Project description:Genetic loss-of-function studies in development, cancer and somatic cell reprogramming have suggested that the group of macroH2A histone variants might function through stabilizing the differentiated state by a yet unknown mechanism. Here, we present results demonstrating that macroH2A variants have a major function in maintaining nuclear organization and heterochromatin architecture. Specifically, we find that a substantial amount of macroH2A is associated with heterochromatic repeat sequences. We further identify macroH2A on sites of interstitial heterochromatin decorated by H3K9me3. Loss of macroH2A leads to major defects in nuclear organization including reduced nuclear circularity, disruption of nucleoli and a global loss of dense heterochromatin. Domains formed by repeat sequences when depleted of macroH2A are disorganized, expanded and fragmented and mildly re-expressed. On the molecular level we find that macroH2A is required for the interaction of repeat sequences with the nucleostructural protein Lamin B1. Taken together our results argue that a major function of macroH2A histone variants is to link nucleosome composition to higher order chromatin architecture.
Project description:MacroH2A histone variants have a major role in nuclear organization and large-scale 3D chromatin architecture. How these alterations impinge on the behaviour of cancer cells is not known. Here, we describe the analysis of the total macroH2A loss of function phenotype in a model of hepatoblastoma, the main childhood liver cancer. Performing transcriptomic analyses in xenografts and cell cultures, we find that macroH2A modulated the response of cancer cells to paracrine inflammatory signalling. Specifically, ablation of macroH2A ablation neutralized the induction of a large subset of genes by TNFα and led to the hyperactivation of another subset of genes. Among the top macroH2A-sensitive genes we find the cancer-related gene DKK1 . Depletion of macroH2A rendered the DKK1 gene hypersensitive to TNFα signalling boosting the secretion of DKK1 protein. On the gene regulation level, this was mediated by an alteration of the local chromatin structure and facilitated activation of distal enhancer elements. The study of human samples of hepatoblastoma showed that DKK1 is strongly upregulated in tumors and associated with poor patient outcome. Taken together our results suggest that the regulation of 3D chromatin architecture by macroH2A histone variants has a central role in the response and regulation of paracrine signalling that might be relevant for the interaction of cancers with immune cells and other cells in their microenvironment.
Project description:MacroH2A histone variants have a major role in nuclear organization and large-scale 3D chromatin architecture. How these alterations impinge on the behaviour of cancer cells is not known. Here, we describe the analysis of the total macroH2A loss of function phenotype in a model of hepatoblastoma, the main childhood liver cancer. Performing transcriptomic analyses in xenografts and cell cultures, we find that macroH2A modulated the response of cancer cells to paracrine inflammatory signalling. Specifically, ablation of macroH2A ablation neutralized the induction of a large subset of genes by TNFα and led to the hyperactivation of another subset of genes. Among the top macroH2A-sensitive genes we find the cancer-related gene DKK1 . Depletion of macroH2A rendered the DKK1 gene hypersensitive to TNFα signalling boosting the secretion of DKK1 protein. On the gene regulation level, this was mediated by an alteration of the local chromatin structure and facilitated activation of distal enhancer elements. The study of human samples of hepatoblastoma showed that DKK1 is strongly upregulated in tumors and associated with poor patient outcome. Taken together our results suggest that the regulation of 3D chromatin architecture by macroH2A histone variants has a central role in the response and regulation of paracrine signalling that might be relevant for the interaction of cancers with immune cells and other cells in their microenvironment.
Project description:MacroH2A histone variants have a major role in nuclear organization and large-scale 3D chromatin architecture. How these alterations impinge on the behaviour of cancer cells is not known. Here, we describe the analysis of the total macroH2A loss of function phenotype in a model of hepatoblastoma, the main childhood liver cancer. Performing transcriptomic analyses in xenografts and cell cultures, we find that macroH2A modulated the response of cancer cells to paracrine inflammatory signalling. Specifically, ablation of macroH2A ablation neutralized the induction of a large subset of genes by TNFα and led to the hyperactivation of another subset of genes. Among the top macroH2A-sensitive genes we find the cancer-related gene DKK1 . Depletion of macroH2A rendered the DKK1 gene hypersensitive to TNFα signalling boosting the secretion of DKK1 protein. On the gene regulation level, this was mediated by an alteration of the local chromatin structure and facilitated activation of distal enhancer elements. The study of human samples of hepatoblastoma showed that DKK1 is strongly upregulated in tumors and associated with poor patient outcome. Taken together our results suggest that the regulation of 3D chromatin architecture by macroH2A histone variants has a central role in the response and regulation of paracrine signalling that might be relevant for the interaction of cancers with immune cells and other cells in their microenvironment.
