The paraflagellar rod of kinetoplastid parasites: from structure to components and function

Trypanosome doublet microtubule structures reveal flagellum assembly and motility mechanisms

The flagellum of Trypanosoma brucei drives the parasite's characteristic screw-like motion and is essential for its replication, transmission, and pathogenesis. However, the molecular details of this process remain unclear. Here, we present high-resolution (up to 2.8 angstrom) cryo-electron microscopy structures of T. brucei flagellar doublet microtubules (DMTs). Integrated modeling identified 154 different axonemal proteins inside and outside the DMT and, together with genetic and proteomic interrogation, revealed conserved and trypanosome-specific foundations of flagellum assembly and motility. We captured axonemal dynein motors in their pre-power stroke state. Comparing atomic models between pre- and post-power strokes defined how dynein structural changes drive sliding of adjacent DMTs during flagellar beating. This study illuminates structural dynamics underlying flagellar motility and identifies pathogen-specific proteins to consider for therapeutic interventions targeting neglected diseases.

Cytoplasmic preassembly of the flagellar outer dynein arm complex in Trypanosoma brucei

The outer dynein arm (ODA) is a large, multimeric protein complex essential for ciliary motility. The composition and assembly of ODA are best characterized in the green algae Chlamydomonas reinhardtii, where individual ODA subunits are synthesized and preassembled into a mature complex in the cytosol prior to ciliary import. The single-cellular parasite Trypanosoma brucei contains a motile flagellum essential for cell locomotion and pathogenesis. Similar to human motile cilia, T. brucei flagellum contains a two-headed ODA complex arranged at 24 nm intervals along the axonemal microtubule doublets. The subunit composition and the preassembly of the ODA complex in T. brucei, however, have not been investigated. In this study, we affinity-purified the ODA complex from T. brucei cytoplasmic extract. Proteomic analyses revealed the presence of two heavy chains (ODAα and ODAβ), two intermediate chains (IC1and IC2) and several light chains. We showed that both heavy chains and both intermediate chains are indispensable for flagellar ODA assembly. Our study also provided biochemical evidence supporting the presence of a cytoplasmic, preassembly pathway for T. brucei ODA.

Spatial confinement of Trypanosoma brucei in microfluidic traps provides a new tool to study free swimming parasites

Trypanosoma brucei is the causative agent of African trypanosomiasis and is transmitted by the tsetse fly (Glossina spp.). All stages of this extracellular parasite possess a single flagellum that is attached to the cell body and confers a high degree of motility. While several stages are amenable to culture in vitro, longitudinal high-resolution imaging of free-swimming parasites has been challenging, mostly due to the rapid flagellar beating that constantly twists the cell body. Here, using microfabrication, we generated various microfluidic devices with traps of different geometrical properties. Investigation of trap topology allowed us to define the one most suitable for single T. brucei confinement within the field of view of an inverted microscope while allowing the parasite to remain motile. Chips populated with V-shaped traps allowed us to investigate various phenomena in cultured procyclic stage wild-type parasites, and to compare them with parasites whose motility was altered upon knockdown of a paraflagellar rod component. Among the properties that we investigated were trap invasion, parasite motility, and the visualization of organelles labelled with fluorescent dyes. We envisage that this tool we have named "Tryp-Chip" will be a useful tool for the scientific community, as it could allow high-throughput, high-temporal and high-spatial resolution imaging of free-swimming T. brucei parasites.

The Intracellular Amastigote of Trypanosoma cruzi Maintains an Actively Beating Flagellum

Throughout its complex life cycle, the uniflagellate parasitic protist, Trypanosoma cruzi, adapts to different host environments by transitioning between elongated motile extracellular stages and a nonmotile intracellular amastigote stage that replicates in the cytoplasm of mammalian host cells. Intracellular T. cruzi amastigotes retain a short flagellum that extends beyond the opening of the flagellar pocket with access to the extracellular milieu. Contrary to the long-held view that the T. cruzi amastigote flagellum is inert, we report that this organelle is motile and displays quasiperiodic beating inside mammalian host cells. Kymograph analysis determined an average flagellar beat frequency of ~0.7 Hz for intracellular amastigotes and similar beat frequencies for extracellular amastigotes following their isolation from host cells. Inhibitor studies reveal that flagellar motility in T. cruzi amastigotes is critically dependent on parasite mitochondrial oxidative phosphorylation. These novel observations reveal that flagellar motility is an intrinsic property of T. cruzi amastigotes and suggest that this organelle may play an active role in the parasite infection process. IMPORTANCE Understanding the interplay between intracellular pathogens and their hosts is vital to the development of new treatments and preventive strategies. The intracellular "amastigote" stage of the Chagas disease parasite, Trypanosoma cruzi, is a critical but understudied parasitic life stage. Previous work established that cytosolically localized T. cruzi amastigotes engage physically and selectively with host mitochondria using their short, single flagellum. The current study was initiated to examine the dynamics of the parasite flagellum-host mitochondrial interaction through live confocal imaging and led to the unexpected discovery that the T. cruzi amastigote flagellum is motile.

Proximity-dependent biotinylation and identification of flagellar proteins in Trypanosoma cruzi

The flagellated kinetoplastid protozoan and causative agent of human Chagas disease, Trypanosoma cruzi , inhabits both invertebrate and mammalian hosts over the course of its complex life cycle. In these disparate environments, T. cruzi uses its single flagellum to propel motile life stages and in some instances, to establish intimate contact with the host. Beyond its role in motility, the functional capabilities of the T. cruzi flagellum have not been defined. Moreover, the lack of proteomic information for this organelle, in any parasite life stage, has limited functional investigation. In this study, we employed a proximity-dependent biotinylation approach based on the differential targeting of the biotin ligase, TurboID, to the flagellum or cytosol in replicative stages of T. cruzi , to identify flagellar-enriched proteins by mass spectrometry. Proteomic analysis of the resulting biotinylated protein fractions yielded 218 candidate flagellar proteins in T. cruzi epimastigotes (insect stage) and 99 proteins in intracellular amastigotes (mammalian stage). Forty of these flagellar-enriched proteins were common to both parasite life stages and included orthologs of known flagellar proteins in other trypanosomatid species, proteins specific to the T. cruzi lineage and hypothetical proteins. With the validation of flagellar localization for several of the identified candidates, our results demonstrate that TurboID-based proximity proteomics is an effective tool for probing subcellular compartments in T. cruzi . The proteomic datasets generated in this work offer a valuable resource to facilitate functional investigation of the understudied T. cruzi flagellum.

Ciliary mechanosensation - roles of polycystins and mastigonemes

Cilia are surface-exposed organelles that provide motility and sensory functions for cells, and it is widely believed that mechanosensation can be mediated through cilia. Polycystin-1 and -2 (PC-1 and PC-2, respectively) are transmembrane proteins that can localize to cilia; however, the molecular mechanisms by which polycystins contribute to mechanosensation are still controversial. Studies detail two prevailing models for the molecular roles of polycystins on cilia; one stresses the mechanosensation capabilities and the other unveils their ligand-receptor nature. The discovery that polycystins interact with mastigonemes, the 'hair-like' protrusions of flagella, is a novel finding in identifying the interactors of polycystins in cilia. While the functions of polycystins proposed by both models may coexist in cilia, it is hoped that a precise understanding of the mechanism of action of polycystins can be achieved by uncovering their distribution and interacting factors inside cilia. This will hopefully provide a satisfying answer to the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD), which is caused by mutations in PC-1 and PC-2. In this Review, we discuss the characteristics of polycystins in the context of cilia and summarize the functions of mastigonemes in unicellular ciliates. Finally, we compare flagella and molecular features of PC-2 between unicellular and multicellular organisms, with the aim of providing new insights into the ciliary roles of polycystins in general.

