INO80 Chromatin Remodeling Coordinates Metabolic Homeostasis with Cell Division

Uncharacterized yeast gene YBR238C, an effector of TORC1 signaling in a mitochondrial feedback loop, accelerates cellular aging via HAP4- and RMD9-dependent mechanisms

Uncovering the regulators of cellular aging will unravel the complexity of aging biology and identify potential therapeutic interventions to delay the onset and progress of chronic, aging-related diseases. In this work, we systematically compared genesets involved in regulating the lifespan of Saccharomyces cerevisiae (a powerful model organism to study the cellular aging of humans) and those with expression changes under rapamycin treatment. Among the functionally uncharacterized genes in the overlap set, YBR238C stood out as the only one downregulated by rapamycin and with an increased chronological and replicative lifespan upon deletion. We show that YBR238C and its paralog RMD9 oppositely affect mitochondria and aging. YBR238C deletion increases the cellular lifespan by enhancing mitochondrial function. Its overexpression accelerates cellular aging via mitochondrial dysfunction. We find that the phenotypic effect of YBR238C is largely explained by HAP4- and RMD9-dependent mechanisms. Furthermore, we find that genetic- or chemical-based induction of mitochondrial dysfunction increases TORC1 (Target of Rapamycin Complex 1) activity that, subsequently, accelerates cellular aging. Notably, TORC1 inhibition by rapamycin (or deletion of YBR238C) improves the shortened lifespan under these mitochondrial dysfunction conditions in yeast and human cells. The growth of mutant cells (a proxy of TORC1 activity) with enhanced mitochondrial function is sensitive to rapamycin whereas the growth of defective mitochondrial mutants is largely resistant to rapamycin compared to wild type. Our findings demonstrate a feedback loop between TORC1 and mitochondria (the TORC1-MItochondria-TORC1 (TOMITO) signaling process) that regulates cellular aging processes. Hereby, YBR238C is an effector of TORC1 modulating mitochondrial function.

The chromatin remodeler Ino80 regulates yeast stress tolerance and cell metabolism through modulating nitrogen catabolite repression

Chromatin remodelers are important in maintaining the dynamic chromatin state in eukaryotic cells, which is essential for epigenetic regulation. Among the remodelers, the multi-subunits complex INO80 plays crucial roles in transcriptional regulation. However, current knowledge of chromatin regulation of the core subunit Ino80 on stress adaptation remains mysterious. Here we revealed that overexpressing the chromatin remodeler Ino80 elevated tolerance to multiple stresses in budding yeast Saccharomyces cerevisiae. Analyses of differential chromatin accessibility and global transcription levels revealed an enrichment of genes involved in NCR (nitrogen catabolite repression) under acetic acid stress. We demonstrated that Ino80 overexpression reduced the histone H3 occupancy in the promoter region of the glutamate dehydrogenase gene GDH2 and the allantoinase gene DAL1. Consistently, the decreased occupancy of nucleosome was revealed in the Ino80-inactivation mutant. Further analyses showed that Ino80 was recruited to the specific DNA locus in the promoter region of GDH2. Consistently, Ino80 overexpression facilitated the utilization of non-preferred nitrogen source to enhance ethanol yield under prolonged acetic acid stress. These results demonstrate that Ino80 plays a crucial role in coordinating carbon and nitrogen metabolism during stress adaptation.

INO80 Is Required for the Cell Cycle Control, Survival, and Differentiation of Mouse ESCs by Transcriptional Regulation

Precise regulation of the cell cycle of embryonic stem cells (ESCs) is critical for their self-maintenance and differentiation. The cell cycle of ESCs differs from that of somatic cells and is different depending on the cell culture conditions. However, the cell cycle regulation in ESCs via epigenetic mechanisms remains unclear. Here, we showed that the ATP-dependent chromatin remodeler Ino80 regulates the cell cycle genes in ESCs under primed conditions. Ino80 loss led to a significantly extended length of the G1-phase in ESCs grown under primed culture conditions. Ino80 directly bound to the transcription start site and regulated the expression of cell cycle-related genes. Furthermore, Ino80 loss induced cell apoptosis. However, the regulatory mechanism of Ino80 in differentiating ESC cycle slightly differed; an extended S-phase was detected in differentiating inducible Ino80 knockout ESCs. RNA-seq analysis of differentiating ESCs revealed that the expression of genes associated with organ development cell cycle is persistently altered in Ino80 knockout cells, suggesting that cell cycle regulation by Ino80 is not limited to undifferentiated ESCs. Therefore, our study establishes the function of Ino80 in ESC cycle via transcriptional regulation, at least partly. Moreover, this Ino80 function may be universal to other cell types.

