Mix genes and hematopoiesis. (A) Mix genes pattern mesoderm to a ventral (hematopoietic) fate. Embryos were injected with mRNA at the one-cell stage in the animal pole (1 ng of each RNA), animal caps were explanted at stage 8 and cultured to sibling stage 36 in the presence of bFGF, and expression of globin RNA was examined by RT-PCR. M11 is a dominant negative mutant of Mix.1. (B) Mix genes induce erythroid cells in animal pole explants. Embryos were injected with plasmid DNA (300 pg, pcDNA3.0) at the one-cell stage in the animal pole and animal caps were explanted at stage 8 and cultured in the presence of basic FGF (20 ng/ml) to sibling stage 36. Disaggregated animal caps were stained with O-dianisidine (T.L.H., Y.Z., P.E.M., and L.I.Z., manuscript submitted), cytocentrifuged onto glass slides, and photographed at ×200.