The newly discovered insect order Mantophasmatodea contains a novel member of the adipokinetic hormone family of peptides

Comparative analysis of adipokinetic hormones and their receptors in Blattodea reveals novel patterns of gene evolution

Adipokinetic hormone (AKH) is a neuropeptide produced in the insect corpora cardiaca that plays an essential role in mobilising carbohydrates and lipids from the fat body to the haemolymph. AKH acts by binding to a rhodopsin-like G protein-coupled receptor (GPCR), the adipokinetic hormone receptor (AKHR). In this study, we tackle AKH ligand and receptor gene evolution as well as the evolutionary origins of AKH gene paralogues from the order Blattodea (termites and cockroaches). Phylogenetic analyses of AKH precursor sequences point to an ancient AKH gene duplication event in the common ancestor of Blaberoidea, yielding a new group of putative decapeptides. In total, 16 different AKH peptides from 90 species were obtained. Two octapeptides and seven putatively novel decapeptides are predicted for the first time. AKH receptor sequences from 18 species, spanning solitary cockroaches and subsocial wood roaches as well as lower and higher termites, were subsequently acquired using classical molecular methods and in silico approaches employing transcriptomic data. Aligned AKHR open reading frames revealed 7 highly conserved transmembrane regions, a typical arrangement for GPCRs. Phylogenetic analyses based on AKHR sequences support accepted relationships among termite, subsocial (Cryptocercus spp.) and solitary cockroach lineages to a large extent, while putative post-translational modification sites do not greatly differ between solitary and subsocial roaches and social termites. Our study provides important information not only for AKH and AKHR functional research but also for further analyses interested in their development as potential candidates for biorational pest control agents against invasive termites and cockroaches.

Mass Spectrometric Proof of Predicted Peptides: Novel Adipokinetic Hormones in Insects

The importance of insects in our ecosystems is undeniable. The indiscriminate use of broad-spectrum insecticides is a factor in the decline in insect biomass. We identify and sequence a prominent neuropeptide hormone in insects with an overarching goal to elucidate relatedness and create a database of bioactive peptides that could inform possible cross-activity in biological assays for the identification of a biorational lead compound. The major task of an adipokinetic hormone (AKH) in an insect is the regulation of metabolic events, such as carbohydrate and lipid breakdown in storage tissue during intense muscular work. From genomic and/or transcriptomic information one may predict the genes encoding neuropeptides such as the AKHs of insects. Definite elucidation of the primary structure of the mature peptide with putative post-translational modifications needs analytical chemical methods. Here we use high-resolution mass spectrometry coupled with liquid chromatography to identify unequivocally the AKHs of five insect species (one cockroach, two moths, and two flies) of which either genomic/transcriptomic information was available or sequences from related species. We confirm predicted sequences and discover novel AKH sequences, including one with a post-translational hydroxyproline modification. The additional sequences affirm an evolutionary pattern of dipteran AKHs and a conserved pattern in crambid moths.

The Adipokinetic Peptides of Hemiptera: Structure, Function, and Evolutionary Trends

The Hemiptera comprise the most species-rich order of the hemimetabolous insects. Members of a number of superfamilies, most notably especially the more basal ones such as white flies, psyllids and aphids, belong to the most destructive agricultural insects known worldwide. At the other end of the phylogenetic tree are hemipterans that are notorious medical pests (e.g. kissing bugs). Most of the hemipteran species are good flyers, and lipid oxidation plays a pivotal role to power the contraction of flight muscles and, in aquatic water bugs, also deliver the ATP for the extensive swimming action of the leg muscles. Mobilization of stored lipids (mostly triacylglycerols in the fat body) to circulating diacylglycerols in the hemolymph is regulated by a set of small neuropeptides, the adipokinetic hormones (AKHs). We searched the literature and publicly available databases of transcriptomes and genomes to present here AKH sequences from 191 hemipteran species. Only few of these peptides were sequenced via Edman degradation or mass spectrometry, and even fewer were characterized with molecular biology methods; thus, the majority of the AKHs we have identified by bioinformatics are merely predicted sequences at this stage. Nonetheless, a total of 42 AKH primary sequences are assigned to Hemiptera. About 50% of these structures occur also in other insect orders, while the remaining 50% are currently unique for Hemiptera. We find 9 novel AKHs not shown to be synthesized before in any insect. Most of the hemipteran AKHs are octapeptides (28) but there is an impressive number of decapeptides (12) compared to other speciose orders such as Diptera and Lepidoptera. We attempt to construct a hypothetical molecular peptide evolution of hemipteran AKHs and find quite a bit of overlapping with current phylogenetic ideas of the Hemiptera. Lastly, we discuss the possibility to use the sequence of the aphid AKH as lead peptide for the research into a peptide mimetic fulfilling criteria of a green insecticide.

