The tick Ixodes scapularis has five different GPCRs specifically activated by ACP (adipokinetic hormone/corazonin-related peptide).

Insects have about 50 neuropeptide genes and about 70 genes, coding for neuropeptide G protein-coupled receptors (GPCRs). An important, but small family of evolutionarily related insect neuropeptides consists of adipokinetic hormone (AKH), corazonin, and AKH/corazonin-related peptide (ACP). Normally, insects have one specific GPCR for each of these neuropeptides. The tick Ixodes scapularis is not an insect, but belongs to the subphylum Chelicerata, which comprises ticks, scorpions, mites, spiders, and horseshoe crabs. Many of the neuropeptides and neuropeptide GPCRs occurring in insects, also occur in chelicerates, illustrating that insects and chelicerates are evolutionarily closely related. The tick I. scapularis is an ectoparasite and health risk for humans, because it infects its human host with dangerous pathogens during a blood meal. Understanding the biology of ticks will help researchers to prevent tick-borne diseases. By annotating the I. scapularis genome sequence, we previously found that ticks contain as many as five genes, coding for presumed ACP receptors. In the current paper, we cloned these receptors and expressed each of them in Chinese Hamster Ovary (CHO) cells. Each expressed receptor was activated by nanomolar concentrations of ACP, demonstrating that all five receptors were functional ACP receptors. Phylogenetic tree analyses showed that the cloned tick ACP receptors were mostly related to insect ACP receptors and, next, to insect AKH receptors, suggesting that ACP receptor genes and AKH receptor genes originated by gene duplications from a common ancestor. Similar duplications have probably occurred for the ligand genes, during a process of ligand/receptor co-evolution. Interestingly, chelicerates, in contrast to all other arthropods, do not have AKH or AKH receptor genes. Therefore, the ancestor of chelicerates might have lost AKH and AKH receptor genes and functionally replaced them by ACP and ACP receptor genes. For the small family of AKH, ACP, and corazonin receptors and their ligands, gene losses and gene gains occur frequently between the various ecdysozoan clades. Tardigrades, for example, which are well known for their survival in extreme environments, have as many as ten corazonin receptor genes and six corazonin peptide genes, while insects only have one of each, or none.

Cloning and deorphanization of three inotocin (insect oxytocin/vasopressin-like) receptors and their ligand from the tick Ixodes scapularis.

Many insects produce the cyclic neuropeptide inotocin (CLITNCPRGamide), which is the insect orthologue of the mammalian neuropeptides oxytocin and vasopressin. These insects also have one inotocin G protein-coupled receptor (GPCR), which is the orthologue of the mammalian oxytocin and vasopressin receptors. The tick Ixodes scapularis belongs to the subphylum Chelicerata, an arthropod taxon different from insects, to which also spiders, scorpions, and mites belong. I. scapularis is an ectoparasite and a health risk for humans, because it transfers pathogenic microorganisms to its human host during a blood meal, thereby causing serious neurological diseases, among them Lyme disease and tick-borne encephalitis (TBE). By annotating the genomic sequence of I. scapularis, we previously found one presumed tick inotocin preprohormone gene and, in contrast to insects, three genes coding for presumed inotocin GPCRs. We now find that these GPCR genes cluster on one genomic contig, suggesting that they originated by recent gene duplications. Closely located on the same contig are also four adipokinetic hormone/corazonin-related peptide (ACP) GPCR genes, and one crustacean cardioactive peptide (CCAP) GPCR gene, suggesting evolutionary relationships. These evolutionary relationships are confirmed by phylogenetic tree analyses of their gene products. We also cloned the tick inotocin preprohormone, which has a structural organization closely resembling mammalian oxytocin and vasopressin preprohormones, including the presence of a conserved neurophysin sequence, having seven cystine bridges. This neurophysin sequence has two cystine-knot domains, but in contrast to mammalian neurophysins, the tick neurophysin contains a canonical prohormone convertase cleavage signal and a peptide C-terminal amidation sequence (GKR), suggesting cleavage into two biologically active cystine-knot peptides. This cleavage/amidation sequence occurs in neurophysins from most hard tick species, but not in other chelicerates. Mature tick inotocin is different from insect inotocin and has the sequence CFITNCPPGamide. Finally, we cloned and stably expressed the three tick inotocin receptors in Chinese Hamster Ovary cells and found that each of them was activated by nanomolar concentrations of tick inotocin (EC50 for ITR1 = 1.6 × 10-8 M; EC50 for ITR2 = 5.8 × 10-9 M; EC50 for ITR3 = 9.3 × 10-9 M), thereby establishing that they are genuine tick inotocin receptors.

