Fig. 3. Morphological defects seen in Elf5 homozygous mutant embryos. (A) Elf5^-/- embryos could usually be morphologically recognised at E6.5 by their reduced size and the lack of the embryonic-extraembryonic constriction (arrow). (B,C) Haematoxylin and Eosin-stained sagittal cross sections revealed the presence of ectoderm, EPC and visceral endoderm (ve) in homozygous E7.5 mutants (C), but the absence of chorion (ch) and mesoderm (m), which are readily detectable in wild-type littermates (B). (D) At E8.5, approximately half of the Elf5 mutants did not express the pan mesodermal marker T (phenotypically more severe type I mutants), whereas the other half expressed T ectopically (type II mutants). (E) By E8.5, Elf5^-/- embryo epithelium displayed an anterior neuroectodermal character, as shown by whole-mount in situ hybridisation with Otx2. D, distal; ee, embryonic ectoderm; P, proximal.