TUBGCP6

TUBGCP6 (GCP6) is a core structural subunit of the human γ-tubulin ring complex (γ-TuRC) that scaffolds the microtubule-nucleating machinery at centrosomes (PMID:11694571). Within the γ-TuRC, GCP6 partners with GCP4 and GCP5 to form a salt-resistant sub-complex containing two copies of GCP4 and one each of GCP5 and GCP6; this sub-complex assembles independently of γ-tubulin small complexes (γTuSCs) and, when combined with γTuSC-containing extracts, reconstitutes nucleation-competent γ-TuRCs, with GCP6-specific sequence extensions contributing to ring assembly and stabilization (PMID:32317396). GCP6 is essential for centriole duplication: it localizes to the pericentriolar material and distal centrioles, is a direct substrate of the master centriole-duplication kinase Plk4, and its depletion blocks γ-TuRC assembly, depletes centrosomal γ-tubulin, reduces centriole number, and produces monopolar spindles (PMID:22302995). In polarized epithelial cells, GCP6 anchors γ-TuRC/MTOCs to keratin intermediate filaments through its C-terminal region, an interaction switched off by Cdk1-mediated phosphorylation at S1397, thereby positioning microtubule-nucleating activity at the apical domain (PMID:17182859). GCP6 protein levels are set post-transcriptionally by efficient splicing of its intron-rich pre-mRNA: the splicing factors WBP11 and the U2 snRNP component SF3B14 are required to prevent intron retention, and their loss collapses GCP6 levels and phenocopies centriole/spindle defects (PMID:31874114, PMID:34954520). Loss of tubgcp6 in zebrafish causes mitotic arrest, disorganized spindles, and p53-dependent apoptosis, driving hematopoietic stem/progenitor cell exhaustion (PMID:42092188).

1. 2001 High

   Established GCP6 as a genuine subunit of the microtubule-nucleating γ-TuRC, defining the molecular machine in which it acts rather than treating it as an orphan centrosomal protein.

   Evidence Purification of human γ-TuRC with mass-spectrometry subunit identification, in vitro microtubule nucleation assay, and immunolocalization

   PMID:11694571

   Open questions at the time

   • Stoichiometry and structural position of GCP6 within the ring not resolved
   • Functional contribution of GCP6 to nucleation versus structural scaffolding not separated
2. 2006 High

   Showed that GCP6 does more than scaffold nucleation—it physically tethers MTOCs to the cytoskeleton, explaining how nucleating activity is spatially positioned in polarized cells and how that positioning is cell-cycle regulated.

   Evidence Yeast two-hybrid, in vitro binding of purified GCP6 to keratins, shRNA knockdown in CACO-2 cells, and S1397D phosphomimetic mutagenesis

   PMID:17182859

   Open questions at the time

   • Whether the keratin interaction operates outside epithelial cell types unknown
   • Identity of the kinase driving S1397 phosphorylation in vivo beyond Cdk1 not established
3. 2012 High

   Placed GCP6 downstream of Plk4, linking γ-TuRC assembly directly to the centriole duplication program and demonstrating its requirement for bipolar spindle formation.

   Evidence siRNA depletion, co-immunoprecipitation with Plk4, in vitro Plk4 kinase assay, and centriole counting by immunofluorescence

   PMID:22302995

   Open questions at the time

   • Phosphosites on GCP6 targeted by Plk4 not mapped
   • Mechanistic link between GCP6 phosphorylation and centriole assembly not defined
4. 2019 High

   Revealed that GCP6 abundance is rate-limiting for centriole duplication and is controlled post-transcriptionally, identifying intron retention as a regulatory chokepoint for the protein.

   Evidence WBP11 siRNA/shRNA depletion, RNA-seq detection of TUBGCP6 intron retention, western blot, and centriole duplication assays

   PMID:31874114

   Open questions at the time

   • Why TUBGCP6 is especially sensitive to splicing efficiency not explained
   • Direct binding of WBP11 to TUBGCP6 pre-mRNA versus indirect effect not distinguished
5. 2020 High

   Defined the GCP4/GCP5/GCP6 salt-resistant sub-complex as an assembly-competent module and reconstituted functional γ-TuRC from it, clarifying GCP6's structural role in ring assembly.

   Evidence Biochemical fractionation, salt-resistance assay, in vitro γTuRC reconstitution from sub-complex plus cytoplasmic extracts, nucleation assay, and GCP6 truncation analysis

   PMID:32317396

   Open questions at the time

   • High-resolution structure of GCP6 within the assembled ring not determined
   • Precise function of GCP6 N-terminal extension and grip1–grip2 insertion not dissected
6. 2021 Medium

   Confirmed and extended the splicing-dependent control of GCP6 by implicating the U2 snRNP component SF3B14, reinforcing that spliceosome activity gates GCP6 protein levels and mitotic fidelity.

   Evidence RNAi depletion of SF3B14, RT-PCR of spliced vs unspliced TUBGCP6 mRNA, western blot, and mitotic phenotype imaging

   PMID:34954520

   Open questions at the time

   • Single-study, single-lab finding without reciprocal validation
   • Whether SF3B14 acts directly on TUBGCP6 introns or globally not resolved
7. 2026 Medium

   Connected GCP6 loss to an organ-level phenotype, showing that its requirement for spindle integrity governs stem-cell self-renewal versus differentiation during hematopoiesis.

   Evidence Zebrafish forward genetic screen, positional cloning of a tubgcp6 nonsense allele, time-lapse imaging, lineage tracing, and p53 epistasis

   PMID:42092188

   Open questions at the time

   • Whether the HSPC phenotype reflects centriole/γ-TuRC loss specifically versus general mitotic failure not isolated
   • Relevance to mammalian hematopoiesis not established

• How GCP6's distinct roles—γ-TuRC ring assembly, Plk4-dependent centriole duplication, and intermediate-filament anchoring—are coordinated within a single cell cycle remains unresolved.
• No structural model of GCP6 within the assembled γ-TuRC
• Plk4 phosphosites on GCP6 unmapped
• Integration of splicing-based abundance control with phosphoregulation not addressed