Biochemically identified neuropeptides in a caddisfly (Trichoptera) and a pygmy mole cricket (Orthoptera: Caelifera: Tridactyloidea)

One representative of the order Trichoptera, namely the caddisfly Chaetopteryx villosa, was investigated along with the pygmy mole cricket Xya capensis which is a representative of the most basal superfamily of the caeliferan Orthoptera, that is, the Tridactyloidea. From both clades neuropeptides have not been biochemically characterized before this study. Here, members of the adipokinetic hormone family (AKHs) are sequenced via liquid chromatography (LC)-ion trap mass spectrometry from methanolic extracts from the corpora cardiaca of respective species. The corpora cardiaca were dissected, methanolic extracts prepared, peptides separated by liquid chromatography (LC), and AKHs detected and sequenced by ion trap mass spectrometry. Both species investigated contain an octapeptide AKH: the trichopteran species has the peptide with the sequence pGlu-Leu-Thr-Phe-Thr-Pro-Ser-Trp amide; the ambiguity of the isobaric amino acids Leu and Ile at position two was solved by comparing retention times on LC and by co-elution with the synthetic Leu² -form. This peptide is known as Aedae-AKH and found in certain dipteran species and in an alderfly (Megaloptera). The tridactyloid species contains the peptide with the sequence pGlu-Val-Asn-Phe-Ser-Pro-Gly-Trp amide which had first been identified in a member of the order Mantophasmatodea and is called Manto-CC. Comparisons are made between the AKH complements of the sister groups Trichoptera and Lepidoptera and their possible relatedness and, on the other hand, between the AKH of X. capensis with those of closely related caeliferan superfamilies. The biology of the two studied species is used to speculate about a possible function of the elucidated hormones. Lastly, the use of a larval stage as starting material for structural neuropeptide information is discussed.

Neuropeptide discovery in Symphylella vulgaris (Myriapoda, Symphyla): In silico prediction of the first myriapod peptidome

Arthropods have contributed greatly to our understanding of peptidergic control of physiology and behavior, and being the largest and most diverse animal phylum, represent a model for investigating peptide hormone evolution. Surprisingly, one arthropod subphylum, the Myriapoda, is uninvestigated in terms of its peptide hormones. The public deposition of a transcriptome for Symphylella vulgaris, a pseudocentipede, provides a means for peptide discovery in myriapods. Here, in silico transcriptome mining was used to identify 47 S. vulgaris neuropeptide-encoding transcripts within this dataset. The identified transcripts allowed for the deduction of 31 unique pre/preprohormone sequences, with 97 distinct mature peptides predicted from the deduced proteins. The predicted S. vulgaris peptidome includes members of the adipokinetic hormone/red pigment concentrating hormone, adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin C (AST-C), allatotropin, CCHamide, crustacean cardioactive peptide, GSEFLamide, insulin-like peptide, intocin, proctolin, pyrokinin, short neuropeptide F, SIFamide and sulfakinin families. This is the first, and thus far only, peptidome predicted for a myriapod. Of particular note were a modified AST-C, TYWKQCAFNAVSRFamide, that lacks one of two cysteine residues (i.e. one at position 13) stereotypically present in members of this peptide family (and hence is missing the disulfide bridge that spans these residues) and a SIFamide, PPFNGSIFamide, that is truncated due to a lysine for arginine substitution in the dibasic residue pair commonly located at positions 3 and 4 of stereotypical full-length isoforms (e.g. the crustacean peptide GYRKPPFNGSIFamide). The peptides predicted here represent the only extant resource for initiating investigations of native peptidergic signaling in the Myriapoda.

