Strategic expression of ion transport peptide gene products in central and peripheral neurons of insects

Ion transport peptide and ion transport peptide-like regulate ecdysis behavior and water transport during ecdysis in Gryllus bimaculatus

Ion transport peptide (ITP) and ITP-like (ITPLs) are pleiotropic bioactive peptides in insects. Although the contribution of these peptides to ecdysis has been studied, the precise regulatory mechanisms remain poorly understood. Here, we characterized the functions of itp and itpl variants in the two-spotted cricket, Gryllus bimaculatus. Reverse transcription-quantitative PCR and whole-mount in situ hybridization revealed that itp was expressed in the brain and terminal abdominal ganglion, whereas itpl variants were expressed in all ganglia of the central nervous system. Simultaneous knockdown of itp and itpls disrupted ecdysis behavior and water transport from the gut into the hemolymph during molting. Nevertheless, knockdown of itpls without influencing itp expression did not significantly affect ecdysis behavior but caused a reduction in hemolymph mass. Although water transport into the hemolymph is considered necessary for the swelling required to split the old cuticle layers during molting, a rescue experiment by injection of water or cricket Ringer's solution into the hemolymph of knockdown crickets did not recover the normal phenotype. Therefore, we propose that ITP/ITPL control ecdysis behavior probably not by regulating water transport from the gut into the hemolymph in crickets.

Molecular characterization, localization, and physiological roles of ITP and ITP-L in the mosquito, Aedes aegypti

The insect ion transport peptide (ITP) and its alternatively spliced variant, ITP-like peptide (ITP-L), belong to the crustacean hyperglycemic hormone family of peptides and are widely conserved among insect species. While limited, studies have characterized the ITP/ITP-L signaling system within insects, and putative functions including regulation of ion and fluid transport, ovarian maturation, and thirst/excretion have been proposed. Herein, we aimed to molecularly investigate Itp and Itp-l expression profiles in the mosquito, Aedes aegypti, examine peptide immunolocalization and distribution within the adult central nervous system, and elucidate physiological roles for these neuropeptides. Transcript expression profiles of both AedaeItp and AedaeItp-l revealed distinct enrichment patterns in adults, with AedaeItp expressed in the brain and AedaeItp-l expression predominantly within the abdominal ganglia. Immunohistochemical analysis within the central nervous system revealed expression of AedaeITP peptide in a number of cells in the brain and in the terminal ganglion. Comparatively, AedaeITP-L peptide was localized solely within the pre-terminal abdominal ganglia of the central nervous system. Interestingly, prolonged desiccation stress caused upregulation of AedaeItp and AedaeItp-l levels in adult mosquitoes, suggesting possible functional roles in water conservation and feeding-related activities. RNAi-mediated knockdown of AedaeItp caused an increase in urine excretion, while knockdown of both AedaeItp and AedaeItp-l reduced blood feeding and egg-laying in females as well as hindered egg viability, suggesting roles in reproductive physiology and behavior. Altogether, this study identifies AedaeITP and AedaeITP-L as key pleiotropic hormones, regulating various critical physiological processes in the disease vector, A. aegypti.

Wing expansion functional analysis of ion transport peptide gene in Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

Ion transport peptide (ITP), a superfamily of arthropod neuropeptides, serves a crucial role in regulating various physiological processes such as diuresis, ecdysis behavior, and wing expansion. However, the molecular characteristics, expression profile, and role of ITP in Sogatella furcifera are poorly understood. To elucidate the characteristics and biological function of ITP in S. furcifera, we employed reverse transcription-polymerase chain reaction (RT-PCR) and RNA interference (RNAi) methods. The identified SfITP gene encodes 117 amino acids. The expression of SfITP gradually increased followed the formation of 3-day-old of 5th instar nymph, peaking initially at 40 min after eclosion, and reaching another peak 24 h after eclosion, with particularly high expression levels in thorax and wing tissues. Notably, SfITP RNAi in 3rd instar nymphs of S. furcifera significantly inhibited the transcript levels of SfITP, resulting in 55% mortality and 78% wing deformity. These findings suggests that SfITP is involved in the regulation of wing expansion in S. furcifera, providing insights into the regulation of insect wing expansion and contributing to the molecular understanding of this process.

Managing fuels and fluids: Network integration of osmoregulatory and metabolic hormonal circuits in the polymodal control of homeostasis in insects

Osmoregulation in insects is an essential process whereby changes in hemolymph osmotic pressure induce the release of diuretic or antidiuretic hormones to recruit individual osmoregulatory responses in a manner that optimizes overall homeostasis. However, the mechanisms by which different osmoregulatory circuits interact with other homeostatic networks to implement the correct homeostatic program remain largely unexplored. Surprisingly, recent advances in insect genetics have revealed several important metabolic functions are regulated by classic osmoregulatory pathways, suggesting that internal cues related to osmotic and metabolic perturbations are integrated by the same hormonal networks. Here, we review our current knowledge on the network mechanisms that underpin systemic osmoregulation and discuss the remarkable parallels between the hormonal networks that regulate body fluid balance and those involved in energy homeostasis to provide a framework for understanding the polymodal optimization of homeostasis in insects.

