Quantification of CFU-GMs and cell cycle analysis. (A) Bone marrow cells harvested from individual WT (n = 3), KO (n = 3), and 9:1 (KO/WT) chimeric (n = 8) mice were plated in methylcellulose with (solid bars) and without (dotted bars) G418 (1 mg/mL) and cultured in conditions supporting the growth of CFU-GMs. The number of colonies is reported per mouse femur. Cultures of wild-type and KO cells served as controls to confirm the ability of G418 to selectively inhibit the growth of wild-type colonies. (B) The number of CFU-GMs in S-phase from 9:1 KO/WT chimeric mice (n = 6) was determined by means of an H³-thymidine suicide assay. Selective growth in G418 was used to discriminate between WT and KO CFU-GMs. Data represent the mean ± SD.