Sequential analysis of alpha- and beta-globin gene expression during erythropoietic differentiation from primate embryonic stem cells.

The temporal pattern of embryonic, fetal, and adult globin expression in the alpha (zeta --> alpha) and beta (epsilon --> gamma and gamma --> beta) clusters were quantitatively analyzed at the transcriptional and translational levels in erythrocytes induced from primate embryonic stem cells in vitro. When vascular endothelial growth factor receptor-2(high) CD34(+) cells were harvested and reseeded onto OP9 stromal cells, two-wave erythropoiesis occurred sequentially. Immunostaining and real-time reverse transcription-polymerase chain reaction analyses of floating mature erythrocytes revealed that globin switches occurred in parallel with the erythropoietic transition. Colony-forming assays showed replacement of primitive clonogenic progenitor cells with definitive cells during culturing. A decline in embryonic zeta- and epsilon-globin expression at the translational level occurred in individual definitive erythroid progenitors. Expression of beta-globin in individual definitive erythroid progenitors was upregulated in the presence of OP9 stromal cells. Thus, this system reproduces early hematopoietic development in vitro and can serve as a model for analyzing the mechanisms of the globin switch in humans.