Rescue of definitive erythropoiesis by conditional expression of GATA-1. (A) May-Giemsa and benzidine staining of EryDs differentiated from control ES cells and TET-G1KO cells at day 12 of induction. TET-G1KO cells were cultured in the presence (100 ng/mL) or absence of tetracycline from day 5. (B) Number of cells at day 12 of induction. Control ES cells and TET-G1KO cells were cultured with medium containing tetracycline as shown. Data are means ± SD of 6 samples. The numbers of cells at 6 to 100 ng/mL tetracycline were significantly lower than the number at 0 ng/mL tetracycline (P < .001 by Student t test). (C) Percentage of benzidine-positive cells at day 12 of induction. TET-G1KO cells were cultured in the presence (100 ng/mL) or absence of tetracycline as shown. Data are means ± SD of 6 samples. (D) Number of cells at day 12 of induction after the conditional expression of GATA-1 for shorter periods, as shown. Data are means ± SD of 6 samples. The cell numbers for TET(+), D5-8, and D5-9 differ significantly from that of D5-12 (P < .05 by Student t test). The cell numbers for D5-8 to D5-12 differ significantly from that of TET(+) (P < .001 by Student t test). (E) Western blot of GATA-1 at day 11 after the conditional expression of GATA-1 for the indicated periods. (F) Percentages of dead cells after the expression of GATA-1. GATA-1 was expressed from day 5 to 8, or from day 5 to 11, as shown. The percentage of dead cells was counted by trypan blue staining at days 9 to 11. Data are means ± SD of 6 samples. *Data that are significantly different from those of control and D5-11 (P < .01 by Student t test). (G) Percentages of dead cells at day 11 of induction. Control ES cells and TET-G1KO cells were cultured with medium containing tetracycline as shown. Data are means ± SD of 6 samples. There are no significant differences between the percentages at 2 to 6 ng/mL of tetracycline and that of control.