LocustDB: a relational database for the transcriptome and biology of the migratory locust (Locusta migratoria)

Population Density-Dependent Developmental Regulation in Migratory Locust

Insect development is intricately governed by hormonal signaling pathways, yet the pivotal upstream regulator that potentiates hormone activation remains largely elusive. The migratory locust, Locusta migratoria, exhibits population density-dependent phenotypic plasticity, encompassing traits such as flight capability, body coloration, and behavior. In this study, we elucidated a negative correlation between population density and ontogenetic development during the nymphal stage of locusts. We found that the level of density influences the developmental trajectory by modulating transcript abundance within the ecdysone signaling pathway, with knockdown of the prothoracicotropic hormone (PTTH) resulting in developmental delay. Transcriptomic analysis of locust brains across solitary and gregarious phases revealed significant differential expression of genes involved in various pathways, including protein synthesis, energy metabolism, hormonal regulation, and immunity. Notably, knockdown experiments targeting two energy regulators, adipokinetic hormone (AKH) and insulin-like polypeptide 1 (ilp1), failed to elicit changes in the developmental process in solitary locusts. However, knockdown of immunoglobulin (IG) significantly shortened the developmental time in higher-density populations. Collectively, our findings underscore the regulatory role of population density in determining developmental duration and suggest that an immune-related gene contributes to the observed differences in developmental patterns.

The DOMON domain protein LmKnk contributes to correct chitin content, pore canal formation and lipid deposition in the cuticle of Locusta migratoria during moulting

Insects prevent uncontrolled penetration of water and xenobiotics by producing an impermeable cuticle. The major component of the cuticle is chitin that adopts a crystalline structure thereby contributing to cuticle stability. Our understanding of the contribution of chitin to the cuticle barrier function is limited. Here, we studied the role of the DOMON domain protein Knickkopf (LmKnk) that is involved in chitin organization and cuticle permeability in the migratory locust Locusta migratoria. We show that LmKnk localizes to the chitin layer in the newly produced cuticle. Injection of double-stranded RNA targeting LmKnk (dsLmKnk) in locust nymphs caused failure of moulting to the next stage. Histological experiments revealed that apolysis, i.e., the detachment of the old cuticle from the body surface, was normal; however, the newly synthesized cuticle was thinner than the cuticle of the control insects. Indeed, chitin content dropped after suppression of LmKnk expression. As seen by transmission electron microscopy, crystalline chitin organization was lost in dsLmKnk-treated insects. In addition, the structure of pore canals, which are lipid transporting routes in the cuticle, was abnormal. Consistently, their content was reduced and, probably by consequence, lipid deposition on the cuticle was decreased after injection of dsLmKnk. Suppression of LmKnk transcript levels rendered L. migratoria more susceptible to each of four selected insecticides including malathion, chlorpyrifos, carbaryl and deltamethrin. Overall, our data show that LmKnk is needed for correct chitin amounts and organization, and their changes ultimately affect cuticular permeability in L. migratoria.

Comparative analysis of phenotypic plasticity sheds light on the evolution and molecular underpinnings of locust phase polyphenism

Locusts exhibit one of nature's most spectacular examples of complex phenotypic plasticity, in which changes in density cause solitary and cryptic individuals to transform into gregarious and conspicuous locusts forming large migrating swarms. We investigated how these coordinated alternative phenotypes might have evolved by studying the Central American locust and three closely related non-swarming grasshoppers in a comparative framework. By experimentally isolating and crowding during nymphal development, we induced density-dependent phenotypic plasticity and quantified the resulting behavioural, morphological, and molecular reaction norms. All four species exhibited clear plasticity, but the individual reaction norms varied among species and showed different magnitudes. Transcriptomic responses were species-specific, but density-responsive genes were functionally similar across species. There were modules of co-expressed genes that were highly correlated with plastic reaction norms, revealing a potential molecular basis of density-dependent phenotypic plasticity. These findings collectively highlight the importance of studying multiple reaction norms from a comparative perspective.

20-Hydroxyecdysone regulates the prophenoloxidase cascade to immunize Metarhizium anisopliae in Locusta migratoria

BACKGROUND

PPO (prophenoloxidase) cascade plays an important role in resisting invasion of entomogenous fungus. The 20-hydroxyecdysone (20E) exerts potent effect on the innate immunity in many insects. However, whether 20E controls the PPO cascade system against fungi and the regulatory mechanism in insects remains unclear.

RESULTS

In this study, both the proteome and transcriptome of Locusta migratoria were determined followed by the induction of 20E. Pattern recognition receptor GNBP-2 (Gram-negative binding proteins) has been identified that responded to 20E at both messenger RNA (mRNA) and protein levels. The PPO gene expression in fat body and PO (phenoloxidase) activity in plasma was found significantly induced after 20E injection and during the high-20E developmental stage. However, when 20E signal was blocked by RNA interference (RNAi) of ecdysone receptor, the expression level of PPO and PO activity failed to be increased by 20E. Thus, 20E could not significantly induce the expression of PPO gene and PO activity after RNAi of GNBP-2. Furthermore, 20E treatment notably enhanced the resistance of L. migratoria against Metarhizium anisopliae. Followed by of GNBP-2 silencing, the mortality of nymphs was significantly increased under the stress of Metarhizium anisopliae, and 20E injection could not increase the resistance.

CONCLUSION

The 20E regulates the PPO system to resist fungal invasion via regulating GNBP-2 in worldwide pest L. migratoria. Our results provide insight into the mechanism of how 20E enhances the antimicrobial immunity, and will be beneficial for modification of entomogenous fungi targeting on hormones and the immune system. © 2020 Society of Chemical Industry.

Crustacean neuroparsins-a mini-review

Crustacean neuroparsins are poly-cysteine rich neuropeptides that share some similarities with the ovary ecdysteroidogenesis hormone (OEH) of mosquitoes, the N-terminal end of the growth factor binding protein region of the vertebrate and mollusk insulin-like growth factor binding protein and single insulin binding domain protein. Neuroparsins can promote reproduction and neurite outgrowth in various insects. Though many studies have been made in insects, the amount of work reported in crustaceans is still limited. This review emphasizes the neuroparsins found in decapod crustaceans with references to the neuroparsin first discovered in insects. To be more complete in identifying all the neuroparsin members and to understand the structure/function relationship within a single species, we have collected all neuroparsins from the GenBank and our transcriptome datasets. Then, we employed a comparative approach to study the sequence homology, tissue expression patterns, making predictions of their function and the evolutionary relationship particularly in decapod crustaceans. Results from alignment and phylogenetic studies indicated that crustacean neuroparsins consist of unique feature that can be used as criteria for their classification. These features include the presence of 12 cysteine residues in the mature peptide, the strict spacing between these cysteine residues and the size of the mature peptide. Because of the limited data on the expression information, the functions of most neuroparsin are unknown. The review will focus on the site of synthesis, expression, functions, the sequence homology and the evolutionary relationship of this group of neurohormones.

LmCDA1 organizes the cuticle by chitin deacetylation in Locusta migratoria

Cells produce an extracellular matrix (ECM) with a stereotypic organization that is important for tissue function. The insect cuticle is a layered ECM that mainly consists of the polysaccharide chitin and associated proteins adopting a quasi-crystalline structure. Our understanding of the molecular mechanisms deployed during construction of the highly ordered protein-chitin ECM so far is limited. In this study, we report on the role of the chitin deacetylase 1 (LmCDA1) in the organization of the protein-chitin ECM in the migratory locust Locusta migratoria, and LmCDA1 localizes predominantly to the apical tier of the protein-chitin ECM, but it is also found in lower regions. Reduction of LmCDA1 function correlates with lower amounts of chitin and impedes conversion of chitin to chitosan by deacetylation. Establishment of the quasi-crystalline architecture of the protein-chitin ECM is, however, independent of LmCDA1 activity, but it is dependent on another chitin deacetylase, LmCDA2, which has no detectable effects on chitin deacetylation and, as shown previously, no influence on chitin content. Our data reveal that LmCDA1 and LmCDA2 act in parallel and independently from each other in defining the dimensions of the cuticle. Both enzymes are non-uniformly distributed within the protein-chitin matrix, suggesting a site-autonomous function.