A corazonin G protein-coupled receptor gene in the tick Ixodes scapularis yields two splice variants, each coding for a specific corazonin receptor.

We have identified a corazonin G protein-coupled receptor (GPCR) gene in the tick Ixodes scapularis, which likely plays a central role in the physiology and behavior of this ectoparasite. This receptor gene is unusually large (1.133 Mb) and yields two corazonin (CRZ) receptor splice variants, where nearly half of the coding regions are exchanged: CRZ-Ra (containing exon 2, exon 3, and exon 4 of the gene) and CRZ-Rb (containing exon 1, exon 3, and exon 4 of the gene). CRZ-Ra codes for a GPCR with a canonical DRF sequence at the border of the third transmembrane helix and the second intracellular loop. The positively-charged R residue from the DRF sequence is important for coupling of G proteins after activation of a GPCR. CRZ-Rb, in contrast, codes for a GPCR with an unusual DQL sequence at this position, still retaining a negatively-charged D residue, but lacking a positively-charged R residue, suggesting different G protein coupling. Another difference between the two splice variants is that exon 2 from CRZ-Ra codes for an N-terminal signal sequence. Normally, GPCRs do not have N-terminal signal sequences, although a few mammalian GPCRs have. In the tick CRZ-Ra, the signal sequence probably assists with inserting the receptor correctly into the RER membrane. We stably transfected Chinese Hamster Ovary cells with each of the two splice variants and carried out bioluminescence bioassays that also included the use of the human promiscuous G protein G16. CRZ-Ra turned out to be selective for I. scapularis corazonin (EC50 = 10-8 M) and could not be activated by related neuropeptides like adipokinetic hormone (AKH) and AKH/corazonin-related peptide (ACP). Similarly, also CRZ-Rb could only be activated by corazonin, although about 4-fold higher concentrations were needed to activate it (EC50 = 4 x 10-8 M). The genomic organization of the tick corazonin GPCR gene is similar to that of the insect AKH and ACP receptor genes. This similar genomic organization can also be found in the human gonadotropin-releasing hormone (GnRH) receptor gene, confirming previous conclusions that the corazonin, AKH, and ACP receptor genes are the true arthropod orthologues of the human GnRH receptor gene.

An evolutionary genomics view on neuropeptide genes in Hydrozoa and Endocnidozoa (Myxozoa).

BACKGROUND: The animal phylum Cnidaria consists of six classes or subphyla: Hydrozoa, Scyphozoa, Cubozoa, Staurozoa, Anthozoa, and Endocnidozoa. Cnidarians have an early evolutionary origin, diverging before the emergence of the Bilateria. Extant members from this phylum, therefore, are important resources for understanding the evolution of the nervous system. Cnidarian nervous systems are strongly peptidergic. Using genomics, we have recently shown that three neuropeptide families (the X1PRX2amides, GRFamides, and GLWamides) are wide-spread in four (Scyphozoa, Cubozoa, Staurozoa, Anthozoa) out of six cnidarian classes or subphyla, suggesting that these three neuropeptide families emerged in the common cnidarian ancestor. In the current paper, we analyze the remaining cnidarian class, Hydrozoa, and the subphylum Endocnidozoa, to make firm conclusions about the evolution of neuropeptide genes in Cnidaria. RESULTS: We analyzed sixteen hydrozoan species with a sequenced genome or transcriptome, using a recently developed software program for discovering neuropeptide genes. These species belonged to various hydrozoan subclasses and orders, among them the laboratory models Hydra, Hydractinia, and Clytia. We found that each species contained three to five neuropeptide families. A common feature for all hydrozoans was that they contained genes coding for (i) X1PRX2amide peptides, (ii) GRFamide peptides, and (iii) GLWamide peptides. These results support our previous conclusions that these three neuropeptide families evolved early in evolution. In addition to these three neuropeptide families, hydrozoans expressed up to two other neuropeptide gene families, which, however, were only occurring in certain animal groups. Endocnidozoa (Myxozoa) are microscopically small endoparasites, which are strongly reduced. For long, it was unknown to which phylum these parasites belonged, but recently they have been associated with cnidarians. We analyzed nine endocnidozoan species and found that two of them (Polypodium hydriforme and Buddenbrockia plumatellae) expressed neuropeptide genes. These genes coded for neuropeptides belonging to the GRFamide and GLWamide families with structures closely resembling them from hydrozoans. CONCLUSIONS: We found X1PRX2amide, GRFamide, and GLWamide peptides in all species belonging to the Hydrozoa, confirming that these peptides originated in the common cnidarian ancestor. In addition, we discovered GRFamide and GLWamide peptide genes in some members of the Endocnidozoa, thereby linking these parasites to Hydrozoa.

