Uridine diphosphate UDP‐glycosyltransferases (UGTs) are detoxification enzymes widely distributed within living organisms. They are involved in the biotransformation of various lipophilic endogenous ...compounds and xenobiotics, including odorants. Several UGTs have been reported in the olfactory organs of mammals and involved in olfactory processing and detoxification within the olfactory mucosa but, in insects, this enzyme family is still poorly studied. Despite recent transcriptomic analyses, the diversity of antennal UGTs in insects has not been investigated. To date, only three UGT cDNAs have been shown to be expressed in insect olfactory organs. In the present study, we report the identification of eleven putative UGTs expressed in the antennae of the model pest insect Spodoptera littoralis. Phylogenetic analysis revealed that these UGTs belong to five different families, highlighting their structural diversity. In addition, two genes, UGT40R3 and UGT46A6, were either specifically expressed or overexpressed in the antennae, suggesting specific roles in this sensory organ. Exposure of male moths to the sex pheromone and to a plant odorant differentially downregulated the transcription levels of these two genes, revealing for the first time the regulation of insect UGTs by odorant exposure. Moreover, the specific antennal gene UGT46A6 was upregulated by insecticide topical application on antennae, suggesting its role in the protection of the olfactory organ towards xenobiotics. This work highlights the structural and functional diversity of UGTs within this highly specialized tissue.
Cytochrome P450 enzymes (P450s) are involved in many physiological functions in insects, such as the metabolism of signal molecules, adaptation to host plants and insecticide resistance. Several ...P450s have been reported in the olfactory organs of insects, the antennae, and have been proposed to play a role in odorant processing and/or xenobiotic metabolism. Despite recent transcriptomic analyses in several species, the diversity of antennal P450s in insects has not yet been investigated. Here, we report the identification of 37 putative P450s expressed in the antennae of the pest moth Spodoptera littoralis, as well as the characterization of a redox partner, cytochrome P450 reductase (CPR). Phylogenetic analysis revealed that S. littoralis P450s belong to four clades defined by their conservation with vertebrate P450s and their cellular localization. Interestingly, the CYP3 and CYP4 clans, which have been described to be mainly involved in the metabolism of plant compounds and xenobiotics, were largely predominant. More surprisingly, two P450s related to ecdysteroid metabolism were also identified. Expression patterns in adult and larval tissues were studied. Eight P450s appeared to be specific to the chemosensory organs, ie the antennae and proboscis, suggesting a specific role in odorant and tastant processing. Moreover, exposure of males to a plant odorant down‐regulated the transcript level of CPR, revealing for the first time the regulation of this gene by odorants within insect antennae. This work suggests that the antennae of insects are a key site for P450‐mediated metabolism of a large range of exogenous and endogenous molecules.
Recent studies have suggested that pheromone-degrading enzymes belonging to the carboxylesterase family could play a role in the dynamics of the olfactory response to acetate sex pheromones in ...insects. Bioinformatic analyses of a male antennal expressed sequence tag library allowed the identification of 19 putative esterase genes expressed in the antennae of the moth Spodoptera littoralis. Phylogenetic analysis revealed that these genes belong to different insect esterase clades, defined by their putative cellular localization and substrate preferences. Interestingly, two of the 19 genes appeared to be antennal specific, suggesting a specific role in olfactory processing. This high esterase diversity suggested that the antennae are the location for intense esterase-based metabolism, against potentially a large range of exogenous and endogenous molecules.
Drosophila melanogaster shows sexually dimorphic cuticular hydrocarbons, with monoenes produced in males and dienes produced in females. Here we describe a female-specific desaturase gene, desatF. ...RNAi knock-down led to a dramatic decrease in female dienes and increase in monoenes paralleled with an increase in copulation latency and a decrease in courtship index and copulation attempts by the males. The desatF gene was also expressed in females from D. sechellia, rich in dienes, but not D. simulans, which produce only monoenes. When hydrocarbons were feminized in D. melanogaster males by targeted expression of the transformer gene, the expression of desatF occurred. These results strongly suggest that desatF is a crucial enzyme for female pheromone biosynthesis and courtship behaviour in D. melanogaster.
