Experimental genetic crosses in tsetse flies of the livestock pathogen Trypanosoma congolense savannah

BACKGROUND

In tropical Africa animal trypanosomiasis is a disease that has severe impacts on the health and productivity of livestock in tsetse fly-infested regions. Trypanosoma congolense savannah (TCS) is one of the main causative agents and is widely distributed across the sub-Saharan tsetse belt. Population genetics analysis has shown that TCS is genetically heterogeneous and there is evidence for genetic exchange, but to date Trypanosoma brucei is the only tsetse-transmitted trypanosome with experimentally proven capability to undergo sexual reproduction, with meiosis and production of haploid gametes. In T. brucei sex occurs in the fly salivary glands, so by analogy, sex in TCS should occur in the proboscis, where the corresponding portion of the developmental cycle takes place. Here we test this prediction using genetically modified red and green fluorescent clones of TCS.

METHODS

Three fly-transmissible strains of TCS were transfected with genes for red or green fluorescent protein, linked to a gene for resistance to the antibiotic hygromycin, and experimental crosses were set up by co-transmitting red and green fluorescent lines in different combinations via tsetse flies, Glossina pallidipes. To test whether sex occurred in vitro, co-cultures of attached epimastigotes of one red and one green fluorescent TCS strain were set up and sampled at intervals for 28 days.

RESULTS

All interclonal crosses of genetically modified trypanosomes produced hybrids containing both red and green fluorescent proteins, but yellow fluorescent hybrids were only present among trypanosomes from the fly proboscis, not from the midgut or proventriculus. It was not possible to identify the precise life cycle stage that undergoes mating, but it is probably attached epimastigotes in the food canal of the proboscis. Yellow hybrids were seen as early as 14 days post-infection. One intraclonal cross in tsetse and in vitro co-cultures of epimastigotes also produced yellow hybrids in small numbers. The hybrid nature of the yellow fluorescent trypanosomes observed was not confirmed by genetic analysis.

CONCLUSIONS

Despite absence of genetic characterisation of hybrid trypanosomes, the fact that these were produced only in the proboscis and in several independent crosses suggests that they are products of mating rather than cell fusion. The three-way strain compatibility observed is similar to that demonstrated previously for T. brucei, indicating that a simple two mating type system does not apply for either trypanosome species.

Development of the livestock pathogen Trypanosoma (Nannomonas) simiae in the tsetse fly with description of putative sexual stages from the proboscis

BACKGROUND

Tsetse-transmitted African animal trypanosomiasis is recognised as an important disease of ruminant livestock in sub-Saharan Africa, but also affects domestic pigs, with Trypanosoma simiae notable as a virulent suid pathogen that can rapidly cause death. Trypanosoma simiae is widespread in tsetse-infested regions, but its biology has been little studied compared to T. brucei and T. congolense.

METHODS

Trypanosoma simiae procyclics were cultured in vitro and transfected using protocols developed for T. brucei. Genetically modified lines, as well as wild-type trypanosomes, were transmitted through tsetse flies, Glossina pallidipes, to study T. simiae development in the tsetse midgut, proventriculus and proboscis. The development of proventricular trypanosomes was also studied in vitro. Image and mensural data were collected and analysed.

RESULTS

A PFR1::YFP line successfully completed development in tsetse, but a YFP::HOP1 line failed to progress beyond midgut infection. Analysis of image and mensural data confirmed that the vector developmental cycles of T. simiae and T. congolense are closely similar, but we also found putative sexual stages in T. simiae, as judged by morphological similarity to these stages in T. brucei. Putative meiotic dividers were abundant among T. simiae trypanosomes in the proboscis, characterised by a large posterior nucleus and two anterior kinetoplasts. Putative gametes and other meiotic intermediates were also identified by characteristic morphology. In vitro development of proventricular forms of T. simiae followed the pattern previously observed for T. congolense: long proventricular trypanosomes rapidly attached to the substrate and shortened markedly before commencing cell division.

CONCLUSIONS

To date, T. brucei is the only tsetse-transmitted trypanosome with experimentally proven capability to undergo sexual reproduction, which occurs in the fly salivary glands. By analogy, sexual stages of T. simiae or T. congolense are predicted to occur in the proboscis, where the corresponding portion of the developmental cycle takes place. While no such stages have been observed in T. congolense, for T. simiae putative sexual stages were abundant in the tsetse proboscis. Although our initial attempt to demonstrate expression of a YFP-tagged, meiosis-specific protein was unsuccessful, the future application of transgenic approaches will facilitate the identification of meiotic stages and hybrids in T. simiae.

Invariant surface glycoprotein 65 of Trypanosoma brucei is a complement C3 receptor

African trypanosomes are extracellular pathogens of mammals and are exposed to the adaptive and innate immune systems. Trypanosomes evade the adaptive immune response through antigenic variation, but little is known about how they interact with components of the innate immune response, including complement. Here we demonstrate that an invariant surface glycoprotein, ISG65, is a receptor for complement component 3 (C3). We show how ISG65 binds to the thioester domain of C3b. We also show that C3 contributes to control of trypanosomes during early infection in a mouse model and provide evidence that ISG65 is involved in reducing trypanosome susceptibility to C3-mediated clearance. Deposition of C3b on pathogen surfaces, such as trypanosomes, is a central point in activation of the complement system. In ISG65, trypanosomes have evolved a C3 receptor which diminishes the downstream effects of C3 deposition on the control of infection.

Trypanosomes evade the immune response through antigenic variation of a surface coat containing variant surface glycoproteins (VSG). They also express invariant surface glycoproteins (ISGs), which are less well understood. Here, Macleod et al. show that ISG65 of T. brucei is a receptor for complement component 3. They provide the crystal structure of T. brucei ISG65 in complex with complement C3d and show evidence that ISG65 is involved in reducing trypanosome susceptibility to C3-mediated clearance in vivo.

Single-cell transcriptomics reveals expression profiles of Trypanosoma brucei sexual stages

Early diverging lineages such as trypanosomes can provide clues to the evolution of sexual reproduction in eukaryotes. In Trypanosoma brucei, the pathogen that causes Human African Trypanosomiasis, sexual reproduction occurs in the salivary glands of the insect host, but analysis of the molecular signatures that define these sexual forms is complicated because they mingle with more numerous, mitotically-dividing developmental stages. We used single-cell RNA-sequencing (scRNAseq) to profile 388 individual trypanosomes from midgut, proventriculus, and salivary glands of infected tsetse flies allowing us to identify tissue-specific cell types. Further investigation of salivary gland parasite transcriptomes revealed fine-scale changes in gene expression over a developmental progression from putative sexual forms through metacyclics expressing variant surface glycoprotein genes. The cluster of cells potentially containing sexual forms was characterized by high level transcription of the gamete fusion protein HAP2, together with an array of surface proteins and several genes of unknown function. We linked these expression patterns to distinct morphological forms using immunofluorescence assays and reporter gene expression to demonstrate that the kinetoplastid-conserved gene Tb927.10.12080 is exclusively expressed at high levels by meiotic intermediates and gametes. Further experiments are required to establish whether this protein, currently of unknown function, plays a role in gamete formation and/or fusion.