Two new genera and two new species of Mantophasmatodea (Insecta, Polyneoptera) from Namibia

Two new species and two new genera (Pachyphasma, Striatophasma) of Mantophasmatodea are described from Namibia. Pachyphasma brandbergense is endemic to the Brandberg massif; Striatophasma occupies an extensive area south of the region inhabited by Mantophasma. Phylogenetic analyses (see Predel et al. in press) suggest a sistergroup relationship of Striatophasma and the South African Austrophasmatidae.

Biological activity of the predicted red pigment-concentrating hormone of Daphnia pulex in a crustacean and an insect

The elucidation of the genome of the waterflea Daphnia pulex made it possible to search for orthologue genes for the crustacean red pigment-concentrating hormone (named Panbo-RPCH after the species Pandalus borealis in which the red pigment-concentrating hormone was first identified); Panbo-RPCH is a member of the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) peptide family. The information pointed to a putative mature RPCH octapeptide in D. pulex with the primary sequence of pGlu-Val-Asn-Phe-Ser-Thr-Ser-Trp amide (=Dappu-RPCH). Since Panbo-RPCH is endogenous in decapod crustaceans and in the green stink bug Nezara viridula, we assayed Dappu-RPCH in the shrimp Palaemon pacificus and in N. viridula. Here we show that this variant member of the AKH/RPCH family has no activity to concentrate the red, brown, yellow and blue pigments in the epithelium of the shrimp at physiological doses but is effective in mobilising lipids in the green stink bug N. viridula. Moreover, since Panbo-RPCH and Dappu-RPCH differ structurally at three positions, viz. Leu(2) to Val(2); Pro(6) to Thr(6); Gly(7) to Ser(7), we tested other members of the peptide family which have single or dual amino acid substitutions at the appropriate positions, for their chromatophorotropic action at physiological doses. These studies show unequivocally that a single change from Gly(7) to Ser(7) (as in the peptide Corpu-AKH) does not inflict any loss of biological activity, and the same is true for a single change from Pro(6) to Thr(6) (represented by the peptide Schgr-AKH-II). The change from Leu(2) to Val(2) (embodied in Manto-CC), however, is accompanied with a substantial loss of chromatophorotropic activity; combinations of Val(2) and Ser(7) (as in Anaim-AKH) or Val(2) and Thr(6) (as in Grybi-AKH) result in almost complete loss of biological activity. Dappu-RPCH with its three substitutions is not active at all in the shrimp at the tested concentration range of up to 30 pmol.

Molecular and functional characterization of adipokinetic hormone receptor and its peptide ligands in Bombyx mori

Neuropeptides of the adipokinetic hormone (AKH) family are among the best studied hormone peptides, but its signaling pathways remain to be elucidated. In this study, we molecularly characterized the signaling of Bombyx AKH receptor (AKHR) and its peptide ligands in HEK293 cells. In HEK293 cells stably expressing AKHR, AKH1 stimulation not only led to a ligand concentration dependent mobilization of intracellular Ca(2+) and cAMP accumulation, but also elicited transient activation of extracellular signal-regulated kinase 1/2 (ERK1/2) pathway. We observed that AKH receptor was rapidly internalized after AKH1 stimulation. We further demonstrated that AKH2 exhibited high activities in cAMP accumulation and ERK1/2 activation on AKHR comparable to AKH1, whereas AKH3 was much less effective.

