Transcriptional basis of the acclimation to high environmental temperature at the olfactory receptor organs of Drosophila melanogaster

Temperature-dependent modulation of odor-dependent behavior in three drosophilid fly species of differing thermal preference

Rapid and ongoing climate change increases global temperature, impacts feeding, and reproduction in insects. The olfaction plays an important underlying role in these behaviors in most insect species. Here, we investigated how changing temperatures affect odor detection and ensuing behavior in three drosophilid flies: Drosophila novamexicana, D. virilis and D. ezoana, species adapted to life in desert, global, and subarctic climates, respectively. Using a series of thermal preference assays, we confirmed that the three species indeed exhibit distinct temperature preferences. Next, using single sensillum recording technique, we classified olfactory sensory neurons (OSNs) present in basiconic sensilla on the antenna of the three species and thereby identified ligands for each OSN type. In a series of trap assays we proceeded to establish the behavioral valence of the best ligands and chose guaiacol, methyl salicylate and isopropyl benzoate as representatives of a repellent, attractant and neutral odor. Next, we assessed the behavioral valence of these three odors in all three species across a thermal range (10-35 °C), with flies reared at 18 °C and 25 °C. We found that both developmental and experimental temperatures affected the behavioral performance of the flies. Our study thus reveals temperature-dependent changes in odor-guided behavior in drosophilid flies.

Natural variation in the maternal and zygotic mRNA complements of the early embryo in Drosophila melanogaster

Background

Maternal gene products supplied to the egg during oogenesis drive the earliest events of development in all metazoans. After the initial stages of embryogenesis, maternal transcripts are degraded as zygotic transcription is activated; this is known as the maternal to zygotic transition (MZT). Recently, it has been shown that the expression of maternal and zygotic transcripts have evolved in the Drosophila genus over the course of 50 million years. However, the extent of natural variation of maternal and zygotic transcripts within a species has yet to be determined. We asked how the maternal and zygotic pools of mRNA vary within and between populations of D. melanogaster. In order to maximize sampling of genetic diversity, African lines of D. melanogaster originating from Zambia as well as DGRP lines originating from North America were chosen for transcriptomic analysis.

Results

Generally, we find that maternal transcripts are more highly conserved, and zygotic transcripts evolve at a higher rate. We find that there is more within-population variation in transcript abundance than between populations and that expression variation is highest post- MZT between African lines.

Conclusions

Determining the natural variation of gene expression surrounding the MZT in natural populations of D. melanogaster gives insight into the extent of how a tightly regulated process may vary within a species, the extent of developmental constraint at both stages and on both the maternal and zygotic genomes, and reveals expression changes allowing this species to adapt as it spread across the world.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08839-4.

Peppers in Diet: Genome-Wide Transcriptome and Metabolome Changes in Drosophila melanogaster

The habanero pepper (Capsicum chinense) is an increasingly important spice and vegetable crop worldwide because of its high capsaicin content and pungent flavor. Diets supplemented with the phytochemicals found in habanero peppers might cause shifts in an organism’s metabolism and gene expression. Thus, understanding how these interactions occur can reveal the potential health effects associated with such changes. We performed transcriptomic and metabolomic analyses of Drosophila melanogaster adult flies reared on a habanero pepper diet. We found 539 genes/59 metabolites that were differentially expressed/accumulated in flies fed a pepper versus control diet. Transcriptome results indicated that olfactory sensitivity and behavioral responses to the pepper diet were mediated by olfactory and nutrient-related genes including gustatory receptors (Gr63a, Gr66a, and Gr89a), odorant receptors (Or23a, Or59a, Or82a, and Orco), and odorant-binding proteins (Obp28a, Obp83a, Obp83b, Obp93a, and Obp99a). Metabolome analysis revealed that campesterol, sitosterol, and sucrose were highly upregulated and azelaic acid, ethyl phosphoric acid, and citric acid were the major metabolites downregulated in response to the habanero pepper diet. Further investigation by integration analysis between transcriptome and metabolome data at gene pathway levels revealed six unique enriched pathways, including phenylalanine metabolism; insect hormone biosynthesis; pyrimidine metabolism; glyoxylate, and dicarboxylate metabolism; glycine, serine, threonine metabolism; and glycerolipid metabolism. In view of the transcriptome and metabolome findings, our comprehensive analysis of the response to a pepper diet in Drosophila have implications for exploring the molecular mechanism of pepper consumption.