Signatures of hybridization in Trypanosoma brucei

Genetic exchange among disease-causing micro-organisms can generate progeny that combine different pathogenic traits. Though sexual reproduction has been described in trypanosomes, its impact on the epidemiology of Human African Trypanosomiasis (HAT) remains controversial. However, human infective and non-human infective strains of Trypanosoma brucei circulate in the same transmission cycles in HAT endemic areas in subsaharan Africa, providing the opportunity for mating during the developmental cycle in the tsetse fly vector. Here we investigated inheritance among progeny from a laboratory cross of T. brucei and then applied these insights to genomic analysis of field-collected isolates to identify signatures of past genetic exchange. Genomes of two parental and four hybrid progeny clones with a range of DNA contents were assembled and analysed by k-mer and single nucleotide polymorphism (SNP) frequencies to determine heterozygosity and chromosomal inheritance. Variant surface glycoprotein (VSG) genes and kinetoplast (mitochondrial) DNA maxi- and minicircles were extracted from each genome to examine how each of these components was inherited in the hybrid progeny. The same bioinformatic approaches were applied to an additional 37 genomes representing the diversity of T. brucei in subsaharan Africa and T. evansi. SNP analysis provided evidence of crossover events affecting all 11 pairs of megabase chromosomes and demonstrated that polyploid hybrids were formed post-meiotically and not by fusion of the parental diploid cells. VSGs and kinetoplast DNA minicircles were inherited biparentally, with approximately equal numbers from each parent, whereas maxicircles were inherited uniparentally. Extrapolation of these findings to field isolates allowed us to distinguish clonal descent from hybridization by comparing maxicircle genotype to VSG and minicircle repertoires. Discordance between maxicircle genotype and VSG and minicircle repertoires indicated inter-lineage hybridization. Significantly, some of the hybridization events we identified involved human infective and non-human infective trypanosomes circulating in the same geographic areas.

Sexual reproduction allows genes from different individuals to be mixed up in the offspring. This is particularly important for disease-causing microbes, because new combinations of harmful traits can arise, potentially leading to more severe outbreaks of disease. Tsetse-transmitted trypanosomes are single-celled parasites that cause severe human and livestock diseases in tropical Africa. During their developmental cycle in the tsetse fly, trypanosomes can mate and produce hybrid trypanosomes, which have one set of chromosomes from each parent. But polyploid hybrids, with more than one set of chromosomes from one or both parents, are often observed too. Here we have investigated how these polyploid hybrids are formed by comparing the genomes of hybrid progeny with those of their parents. Analysis of the large, paired chromosomes of both diploid and polyploid hybrids showed frequent crossovers, which are the hallmark of meiosis, the special form of division that produces haploid gametes. This indicates that the polyploids were formed after meiosis rather than by fusion of the parental diploid cells. We also investigated the inheritance of two other features of trypanosomes: the large family of variant surface glycoprotein (VSG) genes, and the mitochondrial (kinetoplast) DNA. Hybrid clones had inherited about half the VSG genes from each parent, and also showed biparental inheritance of one component of the kinetoplast DNA, the minicircles. We assessed the relatedness of field-collected trypanosomes by comparing their VSG and minicircle repertoires, together with maxicircle genotype. While most isolates shared few VSGs or minicircles, a group of mostly human-infective strains from Uganda had a large proportion of their repertoires in common. Most of these trypanosomes were probably related by clonal descent, but we also identified that some were hybrids by the mismatch between their maxicircle genotype and their VSG and minicircle repertoires. These signals of hybridization were also detected in some of the other field-collected isolates, suggesting that genetic exchange is widespread in nature. Significantly, the hybridization events involved human infective and non-human infective trypanosomes circulating in the same geographic areas, providing a mechanism for the generation of new, potentially more pathogenic, trypanosome strains causing human disease.

Sequential production of gametes during meiosis in trypanosomes

Meiosis is a core feature of eukaryotes that occurs in all major groups, including the early diverging excavates. In this group, meiosis and production of haploid gametes have been described in the pathogenic protist, Trypanosoma brucei, and mating occurs in the salivary glands of the insect vector, the tsetse fly. Here, we searched for intermediate meiotic stages among trypanosomes from tsetse salivary glands. Many different cell types were recovered, including trypanosomes in Meiosis I and gametes. Significantly, we found trypanosomes containing three nuclei with a 1:2:1 ratio of DNA contents. Some of these cells were undergoing cytokinesis, yielding a mononucleate gamete and a binucleate cell with a nuclear DNA content ratio of 1:2. This cell subsequently produced three more gametes in two further rounds of division. Expression of the cell fusion protein HAP2 (GCS1) was not confined to gametes, but also extended to meiotic intermediates. We propose a model whereby the two nuclei resulting from Meiosis I undergo asynchronous Meiosis II divisions with sequential production of haploid gametes.

A receptor for the complement regulator factor H increases transmission of trypanosomes to tsetse flies

Persistent pathogens have evolved to avoid elimination by the mammalian immune system including mechanisms to evade complement. Infections with African trypanosomes can persist for years and cause human and animal disease throughout sub-Saharan Africa. It is not known how trypanosomes limit the action of the alternative complement pathway. Here we identify an African trypanosome receptor for mammalian factor H, a negative regulator of the alternative pathway. Structural studies show how the receptor binds ligand, leaving inhibitory domains of factor H free to inactivate complement C3b deposited on the trypanosome surface. Receptor expression is highest in developmental stages transmitted to the tsetse fly vector and those exposed to blood meals in the tsetse gut. Receptor gene deletion reduced tsetse infection, identifying this receptor as a virulence factor for transmission. This demonstrates how a pathogen evolved a molecular mechanism to increase transmission to an insect vector by exploitation of a mammalian complement regulator.

Trypanosoma congolense: In Vitro Culture and Transfection

Trypanosoma congolense, together with T. vivax and T. brucei, causes African animal trypanosomiasis (AAT), or nagana, a livestock disease carried by bloodsucking tsetse flies in sub-Saharan Africa. These parasitic protists cycle between two hosts: mammal and tsetse fly. The environment offered by each host to the trypanosome is markedly different, and hence the metabolism of stages found in the mammal differs from that of insect stages. For research on new diagnostics and therapeutics, it is appropriate to use the mammalian life cycle stage, bloodstream forms. Insect stages such as procyclics are useful for studying differentiation and also serve as a convenient source of easily cultured, non-infective organisms. Here, we present protocols in current use in our laboratory for the in vitro culture of different life cycle stages of T. congolense-procyclics, epimastigotes, and bloodstream forms-together with methods for transfection enabling the organism to be genetically modified. © 2019 by John Wiley & Sons, Inc.

Fluorescent proteins reveal what trypanosomes get up to inside the tsetse fly

The discovery and development of fluorescent proteins for the investigation of living cells and whole organisms has been a major advance in biomedical research. This approach was quickly exploited by parasitologists, particularly those studying single-celled protists. Here we describe some of our experiments to illustrate how fluorescent proteins have helped to reveal what trypanosomes get up to inside the tsetse fly. Fluorescent proteins turned the tsetse fly from a “black box” into a bright showcase to track trypanosome migration and development within the insect. Crosses of genetically modified red and green fluorescent trypanosomes produced yellow fluorescent hybrids and established the “when” and “where” of trypanosome sexual reproduction inside the fly. Fluorescent-tagging endogenous proteins enabled us to identify the meiotic division stage and gametes inside the salivary glands of the fly and thus elucidate the mechanism of sexual reproduction in trypanosomes. Without fluorescent proteins we would still be in the “dark ages” of understanding what trypanosomes get up to inside the tsetse fly.

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.

