High-resolution scanning electron microscopy of the cytoskeleton of Tritrichomonas foetus

The parabasal filaments of Trichomonas vaginalis: A new filament and observations using 0.8 nm-resolution scanning electron microscopy

Trichomonas vaginalis is the etiologic agent of trichomoniasis, the most common nonviral sexually transmitted infection worldwide, with an estimated 260 million new cases annually. T. vaginalis contains organelles common to all eukaryotic cells, uncommon cell structures such as hydrogenosomes, and a complex and elaborate cytoskeleton constituting the mastigont system. The mastigont system is mainly formed by several proteinaceous structures associated with basal bodies, the pelta-axostylar complex made of microtubules, and striated filaments named the costa and the parabasal filaments (PFs). Although the structural organization of trichomonad cytoskeletons has been analyzed using several techniques, observation using a new generation of scanning electron microscopes with a resolution exceeding 1 nm has allowed more detailed visualization of the three-dimensional organization of the mastigont system. In this study, we have investigated the cytoskeleton of T. vaginalis using a diverse range of scanning probe microscopy techniques, which were complemented by electron tomography and Fast-Fourier methods. This multi-modal approach has allowed us to characterize an unknown parabasal filament and reveal the ultrastructure of other striated fibers that have not been published before. Here, we show the differences in origin, striation pattern, size, localization, and additional details of the PFs, thus improving the knowledge of the cell biology of this parasite.

Contribution of microscopy to a better understanding of the anatomy of pathogenic protists

In this Inaugural Article the author briefly revises its scientific career and how he starts to work with parasitic protozoa. Emphasis is given to his contribution to topics such as a) the structural organization of the surface of protozoa using freeze-fracture and deep-etching; b) the cytoskeleton of protozoa, especially structures such as the subpellicular microtubules of trypanosomatids, the conoid of Toxoplasma gondii, microtubules and inner membrane complex of this protozoan, and the costa of Tritrichomonas foetus; c) the flagellulm of trypanosomatids, that in addition to the axoneme contains a complex network of filaments that constitute the paraflagellar rod; d) special organelles such as the acidocalcisome, hydrogenosome, and glycosome; and e) the highly polarized endocytic pathway found in epimastigote forms of Trypanosoma cruzi.

Expansion Microscopy of trichomonads

Light microscopy has significantly advanced in recent decades, especially concerning the increased resolution obtained in fluorescence images. Here we present the Expansion Microscopy (ExM) technique in two parasites, Trichomonas vaginalis and Tritrichomonas foetus, which significantly improved the localization of distinct proteins closely associated with cytoskeleton by immunofluorescence microscopy. The ExM techniques have been used in various cell types, tissues and other protist parasites. It requires the embedment of the samples in a swellable gel that is highly hydrophilic. As a result, cells are expanded 4.5 times in an isotropic manner, offering a spatial resolution of ∼70 nm. We used this new methodology not only to observe the structural organization of protozoa in more detail but also to increase the resolution by immunofluorescence microscopy of two major proteins such as tubulin, found in structures formed by microtubules, and costain 1, the only protein identified until now in the T. foetus's costa, a unique rod-shaped like structure. The individualized microtubules of the axostyle were seen for the first time in fluorescence microscopy and several other details are presented after this technique.

Unusual Cell Structures and Organelles in Giardia intestinalis and Trichomonas vaginalis Are Potential Drug Targets

This review presents the main cell organelles and structures of two important protist parasites, Giardia intestinalis, and Trichomonas vaginalis; many are unusual and are not found in other eukaryotic cells, thus could be good candidates for new drug targets aimed at improvement of the chemotherapy of diseases caused by these eukaryotic protists. For example, in Giardia, the ventral disc is a specific structure to this parasite and is fundamental for the adhesion and pathogenicity to the host. In Trichomonas, the hydrogenosome, a double membrane-bounded organelle that produces ATP, also can be a good target. Other structures include mitosomes, ribosomes, and proteasomes. Metronidazole is the most frequent compound used to kill many anaerobic organisms, including Giardia and Trichomonas. It enters the cell by passive diffusion and needs to find a highly reductive environment to be reduced to the nitro radicals to be active. However, it provokes several side effects, and some strains present metronidazole resistance. Therefore, to improve the quality of the chemotherapy against parasitic protozoa is important to invest in the development of highly specific compounds that interfere with key steps of essential metabolic pathways or in the functional macromolecular complexes which are most often associated with cell structures and organelles.

