Imperial College London

Professor George K. Christophides

Faculty of Natural SciencesDepartment of Life Sciences

Professor of Infectious Diseases & Immunity
 
 
 
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Contact

 

+44 (0)20 7594 5342g.christophides

 
 
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Location

 

6165Sir Alexander Fleming BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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150 results found

Bailey AJ, Ukegbu CV, Giorgalli M, Besson TRB, Christophides GK, Vlachou Det al., 2023, Intracellular Plasmodium aquaporin 2 is important for sporozoite production in the mosquito vector and malaria transmission., Proc Natl Acad Sci U S A, Vol: 120

Malaria remains a devastating disease and, with current measures failing to control its transmission, there is a need for novel interventions. A family of proteins that have long been pursued as potential intervention targets are aquaporins, which are channels facilitating the movement of water and other solutes across membranes. We identify an aquaporin in malaria parasites and demonstrate that it is important for completion of Plasmodium development in the mosquito vector. Disruption of AQP2 in the human parasite Plasmodium falciparum and the rodent parasite Plasmodium berghei blocks sporozoite production inside oocysts established on mosquito midguts, greatly limiting parasite infection of salivary glands and transmission to a new host. In vivo epitope tagging of AQP2 in P. berghei, combined with immunofluorescence assays, reveals that the protein is localized in vesicle-like organelles found in the cytoplasm of gametocytes, ookinetes, and sporozoites. The number of these organelles varies between individual parasites and lifecycle stages suggesting that they are likely part of a dynamic endomembrane system. Phylogenetic analysis confirms that AQP2 is unique to malaria and closely related parasites and most closely resembles intracellular aquaporins. Structure prediction analyses identify several unusual features, including a large accessory extracellular loop and an arginine-to-phenylalanine substitution in the selectivity filter principally determining pore function, a unique feature among known aquaporins. This in conjunction with the importance of AQP2 for malaria transmission suggests that AQP2 may be a fruitful target of antimalarial interventions.

Journal article

Ukegbu CV, Gomes AR, Giorgalli M, Campos M, Bailey AJ, Besson TRB, Billker O, Vlachou D, Christophides GKet al., 2023, Identification of genes required for<i> Plasmodium</i> gametocyte-to-sporozoite development in the mosquito vector, CELL HOST & MICROBE, Vol: 31, Pages: 1539-+, ISSN: 1931-3128

Journal article

Bailey AJ, Ukegbu CV, Giorgalli M, Besson TRB, Christophides GK, Vlachou Det al., 2023, Intracellular<i>Plasmodium</i>aquaporin 2 is required for sporozoite production in the mosquito vector and malaria transmission

<jats:title>Abstract</jats:title><jats:p>Malaria remains a devastating disease and, with current measures failing to control its transmission, there is a need for novel interventions. A family of proteins that have long been pursued as potential intervention targets are aquaporins which are channels facilitating the movement of water and other solutes across membranes. We identify a new aquaporin in malaria parasites and demonstrate that it is essential for disease transmission through mosquitoes. Disruption of AQP2 in the human parasite<jats:italic>Plasmodium falciparum</jats:italic>and the rodent parasite<jats:italic>Plasmodium berghei</jats:italic>blocks sporozoite production inside oocysts established on mosquito midguts, preventing parasite infection of salivary glands and transmission to a new host.<jats:italic>In vivo</jats:italic>epitope tagging of AQP2 in<jats:italic>P. berghei</jats:italic>, combined with immunofluorescence assays, reveals that the protein is localized in previously uncharacterized organelles found in the cytoplasm of gametocytes, ookinetes and sporozoites. The number of these organelles varies between individual parasites and lifecycle stages suggesting that they are likely part of a dynamic endolysosomal system. Phylogenetic analysis confirms that AQP2 is unique to malaria and closely related parasites and most closely related to other intracellular aquaporins. Structure prediction analyses identify several unusual features, including a large accessory extracellular loop and an arginine-to-phenylalanine substitution in the selectivity filter principally determining pore function, a unique feature not found in any aquaporins studied to date. This in conjunction with the requirement of AQP2 for malaria transmission suggests that AQP2 may be a fruitful new target of novel antimalarial interventions.</jats:p>

