Analysis of Runx1 expression in thymic subsets. The filled and open curves indicate GFP expression in wild-type and Runx1-IRES-GFP^k/k cells, respectively. (A) Thymocytes from age- and sex-matched wild-type and Runx1-IRES-GFP^k/k mice were stained for CD4 and CD8. GFP expression in thymic subsets determined by flow cytometry using the gating strategy depicted in the dot plot. GFP expression in CD4^-CD8^-, CD4⁺CD8⁺, CD4⁺CD8^-, and CD4^-CD8⁺ thymocytes is shown in the accompanying histograms. The MFI of GFP expression of Runx1-IRES-GFP^k/k cells in each subset is indicated. (B) Expression of Runx1 in DN thymocyte subsets. Thymocytes were stained with CD25-PE and CD44-CyC and a cocktail of biotinylated antibodies for CD4, CD8, B220, GR-1, and Mac1; the latter were revealed by staining with SA-APC. Expression of GFP in DN subsets was determined by gating on APC^- CD44⁺CD25^-, CD44⁺CD25⁺, and CD44^-CD25⁺ cells. The MFI of GFP expression of Runx1-IRES-GFP^k/k cells in each subset is indicated.