To understand regulatory systems, it would be useful to uniformly determine how different components contribute to the expression of all other genes. We therefore monitored mRNA expression ...genome-wide, for individual deletions of one-quarter of yeast genes, focusing on (putative) regulators. The resulting genetic perturbation signatures reflect many different properties. These include the architecture of protein complexes and pathways, identification of expression changes compatible with viability, and the varying responsiveness to genetic perturbation. The data are assembled into a genetic perturbation network that shows different connectivities for different classes of regulators. Four feed-forward loop (FFL) types are overrepresented, including incoherent type 2 FFLs that likely represent feedback. Systematic transcription factor classification shows a surprisingly high abundance of gene-specific repressors, suggesting that yeast chromatin is not as generally restrictive to transcription as is often assumed. The data set is useful for studying individual genes and for discovering properties of an entire regulatory system.
Display omitted
•A systems analyses resource reports expression signatures for 1,484 yeast gene knockouts•Analysis reveals pathway branching, connectivity, and responsiveness to perturbations•Four feed-forward loop types are overrepresented in the genetic perturbation network•Transcription factor classification shows an abundance of gene-specific repressors
A comprehensive mRNA expression profiling study reports the effects of over 1,400 individual gene deletions in yeast, focusing on nonessential regulators of gene expression. Analysis of the data indicates a surprisingly high abundance of repressors, suggesting that chromatin itself may not be generally restrictive to transcription, as previously supposed.
FOXO transcription factors are regulators of cellular homeostasis and putative tumor suppressors, yet the role of FOXO in cancer progression remains to be determined. The data on FOXO function, ...particularly for epithelial cancers, are fragmentary and come from studies that focused on isolated aspects of cancer. To clarify the role of FOXO in epithelial cancer progression, we characterized the effects of inducible FOXO activation and loss in a mouse model of metastatic invasive lobular carcinoma. Strikingly, either activation or loss of FOXO function suppressed tumor growth and metastasis. We show that the multitude of cellular processes critically affected by FOXO function include proliferation, survival, redox homeostasis, and PI3K signaling, all of which must be carefully balanced for tumor cells to thrive.
FOXO proteins are not solely tumor suppressors, but also support tumor growth and metastasis by regulating a multitude of cellular processes essential for tumorigenesis.
.
Type I IFNs play critical roles in orchestrating the antiviral defense by inducing direct antiviral activities and shaping the adaptive immune response. Viruses have evolved numerous strategies to ...specifically interfere with IFN production or its downstream mediators, thereby allowing successful infection of the host to occur. The prototypic human gammaherpesvirus EBV, which is associated with infectious mononucleosis and malignant tumors, harbors many immune-evasion proteins that manipulate the adaptive and innate immune systems. In addition to proteins, the virus encodes >40 mature microRNAs for which the functions remain largely unknown. In this article, we identify EBV-encoded miR-BART16 as a novel viral immune-evasion factor that interferes with the type I IFN signaling pathway. miR-BART16 directly targets CREB-binding protein, a key transcriptional coactivator in IFN signaling, thereby inducing CREB-binding protein downregulation in EBV-transformed B cells and gastric carcinoma cells. miR-BART16 abrogates the production of IFN-stimulated genes in response to IFN-α stimulation and it inhibits the antiproliferative effect of IFN-α on latently infected BL cells. By obstructing the type I IFN-induced antiviral response, miR-BART16 provides a means to facilitate the establishment of latent EBV infection and enhance viral replication.
