scholarly journals Exploring different sequence representations and classification methods for the prediction of nucleosome positioning

2018 ◽  
Author(s):  
Nikos Kostagiolas ◽  
Nikiforos Pittaras ◽  
Christoforos Nikolaou ◽  
George Giannakopoulos
Keyword(s):  
Gene Expression ◽  
Dna Sequences ◽  
Large Scale ◽  
Genomic Sequence ◽  
Critical Role ◽  
Regulation Of Gene Expression ◽  
Nucleosome Positioning ◽  
Regulatory Elements ◽  
Machine Learning Algorithms ◽  
N Gram

Nucleosomes form the first level of DNA compaction and thus bear a critical role in the overall genome organization. At the same time, they modulate chromatin accessibility and, through a dynamic equilibrium with other DNA-binding proteins, may shape gene expression. A number of large-scale nucleosome positioning maps, obtained for various genomes, has compelled the importance of nucleosomes in the regulation of gene expression and has shown constraints in the relative positions of nucleosomes to be much stronger around regulatory elements (i.e. promoters, splice junctions and enhancers). At the same time, the great majority of nucleosome positions appears to be rather flexible. Various computational methods have in the past been used in order to capture the sequence determinants of nucleosome positioning but, as the extent to which DNA sequence preferences may guide nucleosome occupancy largely varies, this has proved to be rather difficult. In order to focus on highly specific sequence attributes, in this work we have analyzed two well-defined sets of nucleosome-occupied sites (NOS) and nucleosome-free-regions (NFR) from the genome of S. cerevisiae, with the use of textual representations. We employed 3 different genomic sequence representations (Hidden Markov Models, Bag-of-Words and N-gram Graphs) combined with a number of machine learning algorithms on the task of classifying genomic sequences as nucleosome-free (NFR) or nucleosome-occupied NOS (to be further amended based on updated results). We found that different approaches that involve the usage of different representations or algorithms can be more or less effective at predicting nucleosome positioning based on the textual data of the underlying genomic sequence. More interestingly, we show that N-gram Graphs, a sequence representation that takes into account both k-mer occurrences and relative positioning at various lengths scales is outperforming other methodologies and may thus be a choice of preference for the analysis of DNA sequences with subtle constraints.

scholarly journals Transcriptional Enhancers in Drosophila

Genetics ◽  
2020 ◽  
Vol 216 (1) ◽  
pp. 1-26 ◽  
Author(s):  
Stephen Small ◽  
David N. Arnosti
Keyword(s):  
Gene Expression ◽  
Critical Role ◽  
Regulation Of Gene Expression ◽  
Regulatory Elements ◽  
Comprehensive Analysis ◽  
Special Focus ◽  
Transcriptional Enhancers ◽  
Quantitative Understanding ◽  
Developmental Role

Key discoveries in Drosophila have shaped our understanding of cellular “enhancers.” With a special focus on the fly, this chapter surveys properties of these adaptable cis-regulatory elements, whose actions are critical for the complex spatial/temporal transcriptional regulation of gene expression in metazoa. The powerful combination of genetics, molecular biology, and genomics available in Drosophila has provided an arena in which the developmental role of enhancers can be explored. Enhancers are characterized by diverse low- or high-throughput assays, which are challenging to interpret, as not all of these methods of identifying enhancers produce concordant results. As a model metazoan, the fly offers important advantages to comprehensive analysis of the central functions that enhancers play in gene expression, and their critical role in mediating the production of phenotypes from genotype and environmental inputs. A major challenge moving forward will be obtaining a quantitative understanding of how these cis-regulatory elements operate in development and disease.

The 4D Living Genome

2021 ◽  
Author(s):  
Julianna Arlene Sherman Goelzer
Keyword(s):  
Gene Expression ◽  
Human Genome ◽  
Genomic Sequence ◽  
Critical Role ◽  
Regulation Of Gene Expression ◽  
Correlation Spectroscopy ◽  
Microscopy Technique ◽  
Temporal Aspects ◽  
Key Factor ◽  
Dynamics Simulations

Over the last few decades great advances have been made in our understanding of gene expression and the human genome. In 2003 the human genome was sequenced for the first time, allowing us to discover its true importance in human health. While sequencing the human genome was a great advance, it ultimately created more questions than it answered. It is known that the genomic sequence is extremely important in genome regulation, however recent studies have shown that the 4D (spatiotemporal) organization and dynamics of the living genome plays an equally critical role in regulation of gene expression. A key factor in the spatiotemporal genome is the temporal and spatial coordination of transcription factors required for gene expression. We focus on addressing both the spatial and temporal aspects of the genome through a cutting-edge microscopy technique known as 3D Orbital Tracking Fluorescence Correlation Spectroscopy (3DOT-FCCS) in conjunction with Molecular Dynamics simulations. The synergistic use of these techniques will provide a clearer picture of the rules that govern the human genome.

