Tsetse fly (Diptera: Glossinidae) viviparous reproductive physiology remains to be explored at the molecular level. Adult females carry their young in utero for the duration of embryonic and larval development, all the while supplying their offspring with nutrients in the form of a “milk” substance secreted from a modified accessory gland. Flies give birth to fully developed third instar larvae that pupariate shortly after birth. Here, we describe the spatial and temporal expression dynamics of two reproduction-associated genes and their products synthesized during the first and second gonotrophic cycles. The proteins studied include a putative yolk protein, Glossina morsitans morsitans yolk protein 1 (GmmYP1) and the major protein found in tsetse “milk” secretions (Glossina morsitans morsitans milk gland protein, GmmMGP). Developmental stage and tissue-specific expression of GmmYP1 show its presence exclusively in the reproductive tract of the fly during oogenesis, suggesting that GmmYP1 acts as a vitellogenic protein. Transcripts for GmmMGP are present only in the milk gland tissue and increase in coordination with the process of larvigenesis. Similarly, GmmMGP can be detected at the onset of larvigenesis in the milk gland, and is present during the full duration of pregnancy. Expression of GmmMGP is restricted to the adult stage and is not detected in the immature developmental stages. These phenomena indicate that the protein is transferred from mother to larvae as nourishment during its development. These results demonstrate that both GmmYP1 and GmmMGP are involved in tsetse reproductive biology, the former associated with the process of oogenesis and the latter with larvigenesis.
Viviparous reproduction; Oogenesis; Larvagenesis; Tsetse; Milk gland
The parasite Trypanosoma brucei rhodesiense and its insect vector Glossina morsitans morsitans were used to evaluate the effect of parasite clearance (resistance) as well as the cost of midgut infections on tsetse host fitness. Tsetse flies are viviparous and have a low reproductive capacity, giving birth to only 6–8 progeny during their lifetime. Thus, small perturbations to their reproductive fitness can have a major impact on population densities. We measured the fecundity (number of larval progeny deposited) and mortality in parasite-resistant tsetse females and untreated controls and found no differences. There was, however, a typanosome-specific impact on midgut infections. Infections with an immunogenic parasite line that resulted in prolonged activation of the tsetse immune system delayed intrauterine larval development resulting in the production of fewer progeny over the fly's lifetime. In contrast, parasitism with a second line that failed to activate the immune system did not impose a fecundity cost. Coinfections favored the establishment of the immunogenic parasites in the midgut. We show that a decrease in the synthesis of Glossina Milk gland protein (GmmMgp), a major female accessory gland protein associated with larvagenesis, likely contributed to the reproductive lag observed in infected flies. Mathematical analysis of our empirical results indicated that infection with the immunogenic trypanosomes reduced tsetse fecundity by 30% relative to infections with the non-immunogenic strain. We estimate that a moderate infection prevalence of about 26% with immunogenic parasites has the potential to reduce tsetse populations. Potential repercussions for vector population growth, parasite–host coevolution, and disease prevalence are discussed.
In many cases, parasites adapt to their hosts' biology over time and the extent of their harmful effects gradually diminishes. Insect-transmitted parasites such as African trypanosomes, however, are unusually pathogenic for their mammalian hosts because they rely on their invertebrate hosts for transmission to the next mammalian host. To ensure their maximum transmission, it is essential that parasite infections do not compromise insect host's fitness traits, including longevity and host-finding ability. Our results in tsetse indicate that, as theory predicts, trypanosome infections do not reduce host longevity. Instead, they divert host resources from reproduction and can reduce reproductive output by as much as 30%. Such loss of reproductive fitness occurs as a result of the induction of tsetse's immune responses. A closely related non-immunogenic parasite line does not induce host responses and does not compromise host fecundity. It is possible that host immune responses are needed in the case of the immunogenic line to control the parasite density to prevent excessive host damage. Because tsetse are viviparous and each adult female typically gives rise to only few progeny during their lifetime, even modest costs on reproduction can have a significant impact on host abundance. Our model predicts that if the prevalence of immunogenic parasite infections in tsetse populations reaches over 26%, they begin to have a negative impact on population growth rate. Infection rates as high as 30% have been reported with trypanosomes in the field. Our laboratory findings coupled with our modeling studies now provide a framework to investigate the status of co-infections, host immune activation processes, fecundity outcomes, transmission dynamics, and host virulence phenotypes in natural tsetse–trypanosome populations.
