Characterization of a unique basolateral targeting domain in the Drosophila TGF-B Type II receptor punt

Abstract

In polarized epithelial cells, differential localization of receptors and ligands can control signaling. Drosophila wing imaginal discs are a polarized epithelial layer in which the TGF-B superfamily ligand Dpp is expressed both apically and basolaterally, yet requires a graded distribution throughout the disc to signal properly. We found that Punt, the type II TGF-B receptor that Dpp signals through, is localized specifically at the basolateral membrane, which limits Dpp signaling to the basolateral surface. In characterizing the sequence of Punt, our lab found a unique basolateral targeting domain, the Punt targeting domain (PTD). The PTD is both necessary and sufficient for basolateral localization. Mutation of the insect-conserved portion and whole PTD results in apical mislocalization but characterization of the PTD shows that there is no minimal sequence within the PTD responsible for function. Furthermore, changes in localization of Punt and the other type II receptor Wit affect fly viability.