Vasculogenesis and angiogenesis in the mouse embryo studied using quail/mouse chimeras.

Using quail/chick chimeras, we have previously shown that different embryonic territories are vascularized through two distinct mecanisms, angiogenesis and vasculogenesis. Angiogenesis occurs in tissues of somatopleural origin, vasculogenesis occurs in territories of splanchnopleural origin. The aim of this work was to establish if these modes of vascularization were conserved in the mammalian embryo. Since in vivo manipulations with mammalian embryos are difficult to perform, we used a quail/mouse chimera approach. Mouse limb buds of somatopleural origin, and visceral organ rudiments of splanchnopleural origin, were grafted into the coelomic cavity of 2.5 day-old quail embryos. After four to seven days, the hosts were killed and the origin of the endothelial cells in the mouse tissues was determined by double staining with the quail endothelial and hematopoietic cell-specific marker, QH1 and mouse-specific VEGFR2 and VEGFR3 probes. Our findings show that the great majority of vessels which developed in the mouse limbs was QH1+, indicating that these tissues were vascularized by angiogenesis. Conversely, visceral organs were vascularized through the vasculogenesis process by mouse endothelial cells which differentiated in situ. These results demonstrate for the first time that in the mouse embryo, as previously shown in avian species, the tissues from somatopleural origin are vascularized by angiogenesis, while rudiments of a splanchnopleural origin are vascularized by vasculogenesis, both at vascular and lymphatic levels.