The cell junction protein VAB-9 regulates adhesion and epidermal morphology in C. elegans

Epithelial cell junctions are essential for cell polarity, adhesion and morphogenesis. We have analysed VAB-9, a cell junction protein in Caenorhabditis elegans . VAB-9 is a predicted four-pass integral membrane protein that has greatest similarity to BCMP1 (brain cell membrane protein 1, a member of the PMP22/EMP/Claudin family of cell junction proteins) and localizes to the adherens junction domain of C. elegans apical junctions 1 , 2 , 3 , 4 . Here, we show that VAB-9 requires HMR-1/cadherin for localization to the cell membrane, and both HMP-1/α-catenin and HMP-2/β-catenin for maintaining its distribution at the cell junction. In vab-9 mutants, morphological defects correlate with disorganization of F-actin at the adherens junction; however, localization of the cadherin–catenin complex and epithelial polarity is normal. These results suggest that VAB-9 regulates interactions between the cytoskeleton and the adherens junction downstream of or parallel to α-catenin and/or β-catenin. Mutations in vab-9 enhance adhesion defects through functional loss of the cell junction genes apical junction molecule 1 ( ajm-1 ) and discs large 1 ( dlg-1 ), suggesting that VAB-9 is involved in cell adhesion. Thus, VAB-9 represents the first characterized tetraspan adherens junction protein in C. elegans and defines a new family of such proteins in higher eukaryotes.