Composition and arrangement of intercellular junctions in mammalian and Drosophila epithelia.

(A) Typical arrangement of the epithelial junctional complex in a monolayered mammalian epithelium. The apical membrane domain is labeled in transparent beige color and the basal–lateral membrane domain is labeled in gray color. The ZO (red) is localized apical to the ZA (blue). De (yellow) occur as spot-like junctions on the lateral interface of adjacent cells. (B) Arrangement of typical Drosophila epithelial junctional complex (apical domain, beige; basal–lateral domain, gray). The ZA (blue) forms the most apical junction followed basally by occluding SJs (red). This arrangement of junctional complexes is typical for ectodermally derived epithelia in Drosophila, except for the Malpighian tubules and the gastric caeca. (C) Arrangement of Drosophila epithelial junctional complex in the midgut epithelium. The SJ (red) is localized apical to AJs (blue), which are not organized into a belt-like ZA but occur as spot AJs throughout the basal area of the lateral membrane interfaces. AJ, adherens junction; De, desmosomes; SJ, septate junction; ZA, zonula adherens; ZO, zonula occludens.