H3 lysine 4 di- and tri-methylation deposited by cryptic transcription attenuates promoter activation

Increased H3K9me3 and F-Actin Reorganization in the Rapid Adaptive Response to Hypergravity in Human T Lymphocytes

Our study explored the impact of hypergravity on human T cells, which experience additional acceleration forces beyond Earth's gravity due to various factors, such as pulsatile blood flow, and technology, such as high-performance aircraft flights or spaceflights. We investigated the histone modifications Histone 3 lysine 4 and 9 trimethylation (H3K4me3 and H3K9me3, respectively), as well as the structural and cytoskeletal organization of Jurkat T cells in response to hypergravity. Histone modifications play a crucial role in gene regulation, chromatin organization and DNA repair. In response to hypergravity, we found only minimal changes of H3K4me3 and a rapid increase in H3K9me3, which was sustained for up to 15 min and then returned to control levels after 1 h. Furthermore, rapid changes in F-actin fluorescence were observed within seconds of hypergravity exposure, indicating filament depolymerization and cytoskeletal restructuring, which subsequently recovered after 1 h of hypergravity. Our study demonstrated the rapid, dynamic and adaptive cellular response to hypergravity, particularly in terms of histone modifications and cytoskeletal changes. These responses are likely necessary for maintaining genome stability and structural integrity under hypergravity conditions as they are constantly occurring in the human body during blood cell circulation.

Diverse and dynamic forms of gene regulation by the S. cerevisiae histone methyltransferase Set1

Gene transcription is an essential and highly regulated process. In eukaryotic cells, the structural organization of nucleosomes with DNA wrapped around histone proteins impedes transcription. Chromatin remodelers, transcription factors, co-activators, and histone-modifying enzymes work together to make DNA accessible to RNA polymerase. Histone lysine methylation can positively or negatively regulate gene transcription. Methylation of histone 3 lysine 4 by SET-domain-containing proteins is evolutionarily conserved from yeast to humans. In higher eukaryotes, mutations in SET-domain proteins are associated with defects in the development and segmentation of embryos, skeletal and muscle development, and diseases, including several leukemias. Since histone methyltransferases are evolutionarily conserved, the mechanisms of gene regulation mediated by these enzymes are also conserved. Budding yeast Saccharomyces cerevisiae is an excellent model system to study the impact of histone 3 lysine 4 (H3K4) methylation on eukaryotic gene regulation. Unlike larger eukaryotes, yeast cells have only one enzyme that catalyzes H3K4 methylation, Set1. In this review, we summarize current knowledge about the impact of Set1-catalyzed H3K4 methylation on gene transcription in S. cerevisiae. We describe the COMPASS complex, factors that influence H3K4 methylation, and the roles of Set1 in gene silencing at telomeres and heterochromatin, as well as repression and activation at euchromatic loci. We also discuss proteins that "read" H3K4 methyl marks to regulate transcription and summarize alternate functions for Set1 beyond H3K4 methylation.

Pervasive transcription: a controlled risk

Transcriptome-wide interrogation of eukaryotic genomes has unveiled the pervasive nature of RNA polymerase II transcription. Virtually, any DNA region with an accessible chromatin structure can be transcribed, resulting in a mass production of noncoding RNAs (ncRNAs) with the potential of interfering with gene expression programs. Budding yeast has proved to be a powerful model organism to understand the mechanisms at play to control pervasive transcription and overcome the risks of hazardous disruption of cellular functions. In this review, we focus on the actors and strategies yeasts employ to govern ncRNA production, and we discuss recent findings highlighting the dangers of losing control over pervasive transcription.

New data and collaborations at the Saccharomyces Genome Database: updated reference genome, alleles, and the Alliance of Genome Resources

Saccharomyces cerevisiae is used to provide fundamental understanding of eukaryotic genetics, gene product function, and cellular biological processes. Saccharomyces Genome Database (SGD) has been supporting the yeast research community since 1993, serving as its de facto hub. Over the years, SGD has maintained the genetic nomenclature, chromosome maps, and functional annotation, and developed various tools and methods for analysis and curation of a variety of emerging data types. More recently, SGD and six other model organism focused knowledgebases have come together to create the Alliance of Genome Resources to develop sustainable genome information resources that promote and support the use of various model organisms to understand the genetic and genomic bases of human biology and disease. Here we describe recent activities at SGD, including the latest reference genome annotation update, the development of a curation system for mutant alleles, and new pages addressing homology across model organisms as well as the use of yeast to study human disease.

Non-Coding, RNAPII-Dependent Transcription at the Promoters of rRNA Genes Regulates Their Chromatin State in S. cerevisiae

Pervasive transcription is widespread in eukaryotes, generating large families of non-coding RNAs. Such pervasive transcription is a key player in the regulatory pathways controlling chromatin state and gene expression. Here, we describe long non-coding RNAs generated from the ribosomal RNA gene promoter called UPStream-initiating transcripts (UPS). In yeast, rDNA genes are organized in tandem repeats in at least two different chromatin states, either transcribed and largely depleted of nucleosomes (open) or assembled in regular arrays of nucleosomes (closed). The production of UPS transcripts by RNA Polymerase II from endogenous rDNA genes was initially documented in mutants defective for rRNA production by RNA polymerase I. We show here that UPS are produced in wild-type cells from closed rDNA genes but are hidden within the enormous production of rRNA. UPS levels are increased when rDNA chromatin states are modified at high temperatures or entering/leaving quiescence. We discuss their role in the regulation of rDNA chromatin states and rRNA production.

Ready, SET, Go: Post-translational regulation of the histone lysine methylation network in budding yeast

Histone lysine methylation is a key epigenetic modification that regulates eukaryotic transcription. Here, we comprehensively review the function and regulation of the histone methylation network in the budding yeast and model eukaryote, Saccharomyces cerevisiae. First, we outline the lysine methylation sites that are found on histone proteins in yeast (H3K4me1/2/3, H3K36me1/2/3, H3K79me1/2/3, and H4K5/8/12me1) and discuss their biological and cellular roles. Next, we detail the reduced but evolutionarily conserved suite of methyltransferase (Set1p, Set2p, Dot1p, and Set5p) and demethylase (Jhd1p, Jhd2p, Rph1p, and Gis1p) enzymes that are known to control histone lysine methylation in budding yeast cells. Specifically, we illustrate the domain architecture of the methylation enzymes and highlight the structural features that are required for their respective functions and molecular interactions. Finally, we discuss the prevalence of post-translational modifications on yeast histone methylation enzymes and how phosphorylation, acetylation, and ubiquitination in particular are emerging as key regulators of enzyme function. We note that it will be possible to completely connect the histone methylation network to the cell’s signaling system, given that all methylation sites and cognate enzymes are known, most phosphosites on the enzymes are known, and the mapping of kinases to phosphosites is tractable owing to the modest set of protein kinases in yeast. Moving forward, we expect that the rich variety of post-translational modifications that decorates the histone methylation machinery will explain many of the unresolved questions surrounding the function and dynamics of this intricate epigenetic network.