Combined responses of primary coral polyps and their algal endosymbionts to decreasing seawater pH

With coral reefs declining globally, resilience of these ecosystems hinges on successful coral recruitment. However, knowledge of the acclimatory and/or adaptive potential in response to environmental challenges such as ocean acidification (OA) in earliest life stages is limited. Our combination of physiological measurements, microscopy, computed tomography techniques and gene expression analysis allowed us to thoroughly elucidate the mechanisms underlying the response of early-life stages of corals, together with their algal partners, to the projected decline in oceanic pH. We observed extensive physiological, morphological and transcriptional changes in surviving recruits, and the transition to a less-skeleton/more-tissue phenotype. We found that decreased pH conditions stimulate photosynthesis and endosymbiont growth, and gene expression potentially linked to photosynthates translocation. Our unique holistic study discloses the previously unseen intricate net of interacting mechanisms that regulate the performance of these organisms in response to OA.

Vestigial suppresses apoptosis and cell migration in a manner dependent on the level of JNK-Caspase signaling in the Drosophila wing disc

The Decapentaplegic (Dpp) and Wingless (Wg) signal pathways play important roles in numerous biological processes in Drosophila. The Drosophila vestigial (vg) gene is selectively required for wing imaginal disc cell proliferation, which is essential for the formation of the adult wing and halter structures, and is regulated by Dpp and Wg signaling. Using a Drosophila invasion model of wing epithelium, we showed herein that inhibition of Dpp or Wg signaling promoted cells to migrate across the cell lineage restrictive anterior/posterior (A/P) compartment boundary. Being downstream of both Dpp and Wg signaling, vg can block cell migration induced by loss of either pathway. In addition, suppression of vg is sufficient to induce cell migration across the A/P boundary. Transcriptomic analysis revealed potential downstream genes involved in the cell migration after suppressing vg in the wing disc. We further demonstrated that the c-Jun N-terminal kinase (JNK) signaling promoted cell migration induced by vg suppression by upregulating Caspase activity. Taken together, our results revealed the requirement of Vg for suppressing cell migration and clarified how developmental signals collaborate to stabilize cells along the compartment boundary.

Interpopulational Variations of Odorant-Binding Protein Expression in the Black Cutworm Moth, Agrotis ipsilon

Simple Summary

Odorant-binding proteins (OBPs) are small soluble transporter proteins that are believed to play a key role in insect olfaction. However, there is an emerging set of data that shows a role in insecticide resistance for similar families of binding proteins. The black cutworm Agrotis ipsilon is a migrant species of moth known to feed on multiple types of crops (polyphagous) worldwide. It is therefore likely that the olfactory system of this species can be modulated to adapt to different environments. We compared gene expression between American and European continental populations of the moth. We found continental-specific expression of antennal binding protein X (ABPX) and general odorant-binding protein 2 (GOBP2), suggesting a function of these proteins in migration, environment recognition, crop change and adaptation that are required for a polyphagous species such as A. ipsilon.

Abstract

A long-range migrant species of moth (Agrotis ipsilon) has served as a model to compare the expression profiles of antennal proteins between different continental populations. Our results showed that the American and French populations of the black cutworm moth, A. ipsilon, expressed the same odorant-binding proteins (OBPs), but apparently in different levels. Electrophoretic analysis of antennal protein profiles and reverse transcription polymerase chain reaction using RNA as a template showed significant differences between the two populations in the expression of antennal binding protein-X (ABPX) and general odorant-binding protein-2 (GOBP2). However, the two A. ipsilon populations showed no differences in RNA levels coding for pheromone binding proteins (PBPs), suggesting that the expression of generalist OBPs is population-specific and could be affected by specific odor and/or chemical changes in external environmental conditions. To support the role of ABPX and GOBP2 with expression, the role of ABPX and GOBP2 is discussed in regard to odor detection, memorization and/or degradation of toxic chemical insecticides.

