Loss of Rac2 GTPase increases survival of Scl/p210;Rac2^−/− mice by impairing the LSC/P pool size in vivo. (A) Cumulative survival using the Kaplan-Meier log-rank P test performed among Non-Tg, Scl/p210, and Scl/p210;Rac2^−/− mice (n = 14-22 mice per group). (B-C) Content of (B) Lin⁻Sca1⁻c-kit⁺ (LK) and of (C) Lin⁻Sca1⁺c-kit⁺ (LSK) cells in Non-Tg, Non-Tg;Rac2^−/−, Scl/p210 and Scl/p210;Rac2^−/− spleens. Data represent mean ± SD (n = 8 mice per group). (D) Apoptosis of Non-Tg, Non-Tg;Rac2^−/−, Scl/p210 and Scl/p210;Rac2^−/− hematopoietic progenitors in vivo. Data (normalized with respect to Non-Tg control; mean ± SEM) represent the average of 2 independent experiments including a minimum of 8 mice per group. (E-F) Proliferation of (E) LK and of (F) LSK cells in Non-Tg, Non-Tg;Rac2^−/−, Scl/p210 and Scl/p210;Rac2^−/− spleens in vivo. Proliferation was determined by measuring the uptake of BrdU in vivo. Data (mean ± SD) represent 1 of 3 independent experiments with identical results (n = 4 mice per group). *P < .05 and **P < .005 between the respective groups.