G protein-coupled receptors in Anopheles gambiae

Deciphering the role of glycosaminoglycans in GPCR signaling

G protein-coupled receptors (GPCR) and glycosaminoglycans (GAGs) are two essential components of the cell surface that regulate physiological processes in the body. GPCRs are the most extensive family of transmembrane receptors that control cellular responses to extracellular stimuli, while GAGs are polysaccharides that contribute to the function of the extracellular matrix (ECM). Due to their proximity to the plasma membrane, GAGs participate in signal transduction by interacting with various extracellular molecules and cell surface receptors. GAGs can directly interact with certain GPCRs or their ligands (chemokines, peptide hormones and neuropeptides, structural proteins, and enzymes) from the glutamate receptor family, the rhodopsin receptor family, the adhesion receptor family, and the secretin receptor family. These interactions have recently become an emerging topic, providing a new avenue for understanding how GPCR signaling is regulated. This review discusses our current state of knowledge about the role of GAGs in GPCR signaling and function.

Glucose aversion: a behavioral resistance mechanism in the German cockroach

The German cockroach is a valuable model for research on indoor pest management strategies and for understanding mechanisms of adaptive evolution under intense anthropogenic selection. Under the selection pressure of toxic baits, populations of the German cockroach have evolved a variety of physiological and behavioral resistance mechanisms. In this review, we focus on glucose aversion, an adaptive trait that underlies a behavioral resistance to baits. Taste polymorphism, a change in taste quality of glucose from sweet to bitter, causes cockroaches to avoid glucose-containing baits. We summarize recent findings, including the contribution of glucose aversion to olfactory learning-based avoidance of baits, aversion to other sugars, and assortative mating under sexual selection, which underscores the behavioral phenotype to all oligosaccharides that contain glucose. It is a remarkable example of how anthropogenic selection drove the evolution of an altered gustatory trait that reshapes the foraging ecology and sexual communication.

The larva and adult of Helicoverpa armigera use differential gustatory receptors to sense sucrose

Almost all herbivorous insects feed on plants and use sucrose as a feeding stimulant, but the molecular basis of their sucrose reception remains unclear. Helicoverpa armigera as a notorious crop pest worldwide mainly feeds on reproductive organs of many plant species in the larval stage, and its adult draws nectar. In this study, we determined that the sucrose sensory neurons located in the contact chemosensilla on larval maxillary galea were 100-1000 times more sensitive to sucrose than those on adult antennae, tarsi, and proboscis. Using the Xenopus expression system, we discovered that Gr10 highly expressed in the larval sensilla was specifically tuned to sucrose, while Gr6 highly expressed in the adult sensilla responded to fucose, sucrose and fructose. Moreover, using CRISPR/Cas9, we revealed that Gr10 was mainly used by larvae to detect lower sucrose, while Gr6 was primarily used by adults to detect higher sucrose and other saccharides, which results in differences in selectivity and sensitivity between larval and adult sugar sensory neurons. Our results demonstrate the sugar receptors in this moth are evolved to adapt toward the larval and adult foods with different types and amounts of sugar, and fill in a gap in sweet taste of animals.

Gustatory Receptor 206 Participates in the Foraging Behavior of Larvae of Polyphagous Pest Spodoptera litura

Insect gustatory receptors (GRs) aid in the precise identification of deterrent or stimulant compounds associated with food, mating, and egg-laying. Thus, they are promising targets for developing efficient insecticides. Here, 61 GRs in the chemosensory organs of Spodoptera litura larvae and adults were identified. Among them, SlitGR206 exhibited larval labium (LL)-specific expression characteristics. To explore the role of SlitGR206, a bacterial expression system was established to produce high-quality double-stranded RNA (dsRNA) and suppress SlitGR206 expression in LL. Subsequent behavioral assessments revealed that SlitGR206 silencing influenced larval feeding preferences and absorption. Moreover, it was found to reduce the ability of larvae to forage the five crucial host odorants. These findings demonstrate that SlitGR206 likely plays an indirect regulatory role in host recognition, consequently affecting foraging behavior. This provides a crucial foundation for the analysis of functional diversity among insect GRs and the precise development of nucleic acid pesticides in the future.

Genomic identification and evolutionary analysis of chemosensory receptor gene families in two Phthorimaea pest species: insights into chemical ecology and host adaptation

BACKGROUND

Insects rely on sophisticated sensitive chemosensory systems to sense their complex chemical environment. This sensory process involves a combination of odorant receptors (ORs), gustatory receptors (GRs) and ionotropic receptors (IRs) in the chemosensory system. This study focused on the identification and characterization of these three types of chemosensory receptor genes in two closely related Phthorimaea pest species, Phthorimaea operculella (potato tuber moth) and Phthorimaea absoluta (tomato leaf miner).

RESULTS

Based on manual annotation of the genome, we identified a total of 349 chemoreceptor genes from the genome of P. operculella, including 93 OR, 206 GR and 50 IR genes, while for P. absoluta, we identified 72 OR, 122 GR and 46 IR genes. Through phylogenetic analysis, we observed minimal differences in the number and types of ORs and IRs between the potato tuber moth and tomato leaf miner. In addition, we found that compared with those of tomato leaf miners, the gustatory receptor branch of P. operculella has undergone a large expansion, which may be related to P. absoluta having a narrower host range than P. operculella. Through analysis of differentially expressed genes (DEGs) of male and female antennae, we uncovered 45 DEGs (including 32ORs, 9 GRs, and 4 IRs).

CONCLUSIONS

Our research provides a foundation for exploring the chemical ecology of these two pests and offers new insights into the dietary differentiation of lepidopteran insects, while simultaneously providing molecular targets for developing environmentally friendly pest control methods based on insect chemoreception.

Identification of candidate chemosensory genes in Bactrocera cucurbitae based on antennal transcriptome analysis

The melon fly, Bactrocera cucurbitae (Coquillett) (Tephritidae: Diptera), is an invasive pest that poses a significant threat to agriculture in Africa and other regions. Flies are known to use their olfactory systems to recognise environmental chemical cues. However, the molecular components of the chemosensory system of B. cucurbitae are poorly characterised. To address this knowledge gap, we have used next-generation sequencing to analyse the antenna transcriptomes of sexually immature B. cucurbitae adults. The results have identified 160 potential chemosensory genes, including 35 odourant-binding proteins (OBPs), one chemosensory protein (CSP), three sensory neuron membrane proteins (SNMPs), 70 odourant receptors (ORs), 30 ionotropic receptors (IRs), and 21 gustatory receptors (GRs). Quantitative real-time polymerase chain reaction quantitative polymerase chain reaction was used to validate the results by assessing the expression profiles of 25 ORs and 15 OBPs. Notably, high expression levels for BcucOBP5/9/10/18/21/23/26 were observed in both the female and male antennae. Furthermore, BcucOROrco/6/7/9/13/15/25/27/28/42/62 exhibited biased expression in the male antennae, whereas BcucOR55 showed biased expression in the female antennae. This comprehensive investigation provides valuable insights into insect olfaction at the molecular level and will, thus, help to facilitate the development of enhanced pest management strategies in the future.

Unraveling the G protein-coupled receptor superfamily in aphids: Contractions and duplications linked to phloem feeding

The G Protein-Coupled Receptor (GPCR) superfamily is the largest and most diverse transmembrane receptor family, playing crucial roles in regulating various physiological processes. As one of the most destructive pests, aphids have been subject to previous studies, which revealed fewer GPCR superfamily members in Acyrthosiphon pisum and Aphis gossypii and the loss of multiple neuropeptide GPCRs. To elucidate the contraction patterns and evolutionary features of the aphid GPCR superfamily, we identified 97, 105, and 95 GPCR genes in Rhopalosiphum maidis, A. pisum, and A. gossypii, respectively. Comparative analysis and phylogenetic investigations with other hemipteran insects revealed a contracted GPCR superfamily in aphids. This contraction mainly occurred in biogenic amine receptors, GABA-B-R, and fz families, and several neuropeptide receptors such as ACPR, CrzR, and PTHR were completely lost. This phenomenon may be related to the parasitic nature of aphids. Additionally, several GPCRs associated with aphid feeding and water balance underwent duplication, including Lkr, NPFR, CCHa1-R, and DH-R, Type A LGRs, but the SK/CCKLR that inhibits feeding was completely lost, indicating changes in feeding genes that underpin the aphid's prolonged phloem feeding behavior. Furthermore, we observed fine-tuning in opsins, with reduced long-wavelength opsins and additional duplications of short-wavelength opsin, likely associated with daytime activity. Lastly, we found variations in the number of mthl genes in aphids. In conclusion, our investigation sheds light on the GPCR superfamily in aphids, revealing its association with diet lifestyle and laying the foundation for understanding and developing control strategies for the aphid GPCR superfamily.

