Cell cycle-regulated oscillator coordinates core histone gene transcription through histone acetylation

Gene loss and cis-regulatory novelty shaped core histone gene evolution in the apiculate yeast Hanseniaspora uvarum

Core histone genes display a remarkable diversity of cis-regulatory mechanisms despite their protein sequence conservation. However, the dynamics and significance of this regulatory turnover are not well understood. Here, we describe the evolutionary history of core histone gene regulation across 400 million years in budding yeasts. We find that canonical mode of core histone regulation-mediated by the trans-regulator Spt10-is ancient, likely emerging between 320 and 380 million years ago and is fixed in the majority of extant species. Unexpectedly, we uncovered the emergence of a novel core histone regulatory mode in the Hanseniaspora genus, from its fast-evolving lineage, which coincided with the loss of 1 copy of its paralogous core histone genes. We show that the ancestral Spt10 histone regulatory mode was replaced, via cis-regulatory changes in the histone control regions, by a derived Mcm1 histone regulatory mode and that this rewiring event occurred with no changes to the trans-regulator, Mcm1, itself. Finally, we studied the growth dynamics of the cell cycle and histone synthesis in genetically modified Hanseniaspora uvarum. We find that H. uvarum divides rapidly, with most cells completing a cell cycle within 60 minutes. Interestingly, we observed that the regulatory coupling between histone and DNA synthesis was lost in H. uvarum. Our results demonstrate that core histone gene regulation was fixed anciently in budding yeasts, however it has greatly diverged in the Hanseniaspora fast-evolving lineage.

Maintaining transcriptional homeostasis during cell cycle

The preservation of gene expression patterns that define cellular identity throughout the cell division cycle is essential to perpetuate cellular lineages. However, the progression of cells through different phases of the cell cycle severely disrupts chromatin accessibility, epigenetic marks, and the recruitment of transcriptional regulators. Notably, chromatin is transiently disassembled during S-phase and undergoes drastic condensation during mitosis, which is a significant challenge to the preservation of gene expression patterns between cell generations. This article delves into the specific gene expression and chromatin regulatory mechanisms that facilitate the preservation of transcriptional identity during replication and mitosis. Furthermore, we emphasize our recent findings revealing the unconventional role of yeast centromeres and mitotic chromosomes in maintaining transcriptional fidelity beyond mitosis.

Systematic profiling of subtelomeric silencing factors in budding yeast

Subtelomeric gene silencing is the negative transcriptional regulation of genes located close to telomeres. This phenomenon occurs in a variety of eukaryotes with salient physiological implications, such as cell adherence, virulence, immune-system escape, and ageing. The process has been widely studied in the budding yeast Saccharomyces cerevisiae, where genes involved in this process have been identified mostly on a gene-by-gene basis. Here, we introduce a quantitative approach to study gene silencing, that couples the classical URA3 reporter with GFP monitoring, amenable to high-throughput flow cytometry analysis. This dual silencing reporter was integrated into several subtelomeric loci in the genome, where it showed a gradual range of silencing effects. By crossing strains with this dual reporter at the COS12 and YFR057W subtelomeric query loci with gene-deletion mutants, we carried out a large-scale forward screen for potential silencing factors. The approach was replicable and allowed accurate detection of expression changes. Results of our comprehensive screen suggest that the main players influencing subtelomeric silencing were previously known, but additional potential factors underlying chromatin conformation are involved. We validate and report the novel silencing factor LGE1, a protein with unknown molecular function required for histone H2B ubiquitination. Our strategy can be readily combined with other reporters and gene perturbation collections, making it a versatile tool to study gene silencing at a genome-wide scale.

Regulation of telomere silencing by the core histones-autophagy-Sir2 axis

Telomeres contain compacted heterochromatin, and genes adjacent to telomeres are subjected to transcription silencing. Maintaining telomere structure integrity and transcription silencing is important to prevent the occurrence of premature aging and aging-related diseases. How telomere silencing is regulated during aging is not well understood. Here, we find that the four core histones are reduced during yeast chronological aging, leading to compromised telomere silencing. Mechanistically, histone loss promotes the nuclear export of Sir2 and its degradation by autophagy. Meanwhile, reducing core histones enhances the autophagy pathway, which further accelerates autophagy-mediated Sir2 degradation. By screening the histone mutant library, we identify eight histone mutants and one histone modification (histone methyltransferase Set1-catalyzed H3K4 trimethylation) that regulate telomere silencing by modulating the core histones-autophagy-Sir2 axis. Overall, our findings reveal core histones and autophagy as causes of aging-coupled loss of telomere silencing and shed light on dynamic regulation of telomere structure during aging.

