Quantitative real-time RT-PCR analysis in desert locusts reveals phase dependent differences in neuroparsin transcript levels

Effects of Age, Phase Variation and Pheromones on Male Sperm Storage in the Desert Locust, Schistocerca gregaria

Simple Summary

We investigated male sperm storage in the desert locust Schistocerca gregaria. Phase (solitary or gregarious) did not affect sperm distribution in the vas deferens and seminal vesicle, whereas sperm accumulation of the seminal vesicle in gregarious locusts was promoted more than in solitary ones. Pheromones received from neither mature adults nor nymphs affected sperm distribution in the vas deferens and seminal vesicle. However, sperm accumulation in the seminal vesicle was more promoted in the gregarious locusts which received pheromones from mature adults than those obtained from nymphs at early adult stage, especially seven days after adult emergence.

Abstract

In general, sperm produced in the testis are moved into the seminal vesicle via the vas deferens in insects, where they are stored. How this sperm movement is controlled is less well understood in locusts or grasshoppers. In this study, the effects of age, phase variation and pheromones on male sperm storage were investigated in the desert locust, Schistocerca gregaria (Forskål). In this locust, a pair of ducts, the vasa deferentia, connect the testes to a pair of the long, slender seminal vesicles that are folded approximately thirty times, and where the sperm are stored. We found that phase variation affected the level of sperm storage in the seminal vesicle. Moreover, adult males that detected pheromones emitted by mature adult males showed enhanced sperm storage compared with males that received the pheromones emitted from nymphs: The former, adult male pheromones are known to promote sexual maturation of immature adults of both sexes, whereas the latter, nymphal pheromones delay sexual maturation. Most mature adult males had much sperm in the vasa deferentia at all times examined, suggesting daily sperm movement from the testes to the seminal vesicles via the vasa deferentia. As adult males aged, sperm were accumulated from the proximal part to the distal end of the seminal vesicle. Many sperm remained in the seminal vesicle after mating. These results suggest that young or new sperm located near the proximal part of the seminal vesicle could be used for mating, whereas old sperm not used for mating are stored in the distal part of the seminal vesicle.

Three neuroparsin genes from oriental river prawn, Macrobrachium nipponense, involved in ovary maturation

In this study, we identified three neuroparsin (NP) genes in Macrobrachium nipponense: Mn-NP1, Mn-NP2, and Mn-NP3, encoding 99, 100, and 101 amino acid proteins, respectively. Multiple sequence alignments showed that these genes contained 12 cysteine residues, of which 11 were at conserved positions. The total sequence identity between the genes was 47.5%, and they showed a high degree of sequence identity (> 54% similarity) with other crustacean genes. Phylogenetic tree analysis showed that Mn-NPs were clustered at different branches, indicating that Mn-NPs may have different functions. Tissue distribution data revealed that the three genes were present in males and females during the breeding and nonbreeding season, but their expression patterns differed. Mn-NP1 was highly expressed in the breeding season, in the male testis, and highly expressed in the nonbreeding season, in the female ovary. Mn-NP3 exhibited biased female expression in the breeding and nonbreeding season, with dominant expression in the ovary. All Mn-NPs were detected during embryo development, but with different expression patterns. These data indicated that Mn-NP1 may function during embryonic development, and that Mn-NP2 may be expressed during early embryo cell division, and late larval development. Mn-NP3 expression patterns reflected maternal inheritance, and may be associated with ovarian maturation. These expression data suggested that Mn-NP1 and Mn-NP2 are negatively correlated with ovarian development, with inhibition roles during this development. Mn-NP3 may be involved in vitellogenesis.

Role of neuroparsin 1 in vitellogenesis in the mud crab, Scylla paramamosain

Neuroparsin (NP) is an important neuropeptide in invertebrates. It is well-known that NP displays multiple biological activities, including antidiuretic and inhibition of vitellogenesis in insects. However, the information about its effect in crustaceans is scarce. In this study, the sequence of Sp-NP1 was selected from the transcriptome database from the mud crab, Scylla paramamosain. Sequence analyses indicate that the Sp-NP1 amino acid (AA) sequences consist of a 27 AA signal peptide and a 74 AA mature peptide, which contains 12 cysteine residues. qRT-PCR analysis has revealed that the expressions of Sp-NP1 gene are high in the nervous tissues and extremely low in the ovary and hepatopancreas. In situ hybridization has shown that the positive signals are localized in cell cluster 6 of protocerebrum and cell clusters 10 and 11 of deutocerebrum. The presence of Sp-NP1 in the haemolymph has been detected in S. paramamosain through western blot, which indicates that Sp-NP1 serves as an endocrine factor in the regulation of physiological activities. In vitro experiments have further shown that the mRNA level of vitellogenin in the hepatopancreas notably decreases following administration of recombinant Sp-NP1, while the mRNA level of vitellogenin receptor and cyclin B in the ovary shows no significant differences. Collectively, Sp-NP1 possibly can inhibit the production of vitellogenin in the hepatopancreas and has no direct effect on the ovary in S. paramamosain.

