Neuropeptides of the beetle, Tenebrio molitor identified using MALDI-TOF mass spectrometry and deduced sequences from the Tribolium castaneum genome

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.

MALDI-TOF mass spectrometry approaches to the characterisation of insect neuropeptides

The diversity of insect neuropeptides coupled with the limitations from the small size of the insects themselves combine to make positive identification through peptide sequencing a highly challenging task. The advent of the "soft-ionisation" techniques of MALDI-TOF and electrospray (ESI)-Q-TOF mass spectrometry, coupled with the additional information from insect genome projects have revolutionised the characterisation of insect neuropeptides, such that sequences can now be obtained from just a few cells, where before thousands of insects had to be laboriously dissected, extracted and purified. Some of the procedures that are now used to identify these peptides are described here. Once the neuropeptides have been identified, it then becomes possible to use this knowledge to define physiological functionality.

Identification of myotropic neuropeptides from the brain and corpus cardiacum-corpus allatum complex of the beetle, Zophobas atratus

The neuropeptide profiles of the two major neuro-endocrinological organs, brain and retrocerebral complex corpus cardiacum-corpus allatum (CC/CA) of adult beetles, Zophobas atratus Fabricius (Coleoptera:Tenebrionidae) were analyzed by a combination of high performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight tandem mass spectrometry (MALDI TOF/TOF MS). The homological semi-isolated heart bioassay was used to screen HPLC fractions for myotropic activity in tissues, revealing several cardiostimulatory and cardioinhibitory factors from both the brain and CC/CA. Analysis of HPLC fractions by MALDI-TOF MS identified seven mass ions that could be assigned to other known peptides: leucomyosuppressin (LMS), Tribolium castaneum pyrokinin 2, sulfakinin 1, myoinhibitory peptide 4, a truncated NVP-like peptide, Tenebrio molitor AKH and crustacean cardioactive peptide. In addition, two novel peptides, myosuppressin (pEDVEHVFLRFa), which differs from LMS by one amino acid (E for D at position 4) and pyrokinin-like peptide (LPHYTPRLa) were also identified. To establish cardioactive properties of some of the identified peptides, chemical synthesis was carried out and their activities were tested using the heart bioassay.

GYRKPPFNGSIFamide (Gly-SIFamide) modulates aggression in the freshwater prawn Macrobrachium rosenbergii

The freshwater prawn Macrobrachium rosenbergii is a tropical crustacean with characteristics similar to those of lobsters and crayfish. Adult males develop through three morphological types-small (SC), yellow (YC), and blue claws (BC)-with each representing a level in the dominance hierarchy of a group, BC males being the most dominant. We are interested in understanding the role played by neuropeptides in the mechanisms underlying aggressive behavior and the establishment of dominance hierarchies in this type of prawn. SIFamides are a family of arthropod peptides recently identified in the central nervous system of insects and crustaceans, where it has been linked to olfaction, sexual behavior, and gut endocrine functions. One of the six SIFamide isoforms, GYRKPPFNGSIFamide (Gly-SIFamide), is highly conserved among decapod crustaceans such as crabs and crayfish. We wanted to determine whether Gly-SIFamide plays a role in modulating aggression and dominant behavior in the prawn. To do this, we performed behavioral experiments in which interactions between BC/YC pairs were recorded and quantified before and after injecting Gly-SIFamide directly into the circulating hemolymph of the living animal. Behavioral data showed that aggression among interacting BC/YC prawns was enhanced by injection of Gly-SIFamide, suggesting that this neuropeptide does have a modulatory role for this type of behavior in the prawn.

Does corazonin signal nutritional stress in insects?

