Pre-leukemic Moz^+/−; Eμ-Myc^T/+ mice have reduced numbers of B-cell progenitors compared with Moz^+/+; Eμ-Myc^T/+ controls. (A) Spleen weights in mice relative to overall body weight. (B) Femoral BM cellularity (nucleated cells only). (C) Outline of B-cell development. HSCs differentiate via multipotent progenitors to form CLPs. CLPs differentiate in a stepwise manner through pre-pro B cells, pro–B-cells, pre–B-cells, immature B cells, and eventually into mature B cells. The different cell types can be detected based on the expression of specific cell surface markers (supplemental Table 8). (D) Numbers of B-cell progenitors in the BM. (E) Numbers of B-cell progenitors and mature B cells in the spleen. (F) Quantification of major peripheral blood lineages. Data above are presented as mean ± SEM. Mice were 3- to 4-weeks old. Asterisks indicate a statistically significant difference between Moz^+/− and WT, or between Moz^+/−; Eμ-Myc^T/+ and Moz^+/+; Eμ-Myc^T/+ mice at *P < .05, **P < .01, and ***P < .001. T1/T2, transitory 1/2 B cells.