Transcriptome analysis of the binucleate ciliate Tetrahymena thermophila with asynchronous nuclear cell cycles

Tetrahymena thermophila harbors two functionally and physically distinct nuclei within a shared cytoplasm. During vegetative growth, the "cell cycles" of the diploid micronucleus and polyploid macronucleus are offset. Micronuclear S phase initiates just before cytokinesis and is completed in daughter cells before onset of macronuclear DNA replication. Mitotic micronuclear division occurs mid-cell cycle, while macronuclear amitosis is coupled to cell division. Here we report the first RNA-seq cell cycle analysis of a binucleated ciliated protozoan. RNA was isolated across 1.5 vegetative cell cycles, starting with a macronuclear G1 population synchronized by centrifugal elutriation. Using MetaCycle, 3244 of the 26,000+ predicted genes were shown to be cell cycle regulated. Proteins present in both nuclei exhibit a single mRNA peak that always precedes their macronuclear function. Nucleus-limited genes, including nucleoporins and importins, are expressed before their respective nucleus-specific role. Cyclin D and A/B gene family members exhibit different expression patterns that suggest nucleus-restricted roles. Periodically expressed genes cluster into seven cyclic patterns. Four clusters have known PANTHER gene ontology terms associated with G1/S and G2/M phase. We propose that these clusters encode known and novel factors that coordinate micro- and macronuclear-specific events such as mitosis, amitosis, DNA replication, and cell division.

Epigenetic Changes in Saccharomyces cerevisiae Alters the Aromatic Profile in Alcoholic Fermentation

Epigenetic changes in genomics provide phenotypic modification without DNA sequence alteration. This study shows that benzoic acid, a common food additive and known histone deacetylase inhibitor (HDACi), has an epigenetic effect on Saccharomyces cerevisiae. Benzoic acid stimulated formation of epigenetic histone marks H3K4Me2, H3K27Me2, H3K18ac, and H3Ser10p in S. cerevisiae and altered their phenotypic behavior, resulting in increased production of phenylethyl alcohol and ester compounds during alcoholic fermentation using wine as a representative model system. Our study demonstrates the HDACi activity of certain dietary compounds such as sodium butyrate, curcumin and anacardic acid, suggests the potential use of these dietary compounds in altering S. cerevisiae phenotypes without altering host-cell DNA. This study highlights the potential to use common dietary compounds to exploit epigenetic modifications for various fermentation and biotechnology applications as an alternative to genetic modification. These findings indicate that benzoic acid and other food additives may have potential epigenetic effects on human gut microbiota, in which several yeast species are involved. IMPORTANCE The manuscript investigates and reports for the first time utilizing a non-GMO approach to alter the fermentation process of Pinot Noir wines. We have experimentally demonstrated that certain dietary compounds possess histone deacetylase (HDAC) inhibiting activity and can alter the wine characteristics by potentially altering yeast gene transcription, which was resulted from epigenetic effects. We have previously proposed the term "nutrifermentics" to represent this newly proposed field of research that provides insights on the effect of certain dietary compounds on microbial strains and their potential application in fermentation. This technological approach is a novel way to manipulate microorganisms for innovative food and beverage production with quality attributes catering for consumer's needs. Using a multidisciplinary approach with an emphasis on food fermentation and biotechnology, this study will be substantially useful and of broad interest to food microbiologists and biotechnologists who seek for innovative concepts with real-world application potential.

Unscheduled DNA replication in G1 causes genome instability and damage signatures indicative of replication collisions

DNA replicates once per cell cycle. Interfering with the regulation of DNA replication initiation generates genome instability through over-replication and has been linked to early stages of cancer development. Here, we engineer genetic systems in budding yeast to induce unscheduled replication in a G1-like cell cycle state. Unscheduled G1 replication initiates at canonical S-phase origins. We quantifiy the composition of replisomes in G1- and S-phase and identified firing factors, polymerase α, and histone supply as factors that limit replication outside S-phase. G1 replication per se does not trigger cellular checkpoints. Subsequent replication during S-phase, however, results in over-replication and leads to chromosome breaks and chromosome-wide, strand-biased occurrence of RPA-bound single-stranded DNA, indicating head-to-tail replication collisions as a key mechanism generating genome instability upon G1 replication. Low-level, sporadic induction of G1 replication induces an identical response, indicating findings from synthetic systems are applicable to naturally occurring scenarios of unscheduled replication initiation.