Ultrastructural and Functional Analysis of a Novel Extra-Axonemal Structure in Parasitic Trichomonads

Trichomonas vaginalis and Tritrichomonas foetus are extracellular flagellated parasites that inhabit humans and other mammals, respectively. In addition to motility, flagella act in a variety of biological processes in different cell types, and extra-axonemal structures (EASs) have been described as fibrillar structures that provide mechanical support and act as metabolic, homeostatic, and sensory platforms in many organisms. It has been assumed that T. vaginalis and T. foetus do not have EASs. However, here, we used complementary electron microscopy techniques to reveal the ultrastructure of EASs in both parasites. Such EASs are thin filaments (3-5 nm diameter) running longitudinally along the axonemes and surrounded by the flagellar membrane, forming prominent flagellar swellings. We observed that the formation of EAS increases after parasite adhesion on the host cells, fibronectin, and precationized surfaces. A high number of rosettes, clusters of intramembrane particles that have been proposed as sensorial structures, and microvesicles protruding from the membrane were observed in the EASs. Our observations demonstrate that T. vaginalis and T. foetus can connect to themselves by EASs present in flagella. The protein VPS32, a member of the ESCRT-III complex crucial for diverse membrane remodeling events, the pinching off and release of microvesicles, was found in the surface as well as in microvesicles protruding from EASs. Moreover, we demonstrated that the formation of EAS also increases in parasites overexpressing VPS32 and that T. vaginalis-VPS32 parasites showed greater motility in semisolid agar. These results provide valuable data about the role of the flagellar EASs in the cell-to-cell communication and pathogenesis of these extracellular parasites.

Costain 1 (ARM19800.1) - The first identified protein of the costa of the pathogenic protozoan Tritrichomonas foetus

Protists members of the Trichomonadidae and Tritrichomonadidae families include agents of trichomoniasis that constitute important parasitic diseases in humans and in animals of veterinary interest. One of the characteristic features of these eukaryotic microorganisms is that they contain a fibrous structure known as the costa as an important cytoskeleton structure, that differs in several aspects from other cytoskeleton structures found in eukaryotic cells. Previous proteomic analysis of an enriched costa fraction revealed the presence of several hypothetical proteins. Here we describe the localization of one of the most prevalent protein found in this previously made proteomic assay to confirm its presence in the costa of Tritrichomonas foetus. A peptide sequence of the hypothetical protein ARM19800.1 was selected for the production of specific polyclonal antibodies and its specificity was confirmed by Western Blotting using an enriched costa fraction. Next, the specific localization of the selected protein was evaluated by immunofluorescence and electron microscopy immunocytochemistry. Our observations clearly showed that the ARM 19800.1 protein is indeed localized in the costa and displays an almost periodic labeling pattern. Since this is the first protein identified in the costa, it was designated as costain 1. A better understanding of a structure as peculiar as the costa is of great biological and evolutionary importance due to the fact that it contains unique proteins, it may represent a possible chemotherapy target and it may correspond to antigens of interest in immunodiagnosis and/or vaccine development.

New advances in scanning microscopy and its application to study parasitic protozoa