The regulation of iron is critical for maintaining homeostasis in the tsetse fly (Diptera:Glossinidae), in which both adult sexes are strict blood feeders. We have characterized the cDNAs for two putative iron-binding proteins (IBP) involved in transport and storage; transferrin (GmmTsf1) and ferritin from Glossina morsitans morsitans. GmmTsf1 transcripts are detected in the female fat body and in adult reproductive tissues, and only in the adult developmental stage in a bloodmeal independent manner. In contrast, the ferritin heavy chain (GmmFer1HCH) and light chain (GmmFer2LCH) transcripts are expressed ubiquitously, suggesting a more general role for these proteins in iron transport and storage. Protein domain predictions for each IBP suggest both the conservation and loss of several motifs present in their vertebrate homologues. In concert with many other described insect transferrins, putative secreted GmmTsf1 maintains 3 of the 5 residues necessary for iron-binding in the N-terminal lobe, but exhibits a loss of this iron-binding ability in the C-terminal role as well as a loss of large sequence blocks. Both putative GmmFer1HCH and GmmFer2LCH proteins have signal peptides, similar to other insect ferritins. GmmFer2LCH has lost the 5’UTR iron-responsive element (IRE) and, thus, translation is no longer regulated by cellular iron levels. On the other hand, GmmFer1HCH maintains both the conserved ferroxidase center and the 5’UTR IRE; however, transcript variants suggest a more extensive regulatory mechanism for this subunit.
Iron; ferritin; transferrin; Glossina morsitans morsitans
During pregnancy in the viviparous tsetse fly, lipid mobilization is essential for the production of milk to feed the developing intrauterine larva. Lipophorin (Lp) functions as the major lipid transport protein in insects and closely-related arthropods. In this study, we assessed the role of Lp and the lipophorin receptor (LpR) in the lipid mobilization process during tsetse reproduction. We identified single gene sequences for GmmLp and GmmLpR from the genome of Glossina morsitans morsitans, and measured spatial and temporal expression of gmmlp and gmmlpr during the female reproductive cycle. Our results show that expression of gmmlp is specific to the adult fat body and larvae. In the adult female, gmmlp expression is constitutive. However transcript levels increase in the larva as it matures within the mother’s uterus, reaching peak expression just prior to parturition. GmmLp was detected in the hemolymph of pregnant females and larvae, but not in the uterine fluid or larval gut contents ruling out the possibility of direct transfer of GmmLp from mother to offspring. Transcripts for gmmlpr were detected in the head, ovaries, midgut, milk gland/fat body, ovaries and developing larva. Levels of gmmlpr remain stable throughout the first and second gonotrophic cycles with a slight dip observed during the first gonotrophic cycle. GmmLpR was detected in multiple tissues, including the midgut, fat body, milk gland, spermatheca and head. Knockdown of gmmlp by RNA interference resulted in reduced hemolymph lipid levels, delayed oocyte development and extended larval gestation. Similar suppresion of gmmlpr did not significantly reduce hemolymph lipid levels or oogenesis duration, but did extend the duration of larval development. Thus, GmmLp and GmmLpR function as the primary shuttle for lipids originating from the midgut and fat body to the ovaries and milk gland to supply resources for developing oocytes and larval nourishment, respectively. Once in the milk gland however, lipids are apparently transferred into the developing larva not by lipophorin but by another carrier lipoprotein.
Lipid movement; lipophorin; tsetse development; Glossina
African trypanosomes undergo a complex developmental process in their tsetse fly vector before transmission back to a vertebrate host. Typically, 90% of fly infections fail, most during initial establishment of the parasite in the fly midgut. The specific mechanism(s) underpinning this failure are unknown. We have previously shown that a Glossina-specific, immunoresponsive molecule, tsetse EP protein, is up regulated by the fly in response to gram-negative microbial challenge. Here we show by knockdown using RNA interference that this tsetse EP protein acts as a powerful antagonist of establishment in the fly midgut for both Trypanosoma brucei brucei and T. congolense. We demonstrate that this phenomenon exists in two species of tsetse, Glossina morsitans morsitans and G. palpalis palpalis, suggesting tsetse EP protein may be a major determinant of vector competence in all Glossina species. Tsetse EP protein levels also decline in response to starvation of the fly, providing a possible explanation for increased susceptibility of starved flies to trypanosome infection. As starvation is a common field event, this fact may be of considerable importance in the epidemiology of African trypanosomiasis.
In Africa, tsetse flies transmit the trypanosomes causing the devastating diseases sleeping sickness in man and nagana in domesticated animals. These diseases are major causes of underdevelopment in Africa. Paradoxically, most, but not all, flies are resistant to infection with trypanosomes, but we do not have a clear picture of how flies fight off trypanosomes. Here we show that a particular, tsetse-specific immune responsive protein called tsetse EP acts as a powerful antagonist of trypanosome establishment in the fly midgut. It is known that starvation of flies leads to an increase in their susceptibility to trypanosomes and this may be a considerable factor in the epidemiology of the disease in Africa. Here we demonstrate that starvation leads to a decrease in tsetse EP levels, which may explain how starvation of the fly works to increase its susceptibility.