Project description:Eukaryotic chromatin structure is highly conserved, with the canonical histone proteins revealing only small sequence changes across species. Yet, all vertebrates exhibit three much larger histone H2A variants, macroH2A. A distinctive feature of these atypical histones is the globular macrodomain module, which can bind metabolites and is connected to the histone fold through a flexible linker. MacroH2A variants impact heterochromatin organization, transcription regulation and establish a barrier for cellular reprogramming. However, the mechanisms of how these large H2A variants are incorporated into chromatin and the identity of any chaperones required for histone deposition have remained elusive. Here, we developed a split-GFP-based cellular readout for histone incorporation and conducted a genome-wide mutagenesis screen in haploid human cells to identify proteins that regulate macroH2A dynamics. We identified and validated the histone chaperone ANP32B as a regulator of macroH2A chromatin deposition. ANP32B associates with macroH2A in cells and in vitro binds to histones with low nanomolar affinity. In vitro nucleosome assembly assays show that ANP32B stimulates deposition of macroH2A-H2B and not of H2A-H2B onto tetraso me. In cells, depletion of ANP32B in cells strongly affects global macroH2A deposition, revealing ANP32B as a macroH2A chaperone. Our study highlights the power of haploid cell functional genomics coupled with cellular imaging to identify factors that are required for chromatin plasticity and diversity.
Project description:Histone variants play crucial roles in gene expression, genome integrity and chromosome segregation. However, to what extent histone variants control chromatin architecture remains largely unknown. Here, we show that the previously uncharacterized histone variant H2A.W plays a crucial role in condensation of heterochromatin. Genome-wide profiling of all four types of H2A variants in Arabidopsis shows that H2A.W specifically associates with heterochromatin. H2A.W recruitment is independent of heterochromatic marks H3K9me2 and DNA methylation. Genetic interactions show that H2A.W acts in synergy with CMT3 mediated methylation to maintain genome integrity. In vitro, H2A.W enhances chromatin condensation through a higher propensity to make fiber-to-fiber interactions via its conserved C-terminal motif. In vivo, elimination of H2A.W causes decondensation of heterochromatin and conversely, ectopic expression of H2A.W promotes heterochromatin condensation. These results demonstrate that H2A.W plays critical roles in heterochromatin by promoting higher order chromatin condensation. Since similar H2A.W C-terminal motifs are present in other variant found in mammals and other organisms our findings impact our understanding of heterochromatin condensation in a wide variety of eukaryotic organisms. Two mRNA-seq samples, two bisulfite-seq samples, six ChIP-seq samples.
Project description:Histone variants play crucial roles in gene expression, genome integrity and chromosome segregation. However, to what extent histone variants control chromatin architecture remains largely unknown. Here, we show that the previously uncharacterized histone variant H2A.W plays a crucial role in condensation of heterochromatin. Genome-wide profiling of all four types of H2A variants in Arabidopsis shows that H2A.W specifically associates with heterochromatin. H2A.W recruitment is independent of heterochromatic marks H3K9me2 and DNA methylation. Genetic interactions show that H2A.W acts in synergy with CMT3 mediated methylation to maintain genome integrity. In vitro, H2A.W enhances chromatin condensation through a higher propensity to make fiber-to-fiber interactions via its conserved C-terminal motif. In vivo, elimination of H2A.W causes decondensation of heterochromatin and conversely, ectopic expression of H2A.W promotes heterochromatin condensation. These results demonstrate that H2A.W plays critical roles in heterochromatin by promoting higher order chromatin condensation. Since similar H2A.W C-terminal motifs are present in other variant found in mammals and other organisms our findings impact our understanding of heterochromatin condensation in a wide variety of eukaryotic organisms.
Project description:MacroH2As core histone variants have a unique structure that includes C-terminal nonhistone domain. MacroH2As are highly conserved in vertebrates, and are thought to regulate gene expression. However the nature of genes regulated by macroH2As and the biological significance of macroH2As for the organism remain unclear. Here we examine macroH2A function in vivo by knocking out both macroH2A1 and macroH2A2 in the mouse. We used microarrays to examine how the absence of macroH2A.1 and macroH2A.2 histone variants affect gene expression fasted adult mouse liver.
Project description:MacroH2As core histone variants have a unique structure that includes C-terminal nonhistone domain. MacroH2As are highly conserved in vertebrates, and are thought to regulate gene expression. However the nature of genes regulated by macroH2As and the biological significance of macroH2As for the organism remain unclear. Here we examine macroH2A function in vivo by knocking out both macroH2A1 and macroH2A2 in the mouse. We used microarrays to examine how the absence of macroH2A.1 and macroH2A.2 histone variants affect gene expression late fetal mouse liver.
Project description:MacroH2As core histone variants have a unique structure that includes C-terminal nonhistone domain. MacroH2As are highly conserved in vertebrates, and are thought to regulate gene expression. However the nature of genes regulated by macroH2As and the biological significance of macroH2As for the organism remain unclear. Here we examine macroH2A function in vivo by knocking out both macroH2A1 and macroH2A2 in the mouse. We used microarrays to examine how the absence of macroH2A.1 and macroH2A.2 histone variants affect gene expression fasted adult mouse liver. Two month old male mice were fasted overnight (~16 hours). Mice were sacrificed between 9:00 and 10:00 AM, livers were collected and snap frozen with liquid nitrogen. Total RNA was extract with Trizol (life technologies) following standard protocol.