RNAi-knockdown of the Locusta migratoria nuclear export factor protein results in insect mortality and alterations in gut microbiome

BACKGROUND

The migratory locust Locusta migratoria is one of the most important agricultural pests worldwide. The nuclear export factor 1 (NXF1) protein plays a crucial role in mediating mRNA transport from the nucleus to the cytoplasm. This study evaluates whether NXF1 could be a potential target for RNAi-mediated pest control of L. migratoria.

RESULTS

We cloned and characterized the nuclear export factor lm-nxf1 of L. migratoria. Lm-nxf1 was expressed in all tissues examined, including head, fat body, hemolymph, trunk, leg and midgut, with high expression observed in the hemolymph and fat body. Injection of lm-nxf1 dsRNA into hemolymph resulted in inhibition of mRNA export in hemocytes, which were used as a target for observing mRNA export. Total hemocyte levels were reduced by ca. 97% in lm-nxf1-dsRNA-treated locusts, and high insect mortality occurred with LT₅₀ = 7.75 day as compared with 18.15 day for gfp-dsRNA-treated controls. Further, the locust intestine became atrophy, and the opportunistic pathogens Enterobacter aerogenes, Klebsiella pneumoniae and Enterobacter asburiae were specifically detected in midgut after lm-nxf1 dsRNA treatment.

CONCLUSIONS

The results reveal that knockdown of the lm-nxf1 gene affects the survival of L. migratoria, indicating that lm-nxf1 is a potential target for RNAi-mediated pest control. © 2018 Society of Chemical Industry.

The Cricket Gryllus bimaculatus: Techniques for Quantitative and Functional Genetic Analyses of Cricket Biology

All extant species are an outcome of nature's "experiments" during evolution, and hence multiple species need to be studied and compared to gain a thorough understanding of evolutionary processes. The field of evolutionary developmental biology (evo-devo) aspires to expand the number of species studied, because most functional genetic studies in animals have been limited to a small number of "traditional" model organisms, many of which belong to the same phylum (Chordata). The phylum Arthropoda, and particularly its component class Insecta, possesses many important characteristics that are considered favorable and attractive for evo-devo research, including an astonishing diversity of extant species and a wide disparity in body plans. The development of the most thoroughly investigated insect genetic model system to date, the fruit fly Drosophila melanogaster (a holometabolous insect), appears highly derived with respect to other insects and indeed with respect to most arthropods. In comparison, crickets (a basally branching hemimetabolous insect lineage compared to the Holometabola) are thought to embody many developmental features that make them more representative of insects. Here we focus on crickets as emerging models to study problems in a wide range of biological areas and summarize the currently available molecular, genomic, forward and reverse genetic, imaging and computational tool kit that has been established or adapted for cricket research. With an emphasis on the cricket species Gryllus bimaculatus, we highlight recent efforts made by the scientific community in establishing this species as a laboratory model for cellular biology and developmental genetics. This broad toolkit has the potential to accelerate many traditional areas of cricket research, including studies of adaptation, evolution, neuroethology, physiology, endocrinology, regeneration, and reproductive behavior. It may also help to establish newer areas, for example, the use of crickets as animal infection model systems and human food sources.

20-Hydroxyecdysone activates PGRP-SA mediated immune response in Locusta migratoria

20-hydroxyecdysone (20E) has been implicated in regulating the immune response in insects. Conflicting conclusions on 20E regulating immunity have been reported in model holometabolous species. However, in hemimetabolous insects, the role of 20E as an immune-suppressor or activator and the mechanism remains unclear. The migratory locust Locusta migratoria is a representative member of hemimetabolous insects. Here, digital gene expression (DGE) profiles of Locusta migratoria treated with 20E were analyzed. Pattern recognition receptors [peptidoglycan recognition protein (PGRP-SA), PGRP-LE, and gram-negative binding protein (GNBP3)] and antimicrobial peptides (defensin, diptericin, and i-type lysozyme) were significantly induced by 20E in fat body. These immune-related genes significantly increased their mRNA levels during the high-20E stage. Antibacterial activities in plasma were enhanced after 20E injection and during the high-20E developmental stage. Conversely, when 20E signal was suppressed by RNAi of EcR (ecdysone receptor), the expression levels of these genes and antibacterial activities failed to be increased by 20E injection and during the high-20E developmental stage, and the mortality increased after being infected by entomogenous fungus. The knockdown of PGRP-SA inhibited the expression level of defensin, diptericin and i-type lysozyme in fat body and reduced antibacterial activities in plasma. 20E injection could not significantly induce the expression of antimicrobial peptides after RNAi of PGRP-SA. These results demonstrated that 20E enhanced the immune response by activating PGRP-SA in L. migratoria.

Microarray-based annotation of the gut transcriptome of the migratory locust, Locusta migratoria

The migratory locust, Locusta migratoria, is a serious agricultural pest and important insect model in the study of insect digestion and feeding behaviour. The gut is one of the primary interfaces between the insect and its environment. Nevertheless, knowledge on the gut transcriptome of L. migratoria is still very limited. Here, 48 802 expressed sequence tags were extracted from publicly available databases and their expression in larval gut and/or brain tissue was determined using microarray hybridization. Our data show 2765 transcripts predominantly or exclusively expressed in the gut. Many transcripts had putative functions closely related to the physiological functions of the gut as a muscular digestive organ and as the first barrier against microorganisms and a wide range of toxins. By means of a ranking procedure based on the relative signal intensity, we estimated 15% of the transcripts to show high expression levels, the highest belonging to diverse digestive enzymes and muscle-related proteins. We also found evidence for very high expression of an allergen protein, which could have important implications, as locusts form a traditional food source in various parts of the world, and were also recently added to the list of insects fit for human consumption in Europe. Interestingly, many highly expressed sequences have as yet unknown functions. Taken together, the present data provide significant insight into locust larval gut physiology, and will be valuable for future studies on the insect gut.

Helicoidal Organization of Chitin in the Cuticle of the Migratory Locust Requires the Function of the Chitin Deacetylase2 Enzyme (LmCDA2)

In the three-dimensional extracellular matrix of the insect cuticle, horizontally aligned microfibrils composed of the polysaccharide chitin and associated proteins are stacked either parallel to each other or helicoidally. The underlying molecular mechanisms that implement differential chitin organization are largely unknown. To learn more about cuticle organization, we sought to study the role of chitin deacetylases (CDA) in this process. In the body cuticle of nymphs of the migratory locust Locusta migratoria, helicoidal chitin organization is changed to an organization with unidirectional microfibril orientation when LmCDA2 expression is knocked down by RNA interference. In addition, the LmCDA2-deficient cuticle is less compact suggesting that LmCDA2 is needed for chitin packaging. Animals with reduced LmCDA2 activity die at molting, underlining that correct chitin organization is essential for survival. Interestingly, we find that LmCDA2 localizes only to the initially produced chitin microfibrils that constitute the apical site of the chitin stack. Based on our data, we hypothesize that LmCDA2-mediated chitin deacetylation at the beginning of chitin production is a decisive reaction that triggers helicoidal arrangement of subsequently assembled chitin-protein microfibrils.

