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Simple Summary: Microbial symbionts could intervene with the physiological processes of insect chemoreception, such as changing the processing, transmission, and integration of olfactory or gustatory signals and thereby improve or reduce insect sensitivity to semiochemicals, which in turn adjusts insect behavior. The influence of microbial symbionts on insect chemical communication facilitates the spread of symbionts but could be beneficial or detrimental to insects, which provides the impetus for the co-evolution of symbiotic systems. The association between microbial symbionts and insect chemoreception could be exploited to develop new insect control strategies. Chemical communication is widespread among insects and exploited to adjust their behavior, such as food and habitat seeking and preferences, recruitment, defense, and mate attraction. Recently, many studies have revealed that microbial symbionts could regulate host chemical communication by affecting the synthesis and perception of insect semiochemicals. In this paper, we review recent studies of the influence of microbial symbionts on insect chemoreception. Microbial symbionts may influence insect sensitivity to semiochemicals by regulating the synthesis of odorant-binding proteins or chemosensory proteins and olfactory or gustatory receptors and regulating host neurotransmission, thereby adjusting insect behavior. The manipulation of insect chemosensory behavior by microbial symbionts is conducive to their proliferation and dispersal and provides the impetus for insects to change their feeding habits and aggregation and dispersal behavior, which contributes to population differentiation in insects. Future research is necessary to reveal the material and information exchange between both partners to improve our comprehension of the evolution of chemoreception in insects. Manipulating insect chemoreception physiology by inoculating them with microbes could be utilized as a potential approach to managing insect populations. [ABSTRACT FROM AUTHOR]

Throughout the animal kingdom, our two chemical senses, olfaction and gustation, are defined by two primary factors: genomic architecture of the organisms and their living environment. During the past three years of the global COVID-19 pandemic, these two sensory modalities have drawn much attention at the basic science and clinical levels because of the strong association of olfactory and gustatory dysfunction with viral infection. Loss of our sense of smell alone, or together with a loss of taste, has emerged as a reliable indicator of COVID-19 infection. Previously, similar dysfunctions have been detected in a large cohort of patients with chronic conditions. The research focus remains on understanding the persistence of olfactory and gustatory disturbances in the post-infection phase, especially in cases with long-term effect of infection (long COVID). Also, both sensory modalities show consistent age-related decline in studies aimed to understand the pathology of neurodegenerative conditions. Some studies using classical model organisms show an impact on neural structure and behavior in offspring as an outcome of parental olfactory experience. The methylation status of specific odorant receptors, activated in parents, is passed on to the offspring. Furthermore, experimental evidence indicates an inverse correlation of gustatory and olfactory abilities with obesity. Such diverse lines of evidence emerging from basic and clinical research studies indicate a complex interplay of genetic factors, evolutionary forces, and epigenetic alterations. Environmental factors that regulate gustation and olfaction could induce epigenetic modulation. However, in turn, such modulation leads to variable effects depending on genetic makeup and physiological status. Therefore, a layered regulatory hierarchy remains active and is passed on to multiple generations. In the present review, we attempt to understand the experimental evidence that indicates variable regulatory mechanisms through multilayered and cross-reacting pathways. Our analytical approach will add to enhancement of prevailing therapeutic interventions and bring to the forefront the significance of chemosensory modalities for the evaluation and maintenance of long-term health. [ABSTRACT FROM AUTHOR]

Since antiquity, the sense of smell (olfaction) is considered as a distance sense, just like sight and hearing. Conversely, the sense of taste (gustation) is thought to operate by direct contact, similarly to touch. With the progress of natural sciences, information at molecular, anatomical, and neurobiological levels has also contributed to the taste-smell dichotomy, but much evidence inconsistent with a sharp differentiation of these two senses has emerged, especially when considering species other than humans. In spite of this, conflicting information has been interpreted so that it could conform to the traditional differentiation. As a result, a confirmation bias is currently affecting scientific research on chemosensory systems and is also hindering the development of a satisfactory narrative of the evolution of chemical communication across taxa. From this perspective, the chemosensory dichotomy loses its validity and usefulness. We thus propose the unification of all chemosensory modalities into a single sense, moving toward a synthetic, complex, and interconnected perspective on the gradual processes by which a vast variety of chemicals have become signals that are crucially important to communication among and within cells, organs, and organisms in a wide variety of environmental conditions. [ABSTRACT FROM AUTHOR]

