Molecular characterization of larval peripheral thermosensory responses of the malaria vector mosquito Anopheles gambiae

A Systematical Survey on the TRP Channels Provides New Insight into Its Functional Diversity in Zhikong Scallop (Chlamys farreri)

Transient receptor potential (TRP) channel plays a significant role in mediating various sensory physiological functions. It is widely present in the vertebrate and invertebrate genomes and can be activated by multiple compounds, messenger molecules, temperature, and mechanical stimulation. Mollusks are the second largest phylum of the animal kingdom and are sensitive to environmental factors. However, the molecular underpinnings through which mollusks sense and respond to environmental stimulus are unknown. In this study, we systematically identified and characterized 17 TRP channels (C.FA TRPs, seven subfamilies) in the genome of the Zhikong scallop (Chlamys farreri). All C.FA TRPs had six transmembrane structures (TM1–TM6). The sequences and structural features of C.FA TRPs are highly conserved with TRP channels of other species. Spatiotemporal expression profiling suggested that some C.FA TRPs participated in the early embryonic development of scallops and the sensory process of adult tissues. Notably, the expression of C.FA TRPM3 continuously increased during developmental stages and was highest among all C.FA TRPs. C.FA TRPC-α was specifically expressed in eyes, which may be involved in light transmission of scallop eyes. Under high temperature stress, C.FA TRPA1 and C.FA TRPA1-homolog upregulated significantly, which indicated that the TRPA subfamily is the thermoTRPs channel of scallops. Our results provided the first systematic study of TRP channels in scallops, and the findings will provide a valuable resource for a better understanding of TRP evolution and function in mollusks.

RNAi by Soaking Aedes aegypti Pupae in dsRNA

Simple Summary

Even after decades of control interventions, mosquito-borne diseases still pose a huge threat to humans. Understanding gene functions is important for discovering new targets for mosquito and mosquito-borne disease control. One of the well-established and widely used methods for understanding gene function is RNA-interference (RNAi). The use of RNAi is, however, restricted mostly to adult mosquitoes. A few studies have shown its applicability in mosquito larvae, and just one in pupae. The current double-stranded RNA (dsRNA) delivery methods for RNAi are labor-intensive and require microinjections into mosquitoes (adults, larvae, or pupae). In this study, we present a simple, fast, and less labor-intensive technique for RNAi in the pupal stage by soaking pupae in water containing dsRNA. This method will be useful in studying genes expressed in immature life stages of the mosquitoes and will hopefully open new avenues for identifying mosquito control targets in early life stages.

Abstract

RNA-interference (RNAi) is a standard technique for functional genomics in adult mosquitoes. However, RNAi in immature, aquatic mosquito stages has been challenging. Several studies have shown successful larval RNAi, usually in combination with a carrier molecule. Except for one study in malaria mosquito, Anopheles gambiae, none of the previous studies has explored RNAi in mosquito pupae. Even in the study that used RNAi in pupae, double stranded RNA (dsRNA) was introduced by microinjection. Here, we describe a successful method by soaking pupae in water containing dsRNA without any carrier or osmotic challenge. The knockdown persisted into adulthood. We expect that this simple procedure will be useful in the functional analysis of genes that highly express in pupae or newly emerged adults.

Molecular Characterization of TRPA Subfamily Genes and Function in Temperature Preference in Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

To reveal the mechanism of temperature preference in Tuta absoluta, one of the top 20 plant pests in the world, we cloned and identified TaTRPA1, TaPain, and TaPyx genes by RACE and bioinformatic analysis, and clarified their expression profiles during different development stages using real-time PCR, and revealed their function in preference temperature by RNAi. The full-length cDNA of TaPain was 3136 bp, with a 2865-bp open reading frame encoding a 259.89-kDa protein; and the partial length cDNA of TaPyx was 2326-bp, with a 2025-bp open reading frame encoding a 193.16-kDa protein. In addition, the expression of TaTRPA1 and TaPyx was significantly lower in larvae than other stages, and it was significantly higher in pupae and newly emerging males for TaPain. After feeding target double-stranded RNA (dsRNA), the preferred temperature decreased 2 °C more than the control group. In conclusion, the results firstly indicated the molecular characterization of TRPA subfamily genes and their key role in temperature perception in T. absoluta, and the study will help us to understand the temperature-sensing mechanism in the pest, and will provide some basis for study of other Lepidoptera insects’ temperature preference. Moreover, it is of great significance in enriching the research progress of “thermos TRP”.

Delivery Methods for RNAi in Mosquito Larvae

Mosquito-transmitted diseases pose a threat for a great portion of the world population. Chemical insecticides are the main tool for mosquito control. Heavy dependence on chemicals created several problems such as resistance development in many mosquito species, environmental effects, and human health issues. Other tools for mosquito control were developed and used in some parts of the world. Ribonucleic acid interference (RNAi) is a reverse genetic mechanism that was recently introduced as a new tool for pest control. Regarding mosquito, RNAi was used to study gene function and to discover genes that can be used as targets for control purposes. Several delivery methods are used to induce RNAi in mosquito larvae. Some methods such as injection and soaking are used routinely in RNAi research but have no application in the field. Other methods such as nanoparticles and microbes have some characteristics that make them good candidates for field application. In this report, we will focus on delivery methods for RNAi in mosquito larvae and will give examples for each method.