Journal article

Ukegbu CV, Gomes AR, Giorgalli M, Campos M, Bailey AJ, Besson TRB, Billker O, Vlachou D, Christophides GKet al., 2023, Reverse genetic screen identifies malaria parasite genes required for gametocyte-to-sporozoite development in its mosquito host

<jats:title>Summary</jats:title><jats:p>Malaria remains one of the most devastating infectious diseases. Reverse genetic screens offer a powerful approach to identify genes and molecular processes governing malaria parasite biology. However, sexual reproduction and complex regulation of gene expression and genotype-phenotype associations in the mosquito have hampered the development of screens in this key part of the parasite lifecycle. We designed a genetic approach in the rodent parasite<jats:italic>Plasmodium berghei</jats:italic>, which in conjunction with barcode sequencing allowed us to overcome the fertilization roadblock and screen for gametocyte-expressed genes required for parasite infection of the mosquito<jats:italic>Anopheles coluzzii</jats:italic>. The results confirmed previous findings, validating our approach for scaling up, and identified new genes required for ookinete motility and mosquito midgut infection and for sporozoite development and oocyst egress and salivary gland infection. Our findings can assist efforts to study malaria transmission biology and develop new interventions to control disease transmission.</jats:p>

Journal article

Neira M, Erguler K, Ahmady-Birgani H, AL-Hmoud ND, Fears R, Gogos C, Hobbhahn N, Koliou M, Kostrikis LG, Lelieveld J, Majeed A, Paz S, Rudich Y, Saad-Hussein A, Shaheen M, Tobias A, Christophides Get al., 2023, Climate change and human health in the Eastern Mediterranean and middle east: Literature review, research priorities and policy suggestions, Environmental Research, Vol: 216, Pages: 1-23, ISSN: 0013-9351

Human health is linked to climatic factors in complex ways, and climate change can have profound direct and indirect impacts on the health status of any given region. Susceptibility to climate change is modulated by biological, ecological and socio-political factors such as age, gender, geographic location, socio-economic status, occupation, health status and housing conditions, among other.In the Eastern Mediterranean and Middle East (EMME), climatic factors known to affect human health include extreme heat, water shortages and air pollution. Furthermore, the epidemiology of vector-borne diseases (VBDs) and the health consequences of population displacement are also influenced by climate change in this region.To inform future policies for adaptation and mitigation measures, and based on an extensive review of the available knowledge, we recommend several research priorities for the region. These include the generation of more empirical evidence on exposure-response functions involving climate change and specific health outcomes, the development of appropriate methodologies to evaluate the physical and psychological effects of climate change on vulnerable populations, determining how climate change alters the ecological determinants of human health, improving our understanding of the effects of long-term exposure to heat stress and air pollution, and evaluating the interactions between adaptation and mitigation strategies.Because national boundaries do not limit most climate-related factors expected to impact human health, we propose that adaptation/mitigation policies must have a regional scope, and therefore require collaborative efforts among EMME nations. Policy suggestions include a decisive region-wide decarbonisation, the integration of environmentally driven morbidity and mortality data throughout the region, advancing the development and widespread use of affordable technologies for the production and management of drinking water by non-traditional means, t

Journal article

Habtewold T, Tapanelli S, Masters EKG, Windbichler N, Christophides GKet al., 2022, The circadian clock modulates <i>Anopheles gambiae</i> infection with <i>Plasmodium falciparum</i>, PLOS ONE, Vol: 17, ISSN: 1932-6203

Journal article

Windbichler N, 2022, Gene drive mosquitoes can aid malaria elimination by retarding Plasmodium sporogonic development, Science Advances, Vol: 8, Pages: 1-9, ISSN: 2375-2548

Abstract: Gene drives hold promise for the genetic control of malaria vectors. The development of vector population modification strategies hinges on the availability of effector mechanisms impeding parasite development in transgenic mosquitoes. We augmented a midgut gene of the malaria mosquito Anopheles gambiae to secrete two exogenous antimicrobial peptides, Magainin 2 and Melittin. This small genetic modification, capable of efficient non-autonomous gene drive, hampers oocyst development in both Plasmodium falciparum and Plasmodium berghei. It delays the release of infectious sporozoites while it simultaneously reduces the lifespan of homozygous female transgenic mosquitoes. Modeling the spread of this modification using a large-scale agent-based model of malaria epidemiology reveals that it can break the cycle of disease transmission across a range of transmission intensities.

