Fig. 5. Morphology and histology of Gdf3 mutant embryos. (A) Two Gdf3^-/- embryos at 8.5 dpc, showing a phenotypically wild-type embryo (left) and a severe mutant that consists of an empty visceral yolk sac (right). (B) A Gdf3^-/- mutant at 8.5 dpc displays an abnormal embryonic region and prominent constriction at the embryonic/extra-embryonic boundary (arrowheads); an allantois-like structure (al?) is present. (C) Two Gdf3^-/- embryos at 8.0 dpc, with a phenotypically wild-type embryo (left) and an abnormal embryo (right) with reduced anterior structures (arrow) and an ectopic projection (arrowhead). (D-G) Hematoxylin-Eosin staining of paraffin wax-embedded sections through decidua containing Gdf3^-/- embryos at 7.5 dpc (D,E) and 8.0 dpc (F,G). In comparison with the phenotypically wild-type embryos (D,F), the severely affected mutant in E shows an embryonic/extra-embryonic boundary constriction (arrowheads) and an abnormal embryonic region containing mesoderm (arrows). The less-affected embryo in G lacks an allantois (arrowhead) and has visceral yolk sac-like tissue in place of an amnion (arrows). Scale bars: 200 µm. Abbreviations: al, allantois; am, amnion; ch, chorion; fb, forebrain; mes, mesoderm; ne, neuroectoderm; vys, visceral yolk sac.