BM transplantation experiments. (A-C) Competitive repopulation of Msi2-defective BM cells. Lethally irradiated congenic (CD45.1/2) mice were reconstituted with different ratios of CD45.2⁺ donor BM cells from either Msi2^Gt/Gt or Msi2^+/+ (B6) origin with CD45.1 (B6/SJL) competitor BM cells. Mixtures were transplanted and reconstitution monitored by quantifying the percentage of donor-derived CD45.2⁺ nucleated blood cells in recipients at different times thereafter. Shown are the kinetics of reconstitution of donor-type leukocytes in the peripheral blood (total number of CD45.2⁺ cells), B cells (B220 antigen), T cells (CD4/CD8 antigens), and myeloid cells (Mac-1/Gr-1 antigens). Shown are 1:1 mixtures of WT donor with competitor cells (squares), 1:1 Msi2 donor with competitor cells (circles), and 7:3 Msi2 donor with competitor cells (triangles). At 24 weeks mice were killed and the contribution of CD45.2 cells to the total BM (B) and LSK (C) population was determined. The data are from 2 independent experiments with 3-4 recipient mice per group. (D-G) Noncompetitive BM transplantation. 10⁷ total BM cells were transplanted into lethally irradiated congenic recipients (CD45.1/2). The percentage of donor-derived cells among total blood leukocytes was determined by flow cytometry. (D) Total leukocyte counts were determined at 8, 16, and 20 weeks after transplantation. Mice were killed 20 weeks after transplantation and BM cells were analyzed. (E) FACS plots are shown for LSKs. (F-G) Histogram showing the total numbers of LSK CD34⁻ (HSCs) and LSK CD34⁺ (progenitors) in the transplanted animals. Data shown are from 1 experiment with 4 recipient mice per group. Error bars indicate SEM. *P < .05; **P < .005.