Loss of Notch1 expression in TgE mice results in increased IgM⁺ B cells in the bone marrow. Total cells isolated from the bone marrow of each indicated genotype were stained with B220 and IgM-conjugated antibodies and analyzed by flow cytometry. Live cell populations, designated by forward and side scatter properties, were plotted with IgM and B220, and a representative plot for each genotype is shown (A). (B) The average percentage of B220⁺ cells in the bone marrow for each genotype is indicated plus or minus SE. (C) The average percentage of B cells expressing IgM in the bone marrow from 4 independent experiments is shown. Data are represented as the percentage of B220⁺ cells that express IgM (%B220) as well as the percentage of total bone marrow that is B220⁺IgM⁺ (percentage of total). *P = .04, **P = .03 by t test. Notch1^lox/lox, n = 4 mice; Notch1^lox/lox CD19^+/Cre, n = 4; TgE Notch1^lox/lox, n = 4; TgE Notch1^lox/lox CD19^+/Cre, n = 6.