Represantative hematoxylin and eosin stained placental sections of control and mutant littermates at a magnification of 10x (A) and 20x (B), the bar in each panel corresponds to 100µm. The loss of Rb results in a denser labyrinth layer (L) compared to the control. In the Rb−/−;E2f4−/− placentas, this layer is further compacted and reduced in size. C) In situ hybridization for 4311 (Tpbp) indicates that the spongiotrophoblast layer (Sp) is relatively normal in the mutant placentas. Magnification, 10x. MD, maternal decidua; C, chorionic plate.