25 years of African trypanosome research: From description to molecular dissection and new drug discovery

A role for a Trypanosoma brucei cytosine RNA methyltransferase homolog in ribosomal RNA processing

In Trypanosoma brucei, gene expression is primarily regulated posttranscriptionally making RNA metabolism critical. T. brucei has an epitranscriptome containing modified RNA bases. Yet, the identity of the enzymes catalyzing modified RNA base addition and the functions of the enzymes and modifications remain unclear. Homology searches indicate the presence of numerous T. brucei cytosine RNA methyltransferase homologs. One such homolog, TbNop2 was studied in detail. TbNop2 contains the six highly conserved motifs found in cytosine RNA methyltransferases and is evolutionarily related to the Nop2 protein family required for rRNA modification and processing. RNAi experiments targeting TbNop2 resulted in reduced levels of TbNop2 RNA and protein, and a cessation of parasite growth. Next generation sequencing of bisulfite-treated RNA (BS-seq) detected the presence of two methylation sites in the large rRNA; yet TbNop2 RNAi did not result in a significant reduction of methylation. However, TbNop2 RNAi resulted in the retention of 28S internal transcribed spacer RNAs, indicating a role for TbNop2 in rRNA processing.

Multiple and frequent trypanosomatid co-infections of insects: the Cuban case study

Trypanosomatids are obligate parasites of animals, predominantly insects and vertebrates, and flowering plants. Monoxenous species, representing the vast majority of trypanosomatid diversity, develop in a single host, whereas dixenous species cycle between two hosts, of which primarily insect serves as a vector. To explore in-depth the diversity of insect trypanosomatids including their co-infections, sequence profiling of their 18S rRNA gene was used for true bugs (Hemiptera; 18% infection rate) and flies (Diptera; 10%) in Cuba. Out of 48 species (molecular operational taxonomic units) belonging to the genera Vickermania (16 spp.), Blastocrithidia (7), Obscuromonas (4), Phytomonas (5), Leptomonas/Crithidia (5), Herpetomonas (5), Wallacemonas (2), Kentomonas (1), Angomonas (1) and two unnamed genera (1 + 1), 38 species have been encountered for the first time. The detected Wallacemonas and Angomonas species constitute the most basal lineages of their respective genera, while Vickermania emerged as the most diverse group. The finding of Leptomonas seymouri, which is known to rarely infect humans, confirms that Dysdercus bugs are its natural hosts. A clear association of Phytomonas with the heteropteran family Pentatomidae hints at its narrow host association with the insect rather than plant hosts. With a focus on multiple infections of a single fly host, using deep Nanopore sequencing of 18S rRNA, we have identified co-infections with up to 8 trypanosomatid species. The fly midgut was usually occupied by several Vickermania species, while Herpetomonas and/or Kentomonas species prevailed in the hindgut. Metabarcoding was instrumental for analysing extensive co-infections and also allowed the identification of trypanosomatid lineages and genera.

Purine nucleosides replace cAMP in allosteric regulation of PKA in trypanosomatid pathogens

Cyclic nucleotide binding domains (CNB) confer allosteric regulation by cAMP or cGMP to many signaling proteins, including PKA and PKG. PKA of phylogenetically distant Trypanosoma is the first exception as it is cyclic nucleotide-independent and responsive to nucleoside analogues (Bachmaier et al., 2019). Here, we show that natural nucleosides inosine, guanosine and adenosine are nanomolar affinity CNB ligands and activators of PKA orthologs of the important tropical pathogens Trypanosoma brucei, Trypanosoma cruzi, and Leishmania. The sequence and structural determinants of binding affinity, -specificity and kinase activation of PKAR were established by structure-activity relationship (SAR) analysis, co-crystal structures and mutagenesis. Substitution of two to three amino acids in the binding sites is sufficient for conversion of CNB domains from nucleoside to cyclic nucleotide specificity. In addition, a trypanosomatid-specific C-terminal helix (αD) is required for high affinity binding to CNB-B. The αD helix functions as a lid of the binding site that shields ligands from solvent. Selectivity of guanosine for CNB-B and of adenosine for CNB-A results in synergistic kinase activation at low nanomolar concentration. PKA pulldown from rapid lysis establishes guanosine as the predominant ligand in vivo in T. brucei bloodstream forms, whereas guanosine and adenosine seem to synergize in the procyclic developmental stage in the insect vector. We discuss the versatile use of CNB domains in evolution and recruitment of PKA for novel nucleoside-mediated signaling.

Genome-scale RNA interference profiling of Trypanosoma brucei cell cycle progression defects

Trypanosomatids, which include major pathogens of humans and livestock, are flagellated protozoa for which cell cycle controls and the underlying mechanisms are not completely understood. Here, we describe a genome-wide RNA-interference library screen for cell cycle defects in Trypanosoma brucei. We induced massive parallel knockdown, sorted the perturbed population using high-throughput flow cytometry, deep-sequenced RNAi-targets from each stage and digitally reconstructed cell cycle profiles at a genomic scale; also enabling data visualisation using an online tool ( https://tryp-cycle.pages.dev/ ). Analysis of several hundred genes that impact cell cycle progression reveals >100 flagellar component knockdowns linked to genome endoreduplication, evidence for metabolic control of the G₁-S transition, surface antigen regulatory mRNA-binding protein knockdowns linked to G₂M accumulation, and a putative nucleoredoxin required for both mitochondrial genome segregation and for mitosis. The outputs provide comprehensive functional genomic evidence for the known and novel machineries, pathways and regulators that coordinate trypanosome cell cycle progression.

Leishmania guyanensis M4147 as a new LRV1-bearing model parasite: Phosphatidate phosphatase 2-like protein controls cell cycle progression and intracellular lipid content

Leishmaniasis is a parasitic vector-borne disease caused by the protistan flagellates of the genus Leishmania. Leishmania (Viannia) guyanensis is one of the most common causative agents of the American tegumentary leishmaniasis. It has previously been shown that L. guyanensis strains that carry the endosymbiotic Leishmania RNA virus 1 (LRV1) cause more severe form of the disease in a mouse model than those that do not. The presence of the virus was implicated into the parasite’s replication and spreading. In this respect, studying the molecular mechanisms of cellular control of viral infection is of great medical importance. Here, we report ~30.5 Mb high-quality genome assembly of the LRV1-positive L. guyanensis M4147. This strain was turned into a model by establishing the CRISPR-Cas9 system and ablating the gene encoding phosphatidate phosphatase 2-like (PAP2L) protein. The orthologue of this gene is conspicuously absent from the genome of an unusual member of the family Trypanosomatidae, Vickermania ingenoplastis, a species with mostly bi-flagellated cells. Our analysis of the PAP2L-null L. guyanensis showed an increase in the number of cells strikingly resembling the bi-flagellated V. ingenoplastis, likely as a result of the disruption of the cell cycle, significant accumulation of phosphatidic acid, and increased virulence compared to the wild type cells.

