Sensitivity of transcription factors to DNA methylation.

Dynamic binding of transcription factors (TFs) to regulatory elements controls transcriptional states throughout organism development. Epigenetics modifications, such as DNA methylation mostly within cytosine-guanine dinucleotides (CpGs), have the potential to modulate TF binding to DNA. Although DNA methylation has long been thought to repress TF binding, a more recent model proposes that TF binding can also inhibit DNA methylation. Here, we review the possible scenarios by which DNA methylation and TF binding affect each other. Further in vivo experiments will be required to generalize these models.journal article2019 Nov 222019 11 22importe

cis-Regulatory Requirements for Tissue-Specific Programs of the Circadian Clock

SummaryBackgroundBroadly expressed transcriptions factors (TFs) control tissue-specific programs of gene expression through interactions with local TF networks. A prime example is the circadian clock: although the conserved TFs CLOCK (CLK) and CYCLE (CYC) control a transcriptional circuit throughout animal bodies, rhythms in behavior and physiology are generated tissue specifically. Yet, how CLK and CYC determine tissue-specific clock programs has remained unclear.ResultsHere, we use a functional genomics approach to determine the cis-regulatory requirements for clock specificity. We first determine CLK and CYC genome-wide binding targets in heads and bodies by ChIP-seq and show that they have distinct DNA targets in the two tissue contexts. Computational dissection of CLK/CYC context-specific binding sites reveals sequence motifs for putative partner factors, which are predictive for individual binding sites. Among them, we show that the opa and GATA motifs, differentially enriched in head and body binding sites respectively, can be bound by OPA and SERPENT (SRP). They act synergistically with CLK/CYC in the Drosophila feedback loop, suggesting that they help to determine their direct targets and therefore orchestrate tissue-specific clock outputs. In addition, using in vivo transgenic assays, we validate that GATA motifs are required for proper tissue-specific gene expression in the adult fat body, midgut, and Malpighian tubules, revealing a cis-regulatory signature for enhancers of the peripheral circadian clock.ConclusionsOur results reveal how universal clock circuits can regulate tissue-specific rhythms and, more generally, provide insights into the mechanism by which universal TFs can be modulated to drive tissue-specific programs of gene expression

E2F6 initiates stable epigenetic silencing of germline genes during embryonic development.

In mouse development, long-term silencing by CpG island DNA methylation is specifically targeted to germline genes; however, the molecular mechanisms of this specificity remain unclear. Here, we demonstrate that the transcription factor E2F6, a member of the polycomb repressive complex 1.6 (PRC1.6), is critical to target and initiate epigenetic silencing at germline genes in early embryogenesis. Genome-wide, E2F6 binds preferentially to CpG islands in embryonic cells. E2F6 cooperates with MGA to silence a subgroup of germline genes in mouse embryonic stem cells and in embryos, a function that critically depends on the E2F6 marked box domain. Inactivation of E2f6 leads to a failure to deposit CpG island DNA methylation at these genes during implantation. Furthermore, E2F6 is required to initiate epigenetic silencing in early embryonic cells but becomes dispensable for the maintenance in differentiated cells. Our findings elucidate the mechanisms of epigenetic targeting of germline genes and provide a paradigm for how transient repression signals by DNA-binding factors in early embryonic cells are translated into long-term epigenetic silencing during mouse development

Single amino acid repeats in signal peptides

There has been an increasing interest in single amino acid repeats ever since it was shown that these are the cause of a variety of diseases. Although a systematic study of single amino acid repeats is challenging, they have subsequently been implicated in a number of functional roles. In general surveys, leucine runs were among the most frequent. In the present study, we present a detailed investigation of repeats in signal peptides of secreted and type I membrane proteins in comparison with their mature parts. We focus on eukaryotic species because single amino acid repeats are generally rather rare in archaea and bacteria. Our analysis of over 100 species shows that repeats of leucine (but not of other hydrophobic amino acids) are over-represented in signal peptides. This trend is most pronounced in higher eukaryotes, particularly in mammals. In the human proteome, although less than one-fifth of all proteins have a signal peptide, approximately two-thirds of all leucine repeats are located in these transient regions. Signal peptides are cleaved early from the growing polypeptide chain and then degraded rapidly. This may explain why leucine repeats, which can be toxic, are tolerated at such high frequencies. The substantial fraction of proteins affected by the strong enrichment of repeats in these transient segments highlights the bias that they can introduce for systematic analyses of protein sequences. In contrast to a general lack of conservation of single amino acid repeats, leucine repeats were found to be more conserved than the remaining signal peptide regions, indicating that they may have an as yet unknown functional role

A histone deacetylase adjusts transcription kinetics at coding sequences during Candida albicans morphogenesis.