Tsetse-transmitted trypanosomes are parasitic protists that cause severe human and livestock diseases in tropical Africa. During their developmental cycle in the tsetse fly, these trypanosomes undergo complex cycles of differentiation and proliferation. Here we have investigated part of the developmental cycle of the major livestock pathogen Trypanosoma congolense as it moves from the fly midgut via the foregut to the mouthparts, where it reacquires infectivity to mammalian hosts. This transition is difficult to observe in vivo because of the small numbers of migratory trypanosomes and their inaccessibility in the fly. However, prior to migration, trypanosomes accumulate in the proventriculus, the valve that separates the foregut from the midgut, and we were able to observe the behaviour of these cells in vitro. On release from the proventriculus, these trypanosomes readily attach to a glass microscope slide and then undergo drastic remodelling to become short, stout cells, before each produces a small daughter cell. Each mother cell goes on to produce at least one further daughter trypanosome in the same way, while the daughter cells also proliferate as attached cells. We assume that these events would normally happen in vivo inside the tsetse proboscis. In T. brucei the equivalent developmental transition takes place in the proventriculus or foregut in free-swimming rather than attached cells, and is achieved via an asymmetric division. Thus, despite their close evolutionary relationship, these two trypanosome species have evolved different ways of accomplishing what is essentially the same developmental transition.

Microarchitecture of the tsetse fly proboscis

Background

Tsetse flies (genus Glossina) are large blood-sucking dipteran flies that are important as vectors of human and animal trypanosomiasis in sub-Saharan Africa. Tsetse anatomy has been well described, including detailed accounts of the functional anatomy of the proboscis for piercing host skin and sucking up blood. The proboscis also serves as the developmental site for the infective metacyclic stages of several species of pathogenic livestock trypanosomes that are inoculated into the host with fly saliva. To understand the physical environment in which these trypanosomes develop, we have re-examined the microarchitecture of the tsetse proboscis.

Results

We examined proboscises from male and female flies of Glossina pallidipes using light microscopy and scanning electron microscopy (SEM). Each proboscis was removed from the fly head and either examined intact or dissected into the three constituent components: Labrum, labium and hypopharynx. Our light and SEM images reaffirm earlier observations that the tsetse proboscis is a formidably armed weapon, well-adapted for piercing skin, and provide comparative data for G. pallidipes. In addition, the images reveal that the hypopharynx, the narrow tube that delivers saliva to the wound site, ends in a remarkably ornate and complex structure with around ten finger-like projections, each adorned with sucker-like protrusions, contradicting previous descriptions that show a simple, bevelled end like a hypodermic needle. The function of the finger-like projections is speculative; they appear to be flexible and may serve to protect the hypopharynx from influx of blood or microorganisms, or control the flow of saliva. Proboscises were examined after colonisation by Trypanosoma congolense savannah. Consistent with the idea that colonisation commences in the region nearest the foregut, the highest densities of trypanosomes were found in the region of the labrum proximal to the bulb, although high densities were also found in other regions of the labrum. Trypanosomes were visible through the thin wall of the hypopharynx by both light microscopy and SEM.

Conclusions

We highlight the remarkable architecture of the tsetse proboscis, in particular the intricate structure of the distal end of the hypopharynx. Further work is needed to elucidate the function of this intriguing structure.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2367-2) contains supplementary material, which is available to authorized users.

Trypanosoma congolense: Molecular Toolkit and Resources for Studying a Major Livestock Pathogen and Model Trypanosome

The African trypanosomiases are diseases of humans and their livestock caused by trypanosomes carried by bloodsucking tsetse flies. Although the human pathogen Trypanosoma brucei is the best known, other trypanosome species are of greater concern for animal health in sub-Saharan Africa. In particular, Trypanosomacongolense is a major cattle pathogen, which is as amenable to laboratory culture as T. brucei, with the advantage that its whole life cycle can be recapitulated in vitro. Thus, besides being worthy of study in its own right, T. congolense could be useful as a model of trypanosome development. Here we review the biology of T. congolense, highlighting significant and intriguing differences from its sister, T. brucei. An up-to-date compilation of methods for cultivating and genetically manipulating T. congolense in the laboratory is provided, based on published work and current development of methods in our lab, as well as a description of available molecular resources.

Ultrafast X-Ray Diffraction Studies of the Phase Transitions and Equation of State of Scandium Shock Compressed to 82 GPa

Using x-ray diffraction at the Linac Coherent Light Source x-ray free-electron laser, we have determined simultaneously and self-consistently the phase transitions and equation of state (EOS) of the lightest transition metal, scandium, under shock compression. On compression scandium undergoes a structural phase transition between 32 and 35 GPa to the same bcc structure seen at high temperatures at ambient pressures, and then a further transition at 46 GPa to the incommensurate host-guest polymorph found above 21 GPa in static compression at room temperature. Shock melting of the host-guest phase is observed between 53 and 72 GPa with the disappearance of Bragg scattering and the growth of a broad asymmetric diffraction peak from the high-density liquid.

Dynamics of gamete production and mating in the parasitic protist Trypanosoma brucei

BACKGROUND

Sexual reproduction in Plasmodium falciparum and Trypanosoma brucei occurs in the insect vector and is important in generating hybrid strains with different combinations of parental characteristics. Production of hybrid parasite genotypes depends on the likelihood of co-infection of the vector with multiple strains. In mosquitoes, existing infection with Plasmodium facilitates the establishment of a second infection, although the asynchronicity of gamete production subsequently prevents mating. In the trypanosome/tsetse system, flies become increasingly refractory to infection as they age, so the likelihood of a fly acquiring a second infection also decreases. This effectively restricts opportunities for trypanosome mating to co-infections picked up by the fly on its first feed, unless an existing infection increases the chance of successful second infection as in the Plasmodium/mosquito system.

RESULTS

Using green and red fluorescent trypanosomes, we compared the rates of trypanosome infection and hybrid production in flies co-infected on the first feed, co-infected on a subsequent feed 18 days after emergence, or fed sequentially with each trypanosome clone 18 days apart. Infection rates were highest in the midguts and salivary glands (SG) of flies that received both trypanosome clones in their first feed, and were halved when the infected feed was delayed to day 18. In flies fed the two trypanosome clones sequentially, the second clone often failed to establish a midgut infection and consequently was not present in the SG. Nevertheless, hybrids were recovered from all three groups of infected flies. Meiotic stages and gametes were produced continuously from day 11 to 42 after the infective feed, and in sequentially infected flies, the co-occurrence of gametes led to hybrid formation.

CONCLUSIONS

We found that a second trypanosome strain can establish infection in the tsetse SG 18 days after the first infected feed, with co-mingling of gametes and production of trypanosome hybrids. Establishment of the second strain was severely compromised by the strong immune response of the fly to the existing infection. Although sequential infection provides an opportunity for trypanosome mating, the easiest way for a tsetse fly to acquire a mixed infection is by feeding on a co-infected host.

Campylobacter Species and Neutrophilic Inflammatory Bowel Disease in Cats

BACKGROUND

Inflammatory bowel disease (IBD) is a common cause of signs of gastrointestinal disease in cats. A subset of cats with IBD has neutrophilic inflammation of the intestinal mucosa.

HYPOTHESIS

Neutrophilic enteritis in cats is associated with mucosal invasion by microorganisms, and specifically Campylobacter spp.

ANIMALS

Seven cats with neutrophilic IBD and 8 cats with lymphoplasmacytic IBD.

