{"gene":"TUBGCP2","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":1997,"finding":"Spc97p (yeast ortholog of TUBGCP2) forms a 6S complex with Tub4p (gamma-tubulin) and Spc98p, containing one molecule each of Spc98p and Spc97p and two or more molecules of Tub4p, with no other proteins.","method":"Purification of the Tub4p complex; sucrose gradient fractionation; immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — biochemical purification of reconstituted complex, multiple orthogonal methods (purification, fractionation, immunoprecipitation), replicated across multiple papers","pmids":["9384578"],"is_preprint":false},{"year":1997,"finding":"Spc97p (yeast ortholog of TUBGCP2) and Spc98p mediate binding of the gamma-tubulin (Tub4p) complex to the spindle pole body via their interaction with the N-terminal domain of Spc110p.","method":"Genetic suppression analysis; biochemical pulldown; two-hybrid interaction; immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic and biochemical data across two papers, multiple orthogonal methods","pmids":["9384578","9130700"],"is_preprint":false},{"year":1997,"finding":"Spc97p (yeast ortholog of TUBGCP2) physically interacts with both Tub4p (gamma-tubulin) and Spc98p, and this trimeric complex is required for microtubule organization and SPB duplication; temperature-sensitive spc97 alleles cause spindle defects including failure in SPB separation, spindle formation, and SPB duplication.","method":"Two-hybrid interaction; immunoprecipitation; fractionation; genetic suppression (high-copy SPC98 or TUB4 suppresses spc97 ts alleles); overexpression toxicity assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (two-hybrid, co-IP, genetic epistasis, toxicity suppression), functionally validated in vivo","pmids":["9130700"],"is_preprint":false},{"year":1998,"finding":"Human GCP2 (hGCP2/TUBGCP2) and GCP3 are homologs of yeast Spc97p and Spc98p; they are components of the mammalian gamma-tubulin complex, colocalize with gamma-tubulin at the centrosome, and co-sediment with gamma-tubulin in sucrose gradients.","method":"Stable cell lines expressing epitope-tagged gamma-tubulin; immunoprecipitation; sucrose gradient cosedimentation; colocalization by immunofluorescence; sequence analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, cosedimentation, colocalization, multiple orthogonal methods in one study","pmids":["9566967"],"is_preprint":false},{"year":2002,"finding":"Alp4 (fission yeast ortholog of TUBGCP2) is required for recruitment of the gamma-tubulin complex to the spindle pole body; loss of Alp4 function causes bipolar spindle defects and activates the Mad2 checkpoint, yet untimely activation of the SIN (septation initiation network) drives septation despite monopolar spindles, with Sid1 kinase recruited prematurely to both SPBs instead of one.","method":"Genetic analysis of alp4 mutants; checkpoint activation assays; live-cell imaging of Sid1 kinase localization; cyclin B level measurements at SPB","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined cellular phenotype and pathway placement, single lab","pmids":["11952833"],"is_preprint":false},{"year":2004,"finding":"In fission yeast, Alp4 (TUBGCP2 ortholog) directly interacts with gamma-tubulin (Gtb1); allele-specific suppressors of alp4 mutations map to a small surface region of gamma-tubulin, defining the Alp4-binding interface on gamma-tubulin. Mutant complexes showed altered (increased) stability.","method":"Allele-specific suppressor genetics; mutation mapping; gel filtration; immunoprecipitation","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis combined with biochemical complex stability assay, single lab, two methods","pmids":["15280226"],"is_preprint":false},{"year":2006,"finding":"Overproduction of the C-terminal domain of Alp4 (TUBGCP2 ortholog) in fission yeast alters microtubule dynamics, stabilizing cytoplasmic microtubules, and induces oscillatory nuclear movement via SPB-driven MT pushing forces; this movement depends on microtubule stability rather than dynein or kinesin motors.","method":"Overexpression of Alp4 C-terminal fragment; live-cell imaging; SPB/MT dynamics measurements; genetic analysis (deletion of dhc1, pkl1, klp2)","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with functional readouts, genetic dissection of motor dependence, single lab","pmids":["16611238"],"is_preprint":false},{"year":2006,"finding":"Nuclear-localized C-terminal Alp4 (TUBGCP2 ortholog) induces Wee1-dependent G2 delay, reduces gamma-tubulin complex levels at the SPB, and causes defects in spindle assembly, cytoplasmic microtubule disassembly, and chromosome segregation; cytoplasmic Alp4C induces nuclear oscillation and affects cell polarity markers Bud6 and Tip1. This demonstrates distinct functions for nuclear versus cytoplasmic gamma-tubulin complexes.","method":"Overexpression of