Mulberry-derived miR168a downregulates BmMthl1 to promote physical development and fecundity in silkworms

Plant-derived miRNAs and their interactions with host organisms are considered important factors in regulating host physiological processes. In this study, we investigated the interaction between the silkworm, an oligophagous insect, and its primary food source, mulberry, to determine whether mulberry-derived miRNAs can penetrate silkworm cells and regulate their functions. Our results demonstrated that miR168a from mulberry leaves enters the silkworm hemolymph and binds to the silkworm Argonaute1 BmAGO1, which is transported via vesicles secreted by silkworm cells to exert its regulatory functions. In vivo and in vitro functional studies revealed that miR168a targets the mRNA of silkworm G protein-coupled receptor, BmMthl1, thereby inhibiting its expression and activating the JNK-FoxO pathway. This activation reduces oxidative stress responses, prolongs the lifespan of silkworms, and improves their reproductive capacity. These findings highlight the challenges of replacing mulberry leaves with alternative protein sources and provide a foundation for developing silkworm germplasms suitable for factory rearing.

Characterization of a novel RNAi yeast insecticide that silences mosquito 5-HT1 receptor genes

G protein-coupled receptors (GPCRs), which regulate numerous intracellular signaling cascades that mediate many essential physiological processes, are attractive yet underexploited insecticide targets. RNA interference (RNAi) technology could facilitate the custom design of environmentally safe pesticides that target GPCRs in select target pests yet are not toxic to non-target species. This study investigates the hypothesis that an RNAi yeast insecticide designed to silence mosquito serotonin receptor 1 (5-HTR1) genes can kill mosquitoes without harming non-target arthropods. 5-HTR.426, a Saccharomyces cerevisiae strain that expresses an shRNA targeting a site specifically conserved in mosquito 5-HTR1 genes, was generated. The yeast can be heat-inactivated and delivered to mosquito larvae as ready-to-use tablets or to adult mosquitoes using attractive targeted sugar baits (ATSBs). The results of laboratory and outdoor semi-field trials demonstrated that consumption of 5-HTR.426 yeast results in highly significant mortality rates in Aedes, Anopheles, and Culex mosquito larvae and adults. Yeast consumption resulted in significant 5-HTR1 silencing and severe neural defects in the mosquito brain but was not found to be toxic to non-target arthropods. These results indicate that RNAi insecticide technology can facilitate selective targeting of GPCRs in intended pests without impacting GPCR activity in non-targeted organisms. In future studies, scaled production of yeast expressing the 5-HTR.426 RNAi insecticide could facilitate field trials to further evaluate this promising new mosquito control intervention.

Chromosome-level genome assembly of the deep-sea snail Phymorhynchus buccinoides provides insights into the adaptation to the cold seep habitat

BACKGROUND

The deep-sea snail Phymorhynchus buccinoides belongs to the genus Phymorhynchus (Neogastropoda: Raphitomidae), and it is a dominant specie in the cold seep habitat. As the environment of the cold seep is characterized by darkness, hypoxia and high concentrations of toxic substances such as hydrogen sulfide (H2S), exploration of the diverse fauna living around cold seeps will help to uncover the adaptive mechanisms to this unique habitat. In the present study, a chromosome-level genome of P. buccinoides was constructed and a series of genomic and transcriptomic analyses were conducted to explore its molecular adaptation mechanisms to the cold seep environments.

RESULTS

The assembled genome size of the P. buccinoides was approximately 2.1 Gb, which is larger than most of the reported snail genomes, possibly due to the high proportion of repetitive elements. About 92.0% of the assembled base pairs of contigs were anchored to 34 pseudo-chromosomes with a scaffold N50 size of 60.0 Mb. Compared with relative specie in the shallow water, the glutamate regulative and related genes were expanded in P. buccinoides, which contributes to the acclimation to hypoxia and coldness. Besides, the relatively high mRNA expression levels of the olfactory/chemosensory genes in osphradium indicate that P. buccinoides might have evolved a highly developed and sensitive olfactory organ for its orientation and predation. Moreover, the genome and transcriptome analyses demonstrate that P. buccinoides has evolved a sulfite-tolerance mechanism by performing H2S detoxification. Many genes involved in H2S detoxification were highly expressed in ctenidium and hepatopancreas, suggesting that these tissues might be critical for H2S detoxification and sulfite tolerance.

CONCLUSIONS

In summary, our report of this chromosome-level deep-sea snail genome provides a comprehensive genomic basis for the understanding of the adaptation strategy of P. buccinoides to the extreme environment at the deep-sea cold seeps.

Optogenetic manipulation of Gq- and Gi/o-coupled receptor signaling in neurons and heart muscle cells

G-protein-coupled receptors (GPCRs) transmit signals into cells depending on the G protein type. To analyze the functions of GPCR signaling, we assessed the effectiveness of animal G-protein-coupled bistable rhodopsins that can be controlled into active and inactive states by light application using zebrafish. We expressed Gq- and Gi/o-coupled bistable rhodopsins in hindbrain reticulospinal V2a neurons, which are involved in locomotion, or in cardiomyocytes. Light stimulation of the reticulospinal V2a neurons expressing Gq-coupled spider Rh1 resulted in an increase in the intracellular Ca2+ level and evoked swimming behavior. Light stimulation of cardiomyocytes expressing the Gi/o-coupled mosquito Opn3, pufferfish TMT opsin, or lamprey parapinopsin induced cardiac arrest, and the effect was suppressed by treatment with pertussis toxin or barium, suggesting that Gi/o-dependent regulation of inward-rectifier K+ channels controls cardiac function. These data indicate that these rhodopsins are useful for optogenetic control of GPCR-mediated signaling in zebrafish neurons and cardiomyocytes.

The evolution of borneol repellency in culicine mosquitoes

Insects have developed remarkable adaptations to effectively interact with plant secondary metabolites and utilize them as cues to identify suitable hosts. Consequently, humans have used aromatic plants for centuries to repel mosquitoes. The repellent effects of plant volatile compounds are mediated through olfactory structures present in the antennae, and maxillary palps of mosquitoes. Mosquito maxillary palps contain capitate-peg sensilla, which house three olfactory sensory neurons, of which two are mainly tuned to either carbon dioxide or octenol - two animal host odorants. However, the third neuron, which expresses the OR49 receptor, has remained without a known ecologically-relevant odorant since its initial discovery. In this study, we used odorant mixtures and terpenoid-rich Cannabis essential oils to investigate the activation of OR49. Our results demonstrate that two monoterpenoids, borneol and camphor, selectively activate OR49, and OR9-expressing neurons, as well as the MD3 glomerulus in the antennal lobe. We confirm that borneol repels female mosquitoes, and knocking out the gene encoding the OR49 receptor suppresses the response of the corresponding olfactory sensory neuron. Importantly, this molecular mechanism of action is conserved across culicine mosquito species, underscoring its significance in their olfactory systems.

In Silico Characterisation of the Aedes aegypti Gustatory Receptors

Aedes aegypti, also known as the dengue mosquito or the yellow fewer mosquito, is the vector of dengue, chikungunya, Zika, Mayaro and yellow fever viruses. The A. aegypti genome contains an array of gustatory receptor (GR) proteins that are related to the recognition of taste. In this study, we performed in silico molecular characterization of all 72 A. aegypti GRs reported in the latest version of A. aegypti genome AaegL5. Phylogenetic analysis classified the receptors into three major clads. Multiple GRs were found to encode multiple transcripts. Physicochemical attributes such as the aliphatic index, hydropathicity index and isoelectric point indicated that A. aegypti gustatory receptors are highly stable and are tailored to perform under a variety of cellular environments. Analysis for subcellular localization indicated that all the GRs are located either in the extracellular matrix or the plasma membrane. Results also indicated that the GRs are distributed mainly on chromosomes 2 and 3, which house 22 and 49 GRs, respectively, whereas chromosome 1 houses only one GR. NCBI-CDD analysis showed the presence of a highly conserved 7tm_7 chemosensory receptor protein superfamily that includes gustatory and odorant receptors from insect species Anopheles gambiae and Drosophila melanogaster. Further, three significantly enriched ungapped motifs in the protein sequence of all 72 A. aegypti gustatory receptors were found. High-quality 3D models for the tertiary structures were predicted with significantly higher confidence, along with ligand-binding residues. Prediction of S-nitrosylation sites indicated the presence of target cysteines in all the GRs with close proximity to the ligand-bindings sites within the 3D structure of the receptors. In addition, two highly conserved motifs inside the GR proteins were discovered that house a tyrosine (Y) and a cysteine (C) residue which may serve as targets for NO-mediated tyrosine nitration and S-nitrosylation, respectively. This study will help devise strategies for functional genomic studies of these important receptor molecules in A. aegypti and other mosquito species through in vitro and in vivo studies.