Worldwide, over one million people are getting infected by the parasitic flagellates of the genus Leishmania annually leading to ~30,000 deaths. Notably, there is still no approved vaccine against human leishmaniases. A range of methods of forward and reverse genetics has recently been developed for several model Leishmania species. Unfortunately, these methods are often not transferrable to non-model species, which may be of even greater medical importance. Leishmania guyanensis is one of such cases. It frequently carries a symbiotic RNA virus that contributes to the development of a more aggressive form of leishmaniasis in an experimental murine model. In order to establish and optimize the system for genetic manipulations in L. guyanensis, we sequenced and annotated its genome. Next, we applied the CRISPR-Cas9 technology to target a gene of interest. This approach was validated by ablating a gene encoding a protein involved in lipid metabolism. In this work, we document that deletion of this gene leads to the disturbance of cell cycle and affects the ratio of critical intracellular lipids. We believe that our study will facilitate research into more effective treatment of leishmaniases.

CRISPR/Cas9-induced disruption of Bodo saltans paraflagellar rod-2 gene reveals its importance for cell survival

Developing transfection protocols for marine protists is an emerging field that will allow the functional characterization of protist genes and their roles in organism responses to the environment. We developed a CRISPR/Cas9 editing protocol for Bodo saltans, a free-living kinetoplastid with tolerance to both marine and freshwater conditions and a close non-parasitic relative of trypanosomatids. Our results show that SaCas9/single-guide RNA (sgRNA) ribonucleoprotein (RNP) complex-mediated disruption of the paraflagellar rod 2 gene (BsPFR2) was achieved using electroporation-mediated transfection. The use of CRISPR/Cas9 genome editing can increase the efficiency of targeted homologous recombination when a repair DNA template is provided. Our sequence analysis suggests two mechanisms for repairing double-strand breaks in B. saltans are active; homologous-directed repair (HDR) utilizing an exogenous DNA template that carries an antibiotic resistance gene and likley non-homologous end joining (NHEJ). However, HDR was only achieved when a single (vs. multiple) SaCas9 RNP complex was provided. Furthermore, the biallelic knockout of BsPFR2 was detrimental for the cell, highlighting its essential role for cell survival because it facilitates the movement of food particles into the cytostome. Our Cas9/sgRNA RNP complex protocol provides a new tool for assessing gene functions in B. saltans and perhaps similar protists with polycistronic transcription.

CRISPR-Cas Technology: Emerging Applications in Clinical Microbiology and Infectious Diseases

Through the years, many promising tools for gene editing have been developed including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), CRISPR-associated protein 9 (Cas9), and homing endonucleases (HEs). These novel technologies are now leading new scientific advancements and practical applications at an inimitable speed. While most work has been performed in eukaryotes, CRISPR systems also enable tools to understand and engineer bacteria. The increase in the number of multi-drug resistant strains highlights a necessity for more innovative approaches to the diagnosis and treatment of infections. CRISPR has given scientists a glimmer of hope in this area that can provide a novel tool to fight against antimicrobial resistance. This system can provide useful information about the functions of genes and aid us to find potential targets for antimicrobials. This paper discusses the emerging use of CRISPR-Cas systems in the fields of clinical microbiology and infectious diseases with a particular emphasis on future prospects.

In vitro cultivation of Trypanosoma congolense bloodstream forms: State of the art and advances

Animal African Trypanosomosis (AAT or Nagana) is a severe vector-borne disease caused by protozoan parasites belonging to the Trypanosomatidae family and is usually cyclically transmitted by blood-sucking tsetse flies. AAT remains a major problem in sub-Saharan Africa. Among the main AAT causative agents, Trypanosoma congolense (T. congolense or Tc) is one of the most important trypanosome species, in terms of economic and animal health impacts, infecting cattle and a wide range of animal hosts as well. To advance in AAT prevention and control, it is essential to better understand trypanosome biology and pathogenesis using bloodstream form (BSF) in vitro culture. The in vitro cultivation of T. congolense IL3000 BSF strain is already well established and widely used in research studies and drug activity assays. However, it may probably no longer truly reflect the reality of field trypanosome strains, due to decades of use and subsequent modifications. Here, we propose a novel culture protocol that supports the long-term in vitro growth of the animal-infective BSFs of three Savannah and Forest types of T. congolense strains, including T. congolense clone IL1180, which is not only a field strain but also a commonly-used reference strain in experimental animal assays. We established a homemade culture medium which made it possible to sustain T. congolense IL1180 growth from infected mouse blood for 18 days in axenic conditions. Moreover, we developed an efficient freezing/thawing system that allowed, for the first time, T. congolense IL1180 BSF growth within 30 days after thawing. Our results on T. congolense adaptation to in vitro culture are encouraging for future gene studies using new molecular tools or for new therapeutic drug assays.

2,3-Diphenyl-2,3-dihydro-4H-1,3-thiaza-4-one heterocycles inhibit growth and block completion of cytokinesis in kinetoplastid parasites

Kinetoplastid parasites are model eukaryotes with a complex cell cycle that is highly regulated both spatially and temporally. In addition, diseases caused by these parasites continue to have a significant impact on human and animal health worldwide. While there have been advancements in chemotherapy for these diseases, there is a continual need for an arsenal of compounds that have robust anti-parasite activity with minimal impact on the human host. While investigating a series of 2,3-diphenyl-2,3-dihydro-4H-1,3-thiaza-4-one heterocycles with potential activity against these parasites, we found a pyridothiazinone that inhibits growth of the monoxenous parasite Crithidia fasciculata and two life cycle stages of Trypanosoma brucei. This inhibition is more pronounced in T. brucei and is associated with an unusual pre-abscission cell cycle arrest. Exploring the mode of action for these and related compounds in kinetoplastids may provide tools with which to explore cell cycle regulation in these important organisms.