Identification of olfactory genes of a forensically important blow fly, Aldrichina grahami (Diptera: Calliphoridae)

Background

The time-length between the first colonization of necrophagous insect on the corpse and the beginning of investigation represents the most important forensic concept of minimum post-mortem inference (PMImin). Before colonization, the time spent by an insect to detect and locate a corpse could significantly influence the PMImin estimation. The olfactory system plays an important role in insect food foraging behavior. Proteins like odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs) and sensory neuron membrane proteins (SNMPs) represent the most important parts of this system. Exploration of the above genes and their necrophagous products should facilitate not only the understanding of their roles in forging but also their influence on the period before PMImin. Transcriptome sequencing has been wildly utilized to reveal the expression of particular genes under different temporal and spatial condition in a high throughput way. In this study, transcriptomic study was implemented on antennae of adult Aldrichina grahami (Aldrich) (Diptera: Calliphoridae), a necrophagous insect with forensic significance, to reveal the composition and expression feature of OBPs, CSPs, ORs, IRs and SNMPs genes at transcriptome level.

Method

Antennae transcriptome sequencing of A. grahami was performed using next-generation deep sequencing on the platform of BGISEQ-500. The raw data were deposited into NCBI (PRJNA513084). All the transcripts were functionally annotated using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Differentially expressed genes (DEGs) were analyzed between female and male antennae. The transcripts of OBPs, CSPs, ORs, IRs and SNMPs were identified based on sequence feature. Phylogenetic development of olfactory genes of A. grahami with other species was analyzed using MEGA 5.0. RT-qPCR was utilized to verify gene expression generated from the transcriptome sequencing.

Results

In total, 14,193 genes were annotated in the antennae transcriptome based on the GO and the KEGG databases. We found that 740 DEGs were differently expressed between female and male antennae. Among those, 195 transcripts were annotated as candidate olfactory genes then checked by sequence feature. Of these, 27 OBPs, one CSPs, 49 ORs, six IRs and two SNMPs were finally identified in antennae of A. grahami. Phylogenetic development suggested that some olfactory genes may play a role in food forging, perception of pheromone and decomposing odors.

Conclusion

Overall, our results suggest the existence of gender and spatial expression differences in olfactory genes from antennae of A. grahami. Such differences are likely to greatly influence insect behavior around a corpse. In addition, candidate olfactory genes with predicted function provide valuable information for further studies of the molecular mechanisms of olfactory detection of forensically important fly species and thus deepen our understanding of the period before PMImin.

Comparative transcriptome analysis of the rice leaf folder (Cnaphalocrocis medinalis) to heat acclimation

Background

The rice leaf folder Cnaphalocrocis medinalis Güenée is a serious insect pest of rice in Asia. This pest occurs in summer, and it is sensitive to high temperature. However, the larvae exhibit heat acclimation/adaptation. To understand the underlying mechanisms, we established a heat-acclimated strain via multigenerational selection at 39 °C. After heat shock at 41 °C for 1 h, the transcriptomes of the heat-acclimated (S-39) and unacclimated (S-27) larvae were sequenced, using the unacclimated larvae without exposure to 41 °C as the control.

Results

Five generations of selection at 39 °C led larvae to acclimate to this heat stress. Exposure to 41 °C induced 1160 differentially expressed genes (DEGs) between the heat-acclimated and unacclimated larvae. Both the heat-acclimated and unacclimated larvae responded to heat stress via upregulating genes related to sensory organ development and structural constituent of eye lens, whereas the unacclimated larvae also upregulated genes related to structural constituent of cuticle. Compared to unacclimated larvae, heat-acclimated larvae downregulated oxidoreductase activity-related genes when encountering heat shock. Both the acclimated and unacclimated larvae adjusted the longevity regulating, protein processing in endoplasmic reticulum, antigen processing and presentation, MAPK and estrogen signaling pathway to responsed to heat stress. Additionally, the unacclimated larvae also adjusted the spliceosome pathway, whereas the heat-acclimated larvae adjusted the biosynthesis of unsaturated fatty acids pathway when encountering heat stress. Although the heat-acclimated and unacclimated larvae upregulated expression of heat shock protein genes under heat stress including HSP70, HSP27 and CRYAB, their biosynthesis, metabolism and detoxification-related genes expressed differentially.