Comparative study of neuropeptide signaling systems in Hemiptera

Numerous physiological processes in insects are tightly regulated by neuropeptides and their receptors. Although they form an ancient signaling system, there is still a great deal of variety in neuropeptides and their receptors among different species within the same order. Neuropeptides and their receptors have been documented in many hemipteran insects, but the differences among them have been poorly characterized. Commercial grapevines worldwide are plagued by the bug Daktulosphaira vitifoliae (Hemiptera: Sternorrhyncha). Here, 33 neuropeptide precursors and 48 putative neuropeptide G protein-coupled receptor (GPCR) genes were identified in D. vitifoliae. Their expression profiles at the probe and feeding stages reflected potential regulatory roles in probe behavior. By comparison, we found that the Releasing Hormone-Related Peptides (GnRHs) system of Sternorrhyncha was differentiated from those of the other 2 suborders in Hemiptera. Independent secondary losses of the adipokinetic hormone/corazonin-related peptide receptor (ACP) and corazonin (CRZ) occurred during the evolution of Sternorrhyncha. Additionally, we discovered that the neuropeptide signaling systems of Sternorrhyncha were very different from those of Heteroptera and Auchenorrhyncha, which was consistent with Sternorrhyncha's phylogenetic position at the base of the order. This research provides more knowledge on neuropeptide systems and sets the groundwork for the creation of novel D. vitifoliae management strategies that specifically target these signaling pathways.

Identification and Expression Profiling of the 5-HT Receptor Gene in Harmonia axyridis

It has been found that 5-hydroxytryptamine (5-HT) modulates the feeding of some insects, and this phenomenon was found in Harmonia axyridis (Pallas) by our previous study. An understanding of the 5-HT system in this beetle is helpful for utilizing 5-HT to modulate its predation to improve biological control efficiency, especially in greenhouses in winter in north China. This is because 5-HT influences diapause in insects by modulating the synthesis and release of prothoracic hormone (PTTH) and, therefore, influences feeding. To elucidate the molecular basis of the H. axyridis 5-HT system, reverse-transcription polymerase chain reaction (RT-PCR), multiple sequence alignment, and phylogenetic tree construction were used to identify the 5-HT receptor in H. axyridis, and quantitative real-time PCR (qRT-PCR) was used to analyze the expression pattern of these receptor genes in different developmental stages and in the nervous system (brain + ventral nerve cord), digestive tract, pectoral muscles, and gonads of the adult ladybird. The results showed that four 5-HT receptors were identified in H. axyridis, named 5-HT_1AHar, 5-HT_1BHar, 5-HT₂Har, and 5-HT₇Har. The four receptors were expressed at high levels in the adult stage, especially in 2-day-old adults, with expression levels of 18.72-fold (male) and 14.21-fold (female) of that in eggs for 5-HT_1A, 32.27-fold (male) and 83.58-fold (female) of that in eggs for 5-HT_1B, 36.82-fold (male) and 119.35-fold (female) of that in eggs for 5-HT₂, and 165.47-fold (male) and 115.59-fold (female) of that in eggs for 5-HT₇. The level of expression decreased with the advance of day-age in adults. The levels of expression of 5-HT_1BHar, 5-HT₂Har, and 5-HT₇Har were low at the egg, larval, and pupal stages, and 5-HT_1AHar was not expressed in the larval stage. The four receptors were expressed in the nervous system, digestive tract, pectoral muscles, and male and female gonads. The 5-HT_1AHar was expressed at a high level in the pectoral muscle (6.75-fold of that in the nervous system), 5-HT_1BHar in male gonads (1.02-fold of that in the nervous system) and the nervous system, 5-HT₂Har in male gonads (5.74-fold of that in the nervous system), and 5-HT₇Har in the digestive tract (1.81-fold of that in the nervous system). The results of this study will lay a foundation for research on the function of the 5-HT receptor by RNA interference in the regulation of predation by H. axyridis.

Genome-Wide Identification of G Protein-Coupled Receptors in Ciliated Eukaryotes

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors and play important roles in many physiological processes. As a representative group of protozoa, ciliates represent the highest stage of eukaryotic cell differentiation and evolution in terms of their reproductive mode, two-state karyotype, and extremely diverse cytogenesis patterns. GPCRs have been poorly reported in ciliates. In this study, we identified 492 GPCRs in 24 ciliates. Using the existing classification system for animals, GPCRs in ciliates can be assigned to four families, including families A, B, E, and F. Most (377 members) belong to family A. The number of GPCRs is extremely different in different ciliates; the Heterotrichea ciliates usually have more GPCRs than other ciliates. Parasitic or symbiotic ciliates usually have only a few GPCRs. Gene/genome duplication events seem to play important roles in the expansion of the GPCR superfamily in ciliates. GPCRs in ciliates displayed seven typical domain organizations. GPCRs in an ortholog group are common and conserved in all ciliates. The gene expression analysis of the members in this conserved ortholog group in the model ciliate, Tetrahymena thermophila, suggested that these GPCRs play important roles in the life cycle of ciliates. In summary, this study provides the first comprehensive genome-wide identification of GPCRs in ciliates, improving our understanding of the evolution and function of GPCR in ciliates.

Identification and expression profile analysis of chemosensory genes in pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae)

Insects have highly specialized and sensitive olfactory systems involving several chemosensory genes to locate their mates and hosts or escape from predators. Pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae), has invaded China since 2016 and caused serious damage. Till now, there is no environmentally friendly measure to control this gall midge. Screening molecules with high affinity to target odorant-binding protein to develop highly efficient attractants is a potential pest management method. However, the chemosensory genes in T. japonensis are still unclear. We identified 67 chemosensory-related genes in the transcriptomes of antennae, including 26 OBPs, 2 CSPs, 17 ORs, 3 SNMPs, 6 GRs, and 13 IRs, using high throughput sequencing. Phylogenetic analysis of these six chemosensory gene families among Dipteran was performed to classify and predict the functions. The expression profiles of OBPs, CSPs and ORs were validated by quantitative real-time PCR. 16 of the 26 OBPs were biased expressed in antennae. TjapORco and TjapOR5 were highly expressed in the antenna of unmated male and female adults. The functions of related OBPs and ORs genes were also discussed. These results provide a basis for the functional research on chemosensory genes at the molecular level.

Characterization and expression profiling of G protein-coupled receptors (GPCRs) in Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura is a highly destructive omnivorous pest, and they caused serious damage to various crops. G protein-coupled receptors (GPCRs) mediate dozens of physiological processes including reproduction, development, life span and behaviors, but the information of these receptors has been lacking in S. litura. Here, we methodically identified 122 GPCRs in S. litura and made an assay of their expression patterns in different tissues. Comparing the identified GPCRs with homologous genes of other insects, it is obvious that the subfamily A2 (biogenic amine receptors) and the subfamily A3 (neuropeptide and protein hormone receptors) of S. litura have expanded to a certain extent, which may be related to the omnivorous nature and drought environment resistance of S. litura. Besides, the large Methuselah (Mth)/Methuselah-like (Mthl) subfamily of S. litura may be involved in many physiological functions such as longevity and stress response. Apart from duplicate receptors, the loss of parathyroid hormone receptor (PTHR) and the bride of sevenless (Boss) receptor in the lepidopteran insects may imply a new pattern of wing formation and energy metabolism in lepidopteran insects. In addition, the high expression level of GPCRs in different tissues reflects the functional diversity of GPCRs regulating. Systemic identification and initial characterization of GPCRs in S. litura provide a basis for further studies to reveal the functions of these receptors in regulating physiology and behavior.

