(A) Parasagittal sections of placentas (shown here at E17.5) were stained with anti-CD31 antibody (brown) and hematoxylin (blue) to visualize the anatomical layers: the labyrinth (L), the junctional zone (J) and the decidua (D). Lines indicate layer separations. At this magnification, individual vessels are not visible, but vascular zones appear brownish. (B, C) The surfaces of the 3 layers, as well as total surfaces, were measured on 3 parasagittal sections (separated by approximately 50 μm) for each placenta at E12.5 (B) and E17.5 (C). The mean values were used to calculate the mean surface proportion (SD) of layers from wild-type (n = 8 and 12, for E12.5 and E17.5 placentas, respectively) and Pcdh12−/− (n = 8 and 10 for E12.5 and E17.5 placentas, respectively) placentas. (D, E) For each placenta at E12.5 (D) and E17.5 (E), nuclei were counted on three different areas at high magnification to calculate the cell density. Data represent the mean with SD. A significant difference was observed for labyrinthine cell density in both E12.5 and E17.5 placentas.