Transforming growth factors-beta as regulators of cellular growth and phenotype.

An increasing number of cDNAs and polypeptides have been ascribed to the transforming growth factor-beta (TGF-beta) superfamily. It has become evident that this evolutionally well-conserved gene family has representatives in many organisms, from invertebrates to mammalians. As new members are being identified, the knowledge of their biological significance is derived not only from studies of their effects in various in vitro models, but also of their organismal expression during different stages of embryogenesis and morphogenesis. The major described functions of the TGF-beta and like proteins seem to be the regulation of cell proliferation, phenotype, and differentiation. Part of these effects may be attributed to changes in the adhesive properties of the cells and integrity of their extracellular matrices modulated by TGF-beta. Identification of the new members of the TGF-beta family, their biological effects, cell-surface receptors, and cell or tissue-specific expression will be invaluable in trying to understand the purpose of many seemingly alike multiregulators.