Ecological significance of G protein-coupled receptors in the Pacific oyster (Crassostrea gigas): Pervasive gene duplication and distinct transcriptional response to marine environmental stresses

Marine ecosystems with ocean warming and industry pollution threaten the survival and adaptation of organisms. G protein-coupled receptors (GPCRs) play critical roles in various physiological and toxicological processes in vertebrates and invertebrates. The Pacific oyster (Crassostrea gigas) was widely used to study the adaptation of marine molluscs to coastal environments. In this work, we identified a total of 586 GPCRs in C. gigas genome. The C. gigas GPCRs were divided into five classes (including class A, B, C, E and F) with different degrees of expansion. Meta-analysis of multiple RNA-seq datasets revealed that transcriptional expression patterns of GPCRs in C. gigas were distinct in response to high temperature, salinity, air exposure, heavy metal, ostreid herpes virus 1 (OsHV-1) and Vibrio challenge. This work for the first time characterized the GPCR gene family and provided insights into the potential roles of GPCRs in adaptation of marine molluscs to stressful coastal environment.

Superconserved receptors expressed in the brain: Expression, function, motifs and evolution of an orphan receptor family

GPR27, GPR85 and GPR173 constitute a small family of G protein-coupled receptors (GPCR) that share the distinctive characteristics of being highly conserved throughout vertebrate evolution and predominantly expressed in the brain. Accordingly, they have been coined as "Superconserved Receptors Expressed in the Brain" (SREB), although their expression profile is more complex than what was originally thought. SREBs have no known validated endogenous ligands and are thus labeled as "orphan" receptors. The investigation of this particular category of uncharacterized receptors holds great promise both in terms of physiology and drug development. In the largest GPCR family, the Rhodopsin-like or Class A, around 100 receptors are considered orphans. Because GPCRs are the most successful source of drug targets, the discovery of a novel function or ligand most likely will lead to significant breakthroughs for the discovery of innovative therapies. The high level of conservation is one of the characteristic features of the SREBs. We propose herein a detailed analysis of the putative evolutionary origin of this family. We highlight the properties that distinguish SREBs from other rhodopsin-like GPCRs. We present the current evidence for these receptors downstream signaling pathways and functions. We discuss the pharmacological challenge for the identification of natural or synthetic ligands of orphan receptors like SREBs. The different SREB-related scientific questions are presented with a highlight on what should be addressed in the near future, including the confirmation of published evidence and their validation as drug targets. In particular, we discuss in which pathological conditions these receptors may be of great relevance to solve unmet medical needs.

Silencing the gustatory receptor BtGR11 affects the sensing of sucrose in the whitefly Bemisia tabaci

RNA interference (RNAi) is powerful biotechnology for studying the in vivo functions of key genes. Based on this property, RNAi can also be used for pest control as an effective alternative to chemical pesticides. The management of phloem-sucking pests is a tricky issue in current agricultural and forestry pest control. RNAi can silence key chemoreceptor genes of phloem-sucking pests; thereby regulating the behavior of these pests can be manipulated. So, it is considered to be a promising new type of ecological pest management strategy. In this study, we identified a candidate taste receptor gene, BtGR11, that controls the taste sensitivity to sucrose in the whitefly Bemisia tabaci, which is a serious invasive phloem-sucking pest worldwide. Functional analyses using the Xenopus oocyte expression system and the two-electrode voltage-clamp system revealed that the oocytes expressing BtGR11 responded to sucrose. Furthermore, we found that silencing BtGR11 by RNAi inhibited the function of sensing sucrose in the whitefly. This study reports a key chemoreceptor gene that can be used for the understanding of the gustatory sensing mechanisms of whitefly to deterrent.

Expression of a homologue of a vertebrate non-visual opsin Opn3 in the insect photoreceptors

Insect vision starts with light absorption by visual pigments based on opsins that drive Gq-type G protein-mediated phototransduction. Since Drosophila, the most studied insect in vision research, has only Gq-coupled opsins, the Gq-mediated phototransduction has been solely focused on insect vision for decades. However, genome projects on mosquitos uncovered non-canonical insect opsin genes, members of the Opn3 or c-opsin group composed of vertebrate and invertebrate non-visual opsins. Here, we report that a homologue of Opn3, MosOpn3 (Asop12) is expressed in eyes of a mosquito Anopheles stephensi. In situ hybridization analysis revealed that MosOpn3 is expressed in dorsal and ventral ommatidia, in which only R7 photoreceptor cells express MosOpn3. We also found that Asop9, a Gq-coupled visual opsin, exhibited co-localization with MosOpn3. Spectroscopic analysis revealed that Asop9 forms a blue-sensitive opsin-based pigment. Thus, the Gi/Go-coupled opsin MosOpn3, which forms a green-sensitive pigment, is co-localized with Asop9, a Gq-coupled opsin that forms a blue-sensitive visual pigment. Since these two opsin-based pigments trigger different phototransduction cascades, the R7 photoreceptors could generate complex photoresponses to blue to green light.

This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

Identification of Candidate Chemosensory Gene Families by Head Transcriptomes Analysis in the Mexican Fruit Fly, Anastrepha ludens Loew (Diptera: Tephritidae)

Insect chemosensory systems, such as smell and taste, are mediated by chemosensory receptor and non-receptor protein families. In the last decade, many studies have focused on discovering these families in Tephritidae species of agricultural importance. However, to date, there is no information on the Mexican fruit fly Anastrepha ludens Loew, a priority pest of quarantine importance in Mexico and other countries. This work represents the first effort to identify, classify and characterize the six chemosensory gene families by analyzing two head transcriptomes of sexually immature and mature adults of A. ludens from laboratory-reared and wild populations, respectively. We identified 120 chemosensory genes encoding 31 Odorant-Binding Proteins (OBPs), 5 Chemosensory Proteins (CSPs), 2 Sensory Neuron Membrane Proteins (SNMPs), 42 Odorant Receptors (ORs), 17 Ionotropic Receptors (IRs), and 23 Gustatory Receptors (GRs). The 120 described chemosensory proteins of the Mexican fruit fly significantly contribute to the genetic databases of insects, particularly dipterans. Except for some OBPs, this work reports for the first time the repertoire of olfactory proteins for one species of the genus Anastrepha, which provides a further basis for studying the olfactory system in the family Tephritidae, one of the most important for its economic and social impact worldwide.

A high-quality genome of the dobsonfly Neoneuromus ignobilis reveals molecular convergences in aquatic insects

Neoneuromus ignobilis is an archaic holometabolous aquatic predatory insect. However, a lack of genomic resources hinders the use of whole genome sequencing to explore their genetic basis and molecular mechanisms for adaptive evolution. Here, we provided a high-contiguity, chromosome-level genome assembly of N. ignobilis using high coverage Nanopore and PacBio reads with the Hi-C technique. The final assembly is 480.67 MB in size, containing 12 telomere-ended pseudochromosomes with only 17 gaps. We compared 42 hexapod species genomes including six independent lineages comprising 11 aquatic insects, and found convergent expansions of long wavelength-sensitive and blue-sensitive opsins, thermal stress response TRP channels, and sulfotransferases in aquatic insects, which may be related to their aquatic adaptation. We also detected strong nonrandom signals of convergent amino acid substitutions in aquatic insects. Collectively, our comparative genomic analysis revealed the evidence of molecular convergences in aquatic insects during both gene family evolution and convergent amino acid substitutions.

Full length transcriptomes analysis of cold-resistance of Apis cerana in Changbai Mountain during overwintering period

Apis cerana in Changbai Mountain is an ecological type of Apis cerana, which is an excellent breeding material with cold-resistant developed by long-term natural selection under the ecological conditions. However, the physiological and molecular mechanisms of Changbai Mountain population under cold stress are still unclear. In this study, the Nanopore sequencing was carried out for the transcriptome of Apis cerana in Changbai Mountain in the coldest period of overwintering, which will provide a reference to the cold-resistant mechanism. We determined 5,941 complete ORF sequences, 1,193 lncRNAs, 619 TFs, 10,866 SSRs and functional annotations of 11,599 new transcripts. Our results showed that the myosin family and the C2H2 zinc finger protein transcription factor family possibly have significant impacts on the response mechanism of cold stress during overwintering. In addition, the cold environment alters genes expression profiles in honeybees via different AS and APA mechanisms. These altered genes in Hippo, Foxo, and MARK pathways help them counter the stress of cold in overwinter period. Our results might provide clues about the response of eastern honeybees to extreme cold, and reflect the possible genetic basis of physiological changes.