Distinct functions of three chromatin remodelers in activator binding and preinitiation complex assembly

The nucleosome remodeling complexes (CRs) SWI/SNF, RSC, and Ino80C cooperate in evicting or repositioning nucleosomes to produce nucleosome depleted regions (NDRs) at the promoters of many yeast genes induced by amino acid starvation. We analyzed mutants depleted of the catalytic subunits of these CRs for binding of transcriptional activator Gcn4 and recruitment of TATA-binding protein (TBP) during preinitiation complex (PIC) assembly. RSC and Ino80 were found to enhance Gcn4 binding to both UAS elements in NDRs upstream of promoters and to unconventional binding sites within nucleosome-occupied coding sequences; and SWI/SNF contributes to UAS binding when RSC is depleted. All three CRs are actively recruited by Gcn4 to most UAS elements and appear to enhance Gcn4 binding by reducing nucleosome occupancies at the binding motifs, indicating a positive regulatory loop. SWI/SNF acts unexpectedly in WT cells to prevent excessive Gcn4 binding at many UAS elements, indicating a dual mode of action that is modulated by the presence of RSC. RSC and SWI/SNF collaborate to enhance TBP recruitment at Gcn4 target genes, together with Ino80C, in a manner associated with nucleosome eviction at the TBP binding sites. Cooperation among the CRs in TBP recruitment is also evident at the highly transcribed ribosomal protein genes, while RSC and Ino80C act more broadly than SWI/SNF at the majority of other constitutively expressed genes to stimulate this step in PIC assembly. Our findings indicate a complex interplay among the CRs in evicting promoter nucleosomes to regulate activator binding and stimulate PIC assembly.

ATP-dependent chromatin remodelers (CRs), including SWI/SNF and RSC in budding yeast, are thought to stimulate transcription by repositioning or evicting promoter nucleosomes, and we recently implicated the CR Ino80C in this process as well. The relative importance of these CRs in stimulating activator binding and recruitment of TATA-binding protein (TBP) to promoters is incompletely understood. Examining mutants depleted of the catalytic subunits of these CRs, we determined that RSC and Ino80C stimulate binding of transcription factor Gcn4 to nucleosome-depleted regions, or linkers between genic nucleosomes, at multiple target genes activated by Gcn4 in amino acid-starved cells, frequently via evicting nucleosomes from the Gcn4 binding motifs. At some genes, SWI/SNF functionally complements RSC, while opposing RSC at others to limit Gcn4 binding. The CRs in turn are recruited by Gcn4, consistent with a positive feedback loop that enhances Gcn4 binding. The three CRs also cooperate to enhance TBP recruitment, again involving nucleosome depletion, at both Gcn4 target and highly expressed ribosomal protein genes, whereas only RSC and Ino80C act broadly throughout the genome to enhance this key step in preinitiation complex assembly. Our findings illuminate functional cooperation among multiple CRs in regulating activator binding and promoter activation.

Genome-Wide Analysis of Yeast Metabolic Cycle through Metabolic Network Models Reveals Superiority of Integrated ATAC-seq Data over RNA-seq Data