NLS- and NES-tagged Alp4 C-terminal fragments; subcellular fractionation; live-cell imaging; flow cytometry; immunofluorescence","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional compartment-specific localization with defined phenotypic outcomes, single lab, multiple readouts","pmids":["16611237"],"is_preprint":false},{"year":2013,"finding":"Human GCP2 (TUBGCP2) can functionally replace fission yeast Alp4 for essential vegetative functions, but its N-terminal domain limits full displacement of Alp4 during gamma-TuRC assembly; when Alp4 is present, GCP2 is excluded from the >2000 kDa gamma-TuRC and fractionates as smaller complexes. A chimeric Alp4-GCP2 protein demonstrated the N-terminal domain of GCP2 as the limiting feature.","method":"Cross-species genetic complementation; sucrose gradient fractionation; biochemical analysis of complex incorporation; chimeric protein construction and functional assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic complementation combined with biochemical fractionation and chimeric protein analysis, single lab","pmids":["23886939"],"is_preprint":false},{"year":2019,"finding":"Bi-allelic pathogenic variants in TUBGCP2 (p.Arg333Cys, p.Ala615Pro, p.Arg297Cys, and a splice variant) cause autosomal recessive microcephaly and lissencephaly spectrum disorders in humans, implicating GCP2 as a core component of gamma-TuRC required for neuronal migration.","method":"Exome sequencing; family-based rare variant analysis; GeneMatcher collaboration; brain MRI imaging for cortical malformation phenotyping","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — human genetics with multiple independent families, no in vitro reconstitution but converging variant evidence","pmids":["31630790"],"is_preprint":false},{"year":2020,"finding":"A homozygous TUBGCP2 variant (p.Glu311Lys), predicted to disrupt electrostatic interaction of GCP2 with GCP3, causes faint delocalization of gamma-tubulin during the cell cycle in patient fibroblasts and dysregulation of proteins involved in cytoskeletal assembly, cellular adhesion, and axon guidance, as detected by mass spectrometry proteomics.","method":"Patient primary fibroblast analysis; immunofluorescence for gamma-tubulin localization; mass spectrometry proteomics","journal":"iScience","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single patient fibroblast study, mass spectrometry proteome analysis without direct mechanistic validation of GCP2-GCP3 interaction disruption","pmids":["33458610"],"is_preprint":false}],"current_model":"TUBGCP2 (GCP2/hGCP2) encodes a core structural component of the gamma-tubulin small complex (gamma-TuSC) and ring complex (gamma-TuRC), where it directly binds gamma-tubulin and GCP3 (Spc98p), anchors the complex to the centrosome/spindle pole body via interaction with SPB components such as Spc110p, and is required for microtubule nucleation, spindle assembly, SPB duplication, nuclear positioning, and—in humans—neuronal migration during cortical development; its N-terminal domain influences competitive assembly into the gamma-TuRC, and its activity regulates the balance between nuclear and cytoplasmic microtubule organizing functions."},"narrative":{"mechanistic_narrative":"TUBGCP2 (GCP2) is a core structural subunit of the gamma-tubulin complex that nucleates microtubules from microtubule organizing centers and is required for spindle assembly and centrosome/spindle pole body (SPB) function [PMID:9384578, PMID:9130700, PMID:9566967]. Work on its yeast ortholog Spc97p established that it assembles with gamma-tubulin (Tub4p) and Spc98p (GCP3) into a defined trimeric 6S complex containing one copy each of Spc97p and Spc98p plus gamma-tubulin [PMID:9384578], and that this complex is tethered to the SPB through the N-terminal domain of Spc110p [PMID:9384578, PMID:9130700]. The complex is essential for microtubule organization, SPB duplication and separation, and bipolar spindle formation, with loss-of-function alleles producing monopolar/spindle defects and checkpoint activation [PMID:9130700, PMID:11952833]. In mammals, human GCP2 is a homolog of Spc97p that colocalizes and co-sediments with gamma-tubulin at the centrosome [PMID:9566967], and it binds gamma-tubulin through a defined surface interface mapped on gamma-tubulin and interacts with GCP3 [PMID:15280226]. The N-terminal domain of GCP2 governs competitive incorporation into the large (>2000 kDa) gamma-TuRC [PMID:23886939], and the balance between nuclear and cytoplasmic gamma-tubulin complex activity controls cytoplasmic microtubule stability, nuclear positioning, and cell-cycle progression [PMID:16611238, PMID:16611237]. Bi-allelic pathogenic TUBGCP2 variants cause autosomal recessive microcephaly and lissencephaly spectrum disorders, linking gamma-TuRC function to neuronal migration during cortical development [PMID:31630790].","teleology":[{"year":1997,"claim":"Defined the minimal composition of the gamma-tubulin complex, establishing that the TUBGCP2 ortholog is a stoichiometric structural partner of gamma-tubulin rather than a loosely associated factor.","evidence":"Biochemical purification, sucrose gradient fractionation, and immunoprecipitation of the Tub4p complex in budding yeast","pmids":["9384578"],"confidence":"High","gaps":["Stoichiometry of Tub4p (≥2 copies) not precisely resolved","Higher-order ring assembly not addressed in this minimal complex"]},{"year":1997,"claim":"Showed how the complex is anchored to the spindle pole body, answering how gamma-tubulin nucleation activity is spatially targeted.","evidence":"Genetic suppression, two-hybrid, and biochemical pulldown mapping Spc97p/Spc98p interaction to the N-terminal domain of Spc110p in yeast","pmids":["9384578","9130700"],"confidence":"High","gaps":["Whether the human Spc110p equivalent uses the same anchoring mechanism not addressed"]},{"year":1997,"claim":"Established the in vivo functional requirement of the TUBGCP2 ortholog for SPB duplication, separation, and spindle formation.","evidence":"Temperature-sensitive spc97 alleles, two-hybrid, co-IP, and high-copy genetic suppression by SPC98/TUB4","pmids":["9130700"],"confidence":"High","gaps":["Molecular basis of how complex loss blocks SPB duplication not defined"]},{"year":1998,"claim":"Extended the yeast model to mammals by identifying human GCP2 as a gamma-tubulin complex component at the centrosome.","evidence":"Epitope-tagged gamma-tubulin stable cell lines, co-IP, sucrose gradient cosedimentation, and immunofluorescence colocalization","pmids":["9566967"],"confidence":"High","gaps":["Human complex stoichiometry and ring assembly not resolved","Direct GCP2-gamma-tubulin binding interface in human not mapped here"]},{"year":2002,"claim":"Connected gamma-tubulin complex recruitment to mitotic checkpoint and septation signaling, showing spindle defects feed into cell-cycle control networks.","evidence":"Genetic analysis of fission yeast alp4 mutants, Mad2 checkpoint assays, and live imaging of Sid1 kinase localization","pmids":["11952833"],"confidence":"Medium","gaps":["Single-lab fission yeast data","Direct molecular link between Alp4 loss and premature SIN activation not established"]},{"year":2004,"claim":"Mapped the physical interface between the TUBGCP2 ortholog and gamma-tubulin, defining a specific contact surface required for complex assembly.","evidence":"Allele-specific suppressor genetics with mutation mapping, gel filtration, and immunoprecipitation in fission yeast","pmids":["15280226"],"confidence":"Medium","gaps":["Surface defined genetically rather than by structure","Functional consequence of increased complex stability not fully characterized"]},{"year":2006,"claim":"Revealed that the C-terminal domain regulates cytoplasmic microtubule dynamics and SPB-driven nuclear movement independent of motor proteins.","evidence":"Overexpression of Alp4 C-terminal fragment, live-cell imaging, and genetic deletion of dynein/kinesin motors in fission yeast","pmids":["16611238"],"confidence":"Medium","gaps":["Effect studied via overexpression fragment, not endogenous protein","Mechanism of MT stabilization by the C-terminal domain unknown"]},{"year":2006,"claim":"Distinguished compartment-specific functions of the gamma-tubulin complex, showing nuclear versus cytoplasmic pools have distinct roles in spindle assembly, cell-cycle timing, and polarity.","evidence":"NLS/NES-tagged Alp4 C-terminal fragments, fractionation, live imaging, flow cytometry, and immunofluorescence in fission yeast","pmids":["16611237"],"confidence":"Medium","gaps":["Based on targeted fragment overexpression","Relevance of nuclear/cytoplasmic partitioning to human GCP2 not tested"]},{"year":2013,"claim":"Identified the N-terminal domain of human GCP2 as a determinant of competitive incorporation into the large gamma-TuRC.","evidence":"Cross-species genetic complementation, sucrose gradient fractionation, and chimeric Alp4-GCP2 protein assays","pmids":["23886939"],"confidence":"Medium","gaps":["Molecular basis of N-terminal exclusion from the >2000 kDa complex not resolved","Single-lab heterologous system"]},{"year":2019,"claim":"Linked TUBGCP2 loss-of-function to human disease, establishing gamma-TuRC integrity as essential for neuronal migration and cortical development.","evidence":"Exome sequencing of multiple families with microcephaly/lissencephaly, GeneMatcher, and brain MRI phenotyping","pmids":["31630790"],"confidence":"Medium","gaps":["No in vitro reconstitution of variant effects","Mechanism by which variants impair neuronal migration not directly tested"]},{"year":2020,"claim":"Provided cellular evidence that a disease variant predicted to disrupt the GCP2-GCP3 interaction perturbs gamma-tubulin localization and downstream