title: Trypanosoma brucei histone H1 inhibits RNA polymerase I transcription and is important for parasite fitness in vivo.
abstract: Trypanosoma brucei is a unicellular parasite that causes sleeping sickness in humans. Most of its transcription is constitutive and driven by RNA polymerase II. RNA polymerase I (Pol I) transcribes not only ribosomal RNA genes, but also protein-encoding genes, including variant surface glycoproteins (VSGs) and procyclins. In T. brucei, histone H1 (H1) is required for VSG silencing and chromatin condensation. However, whether H1 has a genome-wide role in transcription is unknown. Here, using RNA sequencing we show that H1 depletion changes the expression of a specific cohort of genes. Interestingly, the predominant effect is partial loss of silencing of Pol I loci, such as VSG and procyclin genes. Labelling of nascent transcripts with 4-thiouridine showed that H1 depletion does not alter the level of labelled Pol II transcripts. In contrast, the levels of 4sU-labelled Pol I transcripts were increased by two- to sixfold, suggesting that H1 preferentially blocks transcription at Pol I loci. Finally, we observed that parasites depleted of H1 grow almost normally in culture but they have a reduced fitness in mice, suggesting that H1 is important for host-pathogen interactions.
authors.affiliation: Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, Edifício Egas Moniz, 1649-028, Lisboa, Portugal.
authors.forename: Ana C
authors.initials: AC
authors.lastname: Pena
authors.forename: Mafalda R
authors.initials: MR
authors.lastname: Pimentel
authors.forename: Helena
authors.initials: H
authors.lastname: Manso
authors.forename: Rita
authors.initials: R
authors.lastname: Vaz-Drago
authors.forename: Daniel
authors.initials: D
authors.lastname: Pinto-Neves
authors.forename: Francisco
authors.initials: F
authors.lastname: Aresta-Branco
authors.forename: Filipa
authors.initials: F
authors.lastname: Rijo-Ferreira
authors.forename: Fabien
authors.initials: F
authors.lastname: Guegan
authors.forename: Luis
authors.initials: L
authors.lastname: Pedro Coelho
authors.forename: Maria
authors.initials: M
authors.lastname: Carmo-Fonseca
authors.forename: Nuno L
authors.initials: NL
authors.lastname: Barbosa-Morais
authors.forename: Luisa M
authors.initials: LM
authors.lastname: Figueiredo
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006657:Histones / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D051379:Mice; D012318:RNA Polymerase I / Q000037:antagonists & inhibitors*; D018085:Regulon; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014353:Trypanosomiasis, African / Q000469:parasitology / Q000473:pathology; D014774:Virulence
chemical_list: D006657:Histones; D012318:RNA Polymerase I