The Spt10 GNAT Superfamily Protein Modulates Development, Cell Cycle Progression and Virulence in the Fungal Insect Pathogen, Beauveria bassiana

Chromatin remodeling is mediated in part by post-translational acetylation/deacetylation modifications of histones. Histone acetyltransferases (HATs), e.g., members of the GNAT/MYST superfamily, activate gene transcription via promotion of euchromatin formation. Here, we characterized a GNAT family HAT, Spt10 (BbSpt10), in the environmentally and economically important fungal insect pathogen, Beauveria bassiana. Targeted gene knockout of BbSpt10 resulted in impaired asexual development and morphogenesis; reduced abilities to utilize various carbon/nitrogen sources; reduced tolerance to heat, fungicides, and DNA damage stress; and attenuated virulence. The ΔBbSpt10 mutant showed disrupted cell cycle development and abnormal hyphal septation patterns. Transcriptome analyses of wild type and ΔBbSpt10 cells revealed the differential expression of 373 genes, including 153 downregulated and 220 upregulated genes. Bioinformatic analyses revealed downregulated genes to be enriched in pathways involved in amino acid metabolism, cellular transportation, cell type differentiation, and virulence, while upregulated genes were enriched in carbon/nitrogen metabolism, lipid metabolism, DNA process, and cell rescue, defense, and virulence. Downregulated virulence genes included hydrophobins, cellular transporters (ABC and MFS multidrug transporters) and cytochrome P450 detoxification genes. These data indicated broad effects of BbSpt10 on fungal development, multi-stress response, and virulence.

Replication stress inhibits synthesis of histone mRNAs in yeast by removing Spt10p and Spt21p from the histone promoters

Proliferating cells coordinate histone and DNA synthesis to maintain correct stoichiometry for chromatin assembly. Histone mRNA levels must be repressed when DNA replication is inhibited to prevent toxicity and genome instability due to free non-chromatinized histone proteins. In mammalian cells, replication stress triggers degradation of histone mRNAs, but it is unclear if this mechanism is conserved from other species. The aim of this study was to identify the histone mRNA decay pathway in the yeast Saccharomyces cerevisiae and determine the mechanism by which DNA replication stress represses histone mRNAs. Using reverse transcription-quantitative PCR and chromatin immunoprecipitation–quantitative PCR, we show here that histone mRNAs can be degraded by both 5′ → 3′ and 3′ → 5′ pathways; however, replication stress does not trigger decay of histone mRNA in yeast. Rather, replication stress inhibits transcription of histone genes by removing the histone gene–specific transcription factors Spt10p and Spt21p from histone promoters, leading to disassembly of the preinitiation complexes and eviction of RNA Pol II from histone genes by a mechanism facilitated by checkpoint kinase Rad53p and histone chaperone Asf1p. In contrast, replication stress does not remove SCB-binding factor transcription complex, another activator of histone genes, from the histone promoters, suggesting that Spt10p and Spt21p have unique roles in the transcriptional downregulation of histone genes during replication stress. Together, our data show that, unlike in mammalian cells, replication stress in yeast does not trigger decay of histone mRNAs but inhibits histone transcription.

Nuclear dihydroxyacetone phosphate signals nutrient sufficiency and cell cycle phase to global histone acetylation

Global histone acetylation varies with changes in the nutrient and cell cycle phases; however, the mechanisms connecting these variations are not fully understood. Herein, we report that nutrient-related and cell-cycle-regulated nuclear acetate regulates global histone acetylation. Histone deacetylation-generated acetate accumulates in the nucleus and induces histone hyperacetylation. The nuclear acetate levels were controlled by glycolytic enzyme triosephosphate isomerase 1 (TPI1). Cyclin-dependent kinase 2 (CDK2), which is phosphorylated and activated by nutrient-activated mTORC1, phosphorylates TPI1 Ser 117 and promotes nuclear translocation of TPI1, decreases nuclear dihydroxyacetone phosphate (DHAP) and induces nuclear acetate accumulation because DHAP scavenges acetate via the formation of 1-acetyl-DHAP. CDK2 accumulates in the cytosol during the late G1/S phases. Inactivation or blockade of nuclear translocation of TPI1 abrogates nutrient-dependent and cell-cycle-dependent global histone acetylation, chromatin condensation, gene transcription and DNA replication. These results identify the mechanism of maintaining global histone acetylation by nutrient and cell cycle signals.