A novel adipokinetic peptide in a water boatman (Heteroptera, Corixidae) and its bioanalogue in a saucer bug (Heteroptera, Naucoridae)

The corpora cardiaca (CC) of two water bug species, the water boatman Corixa punctata and the saucer bug Ilyocoris cimicoides, contain a substance that cause hyperlipemia in the migratory locust. The primary sequence of one octapeptide belonging to the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) family was deduced from the multiple MS(N) electrospray mass data of CC material from each species. Whereas the saucer bug contains the known octapeptide pGlu-Val-Asn-Phe-Ser-Pro-Ser-Trp amide, code-named Anaim-AKH, the water boatman has a novel peptide identified as pGlu-Leu/Ile-Asn-Phe-Ser-Pro-Ser-Trp amide, code-named Corpu-AKH. The ambiguity about the amino acid at position 2, i.e. Leu or Ile, in Corpu-AKH was solved by isolating the peptide in a single-step by reversed-phase HPLC and establishing co-elution with the synthetic peptide containing Leu at position 2. Functionally, the peptides regulate lipid mobilization, as evidenced by an adipokinetic effect after injecting synthetic Anaim-AKH and Corpu-AKH into the respective acceptor species. Swimming activity of I. cimicoides also causes hyperlipemia.

Flight fuel and neuropeptidergic control of fuel mobilisation in the twig wilter, Holopterna alata (Hemiptera, Coreidae)

The corpus cardiacum of the twig wilter Holopterna alata contains a factor that elicits increases in the concentration of lipids in the haemolymph of twig wilters and migratory locusts and causes hypertrehalosaemia in American cockroaches. A hyperlipaemic neuropeptide was isolated from corpora cardiaca of H. alata in a single high-performance liquid chromatography step. The primary sequence of this peptide was assigned by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, biological assay and co-elution with the synthetic peptide. The adipokinetic peptide of H. alata is an octapeptide with the sequence pGlu-Leu-Asn-Phe-Ser-Thr-Gly-Trp amide denoted Schgr-AKH-II which was sequenced previously from the corpora cardiaca of a number of Caelifera, Ensifera and some Hymenoptera. A dose of 1pmol of synthetic Schgr-AKH-II causes a pronounced hyperlipaemic effect in the twig wilter. Physiological experiments with the twig wilter reveal that during flight periods of 3 min, the normally low carbohydrate concentration in the haemolymph is significantly diminished, whereas the lipid concentration stays constant in most cases. During a subsequent rest period of 60 min after a 3 min flight episode, however, the concentration of lipids in the haemolymph increases substantially and significantly, indicating that lipids, too, are a major fuel during flight of twig wilters. This is corroborated by the activation of the enzyme triacylglycerol (TAG) lipase in the fat body, but not in the flight muscles, by injection of 5 pmol of synthetic Schgr-AKH-II, the endogenous adipokinetic hormone that is thought to be released during flight. Moreover, in the thorax there is a significant decrease in the concentration of glycogen and lipids measured after flight plus 60 min of rest compared to non-flown twig wilters, whereas no significant changes were monitored for these substrates stored in the abdomen. When the change in lipid class composition was analysed during flight plus 60 min of rest, TAG which comprised the major class in all compartments analysed (thorax, abdomen, haemolymph) was significantly reduced in abdomen and thorax, and diacylglycerol was significantly increased in all three compartments. From all the data collected, it is concluded that lipids are the major fuel class for flight in H. alata and that the contribution of carbohydrates is minimal.

Gas exchange characteristics, metabolic rate and water loss of the Heelwalker, Karoophasma biedouwensis (Mantophasmatodea: Austrophasmatidae)

