Essential role of platelet-derived growth factor receptor alpha in the development of the intraplacental yolk sac/sinus of Duval in mouse placenta.

Platelet-derived growth factor receptor alpha (PDGFRalpha) is expressed in multiple tissues and exerts its function throughout mouse embryogenesis. Upon screening the PDGFRalpha-expressing tissues in mouse embryos by immunohistochemistry using our established monoclonal antibody against murine PDGFRalpha, we found its expression in an epithelium lining a sinusoidal structure in placenta. This structure was proven to be the sinus of Duval, and the PDGFRalpha-positive epithelium to be the intraplacental yolk sac (IPY). The IPY has been postulated to be a derivative of primitive endoderm because of its morphology and its expression of vitamin D-dependent 9-kDa calcium-binding protein, and to play some roles in materno-fetal transport. In this study, we demonstrated that the IPY develops from primitive endoderm by its invagination into chorioallantoic placenta and continues to strongly express PDGFRalpha until the prenatal stage. Moreover, we found that the IPY is completely absent in PdgfraPh/PdgfraPh mutant embryos, which lack the Pdgfra gene, suggesting that the function of PDGFRalpha is essential to its formation. Hence, PDGFRalpha expressed in the IPY should be listed as a component of the cytokine network of murine placental development.