Project description:The integrated activity of cis-regulatory elements fine-tunes transcriptional programs of mammalian cells by recruiting cell type–specific as well as ubiquitous transcription factors (TFs). Despite their key role in modulating transcription, enhancers are still poorly characterized at the molecular level, and their limited DNA sequence conservation in evolution and variable distance from target genes make their unbiased identification challenging. The coexistence of high mono-methylation and low tri-methylation levels of lysine 4 of histone H3 is considered a signature of enhancers, but a comprehensive view of histone modifications associated to enhancers is still lacking. By combining chromatin immunoprecipitation (ChIP) with mass spectrometry, we investigated cis-regulatory regions in macrophages to comprehensively identify histone marks specifically associated with enhancers, and to profile their dynamics after transcriptional activation elicited by an inflammatory stimulation. The intersection of the proteomics data with ChIP-seq and RNA-seq analyses revealed the existence of novel subpopulations of enhancers, marked by specific histone modification signatures: specifically, H3K36me2/K4me1 marks transcribed enhancers, while H3K36me3/K4me1 and H3K79me2/K4me1 combinations mark distinct classes of intronic enhancers. Thus, our MS analysis of functionally distinct genomic regions revealed the combinatorial code of histone modifications, highlighting the potential of proteomics in addressing fundamental questions in epigenetics.
Project description:The activity of enhancers and promoters fine-tunes the transcriptional program of mammalian cells through the recruitment and interplay between cell type-specific and ubiquitous transcription factors. Despite their key role in modulating transcription, the identification of enhancers is challenged by their limited sequence conservation and highly variable distance from target genes. Although enhancers are characterised by the strong enrichment of mono-methylation at lysine 4 of histone H3, mirrored by low tri-methylation at the same residue, a comprehensive list of enhancers-associated histone post-translational modifications (PTMs) is still lacking. We undertook a proteomics investigation, based on chromatin immunoprecipitation combined with mass spectrometry (MS), to identify histone marks specifically associated to cis-regulatory elements in macrophages, focusing on enhancers. We also profiled their plasticity during the transcriptional activation induced by an inflammatory stimulus. The proteomic analysis suggested novel PTM associations, which were validated by analysis of ChIP- and RNA-seq data, whose intersection revealed the existence of novel sub-populations of enhancers marked by specific signatures: the dual mark H3K4me1/K36me2 labels transcription at enhancers, whereas H3K4me1/K36me3 and H3K4me1/K79me2 tag distinct intronic enhancers. While demonstrating that analyzing restricted genomic regions can disclose the combinatorial language of histone modifications, this study highlights the potential of MS-based proteomics in addressing fundamental questions in epigenetics.
Project description:The activity of enhancers and promoters fine-tunes the transcriptional program of mammalian cells through the recruitment and interplay between cell type-specific and ubiquitous transcription factors. Despite their key role in modulating transcription, the identification of enhancers is challenged by their limited sequence conservation and highly variable distance from target genes. Although enhancers are characterised by the strong enrichment of mono-methylation at lysine 4 of histone H3, mirrored by low tri-methylation at the same residue, a comprehensive list of enhancers-associated histone post-translational modifications (PTMs) is still lacking. We undertook a proteomics investigation, based on chromatin immunoprecipitation combined with mass spectrometry (MS), to identify histone marks specifically associated to cis-regulatory elements in macrophages, focusing on enhancers. We also profiled their plasticity during the transcriptional activation induced by an inflammatory stimulus. The proteomic analysis suggested novel PTM associations, which were validated by analysis of ChIP- and RNA-seq data, whose intersection revealed the existence of novel sub-populations of enhancers marked by specific signatures: the dual mark H3K4me1/K36me2 labels transcription at enhancers, whereas H3K4me1/K36me3 and H3K4me1/K79me2 tag distinct intronic enhancers. While demonstrating that analyzing restricted genomic regions can disclose the combinatorial language of histone modifications, this study highlights the potential of MS-based proteomics in addressing fundamental questions in epigenetics.
Project description:Covalent histone modifications are highly conserved and play multiple roles in eukaryotic transcription regulation. Because of extensive crosstalk between transcriptional processes and histone modifications, steady state observations are insufficient to fully disentangle histone modification networks. As transient perturbation of feedback mechanisms can reveal network structure, we mapped 26 histone modifications genome-wide over a time course following dramatic transcriptional reprogramming – response to diamide stress in yeast. Interestingly, while we observed limited combinatorial complexity in steady-state histone modification patterns, consistent with previous studies, the combinatorial complexity of histone modification space increased modestly during the stress response, resulting from roughly 3% of nucleosomes transiently populating rare histone modification states. We show that most of these short-lived histone mark combinations result from differences in histone modification dynamics that transiently uncouple highly correlated marks, with slow histone methylation changes often lagging the more rapid changes in acetylation. Together, our results provide the first detailed view of an epigenome in transition.