scholarly journals Sophisticated Conversations between Chromatin and Chromatin Remodelers, and Dissonances in Cancer

2021 ◽  
Vol 22 (11) ◽  
pp. 5578
Author(s):  
Cedric R. Clapier
Keyword(s):  
Gene Expression ◽  
Regulation Of Gene Expression ◽  
Structural Diversity ◽  
Nucleosome Positioning ◽  
Basic Mechanism ◽  
Progressive Increase ◽  
Chromatin Organization ◽  
Dna Translocation ◽  
Dynamic Regulation ◽  
Cooperative Action

The establishment and maintenance of genome packaging into chromatin contribute to define specific cellular identity and function. Dynamic regulation of chromatin organization and nucleosome positioning are critical to all DNA transactions—in particular, the regulation of gene expression—and involve the cooperative action of sequence-specific DNA-binding factors, histone modifying enzymes, and remodelers. Remodelers are molecular machines that generate various chromatin landscapes, adjust nucleosome positioning, and alter DNA accessibility by using ATP binding and hydrolysis to perform DNA translocation, which is highly regulated through sophisticated structural and functional conversations with nucleosomes. In this review, I first present the functional and structural diversity of remodelers, while emphasizing the basic mechanism of DNA translocation, the common regulatory aspects, and the hand-in-hand progressive increase in complexity of the regulatory conversations between remodelers and nucleosomes that accompanies the increase in challenges of remodeling processes. Next, I examine how, through nucleosome positioning, remodelers guide the regulation of gene expression. Finally, I explore various aspects of how alterations/mutations in remodelers introduce dissonance into the conversations between remodelers and nucleosomes, modify chromatin organization, and contribute to oncogenesis.

scholarly journals BET bromodomain proteins regulate enhancer function during adipogenesis

2018 ◽  
Vol 115 (9) ◽  
pp. 2144-2149 ◽  
Author(s):  
Jonathan D. Brown ◽  
Zachary B. Feldman ◽  
Sean P. Doherty ◽  
Jaime M. Reyes ◽  
Peter B. Rahl ◽  
...  
Keyword(s):  
Gene Expression ◽  
De Novo ◽  
Critical Role ◽  
Regulatory Elements ◽  
Developmental Transitions ◽  
Adipocyte Cell ◽  
Bromodomain Proteins ◽  
Enhancer Function ◽  
Distal Regulatory Elements ◽  
Expression Program

Developmental transitions are guided by master regulatory transcription factors. During adipogenesis, a transcriptional cascade culminates in the expression of PPARγ and C/EBPα, which orchestrate activation of the adipocyte gene expression program. However, the coactivators controlling PPARγ and C/EBPα expression are less well characterized. Here, we show the bromodomain-containing protein, BRD4, regulates transcription of PPARγ and C/EBPα. Analysis of BRD4 chromatin occupancy reveals that induction of adipogenesis in 3T3L1 fibroblasts provokes dynamic redistribution of BRD4 to de novo super-enhancers proximal to genes controlling adipocyte differentiation. Inhibition of the bromodomain and extraterminal domain (BET) family of bromodomain-containing proteins impedes BRD4 occupancy at these de novo enhancers and disrupts transcription of Pparg and Cebpa, thereby blocking adipogenesis. Furthermore, silencing of these BRD4-occupied distal regulatory elements at the Pparg locus by CRISPRi demonstrates a critical role for these enhancers in the control of Pparg gene expression and adipogenesis in 3T3L1s. Together, these data establish BET bromodomain proteins as time- and context-dependent coactivators of the adipocyte cell state transition.

