Number of CFU-Mk in the hematopoietic tissues of p45 NF-E2 mutant and control mice. Cells isolated from the fetal liver (A) or adult spleen (B and C) of wild-type (+/+), heterozygote (+/−), and p45 NF-E2 mutant homozygote (−/−) mice were cultured as described, and CFU-Mk were scored at 7 days. N = 7 and 8 for control and knockout spleens; 21 and 13 for control and knockout fetal livers, respectively. Data are presented as the number of colonies per 10⁵ (A) or 10⁶ cells (B) or total number of colonies per spleen (C). The modest reduction in CFU-Mk in p45 NF-E2^−/− cultures shown in (A) and (B) were statistically significant, with P = .002 andP < .001, respectively; all other comparisons failed to achieve statistical significance using the Student’s t-test. In experiments for which a distinction was not made between +/+ and +/− (nonmutant) mice, these genotypes are collectively designated as +/?.