Genome-wide subcellular protein map for the flagellate parasite Trypanosoma brucei

Trypanosoma brucei is a model trypanosomatid, an important group of human, animal and plant unicellular parasites. Understanding their complex cell architecture and life cycle is challenging because, as with most eukaryotic microbes, ~50% of genome-encoded proteins have completely unknown functions. Here, using fluorescence microscopy and cell lines expressing endogenously tagged proteins, we mapped the subcellular localization of 89% of the T. brucei proteome, a resource we call TrypTag. We provide clues to function and define lineage-specific organelle adaptations for parasitism, mapping the ultraconserved cellular architecture of eukaryotes, including the first comprehensive 'cartographic' analysis of the eukaryotic flagellum, which is vital for morphogenesis and pathology. To demonstrate the power of this resource, we identify novel organelle subdomains and changes in molecular composition through the cell cycle. TrypTag is a transformative resource, important for hypothesis generation for both eukaryotic evolutionary molecular cell biology and fundamental parasite cell biology.

Three-dimensional flagella structures from animals' closest unicellular relatives, the Choanoflagellates

In most eukaryotic organisms, cilia and flagella perform a variety of life-sustaining roles related to environmental sensing and motility. Cryo-electron microscopy has provided considerable insight into the morphology and function of flagellar structures, but studies have been limited to less than a dozen of the millions of known eukaryotic species. Ultrastructural information is particularly lacking for unicellular organisms in the Opisthokonta clade, leaving a sizeable gap in our understanding of flagella evolution between unicellular species and multicellular metazoans (animals). Choanoflagellates are important aquatic heterotrophs, uniquely positioned within the opisthokonts as the metazoans' closest living unicellular relatives. We performed cryo-focused ion beam milling and cryo-electron tomography on flagella from the choanoflagellate species Salpingoeca rosetta. We show that the axonemal dyneins, radial spokes, and central pair complex in S. rosetta more closely resemble metazoan structures than those of unicellular organisms from other suprakingdoms. In addition, we describe unique features of S. rosetta flagella, including microtubule holes, microtubule inner proteins, and the flagellar vane: a fine, net-like extension that has been notoriously difficult to visualize using other methods. Furthermore, we report barb-like structures of unknown function on the extracellular surface of the flagellar membrane. Together, our findings provide new insights into choanoflagellate biology and flagella evolution between unicellular and multicellular opisthokonts.

Flagellar energy costs across the tree of life

Flagellar-driven motility grants unicellular organisms the ability to gather more food and avoid predators, but the energetic costs of construction and operation of flagella are considerable. Paths of flagellar evolution depend on the deviations between fitness gains and energy costs. Using structural data available for all three major flagellar types (bacterial, archaeal, and eukaryotic), flagellar construction costs were determined for Escherichia coli, Pyrococcus furiosus, and Chlamydomonas reinhardtii. Estimates of cell volumes, flagella numbers, and flagellum lengths from the literature yield flagellar costs for another ~200 species. The benefits of flagellar investment were analysed in terms of swimming speed, nutrient collection, and growth rate; showing, among other things, that the cost-effectiveness of bacterial and eukaryotic flagella follows a common trend. However, a comparison of whole-cell costs and flagellum costs across the Tree of Life reveals that only cells with larger cell volumes than the typical bacterium could evolve the more expensive eukaryotic flagellum. These findings provide insight into the unsolved evolutionary question of why the three domains of life each carry their own type of flagellum.

Finding Correlations Between mRNA and Protein Levels in Leishmania Development: Is There a Discrepancy?

Multiple genes and proteins have been identified as differentially expressed in the stages of the Leishmania life cycle. The differentiation processes are implicated in specific transcriptional and proteomic adjustments driven by gene expression regulation mechanisms. Leishmania parasites lack gene-specific transcriptional control, and gene expression regulation mostly depends on posttranscriptional mechanisms. Due to the lack of transcriptional regulation, criticism regarding the relevance of transcript quantification as a possible and efficient prediction of protein levels is recurrent in studies that use transcriptomic information. The advent of high-throughput technologies has improved the analysis of genomes, transcriptomes and proteomes for different organisms under several conditions. Nevertheless, defining the correlation between transcriptional and proteomic profiles requires arduous and expensive work and remains a challenge in Leishmania. In this review, we analyze transcriptomic and proteomic data for several Leishmania species in two different stages of the parasite life cycle: metacyclogenesis and amastigogenesis (amastigote differentiation). We found a correlation between mRNA and protein levels of 60.9% and 69.8% for metacyclogenesis and amastigogenesis, respectively; showing that majority mRNA and protein levels increase or decrease concomitantly. Among the analyzed genes that did not present correlation indicate that transcriptomic data should be carefully interpreted as protein expression. We also discuss possible explanations and mechanisms involved for this lack of correlation.

A Spef1-interacting microtubule quartet protein in Trypanosoma brucei promotes flagellar inheritance by regulating basal body segregation

The human parasite Trypanosoma brucei contains a motile flagellum that determines the plane of cell division, controls cell morphology, and mediates cell-cell communication. During the cell cycle, inheritance of the newly formed flagellum requires its correct positioning toward the posterior of the cell, which depends on the faithful segregation of multiple flagellum-associated cytoskeletal structures including the basal body, the flagellar pocket collar, the flagellum attachment zone, and the hook complex. A specialized group of four microtubules termed the microtubule quartet (MtQ) originates from the basal body and runs through the flagellar pocket collar and the hook complex to extend, along the flagellum attachment zone, toward the anterior of the cell. However, the physiological function of the MtQ is poorly understood, and few MtQ-associated proteins have been identified and functionally characterized. We report here that an MtQ-localized protein named NHL1 interacts with the microtubule-binding protein TbSpef1 and depends on TbSpef1 for its localization to the MtQ. We show that RNAi-mediated knockdown of NHL1 impairs the segregation of flagellum-associated cytoskeletal structures, resulting in mispositioning of the new flagellum. Furthermore, knockdown of NHL1 also causes misplacement of the cell division plane in dividing trypanosome cells, halts cleavage furrow ingression, and inhibits completion of cytokinesis. These findings uncover a crucial role for the MtQ-associated protein NHL1 in regulating basal body segregation to promote flagellar inheritance in T. brucei.

Structure, function and druggability of the African trypanosome flagellum

African trypanosomes are early branching protists that cause human and animal diseases, termed trypanosomiases. They have been under intensive study for more than 100 years and have contributed significantly to our understanding of eukaryotic biology. The combination of conserved and parasite-specific features mean that their flagellum has gained particular attention. Here, we discuss the different structural features of the flagellum and their role in transmission and virulence. We highlight the possibilities of targeting flagellar function to cure trypanosome infections and help in the fight to eliminate trypanosomiases.

Restriction of intraflagellar transport to some microtubule doublets: An opportunity for cilia diversification?

Cilia are unique eukaryotic organelles and exhibit remarkable conservation across evolution. Nevertheless, very different types of configurations are encountered, raising the question of their evolution. Cilia are constructed by intraflagellar transport (IFT), the movement of large protein complexes or trains that deliver cilia components to the distal tip for assembly. Recent data revealed that IFT trains are restricted to some but not all nine doublet microtubules in the protist Trypanosoma brucei. Here, we propose that restricted positioning of IFT trains could offer potent options for cilia to evolve towards more complex (addition of new structural elements like in spermatozoa) or simpler configuration (loss of some elements like in primary cilia), and therefore be a driver of cilia diversification. We present two hypotheses to explain how IFT trains could be restricted to some doublets, either by a triage process taking place at the basal body level or by the development of molecular differences between ciliary microtubules.

New Vistas in the Biology of the Flagellum—Leishmania Parasites

Like other kinetoplastid protozoa, the flagellum in Leishmania parasites plays central roles throughout the life cycle. Discoveries over the past decade have begun to elucidate flagellar functions at the molecular level in both the insect vector stage promastigotes and intra-macrophage amastigotes. This focused review will highlight recent advances that contribute to understanding flagellar function in the various biological contexts encountered by Leishmania parasites.

