Biology subjects

Weiss, B. L.

Publications and source records attributed to Weiss, B. L..

9 recordsLinked to original sources

bioRxiv2025

PGRP-LA regulates peritrophic matrix synthesis and influences trypanosome infection outcomes in tsetse flies

Peptidoglycan Recognition Proteins (PGRPs) are conserved pattern-recognition receptors that detect microbe-associated molecular patterns (MAMPs) and activate host immune responses. Compared to other dipterans, the tsetse fly (Glossina morsitans morsitans) genome encodes only five PGRPs-PGRP-LA, -LB, -LC, -SA, and -SB - far fewer than most dipterans, likely reflecting its sterile blood diet and streamlined microbiota. Here, we identify PGRP-LA as a critical regulator of peritrophic matrix (PM) integrity in the cardia (proventriculus), the tissue responsible for PM production. The PM is a chitinous sleeve-like barrier that separates the midgut epithelium from the ingested bloodmeal, supporting digestive homeostasis and infection resistance. We show that pgrp-la is prominently expressed in the cardia, transiently induced after a bloodmeal in newly eclosed flies, and reinduced following subsequent feedings, likely in response to blood-constituents or mechanical stretch. This induction is sustained during microbial exposure and prolonged in trypanosome-infected flies. RNAi-mediated reduction of pgrp-la significantly increased the prevalence of midgut trypanosome infections, indicating a protective role during early infection. PGRP-LA did not mediate infection resistance via canonical IMD pathway signaling, as its silencing did not affect antimicrobial peptide expression. Instead, PGRP-LA modulated the expression of PM-associated genes and gut barrier integrity. Silencing pgrp-la reduced PM structure, increased midgut weights and enhanced fly survival following oral challenge with entomopathogen Serratia marcescens, likely due to earlier epithelial immune responses through a compromised PM. Similar phenotypes were observed when flies were fed anti-PGRP-LA antibodies, supporting a structural role for PGRP-LA. In addition, soluble variant surface glycoproteins (sVSGs) from trypanosomes and knockdown of microRNA-275 (miR-275), also decreased pgrp-la expression, suggesting that PGRP-LA is part of a broader regulatory network, including the miR-275/Wingless signaling. Collectively, our results identify PGRP-LA as novel regulator of PM biogenesis and vector competence in tsetse, expanding the functional repertoire of PGRPs in insect gut barrier maintenance beyond canonical immune signaling pathways. Author SummaryInsect vectors such as tsetse flies can be infected with pathogens that cause devastating disease in mammals. To protect themselves insect vectors rely on pattern recognition receptors (PRRs) that detect pathogens and activate the production of antimicrobial peptides (AMPs). Physical barriers in the gut also play an important role in limiting infections. One such barrier is the peritrophic matrix (PM), a sleeve-like structure that lines the insect gut and separates the blood meal and its contents from the underlying cells. For trypanosome parasites, which cause sleeping sickness in humans, the PM is the first barrier they must traverse to colonize the tsetses gut. In this study, we identified a PRR, PGRP-LA, that, unlike related proteins in other insects that activate AMPs, regulates the integrity of the tsetses protective PM barrier. When PGRP-LA was disrupted, the gut barrier weakened, and flies became more susceptible to trypanosome infection. Our work highlights a previously unrecognized role for PGRP-LA in maintaining gut barrier integrity and suggest that targeting this pathway could be a strategy to help reduce parasite transmission.

immunology↗

bioRxiv2025

Endosymbiont hijacking of acylcarnitines regulates insect vector fecundity by suppressing the viability of stored sperm

