Heterodimeric fly glycoprotein hormone-alpha2 (GPA2) and glycoprotein hormone-beta5 (GPB5) activate fly leucine-rich repeat-containing G protein-coupled receptor-1 (DLGR1) and stimulation of human thyrotropin receptors by chimeric fly GPA2 and human GPB5

Evolutionary conserved peptide and glycoprotein hormone-like neuroendocrine systems in C. elegans

Peptides and protein hormones form the largest group of secreted signals that mediate intercellular communication and are central regulators of physiology and behavior in all animals. Phylogenetic analyses and biochemical identifications of peptide-receptor systems reveal a broad evolutionary conservation of these signaling systems at the molecular level. Substantial progress has been made in recent years on characterizing the physiological and putative ancestral roles of many peptide systems through comparative studies in invertebrate models. Several peptides and protein hormones are not only molecularly conserved but also have conserved roles across animal phyla. Here, we focus on functional insights gained in the nematode Caenorhabditis elegans that, with its compact and well-described nervous system, provides a powerful model to dissect neuroendocrine signaling networks involved in the control of physiology and behavior. We summarize recent discoveries on the evolutionary conservation and knowledge on the functions of peptide and protein hormone systems in C. elegans.

Ancestral glycoprotein hormone-receptor pathway controls growth in C. elegans

In vertebrates, thyrostimulin is a highly conserved glycoprotein hormone that, besides thyroid stimulating hormone (TSH), is a potent ligand of the TSH receptor. Thyrostimulin is considered the most ancestral glycoprotein hormone and orthologs of its subunits, GPA2 and GPB5, are widely conserved across vertebrate and invertebrate animals. Unlike TSH, however, the functions of the thyrostimulin neuroendocrine system remain largely unexplored. Here, we identify a functional thyrostimulin-like signaling system in Caenorhabditis elegans. We show that orthologs of GPA2 and GPB5, together with thyrotropin-releasing hormone (TRH) related neuropeptides, constitute a neuroendocrine pathway that promotes growth in C. elegans. GPA2/GPB5 signaling is required for normal body size and acts through activation of the glycoprotein hormone receptor ortholog FSHR-1. C. elegans GPA2 and GPB5 increase cAMP signaling by FSHR-1 in vitro. Both subunits are expressed in enteric neurons and promote growth by signaling to their receptor in glial cells and the intestine. Impaired GPA2/GPB5 signaling causes bloating of the intestinal lumen. In addition, mutants lacking thyrostimulin-like signaling show an increased defecation cycle period. Our study suggests that the thyrostimulin GPA2/GPB5 pathway is an ancient enteric neuroendocrine system that regulates intestinal function in ecdysozoans, and may ancestrally have been involved in the control of organismal growth.

Ancestral glycoprotein hormone and its cognate receptor present in primitive chordate ascidian: Molecular identification and functional characterization

The glycoprotein hormone (GPH) system is fundamentally significant in regulating the physiology of chordates, such as thyroid activity and gonadal function. However, the knowledge of the GPH system in the primitive chordate ascidian species is largely lacking. Here, we reported an ancestral GPH system in the ascidian (Styela clava), which consists of GPH α subunit (Sc-GPA2), GPH β subunit (Sc-GPB5), and the cognate leucine-rich repeat-containing G protein-coupled receptor (Sc-GPHR). Comparative structure analysis revealed that distinct from vertebrate GPH β subunits, Sc-GPB5 was less conserved, showing an atypical N-terminal sequence with a type II transmembrane domain instead of a typical signal peptide. By investigating the presence of recombinant Sc-GPA2 and Sc-GPB5 in cell lysates and culture media of HEK293T cells, we confirmed that these two subunits could be secreted out of the cells via distinct secretory pathways. The deglycosylation experiments demonstrated that N-linked glycosylation only occurred on the conserved cysteine residue (N78) of Sc-GPA2, whereas Sc-GPB5 was non-glycosylated. Although Sc-GPB5 exhibited distinct topology and biochemical properties in contrast to its chordate counterparts, it could still interact with Sc-GPA2 to form a heterodimer. The Sc-GPHR was then confirmed to be activated by tethered Sc-GPA2/GPB5 heterodimer on the Gs-cAMP pathway, suggesting that Sc-GPA2/GPB5 heterodimer-initiated Gs-cAMP signaling pathway is evolutionarily conserved in chordates. Furthermore, in situ hybridization and RT-PCR results revealed the co-expression patterns of Sc-GPA2 and Sc-GPB5 with Sc-GPHR transcripts, respectively in ascidian larvae and adults, highlighting the potential functions of Sc-GPA2/GPB5 heterodimer as an autocrine/paracrine neurohormone in regulating metamorphosis of larvae and physiological functions of adults. Our study systematically investigated the GPA2/GPB5-GPHR system in ascidian for the first time, which offers insights into understanding the function and evolution of the GPH system within the chordate lineage.

Investigating the role of glycoprotein hormone GPA2/GPB5 signaling in reproduction in adult female Rhodnius prolixus