Tsetse flies (Glossina sp.), the African trypanosome vectors, rely on anti-hemostatic compounds for efficient blood feeding. Despite their medical importance, very few salivary proteins have been characterized and functionally annotated.
Here we report on the functional characterisation of a 5′nucleotidase-related (5′Nuc) saliva protein of the tsetse fly Glossina morsitans morsitans. This protein is encoded by a 1668 bp cDNA corresponding at the genomic level with a single-copy 4 kb gene that is exclusively transcribed in the tsetse salivary gland tissue. The encoded 5′Nuc protein is a soluble 65 kDa glycosylated compound of tsetse saliva with a dual anti-hemostatic action that relies on its combined apyrase activity and fibrinogen receptor (GPIIb/IIIa) antagonistic properties. Experimental evidence is based on the biochemical and functional characterization of recombinant protein and on the successful silencing of the 5′nuc translation in the salivary gland by RNA interference (RNAi). Refolding of a 5′Nuc/SUMO-fusion protein yielded an active apyrase enzyme with Km and Vmax values of 43±4 µM and 684±49 nmol Pi/min×mg for ATPase and 49±11 µM and 177±37 nmol Pi/min×mg for the ADPase activity. In addition, recombinant 5′Nuc was found to bind to GPIIb/IIIa with an apparent KD of 92±25 nM. Consistent with these features, 5′Nuc potently inhibited ADP-induced thrombocyte aggregation and even caused disaggregation of ADP-triggered human platelets. The importance of 5′Nuc for the tsetse fly hematophagy was further illustrated by specific RNAi that reduced the anti-thrombotic activities in saliva by approximately 50% resulting in a disturbed blood feeding process.
These data show that this 5′nucleotidase-related apyrase exhibits GPIIb/IIIa antagonistic properties and represents a key thromboregulatory compound of tsetse fly saliva.
Tsetse flies (Glossina spp.) can harbor up to three distinct species of endosymbiotic bacteria that exhibit unique modes of transmission and evolutionary histories with their host. Two mutualist enterics, Wigglesworthia and Sodalis, are transmitted maternally to tsetse flies' intrauterine larvae. The third symbiont, from the genus Wolbachia, parasitizes developing oocytes. In this study, we determined that Sodalis isolates from several tsetse fly species are virtually identical based on a phylogenetic analysis of their ftsZ gene sequences. Furthermore, restriction fragment-length polymorphism analysis revealed little variation in the genomes of Sodalis isolates from tsetse fly species within different subgenera (Glossina fuscipes fuscipes and Glossina morsitans morsitans). We also examined the impact on host fitness of transinfecting G. fuscipes fuscipes and G. morsitans morsitans flies with reciprocal Sodalis strains. Tsetse flies cleared of their native Sodalis symbionts were successfully repopulated with the Sodalis species isolated from a different tsetse fly species. These transinfected flies effectively transmitted the novel symbionts to their offspring and experienced no detrimental fitness effects compared to their wild-type counterparts, as measured by longevity and fecundity. Quantitative PCR analysis revealed that transinfected flies maintained their Sodalis populations at densities comparable to those in flies harboring native symbionts. Our ability to transinfect tsetse flies is indicative of Sodalis ' recent evolutionary history with its tsetse fly host and demonstrates that this procedure may be used as a means of streamlining future paratransgenesis experiments.
Tsetse flies (Diptera: Glossinidae) are the sole vectors of African trypanosomes, the causative agent of sleeping sickness in human and nagana in animals. Like most eukaryotic organisms, Glossina species have established symbiotic associations with bacteria. Three main symbiotic bacteria have been found in tsetse flies: Wigglesworthia glossinidia, an obligate symbiotic bacterium, the secondary endosymbiont Sodalis glossinidius and the reproductive symbiont Wolbachia pipientis. In the present review, we discuss recent studies on the detection and characterization of Wolbachia infections in Glossina species, the horizontal transfer of Wolbachia genes to tsetse chromosomes, the ability of this symbiont to induce cytoplasmic incompatibility in Glossina morsitans morsitans and also how new environment-friendly tools for disease control could be developed by harnessing Wolbachia symbiosis.
Glossina; Wolbachia; Insect symbiosis; Sodalis; Wigglesworthia; Paratransgenesis
Tsetse flies (Diptera: Glossinidae) are vectors of trypanosomes that cause sleeping sickness in humans and nagana in livestock across sub-Saharan Africa. Tsetse control strategies rely on a detailed understanding of the epidemiology and ecology of tsetse together with genetic variation within and among populations. High-resolution nuclear genetic markers are useful tools for elucidation of the genetic basis of phenotypic traits. In this study amplified fragment length polymorphism (AFLP) markers were developed to analyze genetic variation in Glossina morsitans morsitans from laboratory and field-collected populations from Zimbabwe.