Competition between insects and their endosymbiotic bacteria for environmentally limited nutrients can compromise the fitness of both organisms. Tsetse flies, the vectors of pathogenic African trypanosomes, harbor a species and population-specific consortium of vertically transmitted endosymbiotic bacteria that range on the functional spectrum from mutualistic to parasitic. Tsetses indigenous microbiota can include a member of the genus Spiroplasma, and infection with this bacterium causes fecundity-reducing phenotypes in the fly that include a prolonged gonotrophic cycle and a reduction in the motility of stored spermatozoa post-copulation. Herein we demonstrate that Spiroplasma and tsetse spermatozoa compete for fly-derived acylcarnitines, which in other bacteria and animals are used to maintain cell membranes and produce energy. The fat body of mated female flies increases acylcarnitine production in response to infection with Spiroplasma. Additionally, their spermathecae (sperm storage organs), and likely the sperm within, up-regulate expression of carnitine O-palmitoyltransferase-1, which is indicative of increased acylcarnitine metabolism and thus increased energy demand and energy production in this organ. These compensatory measures are insufficient to rescue the motility defect of spermatozoa stored in the spermathecae of Spiroplasma-infected females and thus results in reduced fly fecundity. Tsetses taxonomically simple and highly tractable indigenous microbiota make the fly an efficient model system for studying the biological processes that facilitate the maintenance of bacterial endosymbioses, and how these relationships impact conserved mechanisms (mammalian spermatozoa also use acylcarnitines as an energy source) that regulated animal host fecundity. In the case of insect pests and vectors, a better understanding of the metabolic mechanisms that underlie these associations can lead to the development of novel control strategies. Author SummaryAnimals and the endosymbiotic bacteria that live inside them often compete for nutrients that both organisms require in order to survive. Tsetse flies, which transmit pathogenic African trypanosomes, can house several endosymbionts that have different impacts on their hosts physiological well-being. Female tsetse flies that are infected with one of these bacteria, Spiroplasma, produce fewer offspring than do their uninfected counterparts. In this study we demonstrate that the bacterium and the flys sperm cells (spermatozoa) compete for a specific type of lipid called acylcarnitines. When mated female tsetse flies are experimentally manipulated to produce less acylcarnitine Spiroplasma density decreases. Additionally, spermatozoa stored in the sperm storage organs of acylcarnitine depleted females lose motility and are eventually resorbed, thus rendering the females reproductively sterile. These findings mechanistically demonstrate how endosymbiotic bacteria can manipulate their hosts reproductive potential. In the case of arthropods that transmit pathogenic microbes, this relationship has significant implications for disease transmission and epidemiology.

microbiology↗

bioRxiv2024

Spiroplasma endosymbiont reduction of host lipid synthesis and Stomoxyn-like peptide contribute to trypanosome resistance in the tsetse fly Glossina fuscipes