An Overview on Identification and Regulatory Mechanisms of Long Non-coding RNAs in Fungi

For decades, more and more long non-coding RNAs (lncRNAs) have been confirmed to play important functions in key biological processes of different organisms. At present, most identified lncRNAs and those with known functional roles are from mammalian systems. However, lncRNAs have also been found in primitive eukaryotic fungi, and they have different functions in fungal development, metabolism, and pathogenicity. In this review, we highlight some recent researches on lncRNAs in the primitive eukaryotic fungi, particularly focusing on the identification of lncRNAs and their regulatory roles in diverse biological processes.

Proteasomal Regulation of Mammalian SPT16 in Controlling Transcription

FACT (facilitates chromatin transcription), an essential and evolutionarily conserved heterodimer from yeast to humans, controls transcription and is found to be upregulated in various cancers. However, the basis for such upregulation is not clearly understood. Our recent results deciphering a new ubiquitin-proteasome system regulation of the FACT subunit SPT16 in orchestrating transcription in yeast hint at the involvement of the proteasome in controlling FACT in humans, with a link to cancer. To test this, we carried out experiments in human embryonic kidney (HEK293) cells, which revealed that human SPT16 undergoes ubiquitylation and that its abundance is increased following inhibition of the proteolytic activity of the proteasome, thus implying proteasomal regulation of human SPT16. Furthermore, we find that the increased abundance/expression of SPT16 in HEK293 cells alters the transcription of genes, including ones associated with cancer, and that the proteasomal degradation of SPT16 is impaired in kidney cancer (Caki-2) cells to upregulate SPT16. Like human SPT16, murine SPT16 in C2C12 cells also undergoes ubiquitylation and proteasomal degradation to regulate transcription. Collectively, our results reveal a proteasomal regulation of mammalian SPT16, with physiological relevance in controlling transcription, and implicate such proteasomal control in the upregulation of SPT16 in cancer.

Variation, Variegation and Heritable Gene Repression in S. cerevisiae

Phenotypic heterogeneity provides growth advantages for a population upon changes of the environment. In S. cerevisiae, such heterogeneity has been observed as "on/off" states in the expression of individual genes in individual cells. These variations can persist for a limited or extended number of mitotic divisions. Such traits are known to be mediated by heritable chromatin structures, by the mitotic transmission of transcription factors involved in gene regulatory circuits or by the cytoplasmic partition of prions or other unstructured proteins. The significance of such epigenetic diversity is obvious, however, we have limited insight into the mechanisms that generate it. In this review, we summarize the current knowledge of epigenetically maintained heterogeneity of gene expression and point out similarities and converging points between different mechanisms. We discuss how the sharing of limiting repression or activation factors can contribute to cell-to-cell variations in gene expression and to the coordination between short- and long- term epigenetic strategies. Finally, we discuss the implications of such variations and strategies in adaptation and aging.

Gene repression in S. cerevisiae-looking beyond Sir-dependent gene silencing

Gene silencing by the SIR (Silent Information Region) family of proteins in S. cerevisiae has been extensively studied and has served as a founding paradigm for our general understanding of gene repression and its links to histone deacetylation and chromatin structure. In recent years, our understanding of other mechanisms of gene repression in S.cerevisiae was significantly advanced. In this review, we focus on such Sir-independent mechanisms of gene repression executed by various Histone Deacetylases (HDACs) and Histone Methyl Transferases (HMTs). We focus on the genes regulated by these enzymes and their known mechanisms of action. We describe the cooperation and redundancy between HDACs and HMTs, and their involvement in gene repression by non-coding RNAs or by their non-histone substrates. We also propose models of epigenetic transmission of the chromatin structures produced by these enzymes and discuss these in the context of gene repression phenomena in other organisms. These include the recycling of the epigenetic marks imposed by HMTs or the recycling of the complexes harboring HDACs.

Regulation of alternative polyadenylation in the yeast Saccharomyces cerevisiae by histone H3K4 and H3K36 methyltransferases

Adjusting DNA structure via epigenetic modifications, and altering polyadenylation (pA) sites at which precursor mRNA is cleaved and polyadenylated, allows cells to quickly respond to environmental stress. Since polyadenylation occurs co-transcriptionally, and specific patterns of nucleosome positioning and chromatin modifications correlate with pA site usage, epigenetic factors potentially affect alternative polyadenylation (APA). We report that the histone H3K4 methyltransferase Set1, and the histone H3K36 methyltransferase Set2, control choice of pA site in Saccharomyces cerevisiae, a powerful model for studying evolutionarily conserved eukaryotic processes. Deletion of SET1 or SET2 causes an increase in serine-2 phosphorylation within the C-terminal domain of RNA polymerase II (RNAP II) and in the recruitment of the cleavage/polyadenylation complex, both of which could cause the observed switch in pA site usage. Chemical inhibition of TOR signaling, which causes nutritional stress, results in Set1- and Set2-dependent APA. In addition, Set1 and Set2 decrease efficiency of using single pA sites, and control nucleosome occupancy around pA sites. Overall, our study suggests that the methyltransferases Set1 and Set2 regulate APA induced by nutritional stress, affect the RNAP II C-terminal domain phosphorylation at Ser2, and control recruitment of the 3′ end processing machinery to the vicinity of pA sites.

Metabolic transcriptional memory

Background

Organisms can be primed by metabolic exposures to continue expressing response genes even once the metabolite is no longer available, and can affect the speed and magnitude of responsive gene expression during subsequent exposures. This “metabolic transcriptional memory” can have a profound impact on the survivability of organisms in fluctuating environments.

Scope of review

Here I present several examples of metabolic transcriptional memory in the microbial world and discuss what is known so far regarding the underlying mechanisms, which mainly focus on chromatin modifications, protein inheritance, and broad changes in metabolic network. From these lessons learned in microbes, some insights into the yet understudied human metabolic memory can be gained. I thus discuss the implications of metabolic memory in disease progression in humans – i.e., the memory of high blood sugar exposure and the resulting effects on diabetic complications.

Major conclusions

Carbon source shifts from glucose to other less preferred sugars such as lactose, galactose, and maltose for energy metabolism as well as starvation of a signal transduction precursor sugar inositol are well-studied examples of metabolic transcriptional memory in Escherichia coli and Saccharomyces cerevisiae. Although the specific factors guiding metabolic transcriptional memory are not necessarily conserved from microbes to humans, the same basic mechanisms are in play, as is observed in hyperglycemic memory. Exploration of new metabolic transcriptional memory systems as well as further detailed mechanistic analyses of known memory contexts in microbes is therefore central to understanding metabolic memory in humans, and may be of relevance for the successful treatment of the ever-growing epidemic of diabetes.

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Metabolic exposures can prime genes to have memory.