Journal article

Ellis D, Avraam GP, Hoermann A, Wyer CASP, Ong YX, Christophides GP, Windbichler Net al., 2022, Testing non-autonomous antimalarial gene drive effectors using self-eliminating drivers in the African mosquito vector <i>Anopheles gambiae</i>, PLOS GENETICS, Vol: 18, ISSN: 1553-7404

Journal article

Hoermann A, Habtewold T, Selvaraj P, Del Corsano G, Capriotti P, Inghilterra MG, Kebede TM, Christophides GK, Windbichler Net al., 2022, Gene Drive Mosquitoes Can Aid Malaria Elimination by Retarding Plasmodium Sporogonic Development

<jats:title>Abstract</jats:title><jats:p>Gene drives hold promise for the genetic control of malaria vectors. The development of vector population modification strategies hinges on the availability of effector mechanisms impeding parasite development in transgenic mosquitoes. We augmented a midgut gene of the malaria mosquito <jats:italic>Anopheles gambiae</jats:italic> to secrete two exogenous antimicrobial peptides, Magainin 2 and Melittin. This small genetic modification, capable of efficient non-autonomous gene drive, hampers oocyst development in both <jats:italic>Plasmodium falciparum</jats:italic> and <jats:italic>Plasmodium berghei</jats:italic>. It delays the release of infectious sporozoites while it simultaneously reduces the lifespan of homozygous female transgenic mosquitoes. Modeling the spread of this modification using a large-scale agent-based model of malaria epidemiology reveals that it can break the cycle of disease transmission across a range of endemic settings.</jats:p><jats:sec><jats:title>One sentence summary</jats:title><jats:p>We developed a gene drive effector that retards <jats:italic>Plasmodium</jats:italic> development in transgenic <jats:italic>Anopheles gambiae</jats:italic> mosquitoes via the expression of antimicrobial peptides in the midgut and which is predicted to eliminate malaria under a range of transmission scenarios.</jats:p></jats:sec>

Working paper

Amos B, Aurrecoechea C, Barba M, Barreto A, Basenko EY, Bazant W, Belnap R, Blevins AS, Bohme U, Brestelli J, Brunk BP, Caddick M, Callan D, Campbell L, Christensen MB, Christophides GK, Crouch K, Davis K, DeBarry J, Doherty R, Duan Y, Dunn M, Falke D, Fisher S, Flicek P, Fox B, Gajria B, Giraldo-Calderon G, Harb OS, Harper E, Hertz-Fowler C, Hickman MJ, Howington C, Hu S, Humphrey J, Iodice J, Jones A, Judkins J, Kelly SA, Kissinger JC, Kwon DK, Lamoureux K, Lawson D, Li W, Lies K, Lodha D, Long J, MacCallum RM, Maslen G, McDowell MA, Nabrzyski J, Roos DS, Rund SSC, Schulman SW, Shanmugasundram A, Sitnik V, Spruill D, Starns D, Stoeckert CJ, Tomko SS, Wang H, Warrenfeltz S, Wieck R, Wilkinson PA, Xu L, Zheng Jet al., 2022, VEuPathDB: the eukaryotic pathogen, vector and host bioinformatics resource center, NUCLEIC ACIDS RESEARCH, Vol: 50, Pages: D898-D911, ISSN: 0305-1048

Journal article

Paz S, Majeed A, Christophides GK, 2021, Climate change impacts on infectious diseases in the Eastern Mediterranean and the Middle East (EMME)-risks and recommendations, Climatic Change: an interdisciplinary, international journal devoted to the description, causes and implications of climatic change, Vol: 169, Pages: 1-17, ISSN: 0165-0009

