134 results found
Campos M, Willis K, Rona LDP, et al., 2021, Unravelling population structure heterogeneity within the genome of the malaria vector Anopheles gambiae, BMC Genomics, Vol: 22, ISSN: 1471-2164
Background:Whole genome re-sequencing provides powerful data for population genomic studies, allowing robust inferences of population structure, gene flow and evolutionary history. For the major malaria vector in Africa, Anopheles gambiae, other genetic aspects such as selection and adaptation are also important. In the present study, we explore population genetic variation from genome-wide sequencing of 765 An. gambiae and An. coluzzii specimens collected from across Africa. We used t-SNE, a recently popularized dimensionality reduction method, to create a 2D-map of An. gambiae and An. coluzzii genes that reflect their population structure similarities.Results:The map allows intuitive navigation among genes distributed throughout the so-called “mainland” and numerous surrounding “island-like” gene clusters. These gene clusters of various sizes correspond predominantly to low recombination genomic regions such as inversions and centromeres, and also to recent selective sweeps. Because this mosquito species complex has been studied extensively, we were able to support our interpretations with previously published findings. Several novel observations and hypotheses are also made, including selective sweeps and a multi-locus selection event in Guinea-Bissau, a known intense hybridization zone between An. gambiae and An. coluzzii.Conclusions:Our results present a rich dataset that could be utilized in functional investigations aiming to shed light onto An. gambiae s.l genome evolution and eventual speciation. In addition, the methodology presented here can be used to further characterize other species not so well studied as An. gambiae, shortening the time required to progress from field sampling to the identification of genes and genomic regions under unique evolutionary processes.
Ferdous Z, Fuchs S, Behrends V, et al., 2021, Anopheles coluzziistearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding, PLoS Pathogens, Vol: 17, ISSN: 1553-7366
Vitellogenesis and oocyte maturation require anautogenous female Anopheles mosquitoes to obtain a bloodmeal from a vertebrate host. The bloodmeal is rich in proteins that are readily broken down into amino acids in the midgut lumen and absorbed by the midgut epithelial cells where they are converted into lipids and then transported to other tissues including ovaries. The stearoyl-CoA desaturase (SCD) plays a pivotal role in this process by converting saturated (SFAs) to unsaturated (UFAs) fatty acids; the latter being essential for maintaining cell membrane fluidity amongst other housekeeping functions. Here, we report the functional and phenotypic characterization of SCD1 in the malaria vector mosquito Anopheles coluzzii. We show that RNA interference (RNAi) silencing of SCD1 and administration of sterculic acid (SA), a small molecule inhibitor of SCD1, significantly impact on the survival and reproduction of female mosquitoes following blood feeding. Microscopic observations reveal that the mosquito thorax is quickly filled with blood, a phenomenon likely caused by the collapse of midgut epithelial cell membranes, and that epithelial cells are depleted of lipid droplets and oocytes fail to mature. Transcriptional profiling shows that genes involved in protein, lipid and carbohydrate metabolism and immunity-related genes are the most affected by SCD1 knock down (KD) in blood-fed mosquitoes. Metabolic profiling reveals that these mosquitoes exhibit increased amounts of saturated fatty acids and TCA cycle intermediates, highlighting the biochemical framework by which the SCD1 KD phenotype manifests as a result of a detrimental metabolic syndrome. Accumulation of SFAs is also the likely cause of the potent immune response observed in the absence of infection, which resembles an auto-inflammatory condition. These data provide insights into mosquito bloodmeal metabolism and lipid homeostasis and could inform efforts to develop novel interventions against mosquito-borne
Hoermann A, Tapanelli S, Capriotti P, et al., 2021, Converting endogenous genes of the malaria mosquito into simple non-autonomous gene drives for pope ion replacement, eLife, Vol: 10, Pages: 1-22, ISSN: 2050-084X
Gene drives for mosquito population replacement are promising tools for malaria control. However, there is currently no clear pathway for safely testing such tools in endemic countries. The lack of well-characterized promoters for infection-relevant tissues and regulatory hurdles are further obstacles for their design and use. Here we explore how minimal genetic modifications of endogenous mosquito genes can convert them directly into non-autonomous gene drives without disrupting their expression. We co-opted the native regulatory sequences of three midgut-specific loci of the malaria vector Anopheles gambiae to host a prototypical antimalarial molecule and guide-RNAs encoded within artificial introns that support efficient gene drive. We assess the propensity of these modifications to interfere with the development of Plasmodium falciparum and their effect on fitness. Because of their inherent simplicity and passive mode of drive such traits could form part of an acceptable testing pathway of gene drives for malaria eradication.