The role of HDAC11 in obesity-related metabolic disorders: A critical review

At present, metabolic diseases, such as obesity and diabetes, have become the world's top health threats. These diseases are closely related to the abnormal development and function of adipocytes and metabolic inflammation associated with obesity. Histone deacetylase 11 (HDAC11), with a relatively unique structure and function in the HDAC family, plays a vital role in regulating cell growth, migration, and cell death. Currently, research on new key regulatory functions of HDAC11 in metabolic homeostasis is receiving more and more attention, and HDAC11 has also become a potential therapeutic target in the treatment of obesity and obesity-related diseases. Here, we summarized the latest literature on the role of HDAC11 in regulating the progress of obesity-related metabolic disorders.

Genome-wide variation and transcriptional changes in diverse developmental processes underlie the rapid evolution of seasonal adaptation

Many organisms enter a dormant state in their life cycle to deal with predictable changes in environments over the course of a year. The timing of dormancy is therefore a key seasonal adaptation, and it evolves rapidly with changing environments. We tested the hypothesis that differences in the timing of seasonal activity are driven by differences in the rate of development during diapause in Rhagoletis pomonella, a fly specialized to feed on fruits of seasonally limited host plants. Transcriptomes from the central nervous system across a time series during diapause show consistent and progressive changes in transcripts participating in diverse developmental processes, despite a lack of gross morphological change. Moreover, population genomic analyses suggested that many genes of small effect enriched in developmental functional categories underlie variation in dormancy timing and overlap with gene sets associated with development rate in Drosophila melanogaster Our transcriptional data also suggested that a recent evolutionary shift from a seasonally late to a seasonally early host plant drove more rapid development during diapause in the early fly population. Moreover, genetic variants that diverged during the evolutionary shift were also enriched in putative cis regulatory regions of genes differentially expressed during diapause development. Overall, our data suggest polygenic variation in the rate of developmental progression during diapause contributes to the evolution of seasonality in R. pomonella We further discuss patterns that suggest hourglass-like developmental divergence early and late in diapause development and an important role for hub genes in the evolution of transcriptional divergence.

The Rad53CHK1/CHK2-Spt21NPAT and Tel1ATM axes couple glucose tolerance to histone dosage and subtelomeric silencing

The DNA damage response (DDR) coordinates DNA metabolism with nuclear and non-nuclear processes. The DDR kinase Rad53CHK1/CHK2 controls histone degradation to assist DNA repair. However, Rad53 deficiency causes histone-dependent growth defects in the absence of DNA damage, pointing out unknown physiological functions of the Rad53-histone axis. Here we show that histone dosage control by Rad53 ensures metabolic homeostasis. Under physiological conditions, Rad53 regulates histone levels through inhibitory phosphorylation of the transcription factor Spt21NPAT on Ser276. Rad53-Spt21 mutants display severe glucose dependence, caused by excess histones through two separable mechanisms: dampening of acetyl-coenzyme A-dependent carbon metabolism through histone hyper-acetylation, and Sirtuin-mediated silencing of starvation-induced subtelomeric domains. We further demonstrate that repression of subtelomere silencing by physiological Tel1ATM and Rpd3HDAC activities coveys tolerance to glucose restriction. Our findings identify DDR mutations, histone imbalances and aberrant subtelomeric chromatin as interconnected causes of glucose dependence, implying that DDR kinases coordinate metabolism and epigenetic changes.

