Symmetric pre-TCR segregation in dividing thymocytes. (A) Confocal images of WT fetal mitotic thymocytes at the telophase stage stained with antibodies against CD25 (red), pre-TCR (green), and treated with TOPRO-3 iodide (blue). (B) Percentage of pre-TCR protein contained in each daughter cell at the telophase stage. Quantification of Numb signal was performed as indicated above. A total of 10 telophases were analyzed. Average standard deviation for DC#1 and DC#2 = 4.81. (C) Confocal images of WT fetal mitotic thymocytes at the prophase (top) and metaphase (bottom) stages stained with antibodies against pre-TCR (red), Numb (green), and treated with TOPRO-3 iodide (blue). (D) Confocal images of mitotic Rag2^−/− thymocytes in prophase, metaphase, anaphase, and telophase stages stained with antibodies against CD25 (red), Numb (green), and treated with TOPRO-3 iodide (blue). The images are representative of at least 3 independent experiments. (E) Percentage of Numb protein contained in each daughter cell at the telophase stage of Rag2^−/− thymocytes. Quantification of Numb signal was performed as indicated above. A total of 6 telophases were analyzed. Average standard deviation for DC#1 and DC#2 = 3.79. Horizontal lines in panels B and E represent average values.