RNAi is genetic wand to reduce gene expression specifically and applied to many species. Since knock down of specific gene caused by RNAi is affect to all tissues except neural cell, it is hard to know tissue specific function of interested gene. For examination of tissue specific function of the interested gene, mosaic analysis or tissue specific rescue method is required. In C. elegans , many mutants that have defects in RNAi are isolated. Using
rde-1 , one of RNAi defective mutants, we established tissue specific RNAi system and reported that hypodermis specific RNAi system works well (Inoue et al., 2000 Japanese Worm Meeting). In this meeting, we report the establishment of muscle specific RNAi system and result of application of this system to early expressed embryonic lethal genes. Tissue specific RNAi system is based on tissue specific rescue of RNAi deficient phenotype caused by
rde-1 . For this purpose, tissue specific promoter is required. For establishment of muscle specific RNAi, we used two types of muscle specific promoters,
myo-3 and
hlh-1 . The
myo-3 and
hlh-1 promoters are reported as muscle specific promoter based on the results of GFP or lacZ reporter assay. We checked RNAi efficiency in muscle by
hlh-1 RNAi and in hypodermis by
lin-26 RNAi. Transgenic line harboring
rde-1 mutation and extrachromosomal array expressing
rde-1 under the control of the
myo-3 promoter showed RNAi positive phenotype both in the muscle and hypodermis. However, using the
hlh-1 promoter for the expression of
rde-1 , transgenic line showed RNAi positive phenotype in muscle cells specifically. Using muscle specific RNAi worms, we tried to explore the muscle specific function of
rho-1 and
cdc-42 , small GTPases. Both RNAi of
rho-1 and
cdc-42 caused embryonic lethal phenotype. RNAi of
rho-1 and
cdc-42 to muscle specific RNAi worms caused Unc phenotype, although RNAi of
rho-1 and
cdc-42 to hypodermis specific RNAi worms did not, suggesting that postembryonic functions of
rho-1 and
cdc-42 are important in the muscle cells.