Stat6 Inhibits Human Interleukin-4 Promoter Activity in T Cells

Blood ◽  
1998 ◽  
Vol 92 (12) ◽  
pp. 4529-4538 ◽  
Author(s):  
Steve N. Georas ◽  
John E. Cumberland ◽  
Thomas F. Burke ◽  
Rongbing Chen ◽  
Ulrike Schindler ◽  
...  
Keyword(s):  
Gene Expression ◽  
T Cells ◽  
Molecular Mechanisms ◽  
Critical Role ◽  
Regulatory Elements ◽  
Jurkat Cells ◽  
Proximal Promoter ◽  
Interleukin 4 ◽  
Th2 Cells ◽  
Th Cells

Abstract The differentiation of naive T-helper (Th) cells into cytokine-secreting effector Th cells requires exposure to multiple signals, including exogenous cytokines. Interleukin-4 (IL-4) plays a major role in this process by promoting the differentiation of IL-4–secreting Th2 cells. In Th2 cells, IL-4 gene expression is tightly controlled at the level of transcription by the coordinated binding of multiple transcription factors to regulatory elements in the proximal promoter region. Nuclear factor of activated T cell (NFAT) family members play a critical role in regulating IL-4 transcription and interact with up to five sequences (termed P0 through P4) in the IL-4 promoter. The molecular mechanisms by which IL-4 induces expression of the IL-4 gene are not known, although the IL-4–activated transcription factor signal transducer and activator of transcription 6 (Stat6) is required for this effect. We report here that Stat6 interacts with three binding sites in the human IL-4 promoter by electrophoretic mobility shift assays. These sites overlap the P1, P2, and P4 NFAT elements. To investigate the role of Stat6 in regulating IL-4 transcription, we used Stat6-deficient Jurkat T cells with different intact IL-4 promoter constructs in cotransfection assays. We show that, whereas a multimerized response element from the germline IgE promoter was highly induced by IL-4 in Stat6-expressing Jurkat cells, the intact human IL-4 promoter was repressed under similar conditions. We conclude that the function of Stat6 is highly dependent on promoter context and that this factor promotes IL-4 gene expression in an indirect manner.

Chromatin-Modifying Enzymes in T Cell Development

2020 ◽  
Vol 38 (1) ◽  
pp. 397-419
Author(s):  
Michael J. Shapiro ◽  
Virginia Smith Shapiro
Keyword(s):  
Gene Expression ◽  
T Cell ◽  
Biological Effects ◽  
Critical Role ◽  
T Cell Development ◽  
Regulation Of Gene Expression ◽  
Chromatin Accessibility ◽  
Cell Development ◽  
Specific Gene ◽  
Dynamic Regulation

T cell development involves stepwise progression through defined stages that give rise to multiple T cell subtypes, and this is accompanied by the establishment of stage-specific gene expression. Changes in chromatin accessibility and chromatin modifications accompany changes in gene expression during T cell development. Chromatin-modifying enzymes that add or reverse covalent modifications to DNA and histones have a critical role in the dynamic regulation of gene expression throughout T cell development. As each chromatin-modifying enzyme has multiple family members that are typically all coexpressed during T cell development, their function is sometimes revealed only when two related enzymes are concurrently deleted. This work has also revealed that the biological effects of these enzymes often involve regulation of a limited set of targets. The growing diversity in the types and sites of modification, as well as the potential for a single enzyme to catalyze multiple modifications, is also highlighted.

scholarly journals Structure-Function Analysis of VapB4 Antitoxin Identifies Critical Features of a Minimal VapC4 Toxin-Binding Module

2015 ◽  
Vol 197 (7) ◽  
pp. 1197-1207 ◽  
Author(s):  
Guangze Jin ◽  
Martin S. Pavelka ◽  
J. Scott Butler
Keyword(s):  
Gene Expression ◽  
Dna Binding ◽  
Function Analysis ◽  
Critical Role ◽  
Regulation Of Gene Expression ◽  
Binding Domain ◽  
Type Ii ◽  
Toxin Binding ◽  
Dna Binding Specificity ◽  
Amino Acid Side Chains

ABSTRACTBacterial toxin-antitoxin systems play a critical role in the regulation of gene expression, leading to developmental changes, reversible dormancy, and cell death. Type II toxin-antitoxin pairs, composed of protein toxins and antitoxins, exist in nearly all bacteria and are classified into six groups on the basis of the structure of the toxins. The VapBC group comprises the most common type II system and, like other toxin-antitoxin systems, functions to elicit dormancy by inhibiting protein synthesis. Activation of toxin function requires protease degradation of the VapB antitoxin, which frees the VapC toxin from the VapBC complex, allowing it to hydrolyze the RNAs required for translation. Generally, type II antitoxins bind with high specificity to their cognate toxins via a toxin-binding domain and endow the complex with DNA-binding specificity via a DNA-binding domain. Despite the ubiquity of VapBC systems and their critical role in the regulation of gene expression, few functional studies have addressed the details of VapB-VapC interactions. Here we report on the results of experiments designed to identify molecular determinants of the specificity of theMycobacterium tuberculosisVapB4 antitoxin for its cognate VapC4 toxin. The results identify the minimal domain of VapB4 required for this interaction as well as the amino acid side chains required for binding to VapC4. These findings have important implications for the evolution of VapBC toxin-antitoxin systems and their potential as targets of small-molecule protein-protein interaction inhibitors.IMPORTANCEVapBC toxin-antitoxin pairs are the most widespread type II toxin-antitoxin systems in bacteria, where they are thought to play key roles in stress-induced dormancy and the formation of persisters. The VapB antitoxins are critical to these processes because they inhibit the activity of the toxins and provide the DNA-binding specificity that controls the synthesis of both proteins. Despite the importance of VapB antitoxins and the existence of several VapBC crystal structures, little is known about their functional featuresin vivo. Here we report the findings of the first comprehensive structure-function analysis of a VapB toxin. The results identify the minimal toxin-binding domain, its modular antitoxin function, and the specific amino acid side chains required for its activity.