Scanning electron microscopy has been used to observe and study parasitic protozoa for at least 40 years. However, field emission electron sources, as well as improvements in lenses and detectors, brought the resolution power of scanning electron microscopes (SEM) to a new level. Parallel to the refinement of instruments, protocols for preservation of the ultrastructure, immunolabeling, exposure of cytoskeleton and inner structures of parasites and host cells were developed. This review is focused on protozoan parasites of medical and veterinary relevance, e.g., Toxoplasma gondii, Tritrichomonas foetus, Giardia intestinalis, and Trypanosoma cruzi, compilating the main achievements in describing the fine ultrastructure of their surface, cytoskeleton and interaction with host cells. Two new resources, namely, Helium Ion Microscopy (HIM) and Slice and View, using either Focused Ion Beam (FIB) abrasion or Microtome Serial Sectioning (MSS) within the microscope chamber, combined to backscattered electron imaging of fixed (chemically or by quick freezing followed by freeze substitution and resin embedded samples is bringing an exponential amount of valuable information. In HIM there is no need of conductive coating and the depth of field is much higher than in any field emission SEM. As for FIB- and MSS-SEM, high resolution 3-D models of areas and volumes larger than any other technique allows can be obtained. The main results achieved with all these technological tools and some protocols for sample preparation are included in this review. In addition, we included some results obtained with environmental/low vacuum scanning microscopy and cryo-scanning electron microscopy, both promising, but not yet largely employed SEM modalities.

Draft Genome Sequence of Tritrichomonas foetus Strain K

The protist Tritrichomonas foetus (Excavata, Parabasalia) is a parasite that causes bovine and feline trichomonosis. Bovine trichomonosis is a venereal disease that leads to abortion and reproductive problems in herds. Feline trichomonosis affects domestic cats. Here, we report the genome sequence of the T. foetus K strain, isolated in Brazil.

The costa of trichomonads: A complex macromolecular cytoskeleton structure made of uncommon proteins

BACKGROUND INFORMATION

The costa is a prominent striated fibre that is found in protozoa of the Trichomonadidae family that present an undulating membrane. It is composed primarily of proteins that have not yet been explored. In this study, we used cell fractionation to obtain a highly enriched costa fraction whose structure and composition was further analysed by electron microscopy and mass spectrometry.

RESULTS

Electron microscopy of negatively stained samples revealed that the costa, which is a periodic structure with alternating electron-dense and electron-lucent bands, displays three distinct regions, named the head, neck and body. Fourier transform analysis showed that the electron-lucent bands present sub-bands with a regular pattern. An analysis of the costa fraction via one- and two-dimensional electrophoresis and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) allowed the identification of 54 hypothetical proteins. Fourteen of those proteins were considered to be major components of the fraction.

CONCLUSIONS

The costa of T. foetus is a complex and organised cytoskeleton structure made of a large number of proteins which is assembled into filamentous structures. Some of these proteins exhibit uncharacterised domains and no function related according to gene ontology, suggesting that the costa structure may be formed by a new class of proteins that differ from those previously described in other organisms. Seven of these proteins contain prefoldin domains displaying coiled-coil regions. This propriety is shared with proteins of the striated fibres of other protozoan as well as in intermediate filaments.

SIGNIFICANCE

Our observations suggest the presence of a new class of the cytoskeleton filaments in T. foetus. We believe that our data could auxiliate in determining the specific locations of these proteins in the distinct regions that compose the costa, as well as to define the functional roles of each component. Therefore, our study will help in the better understanding of the organisation and function of this structure in unicellular organisms.

The Cytoskeleton of Parabasalian Parasites Comprises Proteins that Share Properties Common to Intermediate Filament Proteins

Certain protist lineages bear cytoskeletal structures that are germane to them and define their individual group. Trichomonadida are excavate parasites united by a unique cytoskeletal framework, which includes tubulin-based structures such as the pelta and axostyle, but also other filaments such as the striated costa whose protein composition remains unknown. We determined the proteome of the detergent-resistant cytoskeleton of Tetratrichomonas gallinarum. 203 proteins with homology to Trichomonas vaginalis were identified, which contain significantly more long coiled-coil regions than control protein sets. Five candidates were shown to associate with previously described cytoskeletal structures including the costa and the expression of a single T. vaginalis protein in T. gallinarum induced the formation of accumulated, striated filaments. Our data suggests that filament-forming proteins of protists other than actin and tubulin share common structural properties with metazoan intermediate filament proteins, while not being homologous. These filament-forming proteins might have evolved many times independently in eukaryotes, or simultaneously in a common ancestor but with different evolutionary trajectories downstream in different phyla. The broad variety of filament-forming proteins uncovered, and with no homologs outside of the Trichomonadida, once more highlights the diverse nature of eukaryotic proteins with the ability to form unique cytoskeletal filaments.