Sugar detection in 3D: Structure of an insect gustatory receptor.

The insect gustatory receptors (Grs) are one of the largest families of ion channels in the animal kingdom. Frank et al.1 unveil the structure of a fructose-sensing Gr and provide insight into its function.

Base Recording: A Technique for Analyzing Responses of Taste Neurons in Drosophila.

Insects taste the external world through taste hairs, or sensilla, that have pores at their tips. When a sensillum comes into contact with a potential food source, compounds from the food source enter through the pore and activate neurons within. For over 50 years, these responses have been recorded using a technique called tip recording. However, this method has major limitations, including the inability to measure neural activity before or after stimulus contact and the requirement for tastants to be soluble in aqueous solutions. We describe here a technique that we call base recording, which overcomes these limitations. Base recording allows the measurement of taste neuron activity before, during, and after the stimulus. Thus, it allows extensive analysis of OFF responses that occur after a taste stimulus. It can be used to study hydrophobic compounds such as long-chain pheromones that have very low solubility in water. In summary, base recording offers the advantages of single-sensillum electrophysiology as a means of measuring neuronal activity - high spatial and temporal resolution, without the need for genetic tools - and overcomes key limitations of the traditional tip recording technique.

Exitron splicing of odor receptor genes in Drosophila.

Proper expression of odor receptor genes is critical for the function of olfactory systems. In this study, we identified exitrons (exonic introns) in four of the 39 Odorant receptor (Or) genes expressed in the Drosophila antenna. Exitrons are sequences that can be spliced out from within a protein-coding exon, thereby altering the encoded protein. We focused on Or88a, which encodes a pheromone receptor, and found that exitron splicing of Or88a is conserved across five Drosophila species over 20 My of evolution. The exitron was spliced out in 15% of Or88a transcripts. Removal of this exitron creates a non-coding RNA rather than an RNA that encodes a stable protein. Our results suggest the hypothesis that in the case of Or88a, exitron splicing could act in neuronal modulation by decreasing the level of functional Or transcripts. Activation of Or88a-expressing olfactory receptor neurons via either optogenetics or pheromone stimulation increased the level of exitron-spliced transcripts, with optogenetic activation leading to a 14-fold increase. A fifth Or can also undergo an alternative splicing event that eliminates most of the canonical open reading frame. Besides these cases of alternative splicing, we found alternative polyadenylation of four Ors, and exposure of Or67c to its ligand ethyl lactate in the antenna downregulated all of its 3' isoforms. Our study reveals mechanisms by which neuronal activity could be modulated via regulation of the levels of Or isoforms.

Diverse mechanisms of taste coding in Drosophila.

Taste systems encode chemical cues that drive vital behaviors. We have elucidated noncanonical features of taste coding using an unconventional kind of electrophysiological analysis. We find that taste neurons of Drosophila are much more sensitive than previously thought. They have a low spontaneous firing frequency that depends on taste receptors. Taste neurons have a dual function as olfactory neurons: They are activated by most tested odorants, including N,N-diethyl-meta-toluamide (DEET), at a distance. DEET can also inhibit certain taste neurons, revealing that there are two modes of taste response: activation and inhibition. We characterize electrophysiological OFF responses and find that the tastants that elicit them are related in structure. OFF responses link tastant identity to behavior: the magnitude of the OFF response elicited by a tastant correlated with the egg laying behavior it elicited. In summary, the sensitivity and coding capacity of the taste system are much greater than previously known.

Pain: The agony and the AstC.

Pain serves critical biological functions, but under some circumstances it is best suppressed. A new study identifies a channel, a neuropeptide, and a pair of neurons in the fly brain that suppress pain.

The rich non-coding RNA landscape of the Drosophila antenna.

Emerging evidence suggests that long non-coding RNAs (lncRNAs) play diverse and critical roles in neural development, function, and disease. Here, we examine neuronal lncRNAs in a model system that offers enormous advantages for deciphering their functions: the Drosophila olfactory system. This system is numerically simple, its neurons are exquisitely well defined, and it drives multiple complex behaviors. We undertake a comprehensive survey of linear and circular lncRNAs in the Drosophila antenna and identify a wealth of lncRNAs enriched in it. We generate an unprecedented lncRNA-to-neuron map, which reveals that olfactory receptor neurons are defined not only by their receptors but also by the combination of lncRNAs they express. We identify species-specific lncRNAs, including many that are expressed primarily in pheromone-sensing neurons and that may act in modulation of pheromonal responses or in speciation. This resource opens many new opportunities for investigating the roles of lncRNAs in the nervous system.

