Embryonic mesoderm and endoderm induction requires the actions of non-embryonic Nodal-related ligands and XXXX .

@entity50021 @entity55487 @entity72922 @entity72923 @entity2270 @entity3392
Vertebrate mesoderm and endoderm formation requires signaling by Nodal-related ligands from the TGFb superfamily. The factors that initiate Nodal-related gene transcription are unknown in most species and the relative contributions of Nodal-related ligands from embryonic, extraembryonic and maternal sources remain uncertain. In @entity3392 , signals from the yolk syncytial layer (YSL), an extraembryonic domain, are required for mesoderm and endoderm induction, and YSL expression of @entity72922 ( @entity72922 ) and @entity50021 accounts for a portion of this activity. A variable requirement of maternally derived @entity72922 for dorsal and anterior @entity2270 formation has also been documented. Here we show that @entity72923 directly activates expression of @entity50021 via binding to its first intron and is required for @entity50021 expression in the YSL. @entity72923 is also required for the Nodal signaling-independent expression component of the @entity55487 (ntla) gene, which is required for posterior (tail) mesoderm formation. Therefore, @entity72923 defines a new pathway upstream of Nodal signaling and posterior mesoderm formation. We further show that the co-disruption of extraembryonic @entity50021 , extraembryonic @entity72922 and maternal @entity72922 eliminates endoderm and anterior (head and trunk) mesoderm, recapitulating the loss of Nodal signaling phenotype. Therefore, non-embryonic sources of Nodal-related ligands account for the complete spectrum of early Nodal signaling requirements. In summary, the induction of mesoderm and endoderm depends upon the combined actions of @entity72923 and Nodal-related ligands from non-embryonic sources.
