title: DNA methylation is dispensable for changes in global chromatin architecture but required for chromocentre formation in early stem cell differentiation.
abstract: Epiblast stem cells (EpiSCs), which are pluripotent cells isolated from early post-implantation mouse embryos (E5.5), show both similarities and differences compared to mouse embryonic stem cells (mESCs), isolated earlier from the inner cell mass (ICM) of the E3.5 embryo. Previously, we have observed that while chromatin is very dispersed in E3.5 ICM, compact chromatin domains and chromocentres appear in E5.5 epiblasts after embryo implantation. Given that the observed chromatin re-organization in E5.5 epiblasts coincides with an increase in DNA methylation, in this study, we aimed to examine the role of DNA methylation in chromatin re-organization during the in vitro conversion of ESCs to EpiSCs. The requirement for DNA methylation was determined by converting both wild-type and DNA methylation-deficient ESCs to EpiSCs, followed by structural analysis with electron spectroscopic imaging (ESI). We show that the chromatin re-organization which occurs in vivo can be re-capitulated in vitro during the ESC to EpiSC conversion. Indeed, after 7 days in EpiSC media, compact chromatin domains begin to appear throughout the nuclear volume, creating a chromatin organization similar to E5 epiblasts and embryo-derived EpiSCs. Our data demonstrate that DNA methylation is dispensable for this global chromatin re-organization but required for the compaction of pericentromeric chromatin into chromocentres.
authors.affiliation: Department of Cell and Molecular Biology, Faculty of Biology, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Vahideh
authors.initials: V
authors.lastname: Hassan-Zadeh
authors.affiliation: Epigenetics Programme, The Babraham Institute, Babraham Research Campus, Cambridge, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Rugg-Gunn
authors.affiliation: Programme in Genetics and Genome Biology, The Hospital for Sick Children, 686 Bay Street, Toronto, ON, M5G 0A4, Canada. david.bazett-jones@sickkids.ca.
authors.forename: David P
authors.initials: DP
authors.lastname: Bazett-Jones
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D002843:Chromatin / Q000378:metabolism* / Q000648:ultrastructure; D019175:DNA Methylation; D053595:Embryonic Stem Cells / Q000378:metabolism* / Q000648:ultrastructure; D044127:Epigenesis, Genetic; D005855:Germ Layers / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046032:Microscopy, Energy-Filtering Transmission Electron
chemical_list: D002843:Chromatin
keywords: Chromatin re-organization; Chromocentres; DNA methylation; Electron spectroscopic imaging (ESI); Embryonic stem cells (ESCs); Epiblast stem cells (EpiSCs)