Tsetse flies (Glossina spp.) vector African trypanosomes that cause devastating diseases in humans and domestic animals. Within the Glossina genus, species in the Palpalis subgroup exhibit greater resistance to trypanosome infections compared to those in the Morsitans subgroup. Varying microbiota composition and species-specific genetic traits can significantly influence the efficiency of parasite transmission. Notably, infections with the endosymbiotic bacterium Spiroplasma have been documented in several Palpalis subgroup species, including Glossina fuscipes fuscipes (Gff). While Spiroplasma infections in Gff are known to hinder trypanosome transmission, the underlying mechanisms remain unknown. To investigate Spiroplasma-mediated factors affecting Gff vector competence, we conducted high-throughput RNA sequencing of the midgut tissue along with functional assays. Our findings reveal elevated oxidative stress in the midgut environment in the presence of Spiroplasma, evidenced by increased expression of nitric oxide synthase, which catalyzes the production of trypanocidal nitric oxide. Additionally, we observed impaired lipid biosynthesis leading to a reduction of this important class of nutrients essential for parasite and host physiologies. In contrast, trypanosome infections in Gffs midgut significantly upregulated various immunity-related genes, including a small peptide, Stomoxyn-like, homologous to Stomoxyns first discovered in the stable fly Stomoxys calcitrans. We observed that the Stomoxyn-like locus is exclusive to the genomes of Palpalis subgroup tsetse species. GffStomoxyn is constitutively expressed in the cardia (proventriculus) and synthetic GffStomoxyn exhibits potent activity against Escherichia coli and bloodstream form of Trypanosoma brucei parasites, while showing no effect against insect stage procyclic forms or tsetses commensal endosymbiont Sodalis in vitro. Reducing GffStomoxyn levels significantly increased trypanosome infection prevalence, indicating its potential trypanocidal role in vivo. Collectively, our results suggest that the enhanced resistance to trypanosomes observed in Spiroplasma-infected Gff may be due to the reduced lipid availability necessary for parasite metabolic maintenance. Furthermore, GffStomoxyn could play a crucial role in the initial immune response(s) against mammalian parasites early in the infection process in the midgut and prevent gut colonization. We discuss the molecular characteristics of GffStomoxyn, its spatial and temporal expression regulation and its microbicidal activity against Trypanosome parasites. Our findings reinforce the nutritional influences of microbiota on host physiology and host-pathogen dynamics. Author SummaryThe tsetse fly, Glossina fuscipes fuscipes (Gff) is of high public health relevance. Gff exhibits strong innate resistance to trypanosomes, especially when infected with the endosymbiotic bacterium Spiroplasma. This study investigated how the bacterium Spiroplasma inside Gff enables them to be resistant to trypanosome infection. Our results indicate alterations in host lipid metabolism with reduction in levels of triglycerides, suggesting a potential metabolic barrier that limits the viability to parasite. In addition, we discovered a small peptide, stomoxyn, exclusively in Gff and related Palpalis tsetse species. We have shown that Gff synthetic Stomoxyn has antibacterial and antitrypanosomal properties and lowering Stomoxyn levels in Gff correlates with increased parasite prevalence. We suggest that strategies to increase Spiroplasma prevalence or enhance stomoxyn expression through paratransgenic approaches could be promising avenues for reducing trypanosomiasis transmission.

molecular biology↗

bioRxiv2022

Heme-induced genes facilitate endosymbiont (Sodalis glossinidius) colonization of the tsetse fly (Glossina morsitans) midgut

Tsetse flies (Glossina spp.) feed exclusively on vertebrate blood. After a blood meal, the enteric endosymbiont Sodalis glossinidius is exposed to various environmental stressors including high levels of heme. To investigate how S. glossinidius morsitans (Sgm, the Sodalis subspecies that resides within the gut of G. morsitans) tolerates the heme-induced oxidative environment of tsetses midgut, we used RNAseq to identify bacterial genes that are differentially expressed in cells cultured in high versus lower heme environments. Our analysis identified 436 genes that were significantly differentially expressed (> or < 2-fold) in the presence of high heme [219 heme-induced genes (HIGs) and 217 heme-repressed genes (HRGs)]. HIGs were enriched in Gene Ontology (GO) terms related to regulation of a variety of biological functions, including gene expression and metabolic processes. We observed that 11 out of 13 Sgm genes that were heme regulated in vitro were similarly regulated in bacteria that resided within tsetses midgut 24 hr (high heme environment) and 96 hr (low heme environment) after the flies had consumed a blood meal. We used intron mutagenesis to make insertion mutations in 12 Sgm HIGs and observed no significant change in growth in vitro in any of the mutant strains in high versus low heme conditions. However, Sgm strains that carried mutations in genes encoding a putative undefined phosphotransferase sugar (PTS) system component (SG2427), fucose transporter (SG0182), bacterioferritin (SG2280), and a DNA-binding protein (SGP1-0002) presented growth and/or survival defects in tsetse midguts as compared to normal Sgm. These findings suggest that the uptake up of sugars and storage of iron represent strategies that Sgm employs to successfully reside within the high heme environment of its tsetse hosts midgut. Our results are of epidemiological relevance, as many hematophagous arthropods house gut-associated bacteria that mediate their hosts competency as a vector of disease-causing pathogens. Author summaryTsetse flies feed exclusively on vertebrate blood. This nutrient source contains large quantities of heme, which can be toxic to the flys associated microorganisms. We investigated the genetic mechanisms that underlie the ability of the bacterial endosymbiont, Sodalis glossinidius, to successfully reside within tsetses heme-rich midgut. Exposure of cultured S. glossinidius to high levels of heme induced changes in the expression of genes that encode proteins involved in transcription, replication and repair of DNA, inorganic ion transport, and carbohydrate transport and metabolism processes. Changes in the expression of several of these same S. glossinidius genes also occurred within tsetses midgut following exposure to a blood meal. S. glossinidius genetically engineered to present mutations in several of these heme regulated genes were unable to successfully colonize tsetses gut. Our results provide insight into how bacteria that live in the gut of blood feeding arthropods mitigate the toxic effects of excessive heme. This information is of epidemiological relevance, as many of these bacteria influence their hosts ability to transmit disease pathogens that cause disease in humans and domesticated animals.

