Anopheles aquasalis transcriptome reveals autophagic responses to Plasmodium vivax midgut invasion

Genomic advances in the study of the mosquito vector during avian malaria infection

Invertebrate host–parasite associations are one of the keystones in order to understand vector-borne diseases. The study of these specific interactions provides information not only about how the vector is affected by the parasite at the gene-expression level, but might also reveal mosquito strategies for blocking the transmission of the parasites. A very well-known vector for human malaria is Anopheles gambiae. This mosquito species has been the main focus for genomics studies determining essential key genes and pathways over the course of a malaria infection. However, to-date there is an important knowledge gap concerning other non-mammophilic mosquito species, for example some species from the Culex genera which may transmit avian malaria but also zoonotic pathogens such as West Nile virus. From an evolutionary perspective, these 2 mosquito genera diverged 170 million years ago, hence allowing studies in both species determining evolutionary conserved genes essential during malaria infections, which in turn might help to find key genes for blocking malaria cycle inside the mosquito. Here, we extensively review the current knowledge on key genes and pathways expressed in Anopheles over the course of malaria infections and highlight the importance of conducting genomic investigations for detecting pathways in Culex mosquitoes linked to infection of avian malaria. By pooling this information, we underline the need to increase genomic studies in mosquito–parasite associations, such as the one in Culex–Plasmodium, that can provide a better understanding of the infection dynamics in wildlife and reduce the negative impact on ecosystems.

Unravelling the genome of the brackish water malaria vector Anopheles aquasalis

Malaria is a severe public health problem in several developing tropical and subtropical countries. Anopheles aquasalis is the primary coastal malaria vector in Central and South America and the Caribbean Islands, and it has the peculiar feature of living in water with large changes in salinity. Recent research has recognised An. aquasalis as an important model for studying the interactions of murine and human Plasmodium parasites. This study presents the complete genome of An. aquasalis and offers insights into its evolution and physiology. The genome is similar in size and gene content to other Neotropical anophelines, with 162 Mb and 12,446 protein-coding genes. There are 1387 single-copy orthologs at the Diptera level (eg. An. gambiae, An. darlingi and Drosophila melanogaster). An. aquasalis diverged from An. darlingi, the primary malaria vector in inland South America, nearly 20 million years ago. Proteins related to ion transport and metabolism belong to the most abundant gene families with 660 genes. We identified gene families relevant to osmosis control (e.g., aquaporins, vacuolar-ATPases, Na+/K+-ATPases, and carbonic anhydrases). Evolutionary analysis suggests that all osmotic regulation genes are under strong purifying selection. We also observed low copy number variation in insecticide resistance and immunity-related genes for all known classical pathways. The data provided by this study offers candidate genes for further studies of parasite-vector interactions and for studies on how anophelines of brackish water deal with the high fluctuation in water salinity. We also established data and insights supporting An. aquasalis as an emerging Neotropical malaria vector model for genetic and molecular studies.

Plasmodium vivax transcriptomics: What is new?

Malaria is the leading human parasitosis and is transmitted through the bite of anopheline mosquitoes infected with parasites of the genus Plasmodium spp. Among the seven species that cause malaria in humans, Plasmodium vivax is the most prevalent species in Latin America. In recent years, there have been an increasing number of reports of clinical complications caused by P. vivax infections, which were previously neglected and underestimated. P. vivax biology remains with large gaps. The emergence of next-generation sequencing technology has ensured a breakthrough in species knowledge. Coupled with this, the deposition of the P. vivax Sal-1 reference genome allowed an increase in transcriptomics projects by accessing messenger RNA. Thus, the regulation of differential gene expression according to the parasite life stage was verified, and several expressed genes were linked to different biological functions. Today, with the progress associated with RNA sequencing technologies, it is possible to detect nuances and obtain robust results. Discoveries provided by transcriptomic studies allow us to understand topics such as RNA expression and regulation and proteins and metabolic pathways involved during different stages of the parasite life cycle. The information obtained enables a better comprehension of immune system evasion mechanisms; invasion and adhesion strategies used by the parasite; as well as new vaccine targets, potential molecular markers, and others therapeutic targets. In this review, we provide new insights into P. vivax biology by summarizing recent findings in transcriptomic studies.