Glycoprotein hormones are essential for regulating various physiological activities in vertebrates and invertebrates. In vertebrates, the classical glycoprotein hormones include follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH) and chorionic gonadotropin (CG), which have crucial roles in growth, development, metabolism, and reproduction. In female mammals, FSH stimulates egg production in the ovaries, whereas LH and CG act as the triggers for follicular ovulation. The more recently discovered heterodimeric glycoprotein hormone GPA2/GPB5 (called thyrostimulin in vertebrates) is suggested to be involved in reproductive processes in arthropods. Here, we focus on understanding the role of GPA2/GPB5 and its receptor, LGR1, in the reproductive success of adult female Rhodnius prolixus, a vector of Chagas disease. qPCR was used to monitor the expression of GPA2 and GPB5 transcripts and their receptor in different tissues. Immunohistochemistry was used to show the distribution of GPB5 in the nervous system and reproductive system, and RNA interference was used to disrupt the glycoprotein hormone signaling pathway. Both subunit transcripts, GPA2 and GPB5, are present in a variety of tissues, with the greatest expression in the central nervous system; whereas the LGR1 transcript is present in peripheral tissues, including the fat body and the reproductive system of adult females. In the adult female, GPB5-like immunoreactive axonal projections are present in the trunk nerves extending onto the reproductive tissues, with processes overlaying the ovaries, oviducts, spermatheca, and bursa, indicating the possibility of neural control by neurons containing GPA2/GPB5. In addition, GPB5-like immunostaining is present in muscles encircling the ovarioles, and in the cytoplasm of trophocytes (nurse cells) located in the tropharium. GPB5-like immunoreactive processes and blebs are also localized to the previtellogenic follicles, suggesting an involvement of this glycoprotein hormone signaling in oocyte development. LGR1 transcript expression increases in the adult female reproductive system post-feeding, a stimulus that initiates reproductive development, adding further support to an involvement in reproduction. We have investigated the effect of LGR1 downregulation on reproductive processes, monitoring the number and the quality of eggs laid, hatching ratio, and production of vitellogenin (Vg), the major yolk protein for developing eggs. Downregulation of LGR1 leads to increases in transcript expression of vitellogenin, RhoprVg1, in the fat body and the vitellogenin receptor, RhoprVgR, in the ovaries. Total protein in the fat body and hemolymph of dsLGR1-injected insects increased compared to controls and associated with this effect was a significant increase in vitellogenin in these tissues. dsLGR1-injection leads to accelerated oogenesis, an increase in the number of eggs produced and laid, an increase in egg size and a reduction in hatching rate. Our results indicate that GPA2/GPB5 signaling acts to delay egg production in adult female R. prolixus.

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.

Neuropeptides in Rhipicephalus microplus and other hard ticks

The synganglion is the central nervous system of ticks and, as such, controls tick physiology. It does so through the production and release of signaling molecules, many of which are neuropeptides. These peptides can function as neurotransmitters, neuromodulators and/or neurohormones, although in most cases their functions remain to be established. We identified and performed in silico characterization of neuropeptides present in different life stages and organs of Rhipicephalus microplus, generating transcriptomes from ovary, salivary glands, fat body, midgut and embryo. Annotation of synganglion transcripts led to the identification of 32 functional categories of proteins, of which the most abundant were: secreted, energetic metabolism and oxidant metabolism/detoxification. Neuropeptide precursors are among the sequences over-represented in R. microplus synganglion, with at least 5-fold higher transcription compared with other stages/organs. A total of 52 neuropeptide precursors were identified: ACP, achatin, allatostatins A, CC and CCC, allatotropin, bursicon A/B, calcitonin A and B, CCAP, CCHamide, CCRFamide, CCH/ITP, corazonin, DH31, DH44, eclosion hormone, EFLamide, EFLGGPamide, elevenin, ETH, FMRFamide myosuppressin-like, glycoprotein A2/B5, gonadulin, IGF, inotocin, insulin-like peptides, iPTH, leucokinin, myoinhibitory peptide, NPF 1 and 2, orcokinin, proctolin, pyrokinin/periviscerokinin, relaxin, RYamide, SIFamide, sNPF, sulfakinin, tachykinin and trissin. Several of these neuropeptides have not been previously reported in ticks, as the presence of ETH that was first clearly identified in Parasitiformes, which include ticks and mites. Prediction of the mature neuropeptides from precursor sequences was performed using available information about these peptides from other species, conserved domains and motifs. Almost all neuropeptides identified are also present in other tick species. Characterizing the role of neuropeptides and their respective receptors in tick physiology can aid the evaluation of their potential as drug targets.

Exploring the role of glycoprotein hormone GPA2/GPB5 in the medically important insect, Rhodnius prolixus

Glycoprotein hormones are formed by the heterodimerization of alpha and beta subunits. In vertebrates, there are five glycoprotein hormones, four of which have a common alpha subunit (GPA1) bound to a specific beta subunit (GPB1, GPB2, GPB3, or GPB4), and the fifth, thyrostimulin, is formed by the dimerization of GPA2 and GPB5 subunits. These hormones mediate physiological events such as development, metabolism, and reproduction, although the functional role of thyrostimulin in vertebrates has not been fully elucidated. Recent reports in invertebrates, specifically in holometabolous insects, suggest that GPA2/GPB5 plays a critical role in development, diuresis, and reproduction. In this study, we clone and characterize the transcripts for the glycoprotein hormone GPA2/GPB5 and its receptor (LGR1) in fifth instar Rhodnius prolixus, a hemimetabolous insect vector of Chagas disease. Sequence analyses reveals considerable identity and similarity between GPA2/GPB5 and LGR1 and those reported in other arthropod species. Quantitative PCR (qPCR) shows that both subunit transcripts, GPA2 and GPB5, and LGR1 transcripts are present in a variety of tissues, with greatest expression of the subunits in the central nervous system (CNS) and highest LGR1 expression in the Malpighian tubules (MT). Results from temporal qPCR analyses reveal a decrease in transcript expression 24 h after feeding, followed by an increase as the days post-feeding advance. Using immunohistochemistry, we show that GPB5 is expressed throughout the CNS, and importantly is present in neurosecretory cells in the brain and abdominal neuromeres and their neurohemal organs, indicating a neurohormonal role for this signaling pathway. A reduction in LGR1 transcript expression (via RNA interference) led to a greater weight loss and mortality rate in unfed insects. In addition, when a blood meal is offered, the insects with reduced LGR1 consume a significantly smaller blood meal and have higher mortality rates as the days post-feeding advance. Overall, the results suggest that the GPA2/GPB5 signaling pathway may play roles during a prolonged unfed state and in feeding-related events.