microbiology↗

bioRxiv2021

Infection with endosymbiotic Spiroplasma disrupts tsetse (Glossina fuscipes fuscipes) metabolic and reproductive homeostasis

Tsetse flies (Glossina spp.) house a population-dependent assortment of microorganisms that can include pathogenic African trypanosomes and maternally transmitted endosymbiotic bacteria, the latter of which mediate numerous aspects of their hosts metabolic, reproductive, and immune physiologies. One of these endosymbionts, Spiroplasma, was recently discovered to reside within multiple tissues of field captured and laboratory colonized tsetse flies grouped in the Palpalis subgenera. In various arthropods, Spiroplasma induces reproductive abnormalities and pathogen protective phenotypes. In tsetse, Spiroplasma infections also induce a protective phenotype by enhancing the flys resistance to infection with trypanosomes. However, the potential impact of Spiroplasma on tsetses viviparous reproductive physiology remains unknown. Herein we employed high-throughput RNA sequencing and laboratory-based functional assays to better characterize the association between Spiroplasma and the metabolic and reproductive physiologies of G. fuscipes fuscipes (Gff), a prominent vector of human disease. Using field-captured Gff, we discovered that Spiroplasma infection induces changes of sex-biased gene expression in reproductive tissues that may be critical for tsetses reproductive fitness. Using a Gff line composed of individuals heterogeneously infected with Spiroplasma, we observed that the bacterium and tsetse host compete for finite nutrients, which negatively impact female fecundity by increasing the length of intrauterine larval development. Additionally, we found that when males are infected with Spiroplasma, the motility of their sperm is compromised following transfer to the female spermatheca. As such, Spiroplasma infections appear to adversely impact male reproductive fitness by decreasing the competitiveness of their sperm. Finally, we determined that the bacterium is maternally transmitted to intrauterine larva at a high frequency, while paternal transmission was also noted in a small number of matings. Taken together, our findings indicate that Spiroplasma exerts a negative impact on tsetse fecundity, an outcome that could be exploited for reducing tsetse population size and thus disease transmission. Author SummaryEndosymbiotic bacteria regulate numerous aspects of their hosts reproductive physiology. Natural populations of the tsetse fly, Glossina fuscipes fuscipes (Gff), house heterogeneous infections with the bacterium Spiroplasma glossinidia. Infection with the bacterium results in the presentation of several phenotypes in both male and female Gff that would put them at a significant reproductive disadvantage when compared to their counterparts that do not house the bacterium. These Spiroplasma induced phenotypes include changes in sex-biased gene expression in the reproductive organs, a depletion in the availability of metabolically critical lipids in pregnant females that results in delayed larval development, and compromised sperm fitness. These findings indicate that Spiroplasma exerts an overall negative impact on both male and female reproductive fitness and thus likely has a profound effect on fly population structure. This outcome, in conjunction with the fact that Spiroplasma infected tsetse are unusually refractory to infection with pathogenic African trypanosomes, indicates that the bacterium could be experimentally exploited to reduce disease transmission through the fly.

