PDGFB regulates the development of the labyrinthine layer of the mouse fetal placenta.

PDGFB is a growth factor which is vital for the completion of normal prenatal development. In this study, we report the phenotypic analysis of placentas from mouse conceptuses that lack a functional PDGFB or PDGFRbeta gene. Placentas of both types of mutant exhibit changes in the labyrinthine layer, including dilated embryonic blood vessels and reduced numbers of both pericytes and trophoblasts. These changes are seen from embryonic day (E) 13.5, which coincides with the upregulation of PDGFB mRNA levels in normal placentas. By E17, modifications in shape, size, and number of the fetal blood vessels in the mutant placentas cause an abnormal ratio of the surface areas between the fetal and the maternal blood vessels in the labyrinthine layer. Our data suggest that PDGFB acts locally to contribute to the development of the labyrinthine layer of the fetal placenta and the formation of a proper nutrient-waste exchange system during fetal development. We point out that the roles of PDGFB/Rbeta signaling in the placenta may be analogous to those in the developing kidney, by controlling pericytes in the labyrinthine layer and mesangial cells in the kidney.