Identification and expression of short neuropeptide F and its receptors in the tick Ixodes ricinus

In Europe, the tick Ixodes ricinus is the most important vector of numerous pathogens that are transmitted during blood feeding on their vertebrate hosts. To elucidate mechanisms controlling blood intake and associated transmission of pathogens we identified and described expression of short neuropeptide F (sNPF) and its receptors which are known to regulate feeding in insects. Using in situ hybridization (ISH) and immunohistochemistry (IHC) we stained numerous neurons producing sNPF in the central nervous system (CNS; synganglion), while a few peripheral neurons were detected anteriorly to the synganglion, and on the surface of the hindgut and leg muscles. Apparent sNPF expression was also found in enteroendocrine cells individually scattered in anterior lobes of the midgut. In silico analyses and BLAST search for sNPF receptors revealed two putative G protein-coupled receptors (sNPFR1 and sNPFR2) in the I. ricinus genome. Aequorin-based functional assay in CHO cells showed that both receptors were specific and sensitive to sNPF in nanomolar concentrations. Increased expression levels of these receptors in the gut during blood intake suggest that sNPF signaling may be involved in regulation of feeding and digestion processes of I. ricinus.

Differential expression of ITP and ITPL indicate multiple functions in the silkworm Bombyx mori

Ion transport peptide (ITP) and a longer ITP-like (ITPL) are alternatively spliced insect neuropeptides involved in the regulation of development and water homeostasis. Using in situ hybridisation and immunohistochemistry, we determined site- and stage-specific expression of each peptide in Bombyx mori. Each peptide was differentially expressed, except for the prominent overlapping expression of both peptides in six pairs of the brain neurosecretory cells Ia₂. After metamorphosis, ITP appeared in the male-specific neurons of the abdominal neuromere 9 (MAN₉) that innervate the reproductive organs. ITPL was detected in a pair of dorsolateral interneurons (IN-DL) in each thoracic and abdominal ganglion, and in the thoracic neurosecretory cells (NS-VTL₂) which terminate in the vicinity of the prothoracic gland. Feeding larvae showed ITPL expression in the abdominal neurosecretory cells M5. ITPL was also expressed in the peripheral L1 neurons that project axons into the thoracic and abdominal transverse nerves. Our results suggest that ITP and ITPL exhibit different sex- and stage-specific functions that may include regulation of reproduction and steroid production. For future functional studies, we identified an upstream regulatory region controlling ITP/ITPL expression in the brain and L1 neurons, and prepared stable transgenic line pITP-Gal4.2 using the piggyBac system.

Expression analysis of peptidergic enteroendocrine cells in the silkworm Bombyx mori

Enteroendocrine cells (ECs) in the insect midgut respond to physiological changes in the intestine by releasing multiple peptides to control food intake, gastrointestinal activity and systemic metabolism. Here, we performed a comprehensive mapping of ECs producing different regulatory peptides in the larval midgut of Bombyx mori. In total, we identified 20 peptide genes expressed in different ECs in specific regions of the midgut. Transcript-specific in situ hybridisation combined with antibody staining revealed approximately 30 subsets of ECs, each producing a unique peptide or a combination of several different peptides. Functional significance of this diversity and specific roles of different enteroendocrine peptides are largely unknown. Results of this study highlight the importance of the midgut as a major endocrine/paracrine source of regulatory molecules in insects and provide important information to clarify functions of ECs during larval feeding and development.

A cytorhabdovirus-based expression vector in Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera

The brown planthopper (BPH, Nilaparvata lugens), the small brown planthopper (SBPH, Laodelphax striatellus), and the white-backed planthopper (WBPH, Sogatella furcifera) are problematic insect pests and cause severe yield losses through phloem sap-sucking and virus transmission. Barley yellow striate mosaic virus (BYSMV), a plant cytorhabdovirus, has been developed as versatile expression platforms in SBPHs and cereal plants. However, bio-safe overexpression vectors based on recombinant BYSMV (rBYSMV) remain to be developed and applied to the three kinds of planthoppers. Here, we found that rBYSMV was able to infect SBPHs, BPHs and WBPHs through microinjection with crude extracts from rBYSMV-infected barley leaves. To ensure bio-safety of the rBYSMV vectors, we generated an rBYSMV mutant by deleting the accessory protein P3, a putative viral movement protein. As expected, the resulting mutant abolished viral systemic infection in barley plants but had no effects on BYSMV infectivity in insect vectors. Subsequently, we used the modified rBYSMV vector to overexpress iron transport peptide (ITP) in the three kinds of planthoppers and revealed the potential functions of ITP. Overall, our results provide bio-safe overexpression platforms to facilitate functional genomics studies of planthoppers.

The Crustacean Hyperglycemic Hormone Superfamily: Progress Made in the Past Decade