cytoskeletal/adhesion/axon-guidance proteomes.","evidence":"Patient primary fibroblast immunofluorescence for gamma-tubulin and mass spectrometry proteomics","pmids":["33458610"],"confidence":"Low","gaps":["Single patient fibroblast study without direct validation of GCP2-GCP3 disruption","Causality between proteome changes and the variant not established"]},{"year":null,"claim":"How specific human TUBGCP2 variants alter gamma-TuRC assembly, microtubule nucleation kinetics, and neuronal migration at the molecular level remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of variant effects on the human complex","No in vitro reconstitution linking variants to nucleation defects","No neuronal-migration assay directly testing patient mutations"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,5]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[3]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[2,4]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9]}],"complexes":["gamma-tubulin small complex (gamma-TuSC)","gamma-tubulin ring complex (gamma-TuRC)"],"partners":["TUBG1","TUBGCP3","TUB4P","SPC98P","SPC110P"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BSJ2","full_name":"Gamma-tubulin complex component 2","aliases":["Gamma-ring complex protein 103 kDa","h103p","hGrip103","Spindle pole body protein Spc97 homolog","hSpc97"],"length_aa":902,"mass_kda":102.5,"function":"Component of the gamma-tubulin ring complex (gTuRC) which mediates microtubule nucleation (PubMed:38305685, PubMed:38609661, PubMed:39321809, PubMed:9566967). The gTuRC regulates the minus-end nucleation of alpha-beta tubulin heterodimers that grow into microtubule protafilaments, a critical step in centrosome duplication and spindle formation (PubMed:38305685, PubMed:38609661, PubMed:39321809). Plays a role in neuronal migration (PubMed:31630790)","subcellular_location":"Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/Q9BSJ2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/TUBGCP2","classification":"Common Essential","n_dependent_lines":1203,"n_total_lines":1208,"dependency_fraction":0.9958609271523179},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"TUBG1","stoichiometry":0.2},{"gene":"UBA1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TUBGCP2","total_profiled":1310},"omim":[{"mim_id":"618737","title":"CORTICAL DYSPLASIA, COMPLEX, WITH OTHER BRAIN MALFORMATIONS 15; CDCBM15","url":"https://www.omim.org/entry/618737"},{"mim_id":"617818","title":"TUBULIN-GAMMA COMPLEX-ASSOCIATED PROTEIN 3; TUBGCP3","url":"https://www.omim.org/entry/617818"},{"mim_id":"617817","title":"TUBULIN-GAMMA COMPLEX-ASSOCIATED PROTEIN 2; TUBGCP2","url":"https://www.omim.org/entry/617817"},{"mim_id":"615656","title":"CHROMOSOME 15q11.2 DELETION SYNDROME","url":"https://www.omim.org/entry/615656"},{"mim_id":"614039","title":"CORTICAL DYSPLASIA, COMPLEX, WITH OTHER BRAIN MALFORMATIONS 1; CDCBM1","url":"https://www.omim.org/entry/614039"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Centrosome","reliability":"Supported"},{"location":"Basal body","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TUBGCP2"},"hgnc":{"alias_symbol":["GCP2","Spc97p","SPBC97","hGCP2","ALP4"],"prev_symbol":[]},"alphafold":{"accession":"Q9BSJ2","domains":[{"cath_id":"-","chopping":"383-507","consensus_level":"high","plddt":82.5586,"start":383,"end":507},{"cath_id":"1.20.120.1900","chopping":"515-631","consensus_level":"medium","plddt":83.0288,"start":515,"end":631},{"cath_id":"1.20.120.1900","chopping":"639-771_817-875","consensus_level":"medium","plddt":83.2556,"start":639,"end":875}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BSJ2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BSJ2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BSJ2-F1-predicted_aligned_error_v6.png","plddt_mean":75.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TUBGCP2","jax_strain_url":"https://www.jax.org/strain/search?query=TUBGCP2"},"sequence":{"accession":"Q9BSJ2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BSJ2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BSJ2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BSJ2"}},"corpus_meta":[{"pmid":"9384578","id":"PMC_9384578","title":"Spc98p and Spc97p of the yeast gamma-tubulin complex mediate binding to the spindle pole body via their interaction with Spc110p.","date":"1997","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9384578","citation_count":201,"is_preprint":false},{"pmid":"9566967","id":"PMC_9566967","title":"The mammalian gamma-tubulin complex contains homologues of the yeast spindle pole body components spc97p and spc98p.","date":"1998","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9566967","citation_count":178,"is_preprint":false},{"pmid":"9130700","id":"PMC_9130700","title":"The spindle pole body component Spc97p interacts with the gamma-tubulin of Saccharomyces cerevisiae and