Differential expression of KDR/VEGFR-2 and CD34 during mesoderm development of the early human embryo

Recent findings on vertebrate embryos have provided compelling evidence for the existence of hemangioblasts, i.e. common precursors for endothelial an d hematopoietic cells, characterized by expression of the VEGFR2/Flk1 recep tor. We describe here a population of KDR+ CD34(-) mesoderm cells that emer ges in early-semitic human embryos, by the beginning of the 4th week of ges tation. In the developing blood vessels, KDR-expressing CD34(-) cells gradu ally coexpress increasing levels of CD34 antigen. Remarkably, as developmen t proceeds, a KDR+ CD34(-) contingent persists in the paraaortic splanchnop leura until just prior to the emergence of aorta-associated hematopoietic c ell clusters. These observations suggest that KDR+ CD34(-) mesodermal cells might represent the putative hemangioblastic precursor of human hematopoie tic and endothelial lineages. (C) 1999 Elsevier Science Ireland Ltd. All ri ghts reserved.