Eba K, Habtewold T, Yewhalaw D, et al., 2021, Anopheles arabiensis hotspots along intermittent rivers drive malaria dynamics in semi-arid areas of Central Ethiopia, Malaria Journal, Vol: 20, Pages: 1-8, ISSN: 1475-2875
BackgroundUnderstanding malaria vector’s population dynamics and their spatial distribution is important to define when and where the largest infection risks occur and implement appropriate control strategies. In this study, the seasonal spatio-temporal dynamics of the malaria vector population and transmission intensity along intermittent rivers in a semi-arid area of central Ethiopia were investigated.MethodsMosquitoes were collected monthly from five clusters, 2 close to a river and 3 away from a river, using pyrethrum spray catches from November 2014 to July 2016. Mosquito abundance was analysed by the mixed Poisson regression model. The human blood index and sporozoite rate was compared between seasons by a logistic regression model.ResultsA total of 2784 adult female Anopheles gambiae sensu lato (s.l.) were collected during the data collection period. All tested mosquitoes (n = 696) were identified as Anopheles arabiensis by polymerase chain reaction. The average daily household count was significantly higher (P = 0.037) in the clusters close to the river at 5.35 (95% CI 2.41–11.85) compared to the clusters away from the river at 0.033 (95% CI 0.02–0.05). Comparing the effect of vicinity of the river by season, a significant effect of closeness to the river was found during the dry season (P = 0.027) and transition from dry to wet season (P = 0.032). Overall, An. arabiensis had higher bovine blood index (62.8%) as compared to human blood index (23.8%), ovine blood index (9.2%) and canine blood index (0.1%). The overall sporozoite rate was 3.9% and 0% for clusters close to and away from the river, respectively. The overall Plasmodium falciparum and Plasmodium vivax entomologic inoculation rates for An. arabiensis in clusters close to the river were 0.8 and 2.2 infective bites per person/year, respectively.ConclusionMosquito abundance and malaria transmission intensity in clusters close to
Ukegbu CV, Christophides GK, Vlachou D, 2021, Identification of three novel plasmodium factors involved in ookinete to oocyst developmental transition, Frontiers in Cellular and Infection Microbiology, Vol: 11, Pages: 1-17, ISSN: 2235-2988
Plasmodium falciparum malaria remains a major cause of global morbidity and mortality, mainly in sub-Saharan Africa. The numbers of new malaria cases and deaths have been stable in the last years despite intense efforts for disease elimination, highlighting the need for new approaches to stop disease transmission. Further understanding of the parasite transmission biology could provide a framework for the development of such approaches. We phenotypically and functionally characterized three novel genes, PIMMS01, PIMMS57, and PIMMS22, using targeted disruption of their orthologs in the rodent parasite Plasmodium berghei. PIMMS01 and PIMMS57 are specifically and highly expressed in ookinetes, while PIMMS22 transcription starts already in gametocytes and peaks in sporozoites. All three genes show strong phenotypes associated with the ookinete to oocyst transition, as their disruption leads to very low numbers of oocysts and complete abolishment of transmission. PIMMS22 has a secondary essential function in the oocyst. Our results enrich the molecular understanding of the parasite-vector interactions and identify PIMMS01, PIMMS57, and PIMMS22 as new targets of transmission blocking interventions.
Habtewold T, Sharma A, Wyer C, et al., 2021, Plasmodium oocysts respond with dormancy to crowding and nutritional stress, Scientific Reports, Vol: 11, ISSN: 2045-2322
Malaria parasites develop as oocysts in the mosquito for several days before they are able to infect a human host. During this time, mosquitoes take bloodmeals to replenish their nutrient and energy reserves needed for flight and reproduction. We hypothesized that these bloodmeals are critical for oocyst growth and that experimental infection protocols, typically involving a single bloodmeal at the time of infection, cause nutritional stress to the developing oocysts. Therefore, enumerating oocysts disregarding their growth and differentiation state may lead to erroneous conclusions about the efficacy of transmission blocking interventions. Here, we examine this hypothesis in Anopheles coluzzii mosquitoes infected with the human and rodent parasites Plasmodium falciparum and Plasmodium berghei, respectively. We show that oocyst growth and maturation rates decrease at late developmental stages as infection intensities increase; an effect exacerbated at very high infection intensities but fully restored with post infection bloodmeals. High infection intensities and starvation conditions reduce RNA Polymerase III activity in oocysts unless supplemental bloodmeals are provided. Our results suggest that oocysts respond to crowding and nutritional stress with a dormancy-like strategy, which urges the development of alternative methods to assess the efficacy of transmission blocking interventions.