The Eastern Mediterranean and Middle East (EMME) region has rapid population growth, large differences in socio-economic levels between developed and developing countries, migration, increased water demand, and ecosystems degradation. The region is experiencing a significant warming trend with longer and warmer summers, increased frequency and severity of heat waves, and a drier climate. While climate change plays an important role in contributing to political instability in the region through displacement of people, food insecurity, and increased violence, it also increases the risks of vector-, water-, and food-borne diseases. Poorer and less educated people, young children and the elderly, migrants, and those with long-term health problems are at highest risk. A result of the inequalities among EMME countries is an inconsistency in the availability of reliable evidence about the impacts on infectious diseases. To help address this gap, a search of the literature was conducted as a basis for related recommended responses and suggested actions for preparedness and prevention. Since climate change already impacts the health of vulnerable populations in the EMME and will have a greater impact in future years, risk assessment and timely design and implementation of health preparedness and adaptation strategies are essential. Joint national and cross-border infectious diseases management systems for more effective preparedness and prevention are needed, supported by interventions that improve the environment. Without such cooperation and effective interventions, climate change will lead to an increasing morbidity and mortality in the EMME from infectious diseases, with a higher risk for the most vulnerable populations.

Journal article

Little TS, Cunningham DA, Vandomme A, Lopez CT, Amis S, Alder C, Addy JWG, McLaughlin S, Hosking C, Christophides G, Reid AJ, Langhorne Jet al., 2021, Analysis of <i>pir</i> gene expression across the <i>Plasmodium</i> life cycle, MALARIA JOURNAL, Vol: 20

Journal article

Tapanelli S, Inghilterra MG, Cai J, Philpott J, Capriotti P, Windbichler N, Christophides GKet al., 2021, Assessment of <i>Plasmodium falciparum</i> infection and fitness of genetically modified <i>Anopheles gambiae</i> aimed at mosquito population replacement

<jats:title>Abstract</jats:title><jats:p>Genetically modified (GM) mosquitoes expressing anti-plasmodial effectors propagating through wild mosquito populations by means of gene drive is a promising tool to support current malaria control strategies. The process of generating GM mosquitoes involves genetic transformation of mosquitoes from a laboratory colony and, often, interbreeding with other GM lines to cross in auxiliary traits. These mosquito colonies and GM lines thus often have different genetic backgrounds and GM lines are invariably highly inbred, which in conjunction with their independent rearing in the laboratory may translate to differences in their susceptibility to malaria parasite infection and life history traits. Here, we show that laboratory <jats:italic>Anopheles gambiae</jats:italic> colonies and GM lines expressing Cas9 and Cre recombinase vary greatly in their susceptibility to <jats:italic>Plasmodium falciparum</jats:italic> NF54 infection. Therefore, the choice of mosquitoes to be used as a reference when conducting infection or life history trait assays requires careful consideration. To address these issues, we established an experimental pipeline involving genetic crosses and genotyping of mosquitoes reared in shared containers throughout their lifecycle. We used this protocol to examine whether GM lines expressing the antimicrobial peptide (AMP) Scorpine in the mosquito midgut interfere with parasite infection and mosquito survival. We demonstrate that Scorpine expression in the Peritrophin 1 (Aper1) genomic locus reduces both <jats:italic>P</jats:italic>. <jats:italic>falciparum</jats:italic> sporozoite prevalence and mosquito lifespan; both these phenotypes are likely to be associated with the disturbance of the midgut microbiota homeostasis. These data lead us to conclude that the Aper1-Sco GM line could be used in proof-of-concept experiments aimed at mosquito populat

Journal article

Campos M, Willis K, Rona LDP, Christophides G, Maccallum Ret 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.

Journal article

Ferdous Z, Fuchs S, Behrends V, Trasanidis N, Vlachou D, Christophides GKet 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

Journal article

Hoermann A, Tapanelli S, Capriotti P, Del Corsano G, Masters EK, Habtewold T, Christophides GK, Windbichler Net 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.

Journal article

Eba K, Habtewold T, Yewhalaw D, Christophides GK, Duchateau Let 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

Journal article

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.

