The splanchnopleura/AGM region is the prime site for the generation of multipotent hemopoietic precursors, in the mouse embryo

The first hemopoietic cells were found in the yolk sac of mammalian embryos . Based on this observation it was postulated that hemopoietic stem cells a re generated in this location. In the last few years, however, increasing e vidence indicates that there is an independent site of hemopoietic cell gen eration, in the embryo proper, designated the paraaortic splanchnopleura/ao rta, gonad, mesonephros region. Precursors of hemopoietic cells are found i n this region before circulation is established between the yolk sac and th e embryo proper. In contrast to the hemopoietic cells found in the yolk sac , the ones found in the embryo proper are multipotent lympho-myeloid precur sors that rapidly acquire the capacity to reconstitute the hemopoietic syst em of adult irradiated recipients. We propose that these are the founder ce lls of adult definitive hematopoiesis, (C) 2000 Elsevier Science Ltd. All r ights reserved.