Fig. 6. Severely affected Eomes^N/+; Nodal^LacZ/+ double heterozygotes fail to rotate the PD axis. (A,A') Nodal expression normally confined to the posterior epiblast at E6.5, (B,B') persists throughout the entire proximal epiblast of Eomes^N/+; Nodal^LacZ/+ double heterozygous embryos. (C-F) AVE-markers (Hex and Cer) remain localized to the distal tip of double heterozygous mutant embryos. (G-L) Consequently posterior marker genes (cripto, Eomes and brachyury) are expressed throughout the proximal epiblast. (M,N) Spc4 is expressed at normal levels in the ExE of mutant embryos, which fails to be displaced proximally. (O-P') From late gastrulation stages onwards, double heterozygous mutants show gross disturbances of germ layer formation, and massive cell accumulations of mesenchymal cells within in the amniotic cavity (arrowhead in P', lacZ staining) and severe constrictions between the embryonic and extra-embryonic regions of the embryo (arrows in P). (Q-T) At E7.5, the mesoderm marker Fgf8 is widely expressed in mutants, whereas Cer1, which marks newly formed DE, fails to be expressed.