ANTIGENIC PROFILES OF ENDOTHELIAL AND HEMATOPOIETIC LINEAGES IN MURINE INTRAEMBRYONIC HEMOGENIC SITES

Two hemogenic sites are present in mouse embryos before the onset of f etal liver hemopoiesis, While the yolk sac provides for immediate eryt hropoiesis, an intraembryonic region encompassing the dorsal aorta pro duces definitive hematopoietic stem cells, as shown experimentally. At early developmental stages this region, that we named paraaortic spla nchnopleura, produces multipotent progenitors. At the time of fetal li ver colonisation, the paraaortic splanchnopleura further evolves into aorta, gonads and mesonephros (AGM) and contains progenitors capable o f long term multilineage reconstitution. Only then are cytologically i dentifiable collections of early hemopoietic cells present in various arteries and in the mesentery, The present report focuses on the antig enic characterisation of immature hemopoietic progenitors in order to trace back the intraembryonic precursors cursors at earlier developmen tal stages. CD34, an antigen expressed by immature progenitors and end othelial cells, labels all potential hemopoietic sites. Markers, suppo sed to counterstain endothelial cells and spare CD34(+) hemopoietic ce lls, also stain various hemopoietic cells. The meaning of these shared antigenic expressions between cells of the endothelial and hemopoieti c lineages in the early embryo is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.