The undecapeptide corazonin, initially discovered from the American cockroach as a strong cardioaccelerator, is now known to be ubiquitously present in arthropods, although it is absent from some species, notably Coleoptera. The structure of its precursor is similar to the GnRH precursor, while it acts through a receptor related to the GnRH receptor; corazonin thus appears to be an arthropod homolog of GnRH. It is produced by neuroendocrine cells in the brain, as well as interneurons in the ventral nerve cord. These two cell types are generally present in insects; in most species there are also other neurons producing corazonin. Its function in insects has remained obscure; its cardioacceleratory effects are limited to a few cockroach species, while in other species different physiological effects have been described. Most spectacularly it induces changes associated with the gregarious phase in migratory locusts and in the silkworm it reduces the size of the cocoon formed. Corazonin is able to induce ecdysis in two moth species, however locusts and flies in which the corazonin gene is no longer expressed, ecdyse normally and, hence, it is not clear whether corazonin is essential for ecdysis. As the corazonin neuroendocrine cells in the brain express receptors for two midgut peptides, it seems likely that their activity is modulated by the midgut endocrine cells. I propose that in insects corazonin might be released under conditions of nutritional stress, which can explain several of the observed physiological effects of this neurohormone.

Role of allatostatin-like factors from the brain of Tenebrio molitor females

The effect of brain extract from females of freshly emerged Tenebrio molitor on ovary, oocyte development, total protein content of hemolymph, and ovary was studied in 4-day-old adult mealworm females. Injections of extracts of 2-brain equivalents into intact (unligatured) Tenebrio females did not affect ovarian and oocyte development. Injections of ligated females, however, with 2-brain equivalents on day 1 and 2 after adult emergence strongly inhibited ovarian growth and oocyte development. At day 4, ligated and injected females did not develop their ovaries and pre-vitellogenic oocytes were not found. The changes in ovarian development correlated with an increase in the concentration of soluble proteins in the hemolymph as compared with the saline-injected controls. Additionally, a strong reduction of total protein content in ovarian tissue was observed. Reverse phase HPLC separation of a methanolic brain extract of T. molitor females showed that fraction 5 has a similar retention time to synthetic cockroach allatostatin. Fraction 5 was eluted at 12.88 min, which was closest to the internal standard Dippu-AST I, which eluted at 12.77 min. An ELISA of fraction 5 from the methanolic brain extract using antibodies against allatostatins Grybi-AST A1 and Grybi-AST B1 from cricket Gryllus bimaculatus showed that fraction 5 cross-reacted with Grybi-AST A1 antibodies. The cross-reactivity was similar to the synthetic allatostatin from D. punctata, which was used as a positive control. These observations demonstrate a possible role for allatostatin-like brain factor(s) in regulating the reproductive cycle of Tenebrio molitor.

Identification of SYWKQCAFNAVSCFamide: a broadly conserved crustacean C-type allatostatin-like peptide with both neuromodulatory and cardioactive properties

The allatostatins comprise three structurally distinct peptide families that regulate juvenile hormone production by the insect corpora allata. A-type family members contain the C-terminal motif -YXFGLamide and have been found in species from numerous arthropod taxa. Members of the B-type family exhibit a -WX(6)Wamide C-terminus and, like the A-type peptides, appear to be broadly conserved within the Arthropoda. By contrast, members of the C-type family, typified by the unblocked C-terminus -PISCF, a pyroglutamine blocked N-terminus, and a disulfide bridge between two internal Cys residues, have only been found in holometabolous insects, i.e. lepidopterans and dipterans. Here, using transcriptomics, we have identified SYWKQCAFNAVSCFamide (disulfide bridging predicted between the two Cys residues), a known honeybee and water flea C-type-like peptide, from the American lobster Homarus americanus (infraorder Astacidea). Using matrix assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), a mass corresponding to that of SYWKQCAFNAVSCFamide was detected in the H. americanus brain, supporting the existence of this peptide and its theorized structure. Furthermore, SYWKQCAFNAVSCFamide was detected by MALDI-FTMS in neural tissues from five additional astacideans as well as 19 members of four other decapod infraorders (i.e. Achelata, Anomura, Brachyura and Thalassinidea), suggesting that it is a broadly conserved decapod peptide. In H. americanus, SYWKQCAFNAVSCFamide is capable of modulating the output of both the pyloric circuit of the stomatogastric nervous system and the heart. This is the first demonstration of bioactivity for this peptide in any species.