functions in microtubule organization and spindle pole body duplication.","date":"1997","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9130700","citation_count":175,"is_preprint":false},{"pmid":"11952833","id":"PMC_11952833","title":"The gamma-tubulin complex protein Alp4 provides a link between the metaphase checkpoint and cytokinesis in fission yeast.","date":"2002","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/11952833","citation_count":31,"is_preprint":false},{"pmid":"31630790","id":"PMC_31630790","title":"Bi-allelic Pathogenic Variants in TUBGCP2 Cause Microcephaly and Lissencephaly Spectrum Disorders.","date":"2019","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31630790","citation_count":28,"is_preprint":false},{"pmid":"15280226","id":"PMC_15280226","title":"Functional dissection of the gamma-tubulin complex by suppressor analysis of gtb1 and alp4 mutations in Schizosaccharomyces pombe.","date":"2004","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/15280226","citation_count":20,"is_preprint":false},{"pmid":"16611238","id":"PMC_16611238","title":"The carboxy-terminus of Alp4 alters microtubule dynamics to induce oscillatory nuclear movement led by the spindle pole body in Schizosaccharomyces pombe.","date":"2006","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/16611238","citation_count":15,"is_preprint":false},{"pmid":"33458610","id":"PMC_33458610","title":"Autosomal recessive variants in TUBGCP2 alter the γ-tubulin ring complex leading to neurodevelopmental disease.","date":"2020","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/33458610","citation_count":12,"is_preprint":false},{"pmid":"16611237","id":"PMC_16611237","title":"Modulation of Alp4 function in Schizosaccharomyces pombe induces novel phenotypes that imply distinct functions for nuclear and cytoplasmic gamma-tubulin complexes.","date":"2006","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/16611237","citation_count":10,"is_preprint":false},{"pmid":"23886939","id":"PMC_23886939","title":"Functional replacement of fission yeast γ-tubulin small complex proteins Alp4 and Alp6 by human GCP2 and GCP3.","date":"2013","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/23886939","citation_count":5,"is_preprint":false},{"pmid":"40448381","id":"PMC_40448381","title":"Thick Corpus Callosum: An Unusual Finding of TUBGCP2-Related Tubulinopathy.","date":"2025","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/40448381","citation_count":1,"is_preprint":false},{"pmid":"40017707","id":"PMC_40017707","title":"TUBGCP2 variants cause lissencephaly spectrum disorders: a case report and literature review.","date":"2025","source":"Frontiers in pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/40017707","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7892,"output_tokens":2812,"usd":0.032928,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10162,"output_tokens":3518,"usd":0.06938,"stage2_stop_reason":"end_turn"},"total_usd":0.102308,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"Spc97p (yeast ortholog of TUBGCP2) forms a 6S complex with Tub4p (gamma-tubulin) and Spc98p, containing one molecule each of Spc98p and Spc97p and two or more molecules of Tub4p, with no other proteins.\",\n      \"method\": \"Purification of the Tub4p complex; sucrose gradient fractionation; immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biochemical purification of reconstituted complex, multiple orthogonal methods (purification, fractionation, immunoprecipitation), replicated across multiple papers\",\n      \"pmids\": [\"9384578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Spc97p (yeast ortholog of TUBGCP2) and Spc98p mediate binding of the gamma-tubulin (Tub4p) complex to the spindle pole body via their interaction with the N-terminal domain of Spc110p.\",\n      \"method\": \"Genetic suppression analysis; biochemical pulldown; two-hybrid interaction; immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic and biochemical data across two papers, multiple orthogonal methods\",\n      \"pmids\": [\"9384578\", \"9130700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Spc97p (yeast ortholog of TUBGCP2) physically interacts with both Tub4p (gamma-tubulin) and Spc98p, and this trimeric complex is required for microtubule organization and SPB duplication; temperature-sensitive spc97 alleles cause spindle defects including failure in SPB separation, spindle formation, and SPB duplication.\",\n      \"method\": \"Two-hybrid interaction; immunoprecipitation; fractionation; genetic suppression (high-copy SPC98 or TUB4 suppresses spc97 ts alleles); overexpression toxicity assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (two-hybrid, co-IP, genetic epistasis, toxicity suppression), functionally validated in vivo\",\n      \"pmids\": [\"9130700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human GCP2 (hGCP2/TUBGCP2) and GCP3 are homologs of yeast Spc97p and Spc98p; they are components of the mammalian gamma-tubulin complex, colocalize with gamma-tubulin at the centrosome, and co-sediment with gamma-tubulin in sucrose gradients.