Normal thymocyte development in c-myc^+/– mice. (A) Thymus cellularity (mean ± SD; n = 5) is shown for wt and c-myc⁺/– mice. *P < .05. (B) Thymocytes from wt and c-myc⁺/– littermates were analyzed for expression of TCRαβ, TCRγδ, CD4, and CD8. The numbers shown represent the percentage of cells within each quadrant. (C) Subpopulations of DN thymocytes in wt and c-myc⁺/– littermates were analyzed for expression of CD44 and CD25 gated on lin^– cells (defined as negative for markers expressed by mature cells such as TCRαβ, TCRγδ, CD3, CD4, CD8, B220, NK1.1, CD11b, and Gr1). (D) Cell-cycle analysis of DN, DP, CD8SP, and CD4SP thymocytes from wt and c-myc⁺/– littermates was performed by Hoechst staining and FACS analysis. The numbers shown represent the mean percentage ± SD of cells in S-G₂-M phases. The results shown are representative of 2 experiments and 5 mice per group (4 months old) were analyzed in each experiment.