TbSAP is a novel chromatin protein repressing metacyclic variant surface glycoprotein expression sites in bloodstream form Trypanosoma brucei

The African trypanosome Trypanosoma brucei is a unicellular eukaryote, which relies on a protective variant surface glycoprotein (VSG) coat for survival in the mammalian host. A single trypanosome has >2000 VSG genes and pseudogenes of which only one is expressed from one of ∼15 telomeric bloodstream form expression sites (BESs). Infectious metacyclic trypanosomes present within the tsetse fly vector also express VSG from a separate set of telomeric metacyclic ESs (MESs). All MESs are silenced in bloodstream form T. brucei. As very little is known about how this is mediated, we performed a whole genome RNAi library screen to identify MES repressors. This allowed us to identify a novel SAP domain containing DNA binding protein which we called TbSAP. TbSAP is enriched at the nuclear periphery and binds both MESs and BESs. Knockdown of TbSAP in bloodstream form trypanosomes did not result in cells becoming more ‘metacyclic-like'. Instead, there was extensive global upregulation of transcripts including MES VSGs, VSGs within the silent VSG arrays as well as genes immediately downstream of BES promoters. TbSAP therefore appears to be a novel chromatin protein playing an important role in silencing the extensive VSG repertoire of bloodstream form T. brucei.

CRISPRing protozoan parasites to better understand the biology of diseases

Precise gene editing techniques are paramount to gain deeper insights into the biological processes such as host-parasite interactions, drug resistance mechanisms, and gene-function relationships. Discovery of CRISPR-Cas9 system has spearheaded mechanistic understanding of protozoan parasite biology as evident from the number of reports in the last decade. Here, we have described the use of CRISPR-Cas9 in understanding the biology of medically important protozoan parasites such as Plasmodium, Leishmania, Trypanosoma, Babesia and Trichomonas. In spite of intrinsic difficulties in genome editing in these protozoan parasites, CRISPR-Cas9 has acted as a catalyst for faster generation of desired transgenic parasites. Modifications in the CRISPR-Cas9 system for improving the efficiency have been useful in better understanding the molecular mechanisms associated with repair of double strand breaks in the parasites. Moreover, improvement in reagents used for CRISPR mediated gene editing have been instrumental in addressing the issue of non-specificity and toxicity for therapeutic use. These application-based modifications may help in further increasing the efficiency of gene editing in protozoan parasites.

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.

A Trypanosoma brucei ORFeome-Based Gain-of-Function Library Identifies Genes That Promote Survival during Melarsoprol Treatment

Trypanosoma brucei is an early branching protozoan parasite that causes human and animal African trypanosomiasis. Forward genetics approaches are powerful tools for uncovering novel aspects of trypanosomatid biology, pathogenesis, and therapeutic approaches against trypanosomiasis. Here, we have generated a T. brucei cloned ORFeome consisting of >90% of the targeted 7,245 genes and used it to make an inducible gain-of-function parasite library broadly applicable to large-scale forward genetic screens. We conducted a proof-of-principle genetic screen to identify genes whose expression promotes survival in melarsoprol, a critical drug of last resort. The 57 genes identified as overrepresented in melarsoprol survivor populations included the gene encoding the rate-limiting enzyme for the biosynthesis of an established drug target (trypanothione), validating the tool. In addition, novel genes associated with gene expression, flagellum localization, and mitochondrion localization were identified, and a subset of those genes increased melarsoprol resistance upon overexpression in culture. These findings offer new insights into trypanosomatid basic biology, implications for drug targets, and direct or indirect drug resistance mechanisms. This study generated a T. brucei ORFeome and gain-of-function parasite library, demonstrated the library's usefulness in forward genetic screening, and identified novel aspects of melarsoprol resistance that will be the subject of future investigations. These powerful genetic tools can be used to broadly advance trypanosomatid research.IMPORTANCE Trypanosomatid parasites threaten the health of more than 1 billion people worldwide. Because their genomes are highly diverged from those of well-established eukaryotes, conservation is not always useful in assigning gene functions. However, it is precisely among the trypanosomatid-specific genes that ideal therapeutic targets might be found. Forward genetics approaches are an effective way to identify novel gene functions. We used an ORFeome approach to clone a large percentage of Trypanosoma brucei genes and generate a gain-of-function parasite library. This library was used in a genetic screen to identify genes that promote resistance to the clinically significant yet highly toxic drug melarsoprol. Hits arising from the screen demonstrated the library's usefulness in identifying known pathways and uncovered novel aspects of resistance mediated by proteins localized to the flagellum and mitochondrion. The powerful new genetic tools generated herein are expected to promote advances in trypanosomatid biology and therapeutic development in the years to come.

Cell-based and multi-omics profiling reveals dynamic metabolic repurposing of mitochondria to drive developmental progression of Trypanosoma brucei

Mitochondrial metabolic remodeling is a hallmark of the Trypanosoma brucei digenetic life cycle because the insect stage utilizes a cost-effective oxidative phosphorylation (OxPhos) to generate ATP, while bloodstream cells switch to aerobic glycolysis. Due to difficulties in acquiring enough parasites from the tsetse fly vector, the dynamics of the parasite's metabolic rewiring in the vector have remained obscure. Here, we took advantage of in vitro-induced differentiation to follow changes at the RNA, protein, and metabolite levels. This multi-omics and cell-based profiling showed an immediate redirection of electron flow from the cytochrome-mediated pathway to an alternative oxidase (AOX), an increase in proline consumption, elevated activity of complex II, and certain tricarboxylic acid (TCA) cycle enzymes, which led to mitochondrial membrane hyperpolarization and increased reactive oxygen species (ROS) levels. Interestingly, these ROS molecules appear to act as signaling molecules driving developmental progression because ectopic expression of catalase, a ROS scavenger, halted the in vitro-induced differentiation. Our results provide insights into the mechanisms of the parasite's mitochondrial rewiring and reinforce the emerging concept that mitochondria act as signaling organelles through release of ROS to drive cellular differentiation.

mSphere of Influence: Expanding the CRISPR Sphere with Single-Locus Proteomics

Lucy Glover’s research focuses on the role of DNA repair and recombination in antigenic variation in the parasite Trypanosoma brucei, the causative agent of both human and animal African trypanosomiasis. In this mSphere of Influence article, she reflects on how “A CRISPR-based approach for proteomic analysis of a single genomic locus” by Z. J. Waldrip, S. D. Byrum, A. J. Storey, J.

Lucy Glover’s research focuses on the role of DNA repair and recombination in antigenic variation in the parasite Trypanosoma brucei, the causative agent of both human and animal African trypanosomiasis. In this mSphere of Influence article, she reflects on how “A CRISPR-based approach for proteomic analysis of a single genomic locus” by Z. J. Waldrip, S. D. Byrum, A. J. Storey, J. Gao, et al. (Epigenetics 9:1207–1211, 2014, https://doi.org/10.4161/epi.29919) made an impact on her research by taking the precision of CRISPR-Cas9 and repurposing it to look at single-locus proteomics. By using this technology in trypanosomes, Dr. Glover and her colleagues could study the dynamic accumulation of repair proteins after specific damage and gain insight into how the location of a double-strand break (DSB) dictates repair pathway choice and how this may influence immune evasion in these parasites.