Histone H3 di- and trimethylation on lysine 4 are major chromatin marks that correlate with active transcription. The influence of these modifications on transcription itself is, however, poorly ...understood. We have investigated the roles of H3K4 methylation in Saccharomyces cerevisiae by determining genome-wide expression-profiles of mutants in the Set1 complex, COMPASS, that lays down these marks. Loss of H3K4 trimethylation has virtually no effect on steady-state or dynamically-changing mRNA levels. Combined loss of H3K4 tri- and dimethylation results in steady-state mRNA upregulation and delays in the repression kinetics of specific groups of genes. COMPASS-repressed genes have distinct H3K4 methylation patterns, with enrichment of H3K4me3 at the 3'-end, indicating that repression is coupled to 3'-end antisense transcription. Further analyses reveal that repression is mediated by H3K4me3-dependent 3'-end antisense transcription in two ways. For a small group of genes including PHO84, repression is mediated by a previously reported trans-effect that requires the antisense transcript itself. For the majority of COMPASS-repressed genes, however, it is the process of 3'-end antisense transcription itself that is the important factor for repression. Strand-specific qPCR analyses of various mutants indicate that this more prevalent mechanism of COMPASS-mediated repression requires H3K4me3-dependent 3'-end antisense transcription to lay down H3K4me2, which seems to serve as the actual repressive mark. Removal of the 3'-end antisense promoter also results in derepression of sense transcription and renders sense transcription insensitive to the additional loss of SET1. The derepression observed in COMPASS mutants is mimicked by reduction of global histone H3 and H4 levels, suggesting that the H3K4me2 repressive effect is linked to establishment of a repressive chromatin structure. These results indicate that in S. cerevisiae, the non-redundant role of H3K4 methylation by Set1 is repression, achieved through promotion of 3'-end antisense transcription to achieve specific rather than global effects through two distinct mechanisms.
The functional organization of eukaryotic genomes correlates with specific patterns of histone methylations. Regulatory regions in genomes such as enhancers and promoters differ in their extent of ...methylation of histone H3 at lysine-4 (H3K4), but it is largely unknown how the different methylation states are specified and controlled. Here, we show that the Kdm5c/Jarid1c/SMCX member of the Kdm5 family of H3K4 demethylases can be recruited to both enhancer and promoter elements in mouse embryonic stem cells and in neuronal progenitor cells. Knockdown of Kdm5c deregulates transcription via local increases in H3K4me3. Our data indicate that by restricting H3K4me3 modification at core promoters, Kdm5c dampens transcription, but at enhancers Kdm5c stimulates their activity. Remarkably, an impaired enhancer function activates the intrinsic promoter activity of Kdm5c-bound distal elements. Our results demonstrate that the Kdm5c demethylase plays a crucial and dynamic role in the functional discrimination between enhancers and core promoters.
Display omitted
► The H3K4me3/2 demethylase Kdm5c interacts with gene-specific transcription factors ► Genomic profiles of Kdm5c in ESCs reveal promoter-proximal and -distal binding ► Kdm5c represses promoter activity but stimulates enhancer function ► Dynamic H3K4me3/2 thus modulates promoter and enhancer function
Regulatory regions of eukaryotic genomes such as enhancers and promoters differ in their extent of methylation of histone H3 at lysine 4 (H3K4). Using embryonic stem cells, Timmers and colleagues report that the Kdm5c/Jarid1c/SMCX demethylase controls H3K4 mono- and trimethylation with different transcriptional outcomes. At promoters, Kdm5c dampens transcription, but at enhancers, Kdm5c stimulates their activity. Impairment of enhancer function activates an intrinsic promoter activity of Kdm5c sites. This demonstrates that Kdm5c plays a dynamic role in the functional discrimination between genomic elements.
Many biochemical, physiological and behavioural processes show circadian rhythms which are generated by an internal time-keeping mechanism referred to as the biological clock. According to rapidly ...developing models, the core oscillator driving this clockis composed of an autoregulatory transcription-(post) translation-based feedback loop involving a set of 'clock' genes,. Molecular clocks do not oscillate with an exact 24-hour rhythmicity but are entrained to solar day/night rhythms by light. The mammalian proteins Cry1 and Cry2, which are members of the family of plant blue-light receptors (cryptochromes) and photolyases, have been proposed as candidate light receptors for photoentrainment of the biological clock. Here we show that mice lacking the Cry1 or Cry2 protein display accelerated and delayed free-running periodicity of locomotor activity, respectively. Strikingly, in the absence of both proteins, an instantaneous and complete loss of free-running rhythmicity is observed. This suggests that, in addition to a possible photoreceptor and antagonistic clock-adjusting function, both proteins are essential for the maintenance of circadian rhythmicity.
Cellular glucose availability is crucial for the functioning of most biological processes. Our understanding of the glucose regulatory system has been greatly advanced by studying the model organism ...Saccharomyces cerevisiae, but many aspects of this system remain elusive. To understand the organisation of the glucose regulatory system, we analysed 91 deletion mutants of the different glucose signalling and metabolic pathways in Saccharomyces cerevisiae using DNA microarrays.