Yeast Genome Maintenance by the Multifunctional PIF1 DNA Helicase Family

The two PIF1 family helicases in Saccharomyces cerevisiae, Rrm3, and ScPif1, associate with thousands of sites throughout the genome where they perform overlapping and distinct roles in telomere length maintenance, replication through non-histone proteins and G4 structures, lagging strand replication, replication fork convergence, the repair of DNA double-strand break ends, and transposable element mobility. ScPif1 and its fission yeast homolog Pfh1 also localize to mitochondria where they protect mitochondrial genome integrity. In addition to yeast serving as a model system for the rapid functional evaluation of human Pif1 variants, yeast cells lacking Rrm3 have proven useful for elucidating the cellular response to replication fork pausing at endogenous sites. Here, we review the increasingly important cellular functions of the yeast PIF1 helicases in maintaining genome integrity, and highlight recent advances in our understanding of their roles in facilitating fork progression through replisome barriers, their functional interactions with DNA repair, and replication stress response pathways.

Bidirectional histone-gene promoters in Aspergillus: characterization and application for multi-gene expression

BACKGROUND

Filamentous fungi are important producers of enzymes and bioactive secondary metabolites and are exploited for industrial purposes. Expression and characterization of biosynthetic pathways requires stable expression of multiple genes in the production host. Fungal promoters are indispensable for the accomplishment of this task, and libraries of promoters that show functionality across diverse fungal species facilitate synthetic biology approaches, pathway expression, and cell-factory construction.

RESULTS

In this study, we characterized the intergenic region between the genes encoding histones H4.1 and H3, from five phylogenetically diverse species of Aspergillus, as bidirectional promoters (Ph4h3). By expression of the genes encoding fluorescent proteins mRFP1 and mCitrine, we show at the translational and transcriptional level that this region from diverse species is applicable as strong and constitutive bidirectional promoters in Aspergillus nidulans. Bioinformatic analysis showed that the divergent gene orientation of h4.1 and h3 appears maintained among fungi, and that the Ph4h3 display conserved DNA motifs among the investigated 85 Aspergilli. Two of the heterologous Ph4h3s were utilized for single-locus expression of four genes from the putative malformin producing pathway from Aspergillus brasiliensis in A. nidulans. Strikingly, heterologous expression of mlfA encoding the non-ribosomal peptide synthetase is sufficient for biosynthesis of malformins in A. nidulans, which indicates an iterative use of one adenylation domain in the enzyme. However, this resulted in highly stressed colonies, which was reverted to a healthy phenotype by co-expressing the residual four genes from the putative biosynthetic gene cluster.

CONCLUSIONS

Our study has documented that Ph4h3 is a strong constitutive bidirectional promoter and a valuable new addition to the genetic toolbox of at least the genus Aspergillus.

DNA damage checkpoint activation impairs chromatin homeostasis and promotes mitotic catastrophe during aging

Genome instability is a hallmark of aging and contributes to age-related disorders such as cancer and Alzheimer's disease. The accumulation of DNA damage during aging has been linked to altered cell cycle dynamics and the failure of cell cycle checkpoints. Here, we use single cell imaging to study the consequences of increased genomic instability during aging in budding yeast and identify striking age-associated genome missegregation events. This breakdown in mitotic fidelity results from the age-related activation of the DNA damage checkpoint and the resulting degradation of histone proteins. Disrupting the ability of cells to degrade histones in response to DNA damage increases replicative lifespan and reduces genomic missegregations. We present several lines of evidence supporting a model of antagonistic pleiotropy in the DNA damage response where histone degradation, and limited histone transcription are beneficial to respond rapidly to damage but reduce lifespan and genomic stability in the long term.

Set1-catalyzed H3K4 trimethylation antagonizes the HIR/Asf1/Rtt106 repressor complex to promote histone gene expression and chronological life span

Aging is the main risk factor for many prevalent diseases. However, the molecular mechanisms regulating aging at the cellular level are largely unknown. Using single cell yeast as a model organism, we found that reducing yeast histone proteins accelerates chronological aging and increasing histone supply extends chronological life span. We sought to identify pathways that regulate chronological life span by controlling intracellular histone levels. Thus, we screened the histone H3/H4 mutant library to uncover histone residues and posttranslational modifications that regulate histone gene expression. We discovered 15 substitution mutations with reduced histone proteins and 5 mutations with increased histone proteins. Among these mutations, we found Set1 complex-catalyzed H3K4me3 promotes histone gene transcription and maintains normal chronological life span. Unlike the canonical functions of H3K4me3 in gene expression, H3K4me3 facilitates histone gene transcription by acting as a boundary to restrict the spread of the repressive HIR/Asf1/Rtt106 complex from histone gene promoters. Collectively, our study identified a novel mechanism by which H3K4me3 antagonizes the HIR/Asf1/Rtt106 repressor complex to promote histone gene expression and extend chronological life span.