Genetic tool development in marine protists: emerging model organisms for experimental cell biology

Diverse microbial ecosystems underpin life in the sea. Among these microbes are many unicellular eukaryotes that span the diversity of the eukaryotic tree of life. However, genetic tractability has been limited to a few species, which do not represent eukaryotic diversity or environmentally relevant taxa. Here, we report on the development of genetic tools in a range of protists primarily from marine environments. We present evidence for foreign DNA delivery and expression in 13 species never before transformed and for advancement of tools for eight other species, as well as potential reasons for why transformation of yet another 17 species tested was not achieved. Our resource in genetic manipulation will provide insights into the ancestral eukaryotic lifeforms, general eukaryote cell biology, protein diversification and the evolution of cellular pathways.

Overview of the role of kinetoplastid surface carbohydrates in infection and host cell invasion: prospects for therapeutic intervention

Kinetoplastid parasites are responsible for serious diseases in humans and livestock such as Chagas disease and sleeping sickness (caused by Trypanosoma cruzi and Trypanosoma brucei, respectively), and the different forms of cutaneous, mucocutaneous and visceral leishmaniasis (produced by Leishmania spp). The limited number of antiparasitic drugs available together with the emergence of resistance underscores the need for new therapeutic agents with novel mechanisms of action. The use of agents binding to surface glycans has been recently suggested as a new approach to antitrypanosomal design and a series of peptidic and non-peptidic carbohydrate-binding agents have been identified as antiparasitics showing efficacy in animal models of sleeping sickness. Here we provide an overview of the nature of surface glycans in three kinetoplastid parasites, T. cruzi, T. brucei and Leishmania. Their role in virulence and host cell invasion is highlighted with the aim of identifying specific glycan-lectin interactions and carbohydrate functions that may be the target of novel carbohydrate-binding agents with therapeutic applications.

Inducible orthogonal aminoacylation demonstrates that charging is required for mitochondrial tRNA import in Trypanosoma brucei

Orthogonal aminoacyl-tRNA synthetase/tRNA pairs have emerged as powerful means of site-specifically introducing non-standard amino acids into proteins in vivo. Using amino acids with crosslinking moieties this method allows the identification of transient protein-protein interactions. Here we have introduced a previously characterized evolved tyrosyl-tRNA synthetase/suppressor tRNA^Tyr pair from E. coli into the parasitic protozoan Trypanosoma brucei. Upon addition of a suitable non-standard amino acid the suppressor tRNA^Tyr was charged and allowed translation of a green fluorescent protein whose gene contained a nonsense mutation. - T. brucei is unusual in that its mitochondrion lacks tRNA genes indicating that all its organellar tRNAs are imported from the cytosol. Expression of the bacterial tyrosyl-tRNA synthetase in our system is tetracycline-inducible. We have therefore used it to demonstrate that cytosolic aminoacylation of the suppressor tRNA^Tyr induces its import into the mitochondrion.

State-of-the-art CRISPR/Cas9 Technology for Genome Editing in Trypanosomatids

CRISPR/Cas9 technology has revolutionized biology. This prokaryotic defense system against foreign DNA has been repurposed for genome editing in a broad range of cell tissues and organisms. Trypanosomatids are flagellated protozoa belonging to the order Kinetoplastida. Some of its most representative members cause important human diseases affecting millions of people worldwide, such as Chagas disease, sleeping sickness and different forms of leishmaniases. Trypanosomatid infections represent an enormous burden for public health and there are no effective treatments for most of the diseases they cause. Since the emergence of the CRISPR/Cas9 technology, the genetic manipulation of these parasites has notably improved. As a consequence, genome editing is now playing a key role in the functional study of proteins, in the characterization of metabolic pathways, in the validation of alternative targets for antiparasitic interventions, and in the study of parasite biology and pathogenesis. In this work we review the different strategies that have been used to adapt the CRISPR/Cas9 system to Trypanosoma cruzi, Trypanosoma brucei, and Leishmania spp., as well as the research progress achieved using these approaches. Thereby, we will present the state-of-the-art molecular tools available for genome editing in trypanosomatids to finally point out the future perspectives in the field.

Trypanostatic activity of geranylacetone: Mitigation of Trypanosoma congolense-associated pathological pertubations and insight into the mechanism of anaemia amelioration using in vitro and in silico models

Trypanosoma congolense is an important pathogen that wreaks havoc in the livestock industry of the African continent. This study evaluated the in vivo antitrypanosomal activity of geranylacetone and its ameliorative effect on the disease-induced anaemia and organ damages as well as its inhibitory effects against trypanosomal sialidase using in vitro and in silico techniques. Geranylacetone was used to treat T. congolense infected rats, at a dose of 50 and 100 mg/kg BW, for 14 days where it was found to reduce the parasite burden in the infected animals. Moreover, 100 mg/kg BW of geranylacetone significantly (p < 0.05) ameliorated the anaemia, hepatic and renal damages caused by the parasite. This is in addition to the alleviation of the parasite-induced hepatosplenomegaly and upsurge in free serum sialic acid levels in the infected animals which were associated with the observed anaemia amelioration by the compound. Consequently, bloodstream T. congolense sialidase was partially purified on DEAE cellulose column and inhibition kinetic studies revealed that the enzyme was inhibited by geranylacetone via an uncompetitive inhibition pattern. In silico analysis using molecular docking with Autodock Vina indicated that geranylacetone binds to trypanosomal sialidase with a minimum free binding energy of -5.8 kcal/mol which was mediated by 26 different kinds of non-covalent interactions excluding hydrogen bond whilst Asp163 and Phe421 had the highest number of the interactions. The data suggests that geranylacetone has trypanostatic activity and could protect animals against the T. congolense-induced anaemia through the inhibition of sialidase and/or the protection of the parasite-induced hepatosplenomegaly.

2018 in review: five hot topics in tropical medicine

The year 2018 heralded many new developments in the field of tropical medicine, including licensure of novel drugs for novel indications, licensure of existing drugs for existing indications but in novel settings, and globalized outbreaks of both vector-borne and zoonotic diseases. We herein describe five top stories in tropical medicine that occurred during 2018, and illuminate the practice-changing development within each story.

