CFU-GM homing assay. Wild-type and G-CSFR^-/- (KO) bone marrow cells were mixed in a 1:1 ratio and injected intravenously into irradiated mice. Cells were recovered from the bone marrow 24 hours after transplantation, and the number of wild-type and KO CFU-GMs measured. The percentage of KO CFU-GMs is shown for 2 independent experiments (group 1, n = 4; group 2, n = 7). The pretransplantation percentage of KO CFU-GMs is shown above each column and is indicated by a single line. Data represent the mean ± SD.