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

Olfactory receptors evolved to provide animals with ecologically and behaviourally relevant information. The resulting extreme sensitivity and discrimination has proven useful to humans, who have therefore co-opted some animals' sense of smell. One aim of machine olfaction research is to replace the use of animal noses and one avenue of such research aims to incorporate olfactory receptors into artificial noses. Here, we investigate how well the olfactory receptors of the fruit fly, Drosophila melanogaster, perform in classifying volatile odourants that they would not normally encounter. We collected a large number of in vivo recordings from individual Drosophila olfactory receptor neurons in response to an ecologically relevant set of 36 chemicals related to wine ('wine set') and an ecologically irrelevant set of 35 chemicals related to chemical hazards ('industrial set'), each chemical at a single concentration. Resampled response sets were used to classify the chemicals against all others within each set, using a standard linear support vector machine classifier and a wrapper approach. Drosophila receptors appear highly capable of distinguishing chemicals that they have not evolved to process. In contrast to previous work with metal oxide sensors, Drosophila receptors achieved the best recognition accuracy if the outputs of all 20 receptor types were used

Coexpression of Two Functional Odor Receptors in One Neuron

SummaryOne of the most fundamental tenets in the field of olfaction is that each olfactory receptor neuron (ORN) expresses a single odorant receptor. However, the one receptor-one neuron principle is difficult to establish rigorously. Here we construct a receptor-to-neuron map for an entire olfactory organ in Drosophila and find that two receptor genes are coexpressed in one class of ORN. Both receptors are functional in an in vivo expression system, they are only 16% identical in amino acid sequence, and the genes that encode them are unlinked. Most importantly, their coexpression has been conserved for >45 million years. Expression of multiple odor receptors in a cell provides an additional degree of freedom for odor coding

A Screen for Genes Expressed in the Olfactory Organs of Drosophila melanogaster Identifies Genes Involved in Olfactory Behaviour

BACKGROUND: For insects the sense of smell and associated olfactory-driven behaviours are essential for survival. Insects detect odorants with families of olfactory receptor proteins that are very different to those of mammals, and there are likely to be other unique genes and genetic pathways involved in the function and development of the insect olfactory system. METHODOLOGY/PRINCIPAL FINDINGS: We have performed a genetic screen of a set of 505 Drosophila melanogaster gene trap insertion lines to identify novel genes expressed in the adult olfactory organs. We identified 16 lines with expression in the olfactory organs, many of which exhibited expression of the trapped genes in olfactory receptor neurons. Phenotypic analysis showed that six of the lines have decreased olfactory responses in a behavioural assay, and for one of these we showed that precise excision of the P element reverts the phenotype to wild type, confirming a role for the trapped gene in olfaction. To confirm the identity of the genes trapped in the lines we performed molecular analysis of some of the insertion sites. While for many lines the reported insertion sites were correct, we also demonstrated that for a number of lines the reported location of the element was incorrect, and in three lines there were in fact two pGT element insertions. CONCLUSIONS/SIGNIFICANCE: We identified 16 new genes expressed in the Drosophila olfactory organs, the majority in neurons, and for several of the gene trap lines demonstrated a defect in olfactory-driven behaviour. Further characterisation of these genes and their roles in olfactory system function and development will increase our understanding of how the insect olfactory system has evolved to perform the same essential function to that of mammals, but using very different molecular genetic mechanisms

A role for the <i>Drosophila </i>zinc transporter Zip88E in protecting against dietary zinc toxicity

Zinc absorption in animals is thought to be regulated in a local, cell autonomous manner with intestinal cells responding to dietary zinc content. The Drosophila zinc transporter Zip88E shows strong sequence similarity to Zips 42C.1, 42C.2 and 89B as well as mammalian Zips 1, 2 and 3, suggesting that it may act in concert with the apically-localised Drosophila zinc uptake transporters to facilitate dietary zinc absorption by importing ions into the midgut enterocytes. However, the functional characterisation of Zip88E presented here indicates that Zip88E may instead play a role in detecting and responding to zinc toxicity. Larvae homozygous for a null Zip88E allele are viable yet display heightened sensitivity to elevated levels of dietary zinc. This decreased zinc tolerance is accompanied by an overall decrease in Metallothionein B transcription throughout the larval midgut. A Zip88E reporter gene is expressed only in the salivary glands, a handful of enteroendocrine cells at the boundary between the anterior and middle midgut regions, and in two parallel strips of sensory cell projections connecting to the larval ventral ganglion. Zip88E expression solely in this restricted subset of cells is sufficient to rescue the Zip88E mutant phenotype. Together, our data suggest that Zip88E may be functioning in a small subset of cells to detect excessive zinc levels and induce a systemic response to reduce dietary zinc absorption and hence protect against toxicity