HAT1 Coordinates Histone Production and Acetylation via H4 Promoter Binding

The energetic costs of duplicating chromatin are large and therefore likely depend on nutrient sensing checkpoints and metabolic inputs. By studying chromatin modifiers regulated by epithelial growth factor, we identified histone acetyltransferase 1 (HAT1) as an induced gene that enhances proliferation through coordinating histone production, acetylation, and glucose metabolism. In addition to its canonical role as a cytoplasmic histone H4 acetyltransferase, we isolated a HAT1-containing complex bound specifically at promoters of H4 genes. HAT1-dependent transcription of H4 genes required an acetate-sensitive promoter element. HAT1 expression was critical for S-phase progression and maintenance of H3 lysine 9 acetylation at proliferation-associated genes, including histone genes. Therefore, these data describe a feedforward circuit whereby HAT1 captures acetyl groups on nascent histones and drives H4 production by chromatin binding to support chromatin replication and acetylation. These findings have important implications for human disease, since high HAT1 levels associate with poor outcomes across multiple cancer types.

Histone supply: Multitiered regulation ensures chromatin dynamics throughout the cell cycle

Mendiratta et al. review the interplay between the different regulatory layers that affect the transcription and dynamics of distinct histone H3 variants along the cell cycle.

As the building blocks of chromatin, histones are central to establish and maintain particular chromatin states associated with given cell fates. Importantly, histones exist as distinct variants whose expression and incorporation into chromatin are tightly regulated during the cell cycle. During S phase, specialized replicative histone variants ensure the bulk of the chromatinization of the duplicating genome. Other non-replicative histone variants deposited throughout the cell cycle at specific loci use pathways uncoupled from DNA synthesis. Here, we review the particular dynamics of expression, cellular transit, assembly, and disassembly of replicative and non-replicative forms of the histone H3. Beyond the role of histone variants in chromatin dynamics, we review our current knowledge concerning their distinct regulation to control their expression at different levels including transcription, posttranscriptional processing, and protein stability. In light of this unique regulation, we highlight situations where perturbations in histone balance may lead to cellular dysfunction and pathologies.

Viral proteins as a potential driver of histone depletion in dinoflagellates

Within canonical eukaryotic nuclei, DNA is packaged with highly conserved histone proteins into nucleosomes, which facilitate DNA condensation and contribute to genomic regulation. Yet the dinoflagellates, a group of unicellular algae, are a striking exception to this otherwise universal feature as they have largely abandoned histones and acquired apparently viral-derived substitutes termed DVNPs (dinoflagellate-viral-nucleoproteins). Despite the magnitude of this transition, its evolutionary drivers remain unknown. Here, using Saccharomyces cerevisiae as a model, we show that DVNP impairs growth and antagonizes chromatin by localizing to histone binding sites, displacing nucleosomes, and impairing transcription. Furthermore, DVNP toxicity can be relieved through histone depletion and cells diminish their histones in response to DVNP expression suggesting that histone reduction could have been an adaptive response to these viral proteins. These findings provide insights into eukaryotic chromatin evolution and highlight the potential for horizontal gene transfer to drive the divergence of cellular systems.

YHMI: a web tool to identify histone modifications and histone/chromatin regulators from a gene list in yeast

Post-translational modifications of histones (e.g. acetylation, methylation, phosphorylation and ubiquitination) play crucial roles in regulating gene expression by altering chromatin structures and creating docking sites for histone/chromatin regulators. However, the combination patterns of histone modifications, regulatory proteins and their corresponding target genes remain incompletely understood. Therefore, it is advantageous to have a tool for the enrichment/depletion analysis of histone modifications and histone/chromatin regulators from a gene list. Many ChIP-chip/ChIP-seq datasets of histone modifications and histone/chromatin regulators in yeast can be found in the literature. Knowing the needs and having the data motivate us to develop a web tool, called Yeast Histone Modifications Identifier (YHMI), which can identify the enriched/depleted histone modifications and the enriched histone/chromatin regulators from a list of yeast genes. Both tables and figures are provided to visualize the identification results. Finally, the high-quality and biological insight of the identification results are demonstrated by two case studies. We believe that YHMI is a valuable tool for yeast biologists to do epigenetics research.