Saccharomyces cerevisiae undergoes robust oscillations to regulate its physiology for adaptation and survival under nutrient-limited conditions. Environmental cues can induce rhythmic metabolic alterations in order to facilitate the coordination of dynamic metabolic behaviors. Of such metabolic processes, the yeast metabolic cycle enables adaptation of the cells to varying nutritional status through oscillations in gene expression and metabolite production levels. In this process, yeast metabolism is altered between diverse cellular states based on changing oxygen consumption levels: quiescent (reductive charging [RC]), growth (oxidative [OX]), and proliferation (reductive building [RB]) phases. We characterized metabolic alterations during the yeast metabolic cycle using a variety of approaches. Gene expression levels are widely used for condition-specific metabolic simulations, whereas the use of epigenetic information in metabolic modeling is still limited despite the clear relationship between epigenetics and metabolism. This prompted us to investigate the contribution of epigenomic information to metabolic predictions for progression of the yeast metabolic cycle. In this regard, we determined altered pathways through the prediction of regulated reactions and corresponding model genes relying on differential chromatin accessibility levels. The predicted metabolic alterations were confirmed via data analysis and literature. We subsequently utilized RNA sequencing (RNA-seq) and assay for transposase-accessible chromatin using sequencing (ATAC-seq) data sets in the contextualization of the yeast model. The use of ATAC-seq data considerably enhanced the predictive capability of the model. To the best of our knowledge, this is the first attempt to use genome-wide chromatin accessibility data in metabolic modeling. The preliminary results showed that epigenomic data sets can pave the way for more accurate metabolic simulations.

IMPORTANCE Dynamic chromatin organization mediates the emergence of condition-specific phenotypes in eukaryotic organisms. Saccharomyces cerevisiae can alter its metabolic profile via regulation of genome accessibility and robust transcriptional oscillations under nutrient-limited conditions. Thus, both epigenetic information and transcriptomic information are crucial in the understanding of condition-specific metabolic behavior in this organism. Based on genome-wide alterations in chromatin accessibility and transcription, we investigated the yeast metabolic cycle, which is a remarkable example of coordinated and dynamic yeast behavior. In this regard, we assessed the use of ATAC-seq and RNA-seq data sets in condition-specific metabolic modeling. To our knowledge, this is the first attempt to use chromatin accessibility data in the reconstruction of context-specific metabolic models, despite the extensive use of transcriptomic data. As a result of comparative analyses, we propose that the incorporation of epigenetic information is a promising approach in the accurate prediction of metabolic dynamics.

Cancer cell metabolism connects epigenetic modifications to transcriptional regulation

Adaptation of cellular function with the nutrient environment is essential for survival. Failure to adapt can lead to cell death and/or disease. Indeed, energy metabolism alterations are a major contributing factor for many pathologies, including cancer, cardiovascular disease, and diabetes. In particular, a primary characteristic of cancer cells is altered metabolism that promotes survival and proliferation even in the presence of limited nutrients. Interestingly, recent studies demonstrate that metabolic pathways produce intermediary metabolites that directly influence epigenetic modifications in the genome. Emerging evidence demonstrates that metabolic processes in cancer cells fuel malignant growth, in part, through epigenetic regulation of gene expression programs important for proliferation and adaptive survival. In this review, recent progress toward understanding the relationship of cancer cell metabolism, epigenetic modification, and transcriptional regulation will be discussed. Specifically, the need for adaptive cell metabolism and its modulation in cancer cells will be introduced. Current knowledge on the emerging field of metabolite production and epigenetic modification will also be reviewed. Alterations of DNA (de)methylation, histone modifications, such as (de)methylation and (de)acylation, as well as chromatin remodeling, will be discussed in the context of cancer cell metabolism. Finally, how these epigenetic alterations contribute to cancer cell phenotypes will be summarized. Collectively, these studies reveal that both metabolic and epigenetic pathways in cancer cells are closely linked, representing multiple opportunities to therapeutically target the unique features of malignant growth.

The biological function of metazoan-specific subunit nuclear factor related to kappaB binding protein of INO80 complex

The INO80 chromatin remodeling complex plays an essential role in the regulation of gene transcription, which participate in a variety of important biological processes in cells including DNA repair and DNA replication. Difference from the yeast INO80 complex, metazoan INO80 complex have the specific subunit G, which is known as nuclear factor related to kappaB binding protein (NFRKB). Recently, NFRKB has been received much attention in many aspects, such as DNA repair, cell pluripotency, telomere protection, and protein activity regulation. To dig the new function of metazoan INO80 complex, a better understanding of the role of NFRKB is required. In this review, we provide an overview of the structure and function of NFRKB and discuss its potential role in cancer treatment and telomere regulation. Overall, this review provides an important reference for further research of the INO80 complex and NFRKB.

