Nodal regulates trophoblast differentiation and placental development.

Nodal has been thought to be an embryo-specific factor that regulates development, but nodal is also expressed in the mouse placenta beginning at midgestation, specifically in the spongiotrophoblasts. In an insertional null nodal mutant, not only is embryonic development disrupted, but mouse placental development is also grossly altered with the loss of the diploid spongiotrophoblasts and labyrinth and an expansion of the polyploid giant cell layer. A hypomorphic mutation in nodal results in an expansion of the giant cell and spongiotrophoblast layers, and a decrease in labyrinthine development. Expression of nodal in trophoblast cell cultures is sufficient to inhibit trophoblast giant cell differentiation, demonstrating that nodal can act directly on trophoblasts. The mechanism of nodal action includes the inhibition of junB gene transcription. These results suggest that nodal may be involved in redirecting trophoblast fate towards the midgestational expansion of the labyrinth region while maintaining the thin layer of trophoblast giant cells and the underlying layer of spongiotrophoblasts that form the boundary between the maternal and extraembryonic compartments.

Nodal and bone morphogenetic protein 5 interact in murine mesoderm formation and implantation.

Mice mutant for the TGF-beta family member, nodal, lack mesoderm and die between E8.5 and E9.5. The short ear-lethal (se(l) ) mutation, a deletion that eliminates Bmp-5, causes a strikingly similar gastrulation defect. Here we analyze se(l);nodal compound mutants and find a dosage effect. Embryos homozygous for one mutation show distinct gastrulation stage defects that depend on whether they are heterozygous or homozygous for the other mutation. Embryos mutant for nodal or se(l);nodal compound mutants fail to execute an antigenic shift indicative of mesoderm differentiation and ectoderm cells are shunted into an apoptotic pathway. Furthermore, we find a novel phenotype in se(l);nodal double mutant litters, in which two to four genetically different embryos are contained within the same deciduum. Both the gastrulation and implantation phenotypes can also arise in short ear-viable (se(v) ) and se(v); nodal mutant mice. These data indicate that loss of Bmp-5 may underlie the se(l) gastrulation phenotype and suggest that nodal and Bmp-5 interact during murine mesoderm formation. Our data also reveal an unsuspected role for Bmp-5 in implantation and the decidual response in the mouse.