In situ hybridization with a GATA-2 antisense probe. (A) Mid-primitive streak stage conceptus with no detectable signal over background in the embryo proper. (B) Late-primitive streak stage conceptus with GATA-2 mRNA expression evident both in the ectoplacental cone (epc) and in trophoblast cells (arrowhead). There is also expression evident in the mesoderm cell masses (arrow). (C) Neural plate stage conceptus with GATA-2 mRNA expression in trophoblast cells (arrowhead) and in mesodermal cell masses (arrow). (D) Early somite stage conceptus with continued signal in trophoblast giant cells (arrowhead). GATA-2 mRNA is detected in the extraembryonic ectoderm of the chorion (open arrow), but has been downregulated in yolk sac blood islands (closed arrow). (E) Higher magnification of the lower region of (D), showing GATA-2 mRNA expression in the chorion (open arrow) and trophoblast giant cells (arrowhead). Sense controls had high generalized background, but no localized signal (data not shown). ac, amniotic cavity; ex, exocoelomic cavity; pc, proamniotic cavity; m, mesoderm; ep, embryo proper. Each scale bar represents 100 μm.