Endocrine-disrupting chemicals encompass a variety of chemicals that may interfere with the endocrine system and produce negative effects on organisms. Among them, bisphenol A is considered a major ...pollutant in numerous countries. The harmful effects of BPA on environmental and human health are intensely studied. However, the effects of BPA on terrestrial insects are still poorly investigated, despite that several plants can accumulate BPA in their tissues, leading to potential contamination of herbivorous insects. Here, we used the leafworm Spodoptera littoralis, a polyphagous species, to study BPA effects on post-embryonic development. We studied the effects of BPA ingestion at environmental doses (e.g., 0.01, 0.1, and 1 μg/g of BPA) and high doses (e.g., 25 μg/g) on larval weight and stage duration, pupal length and sex ratio. BPA effects were investigated in more detail during the last larval instar, a crucial period for preparing pupation and metamorphosis, which are under endocrine control. We monitored the haemolymph concentration of ecdysteroids, hormones controlling moult and metamorphosis, as well as the expression levels of several nuclear receptors involved in the ecdysteroid signalling pathway. Our integrative study showed that, upon exposure doses, BPA can induce various effects on the viability, developmental time, growth and sex ratio. These effects were correlated with a delay of the ecdysteroid peak during the last larval instar and a modification of expression of EcR, USP, E75AB, E75D and Br-c. We provide new evidence about the events that occur after BPA exposure in insect contaminated by food ingestion.
•Ingestion of BPA induced effects on mortality, development and growth.•Ingestion of BPA disrupted the ecdysteroid peak in last larval stage.•BPA disrupted the expression of nuclear receptor in last larval stage.
The shrimp Rimicaris exoculata swarms over high-temperature chimneys at Mid-Atlantic Ridge hydrothermal sites, thriving in a mixture of hot vent fluid (350C) and cold seawater (2C). It may, ...therefore, be subjected to a thermal regime that is assumed to be stressful for animals. Evaluating the stress status of species in their natural environment is a key issue for understanding the thermal biology of metazoans. In the case of deep-sea species, attempts to quantify natural levels of stress proteins are obviously impaired by deleterious decompression effects during sampling. Here we quantified the heat shock protein (hsp70) mRNA expression of shrimps sampled at a depth of 2300 m and recovered at their native pressure. These shrimps were not heat-stressed, as witnessed by their very low level of heat-inducible hsp70, while an important response was evidenced after an experimental 30C exposure. Our data also indicate that R. exoculata was nevertheless attracted by the temperature of fluid emission, and would deal with the harsh thermal conditions through microhabitat selection close to its thermal preferendum (10 to 25C).
Odorant-Degrading Enzymes (ODEs) are supposed to be involved in the signal inactivation step within the olfactory sensilla of insects by quickly removing odorant molecules from the vicinity of the ...olfactory receptors. Only three ODEs have been both identified at the molecular level and functionally characterized: two were specialized in the degradation of pheromone compounds and the last one was shown to degrade a plant odorant.
Previous work has shown that the antennae of the cotton leafworm Spodoptera littoralis, a worldwide pest of agricultural crops, express numerous candidate ODEs. We focused on an esterase overexpressed in males antennae, namely SlCXE7. We studied its expression patterns and tested its catalytic properties towards three odorants, i.e. the two female sex pheromone components and a green leaf volatile emitted by host plants.
SlCXE7 expression was concomitant during development with male responsiveness to odorants and during adult scotophase with the period of male most active sexual behaviour. Furthermore, SlCXE7 transcription could be induced by male exposure to the main pheromone component, suggesting a role of Pheromone-Degrading Enzyme. Interestingly, recombinant SlCXE7 was able to efficiently hydrolyze the pheromone compounds but also the plant volatile, with a higher affinity for the pheromone than for the plant compound. In male antennae, SlCXE7 expression was associated with both long and short sensilla, tuned to sex pheromones or plant odours, respectively. Our results thus suggested that a same ODE could have a dual function depending of it sensillar localisation. Within the pheromone-sensitive sensilla, SlCXE7 may play a role in pheromone signal termination and in reduction of odorant background noise, whereas it could be involved in plant odorant inactivation within the short sensilla.
