Two chloroplastic viroids induce the accumulation of small RNAs associated with posttranscriptional gene silencing.
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In plants, posttranscriptional gene silencing (PTGS) has been reported for cytoplasmic RNAs from endogenous nuclear genes, transgenes, viruses, and, recently, for a viroid with nuclear replication and accumulation. However, phenomena of this kind have not been described for mitochondrial or chloroplastic RNAs. Here we show that viroids that replicate and accumulate in the chloroplast are also targets of PTGS and this process may control viroid titer. (+info)
Rotavirus gene silencing by small interfering RNAs.
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RNA interference is an evolutionarily conserved double-stranded RNA-triggered mechanism for suppressing gene expression. Rotaviruses, the leading cause of severe diarrhea in young children, are formed by three concentric layers of protein, from which the spike protein VP4 projects. Here, we show that a small interfering RNA corresponding to the VP4 gene efficiently inhibits the synthesis of this protein in virus-infected cells. A large proportion of infected cells had no detectable VP4 and the yield of viral progeny was reduced. Most of the virus particles purified from these cells were triple-layered, but lacked VP4, and were poorly infectious. We also show that VP4 might not be required for the last step of virus morphogenesis. The VP4 gene silencing was specific, since the synthesis of VP4 from rotavirus strains that differ in the target sequence was not affected. These findings offer the possibility of carrying out reverse genetics in rotaviruses. (+info)
The Drosophila atypical protein kinase C-ref(2)p complex constitutes a conserved module for signaling in the toll pathway.
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Recent results showed the critical role of the mammalian p62-atypical protein kinase C (aPKC) complex in the activation of NF-kappaB in response to different stimuli. Here we demonstrate using the RNA interference technique on Schneider cells that the Drosophila aPKC (DaPKC) is required for the stimulation of the Toll-signaling pathway, which activates the NF-kappaB homologues Dif and Dorsal. However, DaPKC does not appear to be important for the other Drosophila NF-kappaB signaling cascade, which activates the NF-kappaB homologue Relish in response to lipopolysaccharides. Interestingly, DaPKC functions downstream of the nuclear translocation of Dorsal or Dif, controlling the transcriptional activity of the Drosomycin promoter. We also show that the Drosophila Ref(2)P protein is the homologue of mammalian p62 as it binds to DaPKC, its overexpression is sufficient to activate the Drosomycin but not the Attacin promoter, and its depletion severely impairs Toll signaling. Collectively, these results demonstrate the conservation of the p62-aPKC complex for the control of innate immunity signal transduction in Drosophila melanogaster. (+info)
Mechanisms of AIF-mediated apoptotic DNA degradation in Caenorhabditis elegans.
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Apoptosis-inducing factor (AIF), a mitochondrial oxidoreductase, is released into the cytoplasm to induce cell death in response to apoptotic signals. However, the mechanisms underlying this process have not been resolved. We report that inactivation of the Caenorhabditis elegans AIF homolog wah-1 by RNA interference delayed the normal progression of apoptosis and caused a defect in apoptotic DNA degradation. WAH-1 localized in C. elegans mitochondria and was released into the cytosol and nucleus by the BH3-domain protein EGL-1 in a caspase (CED-3)-dependent manner. In addition, WAH-1 associated and cooperated with the mitochondrial endonuclease CPS-6/endonuclease G (EndoG) to promote DNA degradation and apoptosis. Thus, AIF and EndoG define a single, mitochondria-initiated apoptotic DNA degradation pathway that is conserved between C. elegans and mammals. (+info)
The Drosophila slamdance gene: a mutation in an aminopeptidase can cause seizure, paralysis and neuronal failure.
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We report here the characterization of slamdance (sda), a Drosophila melanogaster "bang-sensitive" (BS) paralytic mutant. This mutant exhibits hyperactive behavior and paralysis following a mechanical "bang" or electrical shock. Electrophysiological analyses have shown that this mutant is much more prone to seizure episodes than normal flies because it has a drastically lowered seizure threshold. Through genetic mapping, molecular cloning, and RNA interference, we have demonstrated that the sda phenotype can be attributed to a mutation in the Drosophila homolog of the human aminopeptidase N (APN) gene. Furthermore, using mRNA in situ hybridization and LacZ staining, we have found that the sda gene is expressed specifically in the central nervous system at particular developmental stages. Together, these results suggest that the bang sensitivity in sda mutants is caused by a defective APN gene that somehow increases seizure susceptibility. Finally, by using the sda mutation as a sensitized background, we have been able to identify a rich variety of sda enhancers and other independent BS mutations. (+info)
Biliverdin reductase: a major physiologic cytoprotectant.
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Bilirubin, an abundant pigment that causes jaundice, has long lacked any clear physiologic role. It arises from enzymatic reduction by biliverdin reductase of biliverdin, a product of heme oxygenase activity. Bilirubin is a potent antioxidant that we show can protect cells from a 10,000-fold excess of H2O2. We report that bilirubin is a major physiologic antioxidant cytoprotectant. Thus, cellular depletion of bilirubin by RNA interference markedly augments tissue levels of reactive oxygen species and causes apoptotic cell death. Depletion of glutathione, generally regarded as a physiologic antioxidant cytoprotectant, elicits lesser increases in reactive oxygen species and cell death. The potent physiologic antioxidant actions of bilirubin reflect an amplification cycle whereby bilirubin, acting as an antioxidant, is itself oxidized to biliverdin and then recycled by biliverdin reductase back to bilirubin. This redox cycle may constitute the principal physiologic function of bilirubin. (+info)
RNA interference-mediated silencing of Sod2 in Drosophila leads to early adult-onset mortality and elevated endogenous oxidative stress.
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Oxidative stress has been widely implicated as an important factor in the aging process. Because mitochondrial respiration is the principal source of reactive oxygen within cells, the mitochondrially localized superoxide dismutase (SOD) 2 is thought to play an important front-line defensive role against aging-related oxidative stress. Although genetic studies with mutants deficient in SOD1, the predominantly cytosolic isoform of SOD, have been instrumental in elucidating the role of reactive oxygen metabolism in aging in Drosophila, the lack of available mutations in the Sod2 gene has hampered an equivalent analysis of the participation of this important antioxidant enzyme in the Drosophila aging model. Here we report that ablation of mitochondrial SOD2 through expression of a GAL4-regulated, inverted-repeat Sod2 RNA-interference transgene in an otherwise normal animal causes increased endogenous oxidative stress, resulting in loss of essential enzymatic components of the mitochondrial respiratory chain and the tricarboxylic acid cycle, enhances sensitivity to applied oxidative stress, and causes early-onset mortality in young adults. In sharp contrast, ablation of SOD2 has no overt effect on the development of larvae and pupae, which may reflect a fundamental transition in oxygen utilization andor reactive oxygen metabolism that occurs during metamorphosis from larval to adult life. (+info)
Functional siRNA expression from transfected PCR products.
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RNA interference (RNAi) is a process in which double-stranded RNA (dsRNA) induces the postranscriptional degradation of homologous transcripts. RNAi can be initiated by exposing cells to dsRNA either via transfection or endogenous expression. In mammalian systems, the sequence-specific RNAi effect has been observed by expression of 21-23 base transcripts capable of forming duplexes, or via expression of short hairpin RNAs. We describe here a facile PCR based strategy for rapid synthesis of siRNA expression units and their testing in mammalian cells. The siRNA expression constructs are constructed by PCR, and the PCR products are directly transfected into mammalian cells resulting in functional expression of siRNAs. This approach should prove useful for identification of optimal siRNA-target combinations and for multiplexing siRNA expression in mammalian cells. (+info)