Genes Encoding the Glycoprotein Hormone GPA2/GPB5 and the Receptor LGR1 in a Female Prawn

In vertebrate reproduction, metabolism, growth and development, essential roles are played by glycoprotein hormones, such as follicle-stimulating hormone (FSH), luteinizing hormone (LH) and thyroid-stimulating hormone (TSH), all of which are heterodimers consisting of two subunits, a structurally identical alpha subunit, and a variable beta subunit, which provides specificity. A 'new' glycoprotein hormone heterodimer identified in both vertebrates and invertebrates, including decapod crustaceans, was shown to be composed of the glycoprotein alpha 2 (GPA2) and glycoprotein beta 5 (GPB5) subunits. The putative receptor for GPA2/GPB5 in invertebrates is the leucine-rich repeat-containing G protein-coupled receptor 1 (LGR1). In this study in the giant freshwater prawn, Macrobrachium rosenbergii, we identified and characterized the GPA2 (MrGPA2), GPB5 (MrGPB5) and LGR1 (MrLGR1) encoding genes and revealed their spatial expression patterns in female animals. Loss-of-function RNA interference (RNAi) experiments in M. rosenbergii females demonstrated a negative correlation between MrGPA2/MrGPB5 silencing and MrLGR1 transcript levels, suggesting a possible ligand-receptor interaction. The relative transcript levels of M. rosenbergii vitellogenin (MrVg) in the hepatopancreas were significantly reduced following MrGPA2/MrGPB5 knockdown. MrLGR1 loss-of-function induced MrVg receptor (MrVgR) transcript levels in the ovary and resulted in significantly larger oocytes in the silenced group compared to the control group. Our results provide insight into the possible role of GPA2/GPB5-LGR1 in female reproduction, as shown by its effect on MrVg and MrVgR expression and on the oocyte development. Here, we suggest that the GPA2/GPB5 heterodimer act as a gonad inhibiting factor in the eyestalk-hepatopancreas-ovary endocrine axis in M. rosenbergii.

Identification and characterization of expression profiles of neuropeptides and their GPCRs in the swimming crab, Portunus trituberculatus

Neuropeptides and their G protein-coupled receptors (GPCRs) regulate multiple physiological processes. Currently, little is known about the identity of native neuropeptides and their receptors in Portunus trituberculatus. This study employed RNA-sequencing and reverse transcription-polymerase chain reaction (RT-PCR) techniques to identify neuropeptides and their receptors that might be involved in regulation of reproductive processes of P. trituberculatus. In the central nervous system transcriptome data, 47 neuropeptide transcripts were identified. In further analyses, the tissue expression profile of 32 putative neuropeptide-encoding transcripts was estimated. Results showed that the 32 transcripts were expressed in the central nervous system and 23 of them were expressed in the ovary. A total of 47 GPCR-encoding transcripts belonging to two classes were identified, including 39 encoding GPCR-A family and eight encoding GPCR-B family. In addition, we assessed the tissue expression profile of 33 GPCRs (27 GPCR-As and six GPCR-Bs) transcripts. These GPCRs were found to be widely expressed in different tissues. Similar to the expression profiles of neuropeptides, 20 of these putative GPCR-encoding transcripts were also detected in the ovary. This is the first study to establish the identify of neuropeptides and their GPCRs in P. trituberculatus, and provide information for further investigations into the effect of neuropeptides on the physiology and behavior of decapod crustaceans.

Coordinated transcriptomics and peptidomics of central nervous system identify neuropeptides and their G protein-coupled receptors in the oriental fruit moth Grapholita molesta

The oriental fruit moth Grapholita molesta is a cosmopolitan pest of orchard, which causes serious economic losses to the fruit production. Neuropeptides and their specific receptors (primarily G protein-coupled receptors, GPCRs) regulate multiple biological functions in insects and represent promising next-generation pest management strategy. Here, we generated a transcriptome of the central nervous system (CNS) of G. molesta. Overall, 57 neuropeptide precursor genes were identified and 128 various mature peptides were predicted from these precursors. Using peptidomic analysis of CNS of G. molesta, we identified total of 28 mature peptides and precursor-related peptides from 16 precursors. A total of 41 neuropeptide GPCR genes belonging to three classes were also identified. These GPCRs and their probable ligands were predicted. Additionally, expression patterns of these 98 genes in various larval tissues were evaluated using quantitative real-time PCR. Taken together, these results will benefit further investigations to determine physiological functions and pharmacological characterization of neuropeptides and their GPCRs in G. molesta; and to develop specific neuropeptide-based agents for this tortricid fruit pest control.

Regulation of ecdysone production in Drosophila by neuropeptides and peptide hormones

In both mammals and insects, steroid hormones play a major role in directing the animal's progression through developmental stages. To maximize fitness outcomes, steroid hormone production is regulated by the environmental conditions experienced by the animal. In insects, the steroid hormone ecdysone mediates transitions between developmental stages and is regulated in response to environmental factors such as nutrition. These environmental signals are communicated to the ecdysone-producing gland via the action of neuropeptide and peptide hormone signalling pathways. While some of these pathways have been well characterized, there is evidence to suggest more signalling pathways than has previously been thought function to control ecdysone production, potentially in response to a greater range of environmental conditions. Here, we review the neuropeptide and peptide hormone signalling pathways known to regulate the production of ecdysone in the model genetic insect Drosophila melanogaster, as well as what is known regarding the environmental signals that trigger these pathways. Areas for future research are highlighted that can further contribute to our overall understanding of the complex orchestration of environmental, physiological and developmental cues that together produce a functioning adult organism.