METHODS

Retrospective review of duodenal biopsy specimens that were collected endoscopically for histologic examination. Cases were identified and selected by searching the histopathology archive for cats with a diagnosis of neutrophilic and lymphoplasmacytic IBD. Fluorescence in situ hybridization (FISH) targeting either all eubacteria or individual Campylobacter spp. was performed on archived samples. Neutrophils were detected on the same samples using a FISH probe for neutrophil elastase.

RESULTS

Campylobacter coli was present in (6/7) cats with neutrophilic IBD and in (1/8) cats with lymphoplasmacytic IBD (P = .009). Cats with neutrophilic IBD had significantly higher number of C. coli (median bacteria 0.7/hpf) in the mucosa than cats with lymphoplasmacytic IBD (median bacteria 0/hpf) (P = 0.002). Colocalization of neutrophils and C. coli was demonstrated, with C. coli closer to the neutrophils than any other bacteria (P < .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Identification of C. coli associated with neutrophilic inflammation suggests that C. coli is able either to produce compounds which stimulate neutrophils or to induce feline intestinal cells to produce neutrophil chemoattractants. This association should allow a directed therapeutic approach in cats with neutrophilic IBD, potentially improving outcome and reducing any zoonotic risk.

Evolutionary diversification of the trypanosome haptoglobin-haemoglobin receptor from an ancestral haemoglobin receptor

The haptoglobin-haemoglobin receptor of the African trypanosome species, Trypanosoma brucei, is expressed when the parasite is in the bloodstream of the mammalian host, allowing it to acquire haem through the uptake of haptoglobin-haemoglobin complexes. Here we show that in Trypanosoma congolense this receptor is instead expressed in the epimastigote developmental stage that occurs in the tsetse fly, where it acts as a haemoglobin receptor. We also present the structure of the T. congolense receptor in complex with haemoglobin. This allows us to propose an evolutionary history for this receptor, charting the structural and cellular changes that took place as it adapted from a role in the insect to a new role in the mammalian host.

DOI:http://dx.doi.org/10.7554/eLife.13044.001

Trypanosomes are single-celled parasites that infect a range of animal hosts. These parasites need a molecule called haem to grow properly and are mostly spread by insects that feed on the blood of mammals. Most haem in mammals is found in red blood cells and is bound to a protein called haemoglobin. When it is released from these cells, haemoglobin forms a complex with another protein called haptoglobin as well.

The best-studied trypanosomes from Africa have a receptor protein on their surface that recognizes the haptoglobin-haemoglobin complex and allows the parasites to obtain haem from their hosts. An African trypanosome called T. brucei causes sleeping sickness in humans, and has a receptor that can only recognize haemoglobin when it is in complex with haptoglobin. However, few trypanosome receptors have been studied to date, and so it was not clear if they all work in the same way.

Trypanosoma congolense is a trypanosome that has a big impact on livestock farmers in sub-Saharan Africa and infects cattle, pigs and goats. Lane-Serff, MacGregor et al. now report that the receptor protein from T. congolense can bind to haemoglobin on its own. A technique called X-ray crystallography was used to reveal the three-dimensional structure of the T. congolense receptor and haemoglobin in fine detail. Further experiments then confirmed that the receptor actually binds more strongly to haemoglobin than it does to the haptoglobin-haemoglobin complex.

Experiments with living parasites showed that T. congolense produces its receptor when it is in the mouthparts of its insect host, the tsetse fly. This is unlike what occurs in T. brucei, which only produces its receptor while it is in the bloodstream of its mammalian host. Lane-Serff, MacGregor et al. suggest that T. congolense’s receptor is more like the receptor found in ancestor of the trypanosomes. This means that, at least once during the evolution of these parasites, this receptor evolved from being a haemoglobin receptor produced in the tsetse fly to a haptoglobin-haemoglobin receptor produced in an infected mammal.

The next step is to investigate the details of the role played by the T. congolense receptor when the parasite is in the tsetse fly. It will also be important to understand how this parasite is still able to grow in the mammalian host’s bloodstream even though it does not produce much of the receptor during this stage.

DOI:http://dx.doi.org/10.7554/eLife.13044.002

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

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

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

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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.

Endochondral fracture healing with external fixation in the Sost knockout mouse results in earlier fibrocartilage callus removal and increased bone volume fraction and strength

Sclerostin deficiency, via genetic knockout or anti-Sclerostin antibody treatment, has been shown to cause increased bone volume, density and strength of calluses following endochondral bone healing. However, there is limited data on the effect of Sclerostin deficiency on the formative early stage of fibrocartilage (non-bony tissue) formation and removal. In this study we extensively investigate the early fibrocartilage callus. Closed tibial fractures were performed on Sost(-/-) mice and age-matched wild type (C57Bl/6J) controls and assessed at multiple early time points (7, 10 and 14days), as well as at 28days post-fracture after bony union. External fixation was utilized, avoiding internal pinning and minimizing differences in stability stiffness, a variable that has confounded previous research in this area. Normal endochondral ossification progressed in wild type and Sost(-/-) mice with equivalent volumes of fibrocartilage formed at early day 7 and day 10 time points, and bony union in both genotypes by day 28. There were no significant differences in rate of bony union; however there were significant increases in fibrocartilage removal from the Sost(-/-) fracture calluses at day 14 suggesting earlier progression of endochondral healing. Earlier bone formation was seen in Sost(-/-) calluses over wild type with greater bone volume at day 10 (221%, p<0.01). The resultant Sost(-/-) united bony calluses at day 28 had increased bone volume fraction compared to wild type calluses (24%, p<0.05), and the strength of the fractured Sost(-/-) tibiae was greater than that that of wild type fractured tibiae. In summary, bony union was not altered by Sclerostin deficiency in externally-fixed closed tibial fractures, but fibrocartilage removal was enhanced and the resultant united bony calluses had increased bone fraction and increased strength.

Spatial control of bone formation using a porous polymer scaffold co-delivering anabolic rhBMP-2 and anti-resorptive agents

Current clinical delivery of recombinant human bone morphogenetic proteins (rhBMPs) utilises freeze-dried collagen. Despite effective new bone generation, rhBMP via collagen can be limited by significant complications due to inflammation and uncontrolled bone formation. This study aimed to produce an alternative rhBMP local delivery system to permit more controllable and superior rhBMP-induced bone formation. Cylindrical porous poly(lactic-co-glycolic acid) (PLGA) scaffolds were manufactured by thermally-induced phase separation. Scaffolds were encapsulated with anabolic rhBMP-2 (20 µg) ± anti-resorptive agents: zoledronic acid (5 µg ZA), ZA pre-adsorbed onto hydroxyapatite microparticles, (5 µg ZA/2% HA) or IkappaB kinase (IKK) inhibitor (10 µg PS-1145). Scaffolds were inserted in a 6-mm critical-sized femoral defect in Wistar rats, and compared against rhBMP-2 via collagen. The regenerate region was examined at 6 weeks by 3D microCT and descriptive histology. MicroCT and histology revealed rhBMP-induced bone was more restricted in the PLGA scaffolds than collagen scaffolds (-92.3% TV, p < 0.01). The regenerate formed by PLGA + rhBMP-2/ZA/HA showed comparable bone volume to rhBMP-2 via collagen, and bone mineral density was +9.1% higher (p < 0.01). Local adjunct ZA/HA or PS-1145 significantly enhanced PLGA + rhBMP-induced bone formation by +78.2% and +52.0%, respectively (p ≤ 0.01). Mechanistically, MG-63 human osteoblast-like cells showed cellular invasion and proliferation within PLGA scaffolds. In conclusion, PLGA scaffolds enabled superior spatial control of rhBMP-induced bone formation over clinically-used collagen. The PLGA scaffold has the potential to avoid uncontrollable bone formation-related safety issues and to customise bone shape by scaffold design. Moreover, local treatment with anti-resorptive agents incorporated within the scaffold further augmented rhBMP-induced bone formation.

