Three-dimensional reconstruction of Trypanosoma cruzi epimastigotes and organelle distribution along the cell division cycle.

Trypanosoma cruzi is the protozoan that causes Chagas disease. It divides in the insect vector gut or in the cytosol of an infected mammalian cell. T. cruzi has one mitochondrion, one Golgi complex, one flagellum, and one cytostome. Here, we provide three-dimensional (3D) models of this protozoan based on images obtained from serial sections on electron microscopy at different stages of the cell cycle. Ultrathin serial sections were obtained from Epon™ embedded parasites, photographed in a transmission electron microscope, and 3D models were generated using Reconstruct and Blender 3D modeling softwares. The localization and distribution of organelles was evaluated and attributed to specific morphological patterns and deduced by distribution of specific markers by immunofluorescence analysis. The new features found in the 3D reconstructions are (1) the electron-dense chromatin is interconnected leaving an internal space for a centrally located nucleolus; (2) The kinetoplast is accommodated within a separated branch of the tubular and single mitochondrion; (3) The disk shaped kinetoplast, which is the mitochondrial DNA, duplicates from the interior in G2 phase; (4) The mitochondrion faces the external membrane and shrinks to accommodate an enlarged number of cytosolic vesicles from G1 to G2; (5) The cytostome progress from the parasite surface toward the posterior end contouring the kinetoplast and nucleus and retracts during cell cycle. These new observations might help understanding how organelles are formed and distributed in early divergent eukaryotic cells and provides a useful method to understand the organelle distribution in small eukaryotic cells.