Figure 1. Schematic of various cell junction arrangements in vertebrates, Drosophila, and C. elegans epithelia. Corresponding cell junction regions either in relative location, function, and/or molecular make-up are indicated with similar colors. Green indicates the tight junction in vertebrates the SAR-like region in C. elegans, the sub-apical region (SAR) in Drosophila. Blue indicates the cadherin-based adherens junction. Red indicates the septate junction in Drosophila and the AJM-1/DLG-1 region in C. elegans. Vertebrates have no precisely analogous structure to the septate junction in epithelia, but share a molecularly similar barrier at the paranodal junction. Vertebrate desmosomes are shown in yellow (A). Lateral views (cutaways) show the nature of the junctional structures in the membranes. Adherens junctions appear as solid bands in the membrane, pleated septate junctions are characterized by regular wave-like strands, and tight junctions appear as irregular but connected anastomosing strands. For simplicity, only the composition of cell junction components in the paracellular space is shown. (B) The most common cellular junctions and representative protein components are listed. Transmembrane proteins are indicated in color (bold) and components unique to vertebrates (other than desmosomes) are underlined.