In C. elegans, mosaic analysis is a powerful genetic tool for determining in which tissue or specific cells a gene of interest is required. For traditional mosaic analysis, a loss-of-function mutant and a genomic fragment that can rescue the mutant phenotype are required. Here we establish an easy and rapid mosaic system using RNAi (RNA mediated interference), using a rde-1 mutant that is resistant to RNAi. Tissue-specific expression of the wild type rde-1 cDNA in rde-1 mutants limits RNAi sensitivity to a specific tissue. We established hypodermal-and muscle-specific RNAi systems by expressing rde-1 cDNA under the control of the lin-26 and hlh-1 promoters, respectively. We confirmed tissue-specific RNAi using two assays: (1) tissue-specific knockdown of GFP expression, and (2) phenocopy of mutations in essential genes that were previously known to function in a tissue-specific manner. We also applied this system to an essential gene, ajm-1, expressed in hypodermis and gut, and show that lethality in ajm-1 mutants is due to loss of expression in hypodermal cells. Although we demonstrate tissue-specific RNAi in hypodermis and muscle, this method could be easily applied to other tissues.
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