The Up-and-Coming-Scientist section of the current issue of the Journal of Membrane Biology features the invited essay by Dr. Mercedes Alfonso-Prieto, Assistant Professor at the Forschungszentrum Jülich (FZJ), Germany, and the Heinrich-Heine University Düsseldorf, Vogt Institute for Brain Research. Dr. Alfonso-Prieto completed her doctoral degree in chemistry at the Barcelona Science Park, Spain, in 2009, pursued post-doctoral research in computational molecular sciences at Temple University, USA, and then, as a Marie Curie post-doctoral fellow at the University of Barcelona, worked on computations of enzyme reactions and modeling of photoswitchable ligands targeting neuronal receptors. In 2016, she joined the Institute for Advanced Science and the Institute for Computational Biomedicine at the FZJ, where she pursues research on modeling and simulation of chemical senses. The invited essay by Dr. Alfonso-Prieto discusses state-of-the-art modeling of molecular receptors involved in chemical sensing – the senses of taste and smell. These receptors, and computational methods to study them, are the focus of Dr. Alfonso-Prieto's research. Recently, Dr. Alfonso-Prieto and colleagues have presented a new methodology to predict ligand binding poses for GPCRs, and extensive computations that deciphered the ligand selectivity determinants of bitter taste receptors. These developments inform our current understanding of how taste occurs at the molecular level. [ABSTRACT FROM AUTHOR]

The olfactory system uses hundreds of odorant receptors (ORs), the largest group of the G-protein-coupled receptor (GPCR) superfamily, to detect a vast array of odorants. Each OR is activated by specific odorous ligands, and like other GPCRs, antagonism can block activation of ORs. Recent studies suggest that odorant antagonisms in mixtures influence olfactory neuron activities, but it is unclear how this affects perception of odor mixtures. In this study, we identified a set of human ORs activated by methanethiol and hydrogen sulfide, two potent volatile sulfur malodors, through large-scale heterologous expression. Screening odorants that block OR activation in heterologous cells identified a set of antagonists, including β-ionone. Sensory evaluation in humans revealed that β-ionone reduced the odor intensity and unpleasantness of methanethiol. Additionally, suppression was not observed when methanethiol and β-ionone were introduced simultaneously to different nostrils. Our study supports the hypothesis that odor sensation is altered through antagonistic interactions at the OR level. [Display omitted] • β-ionone antagonizes activation of odorant receptors responding to sulfur malodors • β-ionone suppresses malodor intensity and unpleasantness in sensory evaluations • No suppression observed when malodor and β-ionone introduced to different nostrils • Odor sensation is likely to be altered via OR-level antagonistic interactions Fukutani et al. identified β-ionone as an antagonist of odorant receptors responding to potent sulfur malodors using heterologous expression. Human sensory evaluations confirmed β-ionone effectively reduced malodor intensity and unpleasantness, highlighting the importance of antagonistic interactions at the odorant receptor level in odor sensation. [ABSTRACT FROM AUTHOR]

• OR2W1 is the most broadly tuned human odorant receptor known. • Two-thirds of its now 153 chemically diverse, known agonists are key food odorants. • Evolutionary younger, selective receptors detect odorants not covered by OR2W1. Mammals perceive a multitude of odorants by their chemical sense of olfaction, a high-dimensional stimulus-detection system, with hundreds of narrowly or broadly tuned receptors, enabling pattern recognition by the brain. Cognate receptor-agonist information, however, is sparse, and the role of broadly tuned odorant receptors for encoding odor quality remains elusive. Here, we screened IL-6-HaloTag®-OR2W1 and haplotypes against 187 out of 230 defined key food odorants using the GloSensor™ system in HEK-293 cells, yielding 48 new agonists. Altogether, key food odorants represent about two-thirds of now 153 reported agonists of OR2W1, the highest number of agonists known for a mammalian odorant receptor. In summary, we characterized OR2W1 as a human odorant receptor, with a chemically diverse but exclusive receptive range, complementary to chemical subgroups covered by evolutionary younger, highly selective receptors. Our data suggest OR2W1 to be suited for participating in the detection of many foodborne odorants. [ABSTRACT FROM AUTHOR]

