Fig. 4. Disturbed mesoderm formation and migration in Smad1 mutants. Whole-mount in-situ hybridization of wild-type (+/+) and mutant (-/-) embryos. (A) T is normally expressed in the primitive streak and in nascent mesoderm of 7.0 dpc wild-type embryos. (B) In Smad1-/- littermates, T expression is patchy and less intense. (C) A posterior view of a Smad1 mutant embryo showing discontinuous T expression. (D) Fgf8, normally expressed in the nascent mesoderm, streak and at the base of the allantois at 7.0 dpc (left), is similarly expressed in mutant embryos (right), but is distorted, owing to the twisted epiblast. (E) Transverse section of the mutant embryo in D, showing Fgf8-expressing cells within the posterior folds (arrowhead). (F) Fgf3, expressed in the extra-embryonic mesoderm and streak in wild-type embryos is also present throughout the extra-embryonic folds of mutant embryos. (G) A transverse section of the mutant in F. Anterior is towards the left in all panels except C. ch, chorion; ep, epiblast; ve, visceral endoderm.
