Project description:Sigma factors are master regulators of bacterial transcription which direct gene expression of specific subsets of genes. In particular, alternative sigma factors are well-known to be key players of bacterial adaptation to changing environments. To elucidate the regulatory network of sigma factors in P. aeruginosa, an integrative approach including sigma factor-dependent mRNA profiling was performed to define the primary regulon of each sigma factor. Sigma factor hyper-expressing strains harboring the sigma factor gene in trans under control of the araBAD promoter and sigma factor deletion mutants were constructed. Under optimal conditions regarding sigma factor activity and optional induction of sigma factor expression, bacteria were harvested and total RNA was extracted. Upon mRNA enrichment, RNA was fragmented and ligated to specific RNA-adapters containing a hexameric barcode sequence for multiplexing. These RNA-libraries were reverse transcribed and amplified resulting in cDNA libraries which were sequenced on Illumina platforms. Sequence reads were separated according to their barcodes and barcode sequences were removed. The short reads were mapped to the genome sequence of the reference strain P. aeruginosa PA14 wild-type using stampy with default settings. The R package DESeq was used for differential gene expression analysis.
Project description:Sigma factors are master regulators of bacterial transcription which direct gene expression of specific subsets of genes. In particular, alternative sigma factors are well-known to be key players of bacterial adaptation to changing environments. To elucidate the regulatory network of sigma factors in P. aeruginosa, an integrative approach including ChIP-seq of 11 polyhistidine-tag sigma factors was performed to define the primary regulon of each sigma factor. Sigma factor genes were fused to a polyhistidine-tag and provided in trans. Under optimal conditions regarding sigma factor activity and induction of sigma factor expression, DNA-sigma factor interactions were conserved by formaldehyde treatment. Upon DNA fragmentation by sonication, the complexes were specifically immunoprecipitated by polyclonal anti-6X His-tag antibodies and the purified DNA was analyzed by Illumina sequencing. DNA enrichment to a control strain was calculated and used for peak calling within promoter region (-500,+100) to identify directly regulated genes/operons.
Project description:Gene regulation via transcription factors influences the metabolic, adaptive and pathogenic capabilities of the organism. We report the transcriptomes of the mutants of six major P. aeruginosa PA14 trancription factors - RhlR, LasR, Anr, GacA, FleQ and CbrB. The P. aeruginosa PA14 transposon mutants were analyzed by RNA-seq. All samples were cultivated in LB medium until reaching an OD600 of 2.0. For each biological replicate, three cultures were pooled for RNA extraction, library preparation and sequencing.
Project description:We analyzed a deletion mutant of the ECF M-OM-^C factor SigX and applied mRNA profiling to define the SigX dependent regulon in P. aeruginosa in response to low osmolarity medium conditions. Furthermore, the combination of transcriptional data with chromatin immunoprecipitation (ChIP) followed by high-throughput sequencing led to the identification of the DNA binding motif of SigX. Genome-wide mapping of SigX-binding regions revealed enrichment of downstream genes involved in fatty acid biosynthesis, type III secretion, swarming and c-di-GMP signaling. In accordance, a sigX deletion mutant exhibited an altered fatty acid composition of the cell membrane, reduced cytotoxicity, impaired swarming activity, elevated c-di-GMP levels and increased biofilm formation. In conclusion, a combination of ChIP-seq with transcriptional profiling and bioinformatic approaches to define consensus DNA binding sequences proved to be effective for the elucidation of the regulon of the alternative M-OM-^C factor SigX revealing its role in complex virulence-associated phenotypes in P. aeruginosa. Transcriptome profiling of the SigX deletion mutant and overexpressing wildtype complemented by ChIP-seq