A total of seven hundred and fifty one loci from laboratory and field populations of G. m. morsitans from Zimbabwe were genotyped using AFLP with seven primer combinations. Analysis identified 335 polymorphic loci. The two populations could be distinguished by cluster and principal components analysis (PCA) analysis, indicating that AFLP markers can be used to separate genetically similar populations; at the same time differences observed between laboratory and field populations were not very great. Among the techniques investigated, the use of acetone was the most reliable method of preservation of tsetse for subsequent extraction of high molecular weight DNA. An interesting finding was that AFLP also enabled robust within-population discrimination of male and female tsetse flies due to their different X chromosome DNA complements.
AFLP represents a useful additional tool to add to the suite of techniques currently available for the genetic analysis of tsetse populations and represents a useful resource for identification of the genetic basis of important phenotypic traits.
Many insects rely on the presence of symbiotic bacteria for proper immune system function. However, the molecular mechanisms that underlie this phenomenon are poorly understood. Adult tsetse flies (Glossina spp.) house 3 symbiotic bacteria that are vertically transmitted from mother to offspring during this insect's unique viviparous mode of reproduction. Larval tsetse that undergo intrauterine development in the absence of their obligate mutualist, Wigglesworthia, exhibit a compromised immune system during adulthood. In this study we characterize the immune phenotype of tsetse that develop in the absence of all of their endogenous symbiotic microbes. Aposymbiotic tsetse (GmmApo) present a severely compromised immune system that is characterized by the absence of phagocytic hemocytes and atypical expression of immunity-related genes. Correspondingly, these flies quickly succumb to infection with normally non-pathogenic E. coli. The susceptible phenotype exhibited by GmmApo adults can be reversed when they receive hemocytes transplanted from wild-type donor flies prior to infection. Furthermore, the process of immune system development can be restored in intrauterine GmmApo larvae when their moms are fed a diet supplemented with Wigglesworthia cell extracts. Our finding that molecular components of Wigglesworthia exhibit immunostimulatory activity within tsetse is representative of a novel evolutionary adaptation that steadfastly links an obligate symbiont with it's host.
Chemosensory proteins (CSPs) are a class of soluble proteins present in high concentrations in the sensilla of insect antennae. It has been proposed that they play an important role in insect olfaction by mediating interactions between odorants and odorant receptors. Here we report, for the first time, the presence of five CSP genes in the tsetse fly Glossina morsitans morsitans, a major vector transmitting nagana in livestock. Real-time quantitative reverse transcription PCR showed that three of the CSPs are expressed in antennae. One of them, GmmCSP2, is transcribed at a very high level and could be involved in olfaction. We also determined expression in the antennae of both males and females at different life stages and with different blood feeding regimes. The transcription of GmmCSP2 was lower in male antennae than in females, with a sharp increase in 10-week-old flies, 48 h after a bloodmeal. Thus there is a clear relationship between CSP gene transcription and host searching behaviour. Genome annotation and phylogenetic analyses comparing G. morsitans morsitans CSPs with those of other Diptera showed rapid evolution after speciation of mosquitoes.
chemosensory protein; tsetse fly; gene expression; trypanosomiasis; nagana
Analysis of the tsetse fly salivary gland EST database revealed the presence of a highly enriched cluster of putative endonuclease genes, including tsal1 and tsal2. Tsal proteins are the major components of tsetse fly (G. morsitans morsitans) saliva where they are present as monomers as well as high molecular weight complexes with other saliva proteins. We demonstrate that the recombinant tsetse salivary gland proteins 1&2 (Tsal1&2) display DNA/RNA non-specific, high affinity nucleic acid binding with KD values in the low nanomolar range and a non-exclusive preference for duplex. These Tsal proteins exert only a residual nuclease activity with a preference for dsDNA in a broad pH range. Knockdown of Tsal expression by in vivo RNA interference in the tsetse fly revealed a partially impaired blood digestion phenotype as evidenced by higher gut nucleic acid, hematin and protein contents.
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.
The teneral phenomenon, as observed in Glossina sp., refers to the increased susceptibility of the fly to trypanosome infection when the first bloodmeal taken is trypanosome-infected. In recent years, the term teneral has gradually become synonymous with unfed, and thus fails to consider the age of the newly emerged fly at the time the first bloodmeal is taken. Furthermore, conflicting evidence exists of the effect of the age of the teneral fly post eclosion when it is given the infected first bloodmeal in determining the infection prevalence. This study demonstrates that it is not the feeding history of the fly but rather the age (hours after eclosion of the fly from the puparium) of the fly when it takes the first (infective) bloodmeal that determines the level of fly susceptibility to trypanosome infection. We examine this phenomenon in male and female flies from two distinct tsetse clades (Glossina morsitans morsitans and Glossina palpalis palpalis) infected with two salivarian trypanosome species, Trypanosoma (Trypanozoon) brucei brucei and Trypanosoma (Nannomonas) congolense using Fisher's exact test to examine differences in infection rates. Teneral tsetse aged less than 24 hours post-eclosion (h.p.e.) are twice as susceptible to trypanosome infection as flies aged 48 h.p.e. This trend is conserved across sex, vector clade and parasite species. The life cycle stage of the parasite fed to the fly (mammalian versus insect form trypanosomes) does not alter this age-related bias in infection. Reducing the numbers of parasites fed to 48 h.p.e., but not to 24 h.p.e. flies, increases teneral refractoriness. The importance of this phenomenon in disease biology in the field as well as the necessity of employing flies of consistent age in laboratory-based infection studies is discussed.
