Tissue morphogenesis is indispensable for living functions of multicellular organisms. We have previously reported that loss-of-function of
gex-2 (Ce-Sra-1) or
gex-3 (Ce-HEM-2) leads to 100% embryonic lethality with abnormal tissue morphogenesis and that these molecules are localized at the cell-cell contact sites of all tissue cells throughout embryogenesis. (K. Kasuya et al., M. Soto et al., 12th international C. elegans meeting) Based on binding in a two-hybrid system and co-localization in immunostaining, GEX-2 and GEX-3 probably form a novel protein complex. GEX-2 and GEX-3 proteins have no significant functional domain. To clarify the molecular mechanisms of GEX-2/GEX-3 functions in tissue morphogenesis, we screened physically and functionally interacting molecules. At first, by a two-hybrid screening, we isolated 29 positive clones that included 6 genes. Next, we performed RNAi of 6 genes. Among them, disruption of W07B3.2 resulted in 100% lethal embryos, some of which showed exploder phenotype of hypodermis and others arrested at the comma-stage. Although both phenotypes were weaker than Gex phenotype, the disorganization of molecular markers of muscle and intestine were also observed in W07B3.2(RNAi) embryos. The GEX-2/GEX-3-like localization pattern of W07B3.2 and the binding of W07B3.2 to GEX-2 and GEX-3 in the immunoprecipitation assay suggested that W07B3.2 functionally related to GEX-2 and GEX-3. W07B3.2 gene product has a repeated structure which is weakly homologous to trichohyalin and raises the possibility to interact with intermediate filaments (IFs). To examine whether W07B3.2 interacts with C. elegans IFs, we performed two-hybrid binding assay. As a result, some IFs interacted with W07B3.2. Co-localization of GEX-2, GEX-3, and W07B3.2 with some IFs suggested that these molecules form a large complex. RNAi of
gex-2,
gex-3, and W07B3.2 eventually caused disorganization of the IF structure. Taken together, we proposed a model that W07B3.2 serves as a bridge between GEX-2/GEX-3 complex and intermediate filaments, and that the large complex essentially functions in tissue morphogenesis in C. elegans.