title: Dimethylated H3K27 Is a Repressive Epigenetic Histone Mark in the Protist Entamoeba histolytica and Is Significantly Enriched in Genes Silenced via the RNAi Pathway.
abstract: RNA interference (RNAi) is a fundamental biological process that plays a crucial role in regulation of gene expression in many organisms. Transcriptional gene silencing (TGS) is one of the important nuclear roles of RNAi. Our previous data show that Entamoeba histolytica has a robust RNAi pathway that links to TGS via Argonaute 2-2 (Ago2-2) associated 27-nucleotide small RNAs with 5'-polyphosphate termini. Here, we report the first repressive histone mark to be identified in E. histolytica, dimethylation of H3K27 (H3K27Me2), and demonstrate that it is enriched at genes that are silenced by RNAi-mediated TGS. An RNAi-silencing trigger can induce H3K27Me2 deposits at both episomal and chromosomal loci, mediating gene silencing. Our data support two phases of RNAi-mediated TGS: an active silencing phase where the RNAi trigger is present and both H3K27Me2 and Ago2-2 concurrently enrich at chromosomal loci; and an established silencing phase in which the RNAi trigger is removed, but gene silencing with H3K27Me2 enrichment persist independently of Ago2-2 deposition. Importantly, some genes display resistance to chromosomal silencing despite induction of functional small RNAs. In those situations, the RNAi-triggering plasmid that is maintained episomally gets partially silenced and has H3K27Me2 enrichment, but the chromosomal copy displays no repressive histone enrichment. Our data are consistent with a model in which H3K27Me2 is a repressive histone modification, which is strongly associated with transcriptional repression. This is the first example of an epigenetic histone modification that functions to mediate RNAi-mediated TGS in the deep-branching eukaryote E. histolytica.
authors.affiliation: Departments of Internal Medicine, Division of Infectious Diseases, School of Medicine, Stanford University, Stanford, California 94305; Department of Molecular Genetics and Enzymology, National Research Centre, Dokki, Egypt.
authors.forename: Bardees M
authors.initials: BM
authors.lastname: Foda
authors.affiliation: Departments of Internal Medicine, Division of Infectious Diseases, School of Medicine, Stanford University, Stanford, California 94305; Departments of Microbiology and Immunology, School of Medicine, Stanford University, Stanford, California 94305. Electronic address: usingh@stanford.edu.
authors.forename: Upinder
authors.initials: U
authors.lastname: Singh
mesh_terms: D000595:Amino Acid Sequence; D060565:Argonaute Proteins / Q000235:genetics* / Q000378:metabolism; D002875:Chromosomes / Q000737:chemistry / Q000378:metabolism; D019175:DNA Methylation; D004748:Entamoeba histolytica / Q000235:genetics* / Q000378:metabolism; D020868:Gene Silencing; D006657:Histones / Q000235:genetics* / Q000378:metabolism; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: D060565:Argonaute Proteins; D006657:Histones; D015800:Protozoan Proteins
keywords: Entamoeba histolytica; H3K27Me2; RNA interference (RNAi); argonaute; chromatin immunoprecipitation (ChiP); epigenetics; gene expression; histone methylation; parasitology; transcriptional gene silencing