\",\n      \"method\": \"Stable cell lines expressing epitope-tagged gamma-tubulin; immunoprecipitation; sucrose gradient cosedimentation; colocalization by immunofluorescence; sequence analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, cosedimentation, colocalization, multiple orthogonal methods in one study\",\n      \"pmids\": [\"9566967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Alp4 (fission yeast ortholog of TUBGCP2) is required for recruitment of the gamma-tubulin complex to the spindle pole body; loss of Alp4 function causes bipolar spindle defects and activates the Mad2 checkpoint, yet untimely activation of the SIN (septation initiation network) drives septation despite monopolar spindles, with Sid1 kinase recruited prematurely to both SPBs instead of one.\",\n      \"method\": \"Genetic analysis of alp4 mutants; checkpoint activation assays; live-cell imaging of Sid1 kinase localization; cyclin B level measurements at SPB\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined cellular phenotype and pathway placement, single lab\",\n      \"pmids\": [\"11952833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In fission yeast, Alp4 (TUBGCP2 ortholog) directly interacts with gamma-tubulin (Gtb1); allele-specific suppressors of alp4 mutations map to a small surface region of gamma-tubulin, defining the Alp4-binding interface on gamma-tubulin. Mutant complexes showed altered (increased) stability.\",\n      \"method\": \"Allele-specific suppressor genetics; mutation mapping; gel filtration; immunoprecipitation\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis combined with biochemical complex stability assay, single lab, two methods\",\n      \"pmids\": [\"15280226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Overproduction of the C-terminal domain of Alp4 (TUBGCP2 ortholog) in fission yeast alters microtubule dynamics, stabilizing cytoplasmic microtubules, and induces oscillatory nuclear movement via SPB-driven MT pushing forces; this movement depends on microtubule stability rather than dynein or kinesin motors.\",\n      \"method\": \"Overexpression of Alp4 C-terminal fragment; live-cell imaging; SPB/MT dynamics measurements; genetic analysis (deletion of dhc1, pkl1, klp2)\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with functional readouts, genetic dissection of motor dependence, single lab\",\n      \"pmids\": [\"16611238\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Nuclear-localized C-terminal Alp4 (TUBGCP2 ortholog) induces Wee1-dependent G2 delay, reduces gamma-tubulin complex levels at the SPB, and causes defects in spindle assembly, cytoplasmic microtubule disassembly, and chromosome segregation; cytoplasmic Alp4C induces nuclear oscillation and affects cell polarity markers Bud6 and Tip1. This demonstrates distinct functions for nuclear versus cytoplasmic gamma-tubulin complexes.\",\n      \"method\": \"Overexpression of NLS- and NES-tagged Alp4 C-terminal fragments; subcellular fractionation; live-cell imaging; flow cytometry; immunofluorescence\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional compartment-specific localization with defined phenotypic outcomes, single lab, multiple readouts\",\n      \"pmids\": [\"16611237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human GCP2 (TUBGCP2) can functionally replace fission yeast Alp4 for essential vegetative functions, but its N-terminal domain limits full displacement of Alp4 during gamma-TuRC assembly; when Alp4 is present, GCP2 is excluded from the >2000 kDa gamma-TuRC and fractionates as smaller complexes. A chimeric Alp4-GCP2 protein demonstrated the N-terminal domain of GCP2 as the limiting feature.\",\n      \"method\": \"Cross-species genetic complementation; sucrose gradient fractionation; biochemical analysis of complex incorporation; chimeric protein construction and functional assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic complementation combined with biochemical fractionation and chimeric protein analysis, single lab\",\n      \"pmids\": [\"23886939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Bi-allelic pathogenic variants in TUBGCP2 (p.Arg333Cys, p.Ala615Pro, p.Arg297Cys, and a splice variant) cause autosomal recessive microcephaly and lissencephaly spectrum disorders in humans, implicating GCP2 as a core component of gamma-TuRC required for neuronal migration.