Meiosis and Haploid Gametes in the Pathogen Trypanosoma brucei

In eukaryote pathogens, sex is an important driving force in spreading genes for drug resistance, pathogenicity, and virulence [1]. For the parasitic trypanosomes that cause African sleeping sickness, mating occurs during transmission by the tsetse vector [2, 3] and involves meiosis [4], but haploid gametes have not yet been identified. Here, we show that meiosis is a normal part of development in the insect salivary glands for all subspecies of Trypanosoma brucei, including the human pathogens. By observing insect-derived trypanosomes during the window of peak expression of meiosis-specific genes, we identified promastigote-like (PL) cells that interacted with each other via their flagella and underwent fusion, as visualized by the mixing of cytoplasmic red and green fluorescent proteins. PL cells had a short, wide body, a very long anterior flagellum, and either one or two kinetoplasts, but only the anterior kinetoplast was associated with the flagellum. Measurement of nuclear DNA contents showed that PL cells were haploid relative to diploid metacyclics. Trypanosomes are among the earliest diverging eukaryotes, and our results support the hypothesis that meiosis and sexual reproduction are ubiquitous in eukaryotes and likely to have been early innovations [5].

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Trypanosoma brucei is a sexual organism

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Meiosis is a normal part of the trypanosome’s life cycle

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Identification of a novel haploid cell type with distinctive morphology

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First visualization of how trypanosomes mate

A modular and optimized single marker system for generating Trypanosoma brucei cell lines expressing T7 RNA polymerase and the tetracycline repressor

Here, we present a simple modular extendable vector system for introducing the T7 RNA polymerase and tetracycline repressor genes into Trypanosoma brucei. This novel system exploits developments in our understanding of gene expression and genome organization to produce a streamlined plasmid optimized for high levels of expression of the introduced transgenes. We demonstrate the utility of this novel system in bloodstream and procyclic forms of Trypanosoma brucei, including the genome strain TREU927/4. We validate these cell lines using a variety of inducible experiments that recapture previously published lethal and non-lethal phenotypes. We further demonstrate the utility of the single marker (SmOx) TREU927/4 cell line for in vivo experiments in the tsetse fly and provide a set of plasmids that enable both whole-fly and salivary gland-specific inducible expression of transgenes.

Psittacid herpesvirus 3 infection in the eclectus parrot (Eclectus roratus) in Australia

Psittacid herpesvirus 3 (PsHV-3) has recently been implicated as the cause of a severe respiratory disease in Bourke's parrots (Neopsephotus bourkii) in the United States. In this report, the clinical manifestations and gross and microscopic lesions of PsHV-3 infection in 2 eclectus parrots (Eclectus roratus) in Australia are described. The presence of a PsHV-3 infection was confirmed by polymerase chain reaction amplification and sequencing of PsHV-3 DNA using degenerate and PsHV-3 primers. Electron microscopy of infected cells demonstrated the assembly of herpesvirus virions as well as intranuclear tubular structures. The detection of PsHV-3 in Australia in 2 eclectus parrots broadens the list of known affected species and confirms the presence of this virus in Australia.

The life cycle of Trypanosoma (Nannomonas) congolense in the tsetse fly

Background

The tsetse-transmitted African trypanosomes cause diseases of importance to the health of both humans and livestock. The life cycles of these trypanosomes in the fly were described in the last century, but comparatively few details are available for Trypanosoma (Nannomonas) congolense, despite the fact that it is probably the most prevalent and widespread pathogenic species for livestock in tropical Africa. When the fly takes up bloodstream form trypanosomes, the initial establishment of midgut infection and invasion of the proventriculus is much the same in T. congolense and T. brucei. However, the developmental pathways subsequently diverge, with production of infective metacyclics in the proboscis for T. congolense and in the salivary glands for T. brucei. Whereas events during migration from the proventriculus are understood for T. brucei, knowledge of the corresponding developmental pathway in T. congolense is rudimentary. The recent publication of the genome sequence makes it timely to re-investigate the life cycle of T. congolense.

Methods

Experimental tsetse flies were fed an initial bloodmeal containing T. congolense strain 1/148 and dissected 2 to 78 days later. Trypanosomes recovered from the midgut, proventriculus, proboscis and cibarium were fixed and stained for digital image analysis. Trypanosomes contained in spit samples from individually caged flies were analysed similarly. Mensural data from individual trypanosomes were subjected to principal components analysis.

Results

Flies were more susceptible to infection with T. congolense than T. brucei; a high proportion of flies infected with T. congolense established a midgut and subsequent proboscis infection, whereas many T. brucei infections were lost in the migration from foregut to salivary glands. In T. congolense, trypomastigotes ceased division in the proventriculus and became uniform in size. The trypanosomes retained trypomastigote morphology during migration via the foregut to the mouthparts and we confirmed that the trypomastigote-epimastigote transition occurred in the proboscis. We found no equivalent to the asymmetric division stage in T. brucei that mediates transition of proventricular trypomastigotes to epimastigotes. In T. congolense extremely long epimastigotes with remarkably elongated posterior ends were observed in both the proboscis and cibarium; no difference was found in the developmental stages in these two organs. Dividing trypomastigotes and epimastigotes were recovered from the proboscis, some of which were in transition from trypomastigote to epimastigote and vice versa. It remains uncertain whether these morphological transitions are mediated by cell division, since we also found non-dividing cells with a variously positioned, juxta-nuclear kinetoplast.

Conclusions

We have presented a detailed description of the life cycle of T. congolense in its tsetse fly vector. During development in the fly T. congolense shares a common migratory pathway with its close relative T. brucei, culminating in the production of small metacyclic trypanosomes that can be inoculated with the saliva. Despite this outward similarity in life cycle, the transitional developmental stages in the foregut and mouthparts are remarkably different in the two trypanosome species.

The Trypanosoma brucei AIR9-like protein is cytoskeleton-associated and is required for nucleus positioning and accurate cleavage furrow placement

AIR9 is a cytoskeleton-associated protein in Arabidopsis thaliana with roles in cytokinesis and cross wall maturation, and reported homologues in land plants and excavate protists, including trypanosomatids. We show that the Trypanosoma brucei AIR9-like protein, TbAIR9, is also cytoskeleton-associated and colocalizes with the subpellicular microtubules. We find it to be expressed in all life cycle stages and show that it is essential for normal proliferation of trypanosomes in vitro. Depletion of TbAIR9 from procyclic trypanosomes resulted in increased cell length due to increased microtubule extension at the cell posterior. Additionally, the nucleus was re-positioned to a location posterior to the kinetoplast, leading to defects in cytokinesis and the generation of aberrant progeny. In contrast, in bloodstream trypanosomes, depletion of TbAIR9 had little effect on nucleus positioning, but resulted in aberrant cleavage furrow placement and the generation of non-equivalent daughter cells following cytokinesis. Our data provide insight into the control of nucleus positioning in this important pathogen and emphasize differences in the cytoskeleton and cell cycle control between two life cycle stages of the T. brucei parasite.

