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Mosquito immune cells, or hemocytes, are integral components of the innate immune responses that define vector competence. To date, the characterization and functional classification of hemocytes has been hindered by the limited availability of genetic resources. Here, we map the composition of mosquito hemocytes by engineering five transgenic Anopheles gambiae lines that express fluorescent proteins under the control of candidate hemocyte promoters. We characterize these five transgenic lines through gene expression and microscopy-based approaches, and examine mosquito immune cell populations by leveraging advanced spectral imaging flow cytometry. We classify mosquito hemocytes into twelve distinct populations based on size, granularity, and ploidy, while defining these hemocyte subtypes based on their phagocytic capacity and the expression of genetic markers. By simultaneously analyzing these morphological and genetic properties, our work highlights the complexity and plasticity of mosquito hemocytes and provides the foundation for deeper investigations into their roles in immunity and pathogen transmission. Classification of mosquito hemocytes into subtypes has thus far relied on morphological properties. Here, the authors develop new genetic resources that facilitate the visualization and analysis of hemocyte subtypes in Anopheles gambiae . By combining the expression of hemocyte-specific genetic markers with the analysis of morphology, ploidy, and phagocytic capacity, the authors identify twelve distinct subtypes, revealing the complexity and plasticity of these immune cells with unprecedented resolution.

Tumor Necrosis Factor-α (TNF-α) is a proinflammatory cytokine and a master regulator of immune cell function in vertebrates. While previous studies have implicated TNF signaling in invertebrate immunity, the roles of TNF in mosquito innate immunity and vector competence have yet to be functionally explored. Herein, we confirm the identification of a conserved TNF-α pathway in Anopheles gambiae consisting of the TNF-α ligand, Eiger, and its cognate receptors Wengen and Grindelwald. Through gene expression analysis, RNAi, and in vivo injection of recombinant TNF-α, we provide direct evidence for the requirement of TNF signaling in regulating mosquito immune cell function by promoting granulocyte midgut attachment, increased granulocyte abundance, and oenocytoid rupture. Moreover, our data demonstrate that TNF signaling is an integral component of anti- Plasmodium immunity that limits malaria parasite survival. Together, our data support the existence of a highly conserved TNF signaling pathway in mosquitoes that mediates cellular immunity and influences Plasmodium infection outcomes, offering potential new approaches to interfere with malaria transmission by targeting the mosquito host.

Anopheles mosquitoes are the sole vector of malaria, the most burdensome vector-borne disease worldwide. At present, strategies for reducing mosquito populations or limiting their ability to transmit disease show the most promise for disease control. Therefore, improving our understanding of mosquito biology and immune function may aid new approaches to limit malaria transmission. Here, we perform genome-wide CRISPR screens in Anopheles mosquito cells to identify genes required for fitness and that confer resistance to clodronate liposomes, which are used to ablate immune cells. The cellular fitness screen identifies 1280 fitness-related genes (393 at highest confidence) that are highly enriched for roles in fundamental cell processes. The clodronate screen identifies resistance factors that impair clodronate liposome function. For the latter, we confirm roles in liposome uptake and processing through in vivo validation in Anopheles gambiae that provide new mechanistic detail of phagolysosome formation and clodronate liposome processing. Altogether, we present a genome-wide CRISPR knockout platform in a major malaria vector and identify genes important for fitness and immune-related processes. Mosquitoes are major vectors for the transmission of many serious pathogens. This study uses genome-wide CRISPR screens in the mosquito, Anopheles gambiae, to reveal new insights into mosquito fitness and the function of clodronate-liposome mediated immune cell ablation.

The putative synergistic action of target-site mutations and enhanced detoxification in pyrethroid resistance in insects has been hypothesized as a major evolutionary mechanism responsible for dramatic consequences in malaria incidence and crop production. Combining genetic transformation and CRISPR/Cas9 genome modification, we generated transgenic Drosophila lines expressing pyrethroid metabolizing P450 enzymes in a genetic background along with engineered mutations in the voltage-gated sodium channel ( para ) known to confer target-site resistance. Genotypes expressing the yellow fever mosquito Aedes aegypti Cyp9J28 while also bearing the para V1016G mutation displayed substantially greater resistance ratio (RR) against deltamethrin than the product of each individual mechanism (RR combined : 19.85 > RR Cyp9J28 : 1.77 × RR V1016G : 3.00). Genotypes expressing Brassicogethes aeneus pollen beetle Cyp6BQ23 and also bearing the para L1014F ( kdr ) mutation, displayed an almost multiplicative RR (RR combined : 75.19 ≥ RR Cyp6BQ23 : 5.74 × RR L1014F : 12.74). Reduced pyrethroid affinity at the target site, delaying saturation while simultaneously extending the duration of P450-driven detoxification, is proposed as a possible underlying mechanism. Combinations of target site and P450 resistance loci might be unfavourable in field populations in the absence of insecticide selection, as they exert some fitness disadvantage in development time and fecundity. These are major considerations from the insecticide resistance management viewpoint in both public health and agriculture.

