Loss of p53 confers clonogenic survival advantage to primary hematopoietic progenitor cells after cytokine deprivation. (A) Early hematopoietic progenitor cells were isolated from fetal livers of WT (p53^+/+), p53^+/−, or p53^−/− E14.5 embryonic mice (n indicates the numbers of embryos analyzed). The c-kit (CD117)–positive and Lineage (Lin)–negative cells were sorted with the use of FACS and cultured in the presence or absence of SCF or IL-3 or both. After 24 hours in culture, cell viability was analyzed as described in Figure 1A. The results shown are means ± SEMs of 4 independent experiments. (B) Cells from panel A were placed into soft agar containing IL-3 plus SCF, and their clonogenicity was determined by counting colonies after 14 days. The n refers to the numbers of embryos analyzed (the n of WT cells cultured in the presence of SCF and IL-3 was 2). The results shown are means ± SEMs of 4 independent experiments.