Dose response of GATA-1 plasmid for globin protein and erythroid cell induction. Embryos were injected with 2, 7.5, 20, and 200 pg of pcDNA3–GATA-1, and animal caps were explanted and cultured with bFGF (200 ng/mL) until sibling embryos were at stage 35. The animal caps were analyzed for globin induction by (A) Western analysis and (B) o-dianisidine staining. The Western analysis was performed as described in Fig 6. The number ofo-dianisidine–positive cells per cap represents the average of two cytospins for each dose of pcDNA3–GATA-1 and was determined as described in Fig 4.