Targeting within hematopoietic progenitor subsets. (A) Diagram of the hierarchical structure of early hematopoietic progenitor populations and the combination of surface markers used for their identification. HSC-SCL-Cre-ER^T;R26R-EYFP mice and controls were injected with tamoxifen for 2 weeks (2 mg per day), and bone marrow analysis was carried out 2.5 weeks after the last tamoxifen injection. The percentages of EYFP-positive cells within (B) the c-kit⁺lineage^–/low (KL) (SD ± 3.0%), (C) the c-kit⁺Sca-1⁺lineage^–/low (KSL) (SD ± 3.9%), and (D) the c-kit⁺Sca-1⁺lineage^–Flk-2^– (KSLF) (SD ± 9.7%) populations were determined by flow cytometry. The highest degree of Cre-mediated recombination was detected within the c-kit⁺Sca-1⁺lineage^–Flk-2^– population and was significantly lower in the c-kit⁺Sca-1⁺ lineage^–/low and c-kit⁺lin^–/low populations, respectively. Representative plots are shown for each population and the indicated percentages represent means (n = 5). Dashed lines represent negative controls. OPP, oligopotent progenitors; LCP, lineage-committed progenitors; lin, lineage; PI, propidium iodide.