A salivary factor binds a cuticular protein and modulates biting by inducing morphological changes in the mosquito labrum

Structural and functional significance of Aedes aegypti AgBR1 flavivirus immunomodulator

Zika virus (ZIKV), an arbovirus, relies on mosquitoes as vectors for its transmission. During blood feeding, mosquitoes inoculate saliva containing various proteins. Recently, AgBR1, an Aedes aegypti salivary gland protein, has gained attention for its immunomodulatory potential, along with another protein, called NeSt1. We have determined the crystal structure of AgBR1 at 1.2 Å resolution. Despite its chitinase-like fold, we demonstrated that AgBR1 does not bind to chitobiose or chitinhexaose, while a key mutation in the catalytic site abrogates enzymatic activity, suggesting that the protein's function has been repurposed. Our study also shows that AgBR1 and NeSt1, when presented to murine primary macrophages, alter cellular pathways related to virus entry by endocytosis, immune response, and cell proliferation. AgBR1 (and NeSt1) do not directly bind to the Zika virus or modulate its replication. We propose that their immunomodulatory effects on Zika virus transmission are through regulation of host-cell response, a consequence of evolutionary cross talk and virus opportunism. These structural and functional insights are prerequisites for developing strategies to halt the spread of mosquito-borne disease.IMPORTANCEOur study informs on the structural and functional significance of a mosquito salivary gland protein, AgBR1 (along with another protein called NeSt1), in the transmission of the Zika virus (ZIKV), a mosquito-borne virus that has caused global health concerns. By analyzing AgBR1's three-dimensional structure in combination with cellular and interaction studies, we discovered that AgBR1 does not function like typical proteins in its family-it does not degrade sugars. However, we show that it primes immune cells in a way that could help the virus enter cells more easily but not by interacting with the virus or altering viral replication. This finding is significant because it reveals how mosquito proteins, repurposed by evolution, can influence virus transmission without the virus's direct presence. Understanding how proteins like AgBR1 work could guide the development of new strategies to prevent Zika virus spread, with potential relevance for other mosquito-borne viruses.

Mosquito Cell Atlas: A single-nucleus transcriptomic atlas of the adult Aedes aegypti mosquito

The female mosquito's remarkable ability to hunt humans and transmit pathogens relies on her unique biology. Here, we present the Mosquito Cell Atlas (MCA), a comprehensive single-nucleus RNA sequencing dataset of more than 367,000 nuclei from 19 dissected tissues of adult female and male Aedes aegypti, providing cellular-level resolution of mosquito biology. We identify novel cell types and expand our understanding of sensory neuron organization of chemoreceptors to all sensory tissues. Our analysis uncovers male-specific cells and sexually dimorphic gene expression in the antenna and brain. In female mosquitoes, we find that glial cells in the brain, rather than neurons, undergo the most extensive transcriptional changes following blood feeding. Our findings provide insights into the cellular basis of mosquito behavior and sexual dimorphism. The MCA aims to serve as a resource for the vector biology community, enabling systematic investigation of cell-type specific expression across all mosquito tissues.

Extrinsic and intrinsic regulation of blood feeding in mosquitoes

Mosquitoes obtain large amounts of blood from hosts in a short period of time. To efficiently obtain high-quality blood without being noticed by the host, mosquitoes sense external factors such as the taste of the host blood and the surrounding environment, and integrate these signals with their own internal information to determine whether to initiate blood feeding and how long to continue feeding. With the development of gene editing and behavior monitoring techniques, the factors that control blood feeding are being identified. Elucidating the factors that contribute to blood feeding is expected to provide new ideas for artificially controlling blood feeding, which has often been overlooked behind host attraction mechanisms. Furthermore, understanding salivary components, mechanisms controlling satiety in feeding, and differences between sugar feeding and blood feeding would help us understand how some mosquitoes have adopted and developed blood feeding over the course of evolution.

Anopheles gambiae lacking AgTRIO probe inefficiently on a mammalian host

Malaria is initiated as Plasmodium sporozoites are injected into the dermis when an infected mosquito probes on a vertebrate host for a blood meal. Factors in the mosquito saliva, such as AgTRIO, can alter the ability of Anopheles gambiae to transmit Plasmodium. We therefore used CRISPR-Cas9-mediated genome editing to generate AgTRIO knockout (KO) A. gambiae and examined the ability of these mosquitoes to probe on a vertebrate host. AgTRIO KO mosquitoes showed a diminished host probing capacity and required repetitive probing to locate a blood resource to complete a blood meal. This increased probing resulted in enhanced Plasmodium transmission to the vertebrate host. Our data demonstrate the importance of the A. gambiae saliva protein AgTRIO in probing and its influence on the ability of mosquitoes to transmit malaria.

The human CD47 checkpoint is targeted by an immunosuppressive Aedes aegypti salivary factor to enhance arboviral skin infectivity

The Aedes aegypti mosquito is a vector of many infectious agents, including flaviviruses such as Zika virus. Components of mosquito saliva have pleomorphic effects on the vertebrate host to enhance blood feeding, and these changes also create a favorable niche for pathogen replication and dissemination. Here, we demonstrate that human CD47, which is known to be involved in various immune processes, interacts with a 34-kilodalton mosquito salivary protein named Nest1. Nest1 is up-regulated in blood-fed female A. aegypti and facilitates Zika virus dissemination in human skin explants. Nest1 has a stronger affinity for CD47 than its natural ligand, signal regulatory protein α, competing for binding at the same interface. The interaction between Nest1 with CD47 suppresses phagocytosis by human macrophages and inhibits proinflammatory responses by white blood cells, thereby suppressing antiviral responses in the skin. This interaction elucidates how an arthropod protein alters the human response to promote arbovirus infectivity.

