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キーワード:
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要旨:
Bacillus thuringiensis (BT) produces toxins that target invertebrates including Caenorhabditis elegans. Known C. elegans defense mechanisms against BT are largely limited to the Cry5B toxin and are not universal. Virulence of Bacillus strains is often highly specific, such that the BT strain DB27 represents one of the most virulent pathogens of C. elegans, but shows no virulence to another nematode model Pristionchus pacificus. To uncover the underlying mechanisms of differential response of the two nematodes to BT DB27 and to reveal C. elegans defense mechanisms against this pathogen we conducted a genetic screen for C. elegans mutants resistant to BT DB27. We identified a BT DB27 resistant C. elegans mutant that is identical to nasp-1, the C. elegans homolog of the nuclear-autoantigenic-sperm protein. Further characterization and gene expression analysis indicate a substantial overlap between genes down regulated in nasp-1 and targets of C. elegans dcr-1/Dicer, suggesting that dcr-1 is repressed in nasp-1 mutants. Indeed, quantitative PCR confirmed down-regulation of dcr-1 in nasp-1 mutants. Consistent with this, nasp-1 exhibits RNAi deficiency and reduced longevity similar to dcr-1 mutant. Building on these surprising findings we further explored a potential role of dcr-1 in C. elegans innate immunity. Indeed, we show that dcr-1 mutant alleles deficient in miRNA processing, but not those deficient only in RNAi, are resistant to BT DB27. Furthermore, dcr-1 overexpression rescues nasp-1 resistance, suggesting that repression of dcr-1 function determines nasp-1 resistance. We identified the collagen col-92 as one of the downstream effectors of nasp-1. Knockdown of col-92 results in hyper-susceptibility of wild-type worms, whereas col-92(RNAi) in a nasp-1 mutant background abrogates resistance indicating that this collagen plays an important role in resistance to DB27. These results uncover a previously unknown role of DCR-1/Dicer in C. elegans antibacterial immunity that is largely associated with miRNA processing.
