GATA-1 induces erythroid cells in cooperation with bFGF. (A) Embryos are injected with pcDNA3–GATA-1 (200 pg) and treated with or without FGF (200 ng/mL). Animal caps are analyzed as described in Fig 1A. The panels are photographed at 20× original magnification. The dark cells in the panel of GATA-1 caps treated with no growth factors are pigmented cells that do not stain witho-dianisidine. (B) The o-dianisidine–positive cells were counted from two cytospins for each experimental condition in a representative experiment. The number of o-dianisidine cells per cap was determined as described in Fig 4.