Hematopoietic progenitor assays. Bone marrow cells from wild-type (WT) or G-CSFR^-/- (KO) mice were plated in methylcellulose-containing media supplemented with the appropriate cytokines for each progenitor type (“Materials and methods”). Hematopoietic colonies containing more than 30 cells were counted after 7 to 10 days and reported as the number of colonies per mouse femur. Data represent the mean ± SD (n = 6 mice minimum, each). Relevant P values are shown.