRNA with TEM ultrastructure\",\n      \"pmids\": [\"40483689\", \"40305080\", \"41422144\", \"40581359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether phase separation is regulated by upstream signals is unknown\", \"The full complement of TTBK2 substrates at distal appendages remains unmapped\", \"Whether the TGF-β phosphoproteome changes are direct or indirect is unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive substrate map for TTBK2 at the centriole, the structural basis for its activation upon CEP164 binding, and the relative contributions of ciliary versus non-ciliary (tau, cytoskeletal) functions to SCA11 pathogenesis remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full-length TTBK2 structure and activation mechanism not determined\", \"Systematic identification of all centriolar substrates not completed\", \"Whether tau phosphorylation contributes to SCA11 independently of ciliary defects is untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 3, 6, 10, 16]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 3, 6, 16]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [2, 6, 8, 12, 14, 15]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 17]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [5, 7, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [2, 6, 7, 9, 10, 15]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 7, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 4, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 5, 7]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CEP164\",\n      \"CEP83\",\n      \"KIF2A\",\n      \"EB1\",\n      \"EB3\",\n      \"HUWE1\",\n      \"CP110\",\n      \"CEP97\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}