Differentiation of Trypanosoma cruzi epimastigotes: Metacyclogenesis and adhesion to substrate are triggered by nutritional stress

Differentiation of Trypanosoma cruzi epimastigotes to metacyclic trypomasti gotes occurs in the insect rectum, after adhesion of the epimastigotes to t he intestinal wall. We investigated the effect of the nutritional stress on the metacyclogenesis process in vitro by incubating epimastigotes in the c hemically defined TAU3AAG medium supplemented with different nutrients. Add ition of fetal bovine serum induced epimastigote growth but inhibited metac yclogenesis. In this medium, few parasites attached to the substrate. Ultra structural analysis demonstrated reservosomes at the posterior end of the e pimastigotes. Incubation of the cells in TAU3AAG medium containing gold-lab eled transferrin resulted in high endocytosis of the marker by both adhered and free-swimming epimastigotes. No intracellular gold particles could be detected in hypomastigotes. Addition of transferrin-gold complexes to adher ed epimastigotes cultivated for 4 days in TAU3AAG medium resulted in decrea se of both metacyclogenesis and adhesion to the substrate, as compared with parasites maintained in transferrin-free medium. Adhesion to the substrate is triggered by nutritional stress, and proteins accumulated in reservosom es are used as energy source during the differentiation. A close relationsh ip exists among nutritional stress, endocytosis of nutrients, adhesion to t he substrate, and cell differentiation in T. cruzi epimastigotes.