Fig. 6. Tetraploid rescue of Map2k1-deficient placentas and fetuses. (A,B) Wild-type and Map2k1^-/- embryos are presented for comparison. (C-E) Tetraploid-aggregation chimeras were prepared from tetraploid wild-type embryos and diploid Map2k1^+/- embryos (D) or Map2k1^-/- ES cells (C,E). After transfer into foster mothers, chimeras were recovered at E11.5 (C) or at E13.5 (D,E) for analysis. Corresponding placentas (F-J) were analyzed by Hematoxylin and Eosin staining. (K-O) Higher magnification images of F-J. (P-T) Higher magnification images of K-O. (C,H,M,R,W) E11.5 chimeras from wild-type tetraploid embryo and Map2k1^-/- ES cells. For comparison, E10.5 wild-type (A,F,K,P,U) and Map2k1^-/- (B,G,L,Q,V) specimens are shown. The normal appearance of E11.5 Map2k1^-/- tetraploid-aggregated embryos (C) and the histology of the placenta (M,R,W) indicated the tetraploid rescue of the Map2k1^-/- phenotype. The tetraploid chimera obtained at E13.5 (E) also showed normal vascularization of the labyrinth region of the placenta (T) when compared to tetraploid control (D,S). However, the gross morphology of the embryo (E) and the absence of embryonic blood cells in the labyrinth (arrows in S; T) suggested some developmental defects. (U-W) Anti-CD31 immunostaining. (X) PCR (upper panel) and western blot (lower panel) analyses were performed to confirm the genotype of the tetraploid embryos shown in C,E. Genotype of the tetraploid embryos and yolk sacs revealed that the embryos were Map2k1^-/-, while the yolk sac, which received a contribution from the embryonic and the extra-embryonic tissues contained both Map2k1 alleles. Map2k1^-/- ES cells (ES 26-4) and Map2k1^+/- embryo DNAs were included as control. No MAP2K1 protein was detected in Map2k1^-/- ES cells (ES 26-4) or in Map2k1^-/- tetraploid chimera presented in C. d, deciduum; g, tropohoblast giant cells; l, labyrinth. y, yolk sac; e, embryo. Scale bars: 1 mm in A-J; 100 µm in K-O; 50 µm in P-W.