Uncovering Divergence in Gene Expression Regulation in the Adaptation of Yeast to Nitrogen Scarcity

Saccharomyces cerevisiae rewires its transcriptional output to survive stressful environments, such as nitrogen scarcity under fermentative conditions. Although divergence in nitrogen metabolism among natural yeast populations has been reported, the impact of regulatory genetic variants modulating gene expression and nitrogen consumption remains to be investigated. Here, we employed an F1 hybrid from two contrasting S. cerevisiae strains, providing a controlled genetic environment to map cis factors involved in the divergence of gene expression regulation in response to nitrogen scarcity. We used a dual approach to obtain genome-wide allele-specific profiles of chromatin accessibility, transcription factor binding, and gene expression through ATAC-seq (assay for transposase accessible chromatin) and RNA-seq (transcriptome sequencing). We observed large variability in allele-specific expression and accessibility between the two genetic backgrounds, with a third of these differences specific to a deficient nitrogen environment. Furthermore, we discovered events of allelic bias in gene expression correlating with allelic bias in transcription factor binding solely under nitrogen scarcity, where the majority of these transcription factors orchestrates the nitrogen catabolite repression regulatory pathway and demonstrates a cis × environment-specific response. Our approach allowed us to find cis variants modulating gene expression, chromatin accessibility, and allelic differences in transcription factor binding in response to low nitrogen culture conditions. IMPORTANCE Historically, coding variants were prioritized when searching for causal mechanisms driving adaptation of natural populations to stressful environments. However, the recent focus on noncoding variants demonstrated their ubiquitous role in adaptation. Here, we performed genome-wide regulatory variation profiles between two divergent yeast strains when facing nitrogen nutritional stress. The open chromatin availability of several regulatory regions changes in response to nitrogen scarcity. Importantly, we describe regulatory events that deviate between strains. Our results demonstrate a widespread variation in gene expression regulation between naturally occurring populations in response to stressful environments.

Epigenomic links from metabolism-methionine and chromatin architecture

Chromatin and associated epigenetic marks provide important platforms for gene regulation in response to metabolic changes associated with environmental exposures, including physiological stress, nutritional deprivation, and starvation. Numerous studies have shown that fluctuations of key metabolites can influence chromatin modifications, but their effects on chromatin structure (e.g. chromatin compaction, nucleosome arrangement, and chromatin loops) and how they appropriately deposit specific chemical modification on chromatin are largely unknown. Here, focusing on methionine metabolism, we discuss recent developments of metabolic effects on chromatin modifications and structure, as well as consequences on gene regulation.

OsARP6 Is Involved in Internode Elongation by Regulating Cell-Cycle-Related Genes

The SWR1 complex (SWR1-C) is important for the deposition of histone variant H2A.Z into chromatin to regulate gene expression. Characterization of SWR1-C subunits in Arabidopsis thaliana has revealed their role in variety of developmental processes. Oryza sativa actin related protein 6 (OsARP6) is a subunit of rice SWR1-C. Its role in rice plant development is unknown. Here, we examined the subcellular localization, expression patterns, and loss of function phenotypes for this protein and found that OsARP6 is a nuclear localized protein, and is broadly expressed. OsARP6 interacted with OsPIE1, a central ATPase subunit of rice SWR1-C. The osarp6 knockout mutants displayed pleiotropic phenotypic alterations in vegetative and reproductive traits, including semi-dwarf phenotype, lower tillers number, short leaf length, changes in spikelet morphology, and seed abortion. Microscopic thin sectioning of the top internode revealed that the dwarf phenotype of osarp6 was due to reduced number of cells rather than reduced cell length. The altered transcript level of genes involved in cell division suggested that OsARP6 affects cell cycle regulation. In addition, H2A.Z levels were reduced at the promoters and transcription start sites (TSS) of the regulated genes in osarp6 plants. Together, these results suggest that OsARP6 is involved in rice plant development, and H2A.Z deposition.

