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Macro histone variants preserve cell identity by preventing the gain of H3K4me2 during reprogramming

ABSTRACT: Transcription factor-induced reprogramming of somatic cells to pluripotency is a very inefficient process, probably due to the existence of important epigenetic barriers that are imposed during differentiation and that contribute to preserve cell identity. In an effort to decipher the molecular nature of these barriers, we followed a genome-wide approach, in which we identified macro histone variants (macroH2A) as highly expressed in human somatic cells but downregulated after reprogramming to pluripotency, as well as strongly induced during differentiation. Knock down of macro histone variants in human keratinocytes increased the efficiency of reprogramming to pluripotency, while overexpression had opposite effects. Genome-wide occupancy profiles show that in human keratinocytes macroH2A.1 preferentially occupies genes that are expressed at low levels and are marked with H3K27me3, including pluripotency-related genes and bivalent developmental regulators, at which its presence prevents the regain of H3K4me2 during reprogramming, over imposing an additional layer of repression that preserves cell identity.

ORGANISM(S): Homo sapiens

PROVIDER: GSE44400 | GEO | 2013/04/03

SECONDARY ACCESSION(S): PRJNA189769

REPOSITORIES: GEO

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Macro histone variants preserve cell identity by preventing the gain of H3K4me2 during reprogramming

Project description:Transcription factor-induced reprogramming of somatic cells to pluripotency is a very inefficient process, probably due to the existence of important epigenetic barriers that are imposed during differentiation and that contribute to preserve cell identity. In an effort to decipher the molecular nature of these barriers, we followed a genome-wide approach, in which we identified macro histone variants (macroH2A) as highly expressed in human somatic cells but downregulated after reprogramming to pluripotency, as well as strongly induced during differentiation. Knock down of macro histone variants in human keratinocytes increased the efficiency of reprogramming to pluripotency, while overexpression had opposite effects. Genome-wide occupancy profiles show that in human keratinocytes macroH2A.1 preferentially occupies genes that are expressed at low levels and are marked with H3K27me3, including pluripotency-related genes and bivalent developmental regulators, at which its presence prevents the regain of H3K4me2 during reprogramming, over imposing an additional layer of repression that preserves cell identity. Gemone wide occupancy of HA:macroH2A.1 in human keratinocytes

2013-04-03 | E-GEOD-44400 | biostudies-arrayexpress

Transcriptional profiling of mouse inner cell mass of the blastocyst, primordial germ cells and cultured pluripotent stem cells

Project description:Pluripotent stem cells are derived from culture of early embryos or the germline, and can be induced by reprogramming of somatic cells. Barriers to reprogramming are expected to exist that stabilize the differentiated state and have tumor suppression functions. However, we have a limited understanding of what such barriers might be. To find novel barriers to reprogramming to pluripotency, we compared the transcriptional profiles of the mouse germline to pluripotent and somatic cells, in vivo and in vitro. There is a remarkable global expression of the transcriptional program for pluripotency in Primordial Germ Cells (PGCs). We identify parallels between PGCs reprogramming to pluripotency and human germ cell tumorigenesis, including the loss of LATS2, a tumor suppressor kinase of the Hippo pathway. We show that knockdown of LATS2 increases the efficiency of induction of pluripotency in human cells. LATS2 RNAi, unlike p53 RNAi, specifically enhances the generation of fully reprogrammed iPS cells without accelerating cell proliferation. We further show that LATS2 represses reprogramming in human cells by post-transcriptionally antagonizing TAZ but not YAP, two downstream effectors of the Hippo pathway. These results reveal transcriptional parallels between germ cell transformation and the generation of iPS cells, and indicate that the Hippo pathway constitutes a barrier to cellular reprogramming. Mouse pluripotent cells isolated directly from embryos or cultured in vitro as stem cells were analyzed using Affymetrix expression microarrays, together with several non-pluripotent cell controls, in 2-6 replicates per sample.

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MacroH2A histone variants maintain nuclear organization and heterochromatin architecture

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.

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BRD9-containing non-canonical BAF chromatin remodeling complex acts as a barrier to somatic cell reprogramming (ATAC-Seq)

Project description:Epigenetic reprogramming requires extensive remodeling of chromatin landscapes to silence gene expression programs which sustain cell identity. ATP-dependent chromatin-remodeling complexes are important regulators of chromatin structure and gene expression; however, the role of Bromodomain containing protein 9 (BRD9) and the associated ncBAF (non-canonical BRG1-associated factors) complex in somatic cell reprogramming remains unknown. Here, we show that inhibition and acute degradation of BRD9 increases the efficiency by which induced pluripotent stem cells (iPSCs) can be generated from human fibroblasts. Genetic suppression of BRD9 as well as ncBAF complex subunit GLTSCR1, but not the closely related BRD7, phenocopied this effect. CRISRP/Cas9-mediated knockout of BRD9 demonstrated that it is dispensable for establishment and maintenance of human pluripotency. Mechanistically, BRD9 inhibition facilitates reprogramming by downregulating somatic cell type-specific genes and decreasing chromatin accessibility at somatic enhancers. Collectively, these results establish BRD9 as an important safeguarding factor for somatic cell identity whose inhibition lowers barriers to reprogramming.

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BRD9-containing non-canonical BAF chromatin remodeling complex acts as a barrier to somatic cell reprogramming (RNA-Seq)

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macroH2A histone variants act as a barrier upon reprogramming towards pluripotency

Project description:Here we report that the histone variant macroH2A acts as a barrier to induced pluripotency. Using fibroblasts isolated from macroH2A double knockout mice, we observed enhanced reprogramming efficiency compared to fibroblasts from wild type animals. We further show that macroH2A isoforms act synergistically in this process. Genomic analysis in wild type fibroblasts reveals that macroH2A1 and H3K27me3 domains co-localize and occupy pluripotency genes. While the absence of macroH2A does not affect H3K27me3 in fibroblasts, macroH2A1 is highly enriched at a set of Utx target genes that are reactivated early during iPS reprogramming.

2013-03-01 | GSE40813 | GEO

Mus musculus

Project description:macroH2A histone variants act as a barrier upon reprogramming towards pluripotency

| PRJNA175035 | ENA

macroH2A histone variants act as a barrier upon reprogramming towards pluripotency

2013-03-01 | E-GEOD-40813 | biostudies-arrayexpress

Transcriptional profiling of mouse inner cell mass of the blastocyst, primordial germ cells and cultured pluripotent stem cells

2012-01-31 | GSE35416 | GEO

The histone chaperone ANP32B regulates chromatin incorporation of the atypical human histone variant macroH2A

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.

2023-11-07 | GSE241387 | GEO

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