Early studies recognizing the importance of the decapod eyestalk in the endocrine regulation of crustacean physiology-molting, metabolism, reproduction, osmotic balance, etc.-helped found the field of crustacean endocrinology. Characterization of putative factors in the eyestalk using distinct functional bioassays ultimately led to the discovery of a group of structurally related and functionally diverse neuropeptides, crustacean hyperglycemic hormone (CHH), molt-inhibiting hormone (MIH), gonad-inhibiting hormone (GIH) or vitellogenesis-inhibiting hormone (VIH), and mandibular organ-inhibiting hormone (MOIH). These peptides, along with the first insect member (ion transport peptide, ITP), constitute the original arthropod members of the crustacean hyperglycemic hormone (CHH) superfamily. The presence of genes encoding the CHH-superfamily peptides across representative ecdysozoan taxa has been established. The objective of this review is to, aside from providing a general framework, highlight the progress made during the past decade or so. The progress includes the widespread identification of the CHH-superfamily peptides, in particular in non-crustaceans, which has reshaped the phylogenetic profile of the superfamily. Novel functions have been attributed to some of the newly identified members, providing exceptional opportunities for understanding the structure-function relationships of these peptides. Functional studies are challenging, especially for the peptides of crustacean and insect species, where they are widely expressed in various tissues and usually pleiotropic. Progress has been made in deciphering the roles of CHH, ITP, and their alternatively spliced counterparts (CHH-L, ITP-L) in the regulation of metabolism and ionic/osmotic hemostasis under (eco)physiological, developmental, or pathological contexts, and of MIH in the stimulation of ovarian maturation, which implicates it as a regulator for coordinating growth (molt) and reproduction. In addition, experimental elucidation of the steric structure and structure-function relationships have given better understanding of the structural basis of the functional diversification and overlapping among these peptides. Finally, an important finding was the first-ever identification of the receptors for this superfamily of peptides, specifically the receptors for ITPs of the silkworm, which will surely give great impetus to the functional study of these peptides for years to come. Studies regarding recent progress are presented and synthesized, and prospective developments remarked upon.

Transcriptomic Analysis of the Kuruma Prawn Marsupenaeus japonicus Reveals Possible Peripheral Regulation of the Ovary

Crustacean reproduction has been hypothesized to be under complex endocrinological regulation by peptide hormones. To further improve our understanding of the mechanisms underlying this complex regulation, knowledge is needed regarding the hormones not only of the central nervous system (CNS) such as the X-organ/sinus gland (XOSG), brain, and thoracic ganglia, but also the peripheral gonadal tissues. For example, in vertebrates, some gonadal peptide hormones including activin, inhibin, follistatin, and relaxin are known to be involved in the reproductive physiology. Therefore, it is highly likely that some peptide factors from the ovary are serving as the signals among peripheral tissues and central nervous tissues in crustaceans. In this work, we sought to find gonadal peptide hormones and peptide hormone receptors by analyzing the transcriptome of the ovary of the kuruma prawn Marsupenaeus japonicus. The generated ovarian transcriptome data led to the identification of five possible peptide hormones, including bursicon-α and -β, the crustacean hyperglycemic hormone (CHH)-like peptide, insulin-like peptide (ILP), and neuroparsin-like peptide (NPLP). Dominant gene expressions for the bursicons were observed in the thoracic ganglia and the ovary, in the CNS for the CHH-like peptide, in the heart for NPLP, and in the ovary for ILP. Since the gene expressions of CHH-like peptide and NPLP were affected by a CHH (Penaeus japonicus sinus gland peptide-I) from XOSG, we produced recombinant peptides for CHH-like peptide and NPLP using Escherichia coli expression system to examine their possible peripheral regulation. As a result, we found that the recombinant NPLP increased vitellogenin gene expression in incubated ovarian tissue fragments. Moreover, contigs encoding putative receptors for insulin-like androgenic gland factor, insulin, neuroparsin, and neuropeptide Y/F, as well as several contigs encoding orphan G-protein coupled receptors and receptor-type guanylyl cyclases were also identified in the ovarian transcriptome. These results suggest that reproductive physiology in crustaceans is regulated by various gonadal peptide hormones, akin to vertebrates.

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

Developmental and sex-specific differences in expression of neuropeptides derived from allatotropin gene in the silkmoth Bombyx mori

Allatotropin (AT) and related neuropeptides are widespread bioactive molecules that regulate development, food intake and muscle contractions in insects and other invertebrates. In moths, alternative splicing of the at gene generates three mRNA precursors encoding AT with different combinations of three structurally similar AT-like peptides (ATLI-III). We used in situ hybridization and immunohistochemistry to map the differential expression of these transcripts during the postembryonic development of Bombyx mori. Transcript encoding AT alone was expressed in numerous neurons of the central nervous system and frontal ganglion, whereas transcripts encoding AT with ATLs were produced by smaller specific subgroups of neurons in larval stages. Metamorphosis was associated with considerable developmental changes and sex-specific differences in the expression of all transcripts. The most notable was the appearance of AT/ATL transcripts (1) in the brain lateral neurosecretory cells producing prothoracicotropic hormone; (2) in the male-specific cluster of about 20 neurons in the posterior region of the terminal abdominal ganglion; (3) in the female-specific medial neurons in the abdominal ganglia AG2-7. Immunohistochemical staining showed that these neurons produced a mixture of various neuropeptides and innervated diverse peripheral organs. Our data suggest that AT/ATL neuropeptides are involved in multiple stage- and sex-specific functions during the development of B. mori.