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Memory of carbon source shifts occurs in all kingdoms of life.

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Memory is maintained through multiple mechanisms including chromatin modifications, proteins, and metabolic network.

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Metabolic transcriptional memory in unicellular organisms is a part of “bet-hedging” strategies to ensure survival.

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Hyperglycemic memory in humans contributes to diabetes and aging.

Endogenous RNAi pathway evolutionarily shapes the destiny of the antisense lncRNAs transcriptome

A genome-wide comparative analysis of “cryptic” aslncRNAs decay in RNAi-capable and RNAi-deficient budding yeasts suggests an evolutionary contribution of RNAi in shaping the aslncRNAs transcriptome.

Antisense long noncoding (aslnc)RNAs are extensively degraded by the nuclear exosome and the cytoplasmic exoribonuclease Xrn1 in the budding yeast Saccharomyces cerevisiae, lacking RNAi. Whether the ribonuclease III Dicer affects aslncRNAs in close RNAi-capable relatives remains unknown. Using genome-wide RNA profiling, here we show that aslncRNAs are primarily targeted by the exosome and Xrn1 in the RNAi-capable budding yeast Naumovozyma castellii, Dicer only affecting Xrn1-sensitive aslncRNAs levels in Xrn1-deficient cells. The dcr1 and xrn1 mutants display synergic growth defects, indicating that Dicer becomes critical in the absence of Xrn1. Small RNA sequencing showed that Dicer processes aslncRNAs into small RNAs, with a preference for Xrn1-sensitive aslncRNAs. Consistently, Dicer localizes into the cytoplasm. Finally, we observed an expansion of the exosome-sensitive antisense transcriptome in N. castellii compared with S. cerevisiae, suggesting that the presence of cytoplasmic RNAi has reinforced the nuclear RNA surveillance machinery to temper aslncRNAs expression. Our data provide fundamental insights into aslncRNAs metabolism and open perspectives into the possible evolutionary contribution of RNAi in shaping the aslncRNAs transcriptome.

Antisense transcriptional interference mediates condition-specific gene repression in budding yeast

Pervasive transcription generates many unstable non-coding transcripts in budding yeast. The transcription of such noncoding RNAs, in particular antisense RNAs (asRNAs), has been shown in a few examples to repress the expression of the associated mRNAs. Yet, such mechanism is not known to commonly contribute to the regulation of a given class of genes. Using a mutant context that stabilized pervasive transcripts, we observed that the least expressed mRNAs during the exponential phase were associated with high levels of asRNAs. These asRNAs also overlapped their corresponding gene promoters with a much higher frequency than average. Interrupting antisense transcription of a subset of genes corresponding to quiescence-enriched mRNAs restored their expression. The underlying mechanism acts in cis and involves several chromatin modifiers. Our results convey that transcription interference represses up to 30% of the 590 least expressed genes, which includes 163 genes with quiescence-enriched mRNAs. We also found that pervasive transcripts constitute a higher fraction of the transcriptome in quiescence relative to the exponential phase, consistent with gene expression itself playing an important role to suppress pervasive transcription. Accordingly, the HIS1 asRNA, normally only present in quiescence, is expressed in exponential phase upon HIS1 mRNA transcription interruption.

CFP-1 interacts with HDAC1/2 complexes in C. elegans development

CXXC finger binding protein 1 (CFP-1) is an evolutionarily conserved protein that binds to non-methylated CpG-rich promoters in mammals and Caenorhabditis elegans. This conserved epigenetic regulator is part of the COMPASS complex that contains the H3K4me3 methyltransferase SET1 in mammals and SET-2 in C. elegans. Previous studies have indicated the importance of CFP1 in embryonic stem cell differentiation and cell fate specification. However, neither the function nor the mechanism of action of CFP1 is well understood at the organismal level. Here, we have used cfp-1(tm6369) and set-2(bn129) C. elegans mutants to investigate the function of CFP-1 in gene induction and development. We have characterised C. elegansCOMPASS mutants cfp-1(tm6369) and set-2(bn129) and found that both cfp-1 and set-2 play an important role in the regulation of fertility and development of the organism. Furthermore, we found that both cfp-1 and set-2 are required for H3K4 trimethylation and play a repressive role in the expression of heat shock and salt-inducible genes. Interestingly, we found that cfp-1 but not set-2 genetically interacts with histone deacetylase (HDAC1/2) complexes to regulate fertility, suggesting a function of CFP-1 outside of the COMPASS complex. Additionally, we found that cfp-1 and set-2 independently regulate fertility and development of the organism. Our results suggest that CFP-1 genetically interacts with HDAC1/2 complexes to regulate fertility, independent of its function within the COMPASS complex. We propose that CFP-1 could cooperate with the COMPASS complex and/or HDAC1/2 in a context-dependent manner.

Genetic compensation triggered by mutant mRNA degradation

Genetic robustness, or the ability of an organism to maintain fitness in the presence of mutations, can be achieved via protein feedback loops. Recent evidence suggests that organisms may also respond to mutations by upregulating related gene(s) independently of protein feedback loops, a phenomenon called transcriptional adaptation. However, the prevalence of transcriptional adaptation and its underlying molecular mechanisms are unknown. Here, by analyzing several models of transcriptional adaptation in zebrafish and mouse, we show a requirement for mRNA degradation. Alleles that fail to transcribe the mutated gene do not display transcriptional adaptation and exhibit more severe phenotypes than alleles displaying mutant mRNA decay. Transcriptome analysis reveals the upregulation of a substantial proportion of the genes that exhibit sequence similarity with the mutated gene’s mRNA, suggesting a sequence dependent mechanism. Besides implications for our understanding of disease-causing mutations, these findings will help design mutant alleles with minimal transcriptional adaptation-derived compensation.

Mechanisms of Antisense Transcription Initiation with Implications in Gene Expression, Genomic Integrity and Disease Pathogenesis

Non-coding antisense transcripts arise from the strand opposite the sense strand. Over 70% of the human genome generates non-coding antisense transcripts while less than 2% of the genome codes for proteins. Antisense transcripts and/or the act of antisense transcription regulate gene expression and genome integrity by interfering with sense transcription and modulating histone modifications or DNA methylation. Hence, they have significant pathological and physiological relevance. Indeed, antisense transcripts were found to be associated with various diseases including cancer, diabetes, cardiac and neurodegenerative disorders, and, thus, have promising potentials for prognostic and diagnostic markers and therapeutic development. However, it is not clearly understood how antisense transcription is initiated and epigenetically regulated. Such knowledge would provide new insights into the regulation of antisense transcription, and hence disease pathogenesis with therapeutic development. The recent studies on antisense transcription initiation and its epigenetic regulation, which are limited, are discussed here. Furthermore, we concisely describe how antisense transcription/transcripts regulate gene expression and genome integrity with implications in disease pathogenesis and therapeutic development.

