Understanding the Regulatory Networks of Three LacI Transcriptional Repressors in Clostridium thermocellum DSM1313
ABSTRACT: Clostridium thermocellum is a candidate for cellulosic ethanol production. It expresses enzymes for both cellulose solubilization and its fermentation to produce lignocellulosic ethanol. Understanding how this organism regulates gene expression is of importance for developing a better fundamental understanding of this industrial relevant bacterium. We are primarily interested in gene regulation by three predicted LacI regulators. A previous report of one LacI regulator in C. thermocellum ATCC27405 (Cthe_2808) indicated this was a transcriptional repressor of neighboring genes with repressor activity relieved in the presence of laminaribiose (a β-1,3 disaccharide). The current work is aimed at understanding if a homolog of this LacI transcriptional regulator in C. thermocellum DSM1313 and two others putatively characterized as LacI regulators are in fact global regulatory proteins with extensive regulons or, if like the majority of LacI transcription factors, the regulation is limited to local genomic regions. Each of the three LacI regulators was deleted in C. thermocellum DSM1313. Genome re-sequencing was used to confirm the deletion and ensure nonspecific recombination events were avoided during the gene deletion strategy. Growth of each strain on cellobiose was unaffected by any of the gene deletions under pH controlled fermentations. Global gene expression patterns taken at mid-log phase for each strain identified glycoside hydrolase genes encoding hemicellulases, including cellulosomal enzymes, that were highly up-regulated (up to 9 fold) in the absence of each LacI regulator. Thus suggesting these were repressed under wild type conditions. Electrophoretic mobility shift assays have confirmed LacI transcription factor binding to specific regions of gene promoters with putative motifs ranging from 16-18 bp. Work is ongoing to confirm the specific binding motif recognized by the two previously un-characterized transcription factors and assess the occurrence of this motif in the C. thermocellum DSM1313 genome. The identification of LacI repressor activity on hemicellulose gene expression is a key result of this work and will add to the small body of existing literature on the area of gene regulation in C. thermocellum. Four strains of C. thermocellum DSM1313 including a parental strain (Δhpt) and three others with deletion in lacI transcription factors were characterised by RNA-seq. The strains were grown in 1L bioreactors, cells (from 50 ml samples) were harvested at mid exponential, late exponential and 30 min after acid production halted during the transition to stationary phase. The growth studies were performed in triplicate and thirty six samples were analyzed by RNA-sequencing.
Project description:RNA-seq analysis revealed that genes involved in urea uptake and metabolism were significantly upregulated in the Clo1313_2031 deletion strain, suggesting that deletion of Clo1313_2031 mimics nitrogen starvation in C. thermocellum. Additionally, genes encoding the RNF-complex were also more highly expressed and in turn may have a potential role in increasing ethanol production. Samples for RNA-seq were taken from mid-exponential phase (OD ~ 0.33) batch cultures grown in MTC on 4.5 g/l cellobiose
Project description:Clostridium thermocellum is a promising CBP candidate organism capable of directly converting lignocellulosic biomass to ethanol. Low yields, productivities and growth inhibition prevent industrial deployment of this organism for commodity fuel production. Symptoms of potential redox imbalance such as incomplete substrate utilization, and fermentation products characteristic of overflow metabolism, have been observed during growth. This perceived redox imbalance may be in part responsible for the mentioned bioproductivity limitations. Toward better understanding the redox metabolism of C. thermocellum, we analyzed gene expression, using microarrays, during addition of two stress chemicals (methyl viologen and hydrogen peroxide) which we observed to change fermentation redox potential. High quality RNA was extracted from C. thermocellum grown on cellobiose in chemostat culture and exposed, separately, to methyl viologen and hydrogen peroxide. Transcriptome profiles were obtained at seven time points during actively growing fermentations, 3 minutes, 15 minutes, 35 minutes, 7 hours, 14 hours, 50 hours, and 60 hours after beginning exposure to each stressor. Exposure treatments were carried out in duplicate and reference/untreated samples were taken before and between treatments, after flushing of stressor chemicals and re-equilibration of growth conditions.
Project description:Three-day metatranscriptome of surface gravel plain soils from the Central Namib Desert. Samples were collected at four times (6:00, 12:00, 18:00 and 24:00h) on each day (n=12). rRNA-depleted RNA was used to construct stranded libraries with the ScriptSeq v2 complete kit (Epicentre) adding unique barcodes in TruSeq adapters (ScriptSeq Index PCR primers, set 1, Epicentre). Libraries were single-end sequenced in a NextSeq 500 v2 sequencer, with read length of 75bp.
