Capturing the variant surface glycoprotein repertoire (the VSGnome) of Trypanosoma brucei Lister 427.

Trypanosoma brucei evades the adaptive immune response through the expression of antigenically distinct Variant Surface Glycoprotein (VSG) coats. To understand the progression and mechanisms of VSG switching, and to identify the VSGs expressed in populations of trypanosomes, it is desirable to predetermine the available repertoire of VSG genes (the 'VSGnome'). To date, the catalog of VSG genes present in any strain is far from complete and the majority of current information regarding VSGs is derived from the TREU927 strain that is not commonly used as an experimental model. We have assembled, annotated and analyzed 2563 distinct and previously unsequenced genes encoding complete and partial VSGs of the widely used Lister 427 strain of T. brucei. Around 80% of the VSGnome consists of incomplete genes or pseudogenes. Read-depth analysis demonstrated that most VSGs exist as single copies, but 360 exist as two or more indistinguishable copies. The assembled regions include five functional metacyclic VSG expression sites. One third of minichromosome sub-telomeres contain a VSG (64-67 VSGs on ∼96 minichromosomes), of which 85% appear to be functionally competent. The minichromosomal repertoire is very dynamic, differing among clones of the same strain. Few VSGs are unique along their entire length: frequent recombination events are likely to have shaped (and to continue to shape) the repertoire. In spite of their low sequence conservation and short window of expression, VSGs show evidence of purifying selection, with ∼40% of non-synonymous mutations being removed from the population. VSGs show a strong codon-usage bias that is distinct from that of any other group of trypanosome genes. VSG sequences are generally very divergent between Lister 427 and TREU927 strains of T. brucei, but those that are highly similar are not found in 'protected' genomic environments, but may reflect genetic exchange among populations.

Cross GA ，Kim HS ，Wickstead B 《-》

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

Hutchinson OC ，Picozzi K ，Jones NG ，Mott H ，Sharma R ，Welburn SC ，Carrington M ... -  《-》

VSGs Expressed during Natural T. b. gambiense Infection Exhibit Extensive Sequence Divergence and a Subspecies-Specific Bias towards Type B N-Terminal Domains.

So J ，Sudlow S ，Sayeed A ，Grudda T ，Deborggraeve S ，Ngoyi DM ，Desamber DK ，Wickstead B ，Lejon V ，Mugnier MR ... -  《mBio》

VSG 117 gene is conservatively present and early expressed in Trypanosma evansi YNB stock.

African trypanosomes, including Trypanosoma brucei and the closely related species Trypanosoma evansi, are flagellated unicellular parasites that proliferate extracellularly in the mammalian bloodstream and tissue spaces. They evade host immune system by periodically switching their variant surface glycoprotein (VSG) coat. Each trypanosome possesses a vast archive of VSGs with distinct sequence identity and different strains contain different archive of VSGs. VSG 117 was reported as a widespread VSG detected in the genomes of all the T. brucei strains. In this study, the presence and expression of VSG 117 gene was observed in T. evansi YNB stock by RT-PCR with VSG-specific primers. We further confirmed that this VSG tends to be expressed in the early stage of T. evansi infections (on day 12-15) by immuno-screening the previously isolated infected blood samples. It is possible that the VSG 117 gene evolved and spread through the African trypanosome population via genetic exchange, before T. evansi lost its ability to infect tsetse fly. Our finding provided an evidence of the close evolutionary relationship between T. evansi and T. brucei, in the terms of VSG genes.

Jia Y ，Guo L ，Zhao X ，Suo X ... -  《-》

Switching trypanosome coats: what's in the wardrobe?

Taylor JE ，Rudenko G 《TRENDS IN GENETICS》