Characterization of CFU-derived early PU.1−/− myeloid cells. Normal and PU.1−/− neonate liver cells were grown in methylcellulose CFU plates for 7 days with 50 ng/mL stem cell factor (SCF), 100 U/mL IL-3, 2.5 ng/mL GM-CSF, and 5,000 U/mL M-CSF. (A) Individual PU.1−/− myeloid colonies were harvested and stained with Wright-Giemsa stain. −/− in the upper right-hand corner of the panels indicates PU.1 null colonies. A normal macrophage colony is shown in the lower right-hand panel. (B) Pooled normal or PU.1−/− colonies were examined for NSE activity using -naphthyl acetate as the substrate. The dark staining cells show an NSE-positive reaction. (C) Pooled normal and PU.1−/− colonies were tested for Moma-2 expression. Biotinylated secondary antibody and avidin peroxidase were used to identify Moma-2–expressing cells. Purple staining cells indicate Moma-2 expression. Moma-2 negative neutrophils (N) are indicated in the normal panel.