Fig. 4. LPP3^-/- yolk sacs show abnormal vasculogenesis. (A) External appearance of the yolksac in normal (top) and homozygous mutant (bottom) conceptuses recovered at E10.5. In the mutant note the complete absence of blood vessels and a very delayed embryo with its corresponding amnion that can be observed through the yolk sac. (B,C) Development of the vascular plexus in an E10.5 wild-type yolk sac. Formation and ramification of large blood vessels is evident when blood cells are detected by their endogenous peroxidase activity (B) or by staining endothelial cells using a flk-1 probe (C). (D) PECAM-1 detection of endothelial cells in a wild-type mouse embryo at E8.5 showing the formation of the dorsal aortas. (E,F) An E10.5 LPP3^-/- yolk sac showing a poor development of the vascular plexus. No large blood vessels were formed. Blood cells and endothelial cells were detected as in B and C. (G) PECAM-1 detection of endothelial cells in a LPP3-deficient embryo at E9.5 showing the formation of the dorsal aortas.