Project description:RNAseIII ribonucleases act at the heart of RNA silencing pathways by processing precursor RNAs into mature microRNAs and siRNAs. In the fission yeast Schizosaccharomyces pombe, siRNAs are generated by the RNAseIII enzyme Dcr1 and are required for heterochromatin formation. In this study, we have analyzed the subcellular localization of Dcr1 and found that it accumulates in the nucleus and is enriched at the nuclear periphery. Nuclear accumulation of Dcr1 depends on a short motif which constrains nuclear export promoted by the double-stranded RNA binding domain of Dcr1. Absence of this motif renders Dcr1 mainly cytoplasmic and is accompanied by remarkable changes in gene expression and failure to assemble heterochromatin. Our findings suggest that dicer proteins are shuttling proteins and that the steady-state subcellular levels can be shifted towards either compartment. This has implications for the mechanism of RNAi-mediated heterochromatin assembly and the spatial organization of RNA silencing pathways in general. Small RNA libraries from total RNA isolations of wild-type, dcr1Delta and dcr1DeltaC33 cells and subjected to high-throughput sequencing.
Project description:This project aims to investigate the metabolic pathways expressed by the active microbial community occurring at the deep continental subsurface. Subsurface chemoLithoautotrophic Microbial Ecosystems (SLiMEs) under oligotrophic conditions are supported by H2; however, the overall ecological trophic structures of these communities are poorly understood. Some deep, fluid-filled fractures in the Witwatersrand Basin, South Africa appear to support inverted trophic pyramids wherein methanogens contributing <5% of the total DNA apparently produce CH4 that supports the rest of the community. Here we show the active metabolic relationships of one such trophic structure by combining metatranscriptomic assemblies, metaproteomic and stable isotopic data, and thermodynamic modeling. Four autotrophic β-proteobacteria genera that are capable of oxidizing sulfur by denitrification dominate. They co-occur with sulfate reducers, anaerobic methane oxidizers and methanogens, which each comprises <5% of the total community. Defining trophic levels of microbial chemolithoautotrophs by the number of transfers from the initial abiotic H2-driven CO2 fixation, we propose a top-down cascade influence of the metabolic consumers that enhances the fitness of the metabolic producers to explain the inverted biomass pyramid of a multitrophic SLiME. Symbiotic partnerships are pivotal in the deep biosphere on and potentially beyond the Earth.
Project description:The goal of the ChIP-seq study was to investigate the distribution of the TATA-binding protein (TBP) across the human genome. TBP is the DNA-binding subunit of the basal transcription factor TFIID for RNA polymerase II (pol II) and it also participates in other complexes for the other RNA polymerase. The BTAF1 ATPase forms a stable complex with TBP and regulates its activity in pol II transcription. BTAF1 is believed to mobilize TBP from promoter and non-promoter sites. To test this hypothesis, TBP ChIP samples were prepared from human HeLa cervix carcinoma cells after knock-down of BTAF1 expression and compared to HeLa cells with a control knock-down of GAPDH. GAPDH is a cytosolic enzyme that participates in glycolysis, and its inactivation is not expected to affect the genomic distribution of TBP, and acts as negative control. ChIP samples were sequenced using SOLiD technology along with the INPUT sample to normalize the distribution of background signals within each of the two chromatin samples. 2 ChIP samples + one input sample
Project description:Domains of heterochromatin play important roles in the maintenance and regulation of eukaryotic genomes. However, the repressive nature of heterochromatin combined with its propensity to self-propagate necessitates the existence of robust mechanisms that limit heterochromatin spreading and thereby avoid silencing of expressed genes. A number of specific sequence elements have been found to serve as barriers to heterochromatin spreading; however, the mechanisms by which spreading is curtailed are generally not well understood. Here we uncover a role for PAF complex component Leo1 in regulating heterochromatin cis-spreading. A genetic screen revealed that loss of Leo1 results in spreading of heterochromatin across a centromeric (IRC) boundary element in fission yeast. Similar heterochromatin spreading was seen upon deletion of other components of the PAF complex, but not other factors involved in transcription-coupled chromatin modification, indicating a specific role for the PAF complex in heterochromatin regulation. Loss of Leo1 is associated with reduced levels of H4K16 acetylation at the boundary, while tethering of the H4K16 acetyltransferase Mst1 to boundary chromatin suppresses heterochromatin spreading in leo1Δ cells, suggesting that Leo1 antagonises heterochromatin spreading by facilitating H4K16 acetylation. Interestingly, Leo1 also regulates heterochromatin spreading independently of boundaries, and loss of Leo1 causes redistribution of heterochromatin, in particular resulting in substantial expansion of telomeric heterochromatin domains. The PAF complex is known to be an important regulator of transcription-related chromatin modifications; our findings reveal a previously undescribed role for this complex in global regulation of heterochromatin spreading in cis. 8 samples: input (whole cell extract) and IP from H3K9me2 ChIP in wild-type and leo1Δ cells, in duplicate