Most lepidopteran neuroparsin genes seem functional, but in some domesticated silkworm strains it has a fatal mutation

The primary sequence of the Arthropod neurohormone neuroparsin is so variable that so far no orthologs from moths and butterflies have been characterized, even though classical neurosecretory stains identify cells that are homologous to those producing this hormone in other insect species. Here Lepidopteran cDNAs showing limited sequence similarity to other insect neuroparsins are described. That these cDNAs do indeed code for authentic neuroparsins was confirmed by in situ hybridization in the wax moth, Galleria mellonella, which labeled the neuroparsin neuroendocrine cells. Although in virtually all genome assemblies from Lepidoptera a neuroparsin gene could be identified, the genome assembly from the silkworm, Bombyx mori, has a neuroparsin gene containing a 16 nucleotide deletion that renders this gene nonfunctional. Although only a small number of all silkworm strains carry this deletion, it suggests that the domestication of the silkworm has rendered the function of this neurohormone dispensable.

Juvenile Hormone receptor Met is essential for ovarian maturation in the Desert Locust, Schistocerca gregaria

Juvenile hormones (JH) are key endocrine regulators produced by the corpora allata (CA) of insects. Together with ecdysteroids, as well as nutritional cues, JH coordinates different aspects of insect postembryonic development and reproduction. The function of the recently characterized JH receptor, Methoprene-tolerant (Met), appears to be conserved in different processes regulated by JH. However, its functional interactions with other hormonal signalling pathways seem highly dependent on the feeding habits and on the developmental and reproductive strategies employed by the insect species investigated. Here we report on the effects of RNA interference (RNAi) mediated SgMet knockdown during the first gonadotrophic cycle in female desert locusts (Schistocerca gregaria). This voracious, phytophagous pest species can form migrating swarms that devastate field crops and harvests in several of the world’s poorest countries. A better knowledge of the JH signalling pathway may contribute to the development of novel, more target-specific insecticides to combat this very harmful swarming pest. Using RNAi, we show that the JH receptor Met is essential for ovarian maturation, vitellogenesis and associated ecdysteroid biosynthesis in adult female S. gregaria. Interestingly, knockdown of SgMet also resulted in a significant decrease of insulin-related peptide (SgIRP) and increase of neuroparsin (SgNP) 3 and 4 transcript levels in the fat body, illustrating the existence of an intricate regulatory interplay between different hormonal factors. In addition, SgMet knockdown in females resulted in delayed display of copulation behaviour with virgin males, when compared with dsGFP injected control animals. Moreover, we observed an incapacity of adult dsSgMet injected female locusts to oviposit during the time of the experimental setup. As such, SgMet is an essential gene playing crucial roles in the endocrine communication necessary for successful reproduction of the desert locust.

Transcriptome Analysis of Newly Emerged Honeybees Exposure to Sublethal Carbendazim During Larval Stage

There are increasing concerns regarding the impact of agrochemical pesticides on non-target organisms. Pesticides could cause honeybee abnormal development in response to neurotoxins such as neonicotinoid. However, knowledge of carbendazim, a widespread fungicide in beekeeping practice, influencing on honeybee (Apis mellifera L.) brain development is lacking. Large-scale transcriptome approaches were applied to determine the changes in global gene expression in the brains of newly emerged honeybees after carbendazim exposure during the larval stage. To further understand the effects of carbendazim on the brain development of honeybees, the functions of differentially expressed genes were compared between the treatment and control groups. We found that neuroregulatory genes were down-regulated after carbendazim exposure, which suggest the neurotoxic effects of this fungicide on honeybee nervous system. Carbendazim exposure also altered the expression of genes implicated in metabolism, transport, sensor, and hormone. Notably, larvae in the carbendazim-treated group observed longer time to shift into the dormant pupal state than the control group. Moreover, a low juvenile hormone and high ecdysone titers were found in the treatment group compared to control group. The data is the first report of neurotoxic effects on honeybee caused by carbendazim, and the sublethal carbendazim may disturb honeybee development and is a potential chemical threating the honeybee colonies.