A Family of CSαβ Defensins and Defensin-Like Peptides from the Migratory Locust, Locusta migratoria, and Their Expression Dynamics during Mycosis and Nosemosis

Insect defensins are effector components of the innate defense system. During infection, these peptides may play a role in the control of pathogens by providing protective antimicrobial barriers between epithelial cells and the hemocoel. The cDNAs encoding four defensins of the migratory locust, Locusta migratoria, designated LmDEF 1, 3–5, were identified for the first time by transcriptome-targeted analysis. Three of the members of this CSαβ defensin family, LmDEF 1, 3, and 5, were detected in locust tissues. The pro regions of their sequences have little-shared identities with other insect defensins, though the predicted mature peptides align well with other insect defensins. Phylogenetic analysis indicates a completely novel position of both LmDEF 1 and 3, compared to defensins from hymenopterans. The expression patterns of the genes encoding LmDEFs in the fat body and salivary glands were studied in response to immune-challenge by the microsporidian pathogen Nosema locustae and the fungus Metarhizium anisopliae after feeding or topical application, respectively. Focusing on Nosema-induced immunity, qRT-PCR was employed to quantify the transcript levels of LmDEFs. A higher transcript abundance of LmDEF5 was distributed more or less uniformly throughout the fat body along time. A very low baseline transcription of both LmDEFs 1 and 3 in naïve insects was indicated, and that transcription increases with time or is latent in the fat body or salivary glands of infected nymphs. In the salivary glands, expression of LmDEF3 was 20-40-times higher than in the fat body post-microbial infection. A very low expression of LmDEF3 could be detected in the fat body, but eventually increased with time up to a maximum at day 15. Delayed induction of transcription of these peptides in the fat body and salivary glands 5–15 days post-activation and the differential expression patterns suggest that the fat body/salivary glands of this species are active in the immune response against pathogens. The ability of N. locustae to induce salivary glands as well as fat body expression of defensins raises the possibility that these AMPs might play a key role in the development and/or tolerance of parasitic infections.

Alternative migratory locust phenotypes are associated with differences in the expression of genes encoding the methylation machinery

Despite the importance of locust density-dependent polyphenism as a model system for understanding phenotypic plasticity, there is still much to be learnt about its underlying molecular control. Here we describe the first investigation into the expression of genes encoding the DNA methylation machinery in the migratory locust (Locusta migratoria). We show that the alternative solitarious and gregarious phenotypic states induced by different locust rearing densities are associated with significant differences in the expression of the target genes DNA methyltransferase 1, DNA methyltransferase 2 and methyl-CpG-binding domain protein 2/3. This variation was most pronounced in the embryos of solitarious vs. gregarious mothers. We mapped the embryonic methylation profiles of several intragenic regions and a Long Interspersed Nuclear Element (LINE), each of which is known to be differentially expressed between alternative locust phenotypes or has been directly implicated in phase change. LmI and three genes, adenyl cyclase-associated binding protein 2, choline kinase alpha-like and henna, were methylated. Our results set the stage for future studies investigating the specific role of DNA methylation in the maternal transfer of migratory locust phase polyphenism.

Tissue-Specific Immune Gene Expression in the Migratory Locust, Locusta Migratoria

The ability of hosts to respond to infection involves several complex immune recognition pathways. Broadly conserved pathogen-associated molecular patterns (PAMPs) allow individuals to target a range of invading microbes. Recently, studies on insect innate immunity have found evidence that a single pathogen can activate different immune pathways across species. In this study, expression changes in immune genes encoding peptidoglycan-recognition protein SA (PGRP-SA), gram-negative binding protein 1 (GNBP1) and prophenoloxidase (ProPO) were investigated in Locusta migratoria, following an immune challenge using injected lipopolysaccharide (LPS) solution from Escherichia coli. Since immune activation might also be tissue-specific, gene expression levels were followed across a range of tissue types. For PGRP-SA, expression increased in response to LPS within all seven of the tissue-types assayed and differed significantly between tissues. Expression of GNBP1 similarly varied across tissue types, yet showed no clear expression difference between LPS-injected and uninfected locusts. Increases in ProPO expression in response to LPS, however, could only be detected in the gut sections. This study has revealed tissue-specific immune response to add a new level of complexity to insect immune studies. In addition to variation in recognition pathways identified in previous works, tissue-specificity should be carefully considered in similar works.

Multidimensional approaches for studying plant defence against insects: from ecology to omics and synthetic biology

The biggest challenge for modern biology is to integrate multidisciplinary approaches towards understanding the organizational and functional complexity of biological systems at different hierarchies, starting from the subcellular molecular mechanisms (microscopic) to the functional interactions of ecological communities (macroscopic). The plant-insect interaction is a good model for this purpose with the availability of an enormous amount of information at the molecular and the ecosystem levels. Changing global climatic conditions are abruptly resetting plant-insect interactions. Integration of discretely located heterogeneous information from the ecosystem to genes and pathways will be an advantage to understand the complexity of plant-insect interactions. This review will present the recent developments in omics-based high-throughput experimental approaches, with particular emphasis on studying plant defence responses against insect attack. The review highlights the importance of using integrative systems approaches to study plant-insect interactions from the macroscopic to the microscopic level. We analyse the current efforts in generating, integrating and modelling multiomics data to understand plant-insect interaction at a systems level. As a future prospect, we highlight the growing interest in utilizing the synthetic biology platform for engineering insect-resistant plants.

Octopamine and tyramine respectively regulate attractive and repulsive behavior in locust phase changes

Aggregative and solitary behaviors are universal phenomena in animals. Interestingly, locusts (Locusta migratoria) can reversibly transit their behavior between gregarious and solitary phase through conspecific attraction and repulsion. However, the regulatory mechanism of neurotransmitters underlying attraction and repulsion among locusts remains unknown. In this study, we found gregarious and solitary locusts were attracted or repulsed respectively by gregarious volatiles. Solitary locusts can transform their preference for gregarious volatiles during crowding, whereas gregarious locusts avoided their volatiles during isolation. During crowding and isolation, the activities of octopamine and tyramine signalings were respectively correlated with attraction- and repulsion-response to gregarious volatiles. RNA interference verified that octopamine receptor α (OARα) signaling in gregarious locusts controlled attraction-response, whereas in solitary ones, tyramine receptor (TAR) signaling mediated repulsion-response. Moreover, the activation of OARα signaling in solitary locusts caused the behavioral shift from repulsion to attraction. Enhancement of TAR signaling in gregarious locusts resulted in the behavioral shift from attraction to repulsion. The olfactory preference of gregarious and solitary locusts co-injected by these two monoamines displayed the same tendency as the olfactory perception in crowding and isolation, respectively. Thus, the invertebrate-specific octopamine-OARα and tyramine-TAR signalings respectively mediate attractive and repulsive behavior in behavioral plasticity in locusts.

The contribution of the genomes of a termite and a locust to our understanding of insect neuropeptides and neurohormones

The genomes of the migratory locust Locusta migratoria and the termite Zootermopsis nevadensis were mined for the presence of genes encoding neuropeptides, neurohormones, and their G-protein coupled receptors (GPCRs). Both species have retained a larger number of neuropeptide and neuropeptide GPCRs than the better known holometabolous insect species, while other genes that in holometabolous species appear to have a single transcript produce two different precursors in the locust, the termite or both. Thus, the recently discovered CNMa neuropeptide gene has two transcripts predicted to produce two structurally different CNMa peptides in the termite, while the locust produces two different myosuppressin peptides in the same fashion. Both these species also have a calcitonin gene, which is different from the gene encoding the calcitonin-like insect diuretic hormone. This gene produces two types of calcitonins, calcitonins A and B. It is also present in Lepidoptera and Coleoptera and some Diptera, but absent from mosquitoes and Drosophila. However, in holometabolous insect species, only the B transcript is produced. Their putative receptors were also identified. In contrast, Locusta has a highly unusual gene that codes for a salivation stimulatory peptide. The Locusta genes for neuroparsin and vasopressin are particularly interesting. The neuroparsin gene produces five different transcripts, of which only one codes for the neurohormone identified from the corpora cardiaca. The other four transcripts code for neuroparsin-like proteins, which lack four amino acid residues, and that for that reason we called neoneuroparsins. The number of transcripts for the neoneuroparsins is about 200 times larger than the number of neuroparsin transcripts. The first exon and the putative promoter of the vasopressin genes, of which there are about seven copies in the genome, is very well-conserved, but the remainder of these genes is not. The relevance of these findings is discussed.