Conclusions

The rice leaf folder larvae could acclimate to a high temperature via multigenerational heat selection. The heat-acclimated larvae induced more DEGs to response to heat shock than the unacclimated larvae. The changes in transcript level of genes were related to heat acclimation of larvae, especially these genes in sensory organ development, structural constituent of eye lens, and oxidoreductase activity. The DEGs between heat-acclimated and unacclimated larvae after heat shock were enriched in the biosynthesis and metabolism pathways. These results are helpful to understand the molecular mechanism underlying heat acclimation of insects.

Behavioral and Transcriptional Response to Selection for Olfactory Behavior in Drosophila

The detection, discrimination, and behavioral responses to chemical cues in the environment can have marked effects on organismal survival and reproduction, eliciting attractive or aversive behavior. To gain insight into mechanisms mediating this hedonic valence, we applied thirty generations of divergent artificial selection for Drosophila melanogaster olfactory behavior. We independently selected for positive and negative behavioral responses to two ecologically relevant chemical compounds: 2,3-butanedione and cyclohexanone. We also tested the correlated responses to selection by testing behavioral responses to other odorants and life history traits. Measurements of behavioral responses of the selected lines and unselected controls to additional odorants showed that the mechanisms underlying responses to these odorants are, in some cases, differentially affected by selection regime and generalization of the response to other odorants was only detected in the 2,3-butanedione selection lines. Food consumption and lifespan varied with selection regime and, at times, sex. An analysis of gene expression of both selection regimes identified multiple differentially expressed genes. New genes and genes previously identified in mediating olfactory behavior were identified. In particular, we found functional enrichment of several gene ontology terms, including cell-cell adhesion and sulfur compound metabolic process, the latter including genes belonging to the glutathione S-transferase family. These findings highlight a potential role for glutathione S-transferases in the evolution of hedonic valence to ecologically relevant volatile compounds and set the stage for a detailed investigation into mechanisms by which these genes mediate attraction and aversion.

The Effects of High Fat Diet-Induced Stress on Olfactory Sensitivity, Behaviors, and Transcriptional Profiling in Drosophila melanogaster

High-fat diet (HFD) often causes obesity and it has detrimental effects on the sensory system. In particular, sensory-mediated responses are crucial for maintaining energy balance, as they are involved in a metabolic regulation; however, there is still no clear explanation about the relationship between HFD-induced stress and sensory system. To gain insight on how HFD-induced stress affects olfactory sensitivity and behavioral responses, we have used a Drosophila melanogaster model for olfactory and nutrient-related signaling and accessed physiological, behavioral, and transcriptional changes. We demonstrated that lifespan and climbing ability in HFD-treated flies decreased and that olfactory sensitivity and behavioral responses to odorants were changed. Olfactory sensitivity to eight of ten odorants after 14 days on HFD treatment were reduced, while behavioral attraction was increased to benzaldehyde in flies that were treated with HFD. This behavioral and physiological modification in HFD-treated flies for 14 days was accompanied by a significant decrease in DmOrco gene expression in a peripheral olfactory organ, suggesting that is could be involved in the action of metabolic and sensory signal. Gene expression profiles of antennae showed significant differences on the olfactory receptors, odorant-binding proteins, and insulin signaling. Our results suggested that olfactory sensitivity and behavioral responses to HFD-induced stress are mediated through olfactory and nutrient-related signaling pathways.

The Two Main Olfactory Receptor Families in Drosophila, ORs and IRs: A Comparative Approach

