Expression of Xsl in the ectoderm and activation of c-kit in the mesoderm are required for primitive erythropoiesis. (A) Schematic showing experimental design. Recombinants were cultured until stage 33/34, pooled, and analyzed for expression of globin. (B) Northern blot analysis of globin and odc expression in mesoderm (VM) or ectoderm/mesoderm (Ecto/VM) recombinants generated from control embryos or from embryos that had been injected with Xsl MOs or DN-kit RNA as indicated above each lane.