Effects of different dietary conditions on the expression of trypsin- and chymotrypsin-like protease genes in the digestive system of the migratory locust, Locusta migratoria

While technological advancements have recently led to a steep increase in genomic and transcriptomic data, and large numbers of protease sequences are being discovered in diverse insect species, little information is available about the expression of digestive enzymes in Orthoptera. Here we describe the identification of Locusta migratoria serine protease transcripts (cDNAs) involved in digestion, which might serve as possible targets for pest control management. A total of 5 putative trypsin and 15 putative chymotrypsin gene sequences were characterized. Phylogenetic analysis revealed that these are distributed among 3 evolutionary conserved clusters. In addition, we have determined the relative gene expression levels of representative members in the gut under different feeding conditions. This study demonstrated that the transcript levels for all measured serine proteases were strongly reduced after starvation. On the other hand, larvae of L. migratoria displayed compensatory effects to the presence of Soybean Bowman Birk (SBBI) and Soybean Trypsin (SBTI) inhibitors in their diet by differential upregulation of multiple proteases. A rapid initial upregulation was observed for all tested serine protease transcripts, while only for members belonging to class I, the transcript levels remained elevated after prolonged exposure. In full agreement with these results, we also observed an increase in proteolytic activity in midgut secretions of locusts that were accustomed to the presence of protease inhibitors in their diet, while no change in sensitivity to these inhibitors was observed. Taken together, this paper is the first comprehensive study on dietary dependent transcript levels of proteolytic enzymes in Orthoptera. Our data suggest that compensatory response mechanisms to protease inhibitor ingestion may have appeared early in insect evolution.

Molecular and functional characterization of cDNAs putatively encoding carboxylesterases from the migratory locust, Locusta migratoria

Carboxylesterases (CarEs) belong to a superfamily of metabolic enzymes encoded by a number of genes and are widely distributed in microbes, plants and animals including insects. These enzymes play important roles in detoxification of insecticides and other xenobiotics, degradation of pheromones, regulation of neurodevelopment, and control of animal development. In this study, we characterized a total of 39 full-length cDNAs putatively encoding different CarEs from the migratory locust, Locusta migratoria, one of the most severe insect pests in many regions of the world, and evaluated the role of four CarE genes in insecticide detoxification. Our phylogenetic analysis grouped the 39 CarEs into five different clades including 20 CarEs in clade A, 3 in D, 13 in E, 1 in F and 2 in I. Four CarE genes (LmCesA3, LmCesA20, LmCesD1, LmCesE1), representing three different clades (A, D and E), were selected for further analyses. The transcripts of the four genes were detectable in all the developmental stages and tissues examined. LmCesA3 and LmCesE1 were mainly expressed in the fat bodies and Malpighian tubules, whereas LmCesA20 and LmCesD1 were predominately expressed in the muscles and hemolymph, respectively. The injection of double-stranded RNA (dsRNA) synthesized from each of the four CarE genes followed by the bioassay with each of four insecticides (chlorpyrifos, malathion, carbaryl and deltamethrin) increased the nymphal mortalities by 37.2 and 28.4% in response to malathion after LmCesA20 and LmCesE1 were silenced, respectively. Thus, we proposed that both LmCesA20 and LmCesE1 played an important role in detoxification of malathion in the locust. These results are expected to help researchers reveal the characteristics of diverse CarEs and assess the risk of insecticide resistance conferred by CarEs in the locust and other insect species.

MicroRNA-133 inhibits behavioral aggregation by controlling dopamine synthesis in locusts

Phenotypic plasticity is ubiquitous and primarily controlled by interactions between environmental and genetic factors. The migratory locust, a worldwide pest, exhibits pronounced phenotypic plasticity, which is a population density-dependent transition that occurs between the gregarious and solitary phases. Genes involved in dopamine synthesis have been shown to regulate the phase transition of locusts. However, the function of microRNAs in this process remains unknown. In this study, we report the participation of miR-133 in dopamine production and the behavioral transition by negatively regulating two critical genes, henna and pale, in the dopamine pathway. miR-133 participated in the post-transcriptional regulation of henna and pale by binding to their coding region and 3′ untranslated region, respectively. miR-133 displayed cellular co-localization with henna/pale in the protocerebrum, and its expression in the protocerebrum was negatively correlated with henna and pale expression. Moreover, miR-133 agomir delivery suppressed henna and pale expression, which consequently decreased dopamine production, thus resulting in the behavioral shift of the locusts from the gregarious phase to the solitary phase. Increasing the dopamine content could rescue the solitary phenotype, which was induced by miR-133 agomir delivery. Conversely, miR-133 inhibition increased the expression of henna and pale, resulting in the gregarious-like behavior of solitary locusts; this gregarious phenotype could be rescued by RNA interference of henna and pale. This study shows the novel function and modulation pattern of a miRNA in phenotypic plasticity and provides insight into the underlying molecular mechanisms of the phase transition of locusts.

Phenotypic plasticity refers to the ability of an organism to alter its phenotypes in response to environmental changes. Genetic factors, such as coding and non-coding RNAs, contribute to phenotypic variation. MicroRNAs (miRNAs), which are non-coding RNAs, function as post-transcriptional repressors of gene expression. Migratory locusts show remarkable phenotypic plasticity, referred to as phase transition, which is dependent on population density changes. In the present study, we elucidated the miRNA-133-mediated post-transcriptional mechanisms involved in dopamine production that result in behavioral phase changes. We found that miR-133 directly represses two genes, henna and pale, in the dopamine pathway. Administration of the miR-133 agomir decreased dopamine production and induced a behavioral shift from the gregarious to the solitary phase. Additionally, miR-133 targeted henna in the coding region and pale in the 3′ untranslated region, possibly indicating that different mechanisms of post-transcriptional regulation by miR-133 occur in the dopamine pathway. Moreover, the rescue experiments significantly eliminated the effects of miR-133 overexpression and inhibition on the behavioral phase changes of locusts. Our results demonstrate the role of miR-133 in phenotypic plasticity in locusts, in which the miR-133 regulates behavioral changes by controlling dopamine synthesis.

Molecular mechanisms of phase change in locusts

Phase change in locusts is an ideal model for studying the genetic architectures and regulatory mechanisms associated with phenotypic plasticity. The recent development of genomic and metabolomic tools and resources has furthered our understanding of the molecular basis of phase change in locusts. Thousands of phase-related genes and metabolites have been highlighted using large-scale expressed sequence tags, microarrays, high-throughput transcriptomic sequences, or metabolomic approaches. However, only several key factors, including genes, metabolites, and pathways, have a critical role in phase transition in locusts. For example, CSP (chemosensory protein) and takeout genes, the dopamine pathway, protein kinase A, and carnitines were found to be involved in the regulation of behavioral phase change and gram-negative bacteria-binding proteins in prophylaxical disease resistance of gregarious locusts. Epigenetic mechanisms including small noncoding RNAs and DNA methylation have been implicated. We review these new advances in the molecular basis of phase change in locusts and present some challenges that need to be addressed.