Chabanol E, Behrends V, Prevot G, et al., 2020, Antibiotic Treatment in Anopheles coluzzii Affects Carbon and Nitrogen Metabolism, PATHOGENS, Vol: 9
Debalke S, Habtewold T, Christophides GK, et al., 2020, Stability of the effect of silencing fibronectin type III domain-protein 1 (FN3D1) gene on Anopheles arabiensis reared under different breeding site conditions, PARASITES & VECTORS, Vol: 13, ISSN: 1756-3305
Witmer K, Fraschka S, Vlachou D, et al., 2020, An epigenetic map of malaria parasite development from host to vector, Scientific Reports, Vol: 10, ISSN: 2045-2322
The malaria parasite replicates asexually in the red blood cells of its vertebrate host employing epigenetic mechanisms to regulate gene expression in response to changes in its environment. We used chromatin immunoprecipitation followed by sequencing in conjunction with RNA sequencing to create an epigenomic and transcriptomic map of the developmental transition from asexual blood stages to male and female gametocytes and to ookinetes in the rodent malaria parasite Plasmodium berghei. Across the developmental stages examined, heterochromatin protein 1 associates with variantly expressed gene families localised at subtelomeric regions and variant gene expression based on heterochromatic silencing is observed only in some genes. Conversely, the euchromatin mark histone 3 lysine 9 acetylation (H3K9ac) is abundant in non-heterochromatic regions across all developmental stages. H3K9ac presents a distinct pattern of enrichment around the start codon of ribosomal protein genes in all stages but male gametocytes. Additionally, H3K9ac occupancy positively correlates with transcript abundance in all stages but female gametocytes suggesting that transcription in this stage is independent of H3K9ac levels. This finding together with known mRNA repression in female gametocytes suggests a multilayered mechanism operating in female gametocytes in preparation for fertilization and zygote development, coinciding with parasite transition from host to vector.
James SL, Marshall JM, Christophides GK, et al., 2020, Toward the definition of efficacy and safety criteria for advancing gene drive-modified mosquitoes to field testing, Vector-Borne and Zoonotic Diseases, Vol: 20, Pages: 237-251, ISSN: 1530-3667
Mosquitoes containing gene drive systems are being developed as complementary tools to prevent transmission of malaria and other mosquito-borne diseases. As with any new tool, decision makers and other stakeholders will need to balance risks (safety) and benefits (efficacy) when considering the rationale for testing and deploying gene drive-modified mosquito products. Developers will benefit from standards for judging whether an investigational gene drive product meets acceptability criteria for advancing to field trials. Such standards may be formalized as preferred product characteristics and target product profiles, which describe the desired attributes of the product category and of a particular product, respectively. This report summarizes discussions from two scientific workshops aimed at identifying efficacy and safety characteristics that must be minimally met for an investigational gene drive-modified mosquito product to be deemed viable to move from contained testing to field release and the data that will be needed to support an application for first field release.
Ukegbu CV, Giorgalli M, Tapanelli S, et al., 2020, PIMMS43 is required for malaria parasite immune evasion and sporogonic development in the mosquito vector, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 7363-7373, ISSN: 0027-8424
After being ingested by a female Anopheles mosquito during a bloodmeal on an infected host, and before they can reach the mosquito salivary glands to be transmitted to a new host, Plasmodium parasites must establish an infection of the mosquito midgut in the form of oocysts. To achieve this, they must first survive a series of robust innate immune responses that take place prior to, during, and immediately after ookinete traversal of the midgut epithelium. Understanding how parasites may evade these responses could highlight new ways to block malaria transmission. We show that an ookinete and sporozoite surface protein designated as PIMMS43 (Plasmodium Infection of the Mosquito Midgut Screen 43) is required for parasite evasion of the Anopheles coluzzii complement-like response. Disruption of PIMMS43 in the rodent malaria parasite Plasmodium berghei triggers robust complement activation and ookinete elimination upon mosquito midgut traversal. Silencing components of the complement-like system through RNAi largely restores ookinete-to-oocyst transition but oocysts remain small in size and produce a very small number of sporozoites that additionally are not infectious, indicating that PIMMS43 is also essential for sporogonic development in the oocyst. Antibodies that bind PIMMS43 interfere with parasite immune evasion when ingested with the infectious blood meal and significantly reduce the prevalence and intensity of infection. PIMMS43 genetic structure across African Plasmodium falciparum populations indicates allelic adaptation to sympatric vector populations. These data add to our understanding of mosquito–parasite interactions and identify PIMMS43 as a target of malaria transmission blocking.
