Fig. 1. Reduction of Bmp signaling at the mid-gastrula stage causes expansion of blood and vascular cells into the extreme ventral mesoderm. (A-I) gata1 (A-C), flk1 (D-F), and pax2.1 (G-I) expression in heat-shocked wild-type and transgenic sibling embryos. Transgenic embryos heat shocked at dome stage have a loss or severe reduction in the expression of all three markers (B,E,H). Transgenic embryos heat shocked at 80% epiboly (mid-gastrula) have an expansion of gata1 and flk1 expression into the mesoderm below the tail bud (tb), marked by an arrow. All embryos are flat-mounted with anterior to the top, and images in A,D,G are representative of wild-type embryos from both stages of heat shock.