Moth sex pheromone communication is recognised as a long‐standing model for insect olfaction studies, and a widespread knowledge has been accumulated on this subject thanks to numerous chemical, ...electrophysiological and behavioural studies. A key step has been the identification of candidate sex pheromone receptors, opening new routes to understanding the specificity and sensitivity of this communication system, but only few of these receptors have as yet been functionally characterised. In this context, we aim at unravelling the molecular bases of pheromone reception in the noctuid moth Spodoptera littoralis. Taking advantage of a collection of antennal‐expressed sequence tags, we previously identified three fragments of candidate pheromone receptors in this species. Here, we report full‐length cloning of one of these receptors, named SlitOR6. Both sequence and expression pattern analyses were consistent with its annotation as a pheromone receptor, which we further confirmed by functional characterization. Using Drosophila antennae as a heterologous expression system, we identified a single component of the pheromone blend of S. littoralis, (Z,E)‐9,12‐tetradecadienyl acetate, as the ligand of SlitOR6. Two strategies were employed: (i) expressing SlitOR6 in the majority of Drosophila olfactory neurons, in addition to endogenous receptors, and monitoring the responses to pheromone stimuli by electroantennography; (ii) replacing the Drosophila pheromone receptor OR67d with SlitOR6 and monitoring the response by single sensillum recordings. Results were fully congruent and responses to (Z,E)‐9,12‐tetradecadienyl acetate were highly specific in both heterologous systems. This approach appears to be efficient and reliable for studying moth pheromone receptors in an in vivo context.
A candidate pheromone receptor of the noctuid moth Spodoptera littoralis, was deorphanised using Drosophila antennae as a heterologous expression system. We identified a single component of the pheromone blend of S. littoralis, (Z,E)‐9,12‐tetradecadienyl acetate, as the ligand of this receptor, named SlitOR6. To our knowledge, we report here the first de novo deorphanization of an odorant receptor outside Diptera using heterologous expression in Drosophila.
We have identified an elongase gene,
elo68α, which is specifically transcribed in males. We have characterized the
elo68α open reading frame, expressed it in
fasΔ elo1Δ yeast and showed that it could ...elongate myristoleic and palmitoleic acids, therefore sharing an Elo1 specificity. This elongase was found to be exclusively expressed in male genital system (testis and ejaculatory bulb). Northern blot analysis showed that the
elo68α gene was inducible at low temperatures. One
P-strain mutant for
elo68α and three excision lines for this
P-element were subsequently studied. The excision line with only 1%
elo68α expression showed decreased levels of vaccenyl acetate, a male pheromone produced in the ejaculatory bulb. The induction of
elo68α expression at 21
°C was also paralleled with higher vaccenyl acetate production. These results strongly suggest that
elo68α is involved in the elongation of short unsaturated fatty acids in males and might play a role in vaccenyl acetate biosynthesis.
Alvinocaridid shrimps are emblematic representatives of the deep hydrothermal vent fauna at the Mid-Atlantic Ridge. They are adapted to a mostly aphotic habitat with extreme physicochemical ...conditions in the vicinity of the hydrothermal fluid emissions. Here, we investigated the brain architecture of the vent shrimp
to understand possible adaptations of its nervous system to the hydrothermal sensory landscape. Its brain is modified from the crustacean brain ground pattern by featuring relatively small visual and olfactory neuropils that contrast with well-developed higher integrative centers, the hemiellipsoid bodies. We propose that these structures in vent shrimps may fulfill functions in addition to higher order sensory processing and suggest a role in place memory. Our study promotes vent shrimps as fascinating models to gain insights into sensory adaptations to peculiar environmental conditions, and the evolutionary transformation of specific brain areas in Crustacea.
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