G protein-coupled receptors (GPCRs) in rotifers and cladocerans: Potential applications in ecotoxicology, ecophysiology, comparative endocrinology, and pharmacology

The G protein-coupled receptor (GPCR) superfamily plays a fundamental role in both sensory functions and the regulation of homeostasis, and is highly conserved across the eukaryote taxa. Its functional diversity is related to a conserved seven-transmembrane core and invariant set of intracellular signaling mechanisms. The interplay between these properties is key to the evolutionary success of GPCR. As this superfamily originated from a common ancestor, GPCR genes have evolved via lineage-specific duplications through the process of adaptation. Here we summarized information on GPCR gene families in rotifers and cladocerans based on their evolutionary position in aquatic invertebrates and their potential application in ecotoxicology, ecophysiology, comparative endocrinology, and pharmacology. Phylogenetic analyses were conducted to examine the evolutionary significance of GPCR gene families and to provide structural insight on their role in aquatic invertebrates. In particular, most GPCR gene families have undergone sporadic evolutionary processes, but some GPCRs are highly conserved across species despite the dynamics of GPCR evolution. Overall, this review provides a better understanding of GPCR evolution in aquatic invertebrates and expand our knowledge of the potential application of these receptors in various fields.

Genome-wide identification of 194 G protein-coupled receptor (GPCR) genes from the water flea Daphnia magna

In crustaceans, G protein-coupled receptors (GPCRs) are the largest transmembrane receptor family and function by mediating various environmental stimuli in cells. Understanding GPCR signaling is crucial to better understanding of crustacean endocrinology. GPCRs evolved from early eukaryotes, and genome-wide identification of GPCRs in a particular taxon can provide insight into evolutionary tendencies and adaptive strategies of GPCR response to environmental stimuli. Here, we identified 194 full-length GPCR genes in the water flea Daphnia magna that can be divided into five distinct classes (A, B, C, F, and other). A strong orthologous relationship for amine, neuropeptide, and opsin receptors was found in the phylogenetic comparison of D. magna GPCRs to those of humans and two well-known insects (Drosophila melanogaster and Solenopsis invicta). Our results based on phylogenetic relationships suggest that most GPCRs subfamilies have undergone sporadic evolutionary processes for adaptation to environmental pressures. Despite the dynamics of GPCR evolution, some GPCRs are highly conserved between species. This study provides a better understanding of the evolution of GPCRs and expands our knowledge of the potential physiological mechanisms in D. magna in response to various environmental stimuli.

Genome-wide identification and expression profiling of odorant receptor genes in the malaria vector Anopheles sinensis

Background

The olfactory system plays a crucial role in regulating insect behaviors. The detection of odorants is mainly mediated by various odorant receptors (ORs) that are expressed in the dendrites of olfactory neurons of chemosensilla. Anophelessinensis is a major malaria vector in Eastern Asia and its genome has recently been successfully sequenced and annotated. In this study, we present genome-wide identification and expression profiling of OR genes in different chemosensory tissues of An.sinensis.

Methods

The OR genes were identified using the available genome sequences of An.sinensis. A series of bioinformatics analyses were conducted to investigate the structure, genome distribution, selective pressure and phylogenetic relationships of OR genes, the conserved domains and specific functional sites in the OR amino acid sequences. The expression levels of OR genes were analyzed from transcriptomic data from An.sinensis antennae, proboscis and maxillary palps of both sexes.

Results

A total of 59 putative OR genes have been identified and characterized in An.sinensis. This number is significantly less than that in An.gambiae. Whether this difference is caused by the contraction or expansion of OR genes after divergence of the two species remains unknown. The RNA-seq analysis showed that AsORs have obvious tissue- and sex-specific expression patterns. Most AsORs are highly expressed in the antennae and the expression pattern and number of AsORs expressed in antennae are similar in males and females. However, the relative levels of AsOR transcripts are much higher in female antennae than in male antennae, which indicates that the odor sensitivity is likely to be increased in female mosquitoes. Based on the expression patterns and previous studies, we have speculated on the functions of some OR genes but this needs to be validated by further behavioral, molecular and electrophysiological studies. Further studies are necessary to compare the olfactory-driven behaviors and identify receptors that respond strongly to components of human odors that may act in the process of human recognition.

Conclusions

This is the first genome-wide analysis of the entire repertoire of OR genes in An.sinensis. Characterized features and profiled expression patterns of ORs suggest their involvement in the odorous reception of this species. Our findings provide a basis for further research on the functions of OR genes and additional genetic and behavioral targets for more sustainable management of An.sinensis in the future.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05259-x.

Enantiomeric Discrimination in Insects: The Role of OBPs and ORs

Olfaction is a complex recognition process that is critical for chemical communication in insects. Though some insect species are capable of discrimination between compounds that are structurally similar, little is understood about how this high level of discrimination arises. Some insects rely on discriminating between enantiomers of a compound, demonstrating an ability for highly selective recognition. The role of two major peripheral olfactory proteins in insect olfaction, i.e., odorant-binding proteins (OBPs) and odorant receptors (ORs) has been extensively studied. OBPs and ORs have variable discrimination capabilities, with some found to display highly specialized binding capability, whilst others exhibit promiscuous binding activity. A deeper understanding of how odorant-protein interactions induce a response in an insect relies on further analysis such as structural studies. In this review, we explore the potential role of OBPs and ORs in highly specific recognition, specifically enantiomeric discrimination. We summarize the state of research into OBP and OR function and focus on reported examples in the literature of clear enantiomeric discrimination by these proteins.

Odorant-receptor-mediated regulation of chemosensory gene expression in the malaria mosquito Anopheles gambiae

Mosquitoes locate and approach humans based on the activity of odorant receptors (ORs) expressed on olfactory receptor neurons (ORNs). Olfactogenetic experiments in Anopheles gambiae mosquitoes revealed that the ectopic expression of an AgOR (AgOR2) in ORNs dampened the activity of the expressing neuron. This contrasts with studies in Drosophila melanogaster in which the ectopic expression of non-native ORs in ORNs confers ectopic neuronal responses without interfering with native olfactory physiology. RNA-seq analyses comparing wild-type antennae to those ectopically expressing AgOR2 in ORNs indicated that nearly all AgOR transcripts were significantly downregulated (except for AgOR2). Additional experiments suggest that AgOR2 protein rather than mRNA mediates this downregulation. Using in situ hybridization, we find that AgOR gene choice is active into adulthood and that AgOR2 expression inhibits AgORs from turning on at this late stage. Our study shows that the ORNs of Anopheles mosquitoes (in contrast to Drosophila) are sensitive to a currently unexplored mechanism of AgOR regulation.

Maguire et al. discover that the ectopic expression of an olfactory receptor can downregulate the transcription of endogenous odorant receptors in mosquito olfactory neurons. The onset of mosquito odorant-receptor expression by an olfactory neuron continues into adult stages, and is particularly sensitive to exogenous olfactory reception expression.

Screening for odorant receptor genes expressed in Aedes aegypti involved in host-seeking, blood-feeding and oviposition behaviors

Background

Aedes aegypti is one of the most important vectors of zoonotic diseases worldwide, and its survival and reproductive processes depend heavily on its olfactory system. In this study, the expression levels of all odorant receptor (OR) genes of Ae. aegypti were explored during different physiological periods to identify olfactory genes that may be associated with mosquito blood-feeding and the search for oviposition sites.

Methods

Four experimental groups, consisting of Ae. aegypti males, pre-blood-feeding females, post-blood-feeding females and post-oviposition females, were established. A total of 114 pairs of primers targeting all messenger RNA encoded by OR genes were designed based on the whole genome of Ae. aegypti. The expression of OR genes was evaluated by real-time fluorescence quantitative PCR for relative quantification and the comparison of differences between groups.

Results

A total of 53 differentially expressed OR genes were identified between males and females in Ae. aegypti antennae. Also, eight, eight and 13 differentially expressed OR genes were identified in pre- versus post-blood-feeding females, in pre- versus post-oviposition females and in post-blood-feeding versus post-oviposition females, respectively. In addition, 16 OR genes were significantly differentially expressed in multiple physiological periods of the mosquitoes.

Conclusions

A large number of ORs with significant intergroup differences and high expression levels were screened in this study. Some of these genes are reported for the first time, providing possible targets for the development of mosquito control pathways based on the olfactory system.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05196-9.