Tachykinin-Related Peptides Share a G Protein-Coupled Receptor with Ion Transport Peptide-Like in the Silkworm Bombyx mori

Recently, we identified an orphan Bombyx mori neuropeptide G protein-coupled receptor (BNGR)-A24 as an ion transport peptide-like (ITPL) receptor. BNGR-A24 belongs to the same clade as BNGR-A32 and -A33, which were recently identified as natalisin receptors. Since these three BNGRs share high similarities with known receptors for tachykinin-related peptides (TRPs), we examined whether these BNGRs can function as physiological receptors for five endogenous B. mori TRPs (TK-1–5). In a heterologous expression system, BNGR-A24 acted as a receptor for all five TRPs. In contrast, BNGR-A32 responded only to TK-5, and BNGR-A33 did not respond to any of the TRPs. These findings are consistent with recent studies on the ligand preferences for B. mori natalisins. Furthermore, we evaluated whether the binding of ITPL and TRPs to BNGR-A24 is competitive by using a Ca²⁺ imaging assay. Concomitant addition of a TRP receptor antagonist, spantide I, reduced the responses of BNGR-A24 not only to TK-4 but also to ITPL. The results of a binding assay using fluorescent-labeled BNGR-A24 and ligands demonstrated that the binding of ITPL to BNGR-A24 was inhibited by TK-4 as well as by spantide I, and vice versa. In addition, the ITPL-induced increase in cGMP levels of BNGR-A24-expressing BmN cells was suppressed by the addition of excess TK-4 or spantide I. The intracellular levels of cAMP and cGMP, as second messenger candidates of the TRP signaling, were not altered by the five TRPs, suggesting that these peptides act via different signaling pathways from cAMP and cGMP signaling at least in BmN cells. Taken together, the present findings suggest that ITPL and TRPs are endogenous orthosteric ligands of BNGR-A24 that may activate discrete signaling pathways. This receptor, which shares orthosteric ligands, may constitute an important model for studying ligand-biased signaling.

Identification and characterization of receptors for ion transport peptide (ITP) and ITP-like (ITPL) in the silkworm Bombyx mori

Ion transport peptide (ITP) and its alternatively spliced variant, ITP-like (ITPL), are insect peptides that belong to the crustacean hyperglycemic hormone family. These peptides modulate the homeostatic mechanisms for regulating energy metabolism, molting, and reproduction and are specifically conserved in ecdysozoans. Many of the details of the molecular mechanisms by which crustacean hyperglycemic hormone family peptides exert pleiotropy remain to be elucidated, including characterization of their receptors. Here we identified three Bombyx mori orphan neuropeptide G protein-coupled receptors (BNGRs), BNGR-A2, -A24, and -A34, as receptors for ITP and ITPL (collectively referred to as ITPs). BNGR-A2 and -A34 and BNGR-A24 respond to recombinant ITPs, respectively, with EC50 values of 1.1-2.6 × 10(-8) M, when expressed in a heterologous expression system. These three candidate BNGRs are expressed at larval B. mori tissues targeted by ITPs, with cGMP elevation observed after exposure to recombinant ITPs. ITPs also increased the cGMP level in B. mori ovary-derived BmN cells via membrane-bound and soluble guanylyl cyclases. The simultaneous knockdown of bngr-A2 and -A34 significantly decreased the response of BmN cells to ITP, whereas knockdown of bngr-A24 led to decreased responses to ITPL. Conversely, transient expression of bngr-A24 potentiated the response of BmN cells to ITPL. An in vitro binding assay showed direct interaction between ITPs and heterologously expressed BNGRs in a ligand-receptor-specific manner. Taken together, these data demonstrate that BNGR-A2 and -A34 are ITP receptors and that BNGR-A24 is an ITPL receptor in B. mori.

Endocrine regulation of insect diuresis in the early postgenomic era1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Diuresis, the removal of excess metabolic waste through production of primary urine while maintaining homeostasis, is an important biological process that is tightly regulated by endocrine factors. Several hormonal components that act as diuretic or antidiuretic factors in insects have been identified in the last few decades. Physiological mechanisms responsible for ion and water transport across biological membranes have been intensively studied. The large amount of data rapidly accumulating in the genomics era has led to an increased dependence on reverse genetic and physiological approaches, first identifying candidate genes and subsequently deriving functions. In many cases, the reverse approaches have been highly successful, especially in studies of the receptors for diuretic factors, which are mainly G-protein-coupled receptors. This review summarizes research on insect diuretic and antidiuretic endocrine factors, and their receptors. Emphases of the review are given to the genomics of ligands and their receptors, as well as to their implications for evolution and function.

The CHH-superfamily of multifunctional peptide hormones controlling crustacean metabolism, osmoregulation, moulting, and reproduction

Apart from providing an up-to-date review of the literature, considerable emphasis was placed in this article on the historical development of the field of "crustacean eyestalk hormones". A role of the neurosecretory eyestalk structures of crustaceans in endocrine regulation was recognized about 80 years ago, but it took another half a century until the first peptide hormones were identified. Following the identification of crustacean hyperglycaemic hormone (CHH) and moult-inhibiting hormone (MIH), a large number of homologous peptides have been identified to this date. They comprise a family of multifunctional peptides which can be divided, according to sequences and precursor structure, into two subfamilies, type-I and -II. Recent results on peptide sequences, structure of genes and precursors are described here. The best studied biological activities include metabolic control, moulting, gonad maturation, ionic and osmotic regulation and methyl farnesoate synthesis in mandibular glands. Accordingly, the names CHH, MIH, and GIH/VIH (gonad/vitellogenesis-inhibiting hormone), MOIH (mandibular organ-inhibiting hormone) were coined. The identification of ITP (ion transport peptide) in insects showed, for the first time, that CHH-family peptides are not restricted to crustaceans, and data mining has recently inferred their occurrence in other ecdysozoan clades as well. The long-held tenet of exclusive association with the eyestalk X-organ-sinus gland tract has been challenged by the finding of several extra nervous system sites of expression of CHH-family peptides. Concerning mode of action and the question of target tissues, second messenger mechanisms are discussed, as well as binding sites and receptors. Future challenges are highlighted.