Despite their classical role as transcriptional repressors, several histone deacetylases, including the baker's yeast Set3/Hos2 complex (Set3C), facilitate gene expression. In the dimorphic human pathogen Candida albicans, the homologue of the Set3C inhibits the yeast-to-filament transition, but the precise molecular details of this function have remained elusive. Here, we use a combination of ChIP-Seq and RNA-Seq to show that the Set3C acts as a transcriptional co-factor of metabolic and morphogenesis-related genes in C. albicans. Binding of the Set3C correlates with gene expression during fungal morphogenesis; yet, surprisingly, deletion of SET3 leaves the steady-state expression level of most genes unchanged, both during exponential yeast-phase growth and during the yeast-filament transition. Fine temporal resolution of transcription in cells undergoing this transition revealed that the Set3C modulates transient expression changes of key morphogenesis-related genes. These include a transcription factor cluster comprising of NRG1, EFG1, BRG1, and TEC1, which form a regulatory circuit controlling hyphal differentiation. Set3C appears to restrict the factors by modulating their transcription kinetics, and the hyperfilamentous phenotype of SET3-deficient cells can be reverted by mutating the circuit factors. These results indicate that the chromatin status at coding regions represents a dynamic platform influencing transcription kinetics. Moreover, we suggest that transcription at the coding sequence can be transiently decoupled from potentially conflicting promoter information in dynamic environments

A Histone Deacetylase Adjusts Transcription Kinetics at Coding Sequences during <em>Candida albicans</em> Morphogenesis

<div><p>Despite their classical role as transcriptional repressors, several histone deacetylases, including the baker's yeast Set3/Hos2 complex (Set3C), facilitate gene expression. In the dimorphic human pathogen <em>Candida albicans</em>, the homologue of the Set3C inhibits the yeast-to-filament transition, but the precise molecular details of this function have remained elusive. Here, we use a combination of ChIP–Seq and RNA–Seq to show that the Set3C acts as a transcriptional co-factor of metabolic and morphogenesis-related genes in <em>C. albicans</em>. Binding of the Set3C correlates with gene expression during fungal morphogenesis; yet, surprisingly, deletion of <em>SET3</em> leaves the steady-state expression level of most genes unchanged, both during exponential yeast-phase growth and during the yeast-filament transition. Fine temporal resolution of transcription in cells undergoing this transition revealed that the Set3C modulates transient expression changes of key morphogenesis-related genes. These include a transcription factor cluster comprising of <em>NRG1</em>, <em>EFG1</em>, <em>BRG1</em>, and <em>TEC1</em>, which form a regulatory circuit controlling hyphal differentiation. Set3C appears to restrict the factors by modulating their transcription kinetics, and the hyperfilamentous phenotype of <em>SET3</em>-deficient cells can be reverted by mutating the circuit factors. These results indicate that the chromatin status at coding regions represents a dynamic platform influencing transcription kinetics. Moreover, we suggest that transcription at the coding sequence can be transiently decoupled from potentially conflicting promoter information in dynamic environments.</p> </div

Genome-wide analysis in the mouse embryo reveals the importance of DNA methylation for transcription integrity

DNA methyltrasferases play important role during mouse embryo development. Here the authors reveal the consequences of genetic inactivation of Dnmt1, Dnmt3a and Dnmt3b on the methylome and transcriptome of mouse embryos genome-wide

The <i>C. albicans</i> Set3C is a coding sequence histone deacetylase.

