Isolation and analysis of the genetic diversity of repertoires of VSG expression site containing telomeres from Trypanosoma brucei gambiense, T. b. brucei and T. equiperdum.
Abstract: African trypanosomes (including Trypanosoma brucei) are unicellular parasites which multiply in the mammalian bloodstream. T. brucei has about twenty telomeric bloodstream form Variant Surface Glycoprotein (VSG) expression sites (BESs), of which one is expressed at a time in a mutually exclusive fashion. BESs are polycistronic transcription units, containing a variety of families of expression site associated genes (ESAGs) in addition to the telomeric VSG. These polymorphic ESAG families are thought to play a role in parasite-host adaptation, and it has been proposed that ESAG diversity might be related to host range. Analysis of the genetic diversity of these telomeric gene families has been confounded by the underrepresentation of telomeric sequences in standard libraries. We have previously developed a method to selectively isolate sets of trypanosome BES containing telomeres using Transformation associated recombination (TAR) cloning in yeast. Results: Here we describe the isolation of repertoires of BES containing telomeres from three trypanosome subspecies: Trypanosoma brucei gambiense DAL 972 (causative agent of West-African trypanosomiasis), T. b. brucei EATRO 2340 (a nonhuman infective strain) and T. equiperdum STIB 818 (which causes a sexually transmitted disease in equines). We have sequenced and analysed the genetic diversity at four BES loci (BES promoter region, ESAG6, ESAG5 and ESAG2) from these three trypanosome BES repertoires. Conclusions: With the exception of ESAG2, the BES sequence repertoires derived from T. b. gambiense are both less diverse than and nearly reciprocally monophyletic relative to those from T. b. brucei and T. equiperdum. Furthermore, although we find evidence for adaptive evolution in all three ESAG repertoires in T. b. brucei and T. equiperdum, only ESAG2 appears to be under diversifying selection in T. b. gambiense. This low level of variation in the T. b. gambiense BES sequence repertoires is consistent both with the relatively narrow host range of this subspecies and its apparent long-term clonality. However, our data does not show a clear correlation between size of trypanosome host range and either number of BESs or extent of ESAG genetic diversity.
Publication Date: 2008-08-12 PubMed ID: 18700033PubMed Central: PMC2533676DOI: 10.1186/1471-2164-9-385Google Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study discusses the isolation and analysis of genetic diversity in the blood-forming agent of African trypanosomes, Trypanosoma brucei, and two of its subspecies. Researchers used a method to isolate repertoires of blood-forming Variant Surface Glycoprotein (VSG) sites, examining genetic diversity across four specific loci. Results suggest a low level of variation in Trypanosoma brucei gambiense, which has a narrow host range and displays long-term clonality, but no clear link was found between size of trypanosome host range and either the number of blood-forming VSG sites or level of genetic diversity in expressed site-associated genes (ESAGs).
Research Methodology
- The researchers studied the genetic diversity in Trypanosoma brucei, a unicellular parasite that multiplies in the mammalian bloodstream. The focus was on the subspecies T. b. gambiense, which causes West-African trypanosomiasis, T. b. brucei, a non-human infective strain, and T. equiperdum, which causes a sexually transmitted disease in equines.
- They utilized a previously-developed method to isolate sets of blood-forming VSG sites using Transformation associated recombination (TAR) cloning in yeast. This was to overcome the notorious issue of underrepresentation of telomeric sequences in standard libraries.
Analysis of Genetic Diversity
- The subsequent analysis involved studying genetic diversity at four blood-forming VSG sites (BES promoter region, ESAG6, ESAG5 and ESAG2) from the three trypanosome repertoires.
- With the exception of ESAG2, the BES sequence repertoires from T. b. gambiense were found to be less diverse and almost completely different in evolution compared to those from T. b. brucei and T. equiperdum.
Implications and Conclusions
- Adaptive evolution was recorded in all three ESAG repertoires in T. b. brucei and T. equiperdum, while only ESAG2 seemed to be undergoing diversification in T. b. gambiense.
- The low level of variation in the T. b. gambiense BES sequence repertoires is consistent with its relatively narrow host range and its long-term clonality. However, no definitive link was established between the size of a trypanosome’s host range and either the number of BESs or the extent of ESAG genetic diversity.
- This implies the existence of other factors, beyond the scope of this research, impacting the diversity and adaptive capabilities of these subspecies of Trypanosoma brucei.
Cite This Article
APA
Young R, Taylor JE, Kurioka A, Becker M, Louis EJ, Rudenko G.
(2008).
Isolation and analysis of the genetic diversity of repertoires of VSG expression site containing telomeres from Trypanosoma brucei gambiense, T. b. brucei and T. equiperdum.
BMC Genomics, 9, 385.
https://doi.org/10.1186/1471-2164-9-385 Publication
Researcher Affiliations
- Peter Medawar Building for Pathogen Research, University of Oxford, South Parks Road, Oxford, OX1 3SY, UK. rosanna.young@green.ox.ac
MeSH Terms
- Amino Acid Sequence
- Animals
- Base Sequence
- Cloning, Molecular
- DNA, Protozoan / genetics
- Evolution, Molecular
- Gene Expression
- Gene Library
- Genes, Protozoan
- Genetic Variation
- Molecular Sequence Data
- Phylogeny
- Recombination, Genetic
- Sequence Homology, Amino Acid
- Sequence Homology, Nucleic Acid
- Species Specificity
- Telomere / genetics
- Trypanosoma / genetics
- Trypanosoma brucei brucei / genetics
- Trypanosoma brucei gambiense / genetics
- Variant Surface Glycoproteins, Trypanosoma / genetics
Grant Funding
- Wellcome Trust
- 095161 / Wellcome Trust
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Citations
This article has been cited 18 times.- Kouprina N, Kim JH, Larionov V. Highly Selective, CRISPR/Cas9-Mediated Isolation of Genes and Genomic Loci from Complex Genomes by TAR Cloning in Yeast.. Curr Protoc 2021 Aug;1(8):e207.
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