The Mcl-1 transgene enhances hematopoietic capacity in the bone marrow although peripheral blood pools remain unaltered. (A) Bone marrow cells from nontransgenic (Non-Tr.) and transgenic (Tr.) mice were plated into methylcellulose medium containing factors supporting the growth of either myeloid and erythroid precursors (left set of bars) or B lymphoid precursors (right set of bars). The plating density was 1.5 × 10⁴ cells/35-mm dish for assay of myeloid/erythroid colonies and 4 × 10⁴ cells/35-mm dish for assay of B lymphoid colonies. Colonies were counted after 7 days. The values shown represent the mean ± SD of three independent experiments using four transgenic and three control mice (P < .05 by Student’s t-test). GM, colonies containing myeloid (granulocyte-macrophage) cells; E, colonies containing erythroid cells; GEMM, colonies containing both myeloid and erythroid cells. (B) The bone marrow cells assayed in (A) were cultured in standard medium (containing 10% FBS only) for 24 hours before plating into growth factor–containing methylcellulose medium. The fraction of colony-forming cells remaining on day 1 was calculated by comparison with the number of present on day 0. The significance between nontransgenic and transgenic animals, as determined by Student’st-test, was P < .05 for both GM and lymphoid colonies. (C) Bone marrow from transgenic and nontransgenic mice (10- to 12-weeks-old) was assayed by flow cytometry for the B220 and CD11b cell-surface markers. The total number of cells recovered from the bone marrow averaged 1.5 ± 0.3 (SD) × 10⁷ cells for nontransgenic mice and 1.3 ± 0.1 × 10⁷ cells for the transgenic mice. Bars represent the SE of three animals. The CD11b⁺/B220⁺ ratio is listed on the figure. The significance of the difference in this ratio in nontransgenic as compared with transgenic animals, as assessed by analysis of variance with the Scheffé test, which indicated a P value of <.01. (D) The bone marrow cells assayed in (C) were also assayed for the MP20 and MP12 markers. The percentage of MP20⁺MP12⁺ double-positive cells averaged 11% ± 0.5% (SD) in nontransgenic and 14% ± 2% in transgenic mice. The MP20⁺/MP12⁺ ratio is listed on the figure. The significance of the difference in this ratio in nontransgenic as compared with transgenic animals, as assessed by analysis of variance with the Scheffé test, which indicated aP value of <.05.