Iex-1 is necessary and sufficient for TPO-mediated DSB repair in HSPCs. (A) Percentage of γH2AX-positive LSK cells isolated from nontreated WT and Iex-1^−/− mice. Data are means + SEM (n = 3). (B) Kinetics of γH2AX foci resolution after IR (2 Gy) of WT and Iex-1^−/− LSK cells cultured in complete medium (Comp) or without TPO. (C) WT LSK cells were infected with lentiviruses expressing GFP only or GFP with Iex-1-WT or Iex-1-ΔFTF and treated as in (B). For (B) and (C), the results represent means + SEM of 3 independent experiments performed with pools of 5 to 10 mice. (D) WT and Iex-1^−/− mice were treated with TPO (8 µg/kg) or phosphate-buffered saline 30 minutes before TBI (2 Gy). γH2AX staining in LSK-CD34⁻ cells isolated 16 hours after TBI. (E-F) γH2AX foci (E) and comet tail resolution (F) after IR of WT and Mpl^−/− LSK cells infected as in (C) and cultured in the presence of TPO complete medium. Means + SEM are shown. (E) n = 4. (F) Data are means + SEM of tail moment values analyzed in at least 35 cells.