Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Cell reprogramming requires silencing of a core subset of Polycomb targets.

ABSTRACT: Transcription factor (TF)-induced reprogramming of somatic cells into induced pluripotent stem cells (iPSC) is associated with genome-wide changes in chromatin modifications. Polycomb-mediated histone H3 lysine-27 trimethylation (H3K27me3) has been proposed as a defining mark that distinguishes the somatic from the iPSC epigenome. Here, we dissected the functional role of H3K27me3 in TF-induced reprogramming through the inactivation of the H3K27 methylase EZH2 at the onset of reprogramming. Our results demonstrate that surprisingly the establishment of functional iPSC proceeds despite global loss of H3K27me3. iPSC lacking EZH2 efficiently silenced the somatic transcriptome and differentiated into tissues derived from the three germ layers. Remarkably, the genome-wide analysis of H3K27me3 in Ezh2 mutant iPSC cells revealed the retention of this mark on a highly selected group of Polycomb targets enriched for developmental regulators controlling the expression of lineage specific genes. Erasure of H3K27me3 from these targets led to a striking impairment in TF-induced reprogramming. These results indicate that PRC2-mediated H3K27 trimethylation is required on a highly selective core of Polycomb targets whose repression enables TF-dependent cell reprogramming. Genechip microarray analysis was performed respectively on 4 Ezh2 +/+ iPSC clones (control), 4 Ezh2 M-bM-^HM-^FSET/M-bM-^HM-^FSET iPSC clones (experimental), 3 independent preparations of wild type MEF (reference) and one sample of E14Tg2a embryonic stem cells (reference) using Affymetrix Mouse Gene 1.0 ST arrays. Labeling, hybridization, and washing were performed according to Affymetrix guidelines

ORGANISM(S): Mus musculus

SUBMITTER: Pasquale Laise

PROVIDER: E-GEOD-44972 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Down syndrome (DS) is the most frequent cause of human congenital mental retardation. Cognitive deficits in DS result from perturbations of normal cellular processes both during development and in adult tissues, but the mechanisms underlying DS etiology remain poorly understood. To assess the ability of iPSCs to model DS phenotypes, as a prototypical complex human disease, we generated bona-fide DS and wild-type (WT) non-viral iPSCs by episomal reprogramming. DS iPSCs selectively overexpressed chromosome 21 genes, consistent with gene dosage, which was associated with deregulation of thousands of genes throughout the genome. DS and WT iPSCs were neurally converted at >95% efficiency, and had remarkably similar lineage potency, differentiation kinetics, proliferation and axon extension at early time points. However, at later time points DS cultures showed a two-fold bias towards glial lineages. Moreover, DS neural cultures were up to two times more sensitive to oxidative stress induced apoptosis, and this could be prevented by the anti-oxidant N-acetylcysteine. Our results reveal a striking complexity in the genetic alterations caused by trisomy-21 that are likely to underlie DS developmental phenotypes, and indicate a central role for defective early glial development in establishing developmental defects in DS brains. Furthermore, oxidative stress sensitivity is likely to contribute to the accelerated neurodegeneration seen in DS, and we provide proof of concept for screening corrective therapeutics using DS iPSCs and their derivatives. Non-viral DS iPSCs can therefore recapitulate features of complex human disease in vitro, and provide a renewable and ethically unencumbered discovery platform. Control (WT) and Down Syndrome iPSC lines were generated via episomal reprogramming of human donor fibroblasts. Two iPSC clones conforming to iPS criteria (determined by immunocytochemistry detection of pluripotency markers) were developed from each fibroblast donor. Two control (WT) and DS lines each were further characterized and underwent neural differentiation. Multiple biological replicates of donor fibroblast and iPSC from both control (WT) and DS lines, including 3 euploid DS samples and 3 MEL1 hESC controls (total 54 samples) were hybridized to Illumina HT-12 v4 microarray for gene expression analysis.

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Cell reprogramming requires silencing of a core subset of Polycomb targets.

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