The DDX5/Dbp2 subfamily of DEAD-box RNA helicases

The mammalian DEAD-box RNA helicase DDX5, its paralog DDX17, and their orthologs in Saccharomyces cerevisiae and Drosophila melanogaster, namely Dbp2 and Rm62, define a subfamily of DEAD-box proteins. Members from this subfamily share highly conserved protein sequences and cellular functions. They are involved in multiple steps of RNA metabolism including mRNA processing, microRNA processing, ribosome biogenesis, RNA decay, and regulation of long noncoding RNA activities. The DDX5/Dbp2 subfamily is also implicated in transcription regulation, cellular signaling pathways, and energy metabolism. One emerging theme underlying the diverse cellular functions is that the DDX5/Dbp2 subfamily of DEAD-box helicases act as chaperones for complexes formed by RNA molecules and proteins (RNP) in vivo. This RNP chaperone activity governs the functions of various RNA species through their lifetime. Importantly, mammalian DDX5 and DDX17 are involved in cancer progression when overexpressed through alteration of transcription and signaling pathways, meaning that they are possible targets for cancer therapy. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

Tri-methylation of histone H3 lysine 4 facilitates gene expression in ageing cells

Transcription of protein coding genes is accompanied by recruitment of COMPASS to promoter-proximal chromatin, which methylates histone H3 lysine 4 (H3K4) to form H3K4me1, H3K4me2 and H3K4me3. Here, we determine the importance of COMPASS in maintaining gene expression across lifespan in budding yeast. We find that COMPASS mutations reduce replicative lifespan and cause expression defects in almost 500 genes. Although H3K4 methylation is reported to act primarily in gene repression, particularly in yeast, repressive functions are progressively lost with age while hundreds of genes become dependent on H3K4me3 for full expression. Basal and inducible expression of these genes is also impaired in young cells lacking COMPASS components Swd1 or Spp1. Gene induction during ageing is associated with increasing promoter H3K4me3, but H3K4me3 also accumulates in non-promoter regions and the ribosomal DNA. Our results provide clear evidence that H3K4me3 is required to maintain normal expression of many genes across organismal lifespan.

Bases of antisense lncRNA-associated regulation of gene expression in fission yeast

Antisense (as)lncRNAs can regulate gene expression but the underlying mechanisms and the different cofactors involved remain unclear. Using Native Elongating Transcript sequencing, here we show that stabilization of antisense Exo2-sensitivite lncRNAs (XUTs) results in the attenuation, at the nascent transcription level, of a subset of highly expressed genes displaying prominent promoter-proximal nucleosome depletion and histone acetylation. Mechanistic investigations on the catalase gene ctt1 revealed that its induction following oxidative stress is impaired in Exo2-deficient cells, correlating with the accumulation of an asXUT. Interestingly, expression of this asXUT was also activated in wild-type cells upon oxidative stress, concomitant to ctt1 induction, indicating a potential attenuation feedback. This attenuation correlates with asXUT abundance, it is transcriptional, characterized by low RNAPII-ser5 phosphorylation, and it requires an histone deacetylase activity and the conserved Set2 histone methyltransferase. Finally, we identified Dicer as another RNA processing factor acting on ctt1 induction, but independently of Exo2. We propose that asXUTs could modulate the expression of their paired-sense genes when it exceeds a critical threshold, using a conserved mechanism independent of RNAi.

Bacterial regulatory RNAs: complexity, function, and putative drug targeting

Over the past decade, RNA-deep sequencing has uncovered copious non-protein coding RNAs (npcRNAs) in bacteria. Many of them are key players in the regulation of gene expression, taking part in various regulatory circuits, such as metabolic responses to different environmental stresses, virulence, antibiotic resistance, and host-pathogen interactions. This has contributed to the high adaptability of bacteria to changing or even hostile environments. Their mechanisms include the regulation of transcriptional termination, modulation of translation, and alteration of messenger RNA (mRNA) stability, as well as protein sequestration. Here, the mechanisms of gene expression by regulatory bacterial npcRNAs are comprehensively reviewed and supplemented with well-characterized examples. This class of molecules and their mechanisms of action might be useful targets for the development of novel antibiotics.

Long Noncoding RNAs in Yeast Cells and Differentiated Subpopulations of Yeast Colonies and Biofilms

We summarize current knowledge regarding regulatory functions of long noncoding RNAs (lncRNAs) in yeast, with emphasis on lncRNAs identified recently in yeast colonies and biofilms. Potential regulatory functions of these lncRNAs in differentiated cells of domesticated colonies adapted to plentiful conditions versus yeast colony biofilms are discussed. We show that specific cell types differ in their complements of lncRNA, that this complement changes over time in differentiating upper cells, and that these lncRNAs target diverse functional categories of genes in different cell subpopulations and specific colony types.

Efficient termination of nuclear lncRNA transcription promotes mitochondrial genome maintenance

Most DNA in the genomes of higher organisms does not code for proteins. RNA Polymerase II (Pol II) transcribes non-coding DNA into long non-coding RNAs (lncRNAs), but biological roles of lncRNA are unclear. We find that mutations in the yeast lncRNA CUT60 result in poor growth. Defective termination of CUT60 transcription causes read-through transcription across the ATP16 gene promoter. Read-through transcription localizes chromatin signatures associated with Pol II elongation to the ATP16 promoter. The act of Pol II elongation across this promoter represses functional ATP16 expression by a Transcriptional Interference (TI) mechanism. Atp16p function in the mitochondrial ATP-synthase complex promotes mitochondrial DNA stability. ATP16 repression by TI through inefficient termination of CUT60 therefore triggers mitochondrial genome loss. Our results expand the functional and mechanistic implications of non-coding DNA in eukaryotes by highlighting termination of nuclear lncRNA transcription as mechanism to stabilize an organellar genome.

Native elongating transcript sequencing reveals global anti-correlation between sense and antisense nascent transcription in fission yeast

Antisense transcription can regulate sense gene expression. However, previous annotations of antisense transcription units have been based on detection of mature antisense long noncoding (aslnc)RNAs by RNA-seq and/or microarrays, only giving a partial view of the antisense transcription landscape and incomplete molecular bases for antisense-mediated regulation. Here, we used native elongating transcript sequencing to map genome-wide nascent antisense transcription in fission yeast. Strikingly, antisense transcription was detected for most protein-coding genes, correlating with low sense transcription, especially when overlapping the mRNA start site. RNA profiling revealed that the resulting aslncRNAs mainly correspond to cryptic Xrn1/Exo2-sensitive transcripts (XUTs). ChIP-seq analyses showed that antisense (as)XUT's expression is associated with specific histone modification patterns. Finally, we showed that asXUTs are controlled by the histone chaperone Spt6 and respond to meiosis induction, in both cases anti-correlating with levels of the paired-sense mRNAs, supporting physiological significance to antisense-mediated gene attenuation. Our work highlights that antisense transcription is much more extended than anticipated and might constitute an additional nonpromoter determinant of gene regulation complexity.

