Organ cellularity and numbers of retroviral construct–expressing cells in reconstituted mice. (A) The total number of cells per organ in mice reconstituted with fetal liver stem cells infected with FLAG-CrmA-GFP or GFP control retrovirus was quantified by preparing single-cell suspensions and counting cells in a hemocytometer. (B) The proportion of GFP-expressing cells in each organ was quantified by FACS analysis. (C) The total number of GFP⁺ granulocytes and monocytes in bone marrow (2 femurs and 2 tibias) of reconstituted mice was determined directly by FACS analysis. Data represent mean ± SD from organs of 3 mice of each type. ▪ indicates FLAG-CrmA/GFP; and ▦, GFP vector.