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Histone variant 3 regulates RNA polymerase II transcription termination and dual strand transcription of siRNA loci in Trypanosoma brucei

ABSTRACT: Histone variant 3 (H3V) is a kinetoplastid specific histone variant that is enriched at RNA polymerase II termination sites and telomeres. We previously found that the DNA modification base J, which co-localizes with H3V, functions to prevent readthrough transcription within gene clusters in T. brucei. We now demonstrate a similar role for H3V, where the loss of this histone variant results in increased expression of downstream genes. The effect is larger when both H3V and J are lost. Additionally, removal of H3V results in increased siRNAs from dual strand transcribed loci as well as increased expression of silent VSGs, indicating a role of H3V in the regulation of antigenic variation

ORGANISM(S): Trypanosoma brucei

PROVIDER: GSE69929 | GEO | 2016/01/25

SECONDARY ACCESSION(S): PRJNA287144

REPOSITORIES: GEO

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Histone variant 3 regulates RNA polymerase II transcription termination and dual strand transcription of siRNA loci in Trypanosoma brucei

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Histone variant 3 regulates RNA polymerase II transcription termination and dual strand transcription of siRNA loci in Trypanosoma brucei

Project description:Histone variant 3 (H3V) is a kinetoplastid specific histone variant that is enriched at RNA polymerase II termination sites and telomeres. We previously found that the DNA modification base J, which co-localizes with H3V, functions to prevent readthrough transcription within gene clusters in T. brucei. We now demonstrate a similar role for H3V, where the loss of this histone variant results in increased expression of downstream genes. The effect is larger when both H3V and J are lost. Additionally, removal of H3V results in increased siRNAs from dual strand transcribed loci as well as increased expression of silent VSGs, indicating a role of H3V in the regulation of antigenic variation The role of H3V in regulating transcription termination was investigated using WT and H3V KO T. brucei cell lines. The role of J was also studied by treating each of these cell lines with DMOG, an inhibitor of J synthesis. We used small RNA seq libraries to identify transcriptional changes following the loss of H3V and J.

2016-06-30 | E-GEOD-70229 | biostudies-arrayexpress

The SPARC complex defines RNAPII promoters in Trypanosoma brucei [ChIP-seq]

Project description:Kinetoplastids are a highly divergent lineage of eukaryotes with unusual mechanisms for regulating gene expression. We previously surveyed 65 putative chromatin factors in the kinetoplastid Trypanosoma brucei. Our analyses revealed that the predicted histone methyltransferase SET27 and the Chromodomain protein CRD1 are tightly concentrated at RNAPII transcription start regions (TSRs). Here we report that SET27 and CRD1 together with four biologically novel constituents form the SET27 promoter-associated regulatory complex (SPARC), which is specifically enriched at TSRs. SET27 loss leads to aberrant RNAPII recruitment to promoter sites, accumulation of polyadenylated transcripts upstream of normal transcription start sites, and conversion of some normally unidirectional promoters to bidirectional promoters. Transcriptome analysis in the absence of SET27 revealed upregulated mRNA expression in the vicinity of SPARC peaks on chromosome cores in addition to derepression of genes encoding variant surface glycoproteins (VSGs) located in subtelomeric regions. These analyses uncover a novel chromatin-associated complex required to establish accurate promoter position and directionality.

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Trypanosoma brucei brucei

Project description:Analysis of AnTat1.1 mosaic VSGs in Trypanosoma brucei brucei

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Application of long read sequencing to determine expressed antigen diversity in Trypanosoma brucei infections.

Project description:Antigenic variation is employed by many pathogens to evade the host immune response, and Trypanosoma brucei has evolved a complex system to achieve this phenotype, involving sequential use of variant surface glycoprotein (VSG) genes encoded from a large repertoire of ~2,000 alleles. T. brucei express multiple, sometimes closely related, VSGs in a population at any one time, and the ability to resolve and analyse this diversity has been limited. We applied long read sequencing (PacBio) to VSG amplicons generated from blood extracted from batches of mice sacrificed at time points (days 3, 6, 10 and 12) post-infection with T. brucei TREU927. The data showed that long read sequencing is reliable for resolving allelic differences between VSGs, and demonstrated that there is significant expressed diversity (449 VSGs detected across 20 mice) and across the timeframe of study there was a clear semi-reproducible pattern of expressed diversity (median of 27 VSGs per sample at day 3 post infection (p.i.), 82 VSGs at day 6 p.i., 187 VSGs at day 10 p.i. and 132 VSGs by day 12 p.i.). There was also consistent detection of one VSG dominating expression across replicates at days 3 and 6, and emergence of a second dominant VSG across replicates by day 12, providing further evidence for hierarchical VSG expression, a conclusion that was confirmed by the novel application of diversity analysis to VSG expression. Our results indicate that long read analysis is a reliable tool for resolving diverse allele expression profiles, and provides novel insights into the complexity and nature of VSG expression in trypanosomes, revealing significantly higher diversity than previously shown and identifying mosaic gene formation unprecedentedly early during the infection process.

2018-11-01 | GSE114843 | GEO

The SPARC complex defines RNAPII promoters in Trypanosoma brucei

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2023-03-11 | PXD036454 | Pride

Histone divergence in Trypanosoma brucei results in unique alterations in nucleosome structure

Project description:Eukaryotes have an array of diverse mechanisms for organising and using their genomes, but the histones that make up chromatin are highly conserved. Unusually, histones from Kinetoplastids are highly divergent. The structural and functional consequences of this variation are unknown. Here, we have biochemically characterised nucleosome core particles (NCPs) from the Kinetoplastid parasite Trypanosoma brucei. A structure of the T. brucei NCP reveals that global histone architecture is conserved, but specific sequence alterations lead to distinct DNA and protein interaction interfaces. The T. brucei NCP is unstable and has weakened DNA binding overall. However, dramatic changes at the H2A-H2B interface introduce local reinforcement of DNA contacts. The T. brucei acidic patch has altered topology and is refractory to known binders, indicating that the nature of chromatin interactions in T. brucei may be unique. Overall, our results provide a detailed molecular basis for understanding evolutionary divergence in chromatin structure.

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TbSAP is a novel chromatin protein repressing metacyclic Variant Surface Glycoprotein expression sites in bloodstream form Trypanosoma brucei

Project description:The African trypanosome Trypanosoma brucei is a unicellular eukaryote, which relies on a protective Variant Surface Glycoprotein (VSG) coat for survival in the mammalian host. A single trypanosome has >2000 VSG genes and pseudogenes of which only one is expressed from one of ~15 telomeric bloodstream form expression sites (BESs). Infectious metacyclic trypanosomes present within the tsetse fly vector also express VSG from a separate set of telomeric metacyclic ESs (MESs). All MESs are silenced in bloodstream form T. brucei. As very little is known about how this is mediated, we performed a whole genome RNAi library screen to identify MES repressors. This allowed us to identify a novel SAP domain containing DNA binding protein which we called TbSAP. TbSAP is enriched at the nuclear periphery and binds both MESs and BESs. Knockdown of TbSAP in bloodstream form trypanosomes did not result in cells becoming more ‘metacyclic’-like. Instead, there was extensive global upregulation of transcripts including MES VSGs, VSGs within the silent VSG arrays as well as genes immediately downstream of BES promoters. TbSAP therefore appears to be a novel architectural chromatin protein playing an important role in silencing the extensive VSG repertoire of bloodstream form T. brucei.

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2018-08-24 | GSE118917 | GEO

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