title: Impact of flanking chromosomal sequences on localization and silencing by the human non-coding RNA XIST.
abstract: BACKGROUND
  X-chromosome inactivation is a striking example of epigenetic silencing in which expression of the long non-coding RNA XIST initiates the heterochromatinization and silencing of one of the pair of X chromosomes in mammalian females. To understand how the RNA can establish silencing across millions of basepairs of DNA we have modelled the process by inducing expression of XIST from nine different locations in human HT1080 cells.
  
  
  RESULTS
  Localization of XIST, depletion of Cot-1 RNA, perinuclear localization, and ubiquitination of H2A occurs at all sites examined, while recruitment of H3K9me3 was not observed. Recruitment of the heterochromatic features SMCHD1, macroH2A, H3K27me3, and H4K20me1 occurs independently of each other in an integration site-dependent manner. Silencing of flanking reporter genes occurs at all sites, but the spread of silencing to flanking endogenous human genes is variable in extent of silencing as well as extent of spread, with silencing able to skip regions. The spread of H3K27me3 and loss of H3K27ac correlates with the pre-existing levels of the modifications, and overall the extent of silencing correlates with the ability to recruit additional heterochromatic features.
  
  
  CONCLUSIONS
  The non-coding RNA XIST functions as a cis-acting silencer when expressed from nine different locations throughout the genome. A hierarchy among the features of heterochromatin reveals the importance of interaction with the local chromatin neighborhood for optimal spread of silencing, as well as the independent yet cooperative nature of the establishment of heterochromatin by the non-coding XIST RNA.
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. adkelsey1@gmail.com.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Kelsey
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. yoyo.rolls@gmail.com.
authors.forename: Christine
authors.initials: C
authors.lastname: Yang
authors.affiliation: Ludwig Institute for Cancer Research, University of California at San Diego School of Medicine, La Jolla, CA, USA. dcyleung@ust.hk.|Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China. dcyleung@ust.hk.
authors.forename: Danny
authors.initials: D
authors.lastname: Leung
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. jakub.minks@gmail.com.
authors.forename: Jakub
authors.initials: J
authors.lastname: Minks
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. tom.dixon.mcdougall@alumni.ubc.ca.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dixon-McDougall
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. sbaldry@mail.ubc.ca.
authors.forename: Sarah E L
authors.initials: SE
authors.lastname: Baldry
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. aaron.bogutz@ubc.ca.
authors.forename: Aaron B
authors.initials: AB
authors.lastname: Bogutz
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. louis.lefebvre@ubc.ca.
authors.forename: Louis
authors.initials: L
authors.lastname: Lefebvre
authors.affiliation: Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, Canada. Carolyn.Brown@UBC.Ca.
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Brown
mesh_terms: D041321:Chromosomes, Human, X / Q000235:genetics; D044127:Epigenesis, Genetic; D005260:Female; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D015894:Genome, Human; D006570:Heterochromatin / Q000235:genetics; D006801:Humans; D062085:RNA, Long Noncoding / Q000235:genetics*; D049951:X Chromosome Inactivation / Q000235:genetics*
chemical_list: D006570:Heterochromatin; D062085:RNA, Long Noncoding; C077885:XIST non-coding RNA