ABSTRACT
SUMMARY The earliest inductive event during amphibian embryogenesis is the formation of mesoderm, a key determinant for the vertebrate body plan. While it is established that growth factors inducing mesoderm belong to the TGF-β and FGF families, the identity of the individual genes functioning in vivo is still unclear, though the number of candidates is increasing. The wnt-and Bmp-signaling pathways are involved in dorsal and ventral mesoderm formation, respectively. Further patterning of lateral mesoderm is mediated by the Bmp-4 morphogen, whose function is antagonized by noggin and chordin, both acting in the organizer. Homeobox genes rate among the most prominent groups of transcription factors involved in mesoderm formation. They are regulated by growth factors and themselves induce additional signalling factors, thus leading to a hierarchical cascade of inductive events.
