Molecular and functional analysis of apical junction formation in the gut epithelium of Caenorhabditis elegans.

The Caenorhabditis elegans intestine is a simple and accessible model system to analyze the mechanism of junction assembly. In comparison to Drosophila and vertebrates, the C. elegans apical junction is remarkable because a single electron-dense structure is implicated in complex processes such as epithelial tightness, vectorial transport and cell adhesion. Here we present evidence in support of a heterogeneous molecular assembly of junctional proteins found in Drosophila and vertebrate epithelia associated with different junctions or regions of the plasma membrane. In addition, we show that molecularly diverse complexes participate in different aspects of epithelial maturation in the C. elegans intestine. DLG-1 (Discs large) acts synergistically with the catenin-cadherin complex (HMP-1-HMP-2-HMR-1) and the Ezrin-Radixin-Moesin homolog (ERM-1) to ensure tissue integrity of the intestinal tube. The correct localization of DLG-1 itself depends on AJM-1, a coiled-coil protein. Double depletion of HMP-1 (alpha-catenin) and LET-413 (C. elegans homolog of Drosophila Scribble) suggests that the catenin-cadherin complex is epistatic to LET-413, while additional depletion of subapically expressed CRB-1 (Crumbs) emphasizes a role of CRB-1 concerning apical junction formation in the C. elegans intestine.