Loss of the cytostome-cytopharynx and endocytic ability are late events in Trypanosoma cruzi metacyclogenesis

Abstract

Trypanosoma cruzi epimastigotes uptake nutrients by endocytosis via the cytostome-cytopharynx complex - an anterior opening (cytostome) continuous with a funnel-shaped invagination (cytopharynx) that extends to the posterior of the cell, accompanied by microtubules. During metacyclogenesis - the transformation of epimastigotes into human-infective metacyclic trypomastigotes - the cytostome-cytopharynx complex disappears, as trypomastigotes lose endocytic ability. To date, no studies have examined cytostome-cytopharynx complex disappearance in detail, or determined if endocytic activity persists during metacyclogenesis. Here, we produced 3D reconstructions of metacyclogenesis intermediates (Ia, Ib, Ic) using electron microscopy tomography and focused ion beam-scanning electron microscopy (FIB-SEM), concentrating on the cytostome-cytopharynx complex and adjacent structures, including the preoral ridge (POR). Parasite endocytic potential was examined by incubation of intermediate forms with the endocytic tracer transferrin (Tf)-Au. Ia, Ib and Ic cells were capable of internalizing Tf-Au, and had a shorter cytopharynx than that of epimastigotes, with the cytostome/POR progressively displaced towards the posterior, following the movement of the kinetoplast/flagellar pocket. While some Ic cells had a short cytopharynx with an enlarged proximal end (∼300nm in diameter, larger than that of the cytostome), other Ic cells had no cytopharynx invagination, but retained the cytopharynx microtubules, which were also present in metacyclics. We conclude that cytostome-cytopharynx disappearance and loss of endocytic ability are late events in metacyclogenesis, during which the cytostome is displaced towards the posterior, probably due to a link to the kinetoplast/flagellar pocket. Retention of the cytopharynx microtubules by metacyclics may allow prompt cytostome-cytopharynx reassembly in amastigotes, upon host cell infection.

Benznidazole induces in vitro anaerobic metabolism in Trypanosoma cruzi epimastigotes

“…the metacyclogenesis have been described such as morphology, infectivity and gene expression [10][11][12], the differences in the energetic metabolism throughout the culture growth have not yet been explored. Shah-Simpson et al [13] described the glucose metabolism in epimastigotes, metacyclic trypomastigotes and amastigotes determining the differences in excretion of pyruvate, acetate and alanine.…”

Morphological and Functional Aspects of Cytoskeleton of Trypanosomatids

“…The late intermediate forms did not have a cytopharynx membrane; only the accompanying microtubules remained in this form. In the trypomastigote form, shorter microtubules were still observed [41] (Figure 3C1-C4). …”

Evolution of protein trafficking in kinetoplastid parasites: Complexity and pathogenesis

“…However, T. cruzi epimastigotes possess a cytostome/cytopharynx‐like organelle which has an elongated stiletto‐shaped structure formed by an invagination of the plasma membrane along with sub‐pellicular microtubules . The structure contains a distinct membrane region that is separated from the neighboring flagellar pocket by the preoral ridge and disappears during metacyclogenesis …”