A volatile sex attractant of tsetse flies.

Tsetse flies transmit trypanosomes-parasites that cause devastating diseases in humans and livestock-across much of sub-Saharan Africa. Chemical communication through volatile pheromones is common among insects; however, it remains unknown if and how such chemical communication occurs in tsetse flies. We identified methyl palmitoleate (MPO), methyl oleate, and methyl palmitate as compounds that are produced by the tsetse fly Glossina morsitans and elicit strong behavioral responses. MPO evoked a behavioral response in male-but not virgin female-G. morsitans. G. morsitans males mounted females of another species, Glossina fuscipes, when they were treated with MPO. We further identified a subpopulation of olfactory neurons in G. morsitans that increase their firing rate in response to MPO and showed that infecting flies with African trypanosomes alters the flies' chemical profile and mating behavior. The identification of volatile attractants in tsetse flies may be useful for reducing disease spread.

Sugar sensation and mechanosensation in the egg-laying preference shift of Drosophila suzukii.

The agricultural pest Drosophila suzukii differs from most other Drosophila species in that it lays eggs in ripe, rather than overripe, fruit. Previously, we showed that changes in bitter taste sensation accompanied this adaptation (Dweck et al., 2021). Here, we show that D. suzukii has also undergone a variety of changes in sweet taste sensation. D. suzukii has a weaker preference than Drosophila melanogaster for laying eggs on substrates containing all three primary fruit sugars: sucrose, fructose, and glucose. Major subsets of D. suzukii taste sensilla have lost electrophysiological responses to sugars. Expression of several key sugar receptor genes is reduced in the taste organs of D. suzukii. By contrast, certain mechanosensory channel genes, including no mechanoreceptor potential C, are expressed at higher levels in the taste organs of D. suzukii, which has a higher preference for stiff substrates. Finally, we find that D. suzukii responds differently from D. melanogaster to combinations of sweet and mechanosensory cues. Thus, the two species differ in sweet sensation, mechanosensation, and their integration, which are all likely to contribute to the differences in their egg-laying preferences in nature.

Meeting a threat of the Anthropocene: Taste avoidance of metal ions by Drosophila.

The Anthropocene Epoch poses a critical challenge for organisms: they must cope with new threats at a rapid rate. These threats include toxic chemical compounds released into the environment by human activities. Here, we examine elevated concentrations of heavy metal ions as an example of anthropogenic stressors. We find that the fruit fly Drosophila avoids nine metal ions when present at elevated concentrations that the flies experienced rarely, if ever, until the Anthropocene. We characterize the avoidance of feeding and egg laying on metal ions, and we identify receptors, neurons, and taste organs that contribute to this avoidance. Different subsets of taste receptors, including members of both Ir (Ionotropic receptor) and Gr (Gustatory receptor) families contribute to the avoidance of different metal ions. We find that metal ions activate certain bitter-sensing neurons and inhibit sugar-sensing neurons. Some behavioral responses are mediated largely through neurons of the pharynx. Feeding avoidance remains stable over 10 generations of exposure to copper and zinc ions. Some responses to metal ions are conserved across diverse dipteran species, including the mosquito Aedes albopictus. Our results suggest mechanisms that may be essential to insects as they face challenges from environmental changes in the Anthropocene.

Ir56b is an atypical ionotropic receptor that underlies appetitive salt response in Drosophila.

