Cloning and analysis of Trypanosoma (Nannomonas) congolense ILNat 2.1 VSG gene

Genes encoding various Trypanosoma (Trypanozoon) brucei variable surface glycoproteins (VSGs) show considerable conservation among different members of this species, known as isotypes. The occurrence of isotypes in other salivarian trypanosomes has not been well documented. We have cloned sequences encoding Trypanosoma (Nannomonas) congolense ILNat 2.1 VSG, and used it in DNA blot hybridization analyses of this and other T. congolense clones originating from geographically separate regions of East Africa. The data indicate that the expression of ILNat 2.1 VSG gene proceeds by duplicative transposition resulting in the presence of an extra expression-linked copy in the expressing clones examined. Furthermore the ILNat 2.1 VSG gene sequence is absent or has greatly diverged, in all other T. (N.) congolense clones that belong to different serodemes. This suggests that some T. (N.) congolense VSGs may be limited to their respective antigen repertoires. The data are discussed in the light of their implications for antigenic variation in T. (N.) congolense, and parasite epidemiology.