TORC1 regulates the transcriptional response to glucose and developmental cycle via the Tap42-Sit4-Rrd1/2 pathway in Saccharomyces cerevisiae

BACKGROUND

Target of Rapamycin Complex 1 (TORC1) is a highly conserved eukaryotic protein complex that couples the presence of growth factors and nutrients in the environment with cellular proliferation. TORC1 is primarily implicated in linking amino acid levels with cellular growth in yeast and mammals. Although glucose deprivation has been shown to cause TORC1 inactivation in yeast, the precise role of TORC1 in glucose signaling and the underlying mechanisms remain unclear.

RESULTS

We demonstrate that the presence of glucose in the growth medium is both necessary and sufficient for TORC1 activation. TORC1 activity increases upon addition of glucose to yeast cells growing in a non-fermentable carbon source. Conversely, shifting yeast cells from glucose to a non-fermentable carbon source reduces TORC1 activity. Analysis of transcriptomic data revealed that glucose and TORC1 co-regulate about 27% (1668/6004) of yeast genes. We demonstrate that TORC1 orchestrates the expression of glucose-responsive genes mainly via the Tap42-Sit4-Rrd1/2 pathway. To confirm TORC1's function in glucose signaling, we tested its role in spore germination, a glucose-dependent developmental state transition in yeast. TORC1 regulates the glucose-responsive genes during spore germination and inhibition of TORC1 blocks spore germination.

CONCLUSIONS

Our studies indicate that a regulatory loop that involves activation of TORC1 by glucose and regulation of glucose-responsive genes by TORC1, mediates nutritional control of growth and development in yeast.

Accessible chromatin reveals regulatory mechanisms underlying cell fate decisions during early embryogenesis

This study was conducted to investigate epigenetic landscape across multiple species and identify transcription factors (TFs) and their roles in controlling cell fate decision events during early embryogenesis. We made a comprehensively joint-research of chromatin accessibility of five species during embryogenesis by integration of ATAC-seq and RNA-seq datasets. Regulatory roles of candidate early embryonic TFs were investigated. Widespread accessible chromatin in early embryos overlapped with putative cis-regulatory sequences. Sets of cell-fate-determining TFs were identified. YOX1, a key cell cycle regulator, were found to homologous to clusters of TFs that are involved in neuron and epidermal cell-fate determination. Our research provides an intriguing insight into evolution of cell-fate decision during early embryogenesis among organisms.

Symmetric neural progenitor divisions require chromatin-mediated homologous recombination DNA repair by Ino80

Chromatin regulates spatiotemporal gene expression during neurodevelopment, but it also mediates DNA damage repair essential to proliferating neural progenitor cells (NPCs). Here, we uncover molecularly dissociable roles for nucleosome remodeler Ino80 in chromatin-mediated transcriptional regulation and genome maintenance in corticogenesis. We find that conditional Ino80 deletion from cortical NPCs impairs DNA double-strand break (DSB) repair, triggering p53-dependent apoptosis and microcephaly. Using an in vivo DSB repair pathway assay, we find that Ino80 is selectively required for homologous recombination (HR) DNA repair, which is mechanistically distinct from Ino80 function in YY1-associated transcription. Unexpectedly, sensitivity to loss of Ino80-mediated HR is dependent on NPC division mode: Ino80 deletion leads to unrepaired DNA breaks and apoptosis in symmetric NPC-NPC divisions, but not in asymmetric neurogenic divisions. This division mode dependence is phenocopied following conditional deletion of HR gene Brca2. Thus, distinct modes of NPC division have divergent requirements for Ino80-dependent HR DNA repair.

Nuclear Functions of TOR: Impact on Transcription and the Epigenome

The target of rapamycin (TOR) protein kinase is at the core of growth factor- and nutrient-dependent signaling pathways that are well-known for their regulation of metabolism, growth, and proliferation. However, TOR is also involved in the regulation of gene expression, genomic and epigenomic stability. TOR affects nuclear functions indirectly through its activity in the cytoplasm, but also directly through active nuclear TOR pools. The mechanisms by which TOR regulates its nuclear functions are less well-understood compared with its cytoplasmic activities. TOR is an important pharmacological target for several diseases, including cancer, metabolic and neurological disorders. Thus, studies of the nuclear functions of TOR are important for our understanding of basic biological processes, as well as for clinical implications.