Project description:Two-component systems (TCS) serve as basic stimulus-response coupling mechanisms to allow organisms to sense and respond to a large variety of environmental conditions. In the opportunistic pathogen Pseudomonas aeruginosa, more than 100 genes encode TCS components. To avoid unwanted cross-talk between TCSs, the signaling cascades are usually very specific, with one sensor talking to its cognate response regulator. However, cross-regulation may provide effective means to integrate different environmental stimuli into a harmonized output response and thus to coordinate gene expression in response to complex and challenging habitats. Here, we applied a protein-fragment complementation assay (PCA) and identified a direct interaction of two response regulators of the OmpR/PhoB subfamily, namely PhoB and TctD in P. aeruginosa in vivo. Transcriptional profiling and ChIP-seq analysis uncovered adjacent bipartite binding motifs of the two response regulators in 8 promoter regions, of which 6 showed a common PhoB-TctD binding motif with a fixed spacing between the two motifs. We further demonstrate that phosphate limitation exhibits a PhoB-dependent activating activity on the expression of those genes, whereas the presence of a preferred carbon source inhibits gene expression in a TctD-dependent manner. Thus, the perception and the integration of two important environmental signals are achieved by a titration of the relative amounts of two phosphorylated response regulators that inversely regulate a common subset of genes. In conclusion, our results shed light on the general principles underlying two-component signal transduction pathways and the exploitation of cross-regulation to adapt bacterial behavior to complex environments. Transcriptome profiling of the UCBP-PA14 phoB and tctD mutants complemented by phoB ChIP-seq experiments.
Project description:Ste5 and Far1 function as prototypical scaffold proteins activating a MAP-kinase cascade and polarizing yeast cells in response to pheromones. Here we show that Pkc1-dependent phosphorylation of conserved serine residues in their RING-H2 domains down-regulates pheromone induced signaling upon mechanical stress. Phosphorylation of Ste5 on serine 185 by Pkc1 interferes with its membrane-association in vivo by preventing binding to the receptor linked Gbg protein as determined by in vitro assays. Quantitative readouts of pheromone signaling show that Pkc1 induces rapid dispersal of Ste5 from mating projections upon mechanically-induced cell wall stress as well as during cell-cell fusion, leading to inhibition of MAPK activity and polarized growth. Cells expressing non-phosphorylatable Ste5 (Ste5S185A) undergo increased lysis during mechanical stress and cell-cell fusion compared to wild-type controls, and this effect is exacerbated by simultaneous expression of non-phosphorylatable Far1 (Far13A). Taken together, these results uncover a cross-talk mechanism explaining how mating cells inhibit pheromone signaling upon extrinsic or intrinsic mechanical stress to orchestrate polarized growth and cell-cell fusion.
Project description:Mitochondrial gene expression uses a non-universal genetic code in mammals. Besides reading the conventional AUG codon, mitochondrial (mt-)tRNAMet mediates incorporation of methionine on AUA and AUU codons during translation initiation and on AUA codons during elongation. We show that the RNA methyltransferase NSUN3 localises to mitochondria and interacts with mt-tRNAMet to methylate cytosine 34 (C34) at the wobble position. NSUN3 specifically recognises the anticodon stem loop (ASL) of the tRNA, explaining why a mutation that compromises ASL basepairing leads to disease. We further identify ALKBH1/ABH1 as the dioxygenase responsible for oxidising m5C34 of mt-tRNAMet to generate an f5C34 modification. In vitro codon recognition studies with mitochondrial translation factors reveal preferential utilization of m5C34 mt-tRNAMet in initiation. Depletion of either NSUN3 or ABH1 strongly affects mitochondrial translation in human cells, implying that modifications generated by both enzymes are necessary for mt-tRNAMet function. Together, our data reveal how modifications in mt-tRNAMet are generated by the sequential action of NSUN3 and ABH1, allowing the single mitochondrial tRNAMet to recognise the different codons encoding methionine. HEK293 cell lines expressing His-FLAG-tagged NSUN3 or the His-FLAG tag alone were crosslinked using UV or treated with 5-azacytidine and analysed by CRAC
Project description:In this study we investigated the developmental dynamics of genes targeted in vivo by the transcription factor RAMOSA1, a key regulator of determinacy, and revealed potential mechanisms for repressing branches in distinct stem cell populations in developing maize inflorescences. To identify targets of RA1 and to distinguish direct vs. indirect interactions, we performed Chromatin Immunoprecipitation (ChIP)-seq and compared the results to gene expression data (RNA-seq datasets for Eveland et al., 2013, submitted). We mapped genome-wide occupancy of RA1 and showed that it differently regulates modules of target genes based on spatiotemporal context. Plants expressing complementing RA1 transgenes tagged with HA or YFP were used in parallel experiments. Ear and tassel primordia were collected and tag-specific antibodies were used to pull down RA1 bound to its target loci. Genome-wide analysis of RA1 occupancy revealed thousands of putative binding sites (i.e. peaks significantly enriched (p < 1e-05) compared to input DNA).
