Discussion

Like Trypanosoma brucei, the livestock pathogen Trypanosoma congolense savannah undergoes a complex life cycle in the tsetse vector, involving morphological and metabolic changes that adapt the cells for survival in different niches within the host insect. In T. brucei the trypomastigote-epimastigote transition is achieved by an asymmetric division of proventricular trypanosomes. As T. congolense makes the same trypomastigote-epimastigote transition in moving from the midgut to the fly mouthparts, we have searched for the analogous stage. We find that in T. congolense, the long proventricular trypomastigotes undergo extensive cell remodelling before repeated asymmetric divisions yielding small daughter cells. In T. brucei there is a single asymmetric division, resulting in one long and one short epimastigote. Thus, despite its close evolutionary relationship with T. brucei and shared developmental route within the insect vector, T. congolense is markedly divergent from its sister species.