In general, the mutations do not induce pathway-specific transcriptional responses. Instead, one main transcriptional response is discerned, which varies in direction to mimic either a high or a low glucose response. Detailed analysis uncovers established and new relationships within and between individual pathways and their members. In contrast to signalling components, metabolic components of the glucose regulatory system are transcriptionally more frequently affected. A new network approach is applied that exposes the hierarchical organisation of the glucose regulatory system.
The tight interconnection between the different pathways of the glucose regulatory system is reflected by the main transcriptional response observed. Tps2 and Tsl1, two enzymes involved in the biosynthesis of the storage carbohydrate trehalose, are predicted to be the most downstream transcriptional components. Epistasis analysis of tps2Δ double mutants supports this prediction. Although based on transcriptional changes only, these results suggest that all changes in perceived glucose levels ultimately lead to a shift in trehalose biosynthesis.
The primary limiting factor for effective IVF treatment is successful embryo implantation. Recurrent implantation failure (RIF) is a condition whereby couples fail to achieve pregnancy despite ...consecutive embryo transfers. Here we describe the collection of gene expression profiles from mid-luteal phase endometrial biopsies (n = 115) from women experiencing RIF and healthy controls. Using a signature discovery set (n = 81) we identify a signature containing 303 genes predictive of RIF. Independent validation in 34 samples shows that the gene signature predicts RIF with 100% positive predictive value (PPV). The strength of the RIF associated expression signature also stratifies RIF patients into distinct groups with different subsequent implantation success rates. Exploration of the expression changes suggests that RIF is primarily associated with reduced cellular proliferation. The gene signature will be of value in counselling and guiding further treatment of women who fail to conceive upon IVF and suggests new avenues for developing intervention.
Growth condition perturbation or gene function disruption are commonly used strategies to study cellular systems. Although it is widely appreciated that such experiments may involve indirect effects, ...these frequently remain uncharacterized. Here, analysis of functionally unrelated Saccharyomyces cerevisiae deletion strains reveals a common gene expression signature. One property shared by these strains is slower growth, with increased presence of the signature in more slowly growing strains. The slow growth signature is highly similar to the environmental stress response (ESR), an expression response common to diverse environmental perturbations. Both environmental and genetic perturbations result in growth rate changes. These are accompanied by a change in the distribution of cells over different cell cycle phases. Rather than representing a direct expression response in single cells, both the slow growth signature and ESR mainly reflect a redistribution of cells over different cell cycle phases, primarily characterized by an increase in the G1 population. The findings have implications for any study of perturbation that is accompanied by growth rate changes. Strategies to counter these effects are presented and discussed.
Synopsis
Genetic, stress, or nutrient perturbation of yeast resulting in slower growth yields a common expression signature, previously known as the environmental stress response. This is largely due to a cell cycle population shift and is relevant to many perturbation‐based studies.
Yeast deletion strains with slower growth exhibit a common gene expression signature proportional to their degree of slow growth.
The slow growth signature is also found in wild‐type cells subjected to various environmental perturbations that result in slow growth including the environmental stress response (ESR).
The ESR and the genetic perturbation slow growth signature can largely be explained by a redistribution of cells over cell cycle phases.
Transformation of slow growth‐affected data enriches for finding direct targets of the original perturbation.
Genetic, stress or nutrient perturbation of yeast resulting in slower growth yields a common expression signature, previously known as the environmental stress response. This is largely due to a cell cycle population shift and is relevant to many perturbation‐based studies.
Packaging of DNA into chromatin has a profound impact on gene expression. To understand how changes in chromatin influence transcription, we analyzed 165 mutants of chromatin machinery components in
...Saccharomyces cerevisiae. mRNA expression patterns change in 80% of mutants, always with specific effects, even for loss of widespread histone marks. The data are assembled into a network of chromatin interaction pathways. The network is function based, has a branched, interconnected topology, and lacks strict one-to-one relationships between complexes. Chromatin pathways are not separate entities for different gene sets, but share many components. The study evaluates which interactions are important for which genes and predicts additional interactions, for example between Paf1C and Set3C, as well as a role for Mediator in subtelomeric silencing. The results indicate the presence of gene-dependent effects that go beyond context-dependent binding of chromatin factors and provide a framework for understanding how specificity is achieved through regulating chromatin.
Display omitted
► Loss of chromatin regulators results in highly specific effects on mRNA expression ► These effects are much more specific than the location of regulators or of marks ► The perturbation signatures identify a network of interactions between regulators ► Chromatin interaction pathways are highly branched and interconnected
PDF
