The structure of a conserved telomeric region associated with variant antigen loci in the blood parasite Trypanosoma congolense

Ali Hadi Abbas, Sara Silva Pereira, Simon D'Archivio, Bill Wickstead, Liam J Morrison, Neil Hall, Christiane Hertz-Fowler, Alistair C Darby, Andrew P Jackson

Research output: Contribution to journalArticlepeer-review

Abstract

African trypanosomiasis is a vector-borne disease of humans and livestock caused by African trypanosomes (Trypanosoma spp.). Survival in the vertebrate bloodstream depends on antigenic variation of Variant Surface Glycoproteins (VSG) coating the parasite surface. In T. brucei, a model for antigenic variation, monoallelic VSG expression originates from dedicated VSG expression sites (VES). T. brucei VES have a conserved structure consisting of a telomeric VSG locus downstream of unique, repeat sequences and an independent promoter. Additional protein-coding sequences, known as 'Expression Site Associated Genes (ESAGs)', are also often present and are implicated in diverse, bloodstream-stage functions. T. congolense is a related veterinary pathogen, also displaying VSG-mediated antigenic variation. A T. congolense VES has not been described, making it unclear if regulation of VSG expression is conserved between species. Here, we describe a conserved telomeric region associated with VSG loci from long-read DNA sequencing of two T. congolense strains, which consists of a distal repeat, conserved non-coding elements and other genes besides the VSG; although these are not orthologous to T. brucei ESAGs. Most conserved telomeric regions are associated with accessory minichromosomes, but the same structure may also be associated with megabase chromosomes. We propose that this region represents the T. congolense VES, and through comparison with T. brucei, we discuss the parallel evolution of antigenic switching mechanisms, and unique adaptation of the T. brucei VES for developmental regulation of bloodstream-stage genes. Hence, we provide a basis for understanding antigenic switching in T. congolense and the origins of the African trypanosome VES.

Original languageEnglish
Pages (from-to)2458-2473
JournalGenome Biology and Evolution
Volume10
Issue number9
Early online date25 Aug 2018
DOIs
Publication statusPublished - Sep 2018

Keywords

  • Trypanosoma congolens,
  • variant surface glycoprotein
  • expression site
  • telomere
  • antigenic variation
  • ESAG

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