Bone marrow from TgE Notch1^lox/lox CD19^+/Cre mice forms more colonies in methylcellulose than TgE Notch1^lox/lox mice. Bone marrow cells were plated in methylcellulose with IL-7. After 7 days, the numbers of colonies in 1 cm² were counted in triplicate wells for each genotype. (A) Representative images of colonies formed from bone marrow cells for each genotype. Methylcellulose cultures were viewed with a Nikon SMZ1000 stereomicroscope with an HR Plan Apo 1× WD54 objective (Nikon Instruments, Melville, NY). Images were acquired using a Polaroid Digital Camera model PDM02 and DMC le version V1.25 software (Polaroid, Concord MA) and processed using Adobe Photoshop version 7.0 software (Adobe Systems, San Jose, CA). (B) The number of colonies in 1 cm² of the culture dish was counted in triplicate for each genotype and the average number of colonies for 3 independent experiments is shown plus or minus SE. *P = .001, **P = .03 by t test. (C) Cells from methylcellulose cultures were stained with B220 and CD43 antibodies and analyzed by flow cytometry. The live cell population, designated by forward and side scatter properties, was gated to examine expression of B220 and CD43. A representative plot for each genotype is shown with percentages for each population. Typically, the majority of cells are B220⁺CD43⁺ B cells.