Drosophila olfactory receptors as classifiers for volatiles from disparate real world applications

Behavioral and physiological responses of Drosophila melanogaster and D. suzukii to volatiles from plant essential oils

BACKGROUND

Insects rely on their sense of smell to locate food and hosts, find mates and select sites for laying eggs. Use of volatile compounds, such as essential oils (EOs), to repel insect pests and disrupt their olfaction-driven behaviors has great practical significance in integrated pest management. However, our knowledge on the olfaction-based mechanisms of EO repellency is quite limited.

RESULTS

We evaluated the repellency of peppermint oil and nine plant EO components in Drosophila melanogaster, a model insect for olfaction study, and D. suzukii, a major fruit crop pest. All nine volatiles, menthone, (-)-menthol, menthyl acetate, (R)-(+)-limonene, nerol, (+)-fenchone, (-)-α-thujone, camphor, norcamphor and peppermint oil, elicited repellency in D. melanogaster in a dose-dependent manner. Most of the compounds, except camphor, also elicited repellency in D. suzukii. Menthone, (R)-(+)-limonene and (+)-fenchone were the most potent repellents against D. suzukii. Repellency was reduced or abolished in two D. melanogaster mutants of the odorant receptor co-receptor (Orco), indicating that the observed repellency is odorant receptor (Or)-mediated. Repellency by peppermint oil, menthone, (R)-(+)-limonene, (-)-α-thujone and norcamphor also involves Or-independent mechanism(s). Single sensillum recording from both species revealed that common and distinct Ors and olfactory receptor neurons were activated by these compounds.

CONCLUSIONS

The tested plant EO components evoke repellency by activating multiple Ors in both Drosophila species. Our study provides a foundation for further elucidation of the mechanism of EOs repellency and species-specific olfactory adaptations. © 2021 Society of Chemical Industry.

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

Insect olfactory communication in a complex and changing world

Insect intraspecific olfactory communication occurs in a complex sensory environment. Here we present recent results on how the olfactory system extracts specific information from a sensory background, and integrates it with complementary information to improve odor source localization. Recent advances on mechanisms of olfactory mixture processing, multi-modal integration, as well as plasticity of sensory processing are reviewed. Significant progress in the understanding of neural coding and molecular bases of olfaction reinforce our perception of the tremendous adaptability of insects to a changing environment. However several reports demonstrate that anthropogenic environmental perturbations interfere with insect olfactory communication and might as a consequence significantly alter the functioning of ecosystems and agroecosystems.

Cystathionine β-synthase Deficiency Impairs Vision in the Fruit Fly, Drosophila melanogaster

PURPOSE

Deficiency in Cystathionine β-synthase (CBS) leads to an abnormal accumulation of homocysteine and results in classical homocystinuria, a multi-systemic disorder that affects connective tissue, muscles, the central nervous system, and the eyes. However, the genetic players and mechanisms underlying vision alterations in patients with homocystinuria are little understood.

MATERIALS AND METHODS

The fruit fly, Drosophila melanogaster, is a useful system to investigate the genetic basis of several human diseases, but no study to date has used Drosophila as model of homocystinuria. Here, we use Drosophila genetic tools to down-regulate CBS expression and evaluate its behavioral response to light.

RESULTS

We show that CBS-deficient flies do not display the normal stereotypical behavior of attraction towards a luminous source, known as phototaxis. This behavior cannot be attributed to a motor or olfactory deficiency, but it is most likely related to a lower visual acuity. CBS-deficient flies are overall smaller, but smaller eyes do not explain their lack of phototactic response.

CONCLUSIONS

The vision phenotype of CBS knock-down flies is consistent with severe myopia in homocystinuria patients. We propose to use Drosophila as a model to investigate ocular manifestations underlying homocystinuria.

Current Source Density Analysis of Electroantennogram Recordings: A Tool for Mapping the Olfactory Response in an Insect Antenna

