Identification of a New Member of Transforming Growth Factor-Beta Superfamily inDrosophila:The First Invertebrate Activin Gene

Activins, a subgroup of the transforming growth factor-β (TGF-β) superfamily, have been extensively studied in vertebrates for their roles in growth and development. However, activins are not thought to be expressed in invertebrates. The identification of the first invertebrate activin gene is reported here. A genomic clone representing 102 F region of theDrosophilachromosome 4 is found to encode a putative activin β. The predicted protein sequence has a multibasic protease site that would generate a mature C-terminal peptide containing 113 amino acids showing >60% similarity to the vertebrate activin βB(inhibin βB) sequences. A TGF-β family signature as well as all 9 cysteine residues conserved in the vertebrate activins are also present in this mature peptide sequence. Northern blot and RT-PCR analyses indicated that the activin β gene is expressed in embryo, larva and adult stages ofDrosophila.