LAUSR

ABSTRACT The cytostome–cytopharynx complex is the main site for endocytosis in epimastigotes of Trypanosoma cruzi. It consists of an opening at the plasma membrane surface – the cytostome – followed by a membrane invagination – the cytopharynx. In G1/S cells, this structure is associated with two specific sets of microtubules, a quartet and a triplet. Here, we used electron microscopy and electron tomography to build 3D models of the complex at different stages of the cell cycle. The cytostome–cytopharynx is absent in late G2 and M phase cells, whereas early G2 cells have either a short cytopharynx or no visible complex, with numerous vesicles aligned to the cytostome–cytopharynx microtubules. The microtubule quartet remains visible throughout cell division (albeit in a shorter form), and is duplicated during G2/M. In contrast, the microtubule triplet is absent during late G2/M. Cells in cytokinesis have an invagination of the flagellar pocket membrane likely to represent early stages in cytostome–cytopharynx assembly. Cells in late cytokinesis have two fully developed cytostome–cytopharynx complexes. Our data suggest that the microtubule quartet serves as a guide for new cytostome–cytopharynx assembly. Summary: As shown by focused ion beam scanning electron microscopy, the cytostome–cytopharynx complex of T. cruzi epimastigotes disassembles in mitosis, to assemble again in each daughter cell at the end of cell division.