The composition and abundance of bacterial communities residing in the gut of Glossina palpalis palpalis captured in two sites of southern Cameroon

Background

A number of reports have demonstrated the role of insect bacterial flora on their host’s physiology and metabolism. The tsetse host and vector of trypanosomes responsible for human sleeping sickness (human African trypanosomiasis, HAT) and nagana in animals (African animal trypanosomiasis, AAT) carry bacteria that influence its diet and immune processes. However, the mechanisms involved in these processes remain poorly documented. This underscores the need for increased research into the bacterial flora composition and structure of tsetse flies. The aim of this study was to identify the diversity and relative abundance of bacterial genera in Glossina palpalis palpalis flies collected in two trypanosomiasis foci in Cameroon.

Methods

Samples of G. p. palpalis which were either negative or naturally trypanosome-positive were collected in two foci located in southern Cameroon (Campo and Bipindi). Using the V3V4 and V4 variable regions of the small subunit of the 16S ribosomal RNA gene, we analyzed the respective bacteriome of the flies’ midguts.

Results

We identified ten bacterial genera. In addition, we observed that the relative abundance of the obligate endosymbiont Wigglesworthia was highly prominent (around 99%), regardless of the analyzed region. The remaining genera represented approximately 1% of the bacterial flora, and were composed of Salmonella, Spiroplasma, Sphingomonas, Methylobacterium, Acidibacter, Tsukamurella, Serratia, Kluyvera and an unidentified bacterium. The genus Sodalis was present but with a very low abundance. Globally, no statistically significant difference was found between the bacterial compositions of flies from the two foci, and between positive and trypanosome-negative flies. However, Salmonella and Serratia were only described in trypanosome-negative flies, suggesting a potential role for these two bacteria in fly refractoriness to trypanosome infection. In addition, our study showed the V4 region of the small subunit of the 16S ribosomal RNA gene was more efficient than the V3V4 region at describing the totality of the bacterial diversity.

Conclusions

A very large diversity of bacteria was identified with the discovering of species reported to secrete anti-parasitic compounds or to modulate vector competence in other insects. For future studies, the analyses should be enlarged with larger sampling including foci from several countries.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3402-2) contains supplementary material, which is available to authorized users.

Inhibition of F1 -ATPase from Trypanosoma brucei by its regulatory protein inhibitor TbIF1

Hydrolysis of ATP by the mitochondrial F-ATPase is inhibited by a protein called IF1 . In the parasitic flagellate, Trypanosoma brucei, this protein, known as TbIF1 , is expressed exclusively in the procyclic stage, where the F-ATPase is synthesizing ATP. In the bloodstream stage, where TbIF1 is absent, the F-ATPase hydrolyzes ATP made by glycolysis and compensates for the absence of a proton pumping respiratory chain by translocating protons into the intermembrane space, thereby maintaining the essential mitochondrial membrane potential. We have defined regions and amino acid residues of TbIF1 that are required for its inhibitory activity by analyzing the binding of several modified recombinant inhibitors to F1 -ATPase isolated from the procyclic stage of T. brucei. Kinetic measurements revealed that the C-terminal portion of TbIF1 facilitates homodimerization, but it is not required for the inhibitory activity, similar to the bovine and yeast orthologs. However, in contrast to bovine IF1 , the inhibitory capacity of the C-terminally truncated TbIF1 diminishes with decreasing pH, similar to full length TbIF1 . This effect does not involve the dimerization of active dimers to form inactive tetramers. Over a wide pH range, the full length and C-terminally truncated TbIF1 form dimers and monomers, respectively. TbIF1 has no effect on bovine F1 -ATPase, and this difference in the mechanism of regulation of the F-ATPase between the host and the parasite could be exploited in the design of drugs to combat human and animal African trypanosomiases.

Brain-Penetrant Triazolopyrimidine and Phenylpyrimidine Microtubule Stabilizers as Potential Leads to Treat Human African Trypanosomiasis

In vitro whole-organism screens of Trypanosoma brucei with representative examples of brain-penetrant microtubule (MT)-stabilizing agents identified lethal triazolopyrimidines and phenylpyrimidines with sub-micromolar potency. In mammalian cells, these antiproliferative compounds disrupt MT integrity and decrease total tubulin levels. Their parasiticidal potency, combined with their generally favorable pharmacokinetic properties, which include oral bioavailability and brain penetration, suggest that these compounds are potential leads against human African trypanosomiasis.

Trypanosomatids Are Much More than Just Trypanosomes: Clues from the Expanded Family Tree

Trypanosomes and leishmanias are widely known parasites of humans. However, they are just two out of several phylogenetic lineages that constitute the family Trypanosomatidae. Although dixeny - the ability to infect two hosts - is a derived trait of vertebrate-infecting parasites, the majority of trypanosomatids are monoxenous. Like their common ancestor, the monoxenous Trypanosomatidae are mostly parasites or commensals of insects. This review covers recent advances in the study of insect trypanosomatids, highlighting their diversity as well as genetic, morphological and biochemical complexity, which, until recently, was underappreciated. The investigation of insect trypanosomatids is providing an important foundation for understanding the origin and evolution of parasitism, including colonization of vertebrates and the appearance of human pathogens.

Cultured bloodstream Trypanosoma brucei adapt to life without mitochondrial translation release factor 1

Trypanosoma brucei is an extracellular parasite that alternates between an insect vector (procyclic form) and the bloodstream of a mammalian host (bloodstream form). While it was previously reported that mitochondrial release factor 1 (TbMrf1) is essential in cultured procyclic form cells, we demonstrate here that in vitro bloodstream form cells can tolerate the elimination of TbMrf1. Therefore, we explored if this discrepancy is due to the unique bioenergetics of the parasite since procyclic form cells rely on oxidative phosphorylation; whereas bloodstream form cells utilize glycolysis for ATP production and F_oF₁-ATPase to maintain the essential mitochondrial membrane potential. The observed disruption of intact bloodstream form F_oF₁-ATPases serves as a proxy to indicate that the translation of its mitochondrially encoded subunit A6 is impaired without TbMrf1. While these null mutants have a decreased mitochondrial membrane potential, they have adapted by increasing their dependence on the electrogenic contributions of the ADP/ATP carrier to maintain the mitochondrial membrane potential above the minimum threshold required for T. brucei viability in vitro. However, this inefficient compensatory mechanism results in avirulent mutants in mice. Finally, the depletion of the codon-independent release factor TbPth4 in the TbMrf1 knockouts further exacerbates the characterized mitchondrial phenotypes.

