The Role of and Genetic Suppressors in Epithelial Cell Junction Formation

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 , atypical protein kinase C (aPKC) is required for junction maturation, although how it contributes to this process is poorly understood. A role for the 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 that causes junction breaks in the spermatheca and leads to sterility, we identify intragenic and extragenic suppressors that render mutants fertile. Intragenic suppressors include an unanticipated stop-to-stop mutation in the gene, providing evidence for the importance of stop codon identity in gene activity. One extragenic suppressor is a loss-of-function allele of the homolog , which antagonizes aPKC within epithelia of and mammals, but was not known previously to function in epithelia. Finally, two extragenic suppressors are loss-of-function alleles of -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.