Fig. 1. The underdevelopment of the labyrinthine region in Map2k1^-/- placenta results from reduced proliferation and increased apoptosis. (A) Hematoxylin-Eosin staining of E10.5 wild-type (Map2k1^+/+) and Map2k1^-/- placental sections. (B) Proliferation was detected by immunostaining with phospho-histone H3 antibody and (C) apoptosis was detected by TUNEL assays on paraffin sections from E8.5, E9.5 and E10.5 wild-type and Map2k1^-/- placentas. Arrows indicate examples of mitotic cells (B) and apoptotic cells (C) in the labyrinthine region (or chorioallantoic region at E8.5). The percentage of labyrinthine trophoblasts in proliferation (D) and apoptosis (E) is represented. A statistically significant reduction of the proliferating cell ratio (D) was observed for E9.5 and E10.5 Map2k1^-/- placentas. The apoptotic cell ratio was significantly increased in Map2k1^-/- placenta at all stages analyzed (E). al, allantois; d, deciduum; g, trophoblast giant cells; l, labyrinth. Scale bars: 100 µm in A; 50 µm in B,C.