SIFamide illustrates the rapid evolution in Arthropod neuropeptide research

This review is focussed on SIFamide. This neuropeptide was discovered as a result of an extensive purification process, typical for 20th century physiology, of an extract of 350,000 flesh flies. Our knowledge of SIFamide greatly expanded since the first publication in 1996. Describing the minor and major findings on this peptide is our lead to summarise a number of innovations that recently became common in research on Arthropods. Mass spectrometry, nanoLC, whole mount immunocytochemistry, genome sequencing, deorphanizing receptors and functional gene knock downs are aspects that dramatically improved and changed peptide research. Some of the techniques mentioned in this review were of course applied before 1996, but they were not widespread. Although the focus of the review is on insects we incorporated the data of SIFamide in Crustaceans as well. SIFamide illustrates that crustaceans and insects might have more in common than was previously anticipated. Today, six isoforms of SIFamide are discovered in many crustaceans, several insects and a tick. The sequence of SIFamide is extremely conserved among these species. Deorphanizing its receptor in Drosophila, learned that both the ligand and receptor are impressively conserved, pointing at a crucial function. Immunohistochemistry and mass spectrometry data reveal that SIFamide is present in the crustacean brain and gut, but restricted to four neurons in the insect pars intercerebralis. The immunoreactive patterns in the brain refer to a neuromodulatory role in combining visual, tactile and olfactory input. Eventually, targeted cell ablation and RNAi revealed that SIFamide modulates sexual behaviour in fruit flies.

Neuropeptides associated with the regulation of feeding in insects

The stomatogastric nervous system plays a pivotal role in feeding behaviour. Central to this system is the frontal ganglion, which is responsible for foregut motor activity, and hence the passage of food through the gut. Many insect peptides, which exhibit myoactivity on the visceral muscles of the gut in vitro, have been detected in the stomatogastric nervous system by immunochemical or mass spectrometric techniques. This localisation of myoactive peptides, particularly in the frontal ganglion, implies roles for these peptides in the neural control and modulation of feeding in insects. Insect sulfakinins, tachykinins, allatotropin and proctolin have all been shown to stimulate the foregut muscles, whereas myosuppressins, myoinhibitory peptides and allatostatins all inhibited spontaneous contractions of the foregut in a variety of insects. Some of these peptides, when injected, inhibited feeding in vivo. Both the A-type and B-type allatostatins suppressed feeding activity when injected into the cockroach, Blattella germanica and the Manduca sexta C-type allatostatin and allatotropin inhibited feeding when injected into the larvae of two noctuid moths, Lacanobia oleracea and Spodoptera frugiperda, respectively. Injection of sulfakinins into the fly Phormia regina, the locust Schistocera gregaria and the cockroach B. germanica also suppressed feeding, whereas silencing the sulfakinin gene through the injection of double stranded RNA resulted in an increase in food consumption in the cricket Gryllus bimaculatus. The regulation of feeding in insects is clearly very complex, and involves the interaction of a number of mechanisms, one of which is the release, either centrally or locally, of neuropeptides. However, the role of neuropeptides, their mechanisms of action, interactions with each other, and their release are still poorly understood. It is also unclear why insects possess such a number of different peptides, some with multiples copies or homologues, which stimulate or inhibit gut motility, and how their release, sometimes from the same neurone, is regulated. These neuropeptides may also act at sites other than visceral muscles, such as centrally through the brain or on gut stretch receptors.

