Impaired B-cell development in embryos lacking Sp3. (A) Numbers of total cells and B220⁺ cells in E18.5 liver of the indicated embryos, as determined by flow cytometry. (B) Flow cytometric analyses of the liver and spleen of the individual embryos. Single-cell supsensions were stained with B220 and IgM. Results are displayed as dot plots of lymphocyte gate cells; percentages of cells within the indicated gates are given. (C) Developmental progression of B-lineage cells in vitro. Total BM cells were cultured in the presence of IL-7 for 5 days, and recultured on S17 stromal cells in the absence of IL-7 to induce the formation of mature IgM⁺IgD⁺ B cells. Cultured cells were stained for B220, IgM, and IgD. Results are displayed as B220 versus IgD dot plots. Data shown are from 4 to 15 embryos examined in each group.