Hdac8-deficient LT-HSCs are hypersensitive to p53-mediated apoptosis induced by genotoxic stress. (A) Schematic of experimental design. Hdac8^f/f(y) (control [Ctrl]), Mx1-Cre/Hdac8^f/f(y) (Hdac8^Δ/Δ), or Mx1-Cre/Hdac8^f/f(y)/p53ER^KI/KI (Hdac8^Δ/Δ/p53ER^KI/KI) mice (2 months old) were induced by 7 doses of poly (I:C). Two weeks after induction, phenotypic LT-HSC, ST-HSC, MPP, and MP populations were sorted from BM and underwent irradiation (IR; 3 Gy). Gene expression was analyzed at 24 hours and apoptosis was assessed at 48 hours after exposure to radiation. (B) Representative FACS plots of annexin V/DAPI staining in sorted Ctrl, Hdac8^Δ/Δ, or Hdac8^Δ/Δ/p53ER^KI/KI LT-HSCs with or without IR. (C) Frequency of annexin V⁺ cells in LT-HSC and MPP populations from Ctrl (n = 4), Hdac8^Δ/Δ (n = 5), or Hdac8^Δ/Δ/p53ER^KI/KI (n = 3) with or without IR. (D) Relative expression levels of Puma, Noxa, and Cdkn1a assessed by quantitative reverse transcription polymerase chain reaction in Ctrl (n = 4), Hdac8^Δ/Δ (n = 5), or Hdac8^Δ/Δ/p53ER^KI/KI (n = 3) LT-HSCs with or without IR. (E) Frequency of annexin V⁺ cells in the LT-HSC and MPP compartments of Ctrl (n = 6), Hdac8^Δ/Δ (n = 6), Hdac8^Δ/Δ/p53ER^KI/+ (n = 7), or Hdac8^Δ/Δ/p53ER^KI/KI (n = 3) mice 6 hours after whole-body IR (3 Gy). (F) Frequency of activated caspase 3⁺ cells in the LT-HSC and MPP compartment in Ctrl (n = 6), Hdac8^Δ/Δ (n = 6), Hdac8^Δ/Δ/p53ER^KI/+ (n = 7), or Hdac8^Δ/Δ/p53ER^KI/KI (n = 3) mice 6 hours after whole-body IR (3 Gy) assessed by intracellular staining followed by flow cytometry. Mean ± SEM is shown. *P < .05, **P < .01, ***P < .001.