Neuropeptide precursor gene discovery in the Chagas disease vector Rhodnius prolixus

We show a straightforward workflow combining homology search in Rhodnius prolixus genome sequence with cloning by rapid amplification of cDNA ends and mass spectrometry. We have identified 32 genes and their transcripts that encode a number of neuropeptide precursors leading to 194 putative peptides. We validated by mass spectrometry 82 of those predicted neuropeptides in the brain of R. prolixus to achieve the first comprehensive genomic, transcriptomic and neuropeptidomic analysis of an insect disease vector. Comparisons of available insect neuropeptide sequences revealed that the R. prolixus genome contains most of the conserved neuropeptides in insects, many of them displaying specific features at the sequence level. Some gene families reported here are identified for the first time in the order Hemiptera, a highly biodiverse group of insects that includes many human, animal and plant disease agents.

Identification of chelicerate neuropeptides using bioinformatics of publicly accessible expressed sequence tags

While numerous investigations have focused on the identification of neuropeptides in arthropods, most have been conducted on members of the Hexapoda or Crustacea, and little is currently known about those in the Chelicerata. Here, publicly accessible expressed sequence tags (ESTs) were mined for putative chelicerate neuropeptide-encoding transcripts; the peptides encoded by the ESTs were deduced using on-line peptide prediction programs and homology to known isoforms. Fifty-eight ESTs representing eight peptide families/subfamilies were identified using this strategy. Of note was the prediction of the first authentic chelicerate C-type allatostatin, pQIRYHQCYFNPISCF, from the mite Tetranychus urticae, as well as the prediction a novel allatostatin CC peptide, GEGKMFWRCYFNAVSCF, from both the tick Amblyomma variegatum and the scorpion Mesobuthus gibbosus. Also identified from T. urticae were authentic crustacean cardioactive peptide (CCAP), several peptides belonging to the crustacean hyperglycemic hormone/ion transport peptide superfamily, members of the calcitonin-like diuretic hormone/diuretic hormone 31 family, and several FMRFamide-like peptides, specifically members of the neuropeptide F (NPF) and short neuropeptide F subfamilies. To the best of our knowledge the identifications of CCAP and NPF in T. urticae are the first for the Chelicerata. In addition, several novel orcokinins were identified from the scorpion Scorpiops jendeki and the spider Loxosceles laeta; in S. jendeki previously unknown isoforms of SIFamide, ESRNPPLNGSMFamide and ESKNPPLNGSMFamide, were also predicted. Taken collectively, the data presented in our study expand the catalog of known chelicerate neuropeptides and provide a foundation for future physiological studies of them in these animals.

Molecular evolution of the crustacean hyperglycemic hormone family in ecdysozoans

BACKGROUND

Crustacean Hyperglycemic Hormone (CHH) family peptides are neurohormones known to regulate several important functions in decapod crustaceans such as ionic and energetic metabolism, molting and reproduction. The structural conservation of these peptides, together with the variety of functions they display, led us to investigate their evolutionary history. CHH family peptides exist in insects (Ion Transport Peptides) and may be present in all ecdysozoans as well. In order to extend the evolutionary study to the entire family, CHH family peptides were thus searched in taxa outside decapods, where they have been, to date, poorly investigated.

RESULTS

CHH family peptides were characterized by molecular cloning in a branchiopod crustacean, Daphnia magna, and in a collembolan, Folsomia candida. Genes encoding such peptides were also rebuilt in silico from genomic sequences of another branchiopod, a chelicerate and two nematodes. These sequences were included in updated datasets to build phylogenies of the CHH family in pancrustaceans. These phylogenies suggest that peptides found in Branchiopoda and Collembola are more closely related to insect ITPs than to crustacean CHHs. Datasets were also used to support a phylogenetic hypothesis about pancrustacean relationships, which, in addition to gene structures, allowed us to propose two evolutionary scenarios of this multigenic family in ecdysozoans.

CONCLUSIONS

Evolutionary scenarios suggest that CHH family genes of ecdysozoans originate from an ancestral two-exon gene, and genes of arthropods from a three-exon one. In malacostracans, the evolution of the CHH family has involved several duplication, insertion or deletion events, leading to neuropeptides with a wide variety of functions, as observed in decapods. This family could thus constitute a promising model to investigate the links between gene duplications and functional divergence.

Functions of ion transport peptide and ion transport peptide-like in the red flour beetle Tribolium castaneum

Ion transport peptide (ITP) and ITP-like (ITPL) are highly conserved neuropeptides in insects and crustaceans. We investigated the alternatively spliced variants of ITP/ITPL in Tribolium castaneum to understand their functions. We identified three alternatively spliced transcripts named itp, itpl-1, and itpl-2. Expression patterns of the splice variants investigated by exon-specific in situ hybridization were somewhat different from those previously reported in other insect species. Most importantly, we found for the first time that itpl-1 transcripts are abundantly expressed in the midgut at the late larval stage, showing an expression pattern similar to that of the crustacean hyperglycemic hormone (CHH) in the crab Carcinus maenas. CHH was shown to function by increasing the body volume through fluid absorption, resulting in breakage of the outer shell at the time of molt. Exon-specific RNA interference (RNAi) was designed to distinguish between itp and itpl-1, but we were unable to design a dsRNA uniquely targeting or uniquely excluding itpl-2; therefore, RNAi targeting was limited to either itp/itpl-2 or itpl-1/itpl-2. For dsRNA injections in the larval stages, either RNAi led to gradually increasing mortality in the larval and pupal stages, with 100% cumulative mortality at the time of eclosion or shortly afterward. Developmental deficiencies in the adult tarsal segments were observed after RNAi suppressing either itp/itpl-2 or itpl-1/itpl-2. After dsRNA injections at the pupal stage, the most striking observation was a significant reduction in egg numbers (8% of control) and reduced survival of the offspring (5%) in RNAi targeting itpl-1/itpl-2, while a milder degree of the same phenotype was observed in that targeting itp/itpl-2.

