Unfavorable environments challenge organisms to engage in defensive strategies. A notable example is C. elegans diapause entry in response to food deprivation and other stresses. We found that C. elegans forms dauer larvae in defense against the pathogens P. aeruginosa and S. typhimurium in the second and subsequent generations. The information to form dauers is transmitted to the progeny in the maternal germline. This transgenerational effect correlates with DAF-16 activation and depends on the immune status of the animal and virulence of the pathogen. Importantly, changing F1 worms from S. typhimurium to P. aeruginosa and vice versa, retained their ability to form dauers in the F2, suggesting a common mechanism to induce diapause for both pathogens. Since RNA interference (RNAi) is systemic and transgenerational mechanism, we examined a large group of mutants defective in different forms of RNAi for their ability to grow and form dauers in pathogens. sid-2, sid-3, rde-4, drh-3 and the multiple argonaute mutant MAGO12 grow significantly slower in routinary food E. coli OP50 than wild type animals. Mutants such as ergo-1, sago-1, sago-2, nrd-3 and the multiple argonaute mutant WM126 (defective in germline and somatic RNAi) grow as wild type on E. coli OP50 but slower on pathogens. sid-1, rde-1, WM119 (defective in germline RNAi), sid-5 and alg-2 grow like wild-type animals in pathogens but fail to form dauers in response to pathogens, suggesting a role for systemic, exogenous and germline RNAi in pathogen induced dauer formation.
What is the RNA signal that triggers diapause entry in the F2? To address this question we extracted mRNA and small RNAs from F1 and F2 animals growing on E. coli OP50, S. typhimurium and P. aeruginosa. Furthermore we isolated small RNAs from the bacteria from the intestines of C. elegans. Comparison of the RNAs of animals grown on the E. coli and pathogenic bacteria showed that a number of the same sRNAs were differentially expressed in animals raised on S. typhimurium and P. aeruginosa. The sRNAs found in our experiments include several classes, mainly microRNA (miRNAs), small nucleolar RNAs (snoRNAs), small nuclear RNAs (snRNA) and previously uncharacterized small RNAs. Importantly, some of the transcripts differentially expressed in worms on non-pathogenic vs pathogenic are potential targets of the differentially expressed small RNAs. Currently we are constructing the gene networks underlying dauer formation under pathogenesis. .
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