Human attractive cues and mosquito host-seeking behavior

Female mosquitoes use chemical and physical cues, including vision, smell, heat, and humidity, to orient toward hosts. Body odors are produced by skin resident bacteria that convert metabolites secreted in sweat into odorants that confer the characteristic body scent. Mosquitoes detect these compounds using olfactory receptors in their antennal olfactory receptor neurons. Such information is further integrated with the senses of temperature and humidity, as well as vision, processed in the brain into a behavioral output, leading to host finding. Knowledge of human scent components unveils a variety of odorants that are attractive to mosquitoes, but also odor-triggering repellency. Finding ways to divert human-seeking behavior by female mosquitoes using odorants can possibly mitigate mosquito-borne pathogen transmission.

Characterization of Antennal Chemosensilla and Associated Chemosensory Genes in the Orange Spiny Whitefly, Aleurocanthus spiniferus (Quaintanca)

The insect chemosensory system plays an important role in many aspects of insects' behaviors necessary for their survival. Despite the complexity of this system, an increasing number of studies have begun to understand its structure and function in different insect species. Nonetheless, the chemosensory system in the orange spiny whitefly Aleurocanthus spiniferus, as one of the most destructive insect pests of citrus in tropical Asia, has not been investigated yet. In this study, the sensillum types, morphologies and distributions of the male and female antennae of A. spiniferus were characterized using scanning electron microscopy. In both sexes, six different sensilla types were observed: trichodea sensilla, chaetica sensilla, microtrichia sensilla, coeloconic sensilla, basiconic sensilla, and finger-like sensilla. Moreover, we identified a total of 48 chemosensory genes, including 5 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 3 sensory neuron membrane proteins (SNMPs), 6 odorant receptors (ORs), 8 gustatory receptors (GRs), and 14 ionotropic receptors (IRs) using transcriptome data analysis. Tissue-specific transcriptome analysis of these genes showed predominantly expression in the head (including antennae), whereas CSPs were broadly expressed in both head (including the antennae) and body tissue of adult A. spiniferus. In addition, the expression profiling of selected chemosensory genes at different developmental stages was examined by quantitative real time-PCR which was mapped to the transcriptome. We found that the majority of these genes were highly expressed in adults, while AspiORco, AspiGR1, AspiGR2, and AspiIR4 genes were only detected in the pupal stage. Together, this study provides a basis for future chemosensory and genomic studies in A. spiniferus and closely related species. Furthermore, this study not only provides insights for further research on the molecular mechanisms of A. spiniferus-plant interactions but also provides extensive potential targets for pest control.

Diversity and Molecular Evolution of Odorant Receptor in Hemipteran Insects

Simple Summary

Insects’ behavior and ecology are closely related to their chemosensory systems, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still needed. In this study, we identified and analyzed the OR genes from hemipteran species systematically. The number of OR genes discovered in each species ranged from less than ten to hundreds. Gene gain and loss events of OR have occurred in several species in the seven major clades classified through phylogenetic analysis. Then, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera through positive selection. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.

Abstract

Olfaction is a critical physiologic process for insects to interact with the environment, especially plant-emitted volatiles, during which odorant receptors (ORs) play an essential role in host recognition. Although OR gene evolution has been studied in many insect orders, a comprehensive evolutionary analysis and expression of OR gene gain and loss events among diverse hemipteran species are still required. In this study, we identified and analyzed 887 OR genes from 11 hemipteran species. The number of OR genes discovered in each species ranged from less than ten to hundreds. Phylogenetic analysis revealed that all identified Hemiptera OR genes were classified into seven major clades. Gene gain and loss events of OR have occurred in several species. Then, by positive selection, we discovered the amino acid differences between species to understand the molecular evolution of OR in the order Hemiptera. Additionally, we discussed how evolutionary analysis can aid the study of insect–plant communication. This study lays a foundation for subsequent investigations into the molecular mechanisms of Hemiptera olfactory receptors involved in host recognition.

Repellency Mechanism of Natural Guar Gum-Based Film Incorporated with Citral against Brown Planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

Using of plant essential oil that coevolved as a defense mechanism against agriculture insects is an alternative means of controlling many insect pests. In order to repel brown planthoppers (BPHs), the most notorious rice insect pest, a new film based on guar gum incorporated with citral (GC film) was formulated, which was effective while being environmentally friendly. In this paper, the effect and mechanism of GC film repellency against BPHs were determined. Repellent activity test and olfactory reaction analysis showed that GC film had repellency effect against BPHs, with repellency of 60.00% and 73.93%, respectively. The result of olfactory reaction indicated that GC film repellency against BPHs relied on smell. EPG analysis showed the proportion and mean duration of np waveform were significantly higher than in CK and increased following the treatment concentration, which indicated that GC film affected the recognition of BPHs to rice. Further analysis by RNA sequencing analysis showed a total of 679 genes were significantly upregulated and 284 genes were significantly downregulated in the BPHs fed on the rice sprayed with GC film compared to control. Odorant-binding protein (OBP) gene 797 and gustatory receptor gene (GR)/odorant receptor (OR) gene 13110 showed a significant decrease in differential expression and significant increase in differential expression, respectively. There were 0.66 and 2.55 differential expression multiples between treated BPHs and control, respectively. According to the results described above, we reasoned that GC film repellency against BPHs due to smell, by release of citral, caused the recognition difficulties for BPHs to rice, and OBP gene 797 and GR/OR gene 13110 appeared to be the crucial candidate genes for GC film repellency against BPHs. The present study depicted a clear and consistent repellency effect for GC film against BPHs and preliminarily clarified the mechanism of GC film as a repellent against BPHs, which might offer an alternative approach for control of BPHs in the near future. Our results could also help in the development and improvement of GC films.

Single amino acid residue mediates reciprocal specificity in two mosquito odorant receptors

The southern house mosquito, Culex quinquefasciatus, utilizes two odorant receptors, CquiOR10 and CquiOR2, narrowly tuned to oviposition attractants and well conserved among mosquito species. They detect skatole and indole, respectively, with reciprocal specificity. We swapped the transmembrane (TM) domains of CquiOR10 and CquiOR2 and identified TM2 as a specificity determinant. With additional mutations, we showed that CquiOR10A73L behaved like CquiOR2. Conversely, CquiOR2L74A recapitulated CquiOR10 specificity. Next, we generated structural models of CquiOR10 and CquiOR10A73L using RoseTTAFold and AlphaFold and docked skatole and indole using RosettaLigand. These modeling studies suggested space-filling constraints around A73. Consistent with this hypothesis, CquiOR10 mutants with a bulkier residue (Ile, Val) were insensitive to skatole and indole, whereas CquiOR10A73G retained the specificity to skatole and showed a more robust response than the wildtype receptor CquiOR10. On the other hand, Leu to Gly mutation of the indole receptor CquiOR2 reverted the specificity to skatole. Lastly, CquiOR10A73L, CquiOR2, and CquiOR2L74I were insensitive to 3-ethylindole, whereas CquiOR2L74A and CquiOR2L74G gained activity. Additionally, CquiOR10A73G gave more robust responses to 3-ethylindole than CquiOR10. Thus, we suggest the specificity of these receptors is mediated by a single amino acid substitution, leading to finely tuned volumetric space to accommodate specific oviposition attractants.

Intermolecular interactions drive protein adaptive and co-adaptive evolution at both species and population levels

Proteins are the building blocks for almost all the functions in cells. Understanding the molecular evolution of proteins and the forces that shape protein evolution is essential in understanding the basis of function and evolution. Previous studies have shown that adaptation frequently occurs at the protein surface, such as in genes involved in host–pathogen interactions. However, it remains unclear whether adaptive sites are distributed randomly or at regions associated with particular structural or functional characteristics across the genome, since many proteins lack structural or functional annotations. Here, we seek to tackle this question by combining large-scale bioinformatic prediction, structural analysis, phylogenetic inference, and population genomic analysis of Drosophila protein-coding genes. We found that protein sequence adaptation is more relevant to function-related rather than structure-related properties. Interestingly, intermolecular interactions contribute significantly to protein adaptation. We further showed that intermolecular interactions, such as physical interactions, may play a role in the coadaptation of fast-adaptive proteins. We found that strongly differentiated amino acids across geographic regions in protein-coding genes are mostly adaptive, which may contribute to the long-term adaptive evolution. This strongly indicates that a number of adaptive sites tend to be repeatedly mutated and selected throughout evolution in the past, present, and maybe future. Our results highlight the important roles of intermolecular interactions and coadaptation in the adaptive evolution of proteins both at the species and population levels.