Ecdysis triggering hormone signaling in the yellow fever mosquito Aedes aegypti

At the end of each developmental stage, the yellow fever mosquito Aedes aegypti performs the ecdysis behavioral sequence, a precisely timed series of behaviors that culminates in shedding of the old exoskeleton. Here we describe ecdysis triggering hormone-immunoreactive Inka cells located at branch points of major tracheal trunks and loss of staining coincident with ecdysis. Peptides (AeaETH1, AeaETH2) purified from extracts of pharate 4th instar larvae have--PRXamide C-terminal amino acid sequence motifs similar to ETHs previously identified in moths and flies. Injection of synthetic AeaETHs induced premature ecdysis behavior in pharate larvae, pupae and adults. Two functionally distinct subtypes of ETH receptors (AeaETHR-A, AeaETHR-B) of A. aegypti are identified and show high sensitivity and selectivity to ETHs. Increased ETHR transcript levels and behavioral sensitivity to AeaETHs arising in the hours preceding the 4th instar larva-to-pupa ecdysis are correlated with rising ecdysteroid levels, suggesting steroid regulation of receptor gene expression. Our description of natural and ETH-induced ecdysis in A. aegypti should facilitate future approaches directed toward hormone-based interference strategies for control of mosquitoes as human disease vectors.

Insect ion transport peptides are derived from alternatively spliced genes and differentially expressed in the central and peripheral nervous system

Insect ionic and fluid homeostasis relies upon the Malpighian tubules (MT) and different hindgut compartments. Primary urine formed in MTs is finally modified by ion, solute and water reabsorptive processes primarily in the hindgut under the control of several large peptide hormones. One of these, the ion transport peptide (ITP), is a chloride transport-stimulating and acid secretion-inhibiting hormone similar to crustacean hyperglycaemic hormones (CHHs). In locusts, moths and fruit flies, ITP together with the slightly longer ITPL isoforms, inactive in hindgut bioassays, arise by alternative splicing from very similar itp genes. ITP and ITPL are differentially distributed in (1) pars lateralis/retrocerebral complex neurosecretory cells (NSCs) containing both splice forms, (2) interneurons with either one of the splice forms, (3) hindgut-innervating abdominal ITP neurons (in Drosophila only), and (4) intrinsic, putative sensory NSCs in peripheral neurohaemal perisympathetic/perivisceral organs or transverse nerves (usually containing ITPL). Both splice forms occur as hormones released into the haemolymph in response to feeding or stress stimuli. ITPL mainly released from the peripheral NSCs is discussed as a competitive inhibitor (as established in vitro) of ITP action on yet to be identified hindgut ITP receptors. Furthermore, some evidence has been provided for possible ecdysis-related functions of ITP and/or ITPL in moths. The comparative data on the highly similar gene, precursor and primary structures and similar differential distributions in insect and crustacean NSCs suggest that CHH/ITP and ITPL neuropeptide-producing cells and their gene products share common phylogenetic ancestry.

Identification of a complex peptidergic neuroendocrine network in the hard tick, Rhipicephalus appendiculatus

Neuropeptides are crucial regulators of development and various physiological functions but little is known about their identity, expression and function in vectors of pathogens causing serious diseases, such as ticks. Therefore, we have used antibodies against multiple insect and crustacean neuropeptides to reveal the presence of these bioactive molecules in peptidergic neurons and cells of the ixodid tick Rhipicephalus appendiculatus. These antibodies have detected 15 different immunoreactive compounds expressed in specific central and peripheral neurons associated with the synganglion. Most central neurons arborize in distinct areas of the neuropile or the putative neurohaemal periganglionic sheath of the synganglion. Several large identified neurons in the synganglion project multiple processes through peripheral nerves to form elaborate axonal arborizations on the surface of salivary glands or to terminate in the lateral segmental organs (LSO). Additional neuropeptide immunoreactivity has been observed in intrinsic secretory cells of the LSO. We have also identified two novel clusters of peripheral neurons embedded in the cheliceral and paraspiracular nerves. These neurons project branching axons into the synganglion and into the periphery. Our study has thus revealed a complex network of central and peripheral peptidergic neurons, putative neurohaemal and neuromodulatory structures and endocrine cells in the tick comparable with those found in insect and crustacean neuroendocrine systems. Strong specific staining with a large variety of antibodies also indicates that the tick nervous system and adjacent secretory organs are rich sources of diverse neuropeptides related to those identified in insects, crustaceans or even vertebrates.

