Progressive decline in c-Kit⁺Lin^- progenitor cells in PU.1^-/- embryos. (A) Representative FACS analysis of wild-type and PU.1 knockout embryos between e12.5 and e15.5. The number of embryos representing each genotype is indicated in the legend of Figure 1. Numbers in each plot indicate the percentage of cells within the gated populations. (B) Differences in c-Kit⁺Lin^- cells between +/+ and -/- embryos were statistically significant (P < .05) at all days indicated. (C) Reduction in the total fetal liver cellularity in PU.1^-/- embryos. The number of embryos representing each genotype is indicated in the legend of Figure 1. Error bars indicate SEM.