Ancient endosymbionts have been associated with extreme genome structural stability with little differentiation in gene inventory between sister species. Tsetse flies (Diptera: Glossinidae) harbor an obligate endosymbiont, Wigglesworthia, which has coevolved with the Glossina radiation. We report on the ~720-kb Wigglesworthia genome and its associated plasmid from Glossina morsitans morsitans and compare them to those of the symbiont from Glossina brevipalpis. While there was overall high synteny between the two genomes, a large inversion was noted. Furthermore, symbiont transcriptional analyses demonstrated host tissue and development-specific gene expression supporting robust transcriptional regulation in Wigglesworthia, an unprecedented observation in other obligate mutualist endosymbionts. Expression and immunohistochemistry confirmed the role of flagella during the vertical transmission process from mother to intrauterine progeny. The expression of nutrient provisioning genes (thiC and hemH) suggests that Wigglesworthia may function in dietary supplementation tailored toward host development. Furthermore, despite extensive conservation, unique genes were identified within both symbiont genomes that may result in distinct metabolomes impacting host physiology. One of these differences involves the chorismate, phenylalanine, and folate biosynthetic pathways, which are uniquely present in Wigglesworthia morsitans. Interestingly, African trypanosomes are auxotrophs for phenylalanine and folate and salvage both exogenously. It is possible that W. morsitans contributes to the higher parasite susceptibility of its host species.
Genomic stasis has historically been associated with obligate endosymbionts and their sister species. Here we characterize the Wigglesworthia genome of the tsetse fly species Glossina morsitans and compare it to its sister genome within G. brevipalpis. The similarity and variation between the genomes enabled specific hypotheses regarding functional biology. Expression analyses indicate significant levels of transcriptional regulation and support development- and tissue-specific functional roles for the symbiosis previously not observed in obligate mutualist symbionts. Retention of the genetically expensive flagella within these small genomes was demonstrated to be significant in symbiont transmission and tailored to the unique tsetse fly reproductive biology. Distinctions in metabolomes were also observed. We speculate an additional role for Wigglesworthia symbiosis where infections with pathogenic trypanosomes may depend upon symbiont species-specific metabolic products and thus influence the vector competence traits of different tsetse fly host species.
► VNTRs are highly diagnostic tools for fingerprinting Wolbachia in tsetse flies. ► Multiple infections, free and nuclear insertions into host chromosomes, do exist. ► Some infections can escape detection via hiding as low-titer infections. ► In hybrids Wolbachia can transform into pathogens by loss of replication control.
We demonstrate the high applicability of a novel VNTR-based (Variable-Number-Tandem-Repeat) molecular screening tool for fingerprinting Wolbachia-infections in tsetse flies. The VNTR-141 locus provides reliable and concise differentiation between Wolbachia strains deriving from Glossina morsitans morsitans, Glossina morsitans centralis, and Glossina brevipalpis. Moreover, we show that certain Wolbachia-infections in Glossina spp. are capable of escaping standard PCR screening methods by ‘hiding’ as low-titer infections below the detection threshold. By applying a highly sensitive PCR-blot technique to our Glossina specimen, we were able to enhance the symbiont detection limit substantially and, consequently, trace unequivocally Wolbachia-infections at high prevalence in laboratory-reared G. swynnertoni individuals. To our knowledge, Wolbachia-persistence was reported exclusively for field-collected samples, and at low prevalence only. Finally, we highlight the substantially higher Wolbachia titer levels found in hybrid Glossina compared to non-hybrid hosts and the possible impact of these titers on hybrid host fitness that potentially trigger incipient speciation in tsetse flies.