Most insect species rely on the detection of olfactory cues for critical behaviors for the survival of the species, e.g., finding food, suitable mates and appropriate egg-laying sites. Although insects show a diverse array of molecular receptors dedicated to the detection of sensory cues, two main types of molecular receptors have been described as responsible for olfactory reception in Drosophila, the odorant receptors (ORs) and the ionotropic receptors (IRs). Although both receptor families share the role of being the first chemosensors in the insect olfactory system, they show distinct evolutionary origins and several distinct structural and functional characteristics. While ORs are seven-transmembrane-domain receptor proteins, IRs are related to the ionotropic glutamate receptor (iGluR) family. Both types of receptors are expressed on the olfactory sensory neurons (OSNs) of the main olfactory organ, the antenna, but they are housed in different types of sensilla, IRs in coeloconic sensilla and ORs in basiconic and trichoid sensilla. More importantly, from the functional point of view, they display different odorant specificity profiles. Research advances in the last decade have improved our understanding of the molecular basis, evolution and functional roles of these two families, but there are still controversies and unsolved key questions that remain to be answered. Here, we present an updated review on the advances of the genetic basis, evolution, structure, functional response and regulation of both types of chemosensory receptors. We use a comparative approach to highlight the similarities and differences among them. Moreover, we will discuss major open questions in the field of olfactory reception in insects. A comprehensive analysis of the structural and functional convergence and divergence of both types of receptors will help in elucidating the molecular basis of the function and regulation of chemoreception in insects.

Inter and Intraspecific Genomic Divergence in Drosophila montana Shows Evidence for Cold Adaptation

The genomes of species that are ecological specialists will likely contain signatures of genomic adaptation to their niche. However, distinguishing genes related to ecological specialism from other sources of selection and more random changes is a challenge. Here, we describe the genome of Drosophila montana, which is the most extremely cold-adapted Drosophila species known. We use branch tests to identify genes showing accelerated divergence in contrasts between cold- and warm-adapted species and identify about 250 genes that show differences, possibly driven by a lower synonymous substitution rate in cold-adapted species. We also look for evidence of accelerated divergence between D. montana and D. virilis, a previously sequenced relative, but do not find strong evidence for divergent selection on coding sequence variation. Divergent genes are involved in a variety of functions, including cuticular and olfactory processes. Finally, we also resequenced three populations of D. montana from across its ecological and geographic range. Outlier loci were more likely to be found on the X chromosome and there was a greater than expected overlap between population outliers and those genes implicated in cold adaptation between Drosophila species, implying some continuity of selective process at these different evolutionary scales.

Tuning Insect Odorant Receptors

Among the insect olfactory receptors the odorant receptors (ORs) evolved in parallel to the onset of insect flight. A special property of this receptor type is the capability to adjust sensitivity of odor detection according to previous odor contacts. This article presents a current view on regulatory processes affecting the performance of ORs and proposes a model of mechanisms contributing to OR sensitization.

Chemosensory genes in the antennal transcriptome of two syrphid species, Episyrphus balteatus and Eupeodes corollae (Diptera: Syrphidae)

BACKGROUND

Predatory syrphid larvae are an important natural enemy of aphids in cotton agro-ecosystems in China. Their behaviors in prey foraging, localization and oviposition greatly rely on the perception of chemical cues. As a first step to better understand syrphid olfaction at the molecular level, we have performed a systematic identification of their major chemosensory genes.

RESULTS

Male and female antennal transcriptomes of Episyrphus balteatus and Eupeodes corollae were sequenced and assembled using Illumina HiSeq2000 technology. A total of 154 chemosensory genes in E. balteatus transcriptome, including candidate 51 odorant receptors (ORs), 32 ionotropic receptors (IRs), 14 gustatory receptors (GRs), 49 odorant-binding proteins (OBPs), 6 chemosensory proteins (CSPs) and 2 sensory neuron membrane proteins (SNMPs) were identified. In E. corollae transcriptome, we identified 134 genes including 42 ORs, 23 IRs, 16 GRs, 44 OBPs, 7 CSPs and 2 SNMPs. We have provided full-length sequences of the highly conserved co-receptor Orco, IR8a/25a family and carbon dioxide gustatory receptor in both syrphid species. The expression of candidate OR genes in the two syrphid species was evaluated by semi-quantitative reverse transcription PCR. There were no significant differences of transcript abundances in the respective male and female antenna, which is consistent with differentially expressed genes (DEGs) analysis using the FPKM value. The sequences of candidate chemosensory genes were confirmed and phylogenetic analysis was performed.

CONCLUSIONS

This research comprehensively analyzed and identified many novel candidate chemosensory genes regarding syrphid olfaction. It provides an opportunity for understanding how syrphid insects use chemical cues to conduct their behaviors among tritrophic interactions of plants, herbivorous insects, and natural enemies in agricultural ecosystems.