Repression of Middle Sporulation Genes in Saccharomyces cerevisiae by the Sum1-Rfm1-Hst1 Complex Is Maintained by Set1 and H3K4 Methylation

The conserved yeast histone methyltransferase Set1 targets H3 lysine 4 (H3K4) for mono, di, and trimethylation and is linked to active transcription due to the euchromatic distribution of these methyl marks and the recruitment of Set1 during transcription. However, loss of Set1 results in increased expression of multiple classes of genes, including genes adjacent to telomeres and middle sporulation genes, which are repressed under normal growth conditions because they function in meiotic progression and spore formation. The mechanisms underlying Set1-mediated gene repression are varied, and still unclear in some cases, although repression has been linked to both direct and indirect action of Set1, associated with noncoding transcription, and is often dependent on the H3K4me2 mark. We show that Set1, and particularly the H3K4me2 mark, are implicated in repression of a subset of middle sporulation genes during vegetative growth. In the absence of Set1, there is loss of the DNA-binding transcriptional regulator Sum1 and the associated histone deacetylase Hst1 from chromatin in a locus-specific manner. This is linked to increased H4K5ac at these loci and aberrant middle gene expression. These data indicate that, in addition to DNA sequence, histone modification status also contributes to proper localization of Sum1 Our results also show that the role for Set1 in middle gene expression control diverges as cells receive signals to undergo meiosis. Overall, this work dissects an unexplored role for Set1 in gene-specific repression, and provides important insights into a new mechanism associated with the control of gene expression linked to meiotic differentiation.

Determinants of Histone H3K4 Methylation Patterns

Various factors differentially recognize trimethylated histone H3 lysine 4 (H3K4me3) near promoters, H3K4me2 just downstream, and promoter-distal H3K4me1 to modulate gene expression. This methylation "gradient" is thought to result from preferential binding of the H3K4 methyltransferase Set1/complex associated with Set1 (COMPASS) to promoter-proximal RNA polymerase II. However, other studies have suggested that location-specific cues allosterically activate Set1. Chromatin immunoprecipitation sequencing (ChIP-seq) experiments show that H3K4 methylation patterns on active genes are not universal or fixed and change in response to both transcription elongation rate and frequency as well as reduced COMPASS activity. Fusing Set1 to RNA polymerase II results in H3K4me2 throughout transcribed regions and similarly extended H3K4me3 on highly transcribed genes. Tethered Set1 still requires histone H2B ubiquitylation for activity. These results show that higher-level methylations reflect not only Set1/COMPASS recruitment but also multiple rounds of transcription. This model provides a simple explanation for non-canonical methylation patterns at some loci or in certain COMPASS mutants.

Upregulation of SPS100 gene expression by an antisense RNA via a switch of mRNA isoforms with different stabilities

Pervasive transcription of genomes generates multiple classes of non-coding RNAs. One of these classes are stable long non-coding RNAs which overlap coding genes in antisense direction (asRNAs). The function of such asRNAs is not fully understood but several cases of antisense-dependent gene expression regulation affecting the overlapping genes have been demonstrated. Using high-throughput yeast genetics and a limited set of four growth conditions we previously reported a regulatory function for ∼25% of asRNAs, most of which repress the expression of the sense gene. To further explore the roles of asRNAs we tested more conditions and identified 15 conditionally antisense-regulated genes, 6 of which exhibited antisense-dependent enhancement of gene expression. We focused on the sporulation-specific gene SPS100, which becomes upregulated upon entry into starvation or sporulation as a function of the antisense transcript SUT169. We demonstrate that the antisense effect is mediated by its 3' intergenic region (3'-IGR) and that this regulation can be transferred to other genes. Genetic analysis revealed that SUT169 functions by changing the relative expression of SPS100 mRNA isoforms from a short and unstable transcript to a long and stable species. These results suggest a novel mechanism of antisense-dependent gene regulation via mRNA isoform switching.

The role of epigenetics in lysosomal storage disorders: Uncharted territory

The study of the contribution of epigenetic mechanisms, including DNA methylation, histone modifications, and microRNAs, to human disease has enhanced our understanding of different cellular processes and diseased states, as well as the effect of environmental factors on phenotypic outcomes. Epigenetic studies may be particularly relevant in evaluating the clinical heterogeneity observed in monogenic disorders. The lysosomal storage disorders are Mendelian disorders characterized by a wide spectrum of associated phenotypes, ranging from neonatal presentations to symptoms that develop in late adulthood. Some lack a tight genotype/phenotype correlation. While epigenetics may explain some of the discordant phenotypes encountered in patients with the same lysosomal storage disorder, especially among patients sharing the same genotype, to date, few studies have focused on these mechanisms. We review three common epigenetic mechanisms, DNA methylation, histone modifications, and microRNAs, and highlight their applications to phenotypic variation and therapeutics. Three specific lysosomal storage diseases, Gaucher disease, Fabry disease, and Niemann-Pick type C disease are presented as prototypical disorders with vast clinical heterogeneity that may be impacted by epigenetics. Our goal is to motivate researchers to consider epigenetics as a mechanism to explain the complexities of biological functions and pathologies of these rare disorders.

Independent manipulation of histone H3 modifications in individual nucleosomes reveals the contributions of sister histones to transcription

Histone tail modifications can greatly influence chromatin-associated processes. Asymmetrically modified nucleosomes exist in multiple cell types, but whether modifications on both sister histones contribute equally to chromatin dynamics remains elusive. Here, we devised a bivalent nucleosome system that allowed for the constitutive assembly of asymmetrically modified sister histone H3s in nucleosomes in Saccharomyces cerevisiae. The sister H3K36 methylations independently affected cryptic transcription in gene coding regions, whereas sister H3K79 methylation had cooperative effects on gene silencing near telomeres. H3K4 methylation on sister histones played an independent role in suppressing the recruitment of Gal4 activator to the GAL1 promoter and in inhibiting GAL1 transcription. Under starvation stress, sister H3K4 methylations acted cooperatively, independently or redundantly to regulate transcription. Thus, we provide a unique tool for comparing symmetrical and asymmetrical modifications of sister histone H3s in vivo.

Inside each human cell, about two meters of DNA is wrapped around millions of proteins called histones, forming structures known as nucleosomes. Each nucleosome contains 147 letters of DNA code and two copies of four different histones – H2A, H2B, H3 and H4 – meaning eight proteins in total.

The two copies of each histone protein found in a nucleosome are referred to as “sister” histones and are identical. Histone proteins have long tails that the cell can edit by adding chemical groups at specific positions. This changes the way the cell copies, uses and repairs its DNA. Previous studies show that identical sister histones can end up with different modifications. But, it was not clear what effect this had.

