“…Studies on maintenance of XCI have revealed several principles by which gene silencing is maintained. The factors and mechanisms that have been involved in maintenance of XCI include Xist [ 45 , 60 , 83 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ], DNA methylation [ 83 , 84 , 85 , 88 , 102 , 103 ], histone deacetylation [ 83 ], Polycomb [ 104 , 105 ], H3K9me3 [ 106 ] and macroH2A [ 70 , 107 , 108 ], and likely include additional layers of regulation as well.…”