G protein-coupled receptors that influence lifespan of human and animal models

Humanity has always sought to live longer and for this, multiple strategies have been tried with varying results. In this sense, G protein-coupled receptors (GPCRs) may be a good option to try to prolong our life while maintaining good health since they have a substantial participation in a wide variety of processes of human pathophysiology and are one of the main therapeutic targets. In this way, we present the analysis of a series of GPCRs whose activity has been shown to affect the lifespan of animal and human models, and in which we put a special interest in describing the molecular mechanisms involved. Our compilation of data revealed that the mechanisms most involved in the role of GPCRs in lifespan are those that mimic dietary restriction, those related to insulin signaling and the AMPK and TOR pathways, and those that alter oxidative homeostasis and severe and/or chronic inflammation. We also discuss the possibility of using agonist or antagonist drugs, depending on the beneficial or harmful effects of each GPCR, in order to prolong people's lifespan and healthspan.

Identification and functional characterization of olfactory indolergic receptors in Drosophila melanogaster

Indole-sensitive odorant receptors or indolORs belong to a mosquito-specific expansion as ancient as the Culicidae lineage. Brachyceran flies appeared to lack representative members of this group despite the importance of indolics in this important group of dipterans. To explore whether indolORs occur in other brachyceran species, we searched for candidate indolORs in Drosophila melanogaster. Using phylogenetic tools, we show that D. melanogaster OR30a, OR43a, and OR49b form a distinct monophyletic lineage with mosquito indolORs. To explore a potential functional orthology with indolORs, we expressed these three Drosophila ORs in Xenopus laevis oocytes and measured their responses to a panel of indolic compounds. We provide evidence that OR30a, OR43a, and OR49b exhibit high sensitivity to indoles. Along with the recent discovery of indolORs in the housefly Musca domestica, our findings suggest that indolORs are a widespread feature of the peripheral olfactory systems of Diptera.

Identification and Functional Analysis of G Protein-Coupled Receptors in 20-Hydroxyecdysone Signaling From the Helicoverpa armigera Genome

G protein-coupled receptors (GPCRs) are the largest family of membrane receptors in animals and humans, which transmit various signals from the extracellular environment into cells. Studies have reported that several GPCRs transmit the same signal; however, the mechanism is unclear. In the present study, we identified all 122 classical GPCRs from the genome of Helicoverpa armigera, a lepidopteran pest species. Twenty-four GPCRs were identified as upregulated at the metamorphic stage by comparing the transcriptomes of the midgut at the metamorphic and feeding stages. Nine of them were confirmed to be upregulated at the metamorphic stage. RNA interference in larvae revealed the prolactin-releasing peptide receptor (PRRPR), smoothened (SMO), adipokinetic hormone receptor (AKHR), and 5-hydroxytryptamine receptor (HTR) are involved in steroid hormone 20-hydroxyecdysone (20E)-promoted pupation. Frizzled 7 (FZD7) is involved in growth, while tachykinin-like peptides receptor 86C (TKR86C) had no effect on growth and pupation. Via these GPCRs, 20E regulated the expression of different genes, respectively, including Pten (encoding phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase), FoxO (encoding forkhead box O), BrZ7 (encoding broad isoform Z7), Kr-h1 (encoding Krüppel homolog 1), Wnt (encoding Wingless/Integrated) and cMyc, with hormone receptor 3 (HHR3) as their common regulating target. PRRPR was identified as a new 20E cell membrane receptor using a binding assay. These data suggested that 20E, via different GPCRs, regulates different gene expression to integrate growth and development.

Genome-wide identification of 216 G protein-coupled receptor (GPCR) genes from the marine water flea Diaphanosoma celebensis

G protein-coupled receptors (GPCRs) are considered to have originated from early evolution of eukaryotic species, therefore, the genome-wide identification of GPCR genes can provide insight into the adaptive strategy and evolutionary tendency in an animal taxon. Here, we identified a total 216 full-length GPCR genes in the marine water flea Diaphanosoma celebensis genome, which were classified into five distinct classes (A, B, C, F, and other). Phylogenetic comparison of GPCRs in D. celebensis to those in humans (Homo sapiens), fruitfly (Drosophila melanogaster), and freshwater water flea (Daphnia magna) reveals a high level of orthological relationship of amine, neuropeptide, and opsin receptor repertoire, while purinergic and chemokine receptors were highly differentiated in humans. Our findings suggest sporadic evolutionary processes within the GPCR gene families identified in D. celebensis. In this study, these results may provide a better understanding on the evolution of GPCRs, and expand our knowledge of the cladoceran GPCR gene repertories which in part, mediate cell physiological mechanisms in response to various environmental stimuli.

Molecular and pharmacological characterization of biogenic amine receptors from the diamondback moth, Plutella xylostella

BACKGROUD

Insect biogenic amines play important roles in mediating behavioral and physiological processes. They exert their effects by binding to biogenic amine receptors (BARs), which are specific receptor proteins in the G-protein-coupled receptor superfamily. BAR genes have been cloned and characterized from multiple model insects, including Drosophila melanogaster, Anopheles gambiae, Bombyx mori, Apis mellifera and Tribolium castaneum. However, relatively little work has addressed the molecular properties, expression profiles, and pharmacological characterization of BARs from other insects, including important pests.

RESULTS

In this study, we cloned 17 genes encoding putative biogenic amine receptor proteins from Plutella xylostella, a global pest of Brassica crops. These PxBAR genes were five octopamine receptors (PxOA1, PxOA2B1, PxOA2B2, PxOA2B3, and PxOA3), three tyramine receptors (PxTAR1A, PxTAR1B, and PxTAR2), four dopamine receptors (PxDOP1, PxDOP2, PxDOP3, and PxDopEcR), and five serotonin receptors (Px5-HT_1A , Px5-HT_1B , Px5-HT_2A , Px5-HT_2B , and Px5-HT₇ ). All PxBARs showed considerable sequence identity with orthologous BARs, and phylogenetic analysis clustered the receptors within their respective groups while preserving organismal evolutionary relationships. We investigated their molecular properties and expression profiles, and pharmacologically characterized the dopamine receptor, PxDOP2.

CONCLUSIONS

Our study provides important information and resources on biogenic amine receptors from P. xylostella, which suggests potential target sites for controlling this pest species. © 2021 Society of Chemical Industry.

Expansion and Accelerated Evolution of 9-Exon Odorant Receptors in Polistes Paper Wasps

Independent origins of sociality in bees and ants are associated with independent expansions of particular odorant receptor (OR) gene subfamilies. In ants, one clade within the OR gene family, the 9-exon subfamily, has dramatically expanded. These receptors detect cuticular hydrocarbons (CHCs), key social signaling molecules in insects. It is unclear to what extent 9-exon OR subfamily expansion is associated with the independent evolution of sociality across Hymenoptera, warranting studies of taxa with independently derived social behavior. Here, we describe OR gene family evolution in the northern paper wasp, Polistes fuscatus, and compare it to four additional paper wasp species spanning ∼40 million years of evolutionary divergence. We find 200 putatively functional OR genes in P. fuscatus, matching predictions from neuroanatomy, and more than half of these are in the 9-exon subfamily. Most OR gene expansions are tandemly arrayed at orthologous loci in Polistes genomes, and microsynteny analysis shows species-specific gain and loss of 9-exon ORs within tandem arrays. There is evidence of episodic positive diversifying selection shaping ORs in expanded subfamilies. Values of omega (dN/dS) are higher among 9-exon ORs compared to other OR subfamilies. Within the Polistes OR gene tree, branches in the 9-exon OR clade experience relaxed negative (relaxed purifying) selection relative to other branches in the tree. Patterns of OR evolution within Polistes are consistent with 9-exon OR function in CHC perception by combinatorial coding, with both natural selection and neutral drift contributing to interspecies differences in gene copy number and sequence.

Identification of G protein-coupled receptors required for vitellogenesis and egg development in an insect with panoistic ovary

G protein-coupled receptors (GPCRs), a superfamily of integral transmembrane proteins regulate a variety of physiological processes in insects. Juvenile hormone (JH) is known to stimulate Vitellogenin (Vg) synthesis in the fat body, secretion into the hemolymph and uptake by developing oocytes. However, the role of GPCRs in JH-dependent insect vitellogenesis and oocyte maturation remains elusive. In the present study, we performed transcriptomic analysis and RNA interference (RNAi) screening in vitellogenic females of the migratory locust Locusta migratoria. Of 22 GPCRs identified in ovarian transcriptome, LGR4, OR-A1, OR-A2, Mthl1, Mthl5 and Smo were most abundant in the ovary. By comparison, mAChR-C expressed at higher levels in the fat body, whereas Oct/TyrR, OARβ, AdoR and ADGRA3 were at higher expression levels in the brain. Our RNAi screening demonstrated that knockdown of six GPCRs resulted in defective phenotypes of Vg accumulation in developing oocytes, accompanied by blocked ovarian development and impaired oocyte maturation. While LGR4 and Oct/TyrR appeared to control Vg synthesis in the fat body, OR-A1, OR-A2, mAChR-C and CirlL regulated Vg transportation and uptake. The findings provide fundamental evidence for deciphering the regulatory mechanisms of GPCRs in JH-stimulated insect reproduction.