Fas-associated factor 1 plays a negative regulatory role in the antibacterial immunity of Locusta migratoria

Insect immune responses are precisely regulated to maintain immune balance. In this study, the Fas-associated factor 1 (FAF1) gene of Locusta migratoria manilensis, a homologue of the caspar gene that functions as a specific negative regulator in the antibacterial immunity pathway, was cloned. Gene expression analysis showed that FAF1 was expressed throughout the developmental stages and in all tested tissues, but its transcription levels varied significantly. Thus, FAF1 appears to be tightly regulated and is probably involved in multiple physiological processes. In addition, the antimicrobial peptide gene prolixicin was cloned and characterized. After bacterial challenge, prolixicin was rapidly up-regulated, whereas FAF1 was markedly down-regulated. This result was consistent with the observation that prolixicin was hyperactivated when FAF1 was suppressed by RNA interference. Moreover, after bacterial infection, the survival rate of FAF1-knockdown locusts was much higher than that of the wild-type. Taken together, these findings strongly suggest that FAF1 shares a similar function as caspar in Drosophila and may be involved in the negative regulation of antibacterial immunity in locusts.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Developmental gene discovery in a hemimetabolous insect: de novo assembly and annotation of a transcriptome for the cricket Gryllus bimaculatus

Most genomic resources available for insects represent the Holometabola, which are insects that undergo complete metamorphosis like beetles and flies. In contrast, the Hemimetabola (direct developing insects), representing the basal branches of the insect tree, have very few genomic resources. We have therefore created a large and publicly available transcriptome for the hemimetabolous insect Gryllus bimaculatus (cricket), a well-developed laboratory model organism whose potential for functional genetic experiments is currently limited by the absence of genomic resources. cDNA was prepared using mRNA obtained from adult ovaries containing all stages of oogenesis, and from embryo samples on each day of embryogenesis. Using 454 Titanium pyrosequencing, we sequenced over four million raw reads, and assembled them into 21,512 isotigs (predicted transcripts) and 120,805 singletons with an average coverage per base pair of 51.3. We annotated the transcriptome manually for over 400 conserved genes involved in embryonic patterning, gametogenesis, and signaling pathways. BLAST comparison of the transcriptome against the NCBI non-redundant protein database (nr) identified significant similarity to nr sequences for 55.5% of transcriptome sequences, and suggested that the transcriptome may contain 19,874 unique transcripts. For predicted transcripts without significant similarity to known sequences, we assessed their similarity to other orthopteran sequences, and determined that these transcripts contain recognizable protein domains, largely of unknown function. We created a searchable, web-based database to allow public access to all raw, assembled and annotated data. This database is to our knowledge the largest de novo assembled and annotated transcriptome resource available for any hemimetabolous insect. We therefore anticipate that these data will contribute significantly to more effective and higher-throughput deployment of molecular analysis tools in Gryllus.

Altered immunity in crowded locust reduced fungal (Metarhizium anisopliae) pathogenesis

The stress of living conditions, similar to infections, alters animal immunity. High population density is empirically considered to induce prophylactic immunity to reduce the infection risk, which was challenged by a model of low connectivity between infectious and susceptible individuals in crowded animals. The migratory locust, which exhibits polyphenism through gregarious and solitary phases in response to population density and displays different resistance to fungal biopesticide (Metarhizium anisopliae), was used to observe the prophylactic immunity of crowded animals. We applied an RNA-sequencing assay to investigate differential expression in fat body samples of gregarious and solitary locusts before and after infection. Solitary locusts devoted at least twice the number of genes for combating M. anisopliae infection than gregarious locusts. The transcription of immune molecules such as pattern recognition proteins, protease inhibitors, and anti-oxidation proteins, was increased in prophylactic immunity of gregarious locusts. The differentially expressed transcripts reducing gregarious locust susceptibility to M. anisopliae were confirmed at the transcriptional and translational level. Further investigation revealed that locust GNBP3 was susceptible to proteolysis while GNBP1, induced by M. anisopliae infection, resisted proteolysis. Silencing of gnbp3 by RNAi significantly shortened the life span of gregarious locusts but not solitary locusts. By contrast, gnbp1 silencing did not affect the life span of both gregarious and solitary locusts after M. anisopliae infection. Thus, the GNBP3-dependent immune responses were involved in the phenotypic resistance of gregarious locusts to fungal infection, but were redundant in solitary locusts. Our results indicated that gregarious locusts prophylactically activated upstream modulators of immune cascades rather than downstream effectors, preferring to quarantine rather than eliminate pathogens to conserve energy meanwhile increasing the "distance" of infectious and target individuals. Our study has obvious implications for bio-pesticides management of crowded pests, and for understanding disease epidemics and adaptiveness of pathogens.

Vacuolar ATPase subunit H is essential for the survival and moulting of Locusta migratoria manilensis

Vacuolar (H(+) )-ATPase (V-ATPase) functions as an electrogenic pump, transporting protons from the cytoplasm to the extracellular fluid to generate cell-negative membrane voltage. The V-ATPase subunit H, encoded by Vhasfd, is required for V-ATPase activity. In this study, the gene encoding V-ATPase subunit H from Locusta migratoria manilensis was cloned, and designated as Lm-Vhasfd. The complete cDNA sequence is 2018 bp, with an open reading frame encoding 515 amino acid residues. Semi-quantitative reverse transcription PCR (RT-PCR) showed that Lm-Vhasfd transcription is high in the haemolymph, midgut, trunk and leg, but relatively low in the fat body and head tissues. Injection with a specific double-strand RNA (dsRNA) led to a significant decrease in Lm-Vhasfd mRNA, V-ATPase enzyme activity and ATP concentration. Bioassays showed that silencing Lm-Vhasfd led to the death of individuals and various moulting defects. The accumulative mortality of the RNA interference (RNAi) mutant 11 days post-injection was 96.7%, which was conspicuously higher than that seen in wild type locusts. These RNAi phenotypes demonstrate that Lm-Vhasfd is essential for the growth and moulting of L. migratoria manilensis.

Male reproduction is affected by RNA interference of period and timeless in the desert locust Schistocerca gregaria

In all living organisms, behavior, metabolism and physiology are under the regulation of a circadian clock. The molecular machinery of this clock has been conserved throughout the animal kingdom. Besides regulating the circadian timing of a variety of processes through a central oscillating mechanism in the brain, these circadian clock genes were found to have a function in peripheral tissues in different insects. Here, we provide evidence that the circadian clock genes period (per) and timeless (tim) have a role in the male locust reproduction. A knockdown of either of the two genes has no effect on male sexual maturation or behavior, but progeny output in their untreated female copulation partners is affected. Indeed, the fertilization rates of the eggs are lower for females with a per or tim RNAi copulation partner as compared to the eggs deposited by females that mated with a control male. As the sperm content of the seminal vesicles is higher in per or tim knockdown males, we suggest that this phenotype could be caused by a disturbance of the circadian regulated sperm transfer in the male reproductive organs, or an insufficient maturation of the sperm after release from the testes.

Identification of representative genes of the central nervous system of the locust, Locusta migratoria manilensis by deep sequencing

The shortage of available genomic and transcriptomic data hampers the molecular study on the migratory locust, Locusta migratoria manilensis (L.) (Orthoptera: Acrididae) central nervous system (CNS). In this study, locust CNS RNA was sequenced by deep sequencing. 41,179 unigenes were obtained with an average length of 570 bp, and 5,519 unigenes were longer than 1,000 bp. Compared with an EST database of another locust species Schistocerca gregaria Forsskåi, 9,069 unigenes were found conserved, while 32,110 unigenes were differentially expressed. A total of 15,895 unigenes were identified, including 644 nervous system relevant unigenes. Among the 25,284 unknown unigenes, 9,482 were found to be specific to the CNS by filtering out the previous ESTs acquired from locust organs without CNS's. The locust CNS showed the most matches (18%) with Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) sequences. Comprehensive assessment reveals that the database generated in this study is broadly representative of the CNS of adult locust, providing comprehensive gene information at the transcriptional level that could facilitate research of the locust CNS, including various physiological aspects and pesticide target finding.