Glossina; Wolbachia; Symbiont diversity; Inter-species hybrids; Speciation
δ-octalactone, produced by several Bovidae, has been suggested as a potential repellant of tsetse fly attack. Racemic δ-octalactone was synthesized via an abbreviated route. The product was assayed against 3-day old starved teneral female tsetse flies, Glossina morsitans morsitans Wiedemann (Diptera: Glossinidae), in a choice wind tunnel and found to be a potent tsetse repellent at doses ≥0.05 mg in 200 µl of paraffin oil (0.05 >p >0.01).
allomone; bioassay; choice wind tunnel; olfaction; racemic δ-octalactone synthesis
Unraveling the intricate interactions between Trypanosoma brucei, the protozoan parasite causing African trypanosomiasis, and the tsetse (Glossina) vector remains a challenge. Metacyclic trypanosomes, which inhabit the tsetse salivary glands, transmit the disease and are produced through a complex differentiation and unknown program. By overexpressing a single RNA-binding protein, TbRBP6, in cultured noninfectious trypanosomes, we recapitulated the developmental stages that have been observed in tsetse, including the generation of infective metacyclic forms expressing the variant surface glycoprotein. Thus, events leading to acquisition of infectivity in the insect vector are now accessible to laboratory investigation, providing an opening for new intervention strategies.
The competence of the tsetse fly Glossina pallidipes (Diptera; Glossinidae) to acquire salivary gland hypertrophy virus (SGHV), to support virus replication and successfully transmit the virus depends on complex interactions between Glossina and SGHV macromolecules. Critical requisites to SGHV transmission are its replication and secretion of mature virions into the fly's salivary gland (SG) lumen. However, secretion of host proteins is of equal importance for successful transmission and requires cataloging of G. pallidipes secretome proteins from hypertrophied and non-hypertrophied SGs.
After electrophoretic profiling and in-gel trypsin digestion, saliva proteins were analyzed by nano-LC-MS/MS. MaxQuant/Andromeda search of the MS data against the non-redundant (nr) GenBank database and a G. morsitans morsitans SG EST database, yielded a total of 521 hits, 31 of which were SGHV-encoded. On a false discovery rate limit of 1% and detection threshold of least 2 unique peptides per protein, the analysis resulted in 292 Glossina and 25 SGHV MS-supported proteins. When annotated by the Blast2GO suite, at least one gene ontology (GO) term could be assigned to 89.9% (285/317) of the detected proteins. Five (∼1.8%) Glossina and three (∼12%) SGHV proteins remained without a predicted function after blast searches against the nr database. Sixty-five of the 292 detected Glossina proteins contained an N-terminal signal/secretion peptide sequence. Eight of the SGHV proteins were predicted to be non-structural (NS), and fourteen are known structural (VP) proteins.
SGHV alters the protein expression pattern in Glossina. The G. pallidipes SG secretome encompasses a spectrum of proteins that may be required during the SGHV infection cycle. These detected proteins have putative interactions with at least 21 of the 25 SGHV-encoded proteins. Our findings opens venues for developing novel SGHV mitigation strategies to block SGHV infections in tsetse production facilities such as using SGHV-specific antibodies and phage display-selected gut epithelia-binding peptides.
Tsetse fly (Diptera; Glossinidae) transmits two devastating diseases to farmers (human African Trypanosomiasis; HAT) and their livestock (Animal African Trypanosomiasis; AAT) in 37 sub-Saharan African countries. During the rainy seasons, vast areas of fertile, arable land remain uncultivated as farmers flee their homes due to the presence of tsetse. Available drugs against trypanosomiasis are ineffective and difficult to administer. Control of the tsetse vector by Sterile Insect Technique (SIT) has been effective. This method involves repeated release of sterilized males into wild tsetse populations, which compete with wild type males for females. Upon mating, there is no offspring, leading to reduction in tsetse populations and thus relief from trypanosomiasis. The SIT method requires large-scale tsetse rearing to produce sterile males. However, tsetse colony productivity is hampered by infections with the salivary gland hypertrophy virus, which is transmitted via saliva as flies take blood meals during membrane feeding and often leads to colony collapse. Here, we investigated the salivary gland secretome proteins of virus-infected tsetse to broaden our understanding of virus infection, transmission and pathology. By this approach, we obtain insight in tsetse-hytrosavirus interactions and identified potential candidate proteins as targets for developing biotechnological strategies to control viral infections in tsetse colonies.
To determine and compare the prevalence of trypanosome infections in different livestock species (cattle, pigs and goats) in areas where game animals are scarce and livestock constitute the main food source of tsetse, a survey was conducted on the plateau of the Eastern Province of Zambia in Katete and Petauke districts where Glossina morsitans morsitans is the only tsetse species present. Blood was collected from a total of 734 cattle, 333 goats and 324 pigs originating from 59 villages in both districts and was examined using the buffy coat method and the PCR-RFLP as diagnostic tools.
The prevalence of trypanosome infections differed substantially between livestock species. Using microscopic diagnostic methods, trypanosome infections were detected in 13.5% of the cattle and 0.9% of the pigs. All goats were parasitologically negative. The PCR-RFLP analyses increased the trypanosomiasis prevalence to 33.5, 6.5 and 3.3% in cattle, pigs and goats respectively. The majority of the infections (91.2%) were due to Trypanosoma congolense. The presence of a trypanosome infection in cattle and pigs resulted in a significant decline in the packed cell volume. The outcome of the study clearly shows that despite the availability of goats and pigs, cattle seem to be the major livestock species affected by the disease in trypanosomiasis endemic areas. The high proportion of infections in cattle could be partly attributed to their higher availability and attractiveness to tsetse.
