Effect of lower Gata1 DNA binding activity on erythropoiesis in gata1^T301K/vlt and gata1^T301K/T301K embryos. (A) o-dianisidine staining for hemoglobin (black arrows) to show the reduction or absence of erythrocytes in gata1^T301K/T301K (n = 10/10) and gata1^T301K/vlt (n = 10/10) embryos, respectively, compared with the wild-type (n = 0/20) embryos at 2 dpf. (B) Percentage of GFP⁺ cells in 3 dpf wild-type and gata1^T301K/T301K embryos carrying Tg(gata1:GFP). Fifty to 60 embryos from each genotype were pooled, dissociated, and subjected to flow cytometric analysis. gata1^T301K/T301K embryos showed a 38% reduction in the percentage of GFP⁺ cells compared with the wild-type. (C) Tg(gata1:GFP) as a marker for erythrocytes (red arrows point to the GFP⁺ cells seen in circulation) to show the absence of erythrocytes in the gata1^T301K/vlt embryo (bottom, n = 25/25) compared with the wild-type embryo (top, n = 0/30) at 4 dpf. Original magnification ×50 (A,C).