Keeping track of mosquitoes: a review of tools to track, record and analyse mosquito flight

The health impact of mosquito-borne diseases causes a huge burden on human societies. Recent vector control campaigns have resulted in promising declines in incidence and prevalence of these diseases, notably malaria, but resistance to insecticides and drugs are on the rise, threatening to overturn these gains. Moreover, several vector-borne diseases have re-emerged, requiring prompt and effective response measures. To improve and properly implement vector control interventions, the behaviour of the vectors must be well understood with detailed examination of mosquito flight being an essential component. Current knowledge on mosquito behaviour across its life history is briefly presented, followed by an overview of recent developments in automated tracking techniques for detailed interpretation of mosquito behaviour. These techniques allow highly accurate recording and observation of mating, feeding and oviposition behaviour. Software programmes built with specific algorithms enable quantification of these behaviours. For example, the crucial role of heat on host landing and the multimodal integration of carbon dioxide (CO2) with other host cues, has been unravelled based on three-dimensional tracking of mosquito flight behaviour. Furthermore, the behavioural processes underlying house entry and subsequent host searching and finding can be better understood by analysis of detailed flight recordings. Further potential of these technologies to solve knowledge gaps is discussed. The use of tracking techniques can support or replace existing monitoring tools and provide insights on mosquito behaviour that can lead to innovative and more effective vector-control measures.

The N-terminal Ankyrin Repeat Domain Is Not Required for Electrophile and Heat Activation of the Purified Mosquito TRPA1 Receptor

Temperature sensors are crucial for animals to optimize living conditions. The temperature response of the ion channel transient receptor potential A1 (TRPA1) is intriguing; some orthologs have been reported to be activated by cold and others by heat, but the molecular mechanisms responsible for its activation remain elusive. Single-channel electrophysiological recordings of heterologously expressed and purified Anopheles gambiae TRPA1 (AgTRPA1), with and without the N-terminal ankyrin repeat domain, demonstrate that both proteins are functional because they responded to the electrophilic compounds allyl isothiocyanate and cinnamaldehyde as well as heat. The proteins' similar intrinsic fluorescence properties and corresponding quenching when activated by allyl isothiocyanate or heat suggest lipid bilayer-independent conformational changes outside the N-terminal domain. The results show that AgTRPA1 is an inherent thermo- and chemoreceptor, and analogous to what has been reported for the human TRPA1 ortholog, the N-terminal domain may tune the response but is not required for the activation by these stimuli.

Identification and functional characterization of four transient receptor potential ankyrin 1 variants in Apolygus lucorum (Meyer-Dür)

As signal integrators that respond to various physical and chemical stimuli, transient receptor potential (TRP) channels fulfil critical functional roles in the sensory systems of both vertebrate and invertebrate organisms. Here, four variants of TRP ankyrin 1 (TRPA1) were identified and cloned from the green plant bug, Apolygus lucorum. Spatiotemporal expression profiling across development and in different adult tissues revealed that the highest relative-transcript levels occurred in first-instar nymphs and antennae, respectively. In Xenopus laevis-based functional assays, Apo. lucorum TRPA1-A (AlucTRPA1-A), AlucTRPA1-B and AlucTRPA1-C were activated by increasing the temperature from 20 to 40 °C with no significant desensitization observed after repeated temperature stimuli. The activation temperature of AlucTRPA1-A and AlucTRPA1-B was < 25 °C, whereas the activation temperature of AlucTRPA1-C was between 25 and 30 °C. Amongst the variants, only AlucTRPA1-A and AlucTRPA1-C were directly activated by high concentrations of allyl isothiocyanate, cinnamaldehyde and citronellal. Taken together, these results suggest that AlucTRPA1 variants may function in vivo as both thermal and chemical sensors, with the four variants potentially mediating different physiological functions. This study not only enriches our understanding of TRPA1 function in Hemiptera (Miridae), but also offers a foundation for developing new pest control strategies.

A TRPA1 channel that senses thermal stimulus and irritating chemicals in Helicoverpa armigera

Sensing and responding to changes in the external environment is important for insect survival. Transient receptor potential (TRP) channels are crucial for various sensory modalities including olfaction, vision, hearing, thermosensation and mechanosensation. Here, we identified and characterized a transient receptor potential gene named as HarmTRPA1 in Helicoverpa armigera antennae. HarmTRPA1 was abundantly expressed in the antennae and labial palps. Transcripts of HarmTRPA1 could also be detected in the head and proboscis. Furthermore, functional analyses of HarmTRPA1 were conducted in the Xenopus Oocyte system. The results showed that the HarmTRPA1 channel could be activated by increasing the temperature from 20 to 45 °C. No significant adaptation was observed when the stimulus was repeated. In addition to thermal stimuli, pungent natural compounds including allyl isothiocyanate, cinnamaldehyde and citronellal also activated HarmTRPA1. Taken together, we infer that HarmTRPA1 may function as both a thermal sensor involved in peripheral temperature detection and as a chemical sensor detecting irritating chemicals in vivo. Our data provide valuable insight into the TRPA1 channel in this moth and lay the foundation for developing novel strategies for pest control.

Species-specific temperature sensitivity of TRPA1

Transient receptor potential ankyrin 1 (TRPA1) is a polymodal ion channel sensitive to temperature and chemical stimuli. The importance of temperature and aversive chemical detection for survival has driven the evolutionary diversity of TRPA1 sensitivity. This diversity can be observed in the various roles of TRPA1 in different species, where it is proposed to act as a temperature-insensitive chemosensor, a heat transducer, a noxious cold transducer, or a detector of low-intensity heat for prey localization. Exploring the variation of TRPA1 functions among species provides evolutionary insight into molecular mechanisms that fine-tune thermal and chemical sensitivity, and offers an opportunity to address basic principles of temperature gating in ion channels. A decade of research has yielded a number of hypotheses describing physiological roles of TRPA1, modulators of its activity, and biophysical principles of gating. This review surveys the diversity of TRPA1 adaptations across evolutionary taxa and explores possible mechanisms of TRPA1 activation.