Conservation and Variation in Strategies for DNA Replication of Kinetoplastid Nuclear Genomes

Introduction:

Understanding how the nuclear genome of kinetoplastid parasites is replicated received experimental stimulus from sequencing of the Leishmania major, Trypanosoma brucei and Trypanosoma cruzi genomes around 10 years ago. Gene annotations suggested key players in DNA replication initiation could not be found in these organisms, despite considerable conservation amongst characterised eukaryotes. Initial studies that indicated trypanosomatids might possess an archaeal-like Origin Recognition Complex (ORC), composed of only a single factor termed ORC1/CDC6, have been supplanted by the more recent identification of an ORC in T. brucei. However, the constituent subunits of T. brucei ORC are highly diverged relative to other eukaryotic ORCs and the activity of the complex appears subject to novel, positive regulation. The availability of whole genome sequences has also allowed the deployment of genome-wide strategies to map DNA replication dynamics, to date in T. brucei and Leishmania. ORC1/CDC6 binding and function in T. brucei displays pronounced overlap with the unconventional organisation of gene expression in the genome. Moreover, mapping of sites of replication initiation suggests pronounced differences in replication dynamics in Leishmania relative to T. brucei.

Conclusion:

Here we discuss what implications these emerging data may have for parasite and eukaryotic biology of DNA replication.

Developmental adaptations of trypanosome motility to the tsetse fly host environments unravel a multifaceted in vivo microswimmer system

The highly motile and versatile protozoan pathogen Trypanosoma brucei undergoes a complex life cycle in the tsetse fly. Here we introduce the host insect as an expedient model environment for microswimmer research, as it allows examination of microbial motion within a diversified, secluded and yet microscopically tractable space. During their week-long journey through the different microenvironments of the fly´s interior organs, the incessantly swimming trypanosomes cross various barriers and confined surroundings, with concurrently occurring major changes of parasite cell architecture. Multicolour light sheet fluorescence microscopy provided information about tsetse tissue topology with unprecedented resolution and allowed the first 3D analysis of the infection process. High-speed fluorescence microscopy illuminated the versatile behaviour of trypanosome developmental stages, ranging from solitary motion and near-wall swimming to collective motility in synchronised swarms and in confinement. We correlate the microenvironments and trypanosome morphologies to high-speed motility data, which paves the way for cross-disciplinary microswimmer research in a naturally evolved environment.

Transcriptional Profiling of Midguts Prepared from Trypanosoma/T. congolense-Positive Glossina palpalis palpalis Collected from Two Distinct Cameroonian Foci: Coordinated Signatures of the Midguts' Remodeling As T. congolense-Supportive Niches

Our previous transcriptomic analysis of Glossina palpalis gambiensis experimentally infected or not with Trypanosoma brucei gambiense aimed to detect differentially expressed genes (DEGs) associated with infection. Specifically, we selected candidate genes governing tsetse fly vector competence that could be used in the context of an anti-vector strategy, to control human and/or animal trypanosomiasis. The present study aimed to verify whether gene expression in field tsetse flies (G. p. palpalis) is modified in response to natural infection by trypanosomes (T. congolense), as reported when insectary-raised flies (G. p. gambiensis) are experimentally infected with T. b. gambiense. This was achieved using the RNA-seq approach, which identified 524 DEGs in infected vs. non-infected tsetse flies, including 285 downregulated genes and 239 upregulated genes (identified using DESeq2). Several of these genes were highly differentially expressed, with log2 fold change values in the vicinity of either +40 or −40. Downregulated genes were primarily involved in transcription/translation processes, whereas encoded upregulated genes governed amino acid and nucleotide biosynthesis pathways. The BioCyc metabolic pathways associated with infection also revealed that downregulated genes were mainly involved in fly immunity processes. Importantly, our study demonstrates that data on the molecular cross-talk between the host and the parasite (as well as the always present fly microbiome) recorded from an experimental biological model has a counterpart in field flies, which in turn validates the use of experimental host/parasite couples.

Spatial Organization of Metabolic Enzyme Complexes in Cells

The organization of metabolic multienzyme complexes has been hypothesized to benefit metabolic processes and provide a coordinated way for the cell to regulate metabolism. Historically, their existence has been supported by various in vitro techniques. However, it is only recently that the existence of metabolic complexes inside living cells has come to light to corroborate this long-standing hypothesis. Indeed, subcellular compartmentalization of metabolic enzymes appears to be widespread and highly regulated. On the other hand, it is still challenging to demonstrate the functional significance of these enzyme complexes in the context of the cellular milieu. In this review, we discuss the current understanding of metabolic enzyme complexes by primarily focusing on central carbon metabolism and closely associated metabolic pathways in a variety of organisms, as well as their regulation and functional contributions to cells.

Translational Rodent Models for Research on Parasitic Protozoa-A Review of Confounders and Possibilities

Rodents, in particular Mus musculus, have a long and invaluable history as models for human diseases in biomedical research, although their translational value has been challenged in a number of cases. We provide some examples in which rodents have been suboptimal as models for human biology and discuss confounders which influence experiments and may explain some of the misleading results. Infections of rodents with protozoan parasites are no exception in requiring close consideration upon model choice. We focus on the significant differences between inbred, outbred and wild animals, and the importance of factors such as microbiota, which are gaining attention as crucial variables in infection experiments. Frequently, mouse or rat models are chosen for convenience, e.g., availability in the institution rather than on an unbiased evaluation of whether they provide the answer to a given question. Apart from a general discussion on translational success or failure, we provide examples where infections with single-celled parasites in a chosen lab rodent gave contradictory or misleading results, and when possible discuss the reason for this. We present emerging alternatives to traditional rodent models, such as humanized mice and organoid primary cell cultures. So-called recombinant inbred strains such as the Collaborative Cross collection are also a potential solution for certain challenges. In addition, we emphasize the advantages of using wild rodents for certain immunological, ecological, and/or behavioral questions. The experimental challenges (e.g., availability of species-specific reagents) that come with the use of such non-model systems are also discussed. Our intention is to foster critical judgment of both traditional and newly available translational rodent models for research on parasitic protozoa that can complement the existing mouse and rat models.