Project description:This SuperSeries is composed of the following subset Series: GSE32310: Transcriptome analysis of mediator Med20 mutant and dcr1 mutant in S.pombe GSE35524: Mediator promotes CENP-A incorporation at fission yeast centromeres [ChIP-seq] Refer to individual Series
Project description:Epigenetic mechanisms can be influenced by environmental cues and thus evoke phenotypic variation. This plasticity can be advantageous for adaption, but also detrimental if not under tight control. Although having attracted considerable interest, it remains largely unknown if and how environmental cues such as temperature trigger epigenetic alterations. Using fission yeast, we demonstrate that environmentally induced discontinuous phenotypic variation is buffered by a negative feedback loop that involves the RNase Dicer and the protein disaggregase Hsp104. In the absence of Hsp104, Dicer accumulates in cytoplasmic inclusions and heterochromatin becomes unstable at elevated temperatures, an epigenetic state that is inherited for many generations after the heat stress. Dicer instead averts the toxic aggregation of a prionogenic protein. Our results highlight the importance of feedback regulation in building epigenetic memory and uncover Hsp104 and Dicer as homeostatic controllers that buffer environmentally induced stochastic epigenetic variation and toxic aggregation of prionogenic proteins. wt_spb75 grown at 30°C or 37°C
Project description:Epigenetic mechanisms can be influenced by environmental cues and thus evoke phenotypic variation. This plasticity can be advantageous for adaption, but also detrimental if not under tight control. Although having attracted considerable interest, it remains largely unknown if and how environmental cues such as temperature trigger epigenetic alterations. Using fission yeast, we demonstrate that environmentally induced discontinuous phenotypic variation is buffered by a negative feedback loop that involves the RNase Dicer and the protein disaggregase Hsp104. In the absence of Hsp104, Dicer accumulates in cytoplasmic inclusions and heterochromatin becomes unstable at elevated temperatures, an epigenetic state that is inherited for many generations after the heat stress. Dicer instead averts the toxic aggregation of a prionogenic protein. Our results highlight the importance of feedback regulation in building epigenetic memory and uncover Hsp104 and Dicer as homeostatic controllers that buffer environmentally induced stochastic epigenetic variation and toxic aggregation of prionogenic proteins. Various strains grown at 30°C or 37°C
Project description:Acute leukemia are characterized by deregulation of transcriptional networks that control the lineage specificity of gene expression. The aberrant overexpression of the Spi-1/PU.1 transcription factor leads to erythroleukemia. To determine how Spi-1 mechanistically influences the transcriptional program, we combined a ChIP-seq analysis with transcriptional profiling in cells from an erythroleukemic mouse model. We show that Spi-1 displays a selective DNA-binding that does not often cause transcriptional modulation. We report that Spi-1 controls transcriptional activation and repression through distinct Spi-1 recruitment to chromatin. We revealed several parameters impacting on Spi-1-mediated transcriptional activation. Gene activation is facilitated by Spi-1 occupancy close to transcriptional starting site of genes devoid of CGIs. Moreover, in those regions Spi-1 acts by binding to multiple motifs tightly clustered and with similar orientation. Finally, in contrast to the myeloid and lymphoid B cells in which Spi-1 exerts a physiological activity, in the erythroleukemic cells, lineage-specific cooperating factors do not play a prevalent role in Spi-1-mediated transcriptional activation. Thus, our work describes a new mechanism of gene activation through clustered site occupancy of Spi-1 particularly relevant in regard to the strong expression of Spi-1 in the erythroleukemic cells. Chromatin immunoprecipitations of Spi-1, H3K36me3, RNApolII,mouse IgG followed by sequencing were performed on spleen-derived erythroleukemic cells of spi-1 transgenic mice. In case of Spi-1, reads obtained from the two different mice represent biological replicates and were merged for bioinformatic analysis. Input DNA from each ChIP experiments have been pooled and sequenced as one control.
Project description:Using a high-throughput sequencing approach we quantitatively analyzed the content of viroid-derived siRNAs of an infected tree. Our results show that the entire PLMVd genome is found in the siRNA population. Also both polarities are susceptible to be targeted by the RNAi machinery but specific regions for each polarity are over represented. Those regions, that are not the same for each polarity, do not necessarily correlate with double stranded regions that could be substrate for Dicer-like enzymes. Finally the analysis of the first 5’ nucleotide revealed a bias toward a C or a U in viroid-derived siRNAs, indicating that at least AGO5 and AGO1 can recruit these small RNAs. Analysis of siRNAs population from RNA sample isolated from a viroid-infected tree