Project description:The aim of this experiment was to determine, using MNAse-Seq, how nucleosomes get remodeled during an Msn2 activation timecourse genome-wide. Diploid strain EY2807/ASH79 with genotype TPK1M164G TPK2M147G TPK3M165G msn4::TRP1/LEU2 MSN2-mCherry NHP6a-iRFP::kanMX was used. This strain is PKAas, so upon addition of the inhibitor 1-NM-PP1, Msn2 translocates to the nucleus and activates gene expression. In this experiment, the diploid strain was exposed to 3 uM 1-NM-PP1 for 0, 5, 10, 20 and 40 min and nucleosome positions determined using by crosslinking, MNAse treatment, nucleosomal DNA purification and paired-end high-throughput sequencing (Illumina). Results from transcriptional profiling of yeast with or without Msn2 expression were also deposited at ArrayExpress under accession number E-MTAB-1945 ( https://www.ebi.ac.uk/arrayexpress/experiments/E-MTAB-1945/ ).
Project description:The genomic positions of nucleosomes are a defining feature of the epigenomic state and hence of cell identity. Signal-dependent transcription factors (SDTFs), upon activation, modify the positioning of nucleosomes and cause epigenome remodeling. Here, we developed Markov models of nucleosome wrapping and unwrapping, and fit them to high resolution deep sequencing data of DNA accessibility to reveal biophysical principles of nucleosome dynamics. We found that 1) the dynamics of DNA unwrapping are significantly slower in vivo than reported from in vitro experimental data, 2) there is clear evidence for cooperativity in wrapping and unwrapping, 3) SDTF activity produced highest eviction probability when its binding site is close to but not on top of the nucleosome dyad, and 4) oscillatory SDTFs produce more variability than constant SDTF activities. Our work uncovers the regulatory rules governing nucleosome dynamics in vivo, which can predict epigenomic alterations during inflammation at single nucleosome resolution.
Project description:This SuperSeries is composed of the following subset Series: GSE30897: Nucleosome occupancy in yeast BY4741and a strain lacking MSN2 and MSN4 responding to 20 min treatment with 0.4mM H2O2 GSE30898: Msn2p occupancy dynamics in yeast BY4741 responding to 0.4mM H2O2 over time (0-60 min) GSE30899: Gene expression dynamics in yeast BY4741 and a strain lacking MSN2 and MSN4 responding to 0.4mM H2O2 over time (0-60min) GSE30900: Nucleosome occupancy dynamics in yeast BY4741 responding to 0.4mM H2O2 over time (0-60 min) Refer to individual Series
Project description:Nucleosome positioning can alter the accessibility of DNA-binding proteins to their cognate DNA elements, and thus its precise control is essential for cell identity and function. Mammalian preimplantation embryos undergo temporal changes in gene expression and cell potency, suggesting the involvement of dynamic epigenetic control during this developmental phase. However, the dynamics of nucleosome organization during early development are poorly understood. In this study, using a low-input MNase-seq method, we show that nucleosome positioning is globally obscure in zygotes but becomes well defined during subsequent development. Downregulation of the chromatin assembly in embryonic stem cells can partially reverse nucleosome organization into a zygote-like pattern, suggesting that the chromatin assembly pathway might be linked to fuzzy nucleosomes in zygotes. We also reveal that YY1, a zinc finger containing transcription factor expressed upon zygotic genome activation, regulates the de novo formation of well-positioned nucleosome arrays at the regulatory elements, through identifying YY1-binding sites in 8-cell embryos. The YY1-binding regions acquire H3K27ac enrichment around the 8-cell and morula stages and YY1 depletion impairs the morula-to-blastocyst transition. Thus, our study delineates the remodeling of nucleosome organization and its underlying mechanism during early mouse development.
Project description:RNA-mediated transcriptional silencing prevents deleterious effects of transposon activity and controls the expression of protein-coding genes. It involves long non-coding RNAs (lncRNAs)1, which in Arabidopsis thaliana are produced by a specialized RNA Polymerase V (Pol V)2. lncRNAs guide Argonaute-siRNA complexes to specific genomic loci and mediate the establishment of DNA methylation3,4. The mechanism by which lncRNAs affect chromatin structure and mRNA production remains mostly unknown. Here we identify the SWI/SNF nucleosome remodeling complex as a component of the RNA-mediated transcriptional silencing pathway. We found that SWI3, an essential subunit of the SWI/SNF complex, physically interacts with a lncRNA-binding IDN2 protein5,6. RNA-mediated DNA methylation and transcriptional silencing was compromised in the swi3 mutant. Moreover, targets of SWI/SNF significantly overlapped with genes controlled by Pol V, which shows that the physical interaction reflects a functional relationship. We further found that non-coding transcription by Pol V affects nucleosome positioning on silenced regions. We propose that lncRNAs mediate transcriptional silencing by guiding the SWI/SNF complex and establishing positioned nucleosomes on specific genomic loci. We further propose that guiding ATP-dependent chromatin remodeling complexes may be a more general function of lncRNAs. RNA-seq of 3 samples (Col-0, nrpe1 [a mutant defective in the largest subunit of Pol V and unable to produce lncRNA], swi3b, idn2) with 3 biological replicates.