\",\n      \"method\": \"Exome sequencing; family-based rare variant analysis; GeneMatcher collaboration; brain MRI imaging for cortical malformation phenotyping\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — human genetics with multiple independent families, no in vitro reconstitution but converging variant evidence\",\n      \"pmids\": [\"31630790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A homozygous TUBGCP2 variant (p.Glu311Lys), predicted to disrupt electrostatic interaction of GCP2 with GCP3, causes faint delocalization of gamma-tubulin during the cell cycle in patient fibroblasts and dysregulation of proteins involved in cytoskeletal assembly, cellular adhesion, and axon guidance, as detected by mass spectrometry proteomics.\",\n      \"method\": \"Patient primary fibroblast analysis; immunofluorescence for gamma-tubulin localization; mass spectrometry proteomics\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single patient fibroblast study, mass spectrometry proteome analysis without direct mechanistic validation of GCP2-GCP3 interaction disruption\",\n      \"pmids\": [\"33458610\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TUBGCP2 (GCP2/hGCP2) encodes a core structural component of the gamma-tubulin small complex (gamma-TuSC) and ring complex (gamma-TuRC), where it directly binds gamma-tubulin and GCP3 (Spc98p), anchors the complex to the centrosome/spindle pole body via interaction with SPB components such as Spc110p, and is required for microtubule nucleation, spindle assembly, SPB duplication, nuclear positioning, and—in humans—neuronal migration during cortical development; its N-terminal domain influences competitive assembly into the gamma-TuRC, and its activity regulates the balance between nuclear and cytoplasmic microtubule organizing functions.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TUBGCP2 (GCP2) is a core structural subunit of the gamma-tubulin complex that nucleates microtubules from microtubule organizing centers and is required for spindle assembly and centrosome/spindle pole body (SPB) function [#0, #2, #3]. Work on its yeast ortholog Spc97p established that it assembles with gamma-tubulin (Tub4p) and Spc98p (GCP3) into a defined trimeric 6S complex containing one copy each of Spc97p and Spc98p plus gamma-tubulin [#0], and that this complex is tethered to the SPB through the N-terminal domain of Spc110p [#1]. The complex is essential for microtubule organization, SPB duplication and separation, and bipolar spindle formation, with loss-of-function alleles producing monopolar/spindle defects and checkpoint activation [#2, #4]. In mammals, human GCP2 is a homolog of Spc97p that colocalizes and co-sediments with gamma-tubulin at the centrosome [#3], and it binds gamma-tubulin through a defined surface interface mapped on gamma-tubulin and interacts with GCP3 [#5]. The N-terminal domain of GCP2 governs competitive incorporation into the large (>2000 kDa) gamma-TuRC [#8], and the balance between nuclear and cytoplasmic gamma-tubulin complex activity controls cytoplasmic microtubule stability, nuclear positioning, and cell-cycle progression [#6, #7]. Bi-allelic pathogenic TUBGCP2 variants cause autosomal recessive microcephaly and lissencephaly spectrum disorders, linking gamma-TuRC function to neuronal migration during cortical development [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined the minimal composition of the gamma-tubulin complex, establishing that the TUBGCP2 ortholog is a stoichiometric structural partner of gamma-tubulin rather than a loosely associated factor.\",\n      \"evidence\": \"Biochemical purification, sucrose gradient fractionation, and immunoprecipitation of the Tub4p complex in budding yeast\",\n      \"pmids\": [\"9384578\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of Tub4p (\\u22652 copies) not precisely resolved\", \"Higher-order ring assembly not addressed in this minimal complex\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed how the complex is anchored to the spindle pole body, answering how gamma-tubulin nucleation activity is spatially targeted.\",\n      \"evidence\": \"Genetic suppression, two-hybrid, and biochemical pulldown mapping Spc97p/Spc98p interaction to the N-terminal domain of Spc110p in yeast\",\n      \"pmids\": [\"9384578\", \"9130700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the human Spc110p equivalent uses the same anchoring mechanism not addressed\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Established the in vivo functional requirement of the TUBGCP2 ortholog for SPB duplication, separation, and spindle formation.\",\n      \"evidence\": \"Temperature-sensitive spc97 alleles, two-hybrid, co-IP, and high-copy genetic suppression by SPC98/TUB4\",\n      \"pmids\": [\"9130700\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of how complex loss blocks SPB duplication not defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Extended the yeast model to mammals by identifying human GCP2 as a gamma-tubulin complex component at the centrosome.