Evidence for widespread genomic methylation in the migratory locust, Locusta migratoria (Orthoptera: Acrididae)

The importance of DNA methylation in mammalian and plant systems is well established. In recent years there has been renewed interest in DNA methylation in insects. Accumulating evidence, both from mammals and insects, points towards an emerging role for DNA methylation in the regulation of phenotypic plasticity. The migratory locust (Locusta migratoria) is a model organism for the study of phenotypic plasticity. Despite this, there is little information available about the degree to which the genome is methylated in this species and genes encoding methylation machinery have not been previously identified. We therefore undertook an initial investigation to establish the presence of a functional DNA methylation system in L. migratoria. We found that the migratory locust possesses genes that putatively encode methylation machinery (DNA methyltransferases and a methyl-binding domain protein) and exhibits genomic methylation, some of which appears to be localised to repetitive regions of the genome. We have also identified a distinct group of genes within the L. migratoria genome that appear to have been historically methylated and show some possible functional differentiation. These results will facilitate more detailed research into the functional significance of DNA methylation in locusts.

Microarray-based transcriptomic analysis of differences between long-term gregarious and solitarious desert locusts

Desert locusts (Schistocerca gregaria) show an extreme form of phenotypic plasticity and can transform between a cryptic solitarious phase and a swarming gregarious phase. The two phases differ extensively in behavior, morphology and physiology but very little is known about the molecular basis of these differences. We used our recently generated Expressed Sequence Tag (EST) database derived from S. gregaria central nervous system (CNS) to design oligonucleotide microarrays and compare the expression of thousands of genes in the CNS of long-term gregarious and solitarious adult desert locusts. This identified 214 differentially expressed genes, of which 40% have been annotated to date. These include genes encoding proteins that are associated with CNS development and modeling, sensory perception, stress response and resistance, and fundamental cellular processes. Our microarray analysis has identified genes whose altered expression may enable locusts of either phase to deal with the different challenges they face. Genes for heat shock proteins and proteins which confer protection from infection were upregulated in gregarious locusts, which may allow them to respond to acute physiological challenges. By contrast the longer-lived solitarious locusts appear to be more strongly protected from the slowly accumulating effects of ageing by an upregulation of genes related to anti-oxidant systems, detoxification and anabolic renewal. Gregarious locusts also had a greater abundance of transcripts for proteins involved in sensory processing and in nervous system development and plasticity. Gregarious locusts live in a more complex sensory environment than solitarious locusts and may require a greater turnover of proteins involved in sensory transduction, and possibly greater neuronal plasticity.

Transcriptome analysis of the desert locust central nervous system: production and annotation of a Schistocerca gregaria EST database

BACKGROUND

The desert locust (Schistocerca gregaria) displays a fascinating type of phenotypic plasticity, designated as 'phase polyphenism'. Depending on environmental conditions, one genome can be translated into two highly divergent phenotypes, termed the solitarious and gregarious (swarming) phase. Although many of the underlying molecular events remain elusive, the central nervous system (CNS) is expected to play a crucial role in the phase transition process. Locusts have also proven to be interesting model organisms in a physiological and neurobiological research context. However, molecular studies in locusts are hampered by the fact that genome/transcriptome sequence information available for this branch of insects is still limited.

METHODOLOGY

We have generated 34,672 raw expressed sequence tags (EST) from the CNS of desert locusts in both phases. These ESTs were assembled in 12,709 unique transcript sequences and nearly 4,000 sequences were functionally annotated. Moreover, the obtained S. gregaria EST information is highly complementary to the existing orthopteran transcriptomic data. Since many novel transcripts encode neuronal signaling and signal transduction components, this paper includes an overview of these sequences. Furthermore, several transcripts being differentially represented in solitarious and gregarious locusts were retrieved from this EST database. The findings highlight the involvement of the CNS in the phase transition process and indicate that this novel annotated database may also add to the emerging knowledge of concomitant neuronal signaling and neuroplasticity events.

CONCLUSIONS

In summary, we met the need for novel sequence data from desert locust CNS. To our knowledge, we hereby also present the first insect EST database that is derived from the complete CNS. The obtained S. gregaria EST data constitute an important new source of information that will be instrumental in further unraveling the molecular principles of phase polyphenism, in further establishing locusts as valuable research model organisms and in molecular evolutionary and comparative entomology.

Modulation of behavioral phase changes of the migratory locust by the catecholamine metabolic pathway

The migratory locust, Locusta migratoria, shows a striking phenotypic plasticity. It transitions between solitary and gregarious phases in response to population density changes. However, the molecular mechanism underlying the phase-dependent behavior changes remains elusive. Here we report a genome-wide gene expression profiling of gregarious and solitary nymphs at each stadium of the migratory locust, and we identified the most differentially expressed genes in the fourth stadium of the two phases. Bioinformatics analysis indicated that the catecholamine metabolic pathway was the most significant pathway up-regulated in the gregarious phase. We found pale, henna, and vat1, involved in dopamine biosynthesis and synaptic release, were critical target genes related to behavioral phase changes in the locusts. The roles of these genes in mediating behavioral changes in the gregarious individuals were confirmed by RNAi and pharmacological intervention. A single injection of dopamine or its agonist initiated gregarious behavior. Moreover, continuous and multiple injections of a dopamine agonist coupled with crowding resulted in more pronounced gregarious behavior. Our study thus provides insights into the relationships between genes and behavior in phase transition of this important pest species.

Assessment and validation of a suite of reverse transcription-quantitative PCR reference genes for analyses of density-dependent behavioural plasticity in the Australian plague locust

Background

The Australian plague locust, Chortoicetes terminifera, is among the most promising species to unravel the suites of genes underling the density-dependent shift from shy and cryptic solitarious behaviour to the highly active and aggregating gregarious behaviour that is characteristic of locusts. This is because it lacks many of the major phenotypic changes in colour and morphology that accompany phase change in other locust species. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is the most sensitive method available for determining changes in gene expression. However, to accurately monitor the expression of target genes, it is essential to select an appropriate normalization strategy to control for non-specific variation between samples. Here we identify eight potential reference genes and examine their expression stability at different rearing density treatments in neural tissue of the Australian plague locust.

Results

Taking advantage of the new orthologous DNA sequences available in locusts, we developed primers for genes encoding 18SrRNA, ribosomal protein L32 (RpL32), armadillo (Arm), actin 5C (Actin), succinate dehydrogenase (SDHa), glyceraldehyde-3P-dehydrogenase (GAPDH), elongation factor 1 alpha (EF1a) and annexin IX (AnnIX). The relative transcription levels of these eight genes were then analyzed in three treatment groups differing in rearing density (isolated, short- and long-term crowded), each made up of five pools of four neural tissue samples from 5^th instar nymphs. SDHa and GAPDH, which are both involved in metabolic pathways, were identified as the least stable in expression levels, challenging their usefulness in normalization. Based on calculations performed with the geNorm and NormFinder programs, the best combination of two genes for normalization of gene expression data following crowding in the Australian plague locust was EF1a and Arm. We applied their use to studying a target gene that encodes a Ca²⁺ binding glycoprotein, SPARC, which was previously found to be up-regulated in brains of gregarious desert locusts, Schistocerca gregaria. Interestingly, expression of this gene did not vary with rearing density in the same way in brains of the two locust species. Unlike S. gregaria, there was no effect of any crowding treatment in the Australian plague locust.

Conclusion

Arm and EF1a is the most stably expressed combination of two reference genes of the eight examined for reliable normalization of RT-qPCR assays studying density-dependent behavioural change in the Australian plague locust. Such normalization allowed us to show that C. terminifera crowding did not change the neuronal expression of the SPARC gene, a gregarious phase-specific gene identified in brains of the desert locust, S. gregaria. Such comparative results on density-dependent gene regulation provide insights into the evolution of gregarious behaviour and mass migration of locusts. The eight identified genes we evaluated are also candidates as normalization genes for use in experiments involving other Oedipodinae species, but the rank order of gene stability must necessarily be determined on a case-by-case basis.

