Deletion of Rac1 or Rac1/Rac2 in HSCs affects T-cell development and survival in thymus. (A) Thymic cellularity of Mx-Cre–targeted mice was determined in the indicated genotypes. Single-cell suspensions were prepared from freshly isolated thymus for quantification. (B) The numbers of T-cell subpopulations in thymocytes were determined by anti-CD4, -CD8, -CD44, and -CD25 staining and FACS analysis. (C) The numbers of DN thymocyte subpopulations were determined using additional anti-CD44 and anti-CD25 antibodies and subsequent FACS analysis. (D) The apoptotic cells in thymic T-cell subpopulations were determined by anti-CD4 and -CD8 and annexin V staining followed by flow cytometry. The results are representative of 2 experiments. n = 5 for each genotype. *P < .05; **P < .01. Error bars represent SD.