Cytoskeletal rearrangement is indispensable for tissue formation. Function of intermediate filaments, one of the major cytoskeletal components, in tissue is remained to be clarified due to their difficulty in biochemical and cell biological handling. In this study, we try to examine dynamic function and regulation of intermediate filaments in C. elegans embryonic tissue formation. From C. elegans Genome Sequencing database, we found 11 cytoplasmic intermediate filament genes except one nuclear lamin. Eight genes are reported by Dodemont et al. (1994 ) and three genes are novel. From sequencing homology, these 11 intermediate gene products were revealed to be prototype of many types of mammalian cytoplasmic intermediate filaments. We also performed characterization of MH antibodies reported to be recognized intermediate filaments in C. elegans . Using these MH antibodies, we found that intermediate filaments are expressed from mid phase of embryogenesis, suggesting that intermediate filaments are involved in also embryonic tissue organization. We also found a possible regulatory molecule of intermediate filaments, GEI-4. We previously identified
gex-2 and
gex-3 genes as essential factors for tissue formation. We performed yeast two hybrid screening of interacting molecules with GEX-2 ( gei genes, gex interacting molecule), and obtained 6 genes including GEI-4. GEI-4 shared weak homology to trichohyalin, a mammalian intermediate filament interacting protein. We found interaction between GEI-4 and C. elegans intermediate filaments by yeast two-hybrid method. RNAi of
gei-4 caused an embryonic lethality with disorganization of tissue morphology. Consistent with the interaction of GEI-4 with GEX-2, immunostaining analysis revealed that GEI-4 is colocalized with GEX-2, GEX-3, and many intermediate filaments at the peripheral region of almost all the cells. Terminal phenotypes of
gei-4 ,
gex-2 , and
gex-3 showed disorganization of intermediate filaments. Thus, these results suggest that dynamics of intermediate filaments, regulated by GEX-2/GEX-3/GEI-4 protein complex, is essential for embryonic tissue formation.