Project description:Macrophage activation is associated with profound transcriptional reprogramming. Although much progress has been made in the understanding of macrophage activation, polarization and function, the transcriptional programs regulating these processes remain poorly characterized. We stimulated human macrophages with diverse activation signals, acquiring a dataset of 299 macrophage transcriptomes. Analysis of this dataset revealed a spectrum of macrophage activation states extending the current M1 versus M2-polarization model. Network analyses identified central transcriptional regulators associated with all macrophage activation complemented by regulators related to stimulus-specific programs. Applying these transcriptional programs to human alveolar macrophages from smokers and patients with chronic obstructive pulmonary disease (COPD) revealed an unexpected loss of inflammatory signatures in COPD patients. Finally, by integrating murine data from the ImmGen project we propose a refined, activation-independent core signature for human and murine macrophages. This resource serves as a framework for future research into regulation of macrophage activation in health and disease. To better understand active gene regulation in human macrophages during activation and differentiation in vitro with different stimuli ChIP-sequencing experiments were performed. Enrichment patterns of the permissive histone modification mark trimetylation of histone protein 3 (H3K4me3) and macrophage lineage-specific transcription factor PU.1 were analyzed.
Project description:Epigenetic regulation of gene expression is tightly controlled by the dynamic modification of histones by chemical groups, the diversity of which has largely expanded over the past decade with the discovery of lysine acylations, catalyzed from acyl-coenzymes A. Here, we investigated the dynamics of lysine acetylation and crotonylation on histones H3 and H4 during mouse spermatogenesis. Lysine crotonylation appeared to be of significant abundance compared to acetylation, particularly on Lys27 of histone H3 (H3K27cr) that accumulates in sperm in a cleaved form of H3. We identified the genomic localization of H3K27cr and studied its effects on transcription compared to the classical active mark H3K27ac at promoters and distal enhancers. The presence of both marks was strongly associated with highest gene expression. Assessment of their co-localization with transcription regulators (SLY, SOX30) and chromatin-binding proteins (BRD4, BORIS and CTCF) indicated systematic highest binding when both active marks were present and different selective binding when present alone at chromatin. H3K27cr and H3K27ac finally mark the building of some sperm super-enhancers. This integrated analysis of omics data provides an unprecedented level of understanding of gene expression regulation by H3K27cr in comparison to H3K27ac, and reveals both synergistic and specific actions of each histone modification.
Project description:Through integration of GATA4 genome-wide occupancy and RNA-seq dataset in embryonic conditional knockout heart, we identified a class of the master cardiac regulator GATA4 bound enhancers. With combinatorial assembly of chromatin signatures, we further refined that a unique type of fetal distal GATA4 enhancers enriched for H3K27ac, H3K4me1, but not for H3K4me3 and RNA polymerase II, are reinstated in adult hypertrophic heart. Study Gata4 and histone modifications in E12.5, Adult, Banding and Sham, and to correlate to gene expression and heart function
Project description:Histone modifications play an important role in chromatin organization and transcriptional regulation. Specific combinations of these modifications to the histone tails have been associated with different functional genomic elements: for example, promoters, enhancers and insulators. Despite the enormous amount of genome-wide histone modification data collected in different cells and tissues, little is known about co-occurrence of modifications on the same nucleosome. Here we present a novel, genome-wide quantitative method for combinatorial indexed chromatin immunoprecipitation (Co-ChIP) to characterize the co-occurrence of histone modifications. Using Co-ChIP, we characterize the genome-wide co-occurrence of 15 chromatin marks (70 pairwise combinations), and find unexpected dynamics between the different marks, including co-occurrence of H3K9me1-H3K27ac in super-enhancers. Finally, we apply Co-ChIP to characterize the distribution of the bivalent H3K4me3-H3K27me3 domain in distinct mouse embryonic stem cell (mESC) states as well as in four adult tissues. We observe dynamic changes in 5786 regions and discover both loss and de novo gain of bivalency in key tissue-specific regulatory genes, suggesting a crucial role for bivalent domains following development. Taken together, we demonstrate that Co-ChIP enables routine single molecule characterization of histone mark co-occurrence and probes the previously hidden dynamic interactions of histone modifications.