Hierarchical relationship and Hoechst efflux capacities of ST- and LT-HSCs. (A) A total of 1000 CD45.2 LSKCD34⁺flt3^– (left) or LSKCD34⁺flt3⁺ (right) cells were injected into lethally irradiated CD45.1 recipients, and 14 days later the BM of recipients was evaluated for regeneration of CD45.2 cells with LSKflt3^– and LSKflt3⁺ phenotypes. Figure depicts BM analysis of one representative recipient of each cell population. Results are from 1 of 2 experiments with 3 recipients receiving LSKCD34⁺flt3⁺ cells and 4 recipients receiving LSKCD34⁺flt3^– cells. (B) Lineage-depleted BM cells were stained with Hoechst and antibodies against Sca1, c-kit, CD34, and flt3. Cells were gated as LSKCD34^–flt3^–, LSKCD34⁺flt3^–, and LSKCD34⁺flt3⁺ as indicated, and dual wavelength Hoechst fluorescence investigated for each population. Plots are from 1 representative experiment of 3. Left panel shows Hoechst profile of unfractionated BM cells.