Alteration in DN subsets and in CD25 and CD44 expression in thymuses of Cdk6 mutant mice. (A) Flow cytometric analysis of CD44/CD25 expressing thymocytes from 2-month-old mice. The cells were stained with the “cocktail” of lineage-specific antibodies and CD44 and CD25 antibodies. Lineage-positive cells were electronically “gated out,” and CD44-versus-CD25 profiles of the lineage-negative compartments are presented. Numbers in quadrants indicate the percentage of cells in each subset. (B) Quantification of DN1–4 cells. The bar graph summarizes the percentage of DN1–4 populations from separate experiments. Data are mean ± SE. *P < .05, significantly different from the control levels, which were arbitrarily defined as 1 unit (100%). (See supplemental Table 2 for the animal numbers used.) (C) Flow cytometric analysis of CD25 expression in DN thymocytes. (D) Flow cytometric analysis of CD44 expression in DN thymocytes from WT and KO, and from WT-Δ and K43M, R31C, and DM. (Right) Flow cytometric analysis of CD44 expression in CD4⁺, DP, and CD8⁺ subsets from R31C thymocytes.