Project description:The Xenopus mid-blastula transition (MBT) marks the onset of large-scale zygotic transcription, as well as an increase in cell cycle length and a loss of synchronous cell divisions. Little is known about what triggers the activation of transcription or how newly expressed genes interact with each other. Here we use high-resolution expression profiling to identify three waves of gene activity: a post-fertilization wave involving polyadenylation of maternal transcripts; a broad wave of zygotic transcription detectable as early as the 7th cleavage and extending beyond the MBT at the 12th cleavage; and a shorter post-MBT wave of transcription that becomes apparent as development proceeds. Our studies have also allowed us to define a set of maternal genes whose mRNAs are deadenylated shortly after fertilization, and are likely to be degraded thereafter. Experimental analysis indicates that the polyadenylation of maternal transcripts is necessary for the establishment of proper levels of zygotic transcription at the MBT, and that genes activated in the second wave of expression, including Brachyury and Mixer, contribute to the regulation of genes expressed in the third. Together, our high-resolution time series and experimental studies have yielded a deeper understanding of the temporal organization of gene regulatory networks in the early Time series polyA+ and RiboZero RNA sequencing of Xenopus Embryos covering 0-9.5 hours post fertilization
Project description:In this work we introduce a new high-throughput method, Spec-seq, that directly measures specificity by sequencing. It has several advantages over existing methods to quantify large collections (thousands) of binding site energies in one experiment. Using lac repressor as an example, we show that this method has excellent reproducibility giving energy measurements generally consistent within about 0.1kT. While not measuring in parallel as many different sequences as some of the higher throughput methods, we obtain high accuracies because we measure exactly what is necessary, the relative affinity to a large collection of sequences, without any mathematical fitting procedures or approximations required. It is similar to MITOMI in the number of different sites that can be analyzed in parallel, but it is much simpler to perform, requiring only a means to separate bound and unbound fractions which are then sequenced using standard high throughput, short read sequencing machines that are now readily available. When applied to the lac repressor we obtain, in a single experiment, data covering a large fraction of all the previous studies, plus thousands of additional variants, allowing us to compile a much more comprehensive profile of its specificity. We learn that the lac repressor can bind to sites of different lengths but that the preferred sequence, and the mode of binding, depends on the length. We also apply the method to two other members of the LacI/GalR protein family, PurR and YcjW, to obtain extensive models of their specificity and test the generality of the lac repressor's ability to bind to operators of variable length. We find that the lac repressor is apparently unique in its ability to bind with high affinity to sites of different lengths and with different modes of binding. 4 independent experiments.
Project description:Eukaryotic RNAs with premature termination codons (PTCs) are eliminated by nonsense-mediated decay (NMD). While human nonsense RNA degradation can be initiated either by an endonucleolytic cleavage event near the PTC or through decapping, the individual contribution of these activities on endogenous substrates has remained unresolved. Here we unambiguously establish that SMG6-catalyzed endonucleolysis is the primary initiating step in human nonsense RNA decay. We also show that both protein-coding and ‘non-coding’ genes hosting snoRNAs in their introns produce considerable amounts of NMD-sensitive splice variants, suggesting that these RNAs are merely by-products of a primary snoRNA production process. Finally, genes encoding multiple snoRNAs generally yield elevated numbers of alternative transcript isoforms, enabling the differential expression of individual snoRNAs. These findings demonstrate a hitherto unappreciated potential for decoupling of the individual expression levels of functional exon- and intron-encoded species from such composite genes. HEK293 Flp-In T-Rex cells were subjected to siRNA-mediated depletion of XRN1 and co-depletion of XRN1 with either SMG6 or UPF1. All the treated samples together with the controls were subjected to both RNA-seq and 5'-end-seq. RNA-seq was used for detecting NMD isoforms and their expression levels. 5'-end-seq was used for finding NMD decay intermediates (decapped and endocleaved molecules). CAGE was used to distinguish decapped from endocleaved RNA fragments.
Project description:Next-generation sequencing survey of maize plants exhibiting symptoms of maize lethal necrosis, collected from Kenyan and Ethiopian farmers in August 2014. Up to three samples per site were sequenced, and sites were separated by at least 10km. Data contains maize transcriptome and a variety of RNA viruses.
Project description:To identify Brachyury target genes in vivo and elucidate how Brachyury-mediated regulation contributes to early mouse developmental homeostasis and coordination, we performed mRNA-seq to compare gene expression profiles of WT and Tc/Tc embryos at both E7.5 ~ 8.0 and E10.0 ~ 10.5 WT and Tc/Tc embryos were isolated at both E7.5 ~ 8.0 and E10.0 ~ 10.5. Subsequently, directional mRNA-seq expriments were performed with wild-type and Tc/Tc whole embryos