A comparative genomics study of neuropeptide genes in the cnidarian subclasses Hexacorallia and Ceriantharia.

BACKGROUND: Nervous systems originated before the split of Proto- and Deuterostomia, more than 600 million years ago. Four animal phyla (Cnidaria, Placozoa, Ctenophora, Porifera) diverged before this split and studying these phyla could give us important information on the evolution of the nervous system. Here, we have annotated the neuropeptide preprohormone genes of twenty species belonging to the subclass Hexacorallia or Ceriantharia (Anthozoa: Cnidaria), using thirty-seven publicly accessible genome or transcriptome databases. Studying hexacorals is important, because they are versatile laboratory models for development (e.g., Nematostella vectensis) and symbiosis (e.g., Exaiptasia diaphana) and also are prominent reef-builders. RESULTS: We found that each hexacoral or ceriantharian species contains five to ten neuropeptide preprohormone genes. Many of these preprohormones contain multiple copies of immature neuropeptides, which can be up to 50 copies of identical or similar neuropeptide sequences. We also discovered preprohormones that only contained one neuropeptide sequence positioned directly after the signal sequence. Examples of them are neuropeptides that terminate with the sequence RWamide (the Antho-RWamides). Most neuropeptide sequences are N-terminally protected by pyroglutamyl (pQ) or one or more prolyl residues, while they are C-terminally protected by an amide group. Previously, we isolated and sequenced small neuropeptides from hexacorals that were N-terminally protected by an unusual L-3-phenyllactyl group. In our current analysis, we found that these N-phenyllactyl-peptides are derived from N-phenylalanyl-peptides located directly after the signal sequence of the preprohormone. The N-phenyllactyl- peptides appear to be confined to the hexacorallian order Actiniaria and do not occur in other cnidarians. On the other hand, (1) the neuropeptide Antho-RFamide (pQGRFamide); (2) peptides with the C-terminal sequence GLWamide; and (3) tetrapeptides with the X1PRX2amide consensus sequence (most frequently GPRGamide) are ubiquitous in Hexacorallia. CONCLUSIONS: We found GRFamide, GLWamide, and X1PRX2amide peptides in all tested Hexacorallia. Previously, we discovered these three neuropeptide classes also in Cubozoa, Scyphozoa, and Staurozoa, indicating that these neuropeptides originated in the common cnidarian ancestor and are evolutionarily ancient. In addition to these ubiquitous neuropeptides, other neuropeptides appear to be confined to specific cnidarian orders or subclasses.

De novo transcriptome assembly of the cubomedusa Tripedalia cystophora, including the analysis of a set of genes involved in peptidergic neurotransmission.

BACKGROUND: The phyla Cnidaria, Placozoa, Ctenophora, and Porifera emerged before the split of proto- and deuterostome animals, about 600 million years ago. These early metazoans are interesting, because they can give us important information on the evolution of various tissues and organs, such as eyes and the nervous system. Generally, cnidarians have simple nervous systems, which use neuropeptides for their neurotransmission, but some cnidarian medusae belonging to the class Cubozoa (box jellyfishes) have advanced image-forming eyes, probably associated with a complex innervation. Here, we describe a new transcriptome database from the cubomedusa Tripedalia cystophora. RESULTS: Based on the combined use of the Illumina and PacBio sequencing technologies, we produced a highly contiguous transcriptome database from T. cystophora. We then developed a software program to discover neuropeptide preprohormones in this database. This script enabled us to annotate seven novel T. cystophora neuropeptide preprohormone cDNAs: One coding for 19 copies of a peptide with the structure pQWLRGRFamide; one coding for six copies of a different RFamide peptide; one coding for six copies of pQPPGVWamide; one coding for eight different neuropeptide copies with the C-terminal LWamide sequence; one coding for thirteen copies of a peptide with the RPRAamide C-terminus; one coding for four copies of a peptide with the C-terminal GRYamide sequence; and one coding for seven copies of a cyclic peptide, of which the most frequent one has the sequence CTGQMCWFRamide. We could also identify orthologs of these seven preprohormones in the cubozoans Alatina alata, Carybdea xaymacana, Chironex fleckeri, and Chiropsalmus quadrumanus. Furthermore, using TBLASTN screening, we could annotate four bursicon-like glycoprotein hormone subunits, five opsins, and 52 other family-A G protein-coupled receptors (GPCRs), which also included two leucine-rich repeats containing G protein-coupled receptors (LGRs) in T. cystophora. The two LGRs are potential receptors for the glycoprotein hormones, while the other GPCRs are candidate receptors for the above-mentioned neuropeptides. CONCLUSIONS: By combining Illumina and PacBio sequencing technologies, we have produced a new high-quality de novo transcriptome assembly from T. cystophora that should be a valuable resource for identifying the neuronal components that are involved in vision and other behaviors in cubomedusae.

