Epithelial cells form intercellular junctions to strengthen cell–cell adhesion and limit diffusion, allowing epithelia to function as dynamic tissues and barriers separating internal and external environments. Junctions form as epithelial cells differentiate; clusters of junction proteins first concentrate apically, then mature into continuous junctional belts that encircle and connect each cell. In mammals and Drosophila, atypical protein kinase C (aPKC) is required for junction maturation, although how it contributes to this process is poorly understood. A role for the Caenorhabditis elegans aPKC homolog PKC-3 in junction formation has not been described previously. Here, we show that PKC-3 is essential for junction maturation as epithelia first differentiate. Using a temperature-sensitive allele of pkc-3 that causes junction breaks in the spermatheca and leads to sterility, we identify intragenic and extragenic suppressors that render pkc-3 mutants fertile. Intragenic suppressors include an unanticipated stop-to-stop mutation in the pkc-3 gene, providing evidence for the importance of stop codon identity in gene activity. One extragenic pkc-3 suppressor is a loss-of-function allele of the lethal(2) giant larvae homolog lgl-1, which antagonizes aPKC within epithelia of Drosophila and mammals, but was not known previously to function in C. elegans epithelia. Finally, two extragenic suppressors are loss-of-function alleles of sups-1—a previously uncharacterized gene. We show that SUPS-1 is an apical extracellular matrix protein expressed in epidermal cells, suggesting that it nonautonomously regulates junction formation in the spermatheca. These findings establish a foundation for dissecting the role of PKC-3 and interacting genes in epithelial junction maturation.
The Role of pkc-3 and Genetic Suppressors in Caenorhabditis elegans Epithelial Cell Junction Formation