microbiology↗

bioRxiv2019

Thermal stress responses of Sodalis glossinidius, an indigenous bacterial symbiont of hematophagous tsetse flies

Tsetse flies (Diptera: Glossinidae) house a taxonomically diverse microbiota that includes environmentally acquired bacteria, maternally transmitted symbiotic bacteria, and pathogenic African trypanosomes. Sodalis glossinidius, which is a facultative symbiont that resides intra and extracellularly within multiple tsetse tissues, has been implicated as a mediator of trypanosome infection establishment in the flys gut. Tsetses gut-associated population of Sodalis are subjected to marked temperature fluctuations each time their ectothermic fly host imbibes vertebrate blood. The molecular mechanisms that Sodalis employs to deal with this heat stress are unknown. In this study, we examined the thermal tolerance and heat shock response of Sodalis. When grown on BHI agar plates, the bacterium exhibited the most prolific growth at 25{degrees}C, and did not grow at temperatures above 30{degrees}C. Growth on BHI agar plates at 31{degrees}C was dependent on either the addition of blood to the agar or reduction in oxygen levels. Sodalis was viable in liquid cultures for 24 hours at 30{degrees}C, but began to die upon further exposure. The rate of death increased with increased temperature. Similarly, Sodalis was able to survive for 48 hours within tsetse flies housed at 30{degrees}C, while a higher temperature (37{degrees}C) was lethal. Sodalis genome contains homologues of the heat shock chaperone protein-encoding genes dnaK, dnaJ, and grpE, and their expression was up-regulated in thermally stressed Sodalis, both in vitro and in vivo within tsetse flies. Arrested growth of E. coli dnaK, dnaJ, or grpE mutants under thermal stress was reversed when the cells were transformed with a low copy plasmid that encoded the Sodalis homologues of these genes. The information contained in this study provides insight into how arthropod vector enteric commensals, many of which mediate their hosts ability to transmit pathogens, mitigate heat shock associated with the ingestion of a blood meal.\n\nAUTHOR SUMMARYMicroorganisms associated with insects must cope with fluctuating temperatures. Because symbiotic bacteria influence the biology of their host, how they respond to temperature changes will have an impact on the host and other microorganisms in the host. The tsetse fly and its symbionts represent an important model system for studying thermal tolerance because the fly feeds exclusively on vertebrate blood and is thus exposed to dramatic temperature shifts. Tsetse flies house a microbial community that can consist of symbiotic and environmentally acquired bacteria, viruses, and parasitic African trypanosomes. This work, which makes use of tsetses commensal symbiont, Sodalis glossinidius, is significance because it represents the only examination of thermal tolerance mechanisms in a bacterium that resides indigenously within an arthropod disease vector. A better understanding of the biology of thermal tolerance in Sodalis provides insight into thermal stress survival in other insect symbionts and may yield information to help control vector-borne disease.

microbiology↗

bioRxiv2019

Spatio-temporal distribution of Spiroplasma infections in the tsetse fly (Glossina fuscipes fuscipes) in northern Uganda

