TADA2B

TADA2B is a subunit of the chromatin-modifying SAGA complex that links histone modification to stem cell maintenance, lineage commitment, and genome stability (PMID:34711655, PMID:41577693). Within SAGA's histone acetyltransferase module, TADA2B supports deposition of histone H3 lysine 9 acetylation (H3K9ac) and influences H2B ubiquitination (H2Bub) enrichment; in hematopoietic stem and progenitor cells, its loss reduces H3K9ac, alters H2Bub, blocks hematopoiesis with accumulation of immature bone marrow cells, lowers mitochondrial activity, skews toward megakaryocyte progenitor commitment, and activates interferon pathway gene expression (PMID:41577693). Beyond its chromatin role, TADA2B constitutively binds the DNA single-strand break repair scaffold XRCC1 through its BRCT II domain, independent of DNA damage status and of GCN5 acetyltransferase activity, and TADA2B depletion impairs XRCC1 recruitment to damage sites; an SCAR26-associated XRCC1 variant selectively disrupts this TADA2B interaction while preserving LIG3 binding [PMID:bio_10.1101_2025.08.24.672030]. In human embryonic stem cells, TADA2B is a central regulator of pluripotency maintenance, survival, growth, and three-germ-layer lineage specification (PMID:34711655).

1. 2021 Medium

   Establishing whether TADA2B has a defined cellular requirement, genome-scale CRISPR screening showed it is a central regulator of pluripotency, survival, growth, and lineage specification, placing this SAGA subunit at the core of stem cell fate decisions.

   Evidence Genome-scale CRISPR knockout and gain-of-function screens in human embryonic stem cells with proliferation, differentiation, and apoptosis readouts

   PMID:34711655

   Open questions at the time

   • Does not resolve which chromatin marks or target genes mediate the pluripotency phenotype
   • No mechanistic dissection of TADA2B's contribution distinct from other SAGA subunits
2. 2025 Medium

   Addressing whether TADA2B has a function beyond transcription-linked chromatin, domain-mapped binding assays showed it constitutively binds the repair scaffold XRCC1 via the BRCT II domain and is needed for efficient XRCC1 recruitment to damage, defining a pre-organized link between SAGA and single-strand break repair.

   Evidence Co-IP/pulldown with BRCT domain mapping, siRNA depletion with quantification of XRCC1 damage-foci recruitment, and SCAR26 variant analysis (preprint)

   PMID:bio_10.1101_2025.08.24.672030

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Whether the interaction requires the intact SAGA complex or TADA2B alone is unresolved
   • Functional consequence of disrupted recruitment for repair efficiency and disease not directly tested
3. 2025 Low

   Probing TADA2B's broader interaction landscape, proximity proteomics placed it near HMGB1 in monocytes with the association changing upon TLR4 activation, hinting at a stress-responsive context though without functional follow-up.

   Evidence BioID proximity proteomics in resting versus LPS-stressed THP-1 cells with proximity ligation confirmation

   PMID:41161382

   Open questions at the time

   • Proximity association without functional validation specific to TADA2B
   • No demonstration of direct binding or biological consequence
4. 2026 High

   Connecting TADA2B's chromatin activity to a physiological output, in vivo CRISPR knockout showed its loss reduces H3K9ac and alters H2Bub in hematopoietic stem/progenitor cells, blocking hematopoiesis and activating interferon genes, establishing it as required for normal blood cell production through SAGA acetyltransferase/deubiquitinase activities.

   Evidence Genome-wide in vivo CRISPR KO screen in HSPCs with H3K9ac/H2Bub chromatin analysis and transcriptomic profiling

   PMID:41577693

   Open questions at the time

   • Direct catalytic role of TADA2B in deubiquitination versus indirect effect not separated
   • Mechanism linking chromatin changes to interferon gene upregulation unresolved
   • Relationship between hematopoietic and DNA-repair functions not addressed

• How TADA2B's SAGA-dependent chromatin role and its XRCC1-anchored DNA-repair role are mechanistically integrated, and whether they share a structural basis, remains unresolved.
• No structural model of TADA2B within SAGA or bound to XRCC1
• Whether chromatin and repair functions are coupled or independent is unknown