Profilin is involved in G1 to S phase progression and mitotic spindle orientation during Leishmania donovani cell division cycle

Profilin is a multi-ligand binding protein, which is a key regulator of actin dynamics and involved in regulating several cellular functions. It is present in all eukaryotes, including trypanosomatids such as Leishmania. However, not much is known about its functions in these organisms. Our earlier studies have shown that Leishmania parasites express a single homologue of profilin (LdPfn) that binds actin, phosphoinositides and poly- L- proline motives, and depletion of its intracellular pool to 50%of normal levels affects the cell growth and intracellular trafficking. Here, we show, employing affinity pull-down and mass spectroscopy, that LdPfn interacted with a large number of proteins, including those involved in mRNA processing and protein translation initiation, such as eIF4A1. Further, we reveal, using mRNA Seq analysis, that depletion of LdPfn in Leishmania cells (LdPfn^+/-) resulted in significantly reduced expression of genes which encode proteins involved in cell cycle regulation, mRNA translation initiation, nucleosides and amino acids transport. In addition, we show that in LdPfn^+/- cells, cellular levels of eIF4A1 protein were significantly decreased, and during their cell division cycle, G1-to-S phase progression was delayed and orientation of mitotic spindle altered. These changes were, however, reversed to normal by episomal expression of GFP-LdPfn in LdPfn^+/- cells. Taken together, our results indicate that profilin is involved in regulation of G1-to-S phase progression and mitotic spindle orientation in Leishmania cell cycle, perhaps through its interaction with elF4A1 protein.

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.

The distinctive flagellar proteome of Euglena gracilis illuminates the complexities of protistan flagella adaptation

The eukaryotic flagellum/cilium is a prominent organelle with conserved structure and diverse functions. Euglena gracilis, a photosynthetic and highly adaptable protist, employs its flagella for both locomotion and environmental sensing. Using proteomics of isolated E. gracilis flagella we identify nearly 1700 protein groups, which challenges previous estimates of the protein complexity of motile eukaryotic flagella. We not only identified several unexpected similarities shared with mammalian flagella, including an entire glycolytic pathway and proteasome, but also document a vast array of flagella-based signal transduction components that coordinate gravitaxis and phototactic motility. By contrast, the pellicle was found to consist of > 900 protein groups, containing additional structural and signalling components. Our data identify significant adaptations within the E. gracilis flagellum, many of which are clearly linked to the highly flexible lifestyle.

Structure of the trypanosome paraflagellar rod and insights into non-planar motility of eukaryotic cells

Eukaryotic flagella (synonymous with cilia) rely on a microtubule-based axoneme, together with accessory filaments to carryout motility and signaling functions. While axoneme structures are well characterized, 3D ultrastructure of accessory filaments and their axoneme interface are mostly unknown, presenting a critical gap in understanding structural foundations of eukaryotic flagella. In the flagellum of the protozoan parasite Trypanosoma brucei (T. brucei), the axoneme is accompanied by a paraflagellar rod (PFR) that supports non-planar motility and signaling necessary for disease transmission and pathogenesis. Here, we employed cryogenic electron tomography (cryoET) with sub-tomographic averaging, to obtain structures of the PFR, PFR-axoneme connectors (PACs), and the axonemal central pair complex (CPC). The structures resolve how the 8 nm repeat of the axonemal tubulin dimer interfaces with the 54 nm repeat of the PFR, which consist of proximal, intermediate, and distal zones. In the distal zone, stacked "density scissors" connect with one another to form a "scissors stack network (SSN)" plane oriented 45° to the axoneme axis; and ~370 parallel SSN planes are connected by helix-rich wires into a paracrystalline array with ~90% empty space. Connections from these wires to the intermediate zone, then to overlapping layers of the proximal zone and to the PACs, and ultimately to the CPC, point to a contiguous pathway for signal transmission. Together, our findings provide insights into flagellum-driven, non-planar helical motility of T. brucei and have broad implications ranging from cell motility and tensegrity in biology, to engineering principles in bionics.

Basic Biology of Trypanosoma brucei with Reference to the Development of Chemotherapies

Trypanosoma brucei are protozoan parasites that cause the lethal human disease African sleeping sickness and the economically devastating disease of cattle, Nagana. African sleeping sickness, also known as Human African Trypanosomiasis (HAT), threatens 65 million people and animal trypanosomiasis makes large areas of farmland unusable. There is no vaccine and licensed therapies against the most severe, late-stage disease are toxic, impractical and ineffective. Trypanosomes are transmitted by tsetse flies, and HAT is therefore predominantly confined to the tsetse fly belt in sub-Saharan Africa. They are exclusively extracellular and they differentiate between at least seven developmental forms that are highly adapted to host and vector niches. In the mammalian (human) host they inhabit the blood, cerebrospinal fluid (late-stage disease), skin, and adipose fat. In the tsetse fly vector they travel from the tsetse midgut to the salivary glands via the ectoperitrophic space and proventriculus. Trypanosomes are evolutionarily divergent compared with most branches of eukaryotic life. Perhaps most famous for their extraordinary mechanisms of monoallelic gene expression and antigenic variation, they have also been investigated because much of their biology is either highly unconventional or extreme. Moreover, in addition to their importance as pathogens, many researchers have been attracted to the field because trypanosomes have some of the most advanced molecular genetic tools and database resources of any model system. The following will cover just some aspects of trypanosome biology and how its divergent biochemistry has been leveraged to develop drugs to treat African sleeping sickness. This is by no means intended to be a comprehensive survey of trypanosome features. Rather, I hope to present trypanosomes as one of the most fascinating and tractable systems to do discovery biology.

The biomechanical role of extra-axonemal structures in shaping the flagellar beat of Euglena gracilis

We propose and discuss a model for flagellar mechanics in Euglena gracilis. We show that the peculiar non-planar shapes of its beating flagellum, dubbed 'spinning lasso', arise from the mechanical interactions between two of its inner components, namely, the axoneme and the paraflagellar rod. The spontaneous shape of the axoneme and the resting shape of the paraflagellar rod are incompatible. Thus, the complex non-planar configurations of the coupled system emerge as the energetically optimal compromise between the two antagonistic components. The model is able to reproduce the experimentally observed flagellar beats and the characteristic geometric signature of spinning lasso, namely, traveling waves of torsion with alternating sign along the length of the flagellum.

Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses

Euglenozoa is a species-rich group of protists, which have extremely diverse lifestyles and a range of features that distinguish them from other eukaryotes. They are composed of free-living and parasitic kinetoplastids, mostly free-living diplonemids, heterotrophic and photosynthetic euglenids, as well as deep-sea symbiontids. Although they form a well-supported monophyletic group, these morphologically rather distinct groups are almost never treated together in a comparative manner, as attempted here. We present an updated taxonomy, complemented by photos of representative species, with notes on diversity, distribution and biology of euglenozoans. For kinetoplastids, we propose a significantly modified taxonomy that reflects the latest findings. Finally, we summarize what is known about viruses infecting euglenozoans, as well as their relationships with ecto- and endosymbiotic bacteria.

Metabolomic approach of the antiprotozoal activity of medicinal Piper species used in Peruvian Amazon

ETHNOPHARMACOLOGICAL RELEVANCE

In the Peruvian Amazon as in the tropical countries of South America, the use of medicinal Piper species (cordoncillos) is common practice, particularly against symptoms of infection by protozoal parasites. However, there is few documented information about the practical aspects of their use and few scientific validation. The starting point of this work was a set of interviews of people living in six rural communities from the Peruvian Amazon (Alto Amazonas Province) about their uses of plants from Piper genus: one community of Amerindian native people (Shawi community) and five communities of mestizos. Infections caused by parasitic protozoa take a huge toll on public health in the Amazonian communities, who partly fight it using traditional remedies. Validation of these traditional practices contributes to public health care efficiency and may help to identify new antiprotozoal compounds.

AIMS OF STUDY

To record and validate the use of medicinal Piper species by rural people of Alto Amazonas Province (Peru) and annotate active compounds using a correlation study and a data mining approach.

