title: Retrovirus vector silencing is de novo methylase independent and marked by a repressive histone code.
abstract: Retrovirus vectors are de novo methylated and transcriptionally silent in mammalian stem cells. Here, we identify epigenetic modifications that mark retrovirus-silenced transgenes. We show that murine stem cell virus (MSCV) and human immunodeficiency virus type 1 (HIV-1) vectors dominantly silence a linked locus control region (LCR) beta-globin reporter gene in transgenic mice. MSCV silencing blocks LCR hypersensitive site formation, and silent transgene chromatin is marked differentially by a histone code composed of abundant linker histone H1, deacetylated H3 and acetylated H4. Retrovirus-transduced embryonic stem (ES) cells are silenced predominantly 3 days post-infection, with a small subset expressing enhanced green fluorescent protein to low levels, and silencing is not relieved in de novo methylase-null [dnmt3a-/-;dnmt3b-/-] ES cells. MSCV and HIV-1 sequences also repress reporter transgene expression in Drosophila, demonstrating establishment of silencing in the absence of de novo and maintenance methylases. These findings provide mechanistic insight into a conserved gene silencing mechanism that is de novo methylase independent and that epigenetically marks retrovirus chromatin with a repressive histone code.
authors.affiliation: Programs in Developmental Biology, and Cancer and Blood Research, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, M5G 1X8, Toronto, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Pannell
authors.forename: C S
authors.initials: CS
authors.lastname: Osborne
authors.forename: S
authors.initials: S
authors.lastname: Yao
authors.forename: T
authors.initials: T
authors.lastname: Sukonnik
authors.forename: P
authors.initials: P
authors.lastname: Pasceri
authors.forename: A
authors.initials: A
authors.lastname: Karaiskakis
authors.forename: M
authors.initials: M
authors.lastname: Okano
authors.forename: E
authors.initials: E
authors.lastname: Li
authors.forename: H D
authors.initials: HD
authors.lastname: Lipshitz
authors.forename: J
authors.initials: J
authors.lastname: Ellis
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D005075:Biological Evolution; D002843:Chromatin / Q000235:genetics; D015254:DNA Modification Methylases / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004330:Drosophila / Q000235:genetics; D020868:Gene Silencing; D017930:Genes, Reporter; D005822:Genetic Vectors; D005914:Globins / Q000235:genetics; D015497:HIV-1 / Q000235:genetics; D006657:Histones / Q000235:genetics; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D012190:Retroviridae / Q000235:genetics*
chemical_list: D002843:Chromatin; D017931:DNA Primers; D006657:Histones; D005914:Globins; D015254:DNA Modification Methylases