[Origin and Regulation of Hematopoietic Stem Cells During Embryonic Ontogeny]

Stem cells of various tissues including hematopoietic tissue in the body are derived from embryonic stem cells (ESC). There exists intricated gene regulation during ESC development and its differentiation into hematopoietic stem cells (HSC). In embryo hematopoiesis development, there are two kinds of hematopoietic types, primitive hematopoiesis and definitive hematopoiesis. The theory of the yolk sac of primitive hematopoiesis is well accepted, while the initial site of definitive hematopoiesis still exists controversy. In present opinion, there are at least two independent sites associated with definitive hematopoiesis, those are, yolk sac and para-aortic splanchnopleura (PAS)/aorta-gonad mesonephros (AGM). Study on the hematopoiesis and its regulation during embryonic ontogeny will benefit not only to the dicovery of the mechanism of some blood disorders, but as well to gene therapy and HSC engineering.