Non-canonical binding interactions of the RNA recognition motif (RRM) domains of P34 protein modulate binding within the 5S ribonucleoprotein particle (5S RNP)

RNA binding proteins are involved in many aspects of RNA metabolism. In Trypanosoma brucei, our laboratory has identified two trypanosome-specific RNA binding proteins P34 and P37 that are involved in the maturation of the 60S subunit during ribosome biogenesis. These proteins are part of the T. brucei 5S ribonucleoprotein particle (5S RNP) and P34 binds to 5S ribosomal RNA (rRNA) and ribosomal protein L5 through its N-terminus and its RNA recognition motif (RRM) domains. We generated truncated P34 proteins to determine these domains’ interactions with 5S rRNA and L5. Our analyses demonstrate that RRM1 of P34 mediates the majority of binding with 5S rRNA and the N-terminus together with RRM1 contribute the most to binding with L5. We determined that the consensus ribonucleoprotein (RNP) 1 and 2 sequences, characteristic of canonical RRM domains, are not fully conserved in the RRM domains of P34. However, the aromatic amino acids previously described to mediate base stacking interactions with their RNA target are conserved in both of the RRM domains of P34. Surprisingly, mutation of these aromatic residues did not disrupt but instead enhanced 5S rRNA binding. However, we identified four arginine residues located in RRM1 of P34 that strongly impact L5 binding. These mutational analyses of P34 suggest that the binding site for 5S rRNA and L5 are near each other and specific residues within P34 regulate the formation of the 5S RNP. These studies show the unique way that the domains of P34 mediate binding with the T. brucei 5S RNP.

Trypanosoma brucei TbIF1 inhibits the essential F1-ATPase in the infectious form of the parasite

The mitochondrial (mt) F_oF₁-ATP synthase of the digenetic parasite, Trypanosoma brucei, generates ATP during the insect procyclic form (PF), but becomes a perpetual consumer of ATP in the mammalian bloodstream form (BF), which lacks a canonical respiratory chain. This unconventional dependence on F_oF₁-ATPase is required to maintain the essential mt membrane potential (Δψm). Normally, ATP hydrolysis by this rotary molecular motor is restricted to when eukaryotic cells experience sporadic hypoxic conditions, during which this compulsory function quickly depletes the cellular ATP pool. To protect against this cellular treason, the highly conserved inhibitory factor 1 (IF1) binds the enzyme in a manner that solely inhibits the hydrolytic activity. Intriguingly, we were able to identify the IF1 homolog in T. brucei (TbIF1), but determined that its expression in the mitochondrion is tightly regulated throughout the life cycle as it is only detected in PF cells. TbIF1 appears to primarily function as an emergency brake in PF cells, where it prevented the restoration of the Δψm by F_oF₁-ATPase when respiration was chemically inhibited. In vitro, TbIF1 overexpression specifically inhibits the hydrolytic activity but not the synthetic capability of the F_oF₁-ATP synthase in PF mitochondria. Furthermore, low μM amounts of recombinant TbIF1 achieve the same inhibition of total mt ATPase activity as the F_oF₁-ATPase specific inhibitors, azide and oligomycin. Therefore, even minimal ectopic expression of TbIF1 in BF cells proved lethal as the indispensable Δψm collapsed due to inhibited F_oF₁-ATPase. In summary, we provide evidence that T. brucei harbors a natural and potent unidirectional inhibitor of the vital F_oF₁-ATPase activity that can be exploited for future structure-based drug design.

Enzymes are catalysts that drive both a forward and reverse chemical reaction depending on the thermodynamic properties. F_oF₁-ATP synthase is a multiprotein enzyme that under normal physiological conditions generates ATP. However, when respiration is impeded, this rotary molecular machine reverses and hydrolyzes ATP to pump protons and maintain the essential mitochondrial membrane potential. While this activity is exceptional in most eukaryotic cells, the unique composition of the Trypanosoma brucei mitochondrion dictates that the infectious stage of this human parasite is utterly dependent on the hydrolytic activity of F_oF₁-ATPase. While searching for better chemotherapeutics against Human African Trypanosomiasis, several trypanocidal compounds were determined to interact with this enzyme, but they indiscriminately inhibit both the ATP hydrolytic and synthetic activities. A more promising approach involves the conserved eukaryotic protein IF1, a unidirectional inhibitor that prevents just ATP hydrolysis. Auspiciously, we identified this protein homolog in T. brucei (TbIF1) and its expression is tightly regulated between life stages of the parasite. Importantly, the introduction of exogenous TbIF1 protein specifically inhibits F_oF₁-ATPase and is lethal for the infectious stage of T. brucei. Therefore, we have identified a natural inhibitor of an essential and druggable enzyme that can be exploited for future structure-based drug design.

Identification and characterization of guanosine 5'-monophosphate reductase of Trypanosoma congolense as a drug target

Trypanosoma congolense is one of the most prevalent pathogens which causes trypanosomosis in African animals, resulting in a significant economic loss. In its life cycle, T. congolense is incapable of synthesizing purine nucleotides via a de novo pathway, and thus relies on a salvage pathway to survive. In this study, we identified a gene from T. congolense, TcIL3000_5_1940, as a guanosine 5'-monophosphate reductase (GMPR), an enzyme that modulates the concentration of intracellular guanosine in the pathogen. The recombinant protein was expressed in Escherichia coli, and the gene product was enzymatically confirmed as a unique GMPR, designated as rTcGMPR. This enzyme was constitutively expressed in glycosomes at all of the parasite's developmental stages similar to other purine nucleotide metabolic enzymes. Mycophenolic acid (MPA) was found to inhibit rTcGMPR activity. Hence, it is a potential lead compound for the design of trypanocidal agents, specifically GMPR inhibitor.

Simplifying nature: Towards the design of broad spectrum kinetoplastid inhibitors, inspired by acetogenins

The need for new treatments for the neglected tropical diseases African sleeping sickness, Chagas disease and Leishmaniasis remains urgent with the diseases widespread in tropical regions, affecting the world's very poorest. We have previously reported bis-tetrahydropyran 1,4-triazole analogues designed as mimics of the annonaceous acetogenin natural product chamuvarinin, which maintained trypanocidal activity. Building upon these studies, we here report related triazole compounds with pendant heterocycles, mimicking the original butenolide of the natural product. Analogues were active against T. brucei, with a nitrofuran compound displaying nanomolar trypanocidal activity. Several analogues also showed strong activity against T. cruzi and L. major. Importantly, select compounds gave excellent selectivity over mammalian cells with a furan-based analogue highly selective while remaining active against all three cell lines, thus representing a potential lead for a new broad spectrum kinetoplastid inhibitor.

