Regulation of B cell developmental genes. (A) Ebf1 and Pax5 expression in progenitor B cells from LMC and Stat5b-CA mice and B220⁺, CD19⁺ leukemic cells from lymph nodes of Stat5b-CA x Ebf1^+/− and Stat5b-CA x Pax5^+/− mice were measured by real-time RT-PCR. Blue bars represent expression of Ebf1 and red bars represent expression of Pax5. Each bar is representative of at least three mice from independent experiments. Error bars represent the SEM. (B) Intracellular flow cytometric analysis of PAX5 expression in B220^Int bone marrow cells from Stat5b-CA nonleukemic mice, Ebf1^+/− nonleukemic mice, Stat5b-CA x Ebf1^+/− preleukemic mice, and lymph node cells from Stat5b-CA x Ebf1^+/− leukemic mice. LMC B220 negative cells (PAX5⁻) and LMC B220^Int B cells (PAX5⁺) are controls. All gates shown are based on bone marrow isolated from control C57BL/6 mice. Doublets were gated out and a lymphocyte gate was set based on side and forward scatter properties. Flow plots are representative of three independent experiments for all but the leukemic cells (n = 2). (C) Semiquantitative PCR of CD79a, Blnk, and Gapdh. Serial dilutions were done at 1:5. This figure is representative of three independent experiments representing at least one mouse per experiment. Molecular weights are indicated (base pairs). Flow cytometric analysis of CD19 expression on bone marrow cells from Stat5b-CA nonleukemic mice, Ebf1^+/− nonleukemic mice, Stat5b-CA x Ebf1^+/− preleukemic mice, and lymph nodes cells from Stat5b-CA x Ebf1^+/− leukemic mice. The controls and gates are as in panel B. Flow plots are representative of at least three independent experiments.