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Zscan4 mediates transient remodeling and transcriptional burst of heterochromatin in mouse embryonic stem cells

ABSTRACT: This SuperSeries is composed of the SubSeries listed below. Repetitive sequences such as telomeres, centromeres, and retrotransposons are packed in permanently-condensed and transcriptionally-silenced heterochromatin, whose maintenance is critical for the genome stability. We have recently found that mouse ES cells occasionally go through a unique cell state marked by the transient expression of Zscan4, which plays a key role in long-term genome stability. Here we report our unexpected and counterintuitive finding that the Zscan4+ state is accompanied by a Zscan4-mediated rapid activation and repression of heterochromatin: the burst of transcription from heterochromatin coincided with its transient histone hyperacetylation and DNA demethylation, the clustering of pericentromeric heterochromatin in the perinucleolar region, and the accumulation of chromatin remodeling complexes for both activation (HATs, SWI/SNF) and repression (HDACs, LSD1/KDM1A, NuRD) on heterochromatin. Overall, these findings suggest that ES cells maintain their extraordinary genome stability and immortality by transiently taking extreme measures – a usually forbidden transition to the activated state of heterochromatin.

ORGANISM(S): Mus musculus

PROVIDER: GSE51682 | GEO | 2015/09/10

SECONDARY ACCESSION(S): PRJNA224553

REPOSITORIES: GEO

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Project description:The gold standard for examining pluripotency of stem cells is to see whether cells can contribute to entire body of animals. Here we show that the increased frequency of Zscan4 activation in mouse ES cells not only enhances, but also maintains their developmental potency in long-term cell culture. As the potency increases, even a whole animal can be produced from a single ES cell injected into 4N blastocyst at unusually high success rate. Although Zscan4-activated cells express genes that are also expressed in 2-cell stage mouse embryos, transiently Zscan4-activated state of ES cells is not associated with the high potency of ES cells. It is thus concluded that ES cells acquire higher potency by going through transient Zscan4 activation state more frequently than the regular state. Taken together, our results indicate that frequent activation of Zscan4 can rejuvenate pluripotent stem cells. MC1 ES cells (for pZscan4-Emerald transfection) and R26R6 ES cells (for pZscan4-Cre ERT2 transfection) were grown on gelatin in 6-well plate, 5x10^5cells in suspension were transfected with 1ug of linearized pZscan4-Emerald vector or pZscan4-Cre ERT2 vector using Effectene (QIAGEN) according manufacturer protocol, and plated in gelatin coated 100 mm dishes. Cells were selected with 5 ug/ml blasticidin, colonies were picked on the 8th day, expanded and frozen for further analysis. DNA microarray analysis of pZscan4-Emerald cells was carried out as described. In brief, universal Mouse Reference RNA (Stratagene) were labeled with Cy5-dye, mixed with Cy3-labeled samples, and used for hybridization on the NIA Mouse 44K Microarray v2.2 (manufactured by Agilent Technologies #014117). The intensity of each gene feature was extracted from scanned microarray images using Feature Extraction 9.5.1.1 software (Agilent Technologies). Microarray data analyses were carried out by using an application developed in-house to perform ANOVA and other analyses (NIA Array Analysis software; http://lgsun.grc.nia.nih.gov)

Project description:The generation of induced pluripotent stem cells (iPSCs) by the forced expression of defined transcription factors in somatic cells holds great promise for the future of regenerative medicine. However, due to a poor understanding of the initial reprogramming mechanism, it is difficult to control the efficiency and quality of the iPSCs. Here we show that Zscan4, expressed transiently in 2-cell embryos and embryonic stem cells (ESCs), efficiently produces iPSCs from mouse embryo fibroblasts when coexpressed with Klf4, Oct4, and Sox2. Unlike other factors, Zscan4 is required only for the first few days of iPSC formation. Microarray analysis revealed transient and early induction of preimplantation-specific genes in a Zscan4-dependent manner. Our work indicates that Zscan4 is a previously unidentified potent natural factor that facilitates the reprogramming process through the recapitulation of the early embryonic program. Secondary MEFs were isolated from E13.5 embryos, which were harvested by tetraploid complementation. Secondary MEFs were plated on gelatin-coated 6-well plates at a density of 1x105 cells/well in the complete ES medium. After 24 h incubation, secondary MEFs were fed with complete ES medium with or without Dox (1.5 ?g/ml) and with or without 200 nM Tmx. Culture medium was changed every day. Withdrawal of drugs (Dox or Tmx) was always followed by 1x washing by PBS before changing culture medium. We cotransfected MEFs with PB-Tet-MKOS and either a PB-Tet-Zscan4 or PB-Tet-DsRed (control). These cells were subsequently cultured in the standard iPSC generation condition (Dox+). Unexpectedly, we found that MEFs transfected with a PB-Tet-Zscan4 show consistently higher efficiency of iPSC generation than MEFs transfected with a PB-Tet-DsRed (control). All selected iPSCs expressed pluripotent marker genes according to RT-PCR analysis and were positive for ALP, Nanog, and SSEA-1. These iPSCs also formed embryoid bodies in hanging drops without LIF and could be differentiated in vitro to cells of all three germ layers. We are currently studying whether the presence of Zscan4 has the beneficial effects on iPSCs in terms of genome stability.

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Zscan4 mediates transient remodeling and transcriptional burst of heterochromatin in mouse embryonic stem cells

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