Hbo1 deletion causes hematopoietic failure and death. (A) PCR genotyping (wild-type [WT] Hbo1 allele product 190 bases; floxed Hbo1 allele 283 bases; deleted Hbo1 allele 358 bases²⁴) showing Rosa26-CreERT2 (CreER)-mediated Hbo1 deletion in bone marrow from Hbo1^fl/+;CreER and Hbo1^fl/fl;CreER mice (n = 7 animals per genotype) treated 3× with tamoxifen (150 mg/kg body weight [BW] per dose, doses 48 hours apart). Samples were collected from 1 pair of age- and gender-matched Hbo1^fl/+;CreER and Hbo1^fl/fl;CreER mice when each Hbo1^fl/fl;CreER mouse reached the ethical endpoint. (B) Kaplan-Meier survival curve after CreER-mediated Hbo1 deletion; representative sections from n = 7 animals per genotype examined. (C) Hematoxylin- and eosin-stained sternum sections displaying the bone marrow (n = 7 animals per genotype). (D) Peripheral blood analysis results (n = 7 animals per genotype). (E) Representative FACS plots of LSK cells and HSC^SLAM, MPP^SLAM, and progenitor cells in the bone marrow of Hbo1^fl/+;CreER and Hbo1^fl/fl;CreER mice (n = 7 animals per genotype); percentage of viable cells indicated. Data are displayed as mean ± standard error of the mean (SEM) and were analyzed using a 2-tailed Student t test. Detailed flow cytometry gating strategies are displayed in supplemental Figure 1. HCT, hematocrit; HGB, hemoglobin; RBC, red blood cell count; WBC, white blood cell count.