Project description:We compared the dynamics and mechanisms of resistance development to ceftazidime, meropenem, ciprofloxacin, and ceftolozane-tazobactam in wild-type (PAO1) and mutator (PAOMS, M-bM-^HM-^FmutS) P. aeruginosa. The strains were incubated for 24 h with 0.5 to 64M-CM-^W MICs of each antibiotic in triplicate experiments. The tubes from the highest antibiotic concentration showing growth were reinoculated in fresh medium containing concentrations up to 64M-CM-^W MIC for 7 consecutive days. The susceptibility profiles and resistance mechanisms were assessed in two isolated colonies from each step, antibiotic, and strain. Ceftolozane-tazobactam-resistant mutants were further characterized by whole-genome analysis through RNA sequencing (RNA-seq). The development of high-level resistance was fastest for ceftazidime, followed by meropenem and ciprofloxacin. None of the mutants selected with these antibiotics showed cross-resistance to ceftolozane-tazobactam. On the other hand, ceftolozane-tazobactam resistance development was much slower, and high-level resistance was observed for the mutator strain only. PAO1 derivatives that were moderately resistant (MICs, 4 to 8 ug/ml) to ceftolozane-tazobactam showed only 2 to 4 mutations, which determined global pleiotropic effects associated with a severe fitness cost. High-level-resistant (MICs, 32 to 128 ug/ml) PAOMS derivatives showed 45 to 53 mutations. Major changes in the global gene expression profiles were detected in all mutants, but only PAOMS mutants showed ampC overexpression, which was caused by dacB or ampR mutations. Moreover, all PAOMS mutants contained 1 to 4 mutations in the conserved residues of AmpC (F147L, Q157R, G183D, E247K, or V356I). Complementation studies revealed that these mutations greatly increased ceftolozane-tazobactam and ceftazidime MICs but reduced those of piperacillin-tazobactam and imipenem, compared to those in wild-type ampC. Therefore, the development of high-level resistance to ceftolozane-tazobactam appears to occur efficiently only in a P. aeruginosa mutator background, in which multiple mutations lead to overexpression and structural modifications of AmpC. Mutants of Pseudomonas aeroginosa PAO1 and PAO1 M-bM-^HM-^FmutS against Ceftolozane-tazobactam were generated and analysed using RNA-Seq
Project description:Cells resident in tissues must be resilient to the physical demands of their surroundings. Our current understanding of cellular mechano-signalling is largely based on static systems, but these models do not reproduce the dynamic nature of living tissue. Here, we examined the time-resolved response of primary human mesenchymal stem cells (hMSCs) to periods of cyclic tensile strain (CTS). We observed parallels between morphological changes following low-intensity strain (1 hour, 4% CTS at 1 Hz) and responses to increased substrate stiffness. However, as the strain regime was intensified (CTS at ≥ 2 Hz), we characterised a broad, structured and reversible protein-level response, even as transcription was apparently shut down. Regulation of the linker of nucleo- and cytoskeleton (LINC) complex proteins, and specifically of SUN domain-containing protein 2 (SUN2), was found to decouple mechano-transmission within the cell and hence isolate the nucleus from cellular deformation.