Phenotypically defined HSCs and progenitors. (A) Representative flow cytometric dot-plots of c-kit, sca1, and CD34 surface marker expression, along with cell size, in the Lin⁻ BM compartment of STAT3^−/− and WT littermate mice at 5-6 weeks of age. See Figure 3 for details of the defined subpopulations. Isotype control Abs were used to established positive/negative quadrants and gates for lineage markers, lin cocktail, c-kit, sca1, and CD34 expression, as described previously.²¹  Histo-12 gate (in red histograms) represents cells with negative CD34 expression. (B) Comparative analysis of subpopulations of cells in the Lin⁻ BM compartment from 4 WT/STAT3^−/− mouse pairs. Data in panel B are expressed as means ± 1 SD.