The influence of sex and fly species on the development of trypanosomes in tsetse flies

Unlike other dipteran disease vectors, tsetse flies of both sexes feed on blood and transmit pathogenic African trypanosomes. During transmission, Trypanosoma brucei undergoes a complex cycle of proliferation and development inside the tsetse vector, culminating in production of infective forms in the saliva. The insect manifests robust immune defences throughout the alimentary tract, which eliminate many trypanosome infections. Previous work has shown that fly sex influences susceptibility to trypanosome infection as males show higher rates of salivary gland (SG) infection with T. brucei than females. To investigate sex-linked differences in the progression of infection, we compared midgut (MG), proventriculus, foregut and SG infections in male and female Glossina morsitans morsitans. Initially, infections developed in the same way in both sexes: no difference was observed in numbers of MG or proventriculus infections, or in the number and type of developmental forms produced. Female flies tended to produce foregut migratory forms later than males, but this had no detectable impact on the number of SG infections. The sex difference was not apparent until the final stage of SG invasion and colonisation, showing that the SG environment differs between male and female flies. Comparison of G. m. morsitans with G. pallidipes showed a similar, though less pronounced, sex difference in susceptibility, but additionally revealed very different levels of trypanosome resistance in the MG and SG. While G. pallidipes was more refractory to MG infection, a very high proportion of MG infections led to SG infection in both sexes. It appears that the two fly species use different strategies to block trypanosome infection: G. pallidipes heavily defends against initial establishment in the MG, while G. m. morsitans has additional measures to prevent trypanosomes colonising the SG, particularly in female flies. We conclude that the tsetse-trypanosome interface works differently in G. m. morsitans and G. pallidipes.

In tropical Africa human and livestock diseases caused by parasitic trypanosomes are transmitted by bloodsucking tsetse flies. In the fly, trypanosomes undergo a complex cycle of proliferation and development during their remarkable journey from the midgut to the salivary glands. At every step of the way, the flies mount robust immune defences against trypanosome infection and consequently most flies fail to develop a transmissible infection. Previous work has shown a sex difference in the numbers of salivary gland infections with Trypanosoma brucei: male flies are more susceptible to salivary gland infection than females. Here we explored possible reasons for this. Infections developed in the same way in both male and female flies until the final stage of salivary gland invasion and colonisation. We conclude that the salivary gland environment in the female fly is much more inhospitable for trypanosomes, perhaps because of a greater immune response. Comparison of two different tsetse species showed very different levels of trypanosome resistance in the midgut and salivary glands.

Identification of the meiotic life cycle stage of Trypanosoma brucei in the tsetse fly

Elucidating the mechanism of genetic exchange is fundamental for understanding how genes for such traits as virulence, disease phenotype, and drug resistance are transferred between pathogen strains. Genetic exchange occurs in the parasitic protists Trypanosoma brucei, T. cruzi, and Leishmania major, but the precise cellular mechanisms are unknown, because the process has not been observed directly. Here we exploit the identification of homologs of meiotic genes in the T. brucei genome and demonstrate that three functionally distinct, meiosis-specific proteins are expressed in the nucleus of a single specific cell type, defining a previously undescribed developmental stage occurring within the tsetse fly salivary gland. Expression occurs in clonal and mixed infections, indicating that the meiotic program is an intrinsic but hitherto cryptic part of the developmental cycle of trypanosomes. In experimental crosses, expression of meiosis-specific proteins usually occurred before cell fusion. This is evidence of conventional meiotic division in an excavate protist, and the functional conservation of the meiotic machinery in these divergent organisms underlines the ubiquity and basal evolution of meiosis in eukaryotes.

Evaluation of a multifaceted intervention to limit excessive antipsychotic co-prescribing in schizophrenia out-patients

OBJECTIVE

To evaluate the effect of a multifaceted educational intervention on the frequency of antipsychotic co-prescribing in adult schizophrenia out-patients.

METHOD

Controlled quasi-experimental study performed in two Danish municipalities matched for baseline prevalence of antipsychotic polypharmacy, socioeconomic status and functional level of patients. The intervention was aimed at psychiatric healthcare providers and consisted of 1 day of didactic lectures, six 3-h educational outreach visits and an electronic reminder during drug prescribing.

RESULTS

Between-group use of antipsychotic polypharmacy was compared at baseline (intervention group, N = 232/control group, N = 351) and after 1 year of intervention (intervention group, N = 216/control group, N = 386). The prevalence of antipsychotic polypharmacy at follow-up was not significantly different between treatment settings when adjusting for differences in case-mix (P = 0.07).

CONCLUSION

This multifaceted educational intervention failed to reduce the frequency of antipsychotic co-prescribing, but it suggested that future efforts to improve prescribing practice should address organizational barriers to implementation.

Evidence that low endocytic activity is not directly responsible for human serum resistance in the insect form of African trypanosomes

BACKGROUND

In Trypanosoma brucei, the African trypanosome, endocytosis is developmentally regulated and substantially more active in all known mammalian infective stages. In both mammalian and insect stages endocytic activity is likely required for nutrient acquisition, but in bloodstream forms increased endocytosis is involved in recycling the variant surface glycoprotein and removing host immune factors from the surface. However, a rationale for low endocytic activity in insect stages has not been explored. Here we asked if endocytic down-regulation in the procyclic form was associated with resistance to innate trypanolytic immune factors in the blood meal or tsetse fly midgut.

FINDINGS

Using a well-characterized procyclic parasite with augmented endocytic flux mediated via TbRab5A overexpression, we found that insect stage parasites were able to grow both in the presence of trypanosome lytic factor (TLF) provided in human serum, and also in tsetse flies. Additionally, by placing blood stage parasites in restricted glucose medium, we observed that enlargement of the flagellar pocket, a key morphology associated with defective endocytosis, manifests in parallel with loss of cellular ATP levels.

CONCLUSIONS

These observations suggest that a high rate of endocytosis per se is insufficient to render insect form parasites sensitive to TLF or tsetse-derived trypanocidal factors. However, the data do suggest that endocytosis is energetically burdensome, as endocytic activity is rapidly compromised on energy depletion in bloodstream stages. Hence an important aspect of endocytic modulation in the nutrient-poor tsetse midgut is likely energetic conservation.

The trypanosome Rab-related proteins RabX1 and RabX2 play no role in intracellular trafficking but may be involved in fly infectivity

Background

Rab GTPases constitute the largest subgroup of the Ras superfamily and are primarily involved in vesicle targeting. The full extent of Rab family function is unexplored. Several divergent Rab-like proteins are known but few have been characterized. In Trypanosoma brucei there are sixteen Rab genes, but RabX1, RabX2 and RabX3 are divergent within canonical sequence regions. Where known, trypanosome Rab functions are broadly conserved when orthologous relationships may be robustly established, but specific functions for RabX1, X2 and X3 have yet to be determined. RabX1 and RabX2 originated via tandem duplication and subcellular localization places RabX1 at the endoplasmic reticulum, while RabX2 is at the Golgi complex, suggesting distinct functions. We wished to determine whether RabX1 and RabX2 are involved in vesicle transport or other cellular processes.

