title: Chromatin condensation of Xist genomic loci during oogenesis in mice.
abstract: Repression of maternal Xist (Xm-Xist) during preimplantation in mouse embryos is essential for establishing imprinted X chromosome inactivation. Nuclear transplantation (NT) studies using nuclei derived from non-growing (ng) and full-grown (fg) oocytes have indicated that maternal-specific repressive modifications are imposed on Xm-Xist during oogenesis, as well as on autosomal imprinted genes. Recent studies have revealed that histone H3 lysine 9 trimethylation (H3K9me3) enrichments on Xm-Xist promoter regions are involved in silencing at the preimplantation stages. However, whether H3K9me3 is imposed on Xm-Xist during oogenesis is not known. Here, we dissected the chromatin states in ng and fg oocytes and early preimplantation stage embryos. Chromatin immunoprecipitation experiments against H3K9me3 revealed that there was no significant enrichment within the Xm-Xist region during oogenesis. However, NT embryos with ng nuclei (ngNT) showed extensive Xm-Xist derepression and H3K9me3 hypomethylation of the promoter region at the 4-cell stage, which corresponds to the onset of paternal Xist expression. We also found that the chromatin state at the Xist genomic locus became markedly condensed as oocyte growth proceeded. Although the condensed Xm-Xist genomic locus relaxed during early preimplantation phases, the extent of the relaxation across Xm-Xist loci derived from normally developed oocytes was significantly smaller than those of paternal-Xist and ngNT-Xist genomic loci. Furthermore, Xm-Xist from 2-cell metaphase nuclei became derepressed following NT. We propose that chromatin condensation is associated with imprinted Xist repression and that skipping of the condensation step by NT leads to Xist activation during the early preimplantation phase.
authors.affiliation: Center for Regenerative Medicine, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya, Tokyo 157-8535, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Fukuda
authors.affiliation: Center for Regenerative Medicine, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya, Tokyo 157-8535, Japan Department of Molecular Genetics, Kitasato University Graduate School of Medical Sciences, 1-15-1 Kitasato, Minami, Sagamihara, Kanagawa 252-0374, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Mitani
authors.affiliation: Department of Molecular Genetics, Kitasato University Graduate School of Medical Sciences, 1-15-1 Kitasato, Minami, Sagamihara, Kanagawa 252-0374, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Miyashita
authors.affiliation: Center for Regenerative Medicine, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya, Tokyo 157-8535, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Umezawa
authors.affiliation: Center for Regenerative Medicine, National Research Institute for Child Health and Development, 2-10-1 Okura, Setagaya, Tokyo 157-8535, Japan Department of Stem Cell Research, Fukushima Medical University, 1 Hikarigaoka, Fukushima City, Fukushima 960-1295, Japan akutsu-h@ncchd.go.jp.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Akutsu
mesh_terms: D000818:Animals; D001755:Blastocyst; D002843:Chromatin / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D019175:DNA Methylation; D053595:Embryonic Stem Cells / Q000166:cytology*; D005260:Female; D006657:Histones / Q000378:metabolism; D047468:Immunoprecipitation; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008677:Metaphase; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009865:Oocytes / Q000166:cytology; D009866:Oogenesis / Q000502:physiology*; D011401:Promoter Regions, Genetic; D062085:RNA, Long Noncoding / Q000235:genetics / Q000378:metabolism*; D049951:X Chromosome Inactivation
chemical_list: D002843:Chromatin; D006657:Histones; D062085:RNA, Long Noncoding; C077885:XIST non-coding RNA
keywords: Chromatin condensation; Histone methylation; Imprinted XCI; Nuclear transfer; Oogenesis; Xist