CSP and takeout genes modulate the switch between attraction and repulsion during behavioral phase change in the migratory locust

Behavioral plasticity is the most striking trait in locust phase transition. However, the genetic basis for behavioral plasticity in locusts is largely unknown. To unravel the molecular mechanisms underlying the behavioral phase change in the migratory locust Locusta migratoria, the gene expression patterns over the time courses of solitarization and gregarization were compared by oligonucleotide microarray analysis. Data analysis revealed that several gene categories relevant to peripheral olfactory perception are strongly regulated in a total of 1,444 differentially expressed genes during both time courses. Among these candidate genes, several CSP (chemosensory protein) genes and one takeout gene, LmigTO1, showed higher expression in gregarious and solitarious locusts, respectively, and displayed opposite expression trends during solitarization and gregarization. qRT-PCR experiments revealed that most CSP members and LmigTO1 exhibited antenna-rich expressions. RNA interference combined with olfactory behavioral experiments confirmed that the CSP gene family and one takeout gene, LmigTO1, are involved in the shift from repulsion to attraction between individuals during gregarization and in the reverse transition during solitarization. These findings suggest that the response to locust-emitted olfactory cues regulated by CSP and takeout genes is involved in the behavioral phase change in the migratory locust and provide a previously undescribed molecular mechanism linked to the formation of locust aggregations.

The migratory locust, Locusta migratoria, is a worldwide agricultural pest whose outbreaks can result in plagues during which locusts mass migrate in marching bands and flying swarms. They exhibit striking phenotypic plasticity depending on the population density. They can transform between the barely-visible solitarious phase and the swarm-forming gregarious phase. A key step in the formation of large aggregation is the initial shift from the strong mutual aversion in solitarious locusts to the attraction to each other in gregarious locusts. Previous genomics studies have revealed 532 differentially expressed genes and many regulating small RNAs between the two phases of the migratory locust. Here, we developed a large-scale oligonucleotide microarray to quantify the expression of 9,154 genes during the time courses of isolating gregarious locusts and crowding solitarious locusts. We found that several olfaction-related genes, several CSPs and one takeout, are strongly regulated during both processes and display opposite expression trends in response to population density change. We then identified that these genes mediate the rapid switch of attraction/repulsion behaviors in the migratory locust. Our findings are particularly significant for understanding the process of locust aggregation and may provide new targets to manipulate locust behavior as part of novel management strategies.

Genomics-based approaches to screening carboxylesterase-like genes potentially involved in malathion resistance in oriental migratory locust (Locusta migratoria manilensis)

BACKGROUND

Previous studies have indicated that increased carboxylesterase (CarE) activity is a major mechanism of malathion resistance in field populations of the oriental migratory locust, Locusta migratoria manilensis (Meyen), in China. The aim of the present study was to screen CarE-like genes from a large locust expressed sequence tag (EST) database and to assess their potential roles in malathion resistance.

RESULTS

Twenty-five ESTs derived from different CarE-like genes in the locust EST database were identified, and 12 candidate genes with significantly increased expressions, ranging from 2.6- to 11.6-fold in a field-derived resistant (FR) colony of the locust, were found. These candidate genes were constitutively expressed in all nymph and adult stages, and most of them were predominantly expressed in the gastric caeca and the midgut. Among the 12 genes, two representative genes (LmCarE9 and LmCarE25) were chosen for RNAi followed by malathion bioassay. The nymph mortalities increased from 34.3 to 65.2 and 54.2% respectively after LmCarE9 and LmcarE25 were silenced. These results indicated significant roles of these CarE-like genes in conferring malathion resistance in the locust.

CONCLUSION

Multiple CarE-like genes were involved in malathion resistance in the locust. As validated by RNAi followed by malathion bioassay, LmCarE9 and LmcarE25 played a significant role in conferring malathion resistance.

De novo analysis of transcriptome dynamics in the migratory locust during the development of phase traits

Locusts exhibit remarkable density-dependent phenotype (phase) changes from the solitary to the gregarious, making them one of the most destructive agricultural pests. This phenotype polyphenism arises from a single genome and diverse transcriptomes in different conditions. Here we report a de novo transcriptome for the migratory locust and a comprehensive, representative core gene set. We carried out assembly of 21.5 Gb Illumina reads, generated 72,977 transcripts with N50 2,275 bp and identified 11,490 locust protein-coding genes. Comparative genomics analysis with eight other sequenced insects was carried out to identify the genomic divergence between hemimetabolous and holometabolous insects for the first time and 18 genes relevant to development was found. We further utilized the quantitative feature of RNA-seq to measure and compare gene expression among libraries. We first discovered how divergence in gene expression between two phases progresses as locusts develop and identified 242 transcripts as candidates for phase marker genes. Together with the detailed analysis of deep sequencing data of the 4(th) instar, we discovered a phase-dependent divergence of biological investment in the molecular level. Solitary locusts have higher activity in biosynthetic pathways while gregarious locusts show higher activity in environmental interaction, in which genes and pathways associated with regulation of neurotransmitter activities, such as neurotransmitter receptors, synthetase, transporters, and GPCR signaling pathways, are strongly involved. Our study, as the largest de novo transcriptome to date, with optimization of sequencing and assembly strategy, can further facilitate the application of de novo transcriptome. The locust transcriptome enriches genetic resources for hemimetabolous insects and our understanding of the origin of insect metamorphosis. Most importantly, we identified genes and pathways that might be involved in locust development and phase change, and may thus benefit pest management.

Sexual differentiation in adult insects: male-specific cuticular yellowing in Schistocerca gregaria as a model for reevaluating some current (neuro)endocrine concepts

Changes in the color of the cuticle, days after the completion of hardening, are rare in adult insects. Even more so when such changes are specific to one sexual form and coincide with sexual maturation. Adult males of the desert locust Schistocerca gregaria deposit a well characterized 'yellow protein' in their cuticle about 10 days after the adult molt, but only if they live under crowded (gregarious) conditions. Isolated-reared (solitarious) males do not turn yellow, neither do the females. Upon regrouping, yellowing is quickly induced, but again, only in the males. Juvenile hormone (JH) is involved, but its sex- and phase-specific effect suggests that other factors are also involved. We analyzed the recent and classical literature to find out what should be added or changed to the classical way of thinking on sex differentiation in insects so that a comprehensive conceptual framework could emerge. Undervalued and/or new data on male accessory glands as a possible second site of JH synthesis, on ecdysteroids as possible sex steroids, on the transcription factor fruitless in insects and on the evolutionarily highly conserved transcription factor Foxl2 that, when ablated in mice is responsible for the transdifferentiation of the ovaries into testes, are considered.

Behavioural phase polyphenism in the Australian plague locust (Chortoicetes terminifera)

Swarming and the expression of phase polyphenism are defining characteristics of locust species. Increases in local population density mediate morphological, physiological and behavioural changes within individuals, which correlate with mass marching of juveniles in migratory bands and flying swarms of adults. The Australian plague locust (Chortoicetes terminifera) regularly forms migratory bands and swarms, but is claimed not to express phase polyphenism and has accordingly been used to argue against a central role for phase change in locust swarming. We demonstrate that juvenile C. terminifera express extreme density-dependent behavioural phase polyphenism. Isolated-reared juveniles are sedentary and repelled by conspecifics, whereas crowd-reared individuals are highly active and are attracted to conspecifics. In contrast to other major locust species, however, behavioural phase change does not accumulate across generations, but shifts completely within an individual's lifetime in response to a change in population density.