The set of chemosensory receptors expressed by the olfactory receptor neurons lying in an insect's antennae and maxillary palps define the ability of this insect to perceive the volatile chemicals of its environment. The main two electrophysiological methods of antennal recordings for studying the range of chemicals that activate chemosensory receptors have limitations. Single-sensillum recording (SSR) samples a subset of olfactory receptor neurons and therefore does not reveal the full capacity of an insect to perceive an odor. Electroantennography (EAG), even if less resolutive than SSRs, is sometimes preferred since it samples the activity of a large number of the olfactory receptor neurons. But, at least in flies, the amplitude of the EAG signal is not directly correlated with the degree of sensitivity of the insect to the olfactory compound. Such dual methodology was also used to study mammalian brains, and the current source density (CSD) analysis was developed to bridge the gap between the cellular and the population recordings. This paper details the use of a similar approach adapted to the study of olfactory responses within insects with bulbous antennae. The EAG was recorded at multiple antennal positions and the CSD that generates the EAG potentials were estimated. The method measures the activation of olfactory receptor neurons (ORNs) across the antennae and thus it quantifies the olfactory sensitivity of the insect. It allows a rapid mapping of olfactory responses and thus can be used to guide further SSRs or to determine that two chemicals are detected by independent ORNs. This study further explored biases resulting from a limited number of recording positions or from an approximation of the antennal geometry that should be considered for interpreting the CSD maps. It also shows that the CSD analysis of EAGs is compatible with a gas chromatograph stimulator for analyzing the response to complex odors. Finally, I discuss the origin of the EAG signal in light of the CSD theory.

Artificial selection for odor-guided behavior in Drosophila reveals changes in food consumption

Background

The olfactory system enables organisms to detect chemical cues in the environment and can signal the availability of food or the presence of a predator. Appropriate behavioral responses to these chemical cues are therefore important for organismal survival and can influence traits such as organismal life span and food consumption. However, understanding the genetic mechanisms underlying odor-guided behavior, correlated responses in other traits, and how these constrain or promote their evolution, remain an important challenge. Here, we performed artificial selection for attractive and aversive behavioral responses to four chemical compounds, two aromatics (4-ethylguaiacol and 4-methylphenol) and two esters (methyl hexanoate and ethyl acetate), for thirty generations.

Results

Artificial selection for odor-guided behavior revealed symmetrical responses to selection for each of the four chemical compounds. We then investigated whether selection for odor-guided behavior resulted in correlated responses in life history traits and/or food consumption. We found changes in food consumption upon selection for behavioral responses to aromatics. In many cases, lines selected for increased attraction to aromatics showed an increase in food consumption. We then performed RNA sequencing of lines selected for responses to 4-ethylguaiacol to identify candidate genes associated with odor-guided behavior and its impact on food consumption. We identified 91 genes that were differentially expressed among lines, many of which were associated with metabolic processes. RNAi-mediated knockdown of select candidate genes further supports their role in odor-guided behavior and/or food consumption.

Conclusions

This study identifies novel genes underlying variation in odor-guided behavior and further elucidates the genetic mechanisms underlying the interrelationship between olfaction and feeding.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4233-1) contains supplementary material, which is available to authorized users.

Field-Effect Transistor Biosensor Platform Fused with Drosophila Odorant-Binding Proteins for Instant Ethanol Detection

Odorant-binding proteins (OBPs) have attracted considerable attention as sensing substrates for the development of olfactory biosensors. The Drosophila LUSH protein is an OBP and is known to bind to various alcohols. Technology that uses the LUSH protein has great potential to provide crucial information through odorant detection. In this work, the LUSH protein was used as a sensing substrate to detect the ethanol concentration. Furthermore, we fused the LUSH protein with a silicon-on-insulator (SOI)-based ion-sensitive field-effect transistor (ISFET) to measure the electrical signals that arise from molecular interactions between the LUSH and ethanol. A dual-gate sensing system for self-amplification of the signal resulting from the molecular interaction between the LUSH and ethanol was then used to achieve a much higher sensitivity than a conventional ISFET. In the end, we successfully detected ethanol at concentrations ranging between 0.001 and 1% using the LUSH OBP-fused ISFET olfactory sensor. The OBP-fused SOI-based olfactory ISFET sensor can lead to the development of handheld sensors for various purposes such as detecting toxic chemicals, narcotics control, testing for food freshness, and noninvasive diagnoses.

Advances in explosives analysis--part I: animal, chemical, ion, and mechanical methods

The number and capability of explosives detection and analysis methods have increased substantially since the publication of the Analytical and Bioanalytical Chemistry special issue devoted to Explosives Analysis (Moore and Goodpaster, Anal Bioanal Chem 395(2):245-246, 2009). Here we review and critically evaluate the latest (the past five years) important advances in explosives detection, with details of the improvements over previous methods, and suggest possible avenues towards further advances in, e.g., stand-off distance, detection limit, selectivity, and penetration through camouflage or packaging. The review consists of two parts. This part, Part I, reviews methods based on animals, chemicals (including colorimetry, molecularly imprinted polymers, electrochemistry, and immunochemistry), ions (both ion-mobility spectrometry and mass spectrometry), and mechanical devices. Part II will review methods based on photons, from very energetic photons including X-rays and gamma rays down to the terahertz range, and neutrons.