\",\n      \"evidence\": \"Epitope-tagged gamma-tubulin stable cell lines, co-IP, sucrose gradient cosedimentation, and immunofluorescence colocalization\",\n      \"pmids\": [\"9566967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human complex stoichiometry and ring assembly not resolved\", \"Direct GCP2-gamma-tubulin binding interface in human not mapped here\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Connected gamma-tubulin complex recruitment to mitotic checkpoint and septation signaling, showing spindle defects feed into cell-cycle control networks.\",\n      \"evidence\": \"Genetic analysis of fission yeast alp4 mutants, Mad2 checkpoint assays, and live imaging of Sid1 kinase localization\",\n      \"pmids\": [\"11952833\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab fission yeast data\", \"Direct molecular link between Alp4 loss and premature SIN activation not established\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapped the physical interface between the TUBGCP2 ortholog and gamma-tubulin, defining a specific contact surface required for complex assembly.\",\n      \"evidence\": \"Allele-specific suppressor genetics with mutation mapping, gel filtration, and immunoprecipitation in fission yeast\",\n      \"pmids\": [\"15280226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Surface defined genetically rather than by structure\", \"Functional consequence of increased complex stability not fully characterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Revealed that the C-terminal domain regulates cytoplasmic microtubule dynamics and SPB-driven nuclear movement independent of motor proteins.\",\n      \"evidence\": \"Overexpression of Alp4 C-terminal fragment, live-cell imaging, and genetic deletion of dynein/kinesin motors in fission yeast\",\n      \"pmids\": [\"16611238\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effect studied via overexpression fragment, not endogenous protein\", \"Mechanism of MT stabilization by the C-terminal domain unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Distinguished compartment-specific functions of the gamma-tubulin complex, showing nuclear versus cytoplasmic pools have distinct roles in spindle assembly, cell-cycle timing, and polarity.\",\n      \"evidence\": \"NLS/NES-tagged Alp4 C-terminal fragments, fractionation, live imaging, flow cytometry, and immunofluorescence in fission yeast\",\n      \"pmids\": [\"16611237\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Based on targeted fragment overexpression\", \"Relevance of nuclear/cytoplasmic partitioning to human GCP2 not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified the N-terminal domain of human GCP2 as a determinant of competitive incorporation into the large gamma-TuRC.\",\n      \"evidence\": \"Cross-species genetic complementation, sucrose gradient fractionation, and chimeric Alp4-GCP2 protein assays\",\n      \"pmids\": [\"23886939\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of N-terminal exclusion from the >2000 kDa complex not resolved\", \"Single-lab heterologous system\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Linked TUBGCP2 loss-of-function to human disease, establishing gamma-TuRC integrity as essential for neuronal migration and cortical development.\",\n      \"evidence\": \"Exome sequencing of multiple families with microcephaly/lissencephaly, GeneMatcher, and brain MRI phenotyping\",\n      \"pmids\": [\"31630790\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution of variant effects\", \"Mechanism by which variants impair neuronal migration not directly tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided cellular evidence that a disease variant predicted to disrupt the GCP2-GCP3 interaction perturbs gamma-tubulin localization and downstream cytoskeletal/adhesion/axon-guidance proteomes.\",\n      \"evidence\": \"Patient primary fibroblast immunofluorescence for gamma-tubulin and mass spectrometry proteomics\",\n      \"pmids\": [\"33458610\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single patient fibroblast study without direct validation of GCP2-GCP3 disruption\", \"Causality between proteome changes and the variant not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How specific human TUBGCP2 variants alter gamma-TuRC assembly, microtubule nucleation kinetics, and neuronal migration at the molecular level remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of variant effects on the human complex\", \"No in vitro reconstitution linking variants to nucleation defects\", \"No neuronal-migration assay directly testing patient mutations\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\"gamma-tubulin small complex (gamma-TuSC)\", \"gamma-tubulin ring complex (gamma-TuRC)\"],\n    \"partners\": [\"TUBG1\", \"TUBGCP3\", \"Tub4p\", \"Spc98p\", \"Spc110p\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}