Chromatin-remodeling links metabolic signaling to gene expression

BACKGROUND

ATP-dependent chromatin remodelers are evolutionarily conserved complexes that alter nucleosome positioning to influence many DNA-templated processes, such as replication, repair, and transcription. In particular, chromatin remodeling can dynamically regulate gene expression by altering accessibility of chromatin to transcription factors.

SCOPE OF REVIEW

This review provides an overview of the importance of chromatin remodelers in the regulation of metabolic gene expression. Particular emphasis is placed on the INO80 and SWI/SNF (BAF/PBAF) chromatin remodelers in both yeast and mammals. This review details discoveries from the initial identification of chromatin remodelers in Saccharomyces cerevisiae to recent discoveries in the metabolic requirements of developing embryonic tissues in mammals.

MAJOR CONCLUSIONS

INO80 and SWI/SNF (BAF/PBAF) chromatin remodelers regulate the expression of energy metabolism pathways in S. cerevisiae and mammals in response to diverse nutrient environments. In particular, the INO80 complex organizes the temporal expression of gene expression in the metabolically synchronized S. cerevisiae system. INO80-mediated chromatin remodeling is also needed to constrain cell division during metabolically favorable conditions. Conversely, the BAF/PBAF remodeler regulates tissue-specific glycolytic metabolism and is disrupted in cancers that are dependent on glycolysis for proliferation. The role of chromatin remodeling in metabolic gene expression is downstream of the metabolic signaling pathways, such as the TOR pathway, a critical regulator of metabolic homeostasis. Furthermore, the INO80 and BAF/PBAF chromatin remodelers have both been shown to regulate heart development, the tissues of which have unique requirements for energy metabolism during development. Collectively, these results demonstrate that chromatin remodelers communicate metabolic status to chromatin and are a central component of homeostasis pathways that optimize cell fitness, organismal development, and prevent disease.

Recognition of Histone Crotonylation by Taf14 Links Metabolic State to Gene Expression

Metabolic signaling to chromatin often underlies how adaptive transcriptional responses are controlled. While intermediary metabolites serve as co-factors for histone-modifying enzymes during metabolic flux, how these modifications contribute to transcriptional responses is poorly understood. Here, we utilize the highly synchronized yeast metabolic cycle (YMC) and find that fatty acid β-oxidation genes are periodically expressed coincident with the β-oxidation byproduct histone crotonylation. Specifically, we found that H3K9 crotonylation peaks when H3K9 acetylation declines and energy resources become limited. During this metabolic state, pro-growth gene expression is dampened; however, mutation of the Taf14 YEATS domain, a H3K9 crotonylation reader, results in de-repression of these genes. Conversely, exogenous addition of crotonic acid results in increased histone crotonylation, constitutive repression of pro-growth genes, and disrupted YMC oscillations. Together, our findings expose an unexpected link between metabolic flux and transcription and demonstrate that histone crotonylation and Taf14 participate in the repression of energy-demanding gene expression.

Transcriptional and Epigenetic Regulation by the Mechanistic Target of Rapamycin Complex 1 Pathway