Functional Characterization of Ecdysis Triggering Hormone Receptors (AgETHR-A and AgETHR-B) in the African Malaria Mosquito, Anopheles gambiae

Insect ecdysis behavior, shedding off the old cuticle, is under the control of specific neuropeptides with the top command by the ecdysis triggering hormone (ETH). We characterized the ETH receptor (ETHR) of the malaria mosquito, Anopheles gambiae, by manual annotation of the NCBI gene (AGAP002881) and functional analysis, using a heterologous expression system in a mammalian cell line. The two splicing variants of ETHRs, ecdysis triggering hormone receptors (AgETHR-A and AgETHR-B), a conserved feature among insects, included of four (552 aa) and five exons (635 aa), respectively. The main feature of manual annotation of the receptor was a correction of N-terminal and exon-intron boundaries of an annotated gene (AGAP002881). Interestingly, the functional expression of the receptor in Chinese hamster ovary cells required modification of the transcription initiation site for mammalian Kozak consensus. In the calcium mobilization assay using the heterologous expression of each receptor, AgETHR-B showed a higher sensitivity to AgETH-1 (28 times) and AgETH-2 (320 times) than AgETHR-A. The AgETHRs showed specificity only to the ETH group of peptides but not to other groups carrying the C-termini motifs as PRXamide, such as pyrokinin1/DH and pyrokinin2/PBAN. Ecdysis triggering hormone receptors (AgETHR-B) responded to different ETH variants of other insect species more promiscuously than AgETHR-A.

Phenyl imidazolidin-2-ones antagonize a β-adrenergic-like octopamine receptor in diamondback moth (Plutella xylostella)

BACKGROUND

The diamondback moth (Plutella xylostella) is one of the most destructive lepidopteran pests on cruciferous vegetables. However, resistance has emerged to current chemical and biological insecticides used for P. xylostella control, indicating the necessity of screening new targets on P. xylostella, and finding new insecticides against P. xylostella. In particular, octopamine receptors are representative G protein-coupled receptors found only in invertebrates and are potential targets for identifying novel insecticides.

RESULTS

A β-adrenergic-like octopamine receptor gene (PxOA2B1) was cloned, and its pharmacological characteristics in P. xylostella were studied. The results demonstrated that octopamine could activate the PxOA2B1 receptor, with a half-maximal effective concentration (EC₅₀ ) of 49.5 nm. Amitraz, an insecticide and acaricide, and its metabolite (N-2,4-dimethylphenyl-N'-methylformamidine; DPMF) were also found to act as PxOAB1R agonists. We synthesized phenyl imidazolidin-2-one derivatives 3a-h using DPMF as the lead compound, and compounds 3a-h showed similar antagonist activities as phentolamine, mianserin and chlorpromazine. In particular, 3d, with an EC₅₀ of 25.2 nm, showed very similar antagonist activity to mianserin.

CONCLUSION

This research found that PxOAB1R might be a potential target for P. xylostella control. Phenyl imidazolidin-2-ones could be novel potential antagonists targeted at octopamine receptors and would be useful tools for the design and development of novel insecticides. © 2021 Society of Chemical Industry.

Transcriptome analysis uncover differential regulation in cell cycle, immunity, and metabolism in Anopheles albimanus during immune priming with Plasmodium berghei

In invertebrates, "immunological priming" is considered as the ability to acquire a protective (adaptive) immune response against a pathogen due to previous exposure to the same organism. To date, the mechanism by which this type of adaptive immune response originates in insects is not well understood. In the Anopheles albimanus - Plasmodium berghei model, a DNA synthesis that probably indicates an endoreplication process during priming induction has been evidenced. This work aimed to know the transcriptomic profile in the midguts of An. albimanus after priming induction. Our analysis indicates the participation of regulatory elements of the cell cycle in the immunological priming and points out the importance of the cell cycle regulation in the mosquito midgut.

G-Protein Coupled Receptors (GPCRs) in Insects-A Potential Target for New Insecticide Development

G-protein coupled receptors (GPCRs) play important roles in cell biology and insects' physiological processes, toxicological response and the development of insecticide resistance. New information on genome sequences, proteomic and transcriptome analysis and expression patterns of GPCRs in organs such as the central nervous system in different organisms has shown the importance of these signaling regulatory GPCRs and their impact on vital cell functions. Our growing understanding of the role played by GPCRs at the cellular, genome, transcriptome and tissue levels is now being utilized to develop new targets that will sidestep many of the problems currently hindering human disease control and insect pest management. This article reviews recent work on the expression and function of GPCRs in insects, focusing on the molecular complexes governing the insect physiology and development of insecticide resistance and examining the genome information for GPCRs in two medically important insects, mosquitoes and house flies, and their orthologs in the model insect species Drosophila melanogaster. The tissue specific distribution and expression of the insect GPCRs is discussed, along with fresh insights into practical aspects of insect physiology and toxicology that could be fundamental for efforts to develop new, more effective, strategies for pest control and resistance management.

G-Protein Coupled Receptors (GPCRs): Signaling Pathways, Characterization, and Functions in Insect Physiology and Toxicology

G-protein-coupled receptors (GPCRs) are known to play central roles in the physiology of many organisms. Members of this seven α-helical transmembrane protein family transduce the extracellular signals and regulate intracellular second messengers through coupling to heterotrimeric G-proteins, adenylate cyclase, cAMPs, and protein kinases. As a result of the critical function of GPCRs in cell physiology and biochemistry, they not only play important roles in cell biology and the medicines used to treat a wide range of human diseases but also in insects’ physiological functions. Recent studies have revealed the expression and function of GPCRs in insecticide resistance, improving our understanding of the molecular complexes governing the development of insecticide resistance. This article focuses on the review of G-protein coupled receptor (GPCR) signaling pathways in insect physiology, including insects’ reproduction, growth and development, stress responses, feeding, behaviors, and other physiological processes. Hormones and polypeptides that are involved in insect GPCR regulatory pathways are reviewed. The review also gives a brief introduction of GPCR pathways in organisms in general. At the end of the review, it provides the recent studies on the function of GPCRs in the development of insecticide resistance, focusing in particular on our current knowledge of the expression and function of GPCRs and their downstream regulation pathways and their roles in insecticide resistance and the regulation of resistance P450 gene expression. The latest insights into the exciting technological advances and new techniques for gene expression and functional characterization of the GPCRs in insects are provided.

Sensory gene identification in the transcriptome of the ectoparasitoid Quadrastichus mendeli

Sensory genes play a key role in the host location of parasitoids. To date, the sensory genes that regulate parasitoids to locate gall-inducing insects have not been uncovered. An obligate ectoparasitoid, Quadrastichus mendeli Kim & La Salle (Hymenoptera: Eulophidae: Tetrastichinae), is one of the most important parasitoids of Leptocybe invasa, which is a global gall-making pest in eucalyptus plantations. Interestingly, Q. mendeli can precisely locate the larva of L. invasa, which induces tumor-like growth on the eucalyptus leaves and stems. Therefore, Q. mendeli-L. invasa provides an ideal system to study the way that parasitoids use sensory genes in gall-making pests. In this study, we present the transcriptome of Q. mendeli using high-throughput sequencing. In total, 31,820 transcripts were obtained and assembled into 26,925 unigenes in Q. mendeli. Then, the major sensory genes were identified, and phylogenetic analyses were performed with these genes from Q. mendeli and other model insect species. Three chemosensory proteins (CSPs), 10 gustatory receptors (GRs), 21 ionotropic receptors (IRs), 58 odorant binding proteins (OBPs), 30 odorant receptors (ORs) and 2 sensory neuron membrane proteins (SNMPs) were identified in Q. mendeli by bioinformatics analysis. Our report is the first to obtain abundant biological information on the transcriptome of Q. mendeli that provided valuable information regarding the molecular basis of Q. mendeli perception, and it may help to understand the host location of parasitoids of gall-making pests.