Impaired T-cell development in embryos lacking Sp3. (A) Thymi of E18.5 embryos of one litter (left) and total numbers of thymocytes (right) of the indicated genotypes. (B) Absolute numbers of thymocytes within the indicated thymic subpopulations, as determined by flow cytometry. Tn = CD3^-CD4^-CD8^-; ISP = CD3^-CD8⁺;DP = CD4⁺CD8⁺; and CD4 SP = CD3⁺CD4⁺CD8^-. (C) FSC characteristics of the indicated thymus subpopulations. Cells were analyzed for the expression of CD3, CD4, and CD8, and FSC characteristics are displayed as histogram overlays of Sp3^-/- (bold lines) and Sp3^+/+ (dashed lines) embyros. (D) CD3 and CD69 expression in DP (CD4⁺CD8⁺) and DD (CD4^lowCD8^low) thymocytes. Thymus cell suspensions were gated for CD4 and CD8, and results are displayed as histogram overlays for CD3 and CD69 of Sp3^-/- (bold lines) and Sp3^+/+ (dashed lines) embyros. Data shown are from 2 to 26 embryos in each group.