Nutrient availability impacts health such that nutrient excess states can dysregulate epigenetic and transcriptional pathways to cause many diseases. Increasing evidence implicates aberrant regulation of nutrient signaling cascades as one means of communicating nutrient information to the epigenetic and transcriptional regulatory machinery. One such signaling cascade, the mechanistic target of rapamycin complex 1 (mTORC1), is conserved from yeast to man, and it is deregulated in diverse disease states. The catalytic subunit of the mTORC1 kinase complex (Tor1 or Tor2 in budding yeast and mTor in mammals) phosphorylates several downstream effectors regulating transcriptional and translational responses controlling growth and proliferation. Delineating mechanisms of cytoplasmic nutrient mTORC1 activation continues to be a major research focus. However, Tor kinases not only localize to the cytoplasm but also are found in the nucleus where they selectively bind and regulate genes controlling cellular metabolism and anabolism. The nuclear mTORC1 functions are now beginning to be defined, and they suggest that mTORC1 has a critical role in regulating the complex transcriptional activities required for ribosomal biogenesis. The mTORC1 pathway also interacts with epigenetic regulators required for modifying chromatin structure and function to control gene expression. Because altered nutrient states exert both individual and transgenerational phenotypic changes, mTORC1 signaling to chromatin effectors may have a significant role in mediating the effects of diet and nutrients on the epigenome. This article will discuss the recent inroads into the function of nuclear mTORC1 and its role in epigenetic and transcriptional regulation.

A new experimental platform facilitates assessment of the transcriptional and chromatin landscapes of aging yeast

Replicative aging of Saccharomyces cerevisiae is an established model system for eukaryotic cellular aging. A limitation in yeast lifespan studies has been the difficulty of separating old cells from young cells in large quantities. We engineered a new platform, the Miniature-chemostat Aging Device (MAD), that enables purification of aged cells at sufficient quantities for genomic and biochemical characterization of aging yeast populations. Using MAD, we measured DNA accessibility and gene expression changes in aging cells. Our data highlight an intimate connection between aging, growth rate, and stress. Stress-independent genes that change with age are highly enriched for targets of the signal recognition particle (SRP). Combining MAD with an improved ATAC-seq method, we find that increasing proteasome activity reduces rDNA instability usually observed in aging cells and, contrary to published findings, provide evidence that global nucleosome occupancy does not change significantly with age.

Unraveling Interfaces between Energy Metabolism and Cell Cycle in Plants

Oscillation in energy levels is widely variable in dividing and differentiated cells. To synchronize cell proliferation and energy fluctuations, cell cycle-related proteins have been implicated in the regulation of mitochondrial energy-generating pathways in yeasts and animals. Plants have chloroplasts and mitochondria, coordinating the cell energy flow. Recent findings suggest an integrated regulation of these organelles and the nuclear cell cycle. Furthermore, reports indicate a set of interactions between the cell cycle and energy metabolism, coordinating the turnover of proteins in plants. Here, we discuss how cell cycle-related proteins directly interact with energy metabolism-related proteins to modulate energy homeostasis and cell cycle progression. We provide interfaces between cell cycle and energy metabolism-related proteins that could be explored to maximize plant yield.

Identification of Two Distinct Classes of the Human INO80 Complex Genome-Wide

Chromatin remodeling and histone modifying enzymes play a critical role in shaping the regulatory output of a cell. Although much is known about these classes of proteins, identifying the mechanisms by which they coordinate gene expression programs remains an exciting topic of investigation. One factor that may contribute to the targeting and activity of chromatin regulators is local chromatin landscape. We leveraged genomic approaches and publically-available datasets to characterize the chromatin landscape at targets of the human INO80 chromatin remodeling complex (INO80-C). Our data revealed two classes of INO80-C targets with distinct chromatin signatures. The predominant INO80-C class was enriched for open chromatin, H3K27ac, and representative subunits from each of the three INO80-C modules (RUVBL1, RUVBL2, MCRS1, YY1). We named this class Canonical INO80. Notably, we identified an unexpected class of INO80-C targets that contained only the INO80 ATPase and harbored a repressive chromatin signature characterized by inaccessible chromatin, H3K27me3, and the methyltransferase EZH2. We named this class Non-Canonical INO80 (NC-INO80). Biochemical approaches indicated that INO80-C and the H3K27 acetyltransferase P300 physically interact, suggesting INO80-C and P300 may jointly coordinate chromatin accessibility at Canonical INO80 sites. No interaction was detected between INO80-C and EZH2, indicating INO80-C and EZH2 may engage in a separate form of regulatory crosstalk at NC-INO80 targets. Our data indicate that INO80-C is more compositionally heterogenous at its genomic targets than anticipated. Moreover, our data suggest there is an important link between INO80-C and histone modifying enzymes that may have consequences in developmental and pathological contexts.