This study presents the first physiological information for a member of the wingless Mantophasmatodea, or Heelwalkers. This species shows cyclic gas exchange with no evidence of a Flutter period (more typical of discontinuous gas exchange in insects) and no indication that the spiracles are fully occluded during quiescent metabolism. Standard metabolic rate at 20 degrees C was 21.32+/-2.73 microl CO(2)h(-1) (mean+/-S.E.), with a Q(10) (10-25 degrees C) of 1.7. Increases in V()CO(2) associated with variation in mass and with trial temperature were modulated by an increase in burst period volume and a decline in cycle frequency. Total water loss rate, determined by infrared gas analysis, was 0.876+/-0.08 mg H(2)Oh(-1) (range 0.602-1.577, n=11) whilst cuticular water loss rate, estimated by linear regression of total water loss rate and metabolic rate, was 0.618+/-0.09 mg H(2)Oh(-1) (range 0.341-1.363, n=11). Respiratory water loss rate was therefore no more than 29% of the total rate of water loss. Both total water loss rate and estimated cuticular water loss rate were significantly repeatable, with intraclass correlation coefficients of 0.745 and 0.553, respectively.

Unique translational modification of an invertebrate neuropeptide: a phosphorylated member of the adipokinetic hormone peptide family

Separation of an extract of corpora cardiaca from the protea beetle, Trichostetha fascicularis, by single-step RP (reverse-phase)-HPLC and monitoring of tryptophan fluorescence resulted in two distinctive peaks, the material of which mobilized proline and carbohydrates in a bioassay performed using the beetle. Material from one of these peaks was; however, inactive in the classical bioassays of locusts and cockroaches that are used for detecting peptides belonging to the AKH (adipokinetic hormone) family. After enzymatically deblocking the N-terminal pyroglutamic acid (pGlu) residue in the peptide material and sequencing by Edman degradation, a partial sequence was obtained: (pGlu)-Ile-Asn-Met-Thr-Xaa-Gly-Trp. The complete sequence was deduced from ESI-MS(n) (electrospray ionization multi-stage-MS); position six was identified as a phosphothreonine residue and the C-terminus is amidated. The peptide, code-named Trifa-CC, was chemically synthesized and used in confirmatory experiments to show that the primary structure had been correctly assigned. To our knowledge, this is the first report of a phosphorylated invertebrate neuropeptide. Synthetic Trifa-CC co-elutes with the natural peptide, found in the gland of the protea beetle, after RP-HPLC. Moreover, the natural peptide can be dephosphorylated by alkaline phosphatase and the product of that reaction has the same retention time as a synthetic nonphosphorylated octapeptide which has the same sequence as Trifa-CC. Finally, synthetic Trifa-CC has hypertrehalosaemic and hyperprolinaemic biological activity in the protea beetle, but even high concentrations of synthetic Trifa-CC are inactive in locusts and cockroaches. Hence, the correct peptide structure has been assigned. Trifa-CC of the protea beetle is an unusual member of the AKH family that is unique in its post-translational modification. Since it increases the concentration of carbohydrates and proline in the haemolymph when injected into the protea beetle, and since these substrates are also used during flight, we hypothesize that Trifa-CC controls the mobilization of these metabolites in the protea beetle.

Mass spectral signature for insect adipokinetic hormones

Insect adipokinetic hormones (AKHs) are structurally similar. They consist of 8 to 10 amino acid residues, and are post-translationally modified at the N-terminus (pyroglutamic acid) and at the C-terminus (carboxyamide). They contain aromatic amino acids at position 4 (mostly Phe, in a few cases Tyr) and at position 8 (Trp). Position 9 is always Gly which is used in the octapeptides for the amidation, and the majority of the peptides have no charge. AKHs exhibit a characteristic ion signature both in matrix-assisted laser desorption/ionization (ion pair [M+Na](+)/[M+K]+) and in electrospray mass spectrometry ([M+H+K]2+, [M-17+H]+, [M+H]+, [M+Na]+, [M+K]+). Their high affinity for Na+ and K+ alkali cations is observed even after reversed-phase purification. AKHs rarely form doubly charged ions with protons or sodium while the [M+H+K]2+ ion is often abundant suggesting a special conformation of the larger metal ion complex possibly related to its size. Here, we present analyses of several AKHs of different insect species and discuss their ionization behavior with respect to their sequence. The mass spectral signature observed is useful for AKH detection from mixtures and so an unassigned 990.7 Da molecule was found in dragonfly which is currently under investigation.