THE DROSOPHILA RHOMBOID PROTEIN IS CONCENTRATED IN PATCHES AT THE APICAL CELL-SURFACE

Patterned expression of the Drosophila rhomboid (rho) gene is thought to promote signaling by the EGF receptor (EGER) in specific cell types . In this report we examine the subcellular localization of the Rhombo id protein (Rho) which is predicted to be an integral membrane protein . At the light level, immunocytochemical staining for Rho reveals a sm all number of large patches (or plaques) at or near the apical cell su rface. In some cells Rho plaques colocalize with Armadillo at adherens junctions, while in other cells plaques are only found basal to the a dherens junction. Immunoelectron microscopy reveals that Rho plaques a re composed of a highly localized patch of plasma membrane and a dense ly staining underlying structure. Concentration of Rho in distinct pla ques depends on a balance of synthesis and membrane recycling since in creasing the amount of rho expression or blocking membrane recycling l eads to more uniform cell surface labeling. A limiting cellular compon ent also appears to be required for concentrating Rho in plaques. We d iscuss clustering of Rho in plasma membrane patches with respect to th e proposed role of Rho in promoting EGF-R signaling. (C) 1996 Academic Press, Inc.