Identification of putative peptide paracrines/hormones in the water flea Daphnia pulex (Crustacea; Branchiopoda; Cladocera) using transcriptomics and immunohistochemistry

The cladoceran crustacean Daphnia pulex has emerged as a model species for many biological fields, in particular environmental toxicology and toxicogenomics. Recently, this species has been the subject of an extensive transcriptome project, resulting in the generation and public deposition of over 150,000 expressed sequence tags (ESTs). This resource makes D. pulex an excellent model for protein discovery using bioinformatics. Here, in silico searches of the D. pulex EST database were conducted to identify transcripts encoding putative peptide precursors. Moreover, the mature peptides contained within the deduced prepro-hormones were predicted using online peptide processing programs and homology to known arthropod isoforms. In total, 63 putative peptide-encoding ESTs were identified encompassing 14 distinct peptide families/subfamilies: A-type allatostatin, B-type allatostatin, C-type allatostatin, bursicon (both alpha and beta subunit peptides), crustacean cardioactive peptide (CCAP), crustacean hyperglycemic hormone (CHH)/ion transport peptide (both CHH- and moult-inhibiting hormone-like subfamilies), diuretic hormone (calcitonin-like), ecdysis-triggering hormone (ETH), FMRFamide (both neuropeptide F and short neuropeptide F subfamilies), orcokinin and pigment dispersing hormone. From these transcripts, the structures of 76 full-length/partial peptides were predicted, which included the first C-type allatostatin-like peptide identified from a crustacean, the first crustacean calcitonin-like diuretic hormone, an undescribed CCAP isoform, two hitherto unknown ETH variants, and two new orcokinins. Neuronal localization of several of the identified peptide families was confirmed using immunohistochemitry (i.e. A-type allatostatin, CCAP, FMRFamide and PDH). In addition, immunohistochemical analyses identified other putative neuropeptides for which no ESTs had been found (i.e. corazonin, insect kinin, proctolin, red pigment concentrating hormone, SIFamide, sulfakinin and tachykinin-related peptide). Collectively, the data presented here not only catalog an extensive array of putative D. pulex peptide paracrines/hormones, but also provide a strong foundation for future investigations of the effects of environmental/anthropogenic stressors on peptidergic control in this model organism.

Ion transport peptide splice forms in central and peripheral neurons throughout postembryogenesis of Drosophila melanogaster

Ion transport peptides (ITPs) belong to a large arthropod neuropeptide family including crustacean hyperglycaemic hormones and are antidiuretic hormones in locusts. Because long and short ITP isoforms are generated by alternative splicing from a single gene in locusts and moths, we investigated whether similarly spliced gene products occur in the nervous system of Drosophila melanogaster throughout postembryogenesis. The itp gene CG13586 was reanalyzed, and we found three instead of the two previously annotated alternatively spliced mRNAs. These give rise to three different neuropeptides, two long C-terminally carboxylated isoforms (DrmITPL1 and DrmITPL2, both 87 amino acids) and one short amidated DrmITP (73 amino acids), which were partially identified biochemically. Immunocytochemistry and in situ hybridization reveal nine larval and 14 adult identified neurons: four pars lateralis neurosecretory neurons, three hindgut-innervating neurons in abdominal ganglia, and a stage-specific number of interneurons and peripheral bipolar neurons. The neurosecretory neurons persist throughout postembryogenesis, form release sites in corpora cardiaca, and invade corpora allata. One type of ITP-expressing interneuron exists only in the larval and prepupal subesophageal ganglia, whereas three types of interneurons in the adult brain arise in late pupae and invade circumscribed neuropils in superior median and lateral brain areas. One peripheral bipolar and putative sensory neuron type occurs in the larval, pupal, and adult preterminal abdominal segments. Although the neurosecretory neurons may release DrmITP and DrmITPL2 into the haemolymph, possible physiological roles of the hindgut-innervating and peripheral neurons as well as the interneurons are yet to be identified.

Molecular cloning and differential expression pattern of two structural variants of the crustacean hyperglycemic hormone family from the mud crab Scylla olivacea

Two full-length cDNA sequences encoding a crustacean hyperglycemic hormone (CHH) precursor were cloned from tissues of the mud crab Scylla olivacea. Sco-CHH (S. olivacea CHH) was cloned from eyestalk ganglia, whereas Sco-CHH-L (S. olivacea CHH-like peptide) was cloned from extra-eyestalk tissues (pericardial organ and thoracic ganglia). Each conceptually translated precursor is expected to be processed into a signal peptide, a CHH precursor-related peptide (CPRP), and a mature CHH or CHH-like peptide. The two precursors are identical in amino acid sequence through the 40th residue of the mature peptide, but different from each other substantially in the C-terminus. Both CHH variants contain the six highly conserved cysteine residues characteristic of the CHH family peptides, and share higher sequence identities with other brachyuran CHH sequences than with those of other taxonomic groups. As determined by reverse transcription-polymerase chain reaction (RT-PCR), the transcripts of Sco-CHH and Sco-CHH-L were present in eyestalk ganglia and several extra-eyestalk tissues (the thoracic ganglia, pericardial organ, brain, circumesophageal connectives, and gut). Sco-CHH was the predominant form in eyestalk ganglia, while Sco-CHH-L was the predominant form in several extra-eyestalk tissues. Neither transcript was expressed in the muscle, hepatopancreas, ovary, testis, heart, or gill. Antisera were raised against synthetic peptides corresponding to a stretch of sequence-specific to the C-terminus of Sco-CHH or Sco-CHH-L. Western blot analyses of tissues expressing Sco-CHH and Sco-CHH-L detected a Sco-CHH immunoreactive protein in the sinus gland, and a Sco-CHH-L immunoreactive protein in the pericardial organ. Immunohistochemical analyses of the eyestalk ganglia localized both Sco-CHH and Sco-CHH-L immunoreactivity to the sinus gland, and only Sco-CHH immunoreactivity to the X-organ somata; analyses of the pericardial organs also localized both Sco-CHH and Sco-CHH-L immunoreactivity to the anterior and posterior bars, as well as to longitudinal trunks joining the two bars. The combined data provided supporting evidence that Sco-CHH and Sco-CHH-L are co-localized in the same tissue.

