The three-dimensional structure of the cytostome-cytopharinx complex of Trypanosoma cruzi epimastigotes

Abstract

The cytostome-cytopharinx complex is the main site of endocytosis of Trypanosoma cruzi epimastigotes. Little is known about the detailed morphology of this remarkable structure. We used serial electron tomography and focused ion beam-scanning electron microscopy to reconstruct the entire complex, including the surrounding cytoskeleton and vesicles. Focusing on cells that had taken up gold-labeled tracers, we produced 3D snapshots of the process of endocytosis. The cytostome cytoskeleton was composed of two microtubule sets: a triplet that started underneath the cytostome membrane and a quartet that originated underneath the flagellar pocket membrane and followed the preoral ridge before reaching the cytopharinx. The two sets accompanied the cytopharinx forming a ‘gutter’ and leaving a microtubule-free side, where vesicles were found associated. Cargo was unevenly distributed along the lumen of the cytopharinx, forming clusters. The cytopharinx was slightly longer in the G2 phase of the cell cycle, although it did not reach post nuclear region due to a bend in its path. Therefore, the cytopharinx is a dynamic structure, undergoing remodeling, likely associated with endocytic activity and the preparation for cell division.