Drosophila Stardust interacts with Crumbs to control polarity of epithelia but not neuroblasts.

Establishing cellular polarity is critical for tissue organization and function. Initially discovered in the landmark genetic screen for Drosophila developmental mutants, bazooka, crumbs, shotgun and stardust mutants exhibit severe disruption in apicobasal polarity in embryonic epithelia, resulting in multilayered epithelia, tissue disintegration, and defects in cuticle formation. Here we report that stardust encodes single PDZ domain MAGUK (membrane-associated guanylate kinase) proteins that are expressed in all primary embryonic epithelia from the onset of gastrulation. Stardust colocalizes with Crumbs at the apicolateral boundary, although their expression patterns in sensory organs differ. Stardust binds to the carboxy terminus of Crumbs in vitro, and Stardust and Crumbs are mutually dependent in their stability, localization and function in controlling the apicobasal polarity of epithelial cells. However, for the subset of ectodermal cells that delaminate and form neuroblasts, their polarity requires the function of Bazooka, but not of Stardust or Crumbs.