Neuropeptide discovery in Ixodoidea: an in silico investigation using publicly accessible expressed sequence tags

The Ixodoidea (ticks) are important vectors in the transmission of many human diseases; for example, the blacklegged tick Ixodes scapularis is the major vector in the transmission of Lyme disease, the most frequently reported vector-borne illness in the United States. The development of expressed sequence tags (ESTs) for ixodoidean cDNA libraries, and their public deposition, has generated a rich resource for protein discovery in members of this taxon, thereby providing an opportunity for better understanding the physiology and behavior of these disease vectors. Here, in silico searches of publicly accessible ESTs were conducted to identify transcripts encoding putative ixodoidean neuropeptide precursors, with the mature peptides contained within them predicted using online peptide processing programs and homology to known arthropod sequences. In total, 37 putative neuropeptide-encoding ESTs were identified from three ixodoidean species: I. scapularis (29 ESTs), Rhipicephalus microplus (seven ESTs) and Amblyomma americanum (one EST). Among those identified from I. scapularis were ones predicted to encode isoforms of corazonin, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone (both calcitonin- and corticotropin-releasing factor-like), FMRFamide-related peptide (both short neuropeptide F and sulfakinin subfamilies) orcokinin, proctolin, pyrokinin/periviscerokinin/pheromone biosynthesis activating neuropeptide, SIFamide, and tachykinin-related peptide. Collectively, 80 distinct ixodoidean neuropeptides were characterized from the identified precursors. These results not only expand greatly the number of known/predicted ixodoidean neuropeptides, but also provide a strong foundation for future molecular and physiological investigations of peptidergic control in this important group of disease-transmitting arthropods.

New insights into evolution of crustacean hyperglycaemic hormone in decapods--first characterization in Anomura

The neuropeptides of the crustacean hyperglycaemic hormone (CHH) family are encoded by a multigene family and are involved in a wide spectrum of essential functions. In order to characterize CHH family peptides in one of the last groups of decapods not yet investigated, CHH was studied in two anomurans: the hermit crab Pagurus bernhardus and the squat lobster Galathea strigosa. Using RT-PCR and 3' and 5' RACE methods, a preproCHH cDNA was cloned from the major neuroendocrine organs (X-organs) of these two species. Hormone precursors deduced from these cDNAs in P. bernhardus and G. strigosa are composed of signal peptides of 29 and 31 amino acids, respectively, and CHH precursor-related peptides (CPRPs) of 50 and 40 amino acids, respectively, followed by a mature hormone of 72 amino acids. The presence of these predicted CHHs and their related CPRPs was confirmed by performing MALDI-TOF mass spectrometry on sinus glands, the main neurohaemal organs of decapods. These analyses also suggest the presence, in sinus glands of both species, of a peptide related to the moult-inhibiting hormone (MIH), another member of the CHH family. Accordingly, immunostaining of the X-organ/sinus gland complex of P. bernhardus with heterologous anti-CHH and anti-MIH sera showed the presence of distinct cells producing CHH and MIH-like proteins. A phylogenetic analysis of CHHs, including anomuran sequences, based on maximum-likelihood methods, was performed. The phylogenetic position of this taxon, as a sister group to Brachyura, is in agreement with previously reported results, and confirms the utility of CHH as a molecular model for understanding inter-taxa relationships. Finally, the paraphyly of penaeid CHHs and the structural diversity of CPRPs are discussed.

Identification, developmental expression, and functions of bursicon in the tobacco hawkmoth, Manduca sexta

During posteclosion, insects undergo sequential processes of wing expansion and cuticle tanning. Bursicon, a highly conserved neurohormone implicated in regulation of these processes, was characterized recently as a heterodimeric cystine knot protein in Drosophila melanogaster. Here we report the predicted precursor sequences of bursicon subunits (Masburs and Maspburs) in the moth Manduca sexta. Distinct developmental patterns of mRNA transcript and subunit-specific protein labeling of burs and pburs as well as crustacean cardioactive peptide in neurons of the ventral nervous system were observed in pharate larval, pupal, and adult stages. A subset of bursicon neurons located in thoracic ganglia of larvae expresses ecdysis-triggering hormone (ETH) receptors, suggesting that they are direct targets of ETH. Projections of bursicon neurons within the CNS and to neurohemal secretory sites are consistent with both central signaling and circulatory hormone functions. Intrinsic cells of the corpora cardiaca contain pburs transcripts and pburs-like immunoreactivity, whereas burs transcripts and burs-like immunoreactivity were absent in these cells. Recombinant bursicon induces both wing expansion and tanning, whereas synthetic eclosion hormone induces only wing expansion.