Browse
Submit Data
Databases
API
Help

Dataset Information

24 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

RAP1 is essential for silencing telomeric variant surface glycoprotein genes in Trypanosoma brucei.

ABSTRACT: Trypanosoma brucei expresses variant surface glycoprotein (VSG) genes in a strictly monoallelic fashion in its mammalian hosts, but it is unclear how this important virulence mechanism is enforced. Telomere position effect, an epigenetic phenomenon, has been proposed to play a critical role in VSG regulation, yet no telomeric protein has been identified whose disruption led to VSG derepression. We now identify tbRAP1 as an intrinsic component of the T. brucei telomere complex and a major regulator for silencing VSG expression sites (ESs). Knockdown of tbRAP1 led to derepression of all VSGs in silent ESs, but not VSGs located elsewhere, and resulted in stronger derepression of genes located within 10 kb from telomeres than genes located further upstream. This graduated silencing pattern suggests that telomere integrity plays a key role in tbRAP1-dependent silencing and VSG regulation.

SUBMITTER: Yang X

PROVIDER: S-EPMC2673096 | biostudies-literature | 2009 Apr

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

RAP1 is essential for silencing telomeric variant surface glycoprotein genes in Trypanosoma brucei.

Yang Xiaofeng X Figueiredo Luisa M LM Espinal Amin A Okubo Eiji E Li Bibo B

Cell 20090401 1

Trypanosoma brucei expresses variant surface glycoprotein (VSG) genes in a strictly monoallelic fashion in its mammalian hosts, but it is unclear how this important virulence mechanism is enforced. Telomere position effect, an epigenetic phenomenon, has been proposed to play a critical role in VSG regulation, yet no telomeric protein has been identified whose disruption led to VSG derepression. We now identify tbRAP1 as an intrinsic component of the T. brucei telomere complex and a major regulat ...[more]

PMID: 19345190

Similar Datasets

Antigenic variation in Trypanosoma brucei: a telomeric expression site for variant-specific surface glycoprotein genes with novel features.

Project description:African trypanosomes evade the immune response of their host by periodically changing their variant surface glycoprotein (VSG) coat. Each coat is encoded by a separate VSG gene. Expressed genes are in a telomeric expression site (ES) and there are several sites in each trypanosome. To study the transcription control of VSG genes in Trypanosoma brucei we have analyzed an ES, called the dominant ES (DES), that readily switches off and on. The promoter area of the DES is very similar to that of the 221 ES (Zomerdijk et al., 1990). It can be switched off and on in vivo without detectable DNA alterations in the vicinity of the transcription start and it can drive high transient expression of a reporter gene in transfection experiments. However, there are also two major differences between the DES and the 221 ES. First, one version of the DES contains an additional upstream transcription unit overlapping the VSG gene ES promoter. The presence of this upstram transcription is dispensable, however, for the VSG gene ES promoter is active, even if transcription through this start from the upstream promoter is blocked using UV light. Moreover, a second version of the DES present in another trypanosome variant does not produce these upstream transcripts. Secondly, we find that the inactivation of DES transcription in one trypanosome variant is accompanied by DNA alterations in the DES upstream (greater than 2 kb) of the transcription start; reactivation of DES transcription is accompanied by another alteration far upstream. Although we cannot exclude that these DNA rearrangements are incidental, our results raise the possibility that the activity of ES promoters is negatively controlled in cis by far upstream sequences not included in transfection constructs and that alterations in these sequences may lead to (in)activation of the promoter.

| S-EPMC333887 | biostudies-other

Glycotyping of Trypanosoma brucei variant surface glycoprotein MITat1.8.

Project description:Following a switch from variant surface glycoprotein MITat1.4 to variant surface glycoprotein MITat1.8 expression by Lister strain 427 Trypanosoma brucei brucei parasites, the latter uncharacterized variant surface glycoprotein was analysed. Variant surface glycoprotein MITat1.8 was found to be a disulphide-linked homodimer, containing a complex N-linked glycan at Asn58 and a glycosylphosphatidylinositol membrane anchor attached to Asp419. Mass spectrometric analyses demonstrated that the N-glycan is exclusively Galbeta1-4GlcNAcbeta1-2Manalpha1-3(Galbeta1-4GlcNAcbeta1-2Manalpha1-6)Manbeta1-4GlcNAcbeta1-4GlcNAc and that the conserved Man(3)GlcN-myo-inositol glycosylphosphatidylinositol anchor glycan core is substituted with an average of 4 hexose, most likely galactose, residues. The presence of a complex N-glycan at Asn58 is consistent with the relatively acidic environment of the Asn58 N-glycosylation sequon, that predicts N-glycosylation by T. brucei oligosaccharyltransferase TbSTT3A with a Man(5)GlcNAc(2) structure destined for processing to a paucimannose and/or complex N-glycan (Izquierdo L, Schulz B, Rodrigues JA et al. EMBO J 2009;28:2650-61 [12]).

| S-EPMC2935967 | biostudies-literature

Synchronous expression of individual metacyclic variant surface glycoprotein genes in Trypanosoma brucei.