Habtewold T, Sharma A, Wyer CAS, et al., 2020, Plasmodium oocysts respond with dormancy to crowding and nutritional stress, Publisher: Cold Spring Harbor Laboratory
Malaria parasites develop and grow as oocysts in the mosquito for several days before being able to infect another human. During this time, mosquitoes take regular bloodmeals to replenish their nutrient and energy reserves needed for flight and reproduction. We hypothesized that supplemental bloodmeals are critical for oocyst growth and that experimental infection protocols, typically involving a single bloodmeal, cause nutritional stress to developing oocysts. Therefore, enumerating oocysts independently of their growth and differentiation state may lead to erroneous conclusions regarding the efficacy of malaria transmission blocking interventions. We tested this hypothesis in Anopheles coluzzii mosquitoes infected with human and rodent parasites Plasmodium falciparum and Plasmodium berghei , respectively. We find that oocyst growth rates decrease at late developmental stages as infection intensities increase; an effect exacerbated at very high infection intensities. Oocyst growth and differentiation can be restored by supplemental bloodmeals even at high infection intensities. We show that high infection intensities as well as starvation conditions reduce RNA Polymerase III activity in oocysts unless supplemental bloodmeals are provided. Our data suggest that oocysts respond to crowding and nutritional stress by employing a dormancy-like strategy and urge development of alternative methods to assess the efficacy of transmission blocking interventions.
Rodgers FH, Cai JA, Pitaluga AN, et al., 2020, Functional analysis of the three major PGRPLC isoforms in the midgut of the malaria mosquito Anopheles coluzzii, INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY, Vol: 118, ISSN: 0965-1748
Angrisano F, Sala K, Tapanelli S, et al., 2019, Male-specific protein disulphide isomerase function is essential for plasmodium transmission and a vulnerable target for intervention, Scientific Reports, Vol: 9, ISSN: 2045-2322
Inhibiting transmission of Plasmodium is an essential strategy in malaria eradication, and the biological process of gamete fusion during fertilization is a proven target for this approach. Lack of knowledge of the mechanisms underlying fertilization have been a hindrance in the development of transmission-blocking interventions. Here we describe a protein disulphide isomerase essential for malarial transmission (PDI-Trans/PBANKA_0820300) to the mosquito. We show that PDI-Trans activity is male-specific, surface-expressed, essential for fertilization/transmission, and exhibits disulphide isomerase activity which is up-regulated post-gamete activation. We demonstrate that PDI-Trans is a viable anti-malarial drug and vaccine target blocking malarial transmission with the use of PDI inhibitor bacitracin (98.21%/92.48% reduction in intensity/prevalence), and anti-PDI-Trans antibodies (66.22%/33.16% reduction in intensity/prevalence). To our knowledge, these results provide the first evidence that PDI function is essential for malarial transmission, and emphasize the potential of anti-PDI agents to act as anti-malarials, facilitating the future development of novel transmission-blocking interventions.
Witmer K, Fraschka SAK, Vlachou D, et al., 2019, Epigenetic regulation underlying Plasmodium berghei gene expression during its developmental transition from host to vector, bioRxiv, ISSN: 2045-2322
ABSTRACT Epigenetic regulation of gene expression is an important attribute in the survival and adaptation of the malaria parasite Plasmodium in its human host. Our understanding of epigenetic regulation of gene expression in Plasmodium developmental stages beyond asexual replication in the mammalian host is sparse. We used chromatin immune-precipitation (ChIP) and RNA sequencing to create an epigenetic and transcriptomic map of the murine parasite Plasmodium berghei development from asexual blood stages to male and female gametocytes, and finally, to ookinetes. We show that heterochromatin 1 (HP1) almost exclusively associates with variantly expressed gene families at subtelomeric regions and remains stable across stages and various parasite lines. Variant expression based on heterochromatic silencing is observed only in very few genes. In contrast, the active histone mark histone 3 Lysine 9 acetylation (H3K9ac) is found between heterochromatin boundaries and occurs as a sharp peak around the start codon for ribosomal protein genes. H3K9ac occupancy positively correlates with gene transcripts in asexual blood stages, male gametocytes and ookinetes. Interestingly, H3K9ac occupancy does not correlate with transcript abundance in female gametocytes. Finally, we identify novel DNA motifs upstream of ookinete-specific genes thought to be involved in transcriptional activation upon fertilization.