Detection of Volatile Indicators of Illicit Substances by the Olfactory Receptors of Drosophila melanogaster

Insects can detect a large range of odors with a numerically simple olfactory system that delivers high sensitivity and accurate discrimination. Therefore, insect olfactory receptors hold great promise as biosensors for detection of volatile organic chemicals in a range of applications. The array of olfactory receptor neurons of Drosophila melanogaster is rapidly becoming the bestcharacterized natural nose. We have investigated the suitability of Drosophila receptors as detectors for volatiles with applications in law enforcement, emergency response, and security. We first characterized responses of the majority of olfactory neuron types to a set of diagnostic odorants. Being thus able to correctly identify neurons, we then screened for responses from 38 different types of neurons to 35 agents. We identified 13 neuron types with responses to 13 agents. As individual Drosophila receptor genes have been mapped to neuron types, we can infer which genes confer responsiveness to the neurons. The responses were confirmed for one receptor by expressing it in a nonresponsive neuron. The fly olfactory system is mainly adapted to detect volatiles from fermenting fruits. However, our findings establish that volatiles associated with illicit substances, many of which are of nonnatural origin, are also detected by Drosophila receptors

<i>Zip88E</i> expression in the <i>Zip88E-GAL4</i> expression domain restores dietary zinc tolerance to <i>Zip88E</i>^<i>Δ/Δ</i> mutants.

<p>Mean survival rate of flies raised from first instar larvae on 4 mmol l^-1 ZnCl₂-supplemented media, relative to survival of the same genotype on basal media. Over expression of <i>Zip88E</i>::<i>eGFP</i> driven by <i>Zip88E-GAL4</i> results in a significant increase in survival of <i>Zip88E</i>^<i>Δ/Δ</i> mutants, back to levels comparable with heterozygote controls. Expression of <i>Zip88E</i>::<i>eGFP</i> transgene in heterozygotes had no effect on zinc tolerance. Values are represented as the mean survival relative to survival on basal media ± SD. Means with the same letter are not significantly different. Means with different letters (i.e. A and B) are significantly different (P≤0.05, Two-way ANOVA, n = 3).</p

Expression of a <i>Zip88E</i> reporter gene is highly restricted.

<p>Expression of membrane-bound mCD8::eGFP driven by <i>Zip88E-GAL4</i> in third instar larval tissues. GFP expression was observed in the salivary glands (A, B = negative control), in the ventral ganglion of the central nervous system (C, D = negative control) and in a small number of enteroendocrine cells just anterior to the copper cell region of the midgut (E). All images were recorded on a compound fluorescence microscope at 10x (A, B, E)) or 20x (C, D) magnification. In A-D), larvae were fixed and immune-stained with an α-GFP antibody followed by an FITC-conjugated secondary antibody. In E), native GFP signal without antibody staining was imaged.</p

<i>Zip88E</i> over expression interacts with other zinc transport gene manipulations to disrupt eye development.

<p><i>GMR-GAL4</i> was used to drive ectopic <i>Zip88E</i>::<i>FLAG</i> expression in the developing <i>Drosophila</i> eye, alone and in combination with the over expression and RNAi (IR) knockdown of various <i>Zip</i> and <i>ZnT</i> genes. A) <i>GMR-GAL4-</i>only control. B) <i>GMR>Zip88E</i>::<i>FLAG</i>. C) <i>GMR>ZipFoi</i>::<i>FLAG</i>. D) <i>GMR>Zip88E</i>::<i>FLAG + ZipFoi</i>::<i>FLAG</i>. E) <i>GMR>Zip48C IR</i>. F) <i>GMR>Zip88E</i>::<i>FLAG + Zip48C IR</i>. G) <i>GMR>ZnT33D</i>::<i>FLAG</i>. H) <i>GMR>Zip88E</i>::<i>FLAG + ZnT33D</i>::<i>FLAG</i>. I) <i>GMR>ZnT63C IR</i>. J) <i>GMR>Zip88E</i>::<i>FLAG + ZnT63C IR</i>.</p