GATA-1–mediated erythroid maturation of G1E-ER4 cells. (A) Morphologic maturation and accumulation of hemoglobin after activation of GATA-1. GATA-1 was activated by estradiol at time zero and cells were examined by cytocentrifugation and histologic staining at the indicated time points. MGG indicates May–Grunwald Giemsa stain; BZ, benzidine stain for hemoglobin. Original magnification, × 400. (B) GATA-1–ER expression in G1E-ER4 cells. Western blots of whole cell lysates at various time points after activation of GATA-1–ER by estradiol. MEL cell lysates at 0 and 96 hours after induction of differentiation with 2% dimethyl sulfoxide (DMSO) were used for comparison. There is 10 μg protein per lane. MW indicates molecular weight in kilodaltons.