To adress this issue, there are two questions to answer. What do asymmetric sister histones do in living cells? And, does a modification to one histone affect its sister? Gene editing could help scientists to understand the effect of asymmetrical tail modification by forcing cells to make non-identical sister histones. However, this is challenging because most animals studied in the laboratory have many copies of the genes for histones. Fruit flies, for example, have 23 copies of their histone genes. The single-celled yeast Saccharomyces cerevisiae has only two copies of its histone genes. Yet, even if one of these genes was replaced with a mutant gene and the other left unedited or “wild-type”, there would be nothing to stop the cell from forming nucleosomes in which both sister histones were still identical – that is to say, mutant with mutant or wild-type with wild-type.

Now, Zhou, Liu et al. report a new method that allowed them to edit the tail sequence of one H3 histone but not its sister. First, they searched for, and found, a pair of mutant H3 genes, which encode two extremely similar but different H3 proteins that could bind to each other but not to themselves. As a result, yeast cells with the genes for these proteins could only form nucleosomes in which the sister H3 histones were non-identical. Next, Zhou et al. made a small change to the tail of one of the H3 sisters which meant it could not be modified. The resulting nucleosomes contain one H3 histone with a wild-type tail and one with a mutant tail. The cell could only modify one of them, mimicking natural asymmetrical modifications.

The new technique revealed that modification of one sister does not affect the the other. It also revealed that modifications to sister histones can work both alone and together. In some cases, the cell needs only edit one tail to affect the use of a gene. Other times, it must edit both tails for greatest effect.

This new tool is the first step in understanding the contribution of the tails of sister histones in living cells. In future, it should help to uncover the effect of different combinations of modifications. This could shed light on how cells control the use of different genes.

Genome-wide Identification and Characterization of Natural Antisense Transcripts by Strand-specific RNA Sequencing in Ganoderma lucidum

Ganoderma lucidum is a white-rot fungus best-known for its medicinal and ligninolytic activities. To discover the underlying genes responsible for these activities, we identified and characterized the natural antisense transcripts (NATs) using strand-specific (ss) RNA-seq data obtained from the mycelia, primordia and fruiting bodies. NATs were identified using a custom pipeline and then subjected to functional enrichment and differential expression analyses. A total of 1613 cis- and 244 trans- sense and antisense transcripts were identified. Mapping to GO terms and KEGG pathways revealed that NATs were frequently associated with genes of particular functional categories in particular stages. ssRT-qPCR experiments showed that the expression profiles of 30 of 50 (60%) transcripts were highly correlated with those of the RNA-seq results (r ≥ 0.9). Expression profiles of 22 of 25 (88%) pairs of NATs and STs were highly correlated (p ≤ 0.01), with 15 having r ≥ 0.8 and 4 having r ≤ -0.8. Six lignin-modifying genes and their NATs were analyzed in detail. Diverse patterns of differential expression among different stages and positive and negative correlations were observed. These results suggested that NATs were implicated in gene expression regulation in a function-group and developmental-stage specific manner through complex mechanisms.

Bimodal expression of yeast GAL genes is controlled by a long non-coding RNA and a bifunctional galactokinase

Bimodality in gene expression can generate phenotypic heterogeneity facilitating fitness and growth of isogenic cell populations in suboptimal environments. We investigated the mechanism by which, in conditions of limiting galactose, yeast cell populations activate GAL genes in a bimodal fashion with a cell fraction expressing GAL genes (ON), while the rest subpopulation is kept at the non-expressing (OFF) state. We show that a long non-coding RNA (GAL10-ncRNA) crossing the bidirectional GAL1-10 promoter, decreases the rate by which single cells commit transition to the ON state without affecting the rate of GAL transcription per se in ON cells. This is accomplished by repressing stochastic expression of the bifunctional Gal1p galactokinase, which besides its enzymatic activity acts as an essential inducer of the system under those conditions. We show that once single cells switch to the ON state, the GAL10-ncRNA effect is overridden by accumulating Gal1p levels sufficient to feedback positively on Gal4p, and not by the active transcription of GAL10 that occurs in opposite direction relative to that of GAL10-ncRNA. Conversely, GAL10-ncRNA does not influence transition of ON cells, where Gal4p is active, back to the OFF state. Our model suggests that the functional interplay between GAL10-ncRNA transcription, stochastic Gal1p expression and Gal1p positive feedback on Gal4p constitutes a novel molecular switch mechanism dictating the commitment of individual cells for either metabolic state.

Functional characterisation of long intergenic non-coding RNAs through genetic interaction profiling in Saccharomyces cerevisiae

BACKGROUND

Transcriptome studies have revealed that many eukaryotic genomes are pervasively transcribed producing numerous long non-coding RNAs (lncRNAs). However, only a few lncRNAs have been ascribed a cellular role thus far, with most regulating the expression of adjacent genes. Even less lncRNAs have been annotated as essential hence implying that the majority may be functionally redundant. Therefore, the function of lncRNAs could be illuminated through systematic analysis of their synthetic genetic interactions (GIs).

RESULTS

Here, we employ synthetic genetic array (SGA) in Saccharomyces cerevisiae to identify GIs between long intergenic non-coding RNAs (lincRNAs) and protein-coding genes. We first validate this approach by demonstrating that the telomerase RNA TLC1 displays a GI network that corresponds to its well-described function in telomere length maintenance. We subsequently performed SGA screens on a set of uncharacterised lincRNAs and uncover their connection to diverse cellular processes. One of these lincRNAs, SUT457, exhibits a GI profile associating it to telomere organisation and we consistently demonstrate that SUT457 is required for telomeric overhang homeostasis through an Exo1-dependent pathway. Furthermore, the GI profile of SUT457 is distinct from that of its neighbouring genes suggesting a function independent to its genomic location. Accordingly, we show that ectopic expression of this lincRNA suppresses telomeric overhang accumulation in sut457Δ cells assigning a trans-acting role for SUT457 in telomere biology.

CONCLUSIONS

Overall, our work proposes that systematic application of this genetic approach could determine the functional significance of individual lncRNAs in yeast and other complex organisms.

Coordination of Cell Cycle Progression and Mitotic Spindle Assembly Involves Histone H3 Lysine 4 Methylation by Set1/COMPASS

Methylation of histone H3 lysine 4 (H3K4) by Set1 complex/COMPASS is a hallmark of eukaryotic chromatin, but it remains poorly understood how this post-translational modification contributes to the regulation of biological processes like the cell cycle. Here, we report a H3K4 methylation-dependent pathway in Saccharomyces cerevisiae that governs toxicity toward benomyl, a microtubule destabilizing drug. Benomyl-sensitive growth of wild-type cells required mono- and dimethylation of H3K4 and Pho23, a PHD-containing subunit of the Rpd3L complex. Δset1 and Δpho23 deletions suppressed defects associated with ipl1-2 aurora kinase mutant, an integral component of the spindle assembly checkpoint during mitosis. Benomyl resistance of Δset1 strains was accompanied by deregulation of all four tubulin genes and the phenotype was suppressed by tub2-423 and Δtub3 mutations, establishing a genetic link between H3K4 methylation and microtubule function. Most interestingly, sine wave fitting and clustering of transcript abundance time series in synchronized cells revealed a requirement for Set1 for proper cell-cycle-dependent gene expression and Δset1 cells displayed delayed entry into S phase. Disruption of G1/S regulation in Δmbp1 and Δswi4 transcription factor mutants duplicated both benomyl resistance and suppression of ipl1-2 as was observed with Δset1 Taken together our results support a role for H3K4 methylation in the coordination of cell-cycle progression and proper assembly of the mitotic spindle during mitosis.

