The extension of calbindin-D9k-positive villous endoderm into the periplacental region in the Pdgfraph/ Pdgfraph placenta may reflect invaginating movement of the visceral endoderm, which cannot develop into actual extension and invagination in the absence of PDGFRa. Under normal conditions, this process together with the signal from PDGFRa may lead to rapid proliferation and invagination of the IPY. birth control pills
The orderly arrangement of the maternal blood sinuses, the IPY, and the branching roots of fetal blood vessels may be essential to the formation of a functional unit for special matemo-fetal transport. During placental development, formation of fetal blood vessels begins upon fusion of allantois and chorion at 8.5 dpc, and it proceeds normally in Pdgfraph/Pdgfraph placentas. Thus, the spatial relation of fetal blood vessels and the IPY and the temporal order of formation of these two components strongly suggest that IPY development is guided by the preformed fetal blood vessels. It is well known that in many organs, PDGFRa and its ligands are expressed side by side and play a role in the interaction between these adjacent two tissues . Bidwell et al. reported that the ligands for PDGFRa are expressed in the labyrinthine layer in mouse placenta, and Holmgren et al. reported that the ligands for PDGFRa are expressed in the endothelial cells and smooth muscle cells of fetal blood vessels in human placenta, suggesting that PDGFRa may play a role in the guidance of IPY development.