Trypanosomiasis; Livestock; Epidemiology; Zambia
Tsetse flies (Diptera: Glossinidae) are vectors for trypanosome parasites, the agents of the deadly sleeping sickness disease in Africa. Tsetse also harbor two maternally transmitted enteric mutualist endosymbionts: the primary intracellular obligate Wigglesworthia glossinidia and the secondary commensal Sodalis glossinidius. Both endosymbionts are transmitted to the intrauterine progeny through the milk gland secretions of the viviparous female. We administered various antibiotics either continuously by per os supplementation of the host blood meal diet or discretely by hemocoelic injections into fertile females in an effort to selectively eliminate the symbionts to study their individual functions. A symbiont-specific PCR amplification assay and fluorescence in situ hybridization analysis were used to evaluate symbiont infection outcomes. Tetracycline and rifampin treatments eliminated all tsetse symbionts but reduced the fecundity of the treated females. Ampicillin treatments did not affect the intracellular Wigglesworthia localized in the bacteriome organ and retained female fecundity. The resulting progeny of ampicillin-treated females, however, lacked Wigglesworthia but still harbored the commensal Sodalis. Our results confirm the presence of two physiologically distinct Wigglesworthia populations: the bacteriome-localized Wigglesworthia involved with nutritional symbiosis and free-living Wigglesworthia in the milk gland organ responsible for maternal transmission to the progeny. We evaluated the reproductive fitness, longevity, digestion, and vectorial competence of flies that were devoid of Wigglesworthia. The absence of Wigglesworthia completely abolished the fertility of females but not that of males. Both the male and female Wigglesworthia-free adult progeny displayed longevity costs and were significantly compromised in their blood meal digestion ability. Finally, while the vectorial competence of the young newly hatched adults without Wigglesworthia was comparable to that of their wild-type counterparts, older flies displayed higher susceptibility to trypanosome infections, indicating a role for the mutualistic symbiosis in host immunobiology. The ability to rear adult tsetse that lack the obligate Wigglesworthia endosymbionts will now enable functional investigations into this ancient symbiosis.
Tsetse harbors an obligate symbiont, Wigglesworthia glossinidia,
that must be present during larval maturation for the fly's immune system to
develop and function properly during adulthood.
Beneficial microbial symbionts serve important functions within their hosts,
including dietary supplementation and maintenance of immune system homeostasis.
Little is known about the mechanisms that enable these bacteria to induce specific
host phenotypes during development and into adulthood. Here we used the tsetse fly,
Glossina morsitans, and its obligate mutualist,
Wigglesworthia glossinidia, to investigate the co-evolutionary
adaptations that influence the development of host physiological processes.
Wigglesworthia is maternally transmitted to tsetse's
intrauterine larvae through milk gland secretions. We can produce flies that lack
(GmmWgm−) yet retain their other
symbiotic microbes. Such offspring give rise to adults that exhibit a largely normal
phenotype, with the exception being that they are reproductively sterile. Our results
indicate that when reared under normal environmental conditions
GmmWgm− adults are also
immuno-compromised and highly susceptible to hemocoelic E. coli
infections while age-matched wild-type individuals are refractory. Adults that lack
Wigglesworthia during larval development exhibit exceptionally
compromised cellular and humoral immune responses following microbial challenge,
including reduced expression of genes that encode antimicrobial peptides
(cecropin and attacin), hemocyte-mediated
processes (thioester-containing proteins 2 and 4
and prophenoloxidase), and signal-mediating molecules
(inducible nitric oxide synthase). Furthermore,
GmmWgm− adults harbor a reduced
population of sessile and circulating hemocytes, a phenomenon that likely results
from a significant decrease in larval expression of serpent and
lozenge, both of which are associated with the process of early
hemocyte differentiation. Our results demonstrate that
Wigglesworthia must be present during the development of immature
progeny in order for the immune system to function properly in adult tsetse. This
phenomenon provides evidence of yet another important physiological adaptation that
further anchors the obligate symbiosis between tsetse and
Beneficial bacterial symbionts, which are ubiquitous in nature, are often
characterized by the extent to which they interact with the host. In the case of
mutualistic symbioses, both partners benefit so that each one can inhabit diverse
ecological niches where neither could survive on its own. Unfortunately, little is
known about the functional mechanisms that underlie mutualistic relationships.
