Cell-surface FLT3 expression in hematopoietic stem and progenitor cell subsets. (A) FACS profiles from a representative mouse showing gating strategy for cell-surface FLT3 expression within LSKCD48⁺CD150⁻, LSKCD48⁺CD150⁺, and LSKCD48⁻CD150⁺ BM cells. Numbers indicate mean percentages of FLT3⁺ cells within each of the indicated gates, from 2 pools of BM cells, each from 3 mice. (B) Flt3 mRNA expression of single BM LSK subpopulations. Only cells that were Kit⁺ were included in analysis (86%-94% of all cells investigated). Data are expressed as mean (SD). For each population, a total of 176 cells were analyzed in 2 experiments. (C) Expression of different lineage programs in Flt3⁺ and Flt3⁻ subsets of BM LSK populations. Cells were purified according to the indicated phenotypes and analyzed for expression of transcriptional programs for the GM (Csf3r, Mpo), MkE (Epor, Gata1, Vwf), and lymphoid (Ly; sterile Igh transcript, Rag1, Il7r) lineages. For a population to be classified as positive for a lineage-specific transcriptional program, transcripts of at least one of the aforementioned indicated lineage-specific genes should be detected. Mean (SD) results from 2 independent experiments with 88 single cells analyzed in each experiment. (D) Sorting strategy and purity analysis of LSKFLT3⁻, LSKFLT3^lo, LSKFLT3^int, and LSKFLT3^hi cells isolated from 8- to 12-week-old WT mice. BM LSK cells were as indicated separated into 4 fractions on the basis of differential FLT3 expression. To the right is shown purity analysis for each of the fractions. (E) Mk potential of LSK cells separated on the basis of level of FLT3 expression. A total of 120 cells were plated of each cell population in each experiment. Mean (SD) results from 2 experiments. (F) Erythroid potential of LSK cells separated on the basis of levels of FLT3 expression. A total of 50 cells were plated of each cell population in 2 replicates in each experiment. Mean (SEM) results from 2 experiments.