Discovery of multiple neuropeptide families in the phylum Platyhelminthes

Available evidence shows that short amidated neuropeptides are widespread and have important functions within the nervous systems of all flatworms (phylum Platyhelminthes) examined, and could therefore represent a starting point for new lead drug compounds with which to combat parasitic helminth infections. However, only a handful of these peptides have been characterised, the rigorous exploration of the flatworm peptide signalling repertoire having been hindered by the dearth of flatworm genomic data. Through searches of both expressed sequence tags and genomic resources using the basic local alignment search tool (BLAST), we describe 96 neuropeptides on 60 precursors from 10 flatworm species. Most of these (51 predicted peptides on 14 precursors) are novel and are apparently restricted to flatworms; the remainder comprise nine recognised peptide families including FMRFamide-like (FLPs), neuropeptide F (NPF)-like, myomodulin-like, buccalin-like and neuropeptide FF (NPFF)-like peptides; notably, the latter have only previously been reported in vertebrates. Selected peptides were localised immunocytochemically to the Schistosoma mansoni nervous system. We also describe several novel flatworm NPFs with structural features characteristic of the vertebrate neuropeptide Y (NPY) superfamily, previously unreported characteristics which support the common ancestry of flatworm NPFs with the NPY-superfamily. Our dataset provides a springboard for investigation of the functional biology and therapeutic potential of neuropeptides in flatworms, simultaneously launching flatworm neurobiology into the post-genomic era.

The different effects of structurally related sulfakinins on Drosophila melanogaster odor preference and locomotion suggest involvement of distinct mechanisms

Sulfakinins are myoactive peptides and antifeedant factors. Naturally occurring drosulfakinin I (DSK I; FDDYGHMRFNH(2)) and drosulfakinin II (DSK II; GGDDQFDDYGHMRFNH(2)) contain sulfated or nonsulfated tyrosine. We discovered sDSK II and nsDSK II influenced Drosophila melanogaster larval odor preference. However, sDSK I, nsDSK I, MRFNH(2), and saline did not influence odor preference. We discovered sDSK I and nsDSK I influenced larval locomotion. However, sDSK II, nsDSK II, MRFNH(2), and saline did not influence locomotion. Our novel data suggest distinct mechanisms underlie the effects of DSK I and DSK II peptides on odor preference and locomotion, parameters important to many facets of animal survival.

In silico analyses of peptide paracrines/hormones in Aphidoidea

The Aphidoidea is an insect superfamily comprising most of the known aphid species. While small in size, these animals are of considerable economic importance as many members of this taxon are serious agricultural pests, inflicting physical damage upon crop plants and serving as vectors in the transmission of viral plant diseases. In terms of identifying the paracrines/hormones used to modulate behavior, particularly peptides, members of the Aphidoidea have largely been ignored, as it is not tractable to isolate the large pools of tissue needed for standard biochemical investigations. Here, a bioinformatics approach to peptide discovery has been used to overcome this limitation of scale. Specifically, in silico searches of publicly accessible aphidoidean ESTs were conducted to identify transcripts encoding putative peptides precursors, with the mature peptides contained within them deduced using peptide processing software and homology to known arthropod sequences. In total, 39 ESTs encoding putative peptides precursors were identified from four aphid species: Acyrthosiphon pisum (14 ESTs), Aphis gossypii (four ESTs), Myzus persicae (20 ESTs) and Toxoptera citricida (one EST). These precursors included ones predicted to encode isoforms of B-type allatostatin, crustacean cardioactive peptide, FMRFamide-related peptide (both myosuppressin and short neuropeptide F subfamilies), insect kinin, orcokinin, proctolin, pyrokinin/periviscerokinin/pheromone biosynthesis activating neuropeptide, SIFamide and tachykinin-related peptide. In total, 83 peptides were characterized from the identified precursors, most novel, including two B-type allatostatins possessing the variant -WX(7)Wamide motif, two N-terminally extended proctolin isoforms and an N-terminally truncated and substituted SIFamide. Collectively, these results expand greatly the number of known/predicted aphid peptide paracrines/hormones, and provide a strong foundation for future molecular and physiological investigations of peptidergic control in this insect group.

