Elucidating the origins of the vascular system: A fate map of the vascularendothelial and red blood cell lineages in Xenopus laevis

Required to supply nutrients and oxygen to the growing embryo, the vascular system is the first functional organ system to develop during vertebrate e mbryogenesis. Although there has been substantial progress in identifying t he genetic cascade regulating vascular development, the initial stages of v asculogenesis, namely, the origin of vascular endothelial cells within the early embryo, remain unclear. To address this issue we constructed a fate m ap for specific vascular structures, including the aortic arches, endocardi um, dorsal aorta, cardinal veins, and lateral abdominal veins, as well as f or the red blood cells at the 16-cell stage and the 32-cell stage of Xenopu s laevis. Using genetic markers to identify these cell types, our results s uggest that vascular endothelial cells can arise from virtually every blast omere of the 16-cell-stage and the 32-cell-stage embryo, with different bla stomeres preferentially, though not exclusively, giving rise to specific va scular structures. Similarly, but more surprisingly, every blastomere in th e 16-cell-stage embryo and all but those in the most animal tier of the 32- cell-stage embryo serve as progenitors for red blood cells. Taken together, our results suggest that during normal development, both dorsal and ventra l blastomeres contribute significantly to the vascular endothelial and red blood cell lineages. (C) 1999 Academic Press.