A model of the stage-specific role of RA in human mesoderm and hematopoietic development. VEGF and bFGF efficiently specify KDR⁺PDGFRα⁻ the hemato-vascular lineage from BMP4/Wnt3a-induced T⁺ primitive streak/mesendoderm cells. At this stage, the role of exogenous RA is to induce paraxial mesoderm. At a later stage, RA enhances the generation of hematopoietic progenitors (CD34⁺C-Kit⁺) and decreases erythroid development from hemato-vascular precursors.