Debalke S, Habtewold T, Duchateau L, et al., 2019, The effect of silencing immunity related genes on longevity in a naturally occurring Anopheles arabiensis mosquito population from southwest Ethiopia, Parasites & Vectors, Vol: 12, ISSN: 1756-3305
BackgroundVector control remains the most important tool to prevent malaria transmission. However, it is now severely constrained by the appearance of physiological and behavioral insecticide resistance. Therefore, the development of new vector control tools is warranted. Such tools could include immunization of blood hosts of vector mosquitoes with mosquito proteins involved in midgut homeostasis (anti-mosquito vaccines) or genetic engineering of mosquitoes that can drive population-wide knockout of genes producing such proteins to reduce mosquito lifespan and malaria transmission probability.MethodsTo achieve this, candidate genes related to midgut homeostasis regulation need to be assessed for their effect on mosquito survival. Here, different such candidate genes were silenced through dsRNA injection in the naturally occurring Anopheles arabiensis mosquitoes and the effect on mosquito survival was evaluated.ResultsSignificantly higher mortality rates were observed in the mosquitoes silenced for FN3D1 (AARA003032), FN3D3 (AARA007751) and GPRGr9 (AARA003963) genes as compared to the control group injected with dsRNA against a non-related bacterial gene (LacZ). This observed difference in mortality rate between the candidate genes and the control disappeared when gene-silenced mosquitoes were treated with antibiotic mixtures, suggesting that gut microbiota play a key role in the observed reduction of mosquito survival.ConclusionsWe demonstrated that interference with the expression of the FN3D1, FN3D3 or GPRGr9 genes causes a significant reduction of the longevity of An. arabiensis mosquito in the wild.
Ruiz VMR, Sousa GL, Sneed SD, et al., 2019, Stimulation of a protease targeting the LRIM1/APL1C complex reveals specificity in complement-like pathway activation in Anopheles gambiae, PLOS ONE, Vol: 14, ISSN: 1932-6203
Christophides G, Rona L, Cechetto Carlos B, et al., 2019, A comprehensive analysis of malaria transmission in Brazil, Pathogens and Global Health, Vol: 113, Pages: 1-13, ISSN: 2047-7724
Malaria remains a serious public health problem in Brazil despite a significant drop in the number of cases in the past decade. We conduct a comprehensive analysis of malaria transmission in Brazil to highlight the epidemiologically most relevant components that could help tackle the disease. We consider factors impacting on the malaria burden and transmission dynamics including the geographical occurrence of both autochthonous and imported infections, the distribution and abundance of malaria vectors and records of natural mosquito infections with Plasmodium. Our analysis identifies three discrete malaria transmission systems related to the Amazon rainforest, Atlantic rainforest and Brazilian coast, respectively. The Amazonian system accounts for 99% of all malaria cases in the country. It is largely due to autochthonous P. vivax and P. falciparum transmission by mosquitoes of the Nyssorhynchus subgenus, primarily Anopheles darlingi. Whilst P. vivax transmission is widespread, P. falciparum transmission is restricted to hotspot areas mostly in the States of Amazonas and Acre. This system is the major source of P. vivax exportation to the extra-Amazonian regions that are also affected by importation of P. falciparum from Africa. The Atlantic system comprises autochthonous P. vivax transmission typically by the bromeliad-associated mosquitoes An. cruzii and An. bellator of the Kerteszia subgenus. An. cruzii also transmits simian malaria parasites to humans. The third, widespread but geographically fragmented, system is found along the Brazilian coast and comprises P. vivax transmission mainly by An. aquasalis. We conclude that these geographically and biologically distinct malaria transmission systems require specific strategies for effective disease control.
