title: Constitutive heterochromatin reorganization during somatic cell reprogramming.
abstract: Induced pluripotent stem (iPS) cell reprogramming is a gradual epigenetic process that reactivates the pluripotent transcriptional network by erasing and establishing repressive epigenetic marks. In contrast to loci-specific epigenetic changes, heterochromatin domains undergo epigenetic resetting during the reprogramming process, but the effect on the heterochromatin ultrastructure is not known. Here, we characterize the physical structure of heterochromatin domains in full and partial mouse iPS cells by correlative electron spectroscopic imaging. In somatic and partial iPS cells, constitutive heterochromatin marked by H3K9me3 is highly compartmentalized into chromocentre structures of densely packed chromatin fibres. In contrast, chromocentre boundaries are poorly defined in pluripotent embryonic stem and full iPS cells, and are characterized by unusually dispersed 10 nm heterochromatin fibres in high Nanog-expressing cells, including pluripotent cells of the mouse blastocyst before differentiation. This heterochromatin reorganization accompanies retroviral silencing during conversion of partial iPS cells by MEK/GSK3 2i inhibitor treatment. Thus, constitutive heterochromatin is compacted in partial iPS cells but reorganizes into dispersed 10 nm chromatin fibres as the fully reprogrammed iPS cell state is acquired.
authors.affiliation: Programs in Genetics and Genome Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Eden
authors.initials: E
authors.lastname: Fussner
authors.forename: Ugljesa
authors.initials: U
authors.lastname: Djuric
authors.forename: Mike
authors.initials: M
authors.lastname: Strauss
authors.forename: Akitsu
authors.initials: A
authors.lastname: Hotta
authors.forename: Carolina
authors.initials: C
authors.lastname: Perez-Iratxeta
authors.forename: Fredrik
authors.initials: F
authors.lastname: Lanner
authors.forename: F Jeffrey
authors.initials: FJ
authors.lastname: Dilworth
authors.forename: James
authors.initials: J
authors.lastname: Ellis
authors.forename: David P
authors.initials: DP
authors.lastname: Bazett-Jones
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D065150:Cellular Reprogramming / Q000502:physiology*; D047369:Chromatin Immunoprecipitation; D044127:Epigenesis, Genetic / Q000502:physiology*; D005434:Flow Cytometry; D020868:Gene Silencing; D005822:Genetic Vectors / Q000235:genetics; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006570:Heterochromatin / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D057026:Induced Pluripotent Stem Cells / Q000502:physiology*; D051379:Mice; D046228:Microarray Analysis; D046529:Microscopy, Electron, Transmission; D046032:Microscopy, Energy-Filtering Transmission Electron; D008856:Microscopy, Fluorescence; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D000071317:Nanog Homeobox Protein; D012190:Retroviridae; D012191:Retroviridae Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
chemical_list: D006570:Heterochromatin; D018398:Homeodomain Proteins; D000071317:Nanog Homeobox Protein; C475540:Nanog protein, mouse; D012191:Retroviridae Proteins; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3