LncRNAs: Bridging environmental sensing and gene expression

The survival of all organisms is dependent on complex, coordinated responses to environmental cues. Non-coding RNAs have been identified as major players in regulation of gene expression, with recent evidence supporting roles for long non-coding (lnc)RNAs in both transcriptional and post-transcriptional control. Evidence from our laboratory shows that lncRNAs have the ability to form hybridized structures called R-loops with specific DNA target sequences in S. cerevisiae, thereby modulating gene expression. In this Point of View, we provide an overview of the nature of lncRNA-mediated control of gene expression in the context of our studies using the GAL gene cluster as a model for controlling the timing of transcription.

Evidence for Regulation of ECM3 Expression by Methylation of Histone H3 Lysine 4 and Intergenic Transcription in Saccharomyces cerevisiae

Transcription of nonprotein-coding DNA is widespread in eukaryotes and plays important regulatory roles for many genes, including genes that are misregulated in cancer cells. Its pervasiveness presents the potential for a wealth of diverse regulatory roles for noncoding transcription. We previously showed that the act of transcribing noncoding DNA (ncDNA) across the promoter of the protein-coding SER3 gene in Saccharomyces cerevisiae positions nucleosomes over the upstream activating sequences, leading to strong repression of SER3 transcription. To explore the possibility of other regulatory roles for ncDNA transcription, we selected six candidate S. cerevisiae genes that express ncRNAs over their promoters and analyzed the regulation of one of these genes, ECM3, in detail. Because noncoding transcription can lead to changes in the local chromatin landscape that impinge on the expression of nearby coding genes, we surveyed the effects of various chromatin regulators on the expression of ECM3. These analyses identified roles for the Paf1 complex in positively regulating ECM3 transcription through methylation of histone H3 at lysine 4 (K4) and for Paf1 in controlling the pattern of intergenic transcription at this locus. By deleting a putative promoter for the noncoding transcription unit that lies upstream of ECM3, we provide evidence for a positive correlation between intergenic transcription and ECM3 expression. Our results are consistent with a model in which cotranscriptional methylation of histone H3 K4, mediated by the Paf1 complex and noncoding transcription, leads to activation of ECM3 transcription.

The Eaf3/5/7 Subcomplex Stimulates NuA4 Interaction with Methylated Histone H3 Lys-36 and RNA Polymerase II

NuA4 is the only essential lysine acetyltransferase complex in Saccharomyces cerevisiae, where it has been shown to stimulate transcription initiation and elongation. Interaction with nucleosomes is stimulated by histone H3 Lys-4 and Lys-36 methylation, but the mechanism of this interaction is unknown. Eaf3, Eaf5, and Eaf7 form a subcomplex within NuA4 that may also function independently of the lysine acetyltransferase complex. The Eaf3/5/7 complex and the Rpd3C(S) histone deacetylase complex have both been shown to bind di- and trimethylated histone H3 Lys-36 stimulated by Eaf3. We investigated the role of the Eaf3/5/7 subcomplex in NuA4 binding to nucleosomes. Different phenotypes of eaf3/5/7Δ mutants support functions for the complex as both part of and independent of NuA4. Further evidence for Eaf3/5/7 within NuA4 came from mutations in the subcomplex leading to ∼40% reductions in H4 acetylation in bulk histones, probably caused by binding defects to both nucleosomes and RNA polymerase II. In vitro binding assays showed that Eaf3/5/7 specifically stimulates NuA4 binding to di- and trimethylated histone H3 Lys-36 and that this binding is important for NuA4 occupancy in transcribed ORFs. Consistent with the role of NuA4 in stimulating transcription elongation, loss of EAF5 or EAF7 resulted in a processivity defect. Overall, these results reveal the function of Eaf3/5/7 within NuA4 to be important for both NuA4 and RNA polymerase II binding.

Local potentiation of stress-responsive genes by upstream noncoding transcription

It has been postulated that a myriad of long noncoding RNAs (lncRNAs) contribute to gene regulation. In fission yeast, glucose starvation triggers lncRNA transcription across promoter regions of stress-responsive genes including fbp1 (fructose-1,6-bisphosphatase1). At the fbp1 promoter, this transcription promotes chromatin remodeling and fbp1 mRNA expression. Here, we demonstrate that such upstream noncoding transcription facilitates promoter association of the stress-responsive transcriptional activator Atf1 at the sites of transcription, leading to activation of the downstream stress genes. Genome-wide analyses revealed that ∼50 Atf1-binding sites show marked decrease in Atf1 occupancy when cells are treated with a transcription inhibitor. Most of these transcription-enhanced Atf1-binding sites are associated with stress-dependent induction of the adjacent mRNAs or lncRNAs, as observed in fbp1. These Atf1-binding sites exhibit low Atf1 occupancy and high histone density in glucose-rich conditions, and undergo dramatic changes in chromatin status after glucose depletion: enhanced Atf1 binding, histone eviction, and histone H3 acetylation. We also found that upstream transcripts bind to the Groucho-Tup1 type transcriptional corepressors Tup11 and Tup12, and locally antagonize their repressive functions on Atf1 binding. These results reveal a new mechanism in which upstream noncoding transcription locally magnifies the specific activation of stress-inducible genes via counteraction of corepressors.

Role of Long Noncoding RNAs in Neoplasia: Special Emphasis on Prostate Cancer

Recent advances in sequencing technology have dramatically improved the ability of investigators to study nucleic acid biology. Bolstered by these new and powerful techniques, the field of noncoding RNA (ncRNA) research, in particular, has witnessed a period of significant progress, wherein multiple new and unique species of ncRNA elements have been discovered and characterized. The current categories of ncRNAs include tRNA, rRNA, snoRNA, snRNA, piRNA, miRNA, and lncRNA, among others. The largest of these RNAs are the long noncoding RNAs (lncRNAs) that perform a diverse set of functions within the cell. Importantly, lncRNAs have recently been implicated in the pathogenesis of multiple types of cancer, including breast, lung, gastric, liver, and prostate. This reviews the major lncRNAs currently believed to play a role in human malignancies with a special emphasis on lncRNAs germane to cancer of the prostate gland. Continued investigation of lncRNA will likely prove to be exceedingly valuable, as they may provide novel therapeutic targets for the treatment of cancer. In addition, lncRNAs offer the potential to serve as diagnostic and prognostic biomarkers for cancer. The present state of lncRNA-based strategies for use in the management of cancer will also be highlighted.