Epigenetics and locust life phase transitions

Insects are one of the most successful classes on Earth, reflected in an enormous species richness and diversity. Arguably, this success is partly due to the high degree to which polyphenism, where one genotype gives rise to more than one phenotype, is exploited by many of its species. In social insects, for instance, larval diet influences the development into distinct castes; and locust polyphenism has tricked researchers for years into believing that the drastically different solitarious and gregarious phases might be different species. Solitarious locusts behave much as common grasshoppers. However, they are notorious for forming vast, devastating swarms upon crowding. These gregarious animals are shorter lived, less fecund and transmit their phase characteristics to their offspring. The behavioural gregarisation occurs within hours, yet the full display of gregarious characters takes several generations, as does the reversal to the solitarious phase. Hormones, neuropeptides and neurotransmitters influence some of the phase traits; however, none of the suggested mechanisms can account for all the observed differences, notably imprinting effects on longevity and fecundity. This is why, more recently, epigenetics has caught the interest of the polyphenism field. Accumulating evidence points towards a role for epigenetic regulation in locust phase polyphenism. This is corroborated in the economically important locust species Locusta migratoria and Schistocerca gregaria. Here, we review the key elements involved in phase transition in locusts and possible epigenetic regulation. We discuss the relative role of DNA methylation, histone modification and small RNA molecules, and suggest future research directions.

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.

Dopaminergic modulation of phase reversal in desert locusts

Phenotypic plasticity allows animals to modify their behavior, physiology, and morphology to adapt to environmental change. The global pest, the desert locust, shows two extreme phenotypes; a solitarious phase that is relatively harmless and a gregarious phase that forms swarms and causes extensive agricultural and economic damage. In the field, environmental conditions can drive isolated animals into crowded populations and previous studies have identified the biogenic amine serotonin as a key determinant of this transition. Here we take an integrated approach to investigate the neurochemical, physiological, and behavioral correlates defined by a laboratory based paradigm that mimics facets of swarm break down as gregarious locusts become isolated. Following isolation there was an increased propensity of locusts to avoid conspecifics, and show a reduced locomotion. Changes in choice behavior occurred within 1 h of isolation although isolation-related changes progressed with increased isolation time. Isolation was accompanied by changes in the levels of the biogenic amines dopamine, octopamine, and serotonin within the CNS within 1 h. Dopamine levels were higher in isolated animals and we focused on the role played by this transmitter in synaptic changes that may underpin solitarization. Dopamine reduced synaptic efficacy at a key central synapse between campaniform sensilla (CS) and a fast extensor tibiae motor neuron that is involved in limb movement. We also show that dopamine injection into the haemocoel was sufficient to induce solitarious-like behavior in otherwise gregarious locusts. Further, injection of a dopamine antagonist, fluphenazine, into isolated locusts induced gregarious-like behavior. This highlights that dopaminergic modulation plays an important role in the plasticity underpinning phase transition and sets a context to deepen the understanding of the complementary role that distinct neuromodulators play in polyphenism in locusts.

cDNA cloning and transcript distribution of two novel members of the neuroparsin peptide family in a hemipteran insect (Nezara viridula) and a decapod crustacean (Jasus lalandii)

Two novel neuroparsin (NP) precursor cDNAs were cloned: one from the corpora cardiaca of an insect, the green stink bug Nezara viridula, and the other from the X-organ of a decapod crustacean, the spiny lobster Jasus lalandii. The translated NP precursor consists of 106 amino acid residues in N. viridula and 103 amino acid residues in J. lalandii, with 14 and 12 cysteine residues, respectively, in conserved positions when aligned with known NPs. Reverse transcriptase PCR shows that in both arthropods, NP is expressed in some neural tissues: corpora cardiaca, sub-esophageal ganglion and brain of N. viridula; X-organ, brain, sub-esophageal and thoracic ganglion in J. lalandii. Additionally, NP is also expressed in non-neural tissues, such as fat body, leg muscle, flight muscle, reproductive organs and antennae in N. viridula, and heart and ovary in J. lalandii. There are no major differences in the NP transcript expression in mature and immature stink bugs, and also no difference between male and female stink bugs.