Journal article

Habtewold T, Sharma A, Wyer C, Masters E, Nikolai W, Christophides Get 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.

Journal article

Chabanol E, Behrends V, Prevot G, Christophides GK, Gendrin Met al., 2020, Antibiotic treatment in anopheles coluzzii affects carbon and nitrogen metabolism, Pathogens, Vol: 9, Pages: 1-13, ISSN: 2076-0817

The mosquito microbiota reduces the vector competence of Anopheles to Plasmodium and affects host fitness; it is therefore considered as a potential target to reduce malaria transmission. While immune induction, secretion of antimicrobials and metabolic competition are three typical mechanisms of microbiota-mediated protection against invasive pathogens in mammals, the involvement of metabolic competition or mutualism in mosquito-microbiota and microbiota-Plasmodium interactions has not been investigated. Here, we describe a metabolome analysis of the midgut of Anopheles coluzzii provided with a sugar-meal or a non-infectious blood-meal, under conventional or antibiotic-treated conditions. We observed that the antibiotic treatment affects the tricarboxylic acid cycle and nitrogen metabolism, notably resulting in decreased abundance of free amino acids. Linking our results with published data, we identified pathways which may participate in microbiota-Plasmodium interactions via metabolic interactions or immune modulation and thus would be interesting candidates for future functional studies.

Journal article

Debalke S, Habtewold T, Christophides GK, Duchateau Let 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 and Vectors, Vol: 13, Pages: 1-9, ISSN: 1756-3305

BackgroundMalaria vector mosquitoes acquire midgut microbiota primarily from their habitat. The homeostasis of these microbial communities plays an essential role in the mosquito longevity, the most essential factor in the mosquito vectorial capacity. Our recent study revealed that silencing genes involved in regulation of the midgut homeostasis including FN3D1, FN3D3 and GPRGr9 reduced the survival of female adult Anopheles arabiensis mosquitoes. In the present study, we investigate the stability of the gene silencing efficiency of mosquitoes reared in three different breeding conditions representing distinct larval habitat types: town brick pits in Jimma, flood pools in the rural land of Asendabo and roadside pools in Wolkite.MethodsFirst-instar larvae of An. arabiensis mosquitoes were reared separately using water collected from the three breeding sites. The resulting adult females were micro-injected with dsRNA targeting the FN3D1 gene (AARA003032) and their survival was monitored. Control mosquitoes were injected with dsRNA Lacz. In addition, the load of midgut microbiota of these mosquitoes was determined using flow cytometry.ResultsSurvival of naïve adult female mosquitoes differed between the three sites. Mosquitoes reared using water collected from brick pits and flood pools survived longer than mosquitoes reared using water collected from roadside. However, the FN3D1 gene silencing effect on survival did not differ between the three sites.ConclusionsThe present study revealed that the efficacy of FN3D1 gene silencing is not affected by variation in the larval habitat. Thus, silencing this gene has potential for application throughout sub-Saharan Africa.

Journal article

Witmer K, Fraschka S, Vlachou D, Bartfai R, Christophides Get 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.

Journal article

James SL, Marshall JM, Christophides GK, Okumu FO, Nolan Tet 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.

Journal article

Ukegbu CV, Giorgalli M, Tapanelli S, Rona LDP, Jaye A, Wyer C, Angrisano F, Christophides G, Vlachou Det 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.

Journal article

Habtewold T, Sharma A, Wyer CAS, Masters EKG, Windbichler N, Christophides Get 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.

Working paper

Rodgers FH, Cai JA, Pitaluga AN, Mengin-Lecreulx D, Gendrin M, Christophides GKet 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

Journal article

Ferdous Z, Fuchs S, Behrends V, Trasanidis N, Vlachou D, Christophides Get al., 2020, <i>Anopheles coluzzii</i>stearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding

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

Journal article

Angrisano F, Sala K, Tapanelli S, Christophides G, Blagborough Aet 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.

Journal article

Witmer K, Fraschka SAK, Vlachou D, Bártfai R, Christophides Get 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.

Journal article

Debalke S, Habtewold T, Duchateau L, Christophides Get 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.

Journal article

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