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

Discovery of polypeptide ligand-receptor pairs based on their co-evolution

Sequencing diverse genomes allowed the tracing of orthologous and paralogous genes to understand the co-evolution of polypeptide ligands and receptors. This review documents the discovery of several polypeptide ligands and their cognate receptors mainly expressed in the reproductive tissue using evolutionary genomics. We discussed the sub-functionization of paralogs and co-evolution of ligand-receptor families. Based on the conserved signaling among paralogous receptors and common knock-out phenotypes of ligand-receptor pairs, relationships between relaxin family peptides and leucine-rich repeat-containing, G protein-coupled receptors (LGR) were revealed. We also described the identification of a novel paralogous glycoprotein hormone thyrostimulin and design of a long-acting FSH. Human stresscopin and stresscopin-related peptide, paralogous to CRH, were also identified based on the conserved signaling pathways. Recently, a novel ligand placensin expressed in human placenta was found based on the paralogous relationship with a metabolic hormone asprosin. Placensin likely contributes to stage-dependent increases in insulin resistance during human pregnancy and its elevated secretion was associated with gestational diabetes mellitus. Although many ligands were predicted based on sequence signatures, ligands of shorter sequences have not been identified, together with many "orphan" receptors without known ligands. Future development of tools for predicting ligands and high throughput assays to identify ligand-receptor pairs based on ligand binding and/or signal transduction could advance hormone-based physiology and pathophysiology.

Expression Profiling, Downstream Signaling, and Inter-subunit Interactions of GPA2/GPB5 in the Adult Mosquito Aedes aegypti

GPA2/GPB5 and its receptor constitute a glycoprotein hormone-signaling system native to the genomes of most vertebrate and invertebrate organisms. Unlike the well-studied gonadotropins and thyrotropin, the exact function of GPA2/GPB5 remains elusive, and whether it elicits its functions as heterodimers, homodimers or as independent monomers remains unclear. Here, the glycoprotein hormone signaling system was investigated in adult mosquitoes, where GPA2 and GPB5 subunit expression was mapped and modes of its signaling were characterized. In adult Aedes aegypti mosquitoes, GPA2 and GPB5 transcripts co-localized to bilateral pairs of neuroendocrine cells, positioned within the first five abdominal ganglia of the central nervous system. Unlike GPA2/GPB5 homologs in human and fly, GPA2/GPB5 subunits in A. aegypti lacked evidence of heterodimerization. Rather, cross-linking analysis to determine subunit interactions revealed A. aegypti GPA2 and GPB5 subunits may form homodimers, although treatments with independent subunits did not demonstrate receptor activity. Since mosquito GPA2/GPB5 heterodimers were not evident by heterologous expression, a tethered fusion construct was generated for expression of the subunits as a single polypeptide chain to mimic heterodimer formation. Our findings revealed A. aegypti LGR1 elicited constitutive activity with elevated levels of cAMP. However, upon treatment with recombinant tethered GPA2/GPB5, an inhibitory G protein (Gi/o) signaling cascade is initiated and forskolin-induced cAMP production is inhibited. These results further support the notion that heterodimerization is a requirement for glycoprotein hormone receptor activation and provide novel insight to how signaling is achieved for GPA2/GPB5, an evolutionary ancient neurohormone.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Synteny and phylogenetic analysis of paralogous thyrostimulin beta subunits (GpB5) in vertebrates

At some point early in the vertebrate lineage, two whole genome duplication events (1R, 2R) took place that allowed for the diversification and sub-/neo-functionalization of the glycoprotein hormones (GpHs). All jawed vertebrates possess the GpHs luteinizing hormone (LH), follicle stimulating hormone (FSH), and thyroid stimulating hormone (TSH), each of which are heterodimers with a common alpha subunit and unique beta subunits. In 2002, a novel glycoprotein hormone named thyrostimulin was described to have unique GpA2 and GpB5 subunits that were homologous to the vertebrate alpha and beta subunits. The presence of GpA2 and GpB5 in representative protostomes and deuterostomes indicates their ancestry in the GpH family. There are several reports of GpH subunit evolution, but none have included GpA2 and GpB5 for species in each major vertebrate class. Thus, we addressed the ancestry of two paralogous GpB5 subunits (GpB5a and GpB5b) that were previously only recognized in two teleost species. Our search for orthologous GpB5a and GpB5b sequences in representative vertebrates and phylogenetic analysis, in addition to the currently published evolutionary scenarios of the GpH family, supports that GpB5a and GpB5b are paralogs that arose from the first vertebrate whole genome duplication event (1R). Syntenic analysis supports lineage specific losses of GpB5a in chondrichthyes, basal actinopterygians, and tetrapods, and retention in coelacanth and teleosts. Additionally, we were unable to identify GpA2 transcripts from tilapia mRNA, suggesting that this species does not produce heterodimeric thyrostimulin. While the conserved or even species-specific functional role of thyrostimulin or its individual subunits are still unknown in vertebrates, the analyses presented here provide context for future studies on the functional divergence of the GpH family.

The evolutionary road to invertebrate thyroid hormone signaling: Perspectives for endocrine disruption processes

Thyroid hormones (THs) are the only iodine-containing hormones that play fundamental roles in chordates and non-chordates. The chemical nature, mode of action and the synthesis of THs are well established in mammals and other vertebrates. Although thyroid-like hormones have been detected in protostomes and non-chordate deuterostomes, TH signaling is poorly understood as compared to vertebrates, particularly in protostomes. Therefore, the central objective of this article is to review TH system components and TH-induced effects in non-vertebrate chordates, non-chordate deuterostomes and protostomes based on available genomes and functional information. To accomplish this task, we integrate here the available knowledge on the THs signaling across non-vertebrate chordates, non-chordate deuterostomes and protostomes by considering studies encompassing TH system components and physiological actions of THs. We also address the possible interactions of thyroid disrupting chemicals and their effects in protostomes and non-chordate deuterostomes. Finally, the perspectives on current and future challenges are discussed.