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.

More than two decades of research on insect neuropeptide GPCRs: an overview

This review focuses on the state of the art on neuropeptide receptors in insects. Most of these receptors are G protein-coupled receptors (GPCRs) and are involved in the regulation of virtually all physiological processes during an insect's life. More than 20 years ago a milestone in invertebrate endocrinology was achieved with the characterization of the first insect neuropeptide receptor, i.e., the Drosophila tachykinin-like receptor. However, it took until the release of the Drosophila genome in 2000 that research on neuropeptide receptors boosted. In the last decade a plethora of genomic information of other insect species also became available, leading to a better insight in the functions and evolution of the neuropeptide signaling systems and their intracellular pathways. It became clear that some of these systems are conserved among all insect species, indicating that they fulfill crucial roles in their physiological processes. Meanwhile, other signaling systems seem to be lost in several insect orders or species, suggesting that their actions were superfluous in those insects, or that other neuropeptides have taken over their functions. It is striking that the deorphanization of neuropeptide GPCRs gets much attention, but the subsequent unraveling of the intracellular pathways they elicit, or their physiological functions are often hardly examined. Especially in insects besides Drosophila this information is scarce if not absent. And although great progress made in characterizing neuropeptide signaling systems, even in Drosophila several predicted neuropeptide receptors remain orphan, awaiting for their endogenous ligand to be determined. The present review gives a précis of the insect neuropeptide receptor research of the last two decades. But it has to be emphasized that the work done so far is only the tip of the iceberg and our comprehensive understanding of these important signaling systems will still increase substantially in the coming years.

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.

RNA interference of insulin-related peptide and neuroparsins affects vitellogenesis in the desert locust Schistocerca gregaria

The 'classic' insect hormones, juvenile hormone and 20-hydroxyecdysone, can stimulate vitellogenesis and/or ovarian development in adult females of several insect species. Accumulating evidence also indicates a crucial role in female reproductive physiology for peptide hormones, such as insulin-related peptides (IRPs) and neuroparsins (NPs). Especially in dipteran species, IRP signaling has been shown to regulate female reproductive events. The first NP was originally identified from the migratory locust (Locusta migratoria) as an antigonadotropic factor that delayed vitellogenesis. Moreover, NP family members display sequence similarities with the N-terminal domain of vertebrate insulin-like growth factor binding proteins (IGFBPs). In the current study, RNA interference (RNAi) was employed to investigate the possible involvement of IRP and NPs in the control of the female desert locust (Schistocerca gregaria) reproductive system. The cDNAs encoding an IRP (Scg-IRP) and four NPs (Scg-NPs) had previously been cloned from S. gregaria. An RNAi-mediated knock-down of either Scg-NP or Scg-IRP transcript levels was induced in adult female desert locusts and the subsequent effects were analyzed. Knock-down of the Scg-NPs or Scg-IRP affected vitellogenin transcript levels and oocyte growth in a positive and negative way, respectively. The current findings are indicative for a role of Scg-NPs and Scg-IRP in the control of vitellogenin synthesis. A plausible hypothesis is that Scg-IRP may act as a sensor of the nutritional and metabolic status that determines whether vitellogenesis can occur. That the same processes were affected in opposite ways in both RNAi experiments offers an extra argument for antagonizing roles of Scg-NPs and Scg-IRP.

Endocrinology of reproduction and phase transition in locusts

In the last decade, important progress has been made in the experimental analysis of the endocrine mechanisms controlling reproduction and phase transition in locusts. Phase transition is a very fascinating, but complex, phenomenon of phenotypic plasticity that is triggered by changes in population density and can lead to the formation of extremely devastating hopper bands and adult gregarious locust swarms. While some phase characteristics change within hours, others appear more gradually in the next stage(s), or even in the next generation(s). In adults, the phase status also has a major influence on the process of reproduction. A better understanding of how solitarious locusts become gregarious and how this switch affects reproductive physiology may result in novel strategies to fight locust plagues. In this paper, we will review the current knowledge concerning this close interaction between locust phase polyphenism and reproduction.