MATERIALS AND METHODS

Rural communities were interviewed about traditional medication against parasite infections with medicinal Piper species. Ethnopharmacological surveys were undertaken in five mestizo villages, namely: Nueva Arica, Shucushuyacu, Parinari, Lagunas and Esperanza, and one Shawi community (Balsapuerto village). All communities belong to the Alto Amazonas Province (Loreto region, Peru). Seventeen Piper species were collected according to their traditional use for the treatment of parasitic diseases, 35 extracts (leaves or leaves and stems) were tested in vitro on P. falciparum (3D7 chloroquine-sensitive strain and W2 chloroquine-resistant strain), Leishmania donovani LV9 strain and Trypanosoma brucei gambiense. Assessments were performed on HUVEC cells and RAW 264.7 macrophages. The annotation of active compounds was realized by metabolomic analysis and molecular networking approach.

RESULTS

Nine extracts were active (IC₅₀ ≤ 10 μg/mL) on 3D7 P. falciparum and only one on W2 P. falciparum, six on L. donovani (axenic and intramacrophagic amastigotes) and seven on Trypanosoma brucei gambiense. Only one extract was active on all three parasites (P. lineatum). After metabolomic analyses and annotation of compounds active on Leishmania, P. strigosum and P. pseudoarboreum were considered as potential sources of leishmanicidal compounds.

CONCLUSIONS

This ethnopharmacological study and the associated in vitro bioassays corroborated the relevance of use of Piper species in the Amazonian traditional medicine, especially in Peru. A series of Piper species with few previously available phytochemical data have good antiprotozoal activity and could be a starting point for subsequent promising work. Metabolomic approach appears to be a smart, quick but still limited methodology to identify compounds with high probability of biological activity.

Role for the flagellum attachment zone in Leishmania anterior cell tip morphogenesis

The shape and form of the flagellated eukaryotic parasite Leishmania is sculpted to its ecological niches and needs to be transmitted to each generation with great fidelity. The shape of the Leishmania cell is defined by the sub-pellicular microtubule array and the positioning of the nucleus, kinetoplast and the flagellum within this array. The flagellum emerges from the anterior end of the cell body through an invagination of the cell body membrane called the flagellar pocket. Within the flagellar pocket the flagellum is laterally attached to the side of the flagellar pocket by a cytoskeletal structure called the flagellum attachment zone (FAZ). During the cell cycle single copy organelles duplicate with a new flagellum assembling alongside the old flagellum. These are then segregated between the two daughter cells by cytokinesis, which initiates at the anterior cell tip. Here, we have investigated the role of the FAZ in the morphogenesis of the anterior cell tip. We have deleted the FAZ filament protein, FAZ2 and investigated its function using light and electron microscopy and infection studies. The loss of FAZ2 caused a disruption to the membrane organisation at the anterior cell tip, resulting in cells that were connected to each other by a membranous bridge structure between their flagella. Moreover, the FAZ2 null mutant was unable to develop and proliferate in sand flies and had a reduced parasite burden in mice. Our study provides a deeper understanding of membrane-cytoskeletal interactions that define the shape and form of an individual cell and the remodelling of that form during cell division.

Leishmania are parasites that cause leishmaniasis in humans with symptoms ranging from mild cutaneous lesions to severe visceral disease. The life cycle of these parasites alternates between the human host and the sand fly vector, with distinct forms in both. These different forms have different cell shapes that are adapted for survival in these different environments. Leishmania parasites have an elongated cell shape with a flagellum extending from one end and this shape is due to a protein skeleton beneath the cell membrane. This skeleton is made up of different units one of which is called the flagellum attachment zone (FAZ), that connects the flagellum to the cell body. We have found that one of the proteins in the FAZ called FAZ2 is important for generating the shape of the cell at the point where the flagellum exits the cell. When we deleted FAZ2 we found that the cell membrane at the end of the cell was distorted resulting in unusual connections between the flagella of different cells. We found that the disruption to the cell shape reduces the ability of the parasite to infect mice and develop in the sand fly, which shows the importance of the parasite shape.

The single flagellum of Leishmania has a fixed polarisation of its asymmetric beat

Eukaryotic flagella undertake different beat types as necessary for different functions; for example, the Leishmania parasite flagellum undergoes a symmetric tip-to-base beat for forward swimming and an asymmetric base-to-tip beat to rotate the cell. In multi-ciliated tissues or organisms, the asymmetric beats are coordinated, leading to movement of the cell, organism or surrounding fluid. This coordination involves a polarisation of power stroke direction. Here, we asked whether the asymmetric beat of the single Leishmania flagellum also has a fixed polarisation. We developed high frame rate dual-colour fluorescence microscopy to visualise flagellar-associated structures in live swimming cells. This showed that the asymmetric Leishmania beat is polarised, with power strokes only occurring in one direction relative to the asymmetric flagellar machinery. Polarisation of bending was retained in deletion mutants whose flagella cannot beat but have a static bend. Furthermore, deletion mutants for proteins required for asymmetric extra-axonemal and rootlet-like flagellum-associated structures also retained normal polarisation. Leishmania beat polarisation therefore likely arises from either the nine-fold rotational symmetry of the axoneme structure or is due to differences between the outer doublet decorations.

Highlighted Article: By using high speed, high-resolution fluorescence microscopy of swimming Leishmania cells, we showed that the asymmetric flagellar beat always wafts in the same direction and investigate which structures are involved.

Ubiquitin-Like Modifiers: Emerging Regulators of Protozoan Parasites

Post-translational protein regulation allows for fine-tuning of cellular functions and involves a wide range of modifications, including ubiquitin and ubiquitin-like modifiers (Ubls). The dynamic balance of Ubl conjugation and removal shapes the fates of target substrates, in turn modulating various cellular processes. The mechanistic aspects of Ubl pathways and their biological roles have been largely established in yeast, plants, and mammalian cells. However, these modifiers may be utilised differently in highly specialised and divergent organisms, such as parasitic protozoa. In this review, we explore how these parasites employ Ubls, in particular SUMO, NEDD8, ATG8, ATG12, URM1, and UFM1, to regulate their unconventional cellular physiology. We discuss emerging data that provide evidence of Ubl-mediated regulation of unique parasite-specific processes, as well as the distinctive features of Ubl pathways in parasitic protozoa. We also highlight the potential to leverage these essential regulators and their cognate enzymatic machinery for development of therapeutics to protect against the diseases caused by protozoan parasites.

Control of assembly of extra-axonemal structures: the paraflagellar rod of trypanosomes

Eukaryotic flagella are complex microtubule-based organelles that, in many organisms, contain extra-axonemal structures, such as the outer dense fibres of mammalian sperm and the paraflagellar rod (PFR) of trypanosomes. Flagellum assembly is a complex process occurring across three main compartments, the cytoplasm, the transition zone and the flagellum itself. The process begins with the translation of protein components followed by their sorting and trafficking into the flagellum, transport to the assembly site and incorporation. Flagella are formed from over 500 proteins and the principles governing assembly of the axonemal components are relatively clear. However, the coordination and location of assembly of extra-axonemal structures are less clear. We have discovered two cytoplasmic proteins in Trypanosoma brucei that are required for PFR formation, PFR assembly factors 1 and 2 (PFR-AF1 and PFR-AF2, respectively). Deletion of either PFR-AF1 or PFR-AF2 dramatically disrupted PFR formation and caused a reduction in the amount of major PFR proteins. The existence of cytoplasmic factors required for PFR formation aligns with the concept that processes facilitating axoneme assembly occur across multiple compartments, and this is likely a common theme for extra-axonemal structure assembly.

Biallelic variants in MAATS1 encoding CFAP91, a calmodulin-associated and spoke-associated complex protein, cause severe astheno-teratozoospermia and male infertility

BACKGROUND

Multiple morphological abnormalities of the flagella (MMAF) consistently lead to male infertility due to a reduced or absent sperm motility defined as asthenozoospermia. Despite numerous genes recently described to be recurrently associated with MMAF, more than half of the cases analysed remain unresolved, suggesting that many yet uncharacterised gene defects account for this phenotype METHODS: Exome sequencing was performed on 167 infertile men with an MMAF phenotype. Immunostaining and transmission electron microscopy (TEM) in sperm cells from affected individuals were performed to characterise the ultrastructural sperm defects. Gene inactivation using RNA interference (RNAi) was subsequently performed in Trypanosoma.