Evolution and assembly of Anopheles aquasalis's immune genes: primary malaria vector of coastal Central and South America and the Caribbean Islands

Anophelines are vectors of malaria, the deadliest disease worldwide transmitted by mosquitoes. The availability of genomic data from various Anopheles species allowed evolutionary comparisons of the immune response genes in search of alternative vector control of the malarial parasites. Now, with the Anopheles aquasalis genome, it was possible to obtain more information about the evolution of the immune response genes. Anopheles aquasalis has 278 immune genes in 24 families or groups. Comparatively, the American anophelines possess fewer genes than Anopheles gambiae s. s., the most dangerous African vector. The most remarkable differences were found in the pathogen recognition and modulation families like FREPs, CLIP and C-type lectins. Even so, genes related to the modulation of the expression of effectors in response to pathogens and gene families that control the production of reactive oxygen species were more conserved. Overall, the results show a variable pattern of evolution in the immune response genes in the anopheline species. Environmental factors, such as exposure to different pathogens and differences in the microbiota composition, could shape the expression of this group of genes. The results presented here will contribute to a better knowledge of the Neotropical vector and open opportunities for malaria control in the endemic-affected areas of the New World.

Sexual Dimorphism in Immune Responses and Infection Resistance in Aedes aegypti and Other Hematophagous Insect Vectors

Sexual dimorphism in immune function is prevalent across different species, where males trade their ability to fight pathogens for a practical reproductive function while females favor an extended lifespan. In insects, these differences in immune function reflect an evolutionary life strategy, where females have a presumably more robust immune system than insect males. Here, we evaluate immune functioning in four male and female insect vectors, Aedes aegypti (Diptera, Culicidae), Anopheles aquasalis (Diptera, Culicidae), Lutzomyia longipalpis (Diptera, Psychodidae) and Rhodnius prolixus (Hemiptera, Reduviidae). We show evidence that challenges the concept of immune sexual dimorphism in three of these insect vectors. In the three Diptera species, A. aegypti, A. aquasalis and L. longipalpis that transmit arboviruses, Plasmodium spp. (Haemospororida, Plasmodiidae) and Leishmania spp. (Trypanosomatida, Trypanosomatidae), respectively, unchallenged adult males express higher levels of immune-related genes than adult females and immature developmental stages. The main components of the Toll, IMD, and Jak/STAT pathways and antimicrobial effectors are highly expressed in whole-body males. Additionally, males present lower midgut basal microbiota levels than females. In A. aegypti mosquitoes, the differences in immune gene expression and microbiota levels are established in adult mosquitoes but are not present at the recently emerged adults and pupal stage. Antibiotic treatment does not affect the consistently higher expression of immune genes in males, except defensin, which is reduced significantly after microbiota depletion and restored after re-introduction. Our data suggest that Diptera males have a basal state of activation of the immune system and that activation of a more robust response through systemic immune challenge acutely compromises their survival. The ones who survive clear the infection entirely. Females follow a different strategy where a moderate immune reaction render higher tolerance to infection and survival. In contrast, hematophagous adult males of the Hemiptera vector R. prolixus, which transmits Trypanosoma cruzi, present no differences in immune activation compared to females, suggesting that diet differences between males and females may influence immune sexual dimorphism. These findings expand our understanding of the biology of insect vectors of human pathogens, which can help to direct the development of new strategies to limit vector populations.

Viability and Infectivity of Plasmodium vivax Gametocytes in Short-Term Culture

The control and elimination of malaria caused by Plasmodium vivax both represent a great challenge due to the biological aspects of the species. Gametocytes are the forms responsible for the transmission of the parasite to the vector and the search for new strategies for blocking transmission are essential in a scenario of control and elimination The challenges in this search in regard to P. vivax mainly stem from the lack of a long-term culture and the limitation of studies of gametocytes. This study evaluated the viability and infectivity of P. vivax gametocytes in short-term culture. The samples enriched in gametocytes using Percoll (i), using magnetic-activated cell sorting (MACS^®) (ii), and using non-enriched samples (iii) were evaluated. After the procedures, gametocytes were cultured in IMDM medium for up to 48 h. Cultured P. vivax gametocytes were viable and infectious for up to 48 h, however differences in viability and infectivity were observed in the samples after 12 h of culture in relation to 0 h. Percoll-enriched samples were shown to be viable in culture for longer intervals than those purified using MACS^®. Gametocyte viability after enrichment procedures and short-term culture may provide new avenues in the development of methods for evaluating P. vivax TB.