Salt taste is one of the most ancient of all sensory modalities. However, the molecular basis of salt taste remains unclear in invertebrates. Here, we show that the response to low, appetitive salt concentrations in Drosophila depends on Ir56b, an atypical member of the ionotropic receptor (Ir) family. Ir56b acts in concert with two coreceptors, Ir25a and Ir76b. Mutation of Ir56b virtually eliminates an appetitive behavioral response to salt. Ir56b is expressed in neurons that also sense sugars via members of the Gr (gustatory receptor) family. Misexpression of Ir56b in bitter-sensing neurons confers physiological responses to appetitive doses of salt. Ir56b is unique among tuning Irs in containing virtually no N-terminal region, a feature that is evolutionarily conserved. Moreover, Ir56b is a "pseudo-pseudogene": its coding sequence contains a premature stop codon that can be replaced with a sense codon without loss of function. This stop codon is conserved among many Drosophila species but is absent in a number of species associated with cactus in arid regions. Thus, Ir56b serves the evolutionarily ancient function of salt detection in neurons that underlie both salt and sweet taste modalities.

Sight of parasitoid wasps accelerates sexual behavior and upregulates a micropeptide gene in Drosophila.

Parasitoid wasps inflict widespread death upon the insect world. Hundreds of thousands of parasitoid wasp species kill a vast range of insect species. Insects have evolved defensive responses to the threat of wasps, some cellular and some behavioral. Here we find an unexpected response of adult Drosophila to the presence of certain parasitoid wasps: accelerated mating behavior. Flies exposed to certain wasp species begin mating more quickly. The effect is mediated via changes in the behavior of the female fly and depends on visual perception. The sight of wasps induces the dramatic upregulation in the fly nervous system of a gene that encodes a 41-amino acid micropeptide. Mutational analysis reveals that the gene is essential to the behavioral response of the fly. Our work provides a foundation for further exploration of how the activation of visual circuits by the sight of a wasp alters both sexual behavior and gene expression.

Evolutionary shifts in taste coding in the fruit pest Drosophila suzukii.

Although most Drosophila species lay eggs in overripe fruit, the agricultural pest Drosophila suzukii lays eggs in ripe fruit. We found that changes in bitter taste perception have accompanied this adaptation. We show that bitter-sensing mutants of Drosophila melanogaster undergo a shift in egg laying preference toward ripe fruit. D. suzukii has lost 20% of the bitter-sensing sensilla from the labellum, the major taste organ of the head. Physiological responses to various bitter compounds are lost. Responses to strawberry purées are lost from two classes of taste sensilla. Egg laying is not deterred by bitter compounds that deter other species. Profiling of labellar transcriptomes reveals reduced expression of several bitter Gr genes (gustatory receptors). These findings support a model in which bitter compounds in early ripening stages deter egg laying in most Drosophila species, but a loss of bitter response contributes to the adaptation of D. suzukii to ripe fruit.

A new agricultural pest has recently emerged in the United States and Northern Europe. The invasive species is a type of fruit fly that normally lives in Southeast Asia called Drosophila suzukii (also known as the spotted wing Drosophila). This fly poses a threat to fruit crops ­ including strawberries, blueberries, cherries, peaches and grapes ­ because, while other fruit flies lay eggs in overripe fruit, D. suzukii lays eggs in ripe fruit, leading to agricultural losses. This shift in where fruit flies prefer to lay their eggs is related to changes in the senses of smell and touch, and taste could also play a role. Insects have evolved mechanisms that dissuade them from eating or laying eggs in plants with high levels of toxins, which taste bitter. If D. suzukii is less sensitive to bitter tastes than other flies, this could help explain why it lays eggs in just-ripe fruit, since the levels of certain bitter compounds are higher in the early stages of ripening than later on. To figure out if this is the case, Dweck et al. studied different species of fruit fly. Compared to Drosophila melanogaster (a fruit fly common in America and Europe that is regularly used in scientific studies), D. suzukii had fewer bitter taste receptor neurons on the major taste organ of the fly head. These receptor neurons were also less responsive to a variety of bitter compounds. Next, Dweck et al. tested whether D. melanogaster and D. suzukii showed different preferences for where to lay their eggs by offering them strawberry purées made from fruit at different ripening stages. In this experiment, D. suzukii preferred to lay its eggs on purées made from unripe or just-ripe strawberries, while D. melanogaster showed a preference for fermented (overripe) purée. Furthermore, when D. melanogaster flies were genetically modified so that they became less sensitive to bitter taste, they preferred to lay their eggs in ripe (rather than overripe) fruit, similar to D. suzukii. These results suggest that taste has a major role in the egg laying preferences of D. suzukii. Further research is needed to determine which bitter compounds influence egg-laying decisions in each species of fruit fly, and what receptors respond to these compounds. However, Dweck et al.'s results lay the groundwork for new approaches to reducing D. suzukii's impact on agriculture.