Predicted versus expressed adipokinetic hormones, and other small peptides from the corpus cardiacum-corpus allatum: a case study with beetles and moths

This mass spectrometric study confines itself to peptide masses in the range of 500-1500Da. Adipokinetic hormones (AKHs) that are predicted from the genome of the red flour beetle, Tribolium castaneum, and the silk moth, Bombyx mori, are shown to exist as expressed peptides in the corpora cardiaca (CC) of the respective species as evidenced by various mass spectrometric methods. Additionally, some related species were included in this study, such as the tenebrionid beetles Tribolium brevicornis and Tenebrio molitor, as well as the moths Spodoptera frugiperda, Spodoptera littoralis, Mamestra brassicae and Lacanobia oleracea, to investigate whether AKH peptides are structurally conserved in the same genus or family. Interestingly, the AKH peptide of T. brevicornis is identical to that of T. molitor but not to the ones of its close relative T. castaneum. Moreover, other peptides in T. brevicornis, such as various FXPRL amides (=pyrokinins), also match the complement in T. molitor but differ from those in T. castaneum. All the CC of beetles lacked the signal for the mass of the peptide corazonin. All moths have the nonapeptide Manse-AKH expressed in their CC. In addition, whereas the silk moth has the decapeptide Bommo-AKH as a second peptide, all other moths (all noctuids) express the decapeptide Helze-HrTH. In M. brassicae and L. oleracea a novel amidated Gly-extended Manse-AKH is found as a possible third AKH. The noctuid moth species also all express the same FLRF amide-I, corazonin, and a group-specific isoform of a gamma-PGN-(=gamma-SGNP) peptide. In L. oleracea, however, the latter peptide has a novel sequence which is reported for the first time, and the peptide is code-named Lacol-PK.

Allatoregulatory peptides in Lepidoptera, structures, distribution and functions

Allatoregulatory peptides either inhibit (allatostatins) or stimulate (allatotropins) juvenile hormone (JH) synthesis by the corpora allata (CA) of insects. However, these peptides are pleitropic, the regulation of JH biosynthesis is not their only function. There are currently three allatostatin families (A-, B-, and C-type allatostatins) that inhibit JH biosynthesis, and two structurally unrelated allatotropins. The C-type allatostatin, characterised by its blocked N-terminus and a disulphide bridge between its two cysteine residues, was originally isolated from Manduca sexta. This peptide exists only in a single from in Lepidoptera and is the only peptide that has been shown to inhibit JH synthesis by the CA in vitro in this group of insects. The C-type allatostatin also inhibits spontaneous contractions of the foregut. The A-type allatostatins, which exist in multiple forms in a single insect, have also been characterised from Lepidoptera. This family of peptides does not appear to have any regulatory effect on JH biosynthesis, but does inhibit foregut muscle contractions. Two structurally unrelated allatotropins stimulate JH biosynthesis in Lepidoptera. The first was identified in M. sexta (Manse-AT) and occurs in other moths. The second (Spofr AT2) has only been identified in Spodoptera frugiperda. Manduca sexta allatotropin also stimulates heart muscle contractions and gut peristalsis, and inhibits ion transport across the midgut of larval M. sexta. The C-terminal (amide) pentapeptide of Manse-AT is important for JH biosynthesis activity. The most active conformation of Manse-AS requires the disulphide bridge, although the aromatic residues also have a significant effect on biological activity. Both A- and C-type allatostatins and Manse-AT are localised in neurosecretory cells of the brain and are present in the corpora cardiaca, CA and ventral nerve cord, although variations in localisation exist in different moths and at different stages of development. The presence of Manse-AS and Manse-AT in the CA correlates with the biological activity of these peptides on JH biosynthesis. There is currently no explanation for the presence of A-type allatostatins in the CA. The three peptide types are also co-localised in neurosecretory cells of the frontal ganglion, and are present in the recurrent nerve that supplies the muscles of the gut, particularly the crop and stomodeal valve, in agreement with their role in the regulation of gut peristalsis. There is also evidence that they are expressed in the midgut and reproductive tissues.