Quantitative RT-PCR analysis of pacifastin-related precursor transcripts during the reproductive cycle of solitarious and gregarious desert locusts

In locusts, little is known about the physiological and biochemical mechanisms regulating complex processes, such as reproduction and phase transition. The pacifastin family constitutes a family of peptidic inhibitors of serine proteases that are considered to be important regulators of several physiological processes in arthropods. We have performed a detailed transcript profiling analysis of two pacifastin-related peptide precursors, SGPP-2 and SGPP-4, during the reproductive cycle of adult desert locusts (Schistocerca gregaria). This quantitative real-time (RT)-PCR analysis revealed a temporal regulation of both transcripts, which is paralleled by several events that occur during the reproductive cycle of adult locusts. The observed temporal transcript profiles display a strong tissue-, gender- and phase-dependence. In addition, a partial regregarization experiment suggests that both transcript levels are regulated during phase transition and can be employed as molecular markers of the gregarization process.

The role of hemocytes, serine protease inhibitors and pathogen-associated patterns in prophenoloxidase activation in the desert locust, Schistocerca gregaria

The prophenoloxidase-activating system is an important component of the innate immune response of insects, involved in wound healing and melanotic encapsulation. In this paper we show that in the desert locust, Schistocerca gregaria, hemocytes, challenged with microbial elicitors, are indispensable for the limited proteolytic activation of prophenoloxidase (proPO) in plasma. In addition, we assessed the influence of serine protease inhibitors on the induction of PO-activity in plasma. While soybean Bowman-Birk inhibitor (SBBI) inhibited the PO activation by laminarin-treated hemocytes, the endogenous pacifastin-related inhibitors, SGPI-1 (S. gregaria pacifastin-related inhibitor-1) and SGPI-2 did not affect the PO-activity under similar conditions. On the other hand, real-time PCR analysis revealed that the transcripts, encoding SGPI-1-3, were more abundant in the fat body of immune challenged animals, as compared to control animals.

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.

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.

Regulation of Schistocerca gregaria neuroparsin transcript levels by juvenile hormone and 20-hydroxyecdysone

Neuroparsins (NPs) are small proteins that were originally discovered in the pars intercerebralis-corpus cardiacum neurosecretory complex of the migratory locust brain. From the desert locust, Schistocerca gregaria, we recently cloned four different transcripts, each coding for a distinct NP-related peptide. In addition to the brain, some NP-like precursor (Scg-NPP) transcripts also occur in a number of peripheral tissues, and their expression levels are controlled in a gender- and stage-dependent manner. Previous studies revealed a close correlation between Scg-NPP transcript levels and the gonotrophic cycle. In the present report, we demonstrate that certain Scg-NPP transcript levels are significantly altered upon injection of juvenile hormone (JH) or 20-hydroxyecdysone (20E) in adult gregarious desert locusts (five days after final ecdysis). While Scg-NPP1 transcript levels did not significantly change as a result of hormone treatment (animals were analyzed 24 h after injection), Scg-NPP2, Scg-NPP3, and Scg-NPP4 displayed hormone-dependent regulation in various tissues. Scg-NPP2 and Scg-NPP3 transcript levels significantly increased in the brain of JH-treated locusts. In addition, JH induction of Scg-NPP3 and Scg-NPP4 transcripts was observed in male fat body and in male and female gonads. Furthermore, 20E injection also induced Scg-NPP2, Scg-NPP3, and Scg-NPP4 transcripts in desert locust gonads. This is the first report showing NP-like precursor gene expression in insect ovaries. Our study indicates that the expression levels of some Scg-NPP transcripts are regulated by developmental hormones, suggesting a close correlation between NP expression and the endocrine control of the reproductive cycle.

Neuroparsin transcripts as molecular markers in the process of desert locust (Schistocerca gregaria) phase transition

Desert locust swarms occasionally cause severe ecological and economic damage, particularly in countries of northwest Africa. However, the physiological mechanisms underlying locust phase transition, the switch of the solitarious to the gregarious phase, remain elusive. Therefore, identification of molecular changes linked to this phenomenon represents a primary requirement to start unraveling this enigma. The present paper provides novel information on phase-related molecular markers for locust phase transition. We present a detailed quantitative real-time RT-PCR analysis of two distinct neuroparsin precursor transcripts (Scg-NPP3 and Scg-NPP4) in the brain and in abdominal tissues of gregarious and solitarious desert locusts (Schistocerca gregaria). Our data reveal different temporal changes of these transcripts in the fat body during the adult stage of both phases. We, hereby, present novel scientific evidence for a phase-dependent regulation of these particular peptide hormone encoding transcripts and assign them as possible molecular markers in the process of locust phase transition.