Olfactory Receptors in Non-Chemosensory Organs: The Nervous System in Health and Disease

Olfactory receptors (ORs) and down-stream functional signaling molecules adenylyl cyclase 3 (AC3), olfactory G protein α subunit (Gαolf), OR transporters receptor transporter proteins 1 and 2 (RTP1 and RTP2), receptor expression enhancing protein 1 (REEP1), and UDP-glucuronosyltransferases (UGTs) are expressed in neurons of the human and murine central nervous system (CNS). In vitro studies have shown that these receptors react to external stimuli and therefore are equipped to be functional. However, ORs are not directly related to the detection of odors. Several molecules delivered from the blood, cerebrospinal fluid, neighboring local neurons and glial cells, distant cells through the extracellular space, and the cells’ own self-regulating internal homeostasis can be postulated as possible ligands. Moreover, a single neuron outside the olfactory epithelium expresses more than one receptor, and the mechanism of transcriptional regulation may be different in olfactory epithelia and brain neurons. OR gene expression is altered in several neurodegenerative diseases including Parkinson’s disease (PD), Alzheimer’s disease (AD), progressive supranuclear palsy (PSP) and sporadic Creutzfeldt-Jakob disease (sCJD) subtypes MM1 and VV2 with disease-, region- and subtype-specific patterns. Altered gene expression is also observed in the prefrontal cortex in schizophrenia with a major but not total influence of chlorpromazine treatment. Preliminary parallel observations have also shown the presence of taste receptors (TASRs), mainly of the bitter taste family, in the mammalian brain, whose function is not related to taste. TASRs in brain are also abnormally regulated in neurodegenerative diseases. These seminal observations point to the need for further studies on ORs and TASRs chemoreceptors in the mammalian brain.

Gene set of chemosensory receptors in the polyembryonic endoparasitoid Macrocentrus cingulum

Insects are extremely successful animals whose odor perception is very prominent due to their sophisticated olfactory system. The main chemosensory organ, antennae play a critical role in detecting odor in ambient environment before initiating appropriate behavioral responses. The antennal chemosensory receptor genes families have been suggested to be involved in olfactory signal transduction pathway as a sensory neuron response. The Macrocentrus cingulum is deployed successfully as a biological control agent for corn pest insects from the Lepidopteran genus Ostrinia. In this research, we assembled antennal transcriptomes of M. cingulum by using next generation sequencing to identify the major chemosensory receptors gene families. In total, 112 olfactory receptors candidates (79 odorant receptors, 20 gustatory receptors, and 13 ionotropic receptors) have been identified from the male and female antennal transcriptome. The sequences of all of these transcripts were confirmed by RT-PCR, and direct DNA sequencing. Expression profiles of gustatory receptors in olfactory and non-olfactory tissues were measured by RT-qPCR. The sex-specific and sex-biased chemoreceptors expression patterns suggested that they may have important functions in sense detection which behaviorally relevant to odor molecules. This reported result provides a comprehensive resource of the foundation in semiochemicals driven behaviors at molecular level in polyembryonic endoparasitoid.

Identification and preliminary characterization of chemosensory perception-associated proteins in the melon fly Bactrocera cucurbitae using RNA-seq

An investigation into proteins involved in chemosensory perception in the melon fly, Bactrocera cucurbitae (Diptera: Tephritidae) is described here using a newly generated transcriptome dataset. The melon fly is a major agricultural pest, widely distributed in the Asia-Pacific region and some parts of Africa. For this study, a transcriptome dataset was generated using RNA extracted from 4-day-old adult specimens of the melon fly. The dataset was assembled and annotated via Gene Ontology (GO) analysis. Based on this and similarity searches to data from other species, a number of protein sequences putatively involved in chemosensory reception were identified and characterized in the melon fly. This included the highly conserved "Orco" along with a number of other less conserved odorant binding protein sequences. In addition, several sequences representing putative ionotropic and gustatory receptors were also identified. This study provides a foundation for future functional studies of chemosensory proteins in the melon fly and for making more detailed comparisons to other species. In the long term, this will ultimately help in the development of improved tools for pest management.

