Evolutionary Origins of the Transforming Growth Factor-β Gene Family

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Abstract
A molecular phylogeny for the transforming growth factor-β (TGF-β) 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-β gene family consists of four members: TGF-β1 (= TGF-β4), TGF-β2, TGF-β3, and TGF-β5. The molecular phylogeny and Southern hybridization data also suggest that the proteins for mammalian TGF-β1 and chicken TGF-β4 are the products of homologous rather than duplicated genes. If the gene duplication event that produced the ancestral gene for TGF-β1 occurred before the divergence of birds and mammals, then sufficient time would have elapsed to generate these quite distinct avian and mammalian TGF-β1 proteins. Therefore, the TGF-β family contains four distinct proteins, TGF-β1, 2, 3, and 5