Hematopoietic colony size was reduced in 7-day CFC and 21-day HPP-CFC colonies established from livers of neonatal PU.1 null mice. Individual colonies were aspirated and counted from plates established in triplicate at 5,000 input cells per plate (see Table 2). Results are presented as the mean ± SD of the number of cells per colony. Note that the average PU.1 deficient CFC colony size (▪) at 7 to 10 days was approximately sixfold reduced compared to control (▨) littermates (A). PU.1 deficient HPP-CFC (▪) were reduced in size 3.5-fold compared with control (▨) littermates (B). Colony size = number of cells per colony. These colony sizes were obtained from CFC and HPP-CFC shown in experiment 2, Table 2, and are representative of colony sizes from other experiments.