Mesoderm is committed to hemato-endothelial and cardiac lineages in human embryoid bodies by sequential exposure to cytokines.

Human embryonic stem (hES) cells can differentiate into cells of the three germ layers in vitro and serve as a powerful resource to study mechanisms involved in cell fate decisions. However, it is difficult to promote the directed and efficient differentiation of hES cells toward a specific lineage. Here we establish a stepwise strategy for generating hemato-endothelial and cardiac precursors from hES cells in single culture conditions. The efficiency of committing hES cells to three cell lineages was significantly higher with our approach than with exposure to single or multiple cytokines. Efficiency was determined using quantitative analysis by gene expression, flow cytometry, and colony assays. Several cytokines were sufficient to drive the efficient differentiation of hES cells into specific lineages. Each of these factors appeared to regulate specific steps of differentiation: BMP4 promoted the efficient formation of mesoderm; bFGF induced the differentiation of these mesodermal precursors to the hemangioblast fate; VEGF and TPO were required for the production of committed hematopoietic progenitors. This stepwise control of differentiation in vitro leads to a high frequency of hemato-endothelial and cardiac precursors derived from hES cells and offers a unique model for studying the molecular and cellular events that regulate hematopoiesis and cardiogenesis.