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) (PDGFR(alpha)) is expressed in multiple tissues and exerts its function throughout mouse embryogenesis. Upon screening the PDGFR(alpha)-expressing tissues in mouse embryos by immunohistochemistry using our established monoclonal antibody against murine PDGFR(alpha), 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 PDGFR(alpha)-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 Ddependent 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 PDGFR(alpha) 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 PDGFR(alpha) is essential to its formation. Hence, PDGFR(alpha) expressed in the IPY should be listed as a component of the cytokine network of murine placental development.