Differential expression patterns of GATA-1 and GATA-2 in yolk sac blood islands and giant trophoblast cells at the early somite stage. (A) In situ hybridization with a GATA-1 antisense probe, showing signal in yolk sac blood islands (arrowheads), and lack of signal in trophoblast giant cells (arrows). (B) In situ hybridization with a GATA-2 antisense probe, showing lack of signal in yolk sac blood islands (arrowheads), and presence of signal in trophoblast cells (arrows). Scale bars represent 100 μm.