Large-scale monitoring of pleiotropic regulation of gene expression by the prokaryotic nucleoid-associated protein, H-NS

2001 ◽  
Vol 40 (1) ◽  
pp. 20-36 ◽  
Author(s):  
Florence Hommais ◽  
Evelyne Krin ◽  
Christine Laurent-Winter ◽  
Olga Soutourina ◽  
Alain Malpertuy ◽  
...  
Keyword(s):  
Gene Expression ◽  
Large Scale ◽  
Regulation Of Gene Expression

Identification of a Gain-of-Function SNP Causing a New Model of α-Thalassaemia.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 523-523
Author(s):  
Marco De Gobbi ◽  
Vip Viprakasit ◽  
Pieter J. de Jong ◽  
Yuko Yoshinaga ◽  
Jan-Fang Cheng ◽  
...  
Keyword(s):  
Gene Expression ◽  
Binding Site ◽  
Globin Gene ◽  
Regulation Of Gene Expression ◽  
Histone H3 ◽  
Regulatory Elements ◽  
Causative Mutation ◽  
Regulatory Sequences ◽  
Chromosome 16 ◽  
Upstream Regulatory Sequences

Abstract The human α globin cluster includes an embryonic gene ζ and 2 fetal/adult genes (α2 and α1) arranged along the chromosome in the order in which they are expressed in development (5′-ζ-pseudoζ- αD- α2-α1-𝛉-3′). Fully activated expression of these genes in erythroid cells depends on upstream regulatory elements of which HS-40, located 40kb upstream of the cluster, appears to exert the greatest effect. We have recently shown that during terminal differentiation, key transcription factors (GATA-2, GATA-1, NF-E2, SCL complex) sequentially bind the α promoters and their regulatory elements and a domain of histone acetylation develops which eventually encompasses the entire α globin cluster including the upstream regulatory sequences. α-thalassemia most frequently results from deletions or point mutations affecting the structural α globin genes, but may also result from rare sporadic deletions which remove the upstream regulatory sequences. In a single family α globin expression was silenced by a mutation which drives an anti-sense RNA through the α gene. Alpha thalassemia may also result from inherited and acquired mutations in a trans-acting factor called ATRX. Over the past few years we have continued to screen for new mechanisms which lead to α thalassemia and thereby elucidate new principles underlying the regulation of gene expression in hemopoiesis. Here we describe a new mechanism of α thalassemia occurring in Pacific Islanders in whom we could detect no mutations or rearrangements in the α globin gene locus. Despite this, extensive genetic analysis showed unequivocally that the causative mutation is linked to the terminal 169kb of chromosome 16 (Viprakasit et al accompanying abstract). Analysis of globin synthesis, steady state RNA levels and detection of RNA in situ demonstrated that the mutation downregulates α globin transcription. To identify the mutation, we constructed a new BAC library from an affected homozygote, isolated and re-sequenced the candidate region and focussed further analysis on 8 SNPS within the α globin cluster, one of which creates a new GATA-1 binding site (GACA>GATA). Using primary erythroblasts from normal individuals and patients with this form of thalassemia, together with interspecific hybrids containing either the normal or abnormal copy of chromosome 16, we have shown that this SNP creates a new binding site in vivo for GATA-1 and the SCL complex. Furthermore, the chromatin at this site becomes activated as judged by acetylation of histone H3 and H4 (H3ac2 and H4ac4) and methylation of histone H3 (H3K4me2). Based on these data we postulate that an active transcriptional complex binding this new GATA site created by the SNP-mutation, could distract the upstream regulatory regions, which normally interact with the α globin promoter, and silence α globin gene expression. This model thus represents a new example of α globin gene down-regulation and a new mechanism by which gene expression can be perturbed during hemopoiesis.

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