Unknown,Transcriptomics,Genomics,Proteomics

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An epigenetic mark of polycomb response elements implemented by Trx/MLL/COMPASS

ABSTRACT: In Drosophila, Polycomb Response Elements (PREs) are identified as genomic sequences allowing the maintenance of transcriptional repression in the absence of the initiating signal. Although PREs in Drosophila are well characterized, the existence of mammalian PRE-like elements remains debated. Accumulating evidence supports a model in which CpG islands function to recruit Polycomb-Group complexes (PcG), however, it is not evident which subclasses of CpG islands serve as PREs. Trithorax (Trx), which is required for positive regulation of gene expression in Drosophila, is known to co-bind Drosophila PREs where it is thought to antagonize polycomb-dependent silencing of nearby genes. Here, we demonstrate the existence of Trx-dependent H3K4 dimethylation loci that specifically mark Drosophila PREs and are required for the maintenance of expression of the nearby genes. Similarly, in human cells, we find ~ 3000 MLL1 (human Trx homologue)-dependent H3K4 dimethylation loci, which correlate strongly with CpG island density. In the absence of MLL1 and H3K4 dimethylation at these loci, there is an increase in H3K27 trimethylation levels, suggesting these sites can recruit Polycomb Repressive Complex 2 (PRC2). By inhibiting PRC2-dependent silencing in the absence of MLL1, we establish that a balance exists between MLL1 and PRC2, and their respective capacity to maintain or repress transcription. Thus, by investigating a conserved function between Trx and MLL1, we provide rules for the identification of CpG island subclasses serving as PRE-like sequences within the human genome. To examine changes in histone-modification profiles and gene expression after depletion of Trx in Drosophila S2 cells, and MLL1 in human HCT116 cells. We also treated MLL1-NULL HCT116 cells with GSK126 (5uM) for 4 days and measured changes in gene expression.

ORGANISM(S): Homo sapiens

SUBMITTER: Ali Shilatifard

PROVIDER: E-GEOD-81795 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

An Evolutionary Conserved Epigenetic Mark of Polycomb Response Elements Implemented by Trx/MLL/COMPASS.

Rickels Ryan R Hu Deqing D Collings Clayton K CK Woodfin Ashley R AR Piunti Andrea A Mohan Man M Herz Hans-Martin HM Kvon Evgeny E Shilatifard Ali A

Molecular cell 20160701 2

Polycomb response elements (PREs) are specific DNA sequences that stably maintain the developmental pattern of gene expression. Drosophila PREs are well characterized, whereas the existence of PREs in mammals remains debated. Accumulating evidence supports a model in which CpG islands recruit Polycomb group (PcG) complexes; however, which subset of CGIs is selected to serve as PREs is unclear. Trithorax (Trx) positively regulates gene expression in Drosophila and co-occupies PREs to antagonize P ...[more]

PMID: 27447986

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Project description:Genomic enhancers regulate spatio-temporal gene expression by recruiting specific combinations of transcription factors (TFs). When TFs are bound to active regulatory regions, they displace canonical nucleosomes, making these regions biochemically detectable as nucleosome-depleted regions or accessible/open chromatin. Here we ask whether open chromatin profiling can be used to identify the entire repertoire of active promoters and enhancers underlying tissue-specific gene expression during normal development and oncogenesis in vivo. To this end, we first compare two different approaches to detect open chromatin in vivo using the Drosophila eye primordium as a model system: FAIRE-seq, based on physical separation of open versus closed chromatin; and ATAC-seq, based on preferential integration of a transposon into open chromatin. We find that both methods reproducibly capture the tissue-specific chromatin activity of regulatory regions, including promoters, enhancers, and insulators. Using both techniques, we screened for regulatory regions that become ectopically active during Ras-dependent oncogenesis, and identified 3778 regions that become (over-)activated during tumor development. Next, we applied motif discovery to search for candidate transcription factors that could bind these regions and identified AP-1 and Stat92E as key regulators. We validated the importance of Stat92E in the development of the tumors by introducing a loss of function Stat92E mutant, which was sufficient to rescue the tumor phenotype. Additionally we tested if the predicted Stat92E responsive regulatory regions are genuine, using ectopic induction of JAK/STAT signaling in developing eye discs, and observed that similar chromatin changes indeed occurred. Finally, we determine that these are functionally significant regulatory changes, as nearby target genes are up- or down-regulated. In conclusion, we show that FAIRE-seq and ATAC-seq based open chromatin profiling, combined with motif discovery, is a straightforward approach to identify functional genomic regulatory regions, master regulators, and gene regulatory networks controlling complex in vivo processes. FAIRE-Seq in Drosophila wild type eye-antennal imaginal discs (2 wt strains); ATAC-Seq in Drosophila wild type eye-antennal imaginal discs (3 wt strains) ; FAIRE-Seq in Drosophila Ras/Scrib induced eye disc tumors (1 early and 1 late); ATAC-Seq in Drosophila Ras/Scrib induced eye disc tumors (1 early and 1 late); ATAC-Seq in Drosophila eye discs with Unpaired over-expression (2 biological replicates); CTCF ChIP-seq in Drosophila eye discs; ChIP-seq input in Drosophila eye discs

Dataset Information

An epigenetic mark of polycomb response elements implemented by Trx/MLL/COMPASS

Publications

An Evolutionary Conserved Epigenetic Mark of Polycomb Response Elements Implemented by Trx/MLL/COMPASS.

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