Histological evaluation of H&E-stained sections in the labyrinth zone of murine Cdkn2a-/- (n=5 placentas), Cdkn2a-/-;p53-/- (n=5), p53-/- (n=4), and Cdkn1a-/- (n=3) placentas on day E14.5, compared to WT placentas (n=6). (F−G) Ki67 immunostaining in the labyrinth zones of murine WT , p53-/- ,Cdkn2a-/-, and Cdkn2a-/-;p53-/- placentas, on day E14.5 (n=3 placentas from each genotype). (F) Representative images of Ki67 staining in the labyrinth zone are shown. Positive Ki67 trophoblast cells are indicated with arrows. L, labyrinth. (G) Proliferation scores (n=3 scores, derived from three placentas of each genotype) based on Ki67 staining show enhanced Ki67 expression in the placental labyrinths of Cdkn2a-/- and Cdkn2a-/-;p53-/- placentas relative to WT. Values are means +SEM of three scores for each genotype. *P < 0.05 by a one-tailed unpaired Student's t-test. Data information: Scale bars, 50 µm. 