c-Myb^Plt4/Plt4 LSKs display reduced expression of lymphoid genes. (A) Heat map depicting expression of 27 lymphoid-specific genes that display altered expression in c-Myb^Plt4/Plt4 LSK samples (P < .1). (Left) Expression pattern of these genes in progenitor populations. Pre-GM indicates pre–granulocyte-macrophage progenitor; Mk progenitor, megakaryocyte progenitor; pre–CFU-E, erythroid progenitor pre–colony forming unit; pre-MegE, pre–megakaryocyte-erythroid progenitor. (Right) Expression pattern in c-Myb^+/+ and c-Myb^Plt4/Plt4 LSK samples. Red squares denote up-regulated genes, blue squares denote down-regulated genes, with scale denoting z score, ie, standard deviation from mean expression. (B) Flow cytometry of density-fractionated and lineage-depleted bone marrow of 6- to 9-week-old c-Myb^+/+ and c-Myb^Plt4/Plt4 mice. Upper plots display the proportion of Sca-1⁺c-kit^hi cells among lineage⁻ cells (mean ± SD of 5-6 mice per genotype). Lower plots display the percentage of CD34⁺Flt3⁺ cells within the LSK fraction. Plots are representative of 5 to 6 mice per genotype. (C) Flow cytometry of density-fractionated and lineage-depleted bone marrow of 5- to 7-week-old c-Myb^+/+ and c-Myb^Plt4/Plt4 mice on a Rag1^gfp/+ background. Early lymphoid progenitors were identified as CD27⁺ GFP⁺ cells within the LSK fraction, identified as in panel B. Numbers in plots indicate the proportion of cells in the gated area. Data are the mean ± SD of 6 to 8 mice per genotype. (D) Graph depicting the percentage of LMPPs within the LSK fraction of c-Myb^+/+ and c-Myb^Plt4/Plt4 bone marrow. *P < .05 in test group vs c-Myb^+/+ cells. Data represent the mean ± SEM of 5 to 6 mice per genotype.