Regulation of DNA replication-coupled histone gene expression

The expression of core histone genes is cell cycle regulated. Large amounts of histones are required to restore duplicated chromatin during S phase when DNA replication occurs. Over-expression and excess accumulation of histones outside S phase are toxic to cells and therefore cells need to restrict histone expression to S phase. Misregulation of histone gene expression leads to defects in cell cycle progression, genome stability, DNA damage response and transcriptional regulation. Here, we discussed the factors involved in histone gene regulation as well as the underlying mechanism. Understanding the histone regulation mechanism will shed lights on elucidating the side effects of certain cancer chemotherapeutic drugs and developing potential biomarkers for tumor cells.

Low expression of microRNA-1908 predicts a poor prognosis for patients with ovarian cancer

MicroRNAs (miRs) serve important roles in cancer genesis and progression. The expression of miR-1908 has been reported in a number of types of cancer; however, the clinical significance of miR-1908 in human ovarian cancer (OC) remains unclear. A total of 491 patients with OC from The Cancer Genome Atlas project cohort were selected and divided into two groups according to the median expression level of miR-1908. Univariate and multivariate analyses, using the Kaplan-Meier method and Cox regression, were performed to identify the characteristics that predict OC prognosis. Bioinformatics tools were used to identify potential targets of miR-1908. It was identified that the low expression of miR-1908 is associated with a poor prognosis for OC (P<0.05). The potential target genes of miR-1908 included podocan-like 1, JunB AP-1 transcription factor subunit, homeobox B8, SET binding factor 1 and sirtuin 2; high expression of these five genes additionally predicted a poor prognosis. These results suggest that miR-1908 may be a suitable target for the development of novel approaches in OC diagnosis and therapy in the future.

Comparative transcriptome and proteome analysis reveals a global impact of the nitrogen regulators AreA and AreB on secondary metabolism in Fusarium fujikuroi

The biosynthesis of multiple secondary metabolites in the phytopathogenic ascomycete Fusarium fujikuroi is strongly affected by nitrogen availability. Here, we present the first genome-wide transcriptome and proteome analysis that compared the wild type and deletion mutants of the two major nitrogen regulators AreA and AreB. We show that AreB acts not simply as an antagonist of AreA counteracting the expression of AreA target genes as suggested based on the yeast model. Both GATA transcription factors affect a large and diverse set of common as well as specific target genes and proteins, acting as activators and repressors. We demonstrate that AreA and AreB are not only involved in fungal nitrogen metabolism, but also in the control of several complex cellular processes like carbon metabolism, transport and secondary metabolism. We show that both GATA transcription factors can be considered as master regulators of secondary metabolism as they affect the expression of more than half of the 47 putative secondary metabolite clusters identified in the genome of F. fujikuroi. While AreA acts as a positive regulator of many clusters under nitrogen-limiting conditions, AreB is able to activate and repress gene clusters (e.g. bikaverin) under nitrogen limitation and sufficiency. In addition, ChIP analyses revealed that loss of AreA or AreB causes histone modifications at some of the regulated gene clusters.

Characterisation of functional domains in fission yeast Ams2 that are required for core histone gene transcription

Histone gene expression is regulated in a cell cycle-dependent manner, with a peak at S phase, which is crucial for cell division and genome integrity. However, the detailed mechanisms by which expression of histone genes are tightly regulated remain largely unknown. Fission yeast Ams2, a GATA-type zinc finger motif-containing factor, is required for activation of S phase-specific core histone gene transcription. Here we report the molecular characterisation of Ams2. We show that the zinc finger motif in Ams2 is necessary to bind the histone gene promoter region and to activate histone gene transcription. An N-terminal region of Ams2 acts as a self-interaction domain. Intriguingly, N-terminally truncated Ams2 binds to the histone gene promoters, but does not fully activate histone gene transcription. These observations imply that Ams2 self-interactions are required for efficient core histone gene transcription. Moreover, we show that Ams2 interacts with Teb1, which itself binds to the core histone gene promoters. We discuss the relationships between Ams2 domains and efficient transcription of the core histone genes in fission yeast.