Fig. 1: Characterization of FlipFlop mice.

a, Schematic of altered Cd4 and Cd8α gene loci in FlipFlop mice. Left, surface proteins encoded by altered Cd4^CD8 (4) and Cd8^CD4 (8) gene loci in FlipFlop DP thymocytes. Right, schematic of the altered Cd4^CD8 and Cd8^CD4 gene loci in FlipFlop mice: E, exons; IRES, internal ribosome entry site; pA, polyadenylation signals; NEO, neomycin-resistance cassette. The altered Cd4^CD8 gene locus was obtained from 8in4 mice, which were constructed for this study as described in Extended Data Fig. 1a; the altered Cd8^CD4 gene locus was obtained from 4in8 mice, which were reported previously²⁵. b, TCRβ expression in the thymus and LN from B6 and FlipFlop mice. Total cell number (mean ± s.e.m) is shown above histograms, and numbers within histograms indicate frequency of TCRβ^hi cells (n = 4–7 per strain, representative of 4–7 independent experiments). c, CD4 versus CD8α profile of CD24^-TCRβ⁺ mature thymocytes and TCRβ⁺ LN T cells from B6 and FlipFlop mice. Numbers (mean ± s.e.m) of mature thymocytes and LN T cells is shown above profiles and numbers within profiles indicate frequency of cells in each box (n = 4–7 per strain, representative of 4–7 independent experiments). d, Numbers of CD4 and CD8 T cells in LN (top) and spleen (bottom) from B6 (gray bar) and FlipFlop (black bar) mice (B6: n = 4, FlipFlop: n = 7, representative of 4–5 independent experiments). *P < 0.05, **P < 0.01 (two-tailed unpaired t-test); mean + s.e.m. e, Intracellular staining (ic) of ThPOK and Runx3 of CD4 (blue line) and CD8 (red line) T cells among TCRβ^hi thymocytes (top) and TCRβ⁺ LN T cells (bottom) from B6 and FlipFlop mice. Gray lines in histograms indicate staining with control antibody (Ab; n = 3 per strain, 3 independent experiments). f, ThPOK-GFP (orange line) and Runx3d-YFP (green line) reporter expression in CD4 and CD8 T cells among TCRβ^hi thymocytes (top) and TCRβ⁺ LN T cells (bottom) from B6 and FlipFlop mice (n = 3 per strain, representative of 3 independent experiments).