Tsetse flies (Glossina spp.) are vectors of parasitic trypanosomes, which cause human (HAT) and animal African trypanosomiasis (AAT) in sub-Saharan Africa. In Uganda, Glossina fuscipes fuscipes (Gff) is the main vector of HAT, where it transmits Gambiense disease in the northwest and Rhodesiense disease in central, southeast and western regions. Endosymbionts can influence transmission efficiency of parasites through their insect vectors via conferring a protective effect against the parasite. It is known that the bacterium Spiroplasma is capable of protecting its Drosophila host from infection with a parasitic nematode. This endosymbiont can also impact its hosts population structure via altering host reproductive traits. Here, we used field collections across 26 different Gff sampling sites in northern and western Uganda to investigate the association of Spiroplasma with geographic origin, seasonal conditions, Gff genetic background and sex, and trypanosome infection status. We also investigated the influence of Spiroplasma on Gff vector competence to trypanosome infections under laboratory conditions.\n\nGeneralized linear models (GLM) showed that Spiroplasma probability was correlated with the geographic origin of Gff host and with the season of collection, with higher prevalence found in flies within the Albert Nile (0.42 vs 0.16) and Achwa River (0.36 vs 0.08) watersheds and with higher prevalence detected in flies collected in the intermediate than wet season. In contrast, there was no significant correlation of Spiroplasma prevalence with Gff host genetic background or sex once geographic origin was accounted for in generalized linear models. Additionally, we found a potential negative correlation of Spiroplasma with trypanosome infection, with only 2% of Spiroplasma infected flies harboring trypanosome co-infections. We also found that in a laboratory line of Gff, parasitic trypanosomes are less likely to colonize the midgut in individuals that harbor Spiroplasma infection. These results indicate that Spiroplasma infections in tsetse may be maintained by not only maternal but also via horizontal transmission routes, and Spiroplasma infections may also have important effects on trypanosome transmission efficiency of the host tsetse. Potential functional effects of Spiroplasma infection in Gff could have impacts on vector control approaches to reduce trypanosome infections.\n\nAuthor SummaryWe investigated the association of symbiotic Spiroplasma with the tsetse fly host Glossina fuscipes fuscipes (Gff) to assess if Spiroplasma infections are correlated with Gff genetic background, geography, or season and its interaction with trypanosome parasites. We analyzed distribution and prevalence of Spiroplasma infections across different Gff sampling sites in northern and western Uganda, and found that the symbiont is unevenly distributed and infections have not reached fixation within these sampling sites. We tested for associations with geographic origin of the collections, seasonal environmental conditions at the time of collection, Gff host genetic background and sex, plus trypanosome co-infections. Spiroplasma prevalence was strongly correlated with geographic origin and seasonal environmental conditions. Our parasite infection data suggested a negative correlation of Spiroplasma with trypanosome infection, with only 5 out of 243 flies harboring trypanosome co-infections. We further investigated the influence of Spiroplasma on trypanosome parasite infections in the laboratory. We found that trypanosomes were less likely to establish an infection in Gff individuals that carried Spiroplasma infections. Our results provide new information on host-endosymbiont dynamics in an important human disease vector, and provide evidence that Spiroplasma may confer partial resistance to Gff trypanosome infections. These findings provide preliminary evidence that a symbiont-based control method could be successful in combating tsetse trypanosome transmission to humans and livestock in sub-Saharan Africa.

epidemiology↗

bioRxiv2018

Colonization of the tsetse fly midgut with commensal Enterobacter inhibits trypanosome infection establishment

