Nodal Signaling Pathway. Molecular and genetic studies have unveiled several signaling pathways that act in concert during gastrulation. The Nodal-signaling pathway is an important example. Nodal-related proteins are a subclass of TGF-beta related ligands. Nodal, the founding member of this sub-class, was discovered as a gene essential for mesoderm formation in mice. Dr. Feldman and colleagues subsequently demonstrated that Nodal-related signals are essential for internalization of epiblast cells, for endoderm formation and are key components of the dorsal gastrula (Spemann-Mangold) organizer.