DROSOPHILA DPP SIGNALING IS MEDIATED BY THE PUNT GENE-PRODUCT - A DUAL LIGAND-BINDING TYPE-II RECEPTOR OF THE TGF-BETA RECEPTOR FAMILY

Signaling by TGF beta-related factors requires ligand-induced associat ion between type I and type II transmembrane serine/threonine kinases. In Drosophila, the saxophone (sax) and thick veins (tkv) genes encode type I receptors that mediate signaling by decapentaplegic (dpp), a m ember of the bone morphogenetic protein (BMP) subgroup of TGF beta-typ e factors. In this report, we demonstrate that the Drosophila punt gen e encodes atr-ll, a previously described type II receptor that on its own is able to bind activin but not BMP2, a vertebrate ortholog of dpp . Mutations in punt produce phenotypes similar to those exhibited by t kv, sax, and dpp mutants. Furthermore, punt will bind BMP2 in concert with tkv or sax, forming complexes with these receptors. We suggest th at punt functions as a type II receptor for dpp and propose that BMP s ignaling in vertebrates may also involve sharing of type II receptors by diverse ligands.