Methodology/Principal Findings

Using comparative genomics we find that RabX1 and RabX2 are restricted to trypanosomatids. Gene knockout indicates that RabX1 and RabX2 are non-essential. Simultaneous RNAi knockdown of both RabX1 and RabX2, while partial, was also non-lethal and may suggest non-redundant function, consistent with the distinct locations of the proteins. Analysis of the knockout cell lines unexpectedly failed to uncover a defect in exocytosis, endocytosis or in the morphology or location of multiple markers for the endomembrane system, suggesting that neither RabX1 nor RabX2 has a major role in intracellular transport. However, it was apparent that RabX1 and RabX2 knockout cells displayed somewhat enhanced survival within flies.

Conclusions/Significance

RabX1 and RabX2, two members of the trypanosome Rab subfamily, were shown to have no major detectable role in intracellular transport, despite the localization of each gene product to highly specific endomembrane compartments. These data extend the functional scope of Rab proteins in trypanosomes to include non-canonical roles in differentiation-associated processes in protozoa.

Intraclonal mating occurs during tsetse transmission of Trypanosoma brucei

Background

Mating in Trypanosoma brucei is a non-obligatory event, triggered by the co-occurrence of different strains in the salivary glands of the vector. Recombinants that result from intra- rather than interclonal mating have been detected, but only in crosses of two different trypanosome strains. This has led to the hypothesis that when trypanosomes recognize a different strain, they release a diffusible factor or pheromone that triggers mating in any cell in the vicinity whether it is of the same or a different strain. This idea assumes that the trypanosome can recognize self and non-self, although there is as yet no evidence for the existence of mating types in T. brucei.

Results

We investigated intraclonal mating in T. b. brucei by crossing red and green fluorescent lines of a single strain, so that recombinant progeny can be detected in the fly by yellow fluorescence. For strain 1738, seven flies had both red and green trypanosomes in the salivary glands and, in three, yellow trypanosomes were also observed, although they could not be recovered for subsequent analysis. Nonetheless, both red and non-fluorescent clones from these flies had recombinant genotypes as judged by microsatellite and karyotype analyses, and some also had raised DNA contents, suggesting recombination or genome duplication. Strain J10 produced similar results indicative of intraclonal mating. In contrast, trypanosome clones recovered from other flies showed that genotypes can be transmitted with fidelity. When a yellow hybrid clone expressing both red and green fluorescent protein genes was transmitted, the salivary glands contained a mixture of fluorescent-coloured trypanosomes, but only yellow and red clones were recovered. While loss of the GFP gene in the red clones could have resulted from gene conversion, some of these clones showed loss of heterozygosity and raised DNA contents as in the other single strain transmissions. Our observations suggest that many recombinants are non-viable after intraclonal mating.

Conclusion

We have demonstrated intraclonal mating during fly transmission of T. b. brucei, contrary to previous findings that recombination occurs only when another strain is present. It is thus no longer possible to assume that T. b. brucei remains genetically unaltered after fly transmission.

The heart of darkness: growth and form of Trypanosoma brucei in the tsetse fly

The first description of African trypanosomes was made over a century ago. The importance of the tsetse in transmission and cyclic development of trypanosomes was discovered soon afterwards, and has been the focus of numerous studies since. However, investigation of trypanosomes in tsetse flies requires high resource investment and unusual patience; hence, many facets of trypanosome biology in the tsetse remain to be characterised despite the long history of research. Here, current knowledge and questions about some of the developmental changes in trypanosomes that occur in tsetse flies are summarised, along with recent technical advances that can now be used to provide some answers.

Biological and ecological traits that assist establishment of alien invasive insects

In this study the biological and ecological traits of two groups of phytophagous insect pests were examined to determine attributes that may influence establishment in New Zealand Biological and ecological attributes of a group of insect species that is established in New Zealand were compared with species that are not currently established It was found that the species established in New Zealand had a significantly wider host plant range than species that have not established The lower developmental threshold temperature was on average 4C lower for established species compared with nonestablished species These data suggest that species that establish well in New Zealand have a wide host range and can tolerate lower temperatures compared with those that have not established

The use of yellow fluorescent hybrids to indicate mating in Trypanosoma brucei

Background

Trypanosoma brucei undergoes genetic exchange in its insect vector, the tsetse fly, by an unknown mechanism. The difficulties of working with this experimental system of genetic exchange have hampered investigation, particularly because the trypanosome life cycle stages involved cannot be cultured in vitro and therefore must be examined in the insect. Searching for small numbers of hybrid trypanosomes directly in the fly has become possible through the incorporation of fluorescent reporter genes, and we have previously carried out a successful cross using a reporter-repressor strategy. However, we could not be certain that all fluorescent trypanosomes observed in that cross were hybrids, due to mutations of the repressor leading to spontaneous fluorescence, and we have therefore developed an alternative strategy.

Results

To visualize the production of hybrids in the fly, parental trypanosome clones were transfected with a gene encoding Green Fluorescent Protein (GFP) or Red Fluorescent Protein (RFP). Co-infection of flies with red and green fluorescent parental trypanosomes produced yellow fluorescent hybrids, which were easily visualized in the fly salivary glands. Yellow trypanosomes were not seen in midgut or proventricular samples and first appeared in the glands as epimastigotes as early as 13 days after fly infection. Cloned progeny originating from individual salivary glands had yellow, red, green or no fluorescence and were confirmed as hybrids by microsatellite, molecular karyotype and kinetoplast (mitochondrial) DNA analyses. Hybrid clones showed biparental inheritance of both nuclear and kinetoplast genomes. While segregation and reassortment of the reporter genes and microsatellite alleles were consistent with Mendelian inheritance, flow cytometry measurement of DNA content revealed both diploid and polyploid trypanosomes among the hybrid progeny clones.

Conclusion

The strategy of using production of yellow hybrids to indicate mating in trypanosomes provides a robust and unequivocal system for analysis of genetic exchange. Mating occurred with high frequency in these experimental crosses, limited only by the ability of both parental trypanosomes to invade the salivary glands. Yellow hybrids appeared as soon as trypanosomes invaded the salivary glands, implicating the short, unattached epimastigote as the sexual stage. The recovery of diploid, triploid and tetraploid hybrids in these crosses was surprising as genetic markers appeared to have been inherited according to Mendelian rules. As the polyploid hybrids could have been produced from fusion of unreduced gametes, there is no fundamental conflict with a model of genetic exchange involving meiosis.

Asymmetric cell division as a route to reduction in cell length and change in cell morphology in trypanosomes

African trypanosomes go through at least five developmental stages during their life cycle. The different cellular forms are classified using morphology, including the order of the nucleus, flagellum and kinetoplast along the anterior-posterior axis of the cell, the predominant cell surface molecules and the location within the host. Here, an asymmetrical cell division cycle that is an integral part of the Trypanosoma brucei life cycle has been characterised in further detail through the use of cell cycle stage specific markers. The cell cycle leading to the asymmetric division includes an exquisitely synchronised mitosis and exchange in relative location of organelles along the anterior-posterior axis of the cell. These events are coupled to a change in cell surface architecture. During the asymmetric division, the behaviour of the new flagellum is consistent with a role in determining the location of the plane of cell division, a function previously characterised in procyclic cells. Thus, the asymmetric cell division cycle provides a mechanism for a change in cell morphology and also an explanation for how a reduction in cell length can occur in a cell shaped by a stable microtubule array.