The first myriapod genome sequence reveals conservative arthropod gene content and genome organisation in the centipede Strigamia maritima.

Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.

Complementary symbiont contributions to plant decomposition in a fungus-farming termite.

Termites normally rely on gut symbionts to decompose organic matter but the Macrotermitinae domesticated Termitomyces fungi to produce their own food. This transition was accompanied by a shift in the composition of the gut microbiota, but the complementary roles of these bacteria in the symbiosis have remained enigmatic. We obtained high-quality annotated draft genomes of the termite Macrotermes natalensis, its Termitomyces symbiont, and gut metagenomes from workers, soldiers, and a queen. We show that members from 111 of the 128 known glycoside hydrolase families are represented in the symbiosis, that Termitomyces has the genomic capacity to handle complex carbohydrates, and that worker gut microbes primarily contribute enzymes for final digestion of oligosaccharides. This apparent division of labor is consistent with the Macrotermes gut microbes being most important during the second passage of comb material through the termite gut, after a first gut passage where the crude plant substrate is inoculated with Termitomyces asexual spores so that initial fungal growth and polysaccharide decomposition can proceed with high efficiency. Complex conversion of biomass in termite mounds thus appears to be mainly accomplished by complementary cooperation between a domesticated fungal monoculture and a specialized bacterial community. In sharp contrast, the gut microbiota of the queen had highly reduced plant decomposition potential, suggesting that mature reproductives digest fungal material provided by workers rather than plant substrate.

The A- and B-type muscarinic acetylcholine receptors from Drosophila melanogaster couple to different second messenger pathways.

Muscarinic acetylcholine receptors (mAChRs) are G protein-coupled receptors (GPCRs) that are activated by the agonists acetylcholine and muscarine and blocked by several antagonists, among them atropine. In mammals five mAChRs (m1-m5) exist of which m1, m3, and m5 are coupled to members of the Gq/11 family and m2 and m4 to members of the Gi/0 family. We have recently shown that Drosophila melanogaster and other arthropods have two mAChRs, named A and B, where the A-type has the same pharmacology as the mammalian mAChRs, while the B-type has a very low affinity to muscarine and no affinity to classical antagonists such as atropine. Here, we find that the D. melanogaster A-type mAChR is coupled to Gq/11 and D. melanogaster B-type mAChR to Gi/0. Furthermore, by comparing the second and third intracellular loops of all animal mAChRs for which the G protein coupling has been established, we could identify several amino acid residues likely to be specific for either Gq/11 or Gi/0 coupling. Using these hallmarks for specific mAChR G protein interaction we found that all protostomes with a sequenced genome have one mAChR coupled to Gq/11 and one to four mAChRs coupled to Gi/0. Furthermore, in protostomes, probably all A-type mAChRs are coupled to Gq/11 and all B-type mAChRs to G0/i.

The genome of the leaf-cutting ant Acromyrmex echinatior suggests key adaptations to advanced social life and fungus farming.

We present a high-quality (>100× depth) Illumina genome sequence of the leaf-cutting ant Acromyrmex echinatior, a model species for symbiosis and reproductive conflict studies. We compare this genome with three previously sequenced genomes of ants from different subfamilies and focus our analyses on aspects of the genome likely to be associated with known evolutionary changes. The first is the specialized fungal diet of A. echinatior, where we find gene loss in the ant's arginine synthesis pathway, loss of detoxification genes, and expansion of a group of peptidase proteins. One of these is a unique ant-derived contribution to the fecal fluid, which otherwise consists of "garden manuring" fungal enzymes that are unaffected by ant digestion. The second is multiple mating of queens and ejaculate competition, which may be associated with a greatly expanded nardilysin-like peptidase gene family. The third is sex determination, where we could identify only a single homolog of the feminizer gene. As other ants and the honeybee have duplications of this gene, we hypothesize that this may partly explain the frequent production of diploid male larvae in A. echinatior. The fourth is the evolution of eusociality, where we find a highly conserved ant-specific profile of neuropeptide genes that may be related to caste determination. These first analyses of the A. echinatior genome indicate that considerable genetic changes are likely to have accompanied the transition from hunter-gathering to agricultural food production 50 million years ago, and the transition from single to multiple queen mating 10 million years ago.

The genome of the model beetle and pest Tribolium castaneum.

Tribolium castaneum is a member of the most species-rich eukaryotic order, a powerful model organism for the study of generalized insect development, and an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved the ability to interact with a diverse chemical environment, as shown by large expansions in odorant and gustatory receptors, as well as P450 and other detoxification enzymes. Development in Tribolium is more representative of other insects than is Drosophila, a fact reflected in gene content and function. For example, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, some being expressed in the growth zone crucial for axial elongation in short-germ development. Systemic RNA interference in T. castaneum functions differently from that in Caenorhabditis elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control.

Evolution of the AKH/corazonin/ACP/GnRH receptor superfamily and their ligands in the Protostomia.

In this review we trace the evolutionary connections between GnRH receptors from vertebrates and the receptors for adipokinetic hormone (AKH), AKH/corazonin-related peptide (ACP), and corazonin from arthropods. We conclude that these G protein-coupled receptors (GPCRs) are closely related and have a common evolutionary origin, which dates back to the split of Proto- and Deuterostomia, about 700 million years ago. We propose that in the protostomian lineage, the ancestral GnRH-like receptor gene duplicated as did its GnRH-like ligand gene, followed by diversification, leading to (i) a corazonin receptor gene and a corazonin-like ligand gene, and (ii) an AKH receptor gene and an AKH-like ligand gene in the Mollusca and Annelida. Subsequently, the AKH receptor and ligand genes duplicated once more, yielding the situation that we know from arthropods today, where three independent hormonal systems exist, signalling with AKH, ACP, and corazonin. Our model for the evolution of GnRH signaling in the Protostomia is a striking example of receptor-ligand co-evolution. This model has been developed using several bioinformatics tools (TBLASTN searches, phylogenetic tree analyses), which also helped us to annotate six novel AKH preprohormones and their corresponding AKH sequences from the following molluscs: the sea hare Aplysia californica (AKH sequence: pQIHFSPDWGTamide), the sea slug Tritonia diomedea (pQIHFSPGWEPamide), the fresh water snail Bithynia siamensis goniomphalos (pQIHFTPGWGSamide), the owl limpet Lottia gigantea (pQIHFSPTWGSamide), the oyster Crassostrea gigas (pQVSFSTNWGSamide), and the freshwater pearl mussel Hyriopsis cumingii (pQISFSTNWGSamide). We also found AKHs in the tardigrade Hysibius dujardini (pQLSFTGWGHamide), the rotifer Brachionus calycifloros (pQLTFSSDWSGamide), and the penis worm Priapulus caudatus (pQIFFSKGWRGamide). This is the first report, showing that AKH signaling is widespread in molluscs.

Two types of muscarinic acetylcholine receptors in Drosophila and other arthropods.

Muscarinic acetylcholine receptors (mAChRs) play a central role in the mammalian nervous system. These receptors are G protein-coupled receptors (GPCRs), which are activated by the agonists acetylcholine and muscarine, and blocked by a variety of antagonists. Mammals have five mAChRs (m1-m5). In this study, we cloned two structurally related GPCRs from the fruit fly Drosophila melanogaster, which, after expression in Chinese hamster ovary cells, proved to be muscarinic acetylcholine receptors. One mAChR (the A-type; encoded by gene CG4356) is activated by acetylcholine (EC50, 5 × 10(-8) M) and muscarine (EC50, 6 × 10(-8) M) and blocked by the classical mAChR antagonists atropine, scopolamine, and 3-quinuclidinyl-benzilate (QNB), while the other (the B-type; encoded by gene CG7918) is also activated by acetylcholine, but has a 1,000-fold lower sensitivity to muscarine, and is not blocked by the antagonists. A- and B-type mAChRs were also cloned and functionally characterized from the red flour beetle Tribolium castaneum. Recently, Haga et al. (Nature 2012, 482: 547-551) published the crystal structure of the human m2 mAChR, revealing 14 amino acid residues forming the binding pocket for QNB. These residues are identical between the human m2 and the D. melanogaster and T. castaneum A-type mAChRs, while many of them are different between the human m2 and the B-type receptors. Using bioinformatics, one orthologue of the A-type and one of the B-type mAChRs could also be found in all other arthropods with a sequenced genome. Protostomes, such as arthropods, and deuterostomes, such as mammals and other vertebrates, belong to two evolutionarily distinct lineages of animal evolution that split about 700 million years ago. We found that animals that originated before this split, such as cnidarians (Hydra), had two A-type mAChRs. From these data we propose a model for the evolution of mAChRs.

Review: The evolution of peptidergic signaling in Cnidaria and Placozoa, including a comparison with Bilateria.

Bilateria have bilateral symmetry and are subdivided into Deuterostomia (animals like vertebrates) and Protostomia (animals like insects and mollusks). Neuropeptides occur in both Proto- and Deuterostomia and they are frequently structurally related across these two lineages. For example, peptides belonging to the oxytocin/vasopressin family exist in both clades. The same is true for the G protein-coupled receptors (GPCRs) of these peptides. These observations suggest that these neuropeptides and their GPCRs were already present in the common ancestor of Proto- and Deuterostomia, which lived about 700 million years ago (MYA). Furthermore, neuropeptides and their GPCRs occur in two early-branching phyla that diverged before the emergence of Bilateria: Cnidaria (animals like corals and sea anemones), and Placozoa (small disk-like animals, feeding on algae). The sequences of these neuropeptides and their GPCRs, however, are not closely related to those from Bilateria. In addition, cnidarian neuropeptides and their receptors are not closely related to those from Placozoa. We propose that the divergence times between Cnidaria, Placozoa, and Bilateria might be too long for recognizing sequence identities. Leucine-rich repeats-containing GPCRs (LGRs) are a special class of GPCRs that are characterized by a long N-terminus containing 10-20 leucine-rich domains, which are used for ligand binding. Among the ligands for LGRs are dimeric glycoprotein hormones, and insulin-like peptides, such as relaxin. LGRs have been found not only in Proto- and Deuterostomia, but also in early emerging phyla, such as Cnidaria and Placozoa. Humans have eight LGRs. In our current review, we have revisited the annotations of LGRs from the sea anemone Nematostella vectensis and the placozoan Trichoplax adhaerens. We identified 13 sea anemone LGRs and no less than 46 LGRs from T. adhaerens. All eight human LGRs appear to have orthologues in sea anemones and placozoans. LGRs and their ligands, therefore, have a long evolutionary history, going back to the common ancestor of Cnidaria and Placozoa.

Genomics, transcriptomics, and peptidomics of Daphnia pulex neuropeptides and protein hormones.

We report 43 novel genes in the water flea Daphnia pulex encoding 73 predicted neuropeptide and protein hormones as partly confirmed by RT-PCR. MALDI-TOF mass spectrometry identified 40 neuropeptides by mass matches and 30 neuropeptides by fragmentation sequencing. Single genes encode adipokinetic hormone, allatostatin-A, allatostatin-B, allatotropin, Ala(7)-CCAP, CCHamide, Arg(7)-corazonin, DENamides, CRF-like (DH52) and calcitonin-like (DH31) diuretic hormones, two ecdysis-triggering hormones, two FIRFamides, one insulin, two alternative splice forms of ion transport peptide (ITP), myosuppressin, neuroparsin, two neuropeptide-F splice forms, three periviscerokinins (but no pyrokinins), pigment dispersing hormone, proctolin, Met(4)-proctolin, short neuropeptide-F, three RYamides, SIFamide, two sulfakinins, and three tachykinins. There are two genes for a preprohormone containing orcomyotropin-like peptides and orcokinins, two genes for N-terminally elongated ITPs, two genes (clustered) for eclosion hormones, two genes (clustered) for bursicons alpha, beta, and two genes (clustered) for glycoproteins GPA2, GPB5, three genes for different allatostatins-C (two of them clustered) and three genes for IGF-related peptides. Detailed comparisons of genes or their products with those from insects and decapod crustaceans revealed that the D. pulex peptides are often closer related to their insect than to their decapod crustacean homologues, confirming that branchiopods, to which Daphnia belongs, are the ancestor group of insects.

Three homologous subunits form a high affinity peptide-gated ion channel in Hydra.

Recently, three ion channel subunits of the degenerin (DEG)/epithelial Na(+) channel (ENaC) gene family have been cloned from the freshwater polyp Hydra magnipapillata, the Hydra Na(+) channels (HyNaCs) 2-4. Two of them, HyNaC2 and HyNaC3, co-assemble to form an ion channel that is gated by the neuropeptides Hydra-RFamides I and II. The HyNaC2/3 channel is so far the only cloned ionotropic receptor from cnidarians and, together with the related ionotropic receptor FMRFamide-activated Na(+) channel (FaNaC) from snails, the only known peptide-gated ionotropic receptor. The HyNaC2/3 channel has pore properties, like a low Na(+) selectivity and a low amiloride affinity, that are different from other channels of the DEG/ENaC gene family, suggesting that a component of the native Hydra channel might still be lacking. Here, we report the cloning of a new ion channel subunit from Hydra, HyNaC5. The new subunit is closely related to HyNaC2 and -3 and co-localizes with HyNaC2 and -3 to the base of the tentacles. Coexpression in Xenopus oocytes of HyNaC5 with HyNaC2 and -3 largely increases current amplitude after peptide stimulation and affinity of the channel to Hydra-RFamides I and II. Moreover, the HyNaC2/3/5 channel has altered pore properties and amiloride affinity, more similarly to other DEG/ENaC channels. Collectively, our results suggest that the three homologous subunits HyNaC2, -3, and -5 form a peptide-gated ion channel in Hydra that could contribute to fast synaptic transmission.

Discovery of a novel insect neuropeptide signaling system closely related to the insect adipokinetic hormone and corazonin hormonal systems.

Neuropeptides and their G protein-coupled receptors (GPCRs) play a central role in the physiology of insects. One large family of insect neuropeptides are the adipokinetic hormones (AKHs), which mobilize lipids and carbohydrates from the insect fat body. Other peptides are the corazonins that are structurally related to the AKHs but represent a different neuropeptide signaling system. We have previously cloned an orphan GPCR from the malaria mosquito Anopheles gambiae that was structurally intermediate between the A. gambiae AKH and corazonin GPCRs. Using functional expression of the receptor in cells in cell culture, we have now identified the ligand for this orphan receptor as being pQVTFSRDWNAamide, a neuropeptide that is structurally intermediate between AKH and corazonin and that we therefore named ACP (AKH/corazonin-related peptide). ACP does not activate the A. gambiae AKH and corazonin receptors and, vice versa, AKH and corazonin do not activate the ACP receptor, showing that the ACP/receptor couple is an independent and so far unknown peptidergic signaling system. Because ACP is structurally intermediate between AKH and corazonin and the ACP receptor between the AKH and corazonin receptors, this is a prominent example of receptor/ligand co-evolution, probably originating from receptor and ligand gene duplications followed by mutations and evolutionary selection, thereby yielding three independent hormonal systems. The ACP signaling system occurs in the mosquitoes A. gambiae, Aedes aegypti, and Culex pipiens (Diptera), the silkworm Bombyx mori (Lepidoptera), the red flour beetle Tribolium castaneum (Coleoptera), the parasitic wasp Nasonia vitripennis (Hymenoptera), and the bug Rhodnius prolixus (Hemiptera). However, the ACP system is not present in 12 Drosophila species (Diptera), the honeybee Apis mellifera (Hymenoptera), the pea aphid Acyrthosiphon pisum (Hemiptera), the body louse Pediculus humanus (Phthiraptera), and the crustacean Daphnia pulex, indicating that it has been lost several times during arthropod evolution. In particular, this frequent loss of hormonal systems is unique for arthropods compared with vertebrates.

The Drosophila genes CG14593 and CG30106 code for G-protein-coupled receptors specifically activated by the neuropeptides CCHamide-1 and CCHamide-2.

Recently, a novel neuropeptide, CCHamide, was discovered in the silkworm Bombyx mori (L. Roller et al., Insect Biochem. Mol. Biol. 38 (2008) 1147-1157). We have now found that all insects with a sequenced genome have two genes, each coding for a different CCHamide, CCHamide-1 and -2. We have also cloned and deorphanized two Drosophila G-protein-coupled receptors (GPCRs) coded for by genes CG14593 and CG30106 that are selectively activated by Drosophila CCH-amide-1 (EC(50), 2×10(-9) M) and CCH-amide-2 (EC(50), 5×10(-9) M), respectively. Gene CG30106 (symbol synonym CG14484) has in a previous publication (E.C. Johnson et al., J. Biol. Chem. 278 (2003) 52172-52178) been wrongly assigned to code for an allatostatin-B receptor. This conclusion is based on our findings that the allatostatins-B do not activate the CG30106 receptor and on the recent findings from other research groups that the allatostatins-B activate an unrelated GPCR coded for by gene CG16752. Comparative genomics suggests that a duplication of the CCHamide neuropeptide signalling system occurred after the split of crustaceans and insects, about 410 million years ago, because only one CCHamide neuropeptide gene is found in the water flea Daphnia pulex (Crustacea) and the tick Ixodes scapularis (Chelicerata).

Identification of the Drosophila and Tribolium receptors for the recently discovered insect RYamide neuropeptides.

One year ago, we discovered a new family of insect RYamide neuropeptides, which has the C-terminal consensus sequence FFXXXRYamide, and which is widely occurring in most insects, including the fruitfly Drosophila melanogaster and the red flour beetle Tribolium castaneum (F. Hauser et al., J. Proteome Res. 9 (2010) 5296-5310). Here, we identify a Drosophila G-protein-coupled receptor (GPCR) coded for by gene CG5811 and its Tribolium GPCR ortholog as insect RYamide receptors. The Drosophila RYamide receptor is equally well activated (EC(50), 1×10(-9)M) by the two Drosophila RYamide neuropeptides: RYamide-1 (PVFFVASRYamide) and RYamide-2 (NEHFFLGSRYamide), both contained in a preprohormone coded for by gene CG40733. The Tribolium receptor shows a somewhat higher affinity to Tribolium RYamide-2 (ADAFFLGPRYamide; EC(50), 5×10(-9)M) than to Tribolium RYamide-1 (VQNLATFKTMMRYamide; EC(50), 7×10(-8)M), which might be due to the fact that the last peptide does not completely follow the RYamide consensus sequence rule. There are other neuropeptides in insects that have similar C-terminal sequences (RWamide or RFamide), such as the FMRFamides, sulfakinins, myosuppressins, neuropeptides F, and the various short neuropeptides F. Amazingly, these neuropeptides show no cross-reactivity to the Tribolium RYamide receptor, while the Drosophila RYamide receptor is only very slightly activated by high concentrations (>10(-6)M) of neuropeptide F and short neuropeptide F-1, showing that the two RYamide receptors are quite specific for activation by insect RYamides, and that the sequence FFXXXRYamide is needed for effective insect RYamide receptor activation. Phylogenetic tree analyses and other amino acid sequence comparisons show that the insect RYamide receptors are not closely related to any other known insect or invertebrate/vertebrate receptors, including mammalian neuropeptide Y and insect neuropeptide F and short neuropeptide F receptors. Gene expression data published in Flybase (www.flybase.org) show that the Drosophila CG5811 gene is significantly expressed in the hindgut of adult flies, suggesting a role of insect RYamides in digestion or water reabsorption.

Cloning and identification of an oxytocin/vasopressin-like receptor and its ligand from insects.

More than 20 years ago, an oxytocin/vasopressin-like peptide, CLITNCPRGamide, was isolated from the locust, Locusta migratoria [Proux JP, et al. (1987) Identification of an arginine vasopressin-like diuretic hormone from Locusta migratoria. Biochem Biophys Res Commun 149:180-186]. However, no similar peptide could be identified in other insects, nor could its prohormone be cloned, or its physiological actions be established. Here, we report that the recently sequenced genome from the red flour beetle Tribolium castaneum contains a gene coding for an oxytocin/vasopressin-like peptide, identical to the locust peptide, which we named inotocin (for insect oxytocin/vasopressin-like peptide) and a gene coding for an inotocin G protein-coupled receptor (GPCR). We cloned the Tribolium inotocin preprohormone and the inotocin GPCR and expressed the GPCR in CHO cells. This GPCR is strongly activated by low concentrations of inotocin (EC(50), 5 x 10(-9) M), demonstrating that it is the inotocin receptor. Quantitative RT-PCR (qPCR) showed that in adult Tribolium, the receptor is mainly expressed in the head and much less in the hindgut and Malpighian tubules, suggesting that the inotocin/receptor couple does not play a role in water homeostasis. Surprisingly, qPCR also showed that the receptor is 30x more expressed in the first larval stages than in adult animals. The inotocin/receptor couple can also be found in the recently sequenced genome from the parasitic wasp Nasonia vitripennis but not in any other holometabolous insect with a completely sequenced genome (12 Drosophila species, the malaria mosquito Anopheles gambiae, the yellow fever mosquito Aedes aegypti, the silk worm Bombyx mori, and the honey bee Apis mellifera), suggesting that this neuropeptide system is confined to basal holometabolous insects. Furthermore, we identified an oxytocin/vasopressin-like peptide and receptor in the recently sequenced genome from the water flea Daphnia pulex (Crustacea). To our knowledge, this is the first report on the molecular cloning of an oxytocin/vasopressin-like receptor and its ligand from arthropods.