Technology-enacted abusive supervision and its effect on work and family.

This study examines the effects of technology-enacted abusive supervision, defined as subordinate perceptions of supervisor's use of information and communication technologies (ICTs) to engage in hostile communications. This research was designed to examine if technology-enacted abusive supervision has an impact on both the work and family domains. Based on conservation of resources theory, we theorize that technology-enacted abusive supervision enhances subordinate engagement in emotional labor surface acting, which contributes to emotional exhaustion, which in turn impacts both the work and family domains. Results demonstrate significant paths in both domains. Subordinate perceptions of technology-enacted abusive supervision are positively related to the engagement in technology-enacted incivility through the serial mediation of emotional labor surface acting and emotional exhaustion. Additionally, subordinate perceptions of technology-enacted abusive supervision are positively related to family undermining at home for the subordinate through the serial mediation of emotional labor surface acting, emotional exhaustion, and stress transmission.

The mosquito taste system and disease control.

Mosquitoes are a widely diverse group of organisms, comprising ∼3,500 species that live in an enormous range of habitats. Some species are vectors of diseases that afflict hundreds of millions of people each year. Although understanding of mosquito olfaction has progressed dramatically in recent years, mosquito taste remains greatly understudied. Since taste is essential to feeding, egg laying, and mating decisions in insects, improved understanding of taste in mosquitoes could provide new mechanistic insight into many aspects of their behavior. We provide a guide to current knowledge in the field, and we suggest a wealth of opportunities for research that are now enabled by recent scientific and technological advances. We also propose means by which taste might be exploited in new strategies for mosquito control, which may be urgently needed as the geographical ranges of vector species increase with climate change.

Olfaction: Receptor Antagonistes.

Odor receptors of the mammalian olfactory system have long been known to be activated in combinatorial fashion by odorants. A large-scale study now reveals that inhibition of receptors by odorants is comparably prevalent and combinatorial.

Assessing Discrepancies in Neurocognitive and Patient-Reported Measures of Brain Tumor Survivors.

OBJECTIVES: To examine the association between performance-based neurocognitive and patient-reported cognitive function tests and identify characteristics that may explain observed discrepancies as a means to advance intervention development. SAMPLE & SETTING: 40 adults diagnosed with a primary brain tumor (PBT) (high-grade, n = 35) were recruited from two academic neuro-oncology clinics in North Carolina. METHODS & VARIABLES: Eligibility included a Mini-Mental State Examination score of 24 or greater, having completed cancer treatment, and having tumor stability. Participants completed performance-based neurocognitive and patient-reported cognitive function, demographic, and symptom assessment tests at one time point. RESULTS: Neurocognitive impairments included executive control, memory, and attention. Age, time since diagnosis, and tumor- or treatment-specific variables were not associated with neurocognitive or patient-reported cognitive function. Those reporting worse cognitive impairment tended also to report greater severity of PBT-specific and depressive symptoms. IMPLICATIONS FOR NURSING: Patient-reported cognitive concerns warrant additional assessment for potential interventions to maintain function.

Molecular Logic and Evolution of Bitter Taste in Drosophila.

Taste systems detect a vast diversity of toxins, which are perceived as bitter. When a species adapts to a new environment, its taste system must adapt to detect new death threats. We deleted each of six commonly expressed bitter gustatory receptors (Grs) from Drosophila melanogaster. Systematic analysis revealed that requirements for these Grs differed for the same tastant in different neurons and for different tastants in the same neuron. Responses to some tastants in some neurons required four Grs, including Gr39a. Deletions also produced increased or novel responses, supporting a model of Gr-Gr inhibitory interactions. Coexpression of four Grs conferred several bitter responses to a sugar neuron. We then examined bitter coding in three other Drosophila species. We found major evolutionary shifts. One shift depended on the concerted activity of seven Grs. This work shows how the complex logic of bitter coding provides the capacity to detect innumerable hazards and the flexibility to adapt to new ones.