Characterization and comparative profiling of the small RNA transcriptomes in two phases of locust

High-throughput sequencing of the small RNA transcriptome of locust reveals differences in post-transcriptional regulation between solitary and swarming phases and provides insights into the evolution of insect small RNAs.

Background

All the reports on insect small RNAs come from holometabolous insects whose genome sequence data are available. Therefore, study of hemimetabolous insect small RNAs could provide more insights into evolution and function of small RNAs in insects. The locust is an important, economically harmful hemimetabolous insect. Its phase changes, as a phenotypic plasticity, result from differential gene expression potentially regulated at both the post-transcriptional level, mediated by small RNAs, and the transcriptional level.

Results

Here, using high-throughput sequencing, we characterize the small RNA transcriptome in the locust. We identified 50 conserved microRNA families by similarity searching against miRBase, and a maximum of 185 potential locust-specific microRNA family candidates were identified using our newly developed method independent of locust genome sequence. We also demonstrate conservation of microRNA*, and evolutionary analysis of locust microRNAs indicates that the generation of miRNAs in locusts is concentrated along three phylogenetic tree branches: bilaterians, coelomates, and insects. Our study identified thousands of endogenous small interfering RNAs, some of which were of transposon origin, and also detected many Piwi-interacting RNA-like small RNAs. Comparison of small RNA expression patterns of the two phases showed that longer small RNAs were expressed more abundantly in the solitary phase and that each category of small RNAs exhibited different expression profiles between the two phases.

Conclusions

The abundance of small RNAs in the locust might indicate a long evolutionary history of post-transcriptional gene expression regulation, and differential expression of small RNAs between the two phases might further disclose the molecular mechanism of phase changes.

Neuroparsins, a family of conserved arthropod neuropeptides

Different neuroparsin variants were initially identified as anti-gonadotropic peptides from the pars intercerebralis-corpora cardiaca complex of the migratory locust, Locusta migratoria, and further studies revealed the pleiotropic activities of these peptides. Subsequently, additional neuroparsin-like peptides were discovered from other arthropod species. Studies in mosquitoes and locusts suggest that members of this conserved peptide family are involved in the regulation of insect reproduction and can even serve as molecular markers of the fascinating biological process of locust phase transition. Sequence analysis and multiple alignments revealed pronounced sequence similarities between arthropod neuroparsins and the N-terminal, growth factor binding region of vertebrate and mollusc insulin-like growth factor binding proteins (IGFBP). This observation led to the hypothesis that neuroparsins might interact with endogenous insulin-related peptides. The present paper gives an overview of several neuroparsin family members that have hitherto been described in insects, as well as of a number of newly identified neuroparsin precursors from other species.

Identification and characterization of insect-specific proteins by genome data analysis

Background

Insects constitute the vast majority of known species with their importance including biodiversity, agricultural, and human health concerns. It is likely that the successful adaptation of the Insecta clade depends on specific components in its proteome that give rise to specialized features. However, proteome determination is an intensive undertaking. Here we present results from a computational method that uses genome analysis to characterize insect and eukaryote proteomes as an approximation complementary to experimental approaches.

Results

Homologs in common to Drosophila melanogaster, Anopheles gambiae, Bombyx mori, Tribolium castaneum, and Apis mellifera were compared to the complete genomes of three non-insect eukaryotes (opisthokonts) Homo sapiens, Caenorhabditis elegans and Saccharomyces cerevisiae. This operation yielded 154 groups of orthologous proteins in Drosophila to be insect-specific homologs; 466 groups were determined to be common to eukaryotes (represented by three opisthokonts). ESTs from the hemimetabolous insect Locust migratoria were also considered in order to approximate their corresponding genes in the insect-specific homologs. Stress and stimulus response proteins were found to constitute a higher fraction in the insect-specific homologs than in the homologs common to eukaryotes.

Conclusion

The significant representation of stress response and stimulus response proteins in proteins determined to be insect-specific, along with specific cuticle and pheromone/odorant binding proteins, suggest that communication and adaptation to environments may distinguish insect evolution relative to other eukaryotes. The tendency for low Ka/Ks ratios in the insect-specific protein set suggests purifying selection pressure. The generally larger number of paralogs in the insect-specific proteins may indicate adaptation to environment changes. Instances in our insect-specific protein set have been arrived at through experiments reported in the literature, supporting the accuracy of our approach.

cDNA cloning of heat shock proteins and their expression in the two phases of the migratory locust

The high population density of insects is often a stress factor. Insects synthesize heat shock proteins (Hsps) in response to the impacts of stress through molecular chaperone activity. Locust solitary and gregarious phases occur at low and high population density, respectively. In this study, we compare the expression profiles of the Hsp genes in the two phases of the migratory locust in an attempt to examine the role of Hsps in adaptation to high density populations. The full length cDNAs of Hsp20.5, 20.6, 20.7, 40, 70 and Hsp90 of the migratory locust were cloned and sequenced. The expressional differentiation of the six Hsps in mRNA levels between solitary and gregarious locusts was observed. Results from real-time PCR indicate that the six Hsps are expressed throughout all developmental stages except in the early stage embryo. The expression levels of the six Hsps were significantly upregulated in gregarious locusts. The expressional variations among certain organs, such as the head, thorax and leg of fifth instar nymphs in gregarious locusts were also higher than those in solitary ones. These observations suggest that population density may be an important factor in determining Hsp expression in the locust.

Grasshoppers in research and education: methods for maintenance and production

Insects used in research have traditionally been housed and cared for in the investigator's laboratory. Centralized colony maintenance may be advantageous, but presents unique challenges to animal care staff members, who are more familiar with vertebrate research animals. To fill this potential knowledge gap, the authors share the procedures they have developed at Arizona State University for the housing, husbandry, and breeding of grasshoppers used in research and teaching.

Annotation of novel neuropeptide precursors in the migratory locust based on transcript screening of a public EST database and mass spectrometry

Background

For holometabolous insects there has been an explosion of proteomic and peptidomic information thanks to large genome sequencing projects. Heterometabolous insects, although comprising many important species, have been far less studied. The migratory locust Locusta migratoria, a heterometabolous insect, is one of the most infamous agricultural pests. They undergo a well-known and profound phase transition from the relatively harmless solitary form to a ferocious gregarious form. The underlying regulatory mechanisms of this phase transition are not fully understood, but it is undoubtedly that neuropeptides are involved. However, neuropeptide research in locusts is hampered by the absence of genomic information.

Results

Recently, EST (Expressed Sequence Tag) databases from Locusta migratoria were constructed. Using bioinformatical tools, we searched these EST databases specifically for neuropeptide precursors. Based on known locust neuropeptide sequences, we confirmed the sequence of several previously identified neuropeptide precursors (i.e. pacifastin-related peptides), which consolidated our method. In addition, we found two novel neuroparsin precursors and annotated the hitherto unknown tachykinin precursor. Besides one of the known tachykinin peptides, this EST contained an additional tachykinin-like sequence. Using neuropeptide precursors from Drosophila melanogaster as a query, we succeeded in annotating the Locusta neuropeptide F, allatostatin-C and ecdysis-triggering hormone precursor, which until now had not been identified in locusts or in any other heterometabolous insect. For the tachykinin precursor, the ecdysis-triggering hormone precursor and the allatostatin-C precursor, translation of the predicted neuropeptides in neural tissues was confirmed with mass spectrometric techniques.

Conclusion

In this study we describe the annotation of 6 novel neuropeptide precursors and the neuropeptides they encode from the migratory locust, Locusta migratoria. By combining the manual annotation of neuropeptides with experimental evidence provided by mass spectrometry, we demonstrate that the genes are not only transcribed but also translated into precursor proteins. In addition, we show which neuropeptides are cleaved from these precursor proteins and how they are post-translationally modified.