IDENTIFICATION OF 2 DROSOPHILA TGF-BETA FAMILY MEMBERS IN THE GRASSHOPPER SCHISTOCERCA-AMERICANA

Intercellular signaling molecules of the transforming growth factor-be ta (TGF-beta) superfamily are required for pattern formation in many m ulticellular organisms. The decapentaplegic (dpp) gene of Drosophila m elanogaster has several developmental roles. To improve our understand ing of the evolutionary diversification of this large family we identi fied dpp in the grasshopper Schistocerca americana. S. americana diver ged from D. melanogaster approximately 350 million years ago, utilizes a distinct developmental program, and has a 60-fold-larger genome tha n D. melanogaster. Our analyses indicate a single dpp locus in D. mela nogaster and S. americana, suggesting that dpp copy number does not co rrelate with increasing genome size. Another TGF-beta superfamily memb er, the D. melanogaster gene 60A, is also present in only one copy in each species. Comparison of homologous sequences from D. melanogaster, S. americana, and H. sapiens, representing roughly 900 million years of evolutionary distance, reveals significant constraint on sequence d ivergence for both dpp and 60A. In the signaling portion of the dpp pr otein, the amino acid identity between these species exceeds 74%. Our results for the TGF-beta superfamily are consistent with current hypot heses describing gene duplication and diversification as a frequent re sponse to high levels of selective pressure on individual family membe rs.