IDENTIFICATION OF A DROSOPHILA ACTIVIN RECEPTOR

Activins are cytokines of the transforming growth factor beta superfam ily that control various events during vertebrate embryo development a nd cell differentiation in the adult, and act through transmembrane re ceptors that contain a cytoplasmic protein-serine/threonine kinase dom ain. We describe the identification, deduced primary structure, and ex pression pattern of Atr-II, a receptor serine/threonine kinase found i n Drosophila. With the exception of the spacing of 10 cysteine residue s, the extracellular domain of Atr-II is very dissimilar from those of vertebrate activin receptors, yet it binds activin with high affinity and specificity. The kinase domain sequence of Atr-II is 60% identica l to those of activin receptors from vertebrates, suggesting similarit ies in their signaling mechanisms. Maternal Atr-II transcript and its product are abundant in the oocyte. During development, the highest le vels of Atr-II transcript and protein are observed in the mesoderm and gut. The possible role of an activin signaling system in Drosophila d evelopment is discussed.