Tsetse flies (Glossina spp.) vector pathogenic trypanosomes (Trypanosoma spp.) in sub-Saharan Africa. These parasites cause human and animal African trypanosomiases, which are debilitating diseases that inflict an enormous socio-economic burden on inhabitants of endemic regions. Current disease control strategies rely primarily on treating infected animals and reducing tsetse population densities. However, relevant programs are costly, labor intensive and difficult to sustain. As such, novel strategies aimed at reducing tsetse vector competence require development. Herein we investigated whether an Enterobacter bacterium (Esp_Z), which confers Anopheles gambiae with resistance to Plasmodium, is able to colonize tsetse and induce a trypanosome refractory phenotype in the fly. Esp_Z established stable infections in tsetses gut, and exhibited no adverse effect on the survival of individuals from either group. Flies with established Esp_Z infections in their gut were significantly more refractory to infection with two distinct trypanosome species (T. congolense, 6% infection; T. brucei, 32% infection) than were age-matched flies that did not house the exogenous bacterium (T. congolense, 36% infected; T. brucei, 70% infected). Additionally, 52% of Esp_Z colonized tsetse survived infection with entomopathogenic Serratia marcescens, compared with only 9% of their wild-type counterparts. These parasite and pathogen refractory phenotypes result from the fact that Esp_Z acidifies tsetses midgut environment, which inhibits trypanosome and Serratia growth and thus infection establishment. Finally, we determined that Esp_Z infection does not impact the fecundity of male or female tsetse, nor the ability of male flies to compete with their wild-type counterparts for mates. We propose that Esp_Z could be used as one component of an integrated strategy aimed at reducing the ability of tsetse to transmit pathogenic trypanosomes.\n\nAuthor SummaryTsetse flies transmit pathogenic African trypanosomes, which are the causative agents of socio-economically devastating human and animal African trypanosomiases. These diseases are currently controlled in large part by reducing the population size of tsetse vectors through the use of insecticides, traps and sterile insect technique. However, logistic and monetary hurdles often preclude the prolonged application of procedures necessary to maintain these control programs. Thus, novel strategies, including those aimed at sustainably reducing the ability of tsetse to transmit trypanosomes, are presently under development. Herein we stably colonize tsetse flies with a bacterium (Enterobacter sp. Z, Esp_Z) that acidifies their midgut, thus rendering the environment inhospitable to infection with two distinct, epidemiologically important trypanosome strains as well as an entomopathogenic bacteria. In addition to inducing a trypanosome refractory phenotype, colonization of tsetse with Esp_Z exerts only a modest fitness cost on the fly. Taken together, these findings suggest that Esp_Z could be applied to enhance the effectiveness of currently employed tsetse control programs.

microbiology↗

bioRxiv2017

A fine-tuned vector-parasite dialogue in tsetse’s cardia determines peritrophic matrix integrity and trypanosome transmission success

Arthropod vectors have multiple physical and immunological barriers that impede the development and transmission of parasites to new vertebrate hosts. These barriers include the peritrophic matrix (PM), a chitinous barrier that separates the blood bolus from the midgut epithelia and inturn, modulates vector-microbiota interactions. In tsetse flies, a sleeve-like PM is continuously produced by the cardia organ located at the fore- and midgut junction. African trypanosomes, Trypanosoma brucei, must bypass the PM twice; first to colonize the midgut and secondly to reach the salivary glands (SG), to complete their transmission cycle in tsetse. However, not all flies with midgut infections develop mammalian transmissible SG infections - the reasons for which are unclear. Here, we used transcriptomics, microscopy and functional genomics analyses to understand the factors that regulate parasite migration from midgut to SG. In flies with midgut infections only, parasites fail to cross the PM as they are eliminated from the cardia by reactive oxygen intermediates (ROIs) - albeit at the expense of collateral cytotoxic damage to the cardia. In flies with midgut and SG infections, expression of genes encoding components of the PM is reduced in the cardia, and structural integrity of the PM barrier is compromised. Under these circumstances trypanosomes traverse through the newly secreted and compromised PM. The process of PM attrition that enables the parasites to re-enter into the midgut lumen is apparently mediated by components of the parasites residing in the cardia. Thus, a fine-tuned dialogue between tsetse and trypanosomes at the cardia determines the outcome of PM integrity and trypanosome transmission success.\n\nAuthor summaryInsects are responsible for transmission of parasites that cause deadly diseases in humans and animals. Understanding the key factors that enhance or interfere with parasite transmission processes can result in new control strategies. Here, we report that a proportion of tsetse flies with African trypanosome infections in their midgut can prevent parasites from migrating to the salivary glands, albeit at the expense of collateral damage. In a subset of flies with gut infections, the parasites manipulate the integrity of a midgut barrier, called the peritrophic matrix, and reach the salivary glands for transmission to the next mammal. Either targeting parasite manipulative processes or enhancing peritrophic matrix integrity could reduce parasite transmission.

microbiology↗