Freeze-thaw Caenorhabditis elegans freeze-thaw stress response is regulated by the insulin/IGF-1 receptor daf-2

BACKGROUND

Adaption to cold temperatures, especially those below freezing, is essential for animal survival in cold environments. Freezing is also used for many medical, scientific, and industrial purposes. Natural freezing survival in animals has been extensively studied. However, the underlying mechanisms remain unclear. Previous studies demonstrated that animals survive in extremely cold weather by avoiding freezing or controlling the rate of ice-crystal formation in their bodies, which indicates that freezing survival is a passive thermodynamic process.

RESULTS

Here, we showed that genetic programming actively promotes freezing survival in Caenorhabditis elegans. We found that daf-2, an insulin/IGF-1 receptor homologue, and loss-of-function enhanced survival during freeze-thaw stress, which required the transcription factor daf-16/FOXO and age-independent target genes. In particular, the freeze-thaw resistance of daf-2(rf) is highly allele-specific and has no correlation with lifespan, dauer formation, or hypoxia stress resistance.

CONCLUSIONS

Our results reveal a new function for daf-2 signaling, and, most importantly, demonstrate that genetic programming contributes to freezing survival.

Task-related differential expression of four cytochrome P450 genes in honeybee appendages

In insects, cytochrome P450 monooxygenases (P450s) contribute to phytochemical and pheromone clearance in chemoreception and xenobiotic detoxification in food processing. In eusocial species, P450 expression varies with anatomy and age-related behaviour. Adult honeybees (Apis mellifera) possess appendages differentially equipped for chemoreception; antennae and prothoracic and mesothoracic legs assess food and pheromone signals whereas metathoracic legs transport pollen over long distances. Newly eclosed bees and nurses remain in the hive and neither gather nor process food, whereas foragers collect pollen and nectar, thereby encountering phytochemicals. To understand the functions of cytochrome P450, family 4, subfamily G, polypeptide 11 (CYP4G11) in the honeybee genome, we compared its expression relative to worker age and task to expression of cytochrome P450, family 9, subfamily Q, polypeptides (CYP9Qs) known to metabolize xenobiotics. That CYP4G11 is highly expressed in forager antennae and legs, with highest expression in prothoracic and mesothoracic legs, is consistent with chemosensory perception, whereas weak expression of CYP4G11 in nurses suggests that it may process primarily exogenous rather than endogenous chemical signals. By contrast, and consistent with xenobiotic detoxification, the three CYP9Q transcripts were almost undetectable in newly eclosed workers and highest in foragers, with maximal expression in the metathoracic legs that closely contact pollen phytochemicals. These CYP4G11 expression patterns suggest a role in processing environmental signals, particularly those associated with food.

Chemosensory genes identified in the antennal transcriptome of the blowfly Calliphora stygia

BACKGROUND

Blowflies have relevance in areas of forensic science, agriculture, and medicine, primarily due to the ability of their larvae to develop on flesh. While it is widely accepted that blowflies rely heavily on olfaction for identifying and locating hosts, there is limited research regarding the underlying molecular mechanisms. Using next generation sequencing (Illumina), this research examined the antennal transcriptome of Calliphora stygia (Fabricius) (Diptera: Calliphoridae) to identify members of the major chemosensory gene families necessary for olfaction.

RESULTS

Representative proteins from all chemosensory gene families essential in insect olfaction were identified in the antennae of the blowfly C. stygia, including 50 odorant receptors, 22 ionotropic receptors, 21 gustatory receptors, 28 odorant binding proteins, 4 chemosensory proteins, and 3 sensory neuron membrane proteins. A total of 97 candidate cytochrome P450s and 39 esterases, some of which may act as odorant degrading enzymes, were also identified. Importantly, co-receptors necessary for the proper function of ligand-binding receptors were identified. Putative orthologues for the conserved antennal ionotropic receptors and candidate gustatory receptors for carbon dioxide detection were also amongst the identified proteins.

CONCLUSIONS

This research provides a comprehensive novel resource that will be fundamental for future studies regarding blowfly olfaction. Such information presents potential benefits to the forensic, pest control, and medical areas, and could assist in the understanding of insecticide resistance and targeted control through cross-species comparisons.