Extracellular vesicles shed by Trypanosoma cruzi are linked to small RNA pathways, life cycle regulation, and susceptibility to infection of mammalian cells.

The protozoan parasite Trypanosoma cruzi has a complex life cycle characterized by intracellular and extracellular forms alternating between invertebrate and mammals. To cope with these changing environments, T. cruzi undergoes rapid changes in gene expression, which are achieved essentially at the posttranscriptional level. At present, expanding families of small RNAs are recognized as key players in novel forms of posttranscriptional gene regulation in most eukaryotes. However, T. cruzi lacks canonical small RNA pathways. In a recent work, we reported the presence of alternate small RNA pathways in T. cruzi mainly represented by a homogeneous population of tRNA-derived small RNAs (tsRNAs). In T. cruzi epimastigotes submitted to nutrient starvation, tsRNAs colocalized with an argonaute protein distinctive of trypanosomatids (TcPIWI-tryp) and were recruited to particular cytoplasmic granules. Using epifluorescence and electronic microscopy, we observed that tsRNAs and the TcPIWI-tryp protein were recruited mainly to reservosomes and other intracellular vesicles including endosome-like vesicles and vesicular structures resembling the Golgi complex. These data suggested that, in T. cruzi, tsRNA biogenesis is probably part of endocytic/exocytic routes. We also demonstrated that epimastigotes submitted to nutrient starvation shed high levels of vesicles to the extracellular medium, which carry small tRNAs and TcPIWI-tryp proteins as cargo. At least a fraction of extracellular vesicle cargo was transferred between parasites and to mammalian susceptible cells. Our data afford experimental evidence, indicating that extracellular vesicles shed by T. cruzi promote not only life cycle transition of epimastigotes to trypomastigote forms but also infection susceptibility of mammalian cells.

Gene expression changes induced by Trypanosoma cruzi shed microvesicles in mammalian host cells: relevance of tRNA-derived halves.

At present, noncoding small RNAs are recognized as key players in novel forms of posttranscriptional gene regulation in most eukaryotes. However, canonical small RNA pathways seem to be lost or excessively simplified in some unicellular organisms including Trypanosoma cruzi which lack functional RNAi pathways. Recently, we reported the presence of alternate small RNA pathways in T. cruzi mainly represented by homogeneous populations of tRNA- and rRNA-derived small RNAs, which are secreted to the extracellular medium included in extracellular vesicles. Extracellular vesicle cargo could be delivered to other parasites and to mammalian susceptible cells promoting metacyclogenesis and conferring susceptibility to infection, respectively. Here we analyzed the changes in gene expression of host HeLa cells induced by extracellular vesicles from T. cruzi. As assessed by microarray assays a large set of genes in HeLa cells were differentially expressed upon incorporation of T. cruzi-derived extracellular vesicles. The elicited response modified mainly host cell cytoskeleton, extracellular matrix, and immune responses pathways. Some genes were also modified by the most abundant tRNA-derived small RNAs included in extracellular vesicles. These data suggest that microvesicles secreted by T. cruzi could be relevant players in early events of the T. cruzi host cell interplay.

Life history of Acanthocollaritrema umbilicatum Travassos, Freitas and Bührnheim, 1965 (Digenea: Cryptogonimidae).

The trematode Acanthocollaritrema umbilicatum Travassos, Freitas and Bührnheim 1965 is redescribed and data on its life cycle are provided for the first time. Adults were obtained from the common snook, Centropomus undecimalis (Bloch 1792), and both rediae and cercariae from the snail Heleobia australis (d'Orbigny 1835), a new intermediate host. Metacercariae were found encysted among the scales, fins, and musculature and in the buccal cavity of naturally infected fishes, Poecilia vivipara Bloch and Schneider, 1801, Jenynsia multidentata (Jenyns 1842), and Phalloptychus januarius (Hensel 1868), all new intermediate hosts. The examination of the type and freshly obtained adults of A. umbilicatum has shown that they possess 54-64 circumoral spines, in a double row. Experimental infections were achieved in the intermediate hosts H. australis and P. vivipara.