Increased Notch-regulated transcripts in the absence of Rac1 and Rac2 and Vav-family GEFs. (A) Graphs show mean (± SEM) mRNA expression of Notch1, Notch3, Hes1, Deltex1, and preTα in DN3 and DN4 thymocytes from WT and Rac1^TRac2^−/− mice. Expression of targets is relative to Hprt1 expression in the same samples. (B) Histograms showing expression of intracellular TCRβ (icTCRβ) in DN3 and DN4 thymocytes from WT or Vav1/Vav2/Vav3^−/− mice. Markers indicate cells positive for icTCRβ. Numbers indicate percentage of cells falling into the markers. (C) Graph showing mean (± SEM) number of icTCRβ⁻ DN4 thymocytes in mice of the indicated genotypes. (D) Graphs show mean (± SEM) mRNA expression of Notch1, Notch3, Hes1, and Deltex1 in DN3 and DN4 thymocytes from WT and Vav1/Vav2/Vav3^−/− mice. Colors of bars as in panel C. Expression of targets is relative to Hprt1 expression in the same samples. Statistically significant differences between Rac1^TRac2^−/− or Vav1/Vav2/Vav3^−/− mice and WT mice are indicated (*P < .005; **P < .0005; ***P < .0001).