In vitro differentiation of embryonic stem (ES) cells into embryoid bodies.

Left panel shows undifferentiated ES cells growing on mouse embryonic fibroblasts. Removal of the ES cells from the feeder cells and dispersal into semi-solid media or growth in hanging drop cultures initiates aggregation of cells and spontaneous differentiation. The resulting cystic structures, called embryoid bodies, grow in size over time and support locally organized tissue structures. In the right panel, arrows indicate blood islands consisting of hemoglobinized erythrocytes, mimicking the formation of similar structures in the developing yolk sac of the murine embryo.