Kinetics of primitive hematopoietic development in human EBs. (A) Kinetics of hematopoietic development in H1 hESC-derived EBs. EBs were harvested on the indicated days, and the cells were dissociated and plated in methylcellulose supplemented with hematopoietic cytokines. Ery^P indicates colonies of primitive erythrocytes; Mac, colonies of macrophages; and Ery^PMac, mixed primitive erythroid/macrophage colonies. Bars indicating standard error of the mean number of colonies from 3 cultures are not visible. (B) The top row shows a primitive erythroid colony (left) and primitive erythrocytes (right), whereas the bottom row shows a macrophage colony (left) and macrophages (right). The primitive erythrocytes are from a pool of 10-day-old erythroid colonies generated from day-8 EBs. The macrophages are from the colony shown. Original magnification: for the colonies, × 400; for the cells, × 1000. (C) PCR analyses of 4 individual primitive erythroid colonies from day 8-EBs showing ϵ- and γ- but not β-globin expression. (D) Expression analyses of EBs at different stages of development. Numbers on top represent day of differentiation.