Habtewold T, Tapanelli S, Ellen KG M, et al., 2019, Streamlined SMFA and mosquito dark-feeding regime significantly improve malaria transmission-blocking assay robustness and sensitivity, Malaria Journal, Vol: 18, ISSN: 1475-2875
BackgroundThe development of malaria transmission-blocking strategies including the generation of malaria refractory mosquitoes to replace the wild populations through means of gene drives hold great promise. The standard membrane feeding assay (SMFA) that involves mosquito feeding on parasitized blood through an artificial membrane system is a vital tool for evaluating the efficacy of transmission-blocking interventions. However, despite the availability of several published protocols, the SMFA remains highly variable and broadly insensitive.MethodsThe SMFA protocol was optimized through coordinated culturing of Anopheles coluzzii mosquitoes and Plasmodium falciparum parasite coupled with placing mosquitoes under a strict dark regime before, during, and after the gametocyte feed.ResultsA detailed description of essential steps is provided toward synchronized generation of highly fit An. coluzzii mosquitoes and P. falciparum gametocytes in preparation for an SMFA. A dark-infection regime that emulates the natural vector-parasite interaction system is described, which results in a significant increase in the infection intensity and prevalence. Using this optimal SMFA pipeline, a series of putative transmission-blocking antimicrobial peptides (AMPs) were screened, confirming that melittin and magainin can interfere with P. falciparum development in the vector.ConclusionA robust SMFA protocol that enhances the evaluation of interventions targeting human malaria transmission in laboratory setting is reported. Melittin and magainin are identified as highly potent antiparasitic AMPs that can be used for the generation of refractory Anopheles gambiae mosquitoes.
A first generation of CRISPR-based gene drives has now been tested in the laboratory in a number of organisms, including malaria vector mosquitoes. Challenges for their use in the area-wide genetic control of vector-borne disease have been identified, including the development of target site resistance, their long-term efficacy in the field, their molecular complexity, and practical and legal limitations for field testing of both gene drive and coupled anti-pathogen traits. We have evaluated theoretically the concept of integral gene drive (IGD) as an alternative paradigm for population replacement. IGDs incorporate a minimal set of molecular components, including drive and anti-pathogen effector elements directly embedded within endogenous genes – an arrangement that in theory allows targeting functionally conserved coding sequences without disrupting their function. Autonomous and non-autonomous IGD strains could be generated, optimized, regulated and imported independently. We performed quantitative modeling comparing IGDs with classical replacement drives and show that selection for the function of the hijacked host gene can significantly reduce the establishment of resistant alleles in the population, while drive occurring at multiple genomic loci prolongs the duration of transmission blockage in the face of pre-existing target site variation. IGD thus has potential as a more durable and flexible population replacement strategy.
Christophides GK, Nakhleh J, Osta MA, 2017, The serine protease homolog CLIPA14 modulates the intensity of the immune response in the mosquito Anopheles gambiae, Journal of Biological Chemistry, Vol: 292, Pages: 18217-18226, ISSN: 0021-9258
CLIP domain serine protease homologues (cSPHs) are positive and negative regulators of Anopheles gambiae immune responses mediated by the complement-like protein TEP1 against Plasmodium malaria parasites and other microbial infections. We have previously reported that the SPH CLIPA2 is a negative regulator of the TEP1-mediated response by showing that CLIPA2 knockdown (kd) enhances mosquito resistance to infections with fungi, bacteria and Plasmodium parasites. Here, we identify another SPH, CLIPA14, as a novel regulator of mosquito immunity. We found that CLIPA14 is a hemolymph protein that is rapidly cleaved following a systemic infection. CLIPA14 kd mosquitoes elicited a potent melanization response against Plasmodium berghei ookinetes and exhibited significantly increased resistance to Plasmodium infections as well as to systemic and oral bacterial infections. The activity of the enzyme phenoloxidase, which initiates melanin biosynthesis, dramatically increased in the hemolymph of CLIPA14 kd mosquitoes in response to systemic bacterial infections. Ookinete melanization and hemolymph phenoloxidase activity were further increased after co-silencing CLIPA14 and CLIPA2, suggesting that these two SPHs act in concert to control the melanization response. Interestingly, CLIPA14 RNAi phenotypes and its infection-induced cleavage were abolished in a TEP1 loss-of-function background. Our results suggest that a complex network of SPHs functions downstream of TEP1 to regulate the melanization reaction.