An update and review of arthropod vector sensory systems: Potential targets for behavioural manipulation by parasites and other disease agents

For over a century, vector ecology has been a mainstay of vector-borne disease control. Much of this research has focused on the sensory ecology of blood-feeding arthropods (black flies, mosquitoes, ticks, etc.) with terrestrial vertebrate hosts. Of particular interest are the cues and sensory systems that drive host seeking and host feeding behaviours as they are critical for a vector to locate and feed from a host. An important yet overlooked component of arthropod vector ecology are the phenotypic changes observed in infected vectors that increase disease transmission. While our fundamental understanding of sensory mechanisms in disease vectors has drastically increased due to recent advances in genome engineering, for example, the advent of CRISPR-Cas9, and high-throughput "big data" approaches (genomics, proteomics, transcriptomics, etc.), we still do not know if and how parasites manipulate vector behaviour. Here, we review the latest research on arthropod vector sensory systems and propose key mechanisms that disease agents may alter to increase transmission.

IgE response to Aed al 13 and Aed al 14 recombinant allergens from Aedes albopictus saliva in humans

Background

Mosquito bite is normally associated with mild allergic responses, but severe localized or systemic reactions are also possible. Reliable tools for the diagnosis of mosquito allergy are still unavailable. Here, we investigated the IgE response to 3 potential salivary allergens identified in the saliva of the tiger mosquito Aedes albopictus.

Methods

Serum from 55 adult individuals (28 controls and 27 allergic people), were analysed using an in-house Enzyme Linked ImmunoSorbent Assay (ELISA) against the Salivary Gland Extract (SGE) and the recombinant proteins albD7l2 (Aed al 2), albAntigen5-3 (Aed al 13) and albLIPS-2 (Aed al 14).

Results

Fifteen of the 27 (56%) individuals having hypersensitive reactions to mosquito bites had IgE serum levels recognizing SGE. Negative sera did not show detectable levels of IgE targeting the SGE from the most common sympatric mosquito Culex pipiens. Among the positive individuals, 2 subjects displayed IgE targeting Aed al 2 (13%), while IgE recognizing Aed al 13 and Aed al 14 were detected in ten (67%) and seven (47%) individuals, respectively. Two sera from non-hypersensitive subjects had detectable levels of IgE targeting Aed al 13, suggesting possible cross-reaction with the homologue salivary proteins of multiple mosquito species or, more generally, of hematophagous insects.

Conclusions

Our results indicate that Aed al 13 and Aed al 14 hold the potential to be developed as tools for the diagnosis of allergy to Ae. albopictus bites. Such tools would facilitate epidemiological studies on tiger mosquito allergy in humans and might foster the development of further protein-based assays to investigate cross-species allergies.

Structural and functional characterization of Aedes aegypti pupal cuticle protein that controls dengue virus infection

The pupal cuticle protein from Aedes aegypti (AaPC) inhibits dengue virus (DENV) infection; however, the underlying mechanism of this inhibition remains unknown. Here, we report that AaPC is an intrinsically disordered protein and interacts with domain I/II of the DENV envelope protein via residues Asp59, Asp61, Glu71, Asp73, Ser75, and Asp80. AaPC can directly bind to and cause the aggregation of DENV, which in turn blocks virus infection during the virus-cell fusion stage. AaPC may also influence viral recognition and attachment by interacting with human immune receptors DC-SIGN and CD4. These findings enhance our understanding of the role of AaPC in mitigating viral infection and suggest that AaPC is a potential target for developing inhibitors or antibodies to control dengue virus infection.

Role of Acrostyle Cuticular Proteins in the Retention of an Aphid Salivary Effector

To avoid the activation of plant defenses and ensure sustained feeding, aphids are assumed to use their mouthparts to deliver effectors into plant cells. A recent study has shown that effectors detected near feeding sites are differentially distributed in plant tissues. However, the precise process of effector delivery into specific plant compartments is unknown. The acrostyle, a cuticular organ located at the tip of maxillary stylets that transiently binds plant viruses via its stylin proteins, may participate in this specific delivery process. Here, we demonstrate that Mp10, a saliva effector released into the plant cytoplasm during aphid probing, binds to the acrostyles of Acyrthosiphon pisum and Myzus persicae. The effector probably interacts with Stylin-03 as a lowered Mp10-binding to the acrostyle was observed upon RNAi-mediated reduction in Stylin-03 production. In addition, Stylin-03 and Stylin-01 RNAi aphids exhibited changes in their feeding behavior as evidenced by electrical penetration graph experiments showing longer aphid probing behaviors associated with watery saliva release into the cytoplasm of plant cells. Taken together, these data demonstrate that the acrostyle also has effector binding capacity and supports its role in the delivery of aphid effectors into plant cells.

Vector biology: A mosquito's deadly kiss on the LIPS

A new study identifies a mosquito salivary protein that directly binds to a cuticular partner during biting to reshape the mosquito mouthparts, stimulate salivation and probing, and enhance blood-feeding efficiency. By affecting mosquito-host interactions, this phenomenon could influence pathogen transmission.