Fig. 5. Extra-embryonic expression of LPP3 partially rescues the placental phenotype and reveals abnormal allantoic vasculogenesis. (A) Rosa26LPP3^-/- chimeric embryo recovered at E10.5. In the presence of wild-type extra-embryonic tissue (blue), the allantois from this embryo, entirely derived from LPP3^-/- cells, contacted the chorion (arrow). The embryo is also developmentally delayed. (B) Rosa26LPP3^-/- chimeric embryo recovered at E10.5. This embryo, formed by a mixture of wild-type (blue) and mutant cells showed more advanced development. Compare with the size and stage of development of the littermate embryo shown in A. The allantois also contacted the chorion (not shown). (C) Transverse section through the chorio-allantoic region of the embryo shown in A. The section corresponded to the maximum diameter of the chorioallantoic region. Although LPP^-/- mutant cells (pink) contacted the chorion (arrowheads), the allantois remained as a compact mass of tissue that did not invade the chorion. (D) Transverse section through the chorio-allantoic region of the mixed chimera shown in B. Chorioallantoic placental development was enhanced in the presence of a mixed population of LPP^+/+ (blue) and LPP^-/- cells. Chorionic development was enhanced, as shown by the wavy appearance of the chorion (arrowheads), increased diameter of the placenta and the formation of large allantoic blood vessels (arrow). Note that the endothelial cells from the umbilical cord vessels were predominantly of wild-type genotype (inset, blue cells). (E) Allantois from a 5-somite wild-type embryo cultured for 36 hours. Note that the PECAM1 positive endothelial cells (brown) developed a flat network of thin capillary-like structures. (F) Allantois from a 5-somite LPP3^-/- embryo treated as in E. A mass of PECAM1-positive endothelial cells remained in the center of the explant.