Evolutionary origins of the transforming growth factor-beta gene family

A molecular phylogeny for the transforming growth factor-beta (TGF-beta) gene family based on a comparison of nucleotide sequences is proposed. A phylogenetic tree constructed from these sequences shows that the family evolved from a common ancestral gene that came into existence at about the time of arthropod and chordate divergence. This model suggests that the present day TGF-beta gene family consists of four members: TGF-beta 1 (= TGF-beta 4), TGF-beta 2, TGF-beta 3, and TGF-beta 5. The molecular phylogeny and Southern hybridization data also suggest that the proteins for mammalian TGF-beta 1 and chicken TGF-beta 4 are the products of homologous rather than duplicated genes. If the gene duplication event that produced the ancestral gene for TGF-beta 1 occurred before the divergence of birds and mammals, then sufficient time would have elapsed to generate these quite distinct avian and mammalian TGF-beta 1 proteins. Therefore, the TGF-beta family contains four distinct proteins, TGF-beta 1, 2, 3, and 5.