Conservation of metacyclic variant surface glycoprotein expression sites among different trypanosome isolates

We identified in a Trypanosoma brucei brucei strain (AnTat 1) an expression site for a metacyclic variant surface glycoprotein (MVSG) gene (MVSG) that was previously characterized in a T. b. rhodesiense strain (WRATat 1.1). T he 3.4 kb sequences of the: two expression sites are 99.6% identical, with no differences in the sequence of the 1.5 kb MVSG. Two other MVSGs in the W RATat 1.1 genome are not present in the AnTat 1 genome. In addition, five o ther T. b. brucei and T. b. rhodesiense strains, isolated in the same geogr aphic region as the two former strains, do not contain any of these three M VSGs. Two of these five strains, however, appear to possess a very similar MVSG expression site, but with different MVSGs in it. Thus, the presence of the same MVSG in the same expression site in two different isolates is: un usual and may be the result of genetic exchange in the field between T. b. brucei and T. b. rhodesiense isolates. Analysis of other African trypanosom e strains for the presence of the three WRATat 1.1 MVSG expression sites de monstrated that the expression sites' promoter sequences are much more like ly to be present than are specific MVSGs. suggesting that loss of MVSGs is the result of replacement by other MVSGs. The promoter region of the MVSG e xpression site active in the WRATat 1.1 MVAT7 variant was found to be highl y conserved among T. b. brucei, T. b. rhodesiense and T. b. gambiense group 2 isolates, whereas it does not occur in the T. b. gambiense group 1 isola tes tested. A phylogenetic analysis of this promoter region sequence shows that the T. b. gambiense group 2 isolates: form a monophyletic clade well s eparated from the T. b. brucei/T. b. rhodesiense isolates. Thus, whilst the T. b. brucei, T. b. rhodesiense and T. b. gambiense group 2 isolates are c losely related but heterogenous, molecular tools may be developed to distin guish T. b. gambiense group 2 isolates from the others. (C) 2001 Elsevier S cience B.V. All rights: reserved.