The putative synergistic action of target-sitemutations and enhanced detoxification in pyrethroid resistance in insects has been hypothesized as a major evolutionary mechanismresponsible for dramatic consequences inmalaria incidence and crop production. Combining genetic transformation and CRISPR/Cas9 genome modification,we generated transgenic Drosophila lines expressing pyrethroid metabolizing P450 enzymes in a genetic background along with engineered mutations in the voltage-gated sodium channel (para) known to confer target-site resistance. Genotypes expressing the yellow fever mosquito Aedes aegypti Cyp9J28 while also bearing the para V1016G mutation displayed substantially greater resistance ratio (RR) against deltamethrin than the product of each individual mechanism (RRcombined: 19.85> RRCyp9J28: 1.77×RRV1016G: 3.00). Genotypes expressing Brassicogethes aeneus pollen beetle Cyp6BQ23 and also bearing the para L1014F (kdr) mutation, displayed an almost multiplicative RR (RRcombined: 75.19 ≥ RRCyp6BQ23: 5.74 × RRL1014F: 12.74). Reduced pyrethroid affinity at the target site, delaying saturationwhile simultaneouslyextending the duration of P450-driven detoxification, is proposed as a possible underlying mechanism. Combinations of target site and P450 resistance loci might be unfavourable in field populations in the absence of insecticide selection, as they exert some fitness disadvantage in development time and fecundity. These are major considerations from the insecticide resistance management viewpoint in both public health and agriculture.

The insect steroid hormone ecdysone plays a critical role in insect development. Several recent studies have shown that ecdysone is transported through Organic Anion Transporting Polypeptides (OATPs) in insects such as flies and mosquitoes. However, the conservation of this mechanism across other arthropods and the role of this transporter in canonical ecdysone pathways are less well studied. Herein we functionally characterized the putative ecdysone transporter OATP74D from two major agricultural moth pests: Helicoverpa armigera (cotton bollworm) and Spodoptera frugiperda (fall armyworm). Phylogenetic analysis of OATP transporters across the superphylum Ecdysozoa revealed that Oatp74D is well represented among arthropod species and appeared only at the root of the arthropod lineage. Partial disruption of Oatp74D in S. frugiperda decreased embryo hatching rate and larval survival, suggesting that this gene is essential for development in vivo. Depletion and re-expression of OatP74D in the lepidoptera cell line RP-HzGUT-AW1(MG) confirmed the gene’s role in ecdysone import and demonstrated that OATP74D is essential for the transcriptional activation of ecdysone responsive genes including caspase-3, implicating this transporter in cell death pathways. Establishment of a simple and robust luciferase assay using the RP-HzGUT-AW1(MG) cell line demonstrated that both HaOATP74D and SfOATP74D are inhibited by rifampicin, a well-known organic anion transporter inhibitor. Overall, this work sheds more light on ecdysone uptake mechanisms across insect species and broadens our knowledge of the physiological roles of OATPs in the transportation of endogenous substrates. Competing Interest Statement I have read the journal's policy and the authors of this manuscript have the following competing interests: GS and SD were funded as a part of a joint collaboration between Bayer Crop Sciences (https://www.cropscience.bayer.us/) and the Institute of Biochemistry and Molecular Biology (https://www.imbb.forth.gr/en/). SG and RN are employees of Bayer Crop Sciences and played a role in study design and writing.

Mosquito immune cells, or hemocytes, are integral components of the innate immune responses that define vector competence. However, the lack of genetic resources has limited their characterization and our understanding of their functional roles in immune signaling. To overcome these challenges, we engineered transgenic that express fluorescent proteins under the control of candidate hemocyte promoters. Following the characterization of five transgenic constructs through gene expression and microscopy-based approaches, we examine mosquito immune cell populations by leveraging advanced spectral imaging flow cytometry. Our results comprehensively map the composition of mosquito hemocytes, classifying them into twelve distinct populations based on size, granularity, ploidy, phagocytic capacity, and the expression of PPO6, SPARC, and LRIM15 genetic markers. Together, our novel use of morphological properties and genetic markers provides increased resolution into our understanding of mosquito hemocytes, highlighting the complexity and plasticity of these immune cell populations, while providing the foundation for deeper investigations into their roles in immunity and pathogen transmission.

Tumor Necrosis Factor-α (TNF-α) is a proinflammatory cytokine and a master regulator of immune cell function in vertebrates. While previous studies have implicated TNF signaling in invertebrate immunity, the roles of TNF in mosquito innate immunity and vector competence have yet to be explored. Herein, we confirm the identification of a conserved TNF-α pathway in consisting of the TNF-α ligand, Eiger, and its cognate receptors Wengen and Grindelwald. Through gene expression analysis, RNAi, and injection of recombinant TNF-α, we provide direct evidence for the requirement of TNF signaling in regulating mosquito immune cell function by promoting granulocyte midgut attachment, increased granulocyte abundance, and oenocytoid rupture. Moreover, our data demonstrate that TNF signaling is an integral component of anti- immunity that limits malaria parasite survival. Together, our data support the existence of a highly conserved TNF signaling pathway in mosquitoes that mediates cellular immunity and influences infection outcomes, offering potential new approaches to interfere with malaria transmission by targeting the mosquito host.

mosquitoes are the sole vector of human malaria, the most burdensome vector-borne disease worldwide. Strategies aimed at reducing mosquito populations and limiting their ability to transmit disease show the most promise for disease control. Therefore, gaining an improved understanding of mosquito biology, and specifically that of the immune response, can aid efforts to develop new approaches that limit malaria transmission. Here, we use a genome-wide CRISPR screening approach for the first time in mosquito cells to identify essential genes in and identify genes for which knockout confers resistance to clodronate liposomes, which have been widely used in mammals and arthropods to ablate immune cells. In the essential gene screen, we identified a set of 1280 genes that are highly enriched for genes involved in fundamental cell processes. For the clodronate liposome screen, we identified several candidate resistance factors and confirm their roles in the uptake and processing of clodronate liposomes through validation in , providing new mechanistic detail of phagolysosome formation and clodronate liposome function. In summary, we demonstrate the application of a genome-wide CRISPR knockout platform in a major malaria vector and the identification of genes that are important for fitness and immune-related processes.