<p>(A) Architecture of the <i>S. cerevisiae</i> Set3C. The subunits among which physical interaction was confirmed in <i>C. albicans</i> are colored green (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003118#pgen.1003118.s001" target="_blank">Figure S1B</a>). (B) Physical interaction of Set3 and Hos2. Set3-3HA was immunoprecipitated from whole cell extracts and the interaction was probed by immunoblot detection of a Hos2-9myc allele. (C) Read density profiles of one replicate of a Set3-9myc and an untagged control ChIP-Seq experiment. Genes were divided into binding targets (“targets”) and non-targets (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003118#s4" target="_blank">Materials and Methods</a>). Transcription start site (TSS) denotes the start codon and Transcription termination site (TTS) denotes the stop codon. The read density values between the TSS and TTS were calculated to a percentage scale, and 500 bases upstream of the TSS and downstream of the TTS were included. On the bottom panel only genes with a coding region longer than 1 kilobase were included. (D) Definition of CaSet3C refined target gene set. Each dot corresponds to one ORF. Binding targets of RNAPII transcribed genes are defined as having an at least 2-fold enrichment on one axis and an at least 1.5-fold on the other axis (blue box). Target tRNA loci are defined as having an at least 1.5-fold enrichment on both axes. The complete dataset is found in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003118#pgen.1003118.s011" target="_blank">Tables S4</a> and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003118#pgen.1003118.s012" target="_blank">S5</a>. “<i>r</i>” denotes a Pearson's correlation coefficient. (E) The Set3C functions as histone deacetylase <i>in vivo</i>. Top panel: validation of Set3 and Hos2 binding using the indicated probes around the <i>PFK1</i> and <i>tR(CCG)1</i> loci by qPCR. Values are normalized to a fragment of the <i>ADE2</i> locus. Bottom panel: ChIP experiments were performed with antibodies against acetylated histone H4 and the C-terminus of histone H3. The qPCR values at the probe positions were normalized to a fragment of the telomere of Chromosome 7. The ratio of the signal of the acetylated H4 ChIP and H3 ChIP is shown on the y-axis. Data are shown as mean+SD of three independent experiments. Statistical significance was determined by two-tailed t-test relative to the control values. *P<0.05, **P<0.01, ***P<0.001.</p

Set3C recruitment predicts induction and depletion predicts repression.

<p>(A) Microscopic images of cells undergoing yeast-to-hypha differentiation. The cells at each time point do not correspond to the cells at the other time points. Scale bar corresponds to 5 µm. (B) Transcript landscape of hyphal cells 30 minutes after induction. The fold change in RNA expression between hyphal and yeast cultures at each gene is plotted against the expression level of the gene in wild type yeast cells measured by RNA-Seq. Each dot represents one gene. Set3C binding targets were defined by Set3C ChIP-Seq experiments (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003118#s4" target="_blank">Materials and Methods</a>). The Set3C target genes are divided into yeast-specific, hypha-specific and constitutively bound subgroups. The distribution of RNA fold changes of the genes belonging to each category is shown on the right panel. Statistical significance was determined by the Mann-Whitney U-test relative to the “all targets” set. *P<0.05, **P<0.01, ***P<0.001, ns: not significant. (C) Correlation of RNA fold change and differential ChIP enrichment signals. Each dot corresponds to one gene, and only the genes defined as Set3C binding targets in at least one phase are shown. “<i>r</i>” denotes a Pearson's correlation coefficient. (D) qPCR verification of the correlation on (C). Histone H4 has two loci in <i>C. albicans</i> (<i>HHF1</i> and <i>HHF22</i>), and the primers used in the qPCR bind alleles of both. Data are shown as mean+SD of three independent experiments. Statistical significance was determined by two-tailed t-test. *P<0.05, **P<0.01, ***P<0.001. (E) Comparison of the gene induction profiles of wild type and <i>set3</i>Δ/Δ cells undergoing hyphal differentiation. Fold change between the hyphal and yeast phases for the two genotypes are plotted on the two axes. Each dot corresponds to one gene. The categories of Set3C binding targets are defined as on (B). “<i>r</i>” denotes a Pearson's correlation coefficient, and “m” denotes the slope of the linear regression.</p