Expression of GATA-1 by the conditional regulation by tetracycline, GATA-1 promoter, and retrovirus vector. (A) Western blot of GATA-1 protein expression at days 9 to 12 of induction after the conditional expression of the Gata-1 gene from day 5. (B) Effects of GATA-1 expression driven by the Gata-1 promoter and by the retrovirus vector on definitive erythropoiesis. 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) of tetracycline. G1HRD.GATA-1 and RETROVIRUS show the data for TET-G1KO cells in which GATA-1 was expressed using the Gata-1 promoter and the retroviral vector, respectively.