Hematopoiesis and angiogenesis.

Hematopoiesis is closely linked with angiogenesis, because they interact with each other and have common ancestors: hemangioblasts or hematogenic endothelial cells. The relationship is reasonable, because vascular and hematopoietic systems must develop together in order to establish the body's oxygen-delivery system during organogenesis. Hematopoietic stem cells have been shown to originate from the para-aortic splanchnopleural mesoderm region or aorta-gonads-mesonephros at successive stages. We discuss the molecular events in the differentiation of hematopoietic cells and endothelial cells. Transcription factors SCL/tal-1 and AML1; tyrosine kinase receptors Flk-1, Tie-2, Eph, and the sialomucins; CD34; thrombomucin; and AA4 play important biological roles in these lineages.