Project description:One distinctive feature of the Trypanosoma brucei life cycle is the presence of two discrete populations that are based on differential expression of variant surface glycoproteins (VSGs). Both are adapted to the environmental pressures they face and more importantly, both contribute directly to transmission. Metacyclics in the tsetse fly enable transmission to a new mammalian host, whereas bloodstream trypanosomes must avoid immune destruction to the extent that sufficient numbers are available for transmission, when the insect vector takes a blood meal. At present, there are few investigations on the molecular aspects of parasite biology in the tsetse vector and specifically about the activation of metacyclic VSG gene expression. Here we used an established in vitro differentiation system based on the overexpression of the RNA-binding protein 6 (RBP6), to monitor two metacyclic VSGs (VSG 397 and VSG 653) during development from procyclics to infectious metacyclic forms. We observed that activation of these two mVSGs was simultaneous both at the transcript and protein level, and manifested by the appearance of only one of the mVSGs in individual cells.

| S-EPMC4470760 | biostudies-literature

Trypanosoma brucei brucei variant surface glycoprotein contains non-N-acetylated glucosamine.

Project description:The C-terminal amino acid of the variant surface glycoprotein of the parasitic protozoan Trypanosoma brucei brucei is glycosylated and the oligosaccharide has been shown to contain glucosamine. By acid hydrolysis, HNO2 deamination and 1H-n.m.r. studies we have demonstrated that the amino group of this glucosamine is not N-acetylated and is most probably unmodified.

| S-EPMC1146591 | biostudies-other

Variant Surface Glycoprotein gene repertoires in Trypanosoma brucei have diverged to become strain-specific.

Project description:In a mammalian host, the cell surface of African trypanosomes is protected by a monolayer of a single variant surface glycoprotein (VSG). The VSG is central to antigenic variation; one VSG gene is expressed at any one time and there is a low frequency stochastic switch to expression of a different VSG gene. The genome of Trypanosoma brucei contains a repertoire of > 1000 VSG sequences. The degree of conservation of the genomic VSG repertoire in different strains has not been investigated in detail.Eighteen expressed VSGs from Ugandan isolates were compared with homologues (> 40 % sequence identity) in the two available T. brucei genome sequences. Fourteen homologues were present in the genome of Trypanosoma brucei brucei TREU927 from Kenya and fourteen in the genome of T. b. gambiense Dal972 from Cote d'Ivoire. The Ugandan VSGs averaged 71% and 73 % identity to homologues in T. b. brucei and T. b. gambiense respectively. The sequence divergence between homologous VSGs from the three different strains was not random but was more prevalent in the parts of the VSG believed to interact with the host immune system on the living trypanosome.It is probable that the VSG repertoires in the different isolates contain many common VSG genes. The location of divergence between VSGs is consistent with selection for strain-specific VSG repertoires, possibly to allow superinfection of an animal by a second strain. A consequence of strain-specific VSG repertoires is that any vaccine based on large numbers of VSGs from a single strain will only provide partial protection against other strains.

| S-EPMC1934917 | biostudies-literature

The promoter for a variant surface glycoprotein gene expression site in Trypanosoma brucei.

Project description:The variant-specific surface glycoprotein (VSG) gene 221 of Trypanosoma brucei is transcribed as part of a 60 kb expression site (ES). We have identified the promoter controlling this multigene transcription unit by the use of 221 chromosome-enriched DNA libraries and VSG gene 221 expression site specific transcripts. The start of transcription was determined by hybridization and RNase protection analysis of nascent RNA. The 5' ends of the major transcripts coming from the initiation region map at nucleotide sequences that do not strongly resemble rRNA transcriptional starts even though the transcripts are synthesized by an RNA polymerase highly resistant to alpha-amanitin. The cloned VSG gene 221 ES transcription initiation region promotes high CAT gene expression, when reintroduced by electroporation into T. brucei. We show that the activity of this expression site is controlled at or near transcription initiation in bloodstream trypanosomes. The 221 ES is inactivated without any sequence alteration within 1.4 kb of the transcription start site. This excludes mechanisms of promoter inactivation involving DNA rearrangements in the vicinity of the transcription start site, e.g. promoter inversion or conversion.

| S-EPMC551989 | biostudies-other

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.