Sulforaphane modulates telomerase activity via epigenetic regulation in prostate cancer cell lines

Epidemiologic studies have revealed that diets rich in sulforaphane (SFN), an isothiocyanate present in cruciferous vegetables, are associated with a marked decrease in prostate cancer incidence. The chemo-preventive role of SFN is associated with its histone de-acetylase inhibitor activity. However, the effect of SFN on chromatin composition and dynamic folding, especially in relation to HDAC inhibitor activity, remains poorly understood. In this study, we found that SFN can inhibit the expression and activity of human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase, in 2 prostate cancer cell lines. This decrease in gene expression is correlated with SFN-induced changes in chromatin structure and composition. The SFN-mediated changes in levels of histone post-translational modifications, more specifically acetylation of histone H3 lysine 18 and di-methylation of histone H3 lysine 4, 2 modifications linked with high risk of prostate cancer recurrence, were associated with regulatory elements within the hTERT promoter region. Chromatin condensation may also play a role in SFN-mediated hTERT repression, since expression and recruitment of MeCP2, a known chromatin compactor, were altered in SFN treated prostate cancer cells. Chromatin immuno-precipitation (ChIP) of MeCP2 showed enrichment over regions of the hTERT promoter with increased nucleosome density. These combined results strongly support a role for SFN in the mediation of epigenetic events leading to the repression of hTERT in prostate cancer cells. This ability of SFN to modify chromatin composition and structure associated with target gene expression provides a new model by which dietary phytochemicals may exert their chemoprevention activity.

Regulated Formation of lncRNA-DNA Hybrids Enables Faster Transcriptional Induction and Environmental Adaptation

Long non-coding (lnc)RNAs, once thought to merely represent noise from imprecise transcription initiation, have now emerged as major regulatory entities in all eukaryotes. In contrast to the rapidly expanding identification of individual lncRNAs, mechanistic characterization has lagged behind. Here we provide evidence that the GAL lncRNAs in the budding yeast S. cerevisiae promote transcriptional induction in trans by formation of lncRNA-DNA hybrids or R-loops. The evolutionarily conserved RNA helicase Dbp2 regulates formation of these R-loops as genomic deletion or nuclear depletion results in accumulation of these structures across the GAL cluster gene promoters and coding regions. Enhanced transcriptional induction is manifested by lncRNA-dependent displacement of the Cyc8 co-repressor and subsequent gene looping, suggesting that these lncRNAs promote induction by altering chromatin architecture. Moreover, the GAL lncRNAs confer a competitive fitness advantage to yeast cells because expression of these non-coding molecules correlates with faster adaptation in response to an environmental switch.

Regulation of Antisense Transcription by NuA4 Histone Acetyltransferase and Other Chromatin Regulatory Factors

NuA4 histone lysine (K) acetyltransferase (KAT) promotes transcriptional initiation of TATA-binding protein (TBP)-associated factor (TAF)-dependent ribosomal protein genes. TAFs have also been recently found to enhance antisense transcription from the 3' end of the GAL10 coding sequence. However, it remains unknown whether, like sense transcription of the ribosomal protein genes, TAF-dependent antisense transcription of GAL10 also requires NuA4 KAT. Here, we show that NuA4 KAT associates with the GAL10 antisense transcription initiation site at the 3' end of the coding sequence. Such association of NuA4 KAT depends on the Reb1p-binding site that recruits Reb1p activator to the GAL10 antisense transcription initiation site. Targeted recruitment of NuA4 KAT to the GAL10 antisense transcription initiation site promotes GAL10 antisense transcription. Like NuA4 KAT, histone H3 K4/36 methyltransferases and histone H2B ubiquitin conjugase facilitate GAL10 antisense transcription, while the Swi/Snf and SAGA chromatin remodeling/modification factors are dispensable for antisense, but not sense, transcription of GAL10. Taken together, our results demonstrate for the first time the roles of NuA4 KAT and other chromatin regulatory factors in controlling antisense transcription, thus illuminating chromatin regulation of antisense transcription.

Single-Molecule Imaging Reveals a Switch between Spurious and Functional ncRNA Transcription

Eukaryotic transcription is pervasive, and many of the resulting RNAs are non-coding. It is unknown whether ubiquitous transcription is functional or simply reflects stochastic transcriptional noise. By single-molecule visualization of the dynamic interplay between coding and non-coding transcription at the GAL locus in living yeast cells, we show that antisense GAL10 ncRNA transcription can switch between functional and spurious under different conditions. During galactose induction, GAL10 sense transcription occurs in short stochastic bursts, which are unaffected by transcription of antisense GAL10 ncRNA, even when both are present simultaneously at the same locus. In contrast, when GAL10 is not induced, ncRNA transcription is critical to prevent transcriptional leakage of GAL1 and GAL10. Suppression of ncRNA transcription by strand-specific CRISPR/dCas9 results in transcriptional leakage of the inducer GAL1, leading to a more sensitive transcription activation threshold, an alteration of metabolic switching, and a fitness defect in competition experiments.

Interaction of the Jhd2 Histone H3 Lys-4 Demethylase with Chromatin Is Controlled by Histone H2A Surfaces and Restricted by H2B Ubiquitination

Histone H3 lysine 4 (H3K4) methylation is a dynamic modification. In budding yeast, H3K4 methylation is catalyzed by the Set1-COMPASS methyltransferase complex and is removed by Jhd2, a JMJC domain family demethylase. The catalytic JmjC and JmjN domains of Jhd2 have the ability to remove all three degrees (mono-, di-, and tri-) of H3K4 methylation. Jhd2 also contains a plant homeodomain (PHD) finger required for its chromatin association and H3K4 demethylase functions. The Jhd2 PHD finger associates with chromatin independent of H3K4 methylation and the H3 N-terminal tail. Therefore, how Jhd2 associates with chromatin to perform H3K4 demethylation has remained unknown. We report a novel interaction between the Jhd2 PHD finger and histone H2A. Two residues in H2A (Phe-26 and Glu-57) serve as a binding site for Jhd2 in vitro and mediate its chromatin association and H3K4 demethylase functions in vivo. Using RNA sequencing, we have identified the functional target genes for Jhd2 and the H2A Phe-26 and Glu-57 residues. We demonstrate that H2A Phe-26 and Glu-57 residues control chromatin association and H3K4 demethylase functions of Jhd2 during positive or negative regulation of transcription at target genes. Importantly, we show that H2B Lys-123 ubiquitination blocks Jhd2 from accessing its binding site on chromatin, and thereby, we have uncovered a second mechanism by which H2B ubiquitination contributes to the trans-histone regulation of H3K4 methylation. Overall, our study provides novel insights into the chromatin binding dynamics and H3K4 demethylase functions of Jhd2.