title: Histone variant macroH2A confers resistance to nuclear reprogramming.
abstract: How various layers of epigenetic repression restrict somatic cell nuclear reprogramming is poorly understood. The transfer of mammalian somatic cell nuclei into Xenopus oocytes induces transcriptional reprogramming of previously repressed genes. Here, we address the mechanisms that restrict reprogramming following nuclear transfer by assessing the stability of the inactive X chromosome (Xi) in different stages of inactivation. We find that the Xi of mouse post-implantation-derived epiblast stem cells (EpiSCs) can be reversed by nuclear transfer, while the Xi of differentiated or extraembryonic cells is irreversible by nuclear transfer to oocytes. After nuclear transfer, Xist RNA is lost from chromatin of the Xi. Most epigenetic marks such as DNA methylation and Polycomb-deposited H3K27me3 do not explain the differences between reversible and irreversible Xi. Resistance to reprogramming is associated with incorporation of the histone variant macroH2A, which is retained on the Xi of differentiated cells, but absent from the Xi of EpiSCs. Our results uncover the decreased stability of the Xi in EpiSCs, and highlight the importance of combinatorial epigenetic repression involving macroH2A in restricting transcriptional reprogramming by oocytes.
authors.affiliation: Wellcome Trust Cancer Research UK Gurdon Institute, Cambridge, UK. v.pasque@gurdon.cam.ac.uk
authors.forename: Vincent
authors.initials: V
authors.lastname: Pasque
authors.forename: Astrid
authors.initials: A
authors.lastname: Gillich
authors.forename: Nigel
authors.initials: N
authors.lastname: Garrett
authors.forename: John B
authors.initials: JB
authors.lastname: Gurdon
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D065150:Cellular Reprogramming / Q000235:genetics*; D043171:Chromosomal Instability / Q000235:genetics*; D005260:Female; D005347:Fibroblasts / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D014644:Genetic Variation; D006657:Histones / Q000737:chemistry / Q000235:genetics*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009865:Oocytes / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000737:chemistry* / Q000235:genetics*; D014158:Transcription, Genetic; D049951:X Chromosome Inactivation / Q000235:genetics*; D014981:Xenopus
chemical_list: D006657:Histones; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA; C120756:macroH2A histone