2020-11-04 | GSE160713 | GEO

The essential neutral sphingomyelinase is involved in the trafficking of the variant surface glycoprotein in the bloodstream form of Trypanosoma brucei.

Project description:Sphingomyelin is the main sphingolipid in Trypanosoma brucei, the causative agent of African sleeping sickness. In vitro and in vivo characterization of the T. brucei neutral sphingomyelinase demonstrates that it is directly involved in sphingomyelin catabolism. Gene knockout studies in the bloodstream form of the parasite indicate that the neutral sphingomyelinase is essential for growth and survival, thus highlighting that the de novo biosynthesis of ceramide is unable to compensate for the loss of sphingomyelin catabolism. The phenotype of the conditional knockout has given new insights into the highly active endocytic and exocytic pathways in the bloodstream form of T. brucei. Hence, the formation of ceramide in the endoplasmic reticulum affects post-Golgi sorting and rate of deposition of newly synthesized GPI-anchored variant surface glycoprotein on the cell surface. This directly influences the corresponding rate of endocytosis, via the recycling endosomes, of pre-existing cell surface variant surface glycoprotein. The trypanosomes use this coupled endocytic and exocytic mechanism to maintain the cell density of its crucial variant surface glycoprotein protective coat. TbnSMase is therefore genetically validated as a drug target against African trypanosomes, and suggests that interfering with the endocytic transport of variant surface glycoprotein is a highly desirable strategy for drug development against African trypanosomasis.

| S-EPMC2904498 | biostudies-literature

A LiTat 1.5 variant surface glycoprotein-derived peptide with diagnostic potential for Trypanosoma brucei gambiense.

Project description:To evaluate the accuracy of a peptide, corresponding to the variant surface glycoprotein (VSG) LiTat 1.5 amino acid (AA) sequence 268-281 and identified through alignment of monoclonal antibody selected mimotopes, for diagnosis of Trypanosoma brucei gambiense sleeping sickness.A synthetic biotinylated peptide (peptide 1.5/268-281), native VSG LiTat 1.3 and VSG LiTat 1.5 were tested in an indirect ELISA with 102 sera from patients with HAT and 102 endemic HAT-negative controls.The area under the curve (AUC) of peptide 1.5/268-281 was 0.954 (95% confidence interval 0.918-0.980), indicating diagnostic potential. The areas under the curve of VSG LiTat 1.3 and LiTat 1.5 were 1.000 (0.982-1.000) and 0.997 (0.973-1.000), respectively, and significantly higher than the AUC of peptide 1.5/268-281. On a model of VSG LiTat 1.5, peptide 1.5/268-281 was mapped near the top of the VSG.A biotinylated peptide corresponding to AA 268-281 of VSG LiTat 1.5 may replace the native VSG in serodiagnostic tests, but the diagnostic accuracy is lower than for the full-length native VSG LiTat 1.3 and VSG LiTat 1.5.

| S-EPMC3600074 | biostudies-literature

Blocking variant surface glycoprotein synthesis in Trypanosoma brucei triggers a general arrest in translation initiation.

Project description:BackgroundThe African trypanosome Trypanosoma brucei is covered with a dense layer of Variant Surface Glycoprotein (VSG), which protects it from lysis by host complement via the alternative pathway in the mammalian bloodstream. Blocking VSG synthesis by the induction of VSG RNAi triggers an unusually precise precytokinesis cell-cycle arrest.Methodology/principal findingsHere, we characterise the cells arrested after the induction of VSG RNAi. We were able to rescue the VSG221 RNAi induced cell-cycle arrest through expression of a second different VSG (VSG117 which is not recognised by the VSG221 RNAi) from the VSG221 expression site. Metabolic labeling of the arrested cells showed that blocking VSG synthesis triggered a global translation arrest, with total protein synthesis reduced to less than 1-4% normal levels within 24 hours of induction of VSG RNAi. Analysis by electron microscopy showed that the translation arrest was coupled with rapid disassociation of ribosomes from the endoplasmic reticulum. Polysome analysis showed a drastic decrease in polysomes in the arrested cells. No major changes were found in levels of transcription, total RNA transcript levels or global amino acid concentrations in the arrested cells.ConclusionsThe cell-cycle arrest phenotype triggered by the induction of VSG221 RNAi is not caused by siRNA toxicity, as this arrest can be alleviated if a second different VSG is inserted downstream of the active VSG221 expression site promoter. Analysis of polysomes in the stalled cells showed that the translation arrest is mediated at the level of translation initiation rather than elongation. The cell-cycle arrest induced in the presence of a VSG synthesis block is reversible, suggesting that VSG synthesis and/or trafficking to the cell surface could be monitored during the cell-cycle as part of a specific cell-cycle checkpoint.

| S-EPMC2762041 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data