3D FIB-SEM structural insights into the architecture of sub-pellicular microtubules of Trypanosoma cruzi epimastigotes

From Trypomastigotes to Trypomastigotes: Analyzing the One-Way Intracellular Journey of Trypanosoma cruzi by Ultrastructure Expansion Microscopy

The protozoan parasite Trypanosoma cruzi is the causative agent of Chagas disease, also called American trypanosomiasis. This neglected tropical disease affects millions of individuals across the Americas. To complete its life cycle, T. cruzi parasitizes both vertebrate hosts and its vector, commonly known as the 'kissing bug'. The parasite's survival and proliferation strategies are driven by the diverse environments it encounters. Despite being described by Carlos Chagas in 1909, significant knowledge gaps persist regarding the parasite's various life forms and adaptive capabilities in response to environmental cues. In this study, we employed Ultrastructure Expansion Microscopy to explore the intricate journey of T. cruzi within the host cell. Upon entry into the host cell, trypomastigotes undergo folding, resulting in intermediate forms characterized by a rounded cell body, anterior positioning of basal bodies, and a shortened flagellum. The repositioning of basal bodies and the kinetoplast and the shortening of the flagella mark the culmination of intracellular amastigogenesis. Furthermore, we analyzed intracellular trypomastigogenesis, identifying discrete intermediate forms, including leaf-shaped stages and epimastigote-like forms, which suggests a complex differentiation process. Notably, we did not observe any dividing intracellular epimastigotes, indicating that these may be non-replicative forms within the host cell. Our detailed examination of amastigote cell division revealed semi-closed nuclear mitosis, with mitotic spindle formation independent of basal bodies. This study provides new insights into the morphological and cytoskeletal changes during the intracellular stages of T. cruzi, providing a model for understanding the dynamics of intracellular amastigogenesis and trypomastigogenesis.

Endosymbiosis in trypanosomatids: The bacterium division depends on microtubule dynamism

Microtubules are components of the cytoskeleton that perform essential functions in eukaryotes, such as those related to shape change, motility and cell division. In this context some characteristics of these filaments are essential, such as polarity and dynamic instability. In trypanosomatids, microtubules are integral to ultrastructure organization, intracellular transport and mitotic processes. Some species of trypanosomatids co-evolve with a symbiotic bacterium in a mutualistic association that is marked by extensive metabolic exchanges and a coordinated division of the symbiont with other cellular structures, such as the nucleus and the kinetoplast. It is already established that the bacterium division is microtubule-dependent, so in this work, it was investigated whether the dynamism and remodeling of these filaments is capable of affecting the prokaryote division. To this purpose, Angomonas deanei was treated with Trichostatin A (TSA), a deacetylase inhibitor, and mutant cells for histone deacetylase 6 (HDAC6) were obtained by CRISPR-Cas9. A decrease in proliferation, an enhancement in tubulin acetylation, as well as morphological and ultrastructural changes, were observed in TSA-treated protozoa and mutant cells. In both cases, symbiont filamentation occurred, indicating that prokaryote cell division is dependent on microtubule dynamism.

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.

Implications of Flagellar Attachment Zone Proteins TcGP72 and TcFLA-1BP in Morphology, Proliferation, and Intracellular Dynamics in Trypanosoma cruzi

The highly adaptable parasite Trypanosoma cruzi undergoes complex developmental stages to exploit host organisms effectively. Each stage involves the expression of specific proteins and precise intracellular structural organization. These morphological changes depend on key structures that control intracellular components' growth and redistribution. In trypanosomatids, the flagellar attachment zone (FAZ) connects the flagellum to the cell body and plays a pivotal role in cell expansion and structural rearrangement. While FAZ proteins are well-studied in other trypanosomatids, there is limited knowledge about specific components, organization, and function in T. cruzi. This study employed the CRISPR/Cas9 system to label endogenous genes and conduct deletions to characterize FAZ-specific proteins during epimastigote cell division and metacyclogenesis. In T. cruzi, these proteins exhibited distinct organization compared to their counterparts in T. brucei. TcGP72 is anchored to the flagellar membrane, while TcFLA-1BP is anchored to the membrane lining the cell body. We identified unique features in the organization and function of the FAZ in T. cruzi compared to other trypanosomatids. Deleting these proteins had varying effects on intracellular structures, cytokinesis, and metacyclogenesis. This study reveals specific variations that directly impact the success of cell division and differentiation of this parasite.

Investigating parasites in three dimensions: trends in volume microscopy

To best understand parasite, host, and vector morphologies, host-parasite interactions, and to develop new drug and vaccine targets, structural data should, ideally, be obtained and visualised in three dimensions (3D). Recently, there has been a significant uptake of available 3D volume microscopy techniques that allow collection of data across centimetre (cm) to Angstrom (Å) scales by utilising light, X-ray, electron, and ion sources. Here, we present and discuss microscopy tools available for the collection of 3D structural data, focussing on electron microscopy-based techniques. We highlight their strengths and limitations, such that parasitologists can identify techniques best suited to answer their research questions. Additionally, we review the importance of volume microscopy to the advancement of the field of parasitology.