Moramonas marocensis gen. nov., sp. nov.: a jakobid flagellate isolated from desert soil with a bacteria-like, but bloated mitochondrial genome

A new jakobid genus has been isolated from Moroccan desert soil. The cyst-forming protist Moramonas marocensis gen. nov., sp. nov. has two anteriorly inserted flagella of which one points to the posterior cell pole accompanying the ventral feeding groove and is equipped with a dorsal vane-a feature typical for the Jakobida. It further shows a flagellar root system consisting of singlet microtubular root, left root (R1), right root (R2) and typical fibres associated with R1 and R2. The affiliation of M. marocensis to the Jakobida was confirmed by molecular phylogenetic analyses of the SSU rRNA gene, five nuclear genes and 66 mitochondrial protein-coding genes. The mitochondrial genome has the high number of genes typical for jakobids, and bacterial features, such as the four-subunit RNA polymerase and Shine-Dalgarno sequences upstream of the coding regions of several genes. The M. marocensis mitochondrial genome encodes a similar number of genes as other jakobids, but is unique in its very large genome size (greater than 264 kbp), which is three to four times higher than that of any other jakobid species investigated yet. This increase seems to be due to a massive expansion in non-coding DNA, creating a bloated genome like those of plant mitochondria.

New Approaches to Overcome Transport Related Drug Resistance in Trypanosomatid Parasites

Leishmania and Trypanosoma are members of the Trypanosomatidae family that cause severe human infections such as leishmaniasis, Chagas disease, and sleeping sickness affecting millions of people worldwide. Despite efforts to eradicate them, migrations are expanding these infections to developing countries. There are no vaccines available and current treatments depend only on chemotherapy. Drug resistance is a major obstacle for the treatment of these diseases given that existing drugs are old and limited, with some having severe side effects. Most resistance mechanisms developed by these parasites are related with a decreased uptake or increased efflux of the drug due to mutations or altered expression of membrane transporters. Different new approaches have been elaborated that can overcome these mechanisms of resistance including the use of inhibitors of efflux pumps and drug carriers for both active and passive targeting. Here we review new formulations that have been successfully applied to circumvent resistance related to drug transporters, opening alternative ways to solve drug resistance in protozoan parasitic diseases.

A unified approach towards Trypanosoma brucei functional genomics using Gibson assembly

Trypanosoma brucei is the causative agent of human African trypanosomiasis and nagana in cattle. Recent advances in high throughput phenotypic and interaction screens have identified a wealth of novel candidate proteins for diverse functions such as drug resistance, life cycle progression, and cytoskeletal biogenesis. Characterization of these proteins will allow a more mechanistic understanding of the biology of this important pathogen and could identify novel drug targets. However, methods for rapidly validating and prioritizing these potential targets are still being developed. While gene tagging via homologous recombination and RNA interference are available in T. brucei, a general strategy for creating the most effective constructs for these approaches is lacking. Here, we adapt Gibson assembly, a one-step isothermal process that rapidly assembles multiple DNA segments in a single reaction, to create endogenous tagging, overexpression, and long hairpin RNAi constructs that are compatible with well-established T. brucei vectors. The generality of the Gibson approach has several advantages over current methodologies and substantially increases the speed and ease with which these constructs can be assembled.

An evaluation of Minor Groove Binders as anti-Trypanosoma brucei brucei therapeutics

A series of 32 structurally diverse MGBs, derived from the natural product distamycin, was evaluated for activity against Trypanosoma brucei brucei. Four compounds have been found to possess significant activity, in the nanomolar range, and represent hits for further optimisation towards novel treatments for Human and Animal African Trypanosomiases. Moreover, SAR indicates that the head group linking moiety is a significant modulator of biological activity.

Phosphorylation of eIF2α on Threonine 169 is not required for Trypanosoma brucei cell cycle arrest during differentiation

•

Pleomorphic T. brucei expressing an eIF2α phosphorylation site mutant were made.

•

The mutation did not prevent normal arrest and differentiation into stumpy forms.

•

Mutants differentiate into procyclic forms in vitro and in tsetse flies.

The trypanosome life cycle consists of a series of developmental forms each adapted to an environment in the relevant insect and/or mammalian host. The differentiation process from the mammalian bloodstream form to the insect-midgut procyclic form in Trypanosoma brucei occurs in two steps in vivo. First proliferating ‘slender' bloodstream forms differentiate to non-dividing ‘stumpy' forms arrested in G1. Second, in response to environmental cues, stumpy bloodstream forms re-enter the cell cycle and start to proliferate as procyclic forms after a lag during which both cell morphology and gene expression are modified. Nearly all arrested cells have lower rates of protein synthesis when compared to the proliferating equivalent. In eukaryotes, one mechanism used to regulate the overall rate of protein synthesis involves phosphorylation of the alpha subunit of initiation factor eIF2 (eIF2α). The effect of eIF2α phosphorylation is to prevent the action of eIF2B, the guanine nucleotide exchange factor that activates eIF2 for the next rounds of initiation. To investigate the role of the phosphorylation of eIF2α in the life cycle of T. brucei, a cell line was made with a single eIF2α gene that contained the phosphorylation site, threonine 169, mutated to alanine. These cells were capable of differentiating from proliferating bloodstream form cells into arrested stumpy forms in mice and into procyclic forms in vitro and in tsetse flies. These results indicate that translation attenuation mediated by the phosphorylation of eIF2α on threonine 169 is not necessary for the cell cycle arrest associated with these differentiation processes.

Subverting lysosomal function in Trypanosoma brucei

In this issue of Microbial Cell, Koh and colleagues present data highlighting the utility of the lysosomotropic compound L-leucyl-L-leucyl methyl ester (LeuLeu-OMe) as an anti-Trypanosoma brucei agent, adding to the range of compounds that either directly target lysosomal enzymes or that can be used to subvert the function of the lysosome for parasite destruction.

Cancer in the parasitic protozoans Trypanosoma brucei and Toxoplasma gondii

Cancer is a general name for more than 100 malignant diseases. It is postulated that all cancers start from a single abnormal cell that grows out of control. Untreated cancers can cause serious consequences and deaths. Great progress has been made in cancer research that has significantly improved our knowledge and understanding of the nature and mechanisms of the disease, but the origins of cancer are far from being well understood due to the limitations of suitable model systems and to the complexities of the disease. In view of the fact that cancers are found in various species of vertebrates and other metazoa, here, we suggest that cancer also occurs in parasitic protozoans such as Trypanosoma brucei, a blood parasite, and Toxoplasma gondii, an obligate intracellular pathogen. Without treatment, these protozoan cancers may cause severe disease and death in mammals, including humans. The simpler genomes of these single-cell organisms, in combination with their complex life cycles and fascinating life cycle differentiation processes, may help us to better understand the origins of cancers and, in particular, leukemias.