The inturned protein of Drosophila melanogaster is a cytoplasmic protein located at the cell periphery in wing cells

The inturned (in) gene is a component: of the frizzled (fz) signaling pathw ay that controls the polarity of hairs and bristles in the epidermis of Dro sophila. It appears to act downstream of fz, which encoder a putative recep tor for a tissue polarity signal. The in gene encodes a novel protein that had been suggested to contain two potential transmembrane domains, ii has b een suggested that the in protein interacts with the actin cytoskeleton to regulate the formation of the pupal wing prehairs that become adult hairs. The initiation of prehairs is normally restricted to the vicinity of the di stal most vertex along the epical surface of the pupal wing cells. In an in mutant, prehairs initate at a variety of locations along the apical cell p eriphery. We have used immunofluorescence to study the subcellular localiza tion of the In protein. When expressed in cultured cells, we found that in is a cytoplasmic protein. However, we found that ii is localized in the vic inity of plasma membrane and the cortical actin cytoskeleton of Drosophila wing disc and pupal wing cells. Thus, in wing cells the In protein is local ized to the region of the cell where it appears to function. Th is subcellu lar localization presumably requires the function of other proteins and may represent a regulatory mechanism. Our data suggest that fz does not play a major role in the subcellular localization of In. The In protein is notabl y insoluble in buffers containing high salt and nonionic detergents. This l ack of solubility is significantly reduced in fz and mwh mutants, implying thai it may be related to the mechanism of in function. Dev. Genet. 25:297- 305, 1090. (C) 1999 Wiley-Liss, Inc.