Autophagy in Tenebrio molitor Immunity: Conserved Antimicrobial Functions in Insect Defenses

The yellow mealworm beetle (Tenebrio molitor) has been exploited as an experimental model to unravel the intricacies of cellular and humoral immunity against pathogenic infections. Studies on this insect model have provided valuable insights into the phenotypic plasticity of immune defenses against parasites and pathogens. It has thus been possible to characterize the hemocoelic defenses of T. molitor that rely on the recognition of non-self-components of pathogens by pattern recognition receptors (PRRs). The subsequent signaling cascade activating pathways such as the NF-κB controlled by Toll and IMD pathways lead to the synthesis of antimicrobial peptides (AMPs), onset of hemocyte-driven phagocytosis, and activation of the prophenoloxidase cascade regulating the process of melanization. Nevertheless, the activation of autophagy-mediated defenses of T. molitor against the facultative intracellular gram-positive bacterium Listeria monocytogenes provides clear evidence of the existence of a cross-talk between autophagy and the IMD pathway. Moreover, the identification of several autophagy-related genes (Atgs) in T. molitor transcriptome and expressed sequence tag (EST) databases has contributed to the understanding of the autophagy-signaling cascade triggered by L. monocytogenes challenge. Providing further evidence of the cross-talk hypothesis, TmRelish has been shown to be required not only for regulating the synthesis of AMPs through the PGRP-LE/IMD pathway activation but also for the expression of Atgs in T. molitor larvae following L. monocytogenes challenge. Notably, L. monocytogenes can stimulate the T. molitor innate immune system by producing molecules recognized by the multifunctional PRR (TmPGRP-LE), which stimulates intracellular activation of the IMD pathway and autophagy. Considering the conservation of autophagy components involved in combating intracellular pathogens, it will be interesting to extrapolate a dynamic cross-talk model of immune activation. This review summarizes the most significant findings on the regulation of autophagy in T. molitor during L. monocytogenes infection and on the role of the innate immunity machinery, including the NF-κB pathway, in the control of pathogenic load.

NlATG1 Gene Participates in Regulating Autophagy and Fission of Mitochondria in the Brown Planthopper, Nilaparvata lugens

Autophagy plays multiple roles in regulating various physiological processes in cells. However, we currently lack a systematic analysis of autophagy and the autophagy-related gene 1 ATG1 in the brown planthopper (BPH, Nilaparvata lugens), one of the most destructive of the insect pests of rice. In this study, the full-length cDNA of an autophagy-related gene, NlATG1, was cloned from BPH. Real-time qPCR (RT-qPCR) revealed that this NlATG1 gene was expressed differently across developmental stages, at higher levels in nymphs but lower levels in adults. RNA interference with dsNlATG1 significantly decreased the mRNA level of the target gene to 14.6% at day 4 compared with that of the dsGFP control group. The survival of the dsNlATG1-treated group decreased significantly from day 4 onward, dropping to 48.3% on day 8. Examination using transmission electron microscopy (TEM) showed that epithelial cells of the BPH’s midgut in the dsNlATG1-treated group had less autophagic vacuoles than did the dsGFP control, and knockdown of NlATG1 clearly inhibited the starvation-induced autophagy response in this insect. RNA interference of NlATG1 upregulated the NlFis1 gene involved in mitochondrial fission, leading to reductions in mitochondrial width and area. Furthermore, knockdown of NlATG1 also decreased the ATP content and accumulation of glycogen. Together, these results demonstrate that the NlATG1 gene participates in regulating autophagy and fission of mitochondria in the brown planthopper, making it a potentially promising target for pest control given its key role in autophagy, including maintaining the normal structure and function of mitochondria.