Ukegbu CV, Giogalli M, Yassine H, et al., 2017, Plasmodium berghei P47 is essential for ookinete protection from the Anopheles gambiae complement-like response, Scientific Reports, Vol: 7, ISSN: 2045-2322
Malaria is a mosquito-borne disease affecting millions of people every year. The rodent parasite Plasmodium berghei has served as a model for human malaria transmission studies and played a pivotal role in dissecting the mosquito immune response against infection. The 6-cysteine protein P47, known to be important for P. berghei female gamete fertility, is shown to serve a different function in Plasmodium falciparum, protecting ookinetes from the mosquito immune response. Here, we investigate the function of P. berghei P47 in Anopheles gambiae mosquito infections. We show that P47 is expressed on the surface of both female gametocytes and ookinetes where it serves distinct functions in promoting gametocyte-to-ookinete development and protecting ookinetes from the mosquito complement-like response, respectively. The latter function is essential, as ookinetes lacking P47 are targeted for killing while traversing the mosquito midgut cells and eliminated upon exposure to hemolymph proteins of the complement-like system. Silencing key factors of the complement-like system restores oocyst development and disease transmission to rodent hosts. Our data establish a dual role of P. berghei P47 in vivo and reinforce the use of this parasite to study the impact of the mosquito immune response on human malaria transmission.
Ukegbu CV, Akinosoglou KA, Christophides GKC, et al., 2017, Plasmodium berghei PIMMS2 promotes ookinete invasion of the Anopheles gambiae mosquito midgut, Infection and Immunity, Vol: 85, ISSN: 1098-5522
Mosquito midgut stages of the malaria parasite present an attractive biological system to study host-parasite interactions and develop interventions to block disease transmission. Mosquito infection ensues upon oocyst development that follows ookinete invasion and traversal of the mosquito midgut epithelium. Here, we report the characterization of PIMMS2 (Plasmodium Invasion of Mosquito Midgut Screen candidate 2), a Plasmodium berghei protein with structural similarities to subtilisin-like proteins. PIMMS2 orthologs are present in the genomes of all plasmodia and are mapped between the subtilisin-encoding genes SUB1 and SUB3. P. berghei PIMMS2 is specifically expressed in zygotes and ookinetes and is localized on the ookinete surface. Loss of PIMMS2 function through gene disruption by homologous recombination leads to normal development of motile ookinetes that exhibit severely impaired capacity to traverse the mosquito midgut and transform to oocysts. Genetic complementation of the disrupted locus with a mutated PIMMS2 allele reveals that amino acid residues corresponding to the putative subtilisin-like catalytic triad are important but not essential for the protein function. Our data demonstrate that PIMMS2 is a novel ookinete-specific protein that promotes parasite traversal of the mosquito midgut epithelium and establishment of mosquito infection.
Gendrin MEM, Turlure F, Rodgers FH, et al., 2017, The peptidoglycan recognition proteins PGRPLA and PGRPLB regulate Anopheles immunity to bacteria and affect infection by Plasmodium, Journal of Innate Immunity, Vol: 9, Pages: 333-342, ISSN: 1662-8128
Peptidoglycan recognition proteins (PGRPs) form a family of immune regulators that is conserved from insects to mammals. In the malaria vector mosquito Anophelescoluzzii, the peptidoglycan receptor PGRPLC activates the Imd pathway limiting both the microbiota load and Plasmodiuminfection. Here, we carried out an RNAi screen to examine the role of all seven Anopheles PGRPs in infections with Plasmodium berghei and Plasmodium falciparum. We show that, in addition to PGRPLC, PGRPLA and PGRPS2/S3 also participate in antiparasitic defenses, and that PGRPLB promotes mosquito permissiveness to P. falciparum. We also demonstrate that following a mosquito blood feeding, which promotes growth of the gut microbiota, PGRPLA and PGRPLB positively and negatively regulate the activation of the Imd pathway, respectively. Our data demonstrate that PGRPs are important regulators of the mosquito epithelial immunity and vector competence.
Rodgers FH, Gendrin M, Wyer CAS, et al., 2017, Microbiota-induced peritrophic matrix regulates midgut homeostasis and prevents systemic infection of malaria vector mosquitoes, PLOS Pathogens, Vol: 13, Pages: 1-22, ISSN: 1553-7366
Manipulation of the mosquito gut microbiota can lay the foundations for novel methods for disease transmission control. Mosquito blood feeding triggers a significant, transient increase of the gut microbiota, but little is known about the mechanisms by which the mosquito controls this bacterial growth whilst limiting inflammation of the gut epithelium. Here, we investigate the gut epithelial response to the changing microbiota load upon blood feeding in the malaria vector Anopheles coluzzii. We show that the synthesis and integrity of the peritrophic matrix, which physically separates the gut epithelium from its luminal contents, is microbiota dependent. We reveal that the peritrophic matrix limits the growth and persistence of Enterobacteriaceae within the gut, whilst preventing seeding of a systemic infection. Our results demonstrate that the peritrophic matrix is a key regulator of mosquito gut homeostasis and establish functional analogies between this and the mucus layers of the mammalian gastrointestinal tract.