Electronic noses are artificial devices designed to detect and classify odors, used for many industrial applications but they can also be a tool for fundamental research on the chemical senses. Indeed, one major issue in research on olfaction is that the relationship between the structure of volatile olfactory compounds and the perception they evoke is still little understood. Acknowledging the importance of biology in the equation, the present study offers a new way to approach to stimulus-percept problem in olfaction, 1/ by considering as stimulus the interaction between odorants and olfactory receptors and 2/ by extending the measure of percept and considering the issue of interindividual diversity. To this end, we used a bio-inspired surface resonance plasmon electronic nose (e-nose) and acquired response patterns for 20 representative odorants. We also collected perceptual ratings (on intensity, pleasantness, familiarity, edibility and irritation) and verbal description of the perceptual experience associated to these odorants in a sample of 74 individuals. Combining Principal Component Analysis and Dissimilarity Matrix Analysis, we showed a relationship between the e-nose space and both measures of perception, but only for odorants eliciting homogenous responses among the subjects. This study thus shows the relevance of a bio-inspired e-nose as a model of olfactory receptors interactions for the study of natural olfaction. • A bio-inspired electronic nose was used as a model of the ligand-receptor interaction in human olfactory mucosa. • E-nose's responses were compared to 74 human verbal descriptions and ratings for 20 odorants. • Electronic nose activity was correlated with human perception when the odorants elicited homogenous hedonic responses. [ABSTRACT FROM AUTHOR]

Simple Summary: In this study, we conducted a transcriptome analysis of adult antennae in Plagiodera versicolora (Coleoptera: Chrysomelidae) and identified a total of 98 candidate chemosensory genes, encoding 40 odorant receptors (ORs), 7 ionotropic receptors (IRs), 13 gustatory receptors (GRs), 10 chemosensory proteins (CSPs), 24 odorant binding proteins (OBPs), and 4 sensory neuron membrane proteins (SNMPs). The tissue expression profiles showed that almost all PverOBPs and PverORs were highly expressed in the antennae. In addition, the results revealed that PverOBP10, PverOBP12, PverOBP18, PverOR24, and PverOR35 showed female-biased expression profiles, indicating that these receptors may be involved in some female-specific behaviors such as oviposition site seeking. This work greatly promotes the understanding of the olfactory system and will help provide insight for functional studies of the chemoreception mechanism in P. versicolora. Insects can sense surrounding chemical signals by their accurate chemosensory systems. This system plays a vital role in the life history of insects. Several gene families participate in chemosensory processes, including odorant receptors (ORs), ionotropic receptors (IRs), gustatory receptors (GRs), chemosensory proteins (CSPs), odorant binding proteins (OBPs), and sensory neuron membrane proteins (SNMPs). Plagiodera versicolora (Coleoptera: Chrysomelidae), is a leaf-eating forest pest found in salicaceous trees worldwide. In this study, a transcriptome analysis of male and female adult antennae in P. versicolora individuals was conducted, which identified a total of 98 candidate chemosensory genes including 40 ORs, 7 IRs, 13 GRs, 10 CSPs, 24 OBPs, and 4 SNMPs. Subsequently, the tissue expression profiles of 15 P. versicolora OBPs (PverOBPs) and 39 ORs (PverORs) were conducted by quantitative real-time PCR. The data showed that almost all PverOBPs and PverORs were highly expressed in the male and female antennae. In addition, several OBPs and ORs (PverOBP10, PverOBP12, PverOBP18, PverOR24, and PverOR35) had higher expression levels in female antennae than those in the male antennae, indicating that these genes may be taking part in some female-specific behaviors, such as find mates, oviposition site, etc. This study deeply promotes further understanding of the chemosensory system and functional studies of the chemoreception genes in P. versicolora. [ABSTRACT FROM AUTHOR]

Animals strongly rely on chemical senses to uncover the outside world and adjust their behaviour. Chemical signals are perceived by facial sensitive chemosensors that can be clustered into three families, namely the gustatory (TASR), olfactory (OR, TAAR) and pheromonal (VNR, FPR) receptors. Over recent decades, chemoreceptors were identified in non-facial parts of the body, including the brain. In order to map chemoreceptors within the encephalon, we performed a study based on four brain atlases. The transcript expression of selected members of the three chemoreceptor families and their canonical partners was analysed in major areas of healthy and demented human brains. Genes encoding all studied chemoreceptors are transcribed in the central nervous system, particularly in the limbic system. RNA of their canonical transduction partners (G proteins, ion channels) are also observed in all studied brain areas, reinforcing the suggestion that cerebral chemoreceptors are functional. In addition, we noticed that: (i) bitterness-associated receptors display an enriched expression, (ii) the brain is equipped to sense trace amines and pheromonal cues and (iii) chemoreceptor RNA expression varies with age, but not dementia or brain trauma. Extensive studies are now required to further understand how the brain makes sense of endogenous chemicals. [ABSTRACT FROM AUTHOR]