Loss of Sos1 alleviates MPN phenotypes and prolongs the survival of oncogenic Kras mice in the Vav-Cre system. (A-C) Control (C), Sos1^fl/fl;Vav-Cre (Sos1^−/−), Kras^{LSL G12D/+};Vav-Cre (Kras), and Kras^{LSL G12D/+};Sos1^fl/fl;Vav-Cre (Kras; Sos1^−/−) mice were sacrificed at age 6 weeks. (A) Numbers of WBC (white blood cells) and PLT (platelets) were shown. (B) Quantification of spleen weight. (C) Representative histologic hematoxylin and eosin sections of spleen from Control, Sos1^−/−, Kras, and Kras;Sos1^−/− mice. (D-E) Kras and Kras;Sos1^−/− mice were monitored closely until a moribund stage for terminal analysis. (D) Kaplan-Meier survival curves of different groups of mice were plotted against days after birth. P values were determined using the Log-rank test. (E) Quantification of disease incidence. χ-square analysis was performed. ns, not significant. (F-G) Moribund Kras and Kras;Sos1^−/− mice and age-matched control (C) and Sos1^−/− mice were sacrificed for analysis. (F) Genomic DNAs were extracted from tail and BM cells and genotyped for Sos1 alleles. (G) Western blot analysis of Sos1 expression in BM cells. The results are presented as mean ± standard deviation. *P < .05; **P < .01; ***P < .001.