Growth factors in development: the role of TGF-beta related polypeptide signalling molecules in embryogenesis.

Embryonic induction, the process by which signals from one cell population influence the fate of another, plays an essential role in the development of all organisms so far studied. In many cases, the signalling molecules belong to large families of highly conserved proteins, originally identified as mammalian growth factors. The largest known family is related to Transforming Growth Factor-beta (TGF-beta) and currently consists of at least 24 different members. Genetic studies in Drosophila on the TGF-beta related gene, decapentaplegic (dpp), reveal the existence of conserved mechanisms regulating both the expression of the protein during development and the way in which it interacts with other signalling molecules to generate pattern within embryonic tissues. Comparative studies on another TGF-beta related gene, known as Bone Morphogenetic Protein-4 (BMP-4), in Xenopus and mouse point to a conserved role in specifying posteroventral mesoderm during gastrulation. Analysis of other polypeptide signalling molecules during gastrulation suggests that their interaction in the generation of the overall body plan has also been conserved during vertebrate evolution.