Notch-stimulated Gata3^−/− hematopoietic progenitors fail to generate T cells. (A) Flow cytometric analyses were performed on the thymus of chimeras generated by the injection of CD45.2⁺Gata3^+/− and Gata3^−/− fetal liver cells into sublethally irradiated CD45.1⁺Rag2^−/−Il2rg^−/− recipients. Animals were analyzed 4 weeks after transplantation. All plots are gated on live lymphocytes. (B) Gata3^+/− and Gata3^−/− fetal liver cells were cultured on OP9 stromal cells expressing the Notch-ligand Dll1 (OP9Δ1) or Dll4 (OP9Δ4) in the presence of IL-7 and Flt3L for 2 weeks. Plots show the expression of the indicated surface markers on live CD45.2⁺ lymphocytes. (C) Retroviral transduction of Lin^-CD117⁺ precursors from 2-week Gata3^−/− OP9Δ1 cultures with pMXI-GFP or pMXI-GATA3-GFP retroviral particles. Two weeks after transfection, transduced cells were analyzed for the expression of GFP (left panels). CD45.2⁺ GFP⁺ Lin^- cells were analyzed for the expression of CD44 vs CD25 (middle panels) and CD4 vs CD8 (right panels), respectively.