Gonadotropins and their receptors: coevolution, genetic variants, receptor imaging, and functional antagonists

Gonadotropins belong to the family of dimeric glycoprotein hormones and regulate gonadal physiology mediated by G protein-coupled, seven-transmembrane receptors. These glycoprotein hormones are widely used in the clinic to promote ovarian follicle development and for treating some cases of male infertility. We traced the coevolution of dimeric gonadotropin hormones and their receptors, together with thyrotropin and its receptor. We updated recent findings on human genetic variants of these genes and their association with dizygotic twining, polycystic ovarian syndrome, primary ovarian insufficiency, male-limited precocious puberty, and infertility. In addition to the known physiological roles of gonadotropin-receptor signaling in gonadal tissues, we also discussed emerging understanding of extragonadal functions of gonadotropins in bones and adipose tissues, together with recent advances in in vivo imaging of gonadotropin receptors in live animals. Recent development of gonadotropin receptor agonists and antagonists were summarized with an emphasis on the development of functional antagonists for FSH receptors to alleviate osteoporosis and obesity associated with menopause.

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.

Glycoprotein Hormone Receptor Knockdown Leads to Reduced Reproductive Success in Male Aedes aegypti

Glycoprotein hormone receptors mediate a diverse range of physiological functions in vertebrate and invertebrate organisms. The heterodimeric glycoprotein hormone GPA2/GPB5 and its receptor LGR1, constitute a recently discovered invertebrate neuroendocrine signaling system that remains to be functionally characterized. We previously reported that LGR1 is expressed in the testes of adult Aedes aegypti mosquitoes, where its immunoreactivity is particularly regionalized. Here, we show that LGR1 immunoreactivity is associated with the centriole adjunct of spermatids and is observed transiently during spermatogenesis in mosquitoes, where it may act to mediate the regulation of flagellar development. RNA interference to downregulate LGR1 expression was accomplished by feeding mosquito larvae with bacteria that produced LGR1-specific dsRNA, which led to defects in spermatozoa, characterized with shortened flagella. LGR1 knockdown mosquitoes also retained ∼60% less spermatozoa in reproductive organs and demonstrated reduced fertility compared to controls. To date, the endocrine regulation of spermatogenesis in mosquitoes remains an understudied research area. The distribution of LGR1 and detrimental effects of its knockdown on spermatogenesis in A. aegypti indicates that this heterodimeric glycoprotein hormone signaling system contributes significantly to the regulation of male reproductive biology in this important disease-vector.

Characterization of G-protein coupled receptors from the blackback land crab Gecarcinus lateralis Y organ transcriptome over the molt cycle

BACKGROUND

G-protein coupled receptors (GPCRs) are ancient, ubiquitous, constitute the largest family of transducing cell surface proteins, and are integral to cell communication via an array of ligands/neuropeptides. Molt inhibiting hormone (MIH) is a key neuropeptide that controls growth and reproduction in crustaceans by regulating the molt cycle. It inhibits ecdysone biosynthesis by a pair of endocrine glands (Y-organs; YOs) through binding a yet uncharacterized GPCR, which triggers a signalling cascade, leading to inhibition of the ecdysis sequence. When MIH release stops, ecdysone is synthesized and released to the hemolymph. A peak in ecdysone titer is followed by a molting event. A transcriptome of the blackback land crab Gecarcinus lateralis YOs across molt was utilized in this study to curate the list of GPCRs and their expression in order to better assess which GPCRs are involved in the molt process.

RESULTS

Ninety-nine G. lateralis putative GPCRs were obtained by screening the YO transcriptome against the Pfam database. Phylogenetic analysis classified 49 as class A (Rhodopsin-like receptor), 35 as class B (Secretin receptor), and 9 as class C (metabotropic glutamate). Further phylogenetic analysis of class A GPCRs identified neuropeptide GPCRs, including those for Allatostatin A, Allatostatin B, Bursicon, CCHamide, FMRFamide, Proctolin, Corazonin, Relaxin, and the biogenic amine Serotonin. Three GPCRs clustered with recently identified putative CHH receptors (CHHRs), and differential expression over the molt cycle suggests that they are associated with ecdysteroidogenesis regulation. Two putative Corazonin receptors showed much higher expression in the YOs compared with all other GPCRs, suggesting an important role in molt regulation.

CONCLUSIONS

Molting requires an orchestrated regulation of YO ecdysteroid synthesis by multiple neuropeptides. In this study, we curated a comprehensive list of GPCRs expressed in the YO and followed their expression across the molt cycle. Three putative CHH receptors were identified and could include an MIH receptor whose activation negatively regulates molting. Orthologs of receptors that were found to be involved in molt regulation in insects were also identified, including LGR3 and Corazonin receptor, the latter of which was expressed at much higher level than all other receptors, suggesting a key role in YO regulation.

Functional Characterization of Thyrostimulin in Amphioxus Suggests an Ancestral Origin of the TH Signaling Pathway

Thyrostimulin, consisting of GpA2 and GpB5 subunits, has been identified in amphioxus, but to date, little is known about the roles of GPA2/GPB5‒type hormone in this evolutionarily important animal. We showed here that amphioxus GpA2, GpB5, and TSH receptor (TSHR) represent the archetypes of vertebrate TSHα, TSHβ, and TSHR, respectively, and both gpa2 and gpb5 were coexpressed in the Hatschek pit, a homolog of the vertebrate pituitary, in amphioxus. We also showed that recombinant amphioxus GpA2 and GpB5, like zebrafish TSHα and TSHβ, bound to both amphioxus and zebrafish TSHR and that tethered amphioxus thyrostimulin activated both protein kinase A and protein kinase C pathways in the cells expressing amphioxus TSHR. Moreover, we demonstrated that recombinant amphioxus thyrostimulin induced the production of thyroid hormone (TH) T4. Because genuine TSH is absent in amphioxus and thyrostimulin is the only and sole glycoprotein hormone, our data likely provide evidence that amphioxus thyrostimulin is a functional glycoprotein hormone that plays a role as TSH does in vertebrates. The data also suggest that the TH signaling pathway evolved in the basal chordate more than 500 million years ago.

Cloning and characterization of a second lamprey pituitary glycoprotein hormone, thyrostimulin (GpA2/GpB5)

A novel heterodimeric glycoprotein hormone (GpH) comprised of alpha (GpA2) and beta (GpB5) subunits was discovered in 2002 and called thyrostimulin for its ability to activate the TSH receptor in mammals, but its central function in vertebrates has not been firmly established. We report here the cloning and expression of lamprey (l)GpB5, and its ability to heterodimerize with lGpA2 to form a functional l-thyrostimulin. The full-length cDNA of lGpB5 encodes 174 amino acids with ten conserved cysteine residues and one glycosylation site that is conserved with other vertebrate GpB5 sequences. Phylogenetic and synteny analyses support that lGpB5 belongs to the vertebrate GpB5 clade. Heterodimerization of lGpB5 and lGpA2 was shown by nickel pull-down of histidine-tagged recombinant subunits. RNA transcripts of lGpB5 were detected in the pituitary of lampreys during both parasitic and adult life stages. Intraperitoneal injection with lGnRH-III (100 μg/kg) increased pituitary lGpA2, lGpB5, and lGpHβ mRNA expression in sexually mature, adult female lampreys. A recombinant l-thyrostimulin produced by expression of a fusion gene in Pichia pastoris activated lamprey GpH receptors I and II as measured by cAMP enzymeimmunoassay. In contrast to jawed vertebrates that have pituitary LH, FSH, and TSH, our data support that lampreys only have two functional pituitary GpHs, lGpH and l-thyrostimulin, which consist of lGpA2 and unique beta subunits. It is hypothesized that lGpH and l-thyrostimulin differentially regulate reproductive and thyroid activities in some unknown way(s) in lampreys.

Landmark discoveries in elucidating the origins of the hypothalamic-pituitary system from the perspective of a basal vertebrate, sea lamprey

The hypothalamic-pituitary (HP) system, which is specific to vertebrates, is considered to be an evolutionary innovation that emerged prior to or during the differentiation of the ancestral jawless vertebrates (agnathans) leading to the neuroendocrine control of many complex functions. Along with hagfish, lampreys represent the oldest lineage of vertebrates, agnathans (jawless fish). This review will highlight our discoveries of the major components of the lamprey HP axis. Generally, gnathostomes (jawed vertebrates) have one or two hypothalamic gonadotropin-releasing hormones (GnRH) while lampreys have three hypothalamic GnRHs. GnRH(s) regulate reproduction in all vertebrates via the pituitary. In gnathostomes, there are three classical pituitary glycoprotein hormones (luteinizing hormone, LH; follicle stimulating hormone, FSH; and thyrotropin, TSH) interacting specifically with three receptors, LH-R, FSH-R, and TSH-R, respectively. In general, FSH and LH regulate gonadal activity and TSH regulates thyroidal activity. In contrast to gnathostomes, we propose that lampreys only have two heterodimeric pituitary glycoprotein hormones, lamprey glycoprotein hormone (lGpH) and thyrostimulin, and two lamprey glycoprotein hormone receptors (lGpH-R I and -R II). Our existing data also suggest the existence of a primitive, overlapping yet functional hypothalamic-pituitary-gonadal (HPG) and HP-thyroidal (HPT) endocrine systems in lampreys. The study of basal vertebrates provides promising models for understanding the evolution of the hypothalamic-pituitary-thyroidal and gonadal axes in vertebrates. We hypothesize that the glycoprotein hormone/glycoprotein hormone receptor systems emerged as a link between the neuroendocrine and peripheral control levels during the early stages of gnathostome divergence. Our discovery of a functional HPG axis in lamprey has provided important clues for understanding the forces that ensured a common organization of the hypothalamus and pituitary as essential regulatory systems in all vertebrates. This paper will provide a brief snapshot of my discoveries, collaborations and latest findings including phylogenomic analyses on the origins, co-evolution and divergence of ligand and receptor protein families from the perspective of the lamprey hypothalamic-pituitary system.

Discovery of novel representatives of bilaterian neuropeptide families and reconstruction of neuropeptide precursor evolution in ophiuroid echinoderms

Neuropeptides are a diverse class of intercellular signalling molecules that mediate neuronal regulation of many physiological and behavioural processes. Recent advances in genome/transcriptome sequencing are enabling identification of neuropeptide precursor proteins in species from a growing variety of animal taxa, providing new insights into the evolution of neuropeptide signalling. Here, detailed analysis of transcriptome sequence data from three brittle star species, Ophionotus victoriae, Amphiura filiformis and Ophiopsila aranea, has enabled the first comprehensive identification of neuropeptide precursors in the class Ophiuroidea of the phylum Echinodermata. Representatives of over 30 bilaterian neuropeptide precursor families were identified, some of which occur as paralogues. Furthermore, homologues of endothelin/CCHamide, eclosion hormone, neuropeptide-F/Y and nucleobinin/nesfatin were discovered here in a deuterostome/echinoderm for the first time. The majority of ophiuroid neuropeptide precursors contain a single copy of a neuropeptide, but several precursors comprise multiple copies of identical or non-identical, but structurally related, neuropeptides. Here, we performed an unprecedented investigation of the evolution of neuropeptide copy number over a period of approximately 270 Myr by analysing sequence data from over 50 ophiuroid species, with reference to a robust phylogeny. Our analysis indicates that the composition of neuropeptide ‘cocktails’ is functionally important, but with plasticity over long evolutionary time scales.

Insights Into Sexual Maturation and Reproduction in the Norway Lobster (Nephrops norvegicus) via in silico Prediction and Characterization of Neuropeptides and G Protein-coupled Receptors

Multiple biological processes across development and reproduction are modulated by neuropeptides that are predominantly produced and secreted from an animal's central nervous system. In the past few years, advancement of next-generation sequencing technologies has enabled large-scale prediction of putative neuropeptide genes in multiple non-model species, including commercially important decapod crustaceans. In contrast, knowledge of the G protein-coupled receptors (GPCRs), through which neuropeptides act on target cells, is still very limited. In the current study, we have used in silico transcriptome analysis to elucidate genes encoding neuropeptides and GPCRs in the Norway lobster (Nephrops norvegicus), which is one of the most valuable crustaceans in Europe. Fifty-seven neuropeptide precursor-encoding transcripts were detected, including phoenixin, a vertebrate neurohormone that has not been detected in any invertebrate species prior to this study. Neuropeptide gene expression analysis of immature and mature female N. norvegicus, revealed that some reproduction-related neuropeptides are almost exclusively expressed in immature females. In addition, a total of 223 GPCR-encoding transcripts were identified, of which 116 encode GPCR-A (Rhodopsin), 44 encode GPCR-B (Secretin) and 63 encode other GPCRs. Our findings increase the molecular toolbox of neural signaling components in N. norvegicus, allowing for further advances in the fisheries/larvae culture of this species.

A lamprey view on the origins of neuroendocrine regulation of the thyroid axis

This mini review summarizes the current knowledge of the hypothalamic-pituitary-thyroid (HPT) endocrine system in lampreys, jawless vertebrates. Lampreys and hagfish are the only two extant members of the class of agnathans, the oldest lineage of vertebrates. The high conservation of the hypothalamic-pituitary-gonadal (HPG) axis in lampreys makes the lamprey model highly appropriate for comparative and evolutionary analyses. However, there are still many unknown questions concerning the hypothalamic-pituitary (HP) axis in its regulation of thyroid activities in lampreys. As an example, the hypothalamic and pituitary hormone(s) that regulate the HPT axis have not been confirmed and/or characterized. Similar to gnathostomes (jawed vertebrates), lampreys produce thyroxine (T4) and triiodothyronine (T3) from thyroid follicles that are suggested to be involved in larval development, metamorphosis, and reproduction. The existing data provide evidence of a primitive, overlapping yet functional HPG and HPT endocrine system in lamprey. We hypothesize that lampreys are in an evolutionary intermediate stage of hypothalamic-pituitary development, leading to the emergence of the highly specialized HPG and HPT endocrine axes in jawed vertebrates. Study of the ancient lineage of jawless vertebrates, the agnathans, is key to understanding the origins of the neuroendocrine system in vertebrates.

The role of thyrostimulin and its potential clinical significance

Thyrostimulin is a glycoprotein heterodimer of GPA2 and GPB5, first described in 2002. It is involved in the physiological function of several tissues. Moreover, evidence points towards the ability of thyrostimulin's individual monomers to induce a biological effect, which could denote the circulatory/systemic effects of the molecule when found in higher concentrations. From the evolutionary point of view, thyrostimulin shares a binding epitope with the thyroid-stimulating hormone for the thyroid stimulating hormone receptor, whilst possessing affinity for another unique binding site on the same receptor. Although thyrostimulin can be involved in the hypothalamicpituitary- thyroid axis, its presence in various tissues in an eclectic array of different species renders it multifunctional. From weight loss via increasing metabolic rate to progression of cancer in human ovaries, it is certainly not a signaling molecule to overlook. Furthermore, thyrostimulin has been implicated in bone metabolism, acute illness, and reproductive function. In summary, to our knowledge, this is the first review dealing with the physiological role of thyrostimulin and its potential applications in the clinical practice.

Neuropeptide discovery in Proasellus cavaticus: Prediction of the first large-scale peptidome for a member of the Isopoda using a publicly accessible transcriptome

In silico transcriptome mining is one of the most effective methods for neuropeptide discovery in crustaceans, particularly for species that are small, rare or from geographically inaccessible habitats that make obtaining the large pools of tissue needed for other peptide discovery platforms impractical. Via this approach, large peptidomes have recently been described for members of many of the higher crustacean taxa, one notable exception being the Isopoda; no peptidome has been predicted for any member of this malacostracan order. Using a publicly accessible transcriptome for the isopod Proasellus cavaticus, a subcentimeter subterranean ground water dweller, the first in silico-predicted peptidome for a member of the Isopoda is presented here. BLAST searches employing known arthropod neuropeptide pre/preprohormone queries identified 49 transcripts as encoding putative homologs within the P. cavaticus transcriptome. The proteins deduced from these transcripts allowed for the prediction of 171 distinct mature neuropeptides. The P. cavaticus peptidome includes members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, diuretic hormone 31, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, leucokinin, myosuppressin, neuroparsin, neuropeptide F, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, sulfakinin, tachykinin-related peptide and trissin families, as well as many linker/precursor-related sequences that may or may not represent additional bioactive molecules. Interestingly, many of the predicted P. cavaticus neuropeptides possess structures identical (or nearly so) to those previously described from members of several other malacostracan orders, i.e., the Decapoda, Amphipoda and Euphausiacea, a finding that suggests broad phylogenetic conservation of bioactive peptide structures, and possibly functions, may exist within the Malacostraca.

Evolution of specificity in cartilaginous fish glycoprotein hormones and receptors

Glycoprotein hormones (GpH) interact very specifically with their receptors to mediate hypothalamic-pituitary-peripheral gland endocrine signaling. Vertebrates typically have three functionally distinct GpH endocrine signaling complexes: follicle-stimulating hormone, luteinizing hormone, and thyroid-stimulating hormone, and their receptors. Each hormone consists of a common α subunit bound to one of three different β subunits. Individual hormone subunits and receptors are present in genomes of early metazoans, and a subset of hormone subunits and receptors has been recently characterized in sea lamprey. However, it remains unclear when the full complement of hormone and receptor protein families first appeared, and when specificity of interactions between GpH hormones and receptors first evolved. Here we present phylogenetic analyses showing that the elephant shark (Callorhinchus milii) genome contains sequences representing the current diversity of all hormone subunits and receptors in these co-evolving protein families. We examined specificity of hormone and receptor interactions using functional assays testing reporter gene activation by elephant shark follicle-stimulating hormone, luteinizing hormone, and thyroid-stimulating hormone receptors. We show highly specific, dose-responsive hormone interactions for all three complexes. Our results suggest that co-evolution of specificity between proteins in these endocrine signaling complexes occurred prior to the divergence of Chondrichthyes from the chordate lineage.

Immunohistochemical mapping and transcript expression of the GPA2/GPB5 receptor in tissues of the adult mosquito, Aedes aegypti

GPA2/GPB5 is a glycoprotein hormone found in most bilateral metazoans including the mosquito, Aedes aegypti. To elucidate physiological roles and functions of GPA2/GPB5, we aim to identify prospective target tissues by examining the tissue- and sex-specific expression profile of its receptor, the leucine-rich repeat-containing G protein-coupled receptor 1 (LGR1) in the adult mosquito. Western analyses using a heterologous system with CHO-K1 cells, transiently expressing A. aegypti LGR1, yielded a 112-kDa monomeric band and high-molecular weight multimers, which associated with membrane-protein fractions. Moreover, immunoblot analyses on protein isolated from HEK 293 T cells stably expressing a fusion construct of A. aegypti LGR1-EGFP (LGR1: 105 kDa+EGFP: 27 kDa) yielded a band with a measured molecular weight of 139 kDa that also associated with membrane-protein fractions and upon deglycosylation, migrated as a lower molecular weight band of 132 kDa. Immunocytochemical analysis of HEK 293 T cells stably expressing this fusion construct confirmed EGFP fluorescence and LGR1-like immunoreactivity colocalized primarily to the plasma membrane. Immunohistochemical mapping in adult mosquitoes revealed LGR1-like immunoreactivity is widespread in the alimentary canal. Importantly, LGR1-like immunoreactivity localizes specifically to basolateral regions of epithelia and, in some regions, appeared as punctate intracellular staining, which together indicates a potential role in feeding and/or hydromineral balance. LGR1 transcript expression was also detected in gut regions that exhibited strong LGR1-like immunoreactivity. Interestingly, LGR1 transcript expression and strong LGR1-like immunoreactivity was also identified in reproductive tissues including the testes and ovaries, which together suggests a potential role linked to spermatogenesis and oogenesis in male and female mosquitoes, respectively.

Prediction of a neuropeptidome for the eyestalk ganglia of the lobster Homarus americanus using a tissue-specific de novo assembled transcriptome

In silico transcriptome mining is a powerful tool for crustacean peptidome prediction. Using homology-based BLAST searches and a simple bioinformatics workflow, large peptidomes have recently been predicted for a variety of crustaceans, including the lobster, Homarus americanus. Interestingly, no in silico studies have been conducted on the eyestalk ganglia (lamina ganglionaris, medulla externa, medulla interna and medulla terminalis) of the lobster, although the eyestalk is the location of a major neuroendocrine complex, i.e., the X-organ-sinus gland system. Here, an H. americanus eyestalk ganglia-specific transcriptome was produced using the de novo assembler Trinity. This transcriptome was generated from 130,973,220 Illumina reads and consists of 147,542 unique contigs. Eighty-nine neuropeptide-encoding transcripts were identified from this dataset, allowing for the deduction of 62 distinct pre/preprohormones. Two hundred sixty-two neuropeptides were predicted from this set of precursors; the peptides include members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, bursicon α, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone (CHH), CHH precursor-related peptide, diuretic hormone 31, diuretic hormone 44, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, glycoprotein hormone β5, GSEFLamide, intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide, sulfakinin, tachykinin-related peptide and trissin families. The predicted peptides expand the H. americanus eyestalk ganglia neuropeptidome approximately 7-fold, and include 78 peptides new to the lobster. The transcriptome and predicted neuropeptidome described here provide new resources for investigating peptidergic signaling within/from the lobster eyestalk ganglia.

Transcriptomic identification of starfish neuropeptide precursors yields new insights into neuropeptide evolution

Neuropeptides are evolutionarily ancient mediators of neuronal signalling in nervous systems. With recent advances in genomics/transcriptomics, an increasingly wide range of species has become accessible for molecular analysis. The deuterostomian invertebrates are of particular interest in this regard because they occupy an ‘intermediate' position in animal phylogeny, bridging the gap between the well-studied model protostomian invertebrates (e.g. Drosophila melanogaster, Caenorhabditis elegans) and the vertebrates. Here we have identified 40 neuropeptide precursors in the starfish Asterias rubens, a deuterostomian invertebrate from the phylum Echinodermata. Importantly, these include kisspeptin-type and melanin-concentrating hormone-type precursors, which are the first to be discovered in a non-chordate species. Starfish tachykinin-type, somatostatin-type, pigment-dispersing factor-type and corticotropin-releasing hormone-type precursors are the first to be discovered in the echinoderm/ambulacrarian clade of the animal kingdom. Other precursors identified include vasopressin/oxytocin-type, gonadotropin-releasing hormone-type, thyrotropin-releasing hormone-type, calcitonin-type, cholecystokinin/gastrin-type, orexin-type, luqin-type, pedal peptide/orcokinin-type, glycoprotein hormone-type, bursicon-type, relaxin-type and insulin-like growth factor-type precursors. This is the most comprehