A Conserved Telomeric Region Associated with Variant Antigens in Trypanosoma congolense

What is it about?

Trypanosoma congolense is a blood pathogen that infects cattle in Sub-Saharan Africa. These parasites survive in the bloodstream because they employ antigenic variation, which consists on the sequential replacement of variant antigens in their cell surface. These variant antigens, known as variant surface glycoproteins (VSGs), are located in throughout the genome, but mostly in the subtelomeres and small chromosomes. In this paper, we describe a conserved structure among T. congolense telomeres, that is very abundant in VSGs.

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Why is it important?

VSGs are thought to be expressed from specialised sites in chromosome telomeres. In the human-infective, sister-species, T. brucei, they are expressed from the "Bloodstream Expression Sites", which are conserved structures in the telomeres of some megabase chromosomes. However, in T. congolense, the structure of such apparatus remains unknown. The structure we describe in this paper is analogous to that of T. brucei because it also contains a distal repeat, conserved noncoding elements and other genes besides the VSG. Yet, we see that there is no homology between the conserved features, suggesting a parallel evolution of antigenic switching mechanisms and unique adaptation of the T. brucei VSG expression sites for developmental regulation of bloodstream-stage genes.