Absence of Rac1 and Rac2 does not impair localization of DN thymocytes. Fluorescence images of thymic sections from mixed radiation chimeras reconstituted with bone marrow from either Rac1^+/+Rac2^+/+Rag1^−/−hCD2-iCre/hCD2-GFP (Rag1^−/−hCD2-GFP) or Rac1^flox/floxRac2^−/−Rag1^−/−hCD2-iCre/hCD2-GFP (Rac1^TRac2^−/−Rag1^−/−hCD2-GFP) mice and bone marrow from C57BL/6 mice. Two images are shown for each genotype. Sections were stained with anti-GFP (blue) to identify the DN2/3 thymocytes from the hCD2-GFP–containing strains, anti–pan-cytokeratin (red) to recognize cortical epithelial cells, and MTS10 (green) to identify medullary epithelial cells. Note that GFP⁺ cells are distributed throughout the cortex in both strains. Bar indicates 145 μm.