Insects represent a group of advanced multi-cellular organisms that harbor
well-documented symbiotic associations. One such insect, the tsetse fly, harbors a
maternally transmitted bacterial mutualist called Wigglesworthia
that provides its host with essential metabolites missing from its vertebrate
blood-specific diet. In this study, we further examine the relationship between
tsetse and Wigglesworthia by investigating the interaction between
this bacterium and its host's immune system. We have found that when
Wigglesworthia is absent from tsetse during the maturation of
immature larval stages, subsequent adults are characterized by an underdeveloped
cellular immune system and thus highly susceptible to infection with a normally
non-pathogenic foreign microbe. These findings represent an additional adaptation
that further anchors the steadfast relationship shared between tsetse and its
A key process in the tsetse reproductive cycle is the transfer of essential nutrients and bacterial symbionts from mother to intrauterine offspring. The tissue mediating this transfer is the milk gland. This work focuses upon the localization and function of two milk proteins (milk gland protein (GmmMGP) and transferrin (GmmTsf)) and the tsetse endosymbionts (Sodalis and Wigglesworthia), in the context of milk gland physiology. Fluorescent in situ hybridization (FISH) and immunohistochemical analysis confirm that the milk gland secretory cells synthesize and secrete milk gland protein and transferrin. Knockdown of gmmmgp by double stranded RNA (dsRNA) mediated RNA interference results in reduction of tsetse fecundity, demonstrating its functional importance in larval nutrition and development. Bacterial species-specific in situ hybridizations of milk gland sections reveal large numbers of Sodalis and Wigglesworthia within the lumen of the milk gland. Sodalis is also localized within the cytoplasm of the secretory cells. Within the lumen, Wigglesworthia localize close to the channels leading to the milk storage reservoir of the milk gland secretory cells. We discuss the significance of the milk gland in larval nutrition and in transmission of symbiotic bacteria to developing offspring.
Tsetse; reproduction; milk gland; Sodalis; Wigglesworthia
The tsetse fly Glossina is the vector of the protozoan Trypanosoma brucei spp., which causes Human and Animal African Trypanosomiasis in sub-Saharan African countries. To supplement their unbalanced vertebrate bloodmeal diet, flies permanently harbor the obligate bacterium Wigglesworthia glossinidia, which resides in bacteriocytes in the midgut bacteriome organ as well as in milk gland organ. Tsetse flies also harbor the secondary facultative endosymbionts (S-symbiont) Sodalis glossinidius that infects various tissues and Wolbachia that infects germ cells. Tsetse flies display viviparous reproductive biology where a single embryo hatches and completes its entire larval development in utero and receives nourishments in the form of milk secreted by mother’s accessory glands (milk glands). To analyze the precise tissue distribution of the three endosymbiotic bacteria and to infer the way by which each symbiotic partner is transmitted from parent to progeny, we conducted a Fluorescence In situ Hybridization (FISH) study to survey bacterial spatial distribution across the fly tissues. We show that bacteriocytes are mono-infected with Wigglesworthia, while both Wigglesworthia and Sodalis are present in the milk gland lumen. Sodalis was further seen in the uterus, spermathecae, fat body, milk and intracellular in the milk gland cells. Contrary to Wigglesworthia and Sodalis, Wolbachia were the only bacteria infecting oocytes, trophocytes, and embryos at early embryonic stages. Furthermore, Wolbachia were not seen in the milk gland and in the fat body. This work further highlights the diversity of symbiont interactions in multipartner associations and supports two maternal routes of symbiont inheritance in the tsetse fly: Wolbachia through oocytes, and, Wigglesworthia and Sodalis by means of milk gland bacterial infection at early post-embryonic stages.
Tsetse fly; Glossina; Endosymbiont; FISH; Transmission
Tsetse flies (Diptera: Glossinidae) are an ancient taxon of one genus, Glossina, and limited species diversity. All are exclusively haematophagous and confined to sub-Saharan Africa. The Glossina are the principal vectors of African trypanosomes Trypanosoma sp (Kinetoplastida: Trypanosomatidae) and as such, are of great medical and economic importance. Clearly tsetse flies and trypanosomes are coadapted and evolutionary interactions between them are manifest. Numerous clonally reproducing strains of Trypanosoma sp exist and their genetic diversities and spatial distributions are inadequately known. Here I review the breeding structures of the principle trypanosome vectors, G. morsitans s.l., G. pallidipes, G. palpalis s.l. and G. fuscipes fuscipes. All show highly structured populations among which there is surprisingly little detectable gene flow. Rather less is known of the breeding structure of T. brucei sensu lato vis à vis their vector tsetse flies but many genetically differentiated strains exist in nature. Genetic recombination in Trypanosoma via meiosis has recently been demonstrated in the laboratory thereby furnishing a mechanism of strain differentiation in addition to that of simple mutation. Spatially and genetically representative sampling of both trypanosome species and strains and their Glossina vectors is a major barrier to a comprehensive understanding of their mutual relationships.
Glossina; Trypanosoma; tsetse; gene flow; African trypanosomiasis