Activation of endocytosis as an adaptation to the mammalian host by trypanosomes

Immune evasion in African trypanosomes is principally mediated by antigenic variation, but rapid internalization of surface-bound immune factors may contribute to survival. Endocytosis is upregulated approximately 10-fold in bloodstream compared to procyclic forms, and surface coat remodeling accompanies transition between these life stages. Here we examined expression of endocytosis markers in tsetse fly stages in vivo and monitored modulation during transition from bloodstream to procyclic forms in vitro. Among bloodstream stages nonproliferative stumpy forms have endocytic activity similar to that seen with rapidly dividing slender forms, while differentiation of stumpy forms to procyclic forms is accompanied by rapid down-regulation of Rab11 and clathrin, suggesting that modulation of endocytic and recycling systems accompanies this differentiation event. Significantly, rapid down-regulation of endocytic markers occurs upon entering the insect midgut and expression of Rab11 and clathrin remains low throughout subsequent development, which suggests that high endocytic activity is not required for remodeling the parasite surface or for survival within the fly. However, salivary gland metacyclic forms dramatically increase expression of clathrin and Rab11, indicating that emergence of mammalian infective forms is coupled to reacquisition of a high-activity endocytic-recycling system. These data suggest that high-level endocytosis in Trypanosoma brucei is an adaptation required for viability in the mammalian host.

Dynamics of infection and competition between two strains of Trypanosoma brucei brucei in the tsetse fly observed using fluorescent markers

Background

Genetic exchange occurs between Trypanosoma brucei strains during the complex developmental cycle in the tsetse vector, probably within the salivary glands. Successful mating will depend on the dynamics of co-infection with multiple strains, particularly if intraspecific competition occurs. We have previously used T. brucei expressing green fluorescent protein to study parasite development in the vector, enabling even one trypanosome to be visualized. Here we have used two different trypanosome strains transfected with either green or red fluorescent proteins to study the dynamics of co-infection directly in the tsetse fly.

Results

The majority of infected flies had both trypanosome strains present in the midgut, but the relative proportion of red and green trypanosome strains varied considerably between flies and between different sections of the midgut in individual flies. Colonization of the paired salivary glands revealed greater variability than for midguts, as each gland could be infected with red and/or green trypanosome strains in variable proportions. Salivary glands with a mixed infection appeared to have a higher density of trypanosomes than glands containing a single strain. Comparison of the numbers of red and green trypanosomes in the proventriculus, salivary exudate and glands from individual flies showed no correlation between the composition of the trypanosome population of the proventriculus and foregut and that of the salivary glands. For each compartment examined (midgut, foregut, salivary glands), there was a significantly higher proportion of mixed infections than expected, assuming the null hypothesis that the development of each trypanosome strain is independent.

Conclusion

Both the trypanosome strains used were fully capable of infecting tsetse, but the probabilities of infection with each strain were not independent, there being a significantly higher proportion of mixed infections than expected in each of three compartments examined: midgut, proventriculus and salivary glands. Hence there was no evidence of competition between trypanosome strains, but instead co-infection was frequent. Infection rates in co-infected flies were no different to those found routinely in flies infected with a single strain, ruling out the possibility that one strain enhanced infection with the other. We infer that each fly is either permissive or non-permissive of trypanosome infection with at least 3 sequential checkpoints imposed by the midgut, proventriculus and salivary glands. Salivary glands containing both trypanosome strains appeared to contain more trypanosomes than singly-infected glands, suggesting that lack of competition enhances the likelihood of genetic exchange.

Analysis of a cross between green and red fluorescent trypanosomes

Trypanosoma brucei undergoes genetic exchange in its insect vector, but the mechanism is unknown and no one has yet seen the process. By crossing genetically engineered red and green fluorescent trypanosomes, we have been able to pinpoint the location of genetic exchange in the fly and search for intermediate stages. In experimental crosses of red and green parental trypanosomes, yellow hybrid trypanosomes first appeared in the fly salivary glands as early as 13 days after infection and were observed only in flies with a mixture of red and green trypanosomes in one or both salivary glands. Despite high numbers of flies with mixed infections, yellow trypanosomes were not detected in the fly midgut or proventriculus. The hybrid nature of yellow trypanosomes was confirmed by analysis of molecular karyotypes and microsatellite alleles. As well as yellow hybrids, hybrid trypanosomes with red, green or no fluorescence were also recovered from fly salivary glands. Analysis of microsatellite alleles in parental and progeny clones showed Mendelian inheritance. Our findings are consistent with the hypothesis that mating takes place between trypanosomes in the salivary glands of the fly before they attach to the salivary gland epithelium.

Multiple effects of the lectin-inhibitory sugars D-glucosamine and N-acetyl-glucosamine on tsetse-trypanosome interactions

We are studying early events in the establishment of Trypanosoma brucei in the tsetse midgut using fluorescent trypanosomes to increase visibility. Feeding flies with the lectin-inhibitory sugars D-glucosamine (GlcN) or N-acetyl-glucosamine (GlcNAc) has previously been shown to enhance fly susceptibility to infection with trypanosomes and, as expected, we found that both sugars increased midgut infection rates of Glossina morsitans morsitans with T. brucei. However, GlcNAc did not show the inhibitory effect on salivary gland infection rate reported previously for GlcN. Both sugars significantly slowed the movement of the bloodmeal along the midgut. GlcN also significantly increased the size of the bloodmeal taken and fly mortality. The most surprising finding was that GlcNAc stimulated trypanosome growth not only in the midgut, but also in vitro in the absence of any factor derived from the fly. Thus our direct comparison of the effects of GlcN and GlcNAc on the trypanosome-tsetse interaction has shown that these sugars impact on trypanosome growth and tsetse physiology in different ways and are not interchangeable as suggested in the literature. The sugars cause multiple effects, not restricted solely to the inhibition of midgut lectins. These findings have implications for current models of tsetse susceptibility to trypanosome infection.

Aberrant behavioral effects of a dopamine D1 receptor antagonist and agonist in monkeys: evidence of uncharted dopamine D1 receptor actions

BACKGROUND

Basic research indicates a role for dopamine (DA) D1 antagonism in the treatment of schizophrenia. Clinical trials have not confirmed any role. Besides the defining second messenger (adenylyl cyclase [AC]), DA D1 receptors are linked to other effectors (e.g., phospholipase C [PLC]). Differing actions of DA D1 antagonists upon differing effectors could explain conflicting results between the lab/clinic.

METHODS

In a monkey model in which behavioral effects of DA D1 antagonists/agonists have been well characterized we examined: 1) SKF 83959, biochemically, a DA D1 antagonist, behaviorally a DA D1 agonist, and 2) SKF 83822, biochemically, a DA D1 agonist, which, unlike all previously tested DA D1 agonists, does not also stimulate PLC. SKF 83959 and SKF 83822 were given alone and combined with DA D1 and D2 agonists, antagonists, and dextroamphetamine (AMP).

RESULTS

SKF 83959 acted as a DA D1 agonist (induced oral dyskinesia given alone, counteracted DA D1 antagonist [NNC 756], induced dystonia, and did not inhibit AMP induced behaviors). SKF 83822, unlike previously studied DA D1 agonists, did not induce dyskinesia, but resulted in a state of extreme arousal and locomotor activation without stereotypy, effectively counteracted by NNC 756, but not by SKF 83959 nor raclopride (DA D2 antagonist).

CONCLUSIONS

It is hypothesized that: 1) dyskinesia is linked to PLC stimulation; 2) DA D1 agonism can play a role in the induction of psychosis, via a mechanism linked neither to AC nor PLC, and 3) DA D1 antagonists differ in antipsychotic potential, possibly via this unidentified mechanism.