HBO1 is required for the repopulating ability of HSCs. (A-E) Two million bone marrow donor cells from Hbo1^fl/+;CreER or Hbo1^fl/fl;CreER mice (CD45.2⁺; n = 4 animals per genotype) were collected 1 week after the first dose of tamoxifen and transplanted with 0.5 million WT competitor cells (CD45.1⁺) into 3 lethally irradiated C57BL/6 congenic recipients (CD45.1⁺, 2 doses of 5.5 Gy separated by 3 hours). (A) Experimental design and timeline. (B) Percentage contribution of CD45.2+ donor cells to peripheral white blood cells over time after transplantation assessed by flow cytometry. (C) Representative FACS plots indicating contribution of competitor cells (CD45.1⁺) and donor cells (CD45.2⁺) in peripheral blood 16 weeks after bone marrow transplantation. (D-E) Representative FACS plots and enumeration of the contributions of competitor and donor cells in the HSPC compartments of the bone marrow. Percentages of parental gate are indicated on the FACS plots. Data are displayed as mean ± SEM and were analyzed using a 2-tailed Student t test. The same experiment but using the Mx1-Cre to delete Hbo1 is displayed in supplemental Figure 4.