RESULTS

We identified six unrelated affected patients carrying a homozygous deleterious variants in MAATS1, a gene encoding CFAP91, a calmodulin-associated and spoke-associated complex (CSC) protein. TEM and immunostaining experiments in sperm cells showed severe central pair complex (CPC) and radial spokes defects. Moreover, we confirmed that the WDR66 protein is a physical and functional partner of CFAP91 into the CSC. Study of Trypanosoma MAATS1's orthologue (TbCFAP91) highlighted high sequence and structural analogies with the human protein and confirmed the axonemal localisation of the protein. Knockdown of TbCFAP91 using RNAi impaired flagellar movement led to CPC defects in Trypanosoma as observed in humans.

CONCLUSIONS

We showed that CFAP91 is essential for normal sperm flagellum structure and function in human and Trypanosoma and that biallelic variants in this gene lead to severe flagellum malformations resulting in astheno-teratozoospermia and primary male infertility.

Trypanosomatid parasite dynamically changes the transcriptome during infection and modifies honey bee physiology

It is still not understood how honey bee parasite changes the gene expression to adapt to the host environment and how the host simultaneously responds to the parasite infection by modifying its own gene expression. To address this question, we studied a trypanosomatid, Lotmaria passim, which can be cultured in medium and inhabit the honey bee hindgut. We found that L. passim decreases mRNAs associated with protein translation, glycolysis, detoxification of radical oxygen species, and kinetoplast respiratory chain to adapt to the anaerobic and nutritionally poor honey bee hindgut during the infection. After the long term infection, the host appears to be in poor nutritional status, indicated by the increase and decrease of take-out and vitellogenin mRNAs, respectively. Simultaneous gene expression profiling of L. passim and honey bee during infection by dual RNA-seq provided insight into how both parasite and host modify their gene expressions.

Signal Transduction Pathways as Therapeutic Target for Chagas Disease

Trypanosomatids are a group of flagellated unicellular eukaryotes, causing serious human diseases including Chagas disease (Trypanosoma cruzi), sleeping sickness (Trypanosoma brucei spp.) and Leishmaniasis (Leishmania spp.). The second messenger cAMP is involved in numerous and fundamental processes in these parasites including differentiation between stages, proliferation, osmoregulation, oxidative stress and quorum sensing. Interestingly, its signaling pathway is quite different from that of mammals, including structurally different adenylyl cyclases, the shortage of orthologous effector proteins and the absence of G-protein-coupled-receptors, among others. These characteristics make the proteins involved in these transduction pathways good candidates for therapeutic targets. However, the identification of new unknown druggable targets involves extensive research time and is economically very expensive, making difficult the transition from basic research to the clinical phase. Trypanosomatid PDEs have characteristic binding pockets that allow for a differential inhibition from their human orthologs. Modification in the approved drugs for human to convert them into trypanocidal treatments could lead to more effective therapies, shorter lab time and lower costs. In view of the fact that kinetoplastid PDEs are highly conserved with their mammalian counterparts, and since there are already numerous drugs on the market against human PDEs, the drug repositioning approach is highly promising. The development of new technologies, higher government and industrial involvement and more scientists committed to basic investigation, are the key to ultimately find an effective treatment and cure for the neglected tropical diseases.

Cell Cycle-Dependent Flagellar Disassembly in a Firebug Trypanosomatid Leptomonas pyrrhocoris

Current understanding of flagellum/cilium length regulation focuses on a few model organisms with flagella of uniform length. Leptomonas pyrrhocoris is a monoxenous trypanosomatid parasite of firebugs. When cultivated in vitro, L. pyrrhocoris duplicates every 4.2 ± 0.2 h, representing the shortest doubling time reported for trypanosomatids so far. Each L. pyrrhocoris cell starts its cell cycle with a single flagellum. A new flagellum is assembled de novo, while the old flagellum persists throughout the cell cycle. The flagella in an asynchronous L. pyrrhocoris population exhibited a vast length variation of ∼3 to 24 μm, casting doubt on the presence of a length regulation mechanism based on a single balance point between the assembly and disassembly rate in these cells. Through imaging of live L. pyrrhocoris cells, a rapid, partial disassembly of the existing, old flagellum is observed upon, if not prior to, the initial assembly of a new flagellum. Mathematical modeling demonstrated an inverse correlation between the flagellar growth rate and flagellar length and inferred the presence of distinct, cell cycle-dependent disassembly mechanisms with different rates. On the basis of these observations, we proposed a min-max model that could account for the vast flagellar length range observed for asynchronous L. pyrrhocoris. This model may also apply to other flagellated organisms with flagellar length variation.IMPORTANCE Current understanding of flagellum biogenesis during the cell cycle in trypanosomatids is limited to a few pathogenic species, including Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. The most notable characteristics of trypanosomatid flagella studied so far are the extreme stability and lack of ciliary disassembly/absorption during the cell cycle. This is different from cilia in Chlamydomonas and mammalian cells, which undergo complete absorption prior to cell cycle initiation. In this study, we examined flagellum duplication during the cell cycle of Leptomonas pyrrhocoris With the shortest duplication time documented for all Trypanosomatidae and its amenability to culture on agarose gel with limited mobility, we were able to image these cells through the cell cycle. Rapid, cell cycle-specific flagellum disassembly different from turnover was observed for the first time in trypanosomatids. Given the observed length-dependent growth rate and the presence of different disassembly mechanisms, we proposed a min-max model that can account for the flagellar length variation observed in L. pyrrhocoris.

LeishIF4E1 Deletion Affects the Promastigote Proteome, Morphology, and Infectivity

Leishmania parasites are the causative agents of a broad spectrum of diseases. The parasites migrate between sand-fly vectors and mammalian hosts, adapting to changing environments by driving a regulated program of gene expression, with translation regulation playing a key role. The leishmanias encode six different paralogs of eIF4E, the cap-binding translation initiation factor. Since these vary in function, expression profile, and assemblage, it is assumed that each is assigned a specific role throughout the life cycle. Using the CRISPR-Cas9 system for Leishmania, we generated a null mutant of LeishIF4E1, eliminating both alleles. Although the mutant cells were viable, their morphology was altered and their ability to synthesize the flagellum was impaired. Elimination of LeishIF4E1 affected their protein expression profile and decreased their ability to infect cultured macrophages. Restoring LeishIF4E1 expression restored the affected features. This study highlights the importance of LeishIF4E1 in diverse cellular events during the life cycle of Leishmania.

Leishmania parasites cycle between sand-fly vectors and mammalian hosts, adapting to changing environmental conditions by driving a stage-specific program of gene expression, which is tightly regulated by translation processes. Leishmania encodes six eIF4E orthologs (LeishIF4Es) and five eIF4G candidates, forming different cap-binding complexes with potentially varying functions. Most LeishIF4E paralogs display temperature sensitivity in their cap-binding activity, except for LeishIF4E1, which maintains its cap-binding activity under all conditions. We used the CRISPR-Cas9 system to successfully generate a null mutant of LeishIF4E1 and examine how its elimination affected parasite physiology. Although the LeishIF4E1^–/– null mutant was viable, its growth was impaired, in line with a reduction in global translation. As a result of the mutation, the null LeishIF4E1^–/– mutant had a defective morphology, as the cells were round and unable to grow a normal flagellum. This was further emphasized when the LeishIF4E1^–/– cells failed to develop the promastigote morphology once they shifted from conditions that generate axenic amastigotes (33°C, pH 5.5) back to neutral pH and 25°C, and they maintained their short flagellum and circular structure. Finally, the LeishIF4E1^–/– null mutant displayed difficulty in infecting cultured macrophages. The morphological changes and reduced infectivity of the mutant may be related to differences in the proteomic profile of LeishIF4E1^–/– cells from that of controls. All defects monitored in the LeishIF4E1^–/– null mutant were reversed in the add-back strain, in which expression of LeishIF4E1 was reconstituted, establishing a strong link between the cellular defects and the absence of LeishIF4E1 expression.

IMPORTANCELeishmania parasites are the causative agents of a broad spectrum of diseases. The parasites migrate between sand-fly vectors and mammalian hosts, adapting to changing environments by driving a regulated program of gene expression, with translation regulation playing a key role. The leishmanias encode six different paralogs of eIF4E, the cap-binding translation initiation factor. Since these vary in function, expression profile, and assemblage, it is assumed that each is assigned a specific role throughout the life cycle. Using the CRISPR-Cas9 system for Leishmania, we generated a null mutant of LeishIF4E1, eliminating both alleles. Although the mutant cells were viable, their morphology was altered and their ability to synthesize the flagellum was impaired. Elimination of LeishIF4E1 affected their protein expression profile and decreased their ability to infect cultured macrophages. Restoring LeishIF4E1 expression restored the affected features. This study highlights the importance of LeishIF4E1 in diverse cellular events during the life cycle of Leishmania.

Dramatic changes in gene expression in different forms of Crithidia fasciculata reveal potential mechanisms for insect-specific adhesion in kinetoplastid parasites

Kinetoplastids are a group of parasites that includes several medically-important species. These human-infective species are transmitted by insect vectors in which the parasites undergo specific developmental transformations. For each species, this includes a stage in which parasites adhere to insect tissue via a hemidesmosome-like structure. Although this structure has been described morphologically, it has never been molecularly characterized. We are using Crithidia fasciculata, an insect parasite that produces large numbers of adherent parasites inside its mosquito host, as a model kinetoplastid to investigate both the mechanism of adherence and the signals required for differentiation to an adherent form. An advantage of C. fasciculata is that adherent parasites can be generated both in vitro, allowing a direct comparison to cultured swimming forms, as well as in vivo within the mosquito. Using RNAseq, we identify genes associated with adherence in C. fasciculata. As almost all of these genes have orthologs in other kinetoplastid species, our findings may reveal shared mechanisms of adherence, allowing investigation of a crucial step in parasite development and disease transmission. In addition, dual-RNAseq allowed us to explore the interaction between the parasites and the mosquito. Although the infection is well-tolerated, anti-microbial peptides and other components of the mosquito innate immune system are upregulated. Our findings indicate that C. fasciculata is a powerful model system for probing kinetoplastid-insect interactions.

Kinetoplastids are single-celled parasites that cause devastating human diseases worldwide. Although this group includes many species that infect a variety of hosts, they have a great deal of shared biology. One relatively unexplored aspect of the kinetoplastid life cycle is their ability to adhere to insect tissue. For pathogenic species, adherence is critical for transmission by insect vectors. We have used an insect parasite called Crithidia fasciculata as a model kinetoplastid to reveal shared mechanisms of insect adherence. We have compared gene expression profiles of motile, non-adherent C. fasciculata to those of C. fasciculata adhered to non-living substrates and those attached to the hindgut of mosquitoes. Through this analysis, we have identified a large number of candidate proteins that may mediate adhesion in these and related parasites. In addition, our findings suggest that the mosquito immune system is responding to the presence of parasites in the gut. These results establish a new, robust system to explore the interaction between kinetoplastids and their insect hosts.

Ciliary Proteins: Filling the Gaps. Recent Advances in Deciphering the Protein Composition of Motile Ciliary Complexes

Cilia are highly evolutionarily conserved, microtubule-based cell protrusions present in eukaryotic organisms from protists to humans, with the exception of fungi and higher plants. Cilia can be broadly divided into non-motile sensory cilia, called primary cilia, and motile cilia, which are locomotory organelles. The skeleton (axoneme) of primary cilia is formed by nine outer doublet microtubules distributed on the cilium circumference. In contrast, the skeleton of motile cilia is more complex: in addition to outer doublets, it is composed of two central microtubules and several diverse multi-protein complexes that are distributed periodically along both types of microtubules. For many years, researchers have endeavored to fully characterize the protein composition of ciliary macro-complexes and the molecular basis of signal transduction between these complexes. Genetic and biochemical analyses have suggested that several hundreds of proteins could be involved in the assembly and function of motile cilia. Within the last several years, the combined efforts of researchers using cryo-electron tomography, genetic and biochemical approaches, and diverse model organisms have significantly advanced our knowledge of the ciliary structure and protein composition. Here, we summarize the recent progress in the identification of the subunits of ciliary complexes, their precise intraciliary localization determined by cryo-electron tomography data, and the role of newly identified proteins in cilia.

Genetic dissection of a Leishmania flagellar proteome demonstrates requirement for directional motility in sand fly infections

The protozoan parasite Leishmania possesses a single flagellum, which is remodelled during the parasite’s life cycle from a long motile flagellum in promastigote forms in the sand fly to a short immotile flagellum in amastigotes residing in mammalian phagocytes. This study examined the protein composition and in vivo function of the promastigote flagellum. Protein mass spectrometry and label free protein enrichment testing of isolated flagella and deflagellated cell bodies defined a flagellar proteome for L. mexicana promastigote forms (available via ProteomeXchange with identifier PXD011057). This information was used to generate a CRISPR-Cas9 knockout library of 100 mutants to screen for flagellar defects. This first large-scale knockout screen in a Leishmania sp. identified 56 mutants with altered swimming speed (52 reduced and 4 increased) and defined distinct mutant categories (faster swimmers, slower swimmers, slow uncoordinated swimmers and paralysed cells, including aflagellate promastigotes and cells with curled flagella and disruptions of the paraflagellar rod). Each mutant was tagged with a unique 17-nt barcode, providing a simple barcode sequencing (bar-seq) method for measuring the relative fitness of L. mexicana mutants in vivo. In mixed infections of the permissive sand fly vector Lutzomyia longipalpis, paralysed promastigotes and uncoordinated swimmers were severely diminished in the fly after defecation of the bloodmeal. Subsequent examination of flies infected with a single paralysed mutant lacking the central pair protein PF16 or an uncoordinated swimmer lacking the axonemal protein MBO2 showed that these promastigotes did not reach anterior regions of the fly alimentary tract. These data show that L. mexicana need directional motility for successful colonisation of sand flies.

Leishmania are protozoan parasites, transmitted between mammals by the bite of phlebotomine sand flies. Promastigote forms in the sand fly have a long flagellum, which is motile and used for anchoring the parasites to prevent clearance with the digested blood meal remnants. To dissect flagellar functions and their importance in life cycle progression, we generated here a comprehensive list of >300 flagellar proteins and produced a CRISPR-Cas9 gene knockout library of 100 mutant Leishmania. We studied their behaviour in vitro before examining their fate in the sand fly Lutzomyia longipalpis. Measuring mutant swimming speeds showed that about half behaved differently compared to the wild type: a few swam faster, many slower and some were completely paralysed. We also found a group of uncoordinated swimmers. To test whether flagellar motility is required for parasite migration from the fly midgut to the foregut from where they reach the next host, we infected sand flies with a mixed mutant population. Each mutant carried a unique tag and tracking these tags up to nine days after infection showed that paralysed and uncoordinated Leishmania were rapidly lost from flies. These data indicate that directional swimming is important for successful colonisation of sand flies.

Major Kinds of Drug Targets in Chagas Disease or American Trypanosomiasis

American Trypanosomiasis, a parasitic infection commonly named Chagas disease, affects millions of people all over Latin American countries. Presently, the World Health Organization (WHO) predicts that the number of international infected individuals extends to 7 to 8 million, assuming that more than 10,000 deaths occur annually. The transmission of the etiologic agent, Trypanosoma cruzi, through people migrating to non-endemic world nations makes it an emergent disease. The best promising targets for trypanocidal drugs may be classified into three main groups: Group I includes the main molecular targets that are considered among specific enzymes involved in the essential processes for parasite survival, principally Cruzipain, the major antigenic parasite cysteine proteinase. Group II involves biological pathways and their key specific enzymes, such as Sterol biosynthesis pathway, among others, specific antioxidant defense mechanisms, and bioenergetics ones. Group III includes the atypical organelles /structures present in the parasite relevant clinical forms, which are absent or considerably different from those present in mammals and biological processes related to them. These can be considered potential targets to develop drugs with extra effectiveness and fewer secondary effects than the currently used therapeutics. An improved distinction between the host and the parasite targets will help fight against this neglected disease.

A centriolar FGR1 oncogene partner-like protein required for paraflagellar rod assembly, but not axoneme assembly in African trypanosomes

Proteins of the FGR1 oncogene partner (or FOP) family are found at microtubule organizing centres (MTOCs) including, in flagellate eukaryotes, the centriole or flagellar basal body from which the axoneme extends. We report conservation of FOP family proteins, TbFOPL and TbOFD1, in the evolutionarily divergent sleeping sickness parasite Trypanosoma brucei, showing (in contrast with mammalian cells, where FOP is essential for flagellum assembly) depletion of a trypanosome FOP homologue, TbFOPL, affects neither axoneme nor flagellum elongation. Instead, TbFOPL depletion causes catastrophic failure in assembly of a lineage-specific, extra-axonemal structure, the paraflagellar rod (PFR). That depletion of centriolar TbFOPL causes failure in PFR assembly is surprising because PFR nucleation commences approximately 2 µm distal from the basal body. When over-expressed with a C-terminal myc-epitope, TbFOPL was also observed at mitotic spindle poles. Little is known about bi-polar spindle assembly during closed trypanosome mitosis, but indication of a possible additional MTOC function for TbFOPL parallels MTOC localization of FOP-like protein TONNEAU1 in acentriolar plants. More generally, our functional analysis of TbFOPL emphasizes significant differences in evolutionary cell biology trajectories of FOP-family proteins. We discuss how at the molecular level FOP homologues may contribute to flagellum assembly and function in diverse flagellates.

IFT25 is required for the construction of the trypanosome flagellum

Intraflagellar transport (IFT), the movement of protein complexes responsible for the assembly of cilia and flagella, is remarkably conserved from protists to humans. However, two IFT components (IFT25 and IFT27) are missing from multiple unrelated eukaryotic species. In mouse, IFT25 (also known as HSPB11) and IFT27 are not required for assembly of several cilia with the noticeable exception of the flagellum of spermatozoa. Here, we show that the Trypanosoma brucei IFT25 protein is a proper component of the IFT-B complex and displays typical IFT trafficking. By performing bimolecular fluorescence complementation assays, we reveal that IFT25 and IFT27 interact within the flagellum in live cells during the IFT process. IFT25-depleted cells construct tiny disorganised flagella that accumulate IFT-B proteins (with the exception of IFT27, the binding partner of IFT25) but not IFT-A proteins. This phenotype is comparable to the one following depletion of IFT27 and shows that IFT25 and IFT27 constitute a specific module that is necessary for proper IFT and flagellum construction in trypanosomes. Possible reasons why IFT25 and IFT27 would be required for only some types of cilia are discussed.

Trypanosoma vivax infection in sheep: Different patterns of virulence and pathogenicity associated with differentially expressed proteomes

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Trypanosoma vivax strains exhibit different virulence and pathogenicity patterns.

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TvMT1 strain showed low virulence and high pathogenicity.

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TvLIEM176 strain showed high virulence and moderate pathogenicity.

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Protein expression varies in high virulence/moderate pathogenicity strain vs low virulence/high pathogenicity strain.

Cattle trypanosomosis caused by Trypanosoma vivax is a widely distributed disease in Africa and Latin America. It causes significant losses in the livestock industry and is characterized by fluctuating parasitemia, anemia, fever, lethargy, and weight loss. In this study we evaluated the virulence (capacity to multiply inside the host and to modulate the host response) and pathogenicity (ability to produce disease and/or mortality) patterns of two T. vivax strains (TvMT1 and TvLIEM176) in experimentally-infected sheep and determined the proteins differentially expressed in the proteomes of these two strains. Hematological and clinical parameters were monitored in experimentally-infected versus non-infected sheep for 60 days. All the infected animals developed discernable parasitemia at 3 days post-infection (dpi), and the first parasitemia peak was observed at 6 dpi. The maximum average value of parasitemia was 1.3 × 10⁷ (95% CI, 7.9 × 10⁵–2 × 10⁸) parasites/ml in TvLIEM176-infected animals, and 2.5 × 10⁶ (95% CI, 1.6 × 10⁵–4 × 10⁷) parasites/ml in TvMT1-infected ones. Anemia and clinical manifestations were more severe in the animals infected by TvMT1 strain than in those infected by TvLIEM176. In the proteomic analysis, a total of 29 proteins were identified, of which 14 exhibited significant differences in their expression levels between strains. Proteins with higher expression in TvLIEM176 were: alpha tubulin, beta tubulin, arginine kinase, glucose-regulated protein 78, paraflagellar protein 3, and T-complex protein 1 subunit theta. Proteins with higher expression in TvMT1 were: chaperonin HSP60, T-complex protein 1 subunit alpha, heat shock protein 70, pyruvate kinase, glycerol kinase, inosine-5'-monophosphate dehydrogenase, 73 kDa paraflagellar rod protein, and vacuolar ATP synthase. There was a difference in the virulence and pathogenicity between the T. vivax strains: TvLIEM176 showed high virulence and moderate pathogenicity, whereas TvMT1 showed low virulence and high pathogenicity. The proteins identified in this study are discussed for their potential involvement in strains’ virulence and pathogenicity, to be further defined as biomarkers of severity in T. vivax infections.

Human Kinetoplastid Protozoan Infections: Where Are We Going Next?

Kinetoplastida trypanosomatidae microorganisms are protozoan parasites exhibiting a developmental stage in the gut of insect vectors and tissues of vertebrate hosts. During the vertebrate infective stages, these parasites alter the differential expression of virulence genes, modifying their biological and antigenic properties in order to subvert the host protective immune responses and establish a persistent infection. One of the hallmarks of kinetoplastid parasites is their evasion mechanisms from host immunity, leading to disease chronification. The diseases caused by kinetoplastid parasites are neglected by the global expenditures in research and development, affecting millions of individuals in the low and middle-income countries located mainly in the tropical and subtropical regions. However, investments made by public and private initiatives have over the past decade leveraged important lines of intervention that if well-integrated to health care programs will likely accelerate disease control initiatives. This review summarizes recent advances in public health care principles, including new drug discoveries and their rational use with chemotherapeutic vaccines, and the implementation of control efforts to spatially mapping the kinetoplastid infections through monitoring of infected individuals in epidemic areas. These approaches should bring us the means to track genetic variation of parasites and drug resistance, integrating this knowledge into effective stewardship programs to prevent vector-borne kinetoplastid infections in areas at risk of disease spreading.

Recent advances in trypanosomatid research: genome organization, expression, metabolism, taxonomy and evolution

Unicellular flagellates of the family Trypanosomatidae are obligatory parasites of invertebrates, vertebrates and plants. Dixenous species are aetiological agents of a number of diseases in humans, domestic animals and plants. Their monoxenous relatives are restricted to insects. Because of the high biological diversity, adaptability to dramatically different environmental conditions, and omnipresence, these protists have major impact on all biotic communities that still needs to be fully elucidated. In addition, as these organisms represent a highly divergent evolutionary lineage, they are strikingly different from the common 'model system' eukaryotes, such as some mammals, plants or fungi. A number of excellent reviews, published over the past decade, were dedicated to specialized topics from the areas of trypanosomatid molecular and cell biology, biochemistry, host-parasite relationships or other aspects of these fascinating organisms. However, there is a need for a more comprehensive review that summarizing recent advances in the studies of trypanosomatids in the last 30 years, a task, which we tried to accomplish with the current paper.

Shape-shifting trypanosomes: Flagellar shortening followed by asymmetric division in Trypanosoma congolense from the tsetse proventriculus

Trypanosomatids such as Leishmania and Trypanosoma are digenetic, single-celled, parasitic flagellates that undergo complex life cycles involving morphological and metabolic changes to fit them for survival in different environments within their mammalian and insect hosts. According to current consensus, asymmetric division enables trypanosomatids to achieve the major morphological rearrangements associated with transition between developmental stages. Contrary to this view, here we show that the African trypanosome Trypanosoma congolense, an important livestock pathogen, undergoes extensive cell remodelling, involving shortening of the cell body and flagellum, during its transition from free-swimming proventricular forms to attached epimastigotes in vitro. Shortening of the flagellum was associated with accumulation of PFR1, a major constituent of the paraflagellar rod, in the mid-region of the flagellum where it was attached to the substrate. However, the PFR1 depot was not essential for attachment, as it accumulated several hours after initial attachment of proventricular trypanosomes. Detergent and CaCl2 treatment failed to dislodge attached parasites, demonstrating the robust nature of flagellar attachment to the substrate; the PFR1 depot was also unaffected by these treatments. Division of the remodelled proventricular trypanosome was asymmetric, producing a small daughter cell. Each mother cell went on to produce at least one more daughter cell, while the daughter trypanosomes also proliferated, eventually resulting in a dense culture of epimastigotes. Here, by observing the synchronous development of the homogeneous population of trypanosomes in the tsetse proventriculus, we have been able to examine the transition from proventricular forms to attached epimastigotes in detail in T. congolense. This transition is difficult to observe in vivo as it happens inside the mouthparts of the tsetse fly. In T. brucei, this transition is achieved by asymmetric division of long trypomastigotes in the proventriculus, yielding short epimastigotes, which go on to colonise the salivary glands. Thus, despite their close evolutionary relationship and shared developmental route within the vector, T. brucei and T. congolense have evolved different ways of accomplishing the same developmental transition from proventricular form to attached epimastigote.

Trypanosoma cruzi transcriptome during axenic epimastigote growth curve

BACKGROUND

Trypanosoma cruzi is an important protozoan parasite and the causative agent of Chagas disease. A critical step in understanding T. cruzi biology is the study of cellular and molecular features exhibited during its growth curve.

OBJECTIVES

We aimed to acquire a global view of the gene expression profile of T. cruzi during epimastigote growth.

METHODS

RNA-Seq analysis of total and polysomal/granular RNA fractions was performed along the 10 days T. cruzi epimastigote growth curve in vitro, in addition to cell viability and cell cycle analyses. We also analysed the polysome profile and investigated the presence of granular RNA by FISH and western blotting.

FINDINGS

We identified 1082 differentially expressed genes (DEGs), of which 220 were modulated in both fractions. According to the modulation pattern, DEGs were grouped into 12 clusters and showed enrichment of important gene ontology (GO) terms. Moreover, we showed that by the sixth day of the growth curve, polysomal content declined greatly and the RNA granules content appeared to increase, suggesting that a portion of mRNAs isolated from the sucrose gradient during late growth stages was associated with RNA granules and not only polyribosomes. Furthermore, we discuss several modulated genes possibly involved in T. cruzi growth, mainly during the stationary phase, such as genes related to cell cycle, pathogenesis, metabolic processes and RNA-binding proteins.

RNA-seq analysis reveals differences in transcript abundance between cultured and sand fly-derived Leishmania infantum promastigotes

Leishmania infantum is responsible for human and canine leishmaniasis in the Mediterranean basin, where the major vector is Phlebotomus perniciosus. Because isolation of sufficient parasites from the sand fly gut is technically challenging, axenic cultivation of promastigotes is routinely used to obtain material for biochemical and genetic analyses. Here, we report the use of Spliced Leader RNA-seq (SL-seq) to compare transcript abundance in cultured promastigotes and those obtained from the whole midgut of the sand fly 5 days after infection. SL-seq allows for amplification of RNA from the parasite avoiding contamination with RNA from the gut of the insect. The study has been performed by means of a single technical replicate comparing pools of samples obtained from sand fly-derived (sfPro) and axenic culture promastigotes (acPro). Although there was a moderate correlation (R² = 0.83) in gene expression, 793 genes showed significantly different (≥2-fold, p <0.05) mRNA levels in sand fly-derived promastigotes and in culture, of which 31 were up-regulated ≥8-fold (p < 10^-8 in most cases). These included several genes that are typically up-regulated during metacyclogenesis, suggesting that sand fly-derived promastigotes contain a substantial number of metacyclics, and/or that their differentiation status as metacyclics is more advanced in these populations. Infection experiments and studies evaluating the proportion of metacyclic promastigotes in culture and within the sand fly gut, previously reported by us, support the last hypothesis.

Functional insights into pathogen biology from 3D electron microscopy

In recent years, novel imaging approaches revolutionised our understanding of the cellular and molecular biology of microorganisms. These include advances in fluorescent probes, dynamic live cell imaging, superresolution light and electron microscopy. Currently, a major transition in the experimental approach shifts electron microscopy studies from a complementary technique to a method of choice for structural and functional analysis. Here we review functional insights into the molecular architecture of viruses, bacteria and parasites as well as interactions with their respective host cells gained from studies using cryogenic electron tomography and related methodologies.

Using proteomics as a powerful tool to develop a vaccine against Mediterranean visceral leishmaniasis

Visceral leishmaniasis (VL) is a tropical infectious disease, which is called Mediterranean visceral leishmaniasis (MVL) in the Mediterranean area. In spite of many attempts, no effective commercial vaccine exists for MVL. To find new targets for developing antileishmanial vaccines, knowing parasite antigens that provoke the immune system are on demand. Nowadays, proteomics methods are defined as approaches for analysis of protein profiling of different cells. Within this framework, detection of new antigens is becoming more facilitated. In this review, we aimed to introduce possible targets using proteomics so; they could be used as candidates for developing vaccines against MVL. It can shed new light in the near future on the development of promising vaccines for MVL.

Life Cycle, Ultrastructure, and Phylogeny of New Diplonemids and Their Endosymbiotic Bacteria

Diplonemids represent a hyperdiverse and abundant yet poorly studied group of marine protists. Here we describe two new members of the genus Diplonema (Diplonemea, Euglenozoa), Diplonema japonicum sp. nov. and Diplonema aggregatum sp. nov., based on life cycle, morphology, and 18S rRNA gene sequences. Along with euglenozoan apomorphies, they contain several unique features. Their life cycle is complex, consisting of a trophic stage that is, following the depletion of nutrients, transformed into a sessile stage and subsequently into a swimming stage. The latter two stages are characterized by the presence of tubular extrusomes and the emergence of a paraflagellar rod, the supportive structure of the flagellum, which is prominently lacking in the trophic stage. These two stages also differ dramatically in motility and flagellar size. Both diplonemid species host endosymbiotic bacteria that are closely related to each other and constitute a novel branch within Holosporales, for which a new genus, "Candidatus Cytomitobacter" gen. nov., has been established. Remarkably, the number of endosymbionts in the cytoplasm varies significantly, as does their localization within the cell, where they seem to penetrate the mitochondrion, a rare occurrence.IMPORTANCE We describe the morphology, behavior, and life cycle of two new Diplonema species that established a relationship with two Holospora-like bacteria in the first report of an endosymbiosis in diplonemids. Both endosymbionts reside in the cytoplasm and the mitochondrion, which establishes an extremely rare case. Within their life cycle, the diplonemids undergo transformation from a trophic to a sessile and eventually a highly motile swimming stage. These stages differ in several features, such as the presence or absence of tubular extrusomes and a paraflagellar rod, along with the length of the flagella. These morphological and behavioral interstage differences possibly reflect distinct functions in dispersion and invasion of the host and/or prey and may provide novel insight into the virtually unknown function of diplonemids in the oceanic ecosystem.

A lumenal interrupted helix in human sperm tail microtubules

Eukaryotic flagella are complex cellular extensions involved in many human diseases gathered under the term ciliopathies. Currently, detailed insights on flagellar structure come mostly from studies on protists. Here, cryo-electron tomography (cryo-ET) was performed on intact human spermatozoon tails and showed a variable number of microtubules in the singlet region (inside the end-piece). Inside the microtubule plus end, a novel left-handed interrupted helix which extends several micrometers was discovered. This structure was named Tail Axoneme Intra-Lumenal Spiral (TAILS) and binds directly to 11 protofilaments on the internal microtubule wall, in a coaxial fashion with the surrounding microtubule lattice. It leaves a gap over the microtubule seam, which was directly visualized in both singlet and doublet microtubules. We speculate that TAILS may stabilize microtubules, enable rapid swimming or play a role in controlling the swimming direction of spermatozoa.