Habtewold T, Groom Z, Christophides G, 2017, Immune resistance and tolerance strategies in malaria vector and non-vector mosquitoes, Parasites & Vectors, Vol: 10, ISSN: 1756-3305
BackgroundThe Anopheles gambiae complex consists of species that vary greatly in their capacity to transmit malaria. The mosquito immune system has been identified as a key factor that can influence whether Plasmodium infection establishes within the mosquito vector. This study was designed to investigate the immune responses of An. coluzzii, An. arabiensis and An. quadriannulatus mosquitoes. The first two mosquito species are major vectors of malaria in sub-Saharan Africa, while the third is thought to be a non-vector.MethodsAll three mosquito species were reared in mixed cultures. Their capacity to eliminate P. berghei and regulate midgut bacteria was examined.ResultsOur results revealed large differences in mosquito resistance to P. berghei. In all three mosquito species, immune reactions involving the complement system were triggered when the number of parasites that mosquitoes were challenged with exceeded a certain level, i.e. immune tolerance threshold. This threshold was markedly lower in An. quadriannulatus compared to An. coluzzii and An. arabiensis. We also demonstrated that the level of immune tolerance to P. berghei infection in the haemolymph is inversely correlated with the level of immune tolerance to microbiota observed in the midgut lumen after a blood meal. The malaria non-vector mosquito species, An. quadriannulatus was shown to have a much higher level of tolerance to microbiota in the midgut than An. coluzzii.ConclusionsWe propose a model whereby an increased tolerance to microbiota in the mosquito midgut results in lower tolerance to Plasmodium infection. In this model, malaria non-vector mosquito species are expected to have increased immune resistance in the haemocoel, possibly due to complement priming by microbiota elicitors. We propose that this strategy is employed by the malaria non-vector mosquito, An. quadriannulatus, while An. coluzzii has reduced tolerance to bacterial infection in the midgut and consequently reduced immune resistan
Erguler K, Chandra NL, Proestos Y, et al., 2017, A large-scale stochastic spatiotemporal model for Aedes albopictus-borne chikungunya epidemiology, PLOS ONE, Vol: 12, ISSN: 1932-6203
Habtewold T, Groom Z, Christophides G, 2017, Immune resistance and tolerance strategies in malaria vector and non-vector mosquitoes, Parasite & Vectors
Gendrin MEM, Christophides, Linenberg, et al., 2016, Larval diet affects mosquito development and permissiveness to Plasmodium infection, Scientific Reports, Vol: 6, ISSN: 2045-2322
The larval stages of malaria vector mosquitoes develop in water pools, feeding mostly on microorganisms and environmental detritus. Richness in the nutrient supply to larvae influences the development and metabolism of larvae and adults. Here, we investigated the effects of larval diet on the development, microbiota content and permissiveness to Plasmodium of Anopheles coluzzii. We tested three fish diets often used to rear mosquitoes in the laboratory, including two pelleted diets, Dr. Clarke’s Pool Pellets and Nishikoi Fish Pellets, and one flaked diet, Tetramin Fish-Flakes. Larvae grow and develop faster and produce bigger adults when feeding on both types of pellets compared with flakes. This correlates with a higher microbiota load in pellet-fed larvae, in agreement with the known positive effect of the microbiota on mosquito development. Larval diet also significantly influences the prevalence and intensity of Plasmodium berghei infection in adults, whereby Nishikoi Fish Pellets-fed larvae develop into adults that are highly permissive to parasites and survive longer after infection. This correlates with a lower amount of Enterobacteriaceae in the midgut microbiota. Together, our results shed light on the influence of larval feeding on mosquito development, microbiota and vector competence; they also provide useful data for mosquito rearing.
Dahiya N, Chianese G, Abay SM, et al., 2016, In vitro and ex vivo activity of an Azadirachta indica A.Juss. seed kernel extract on early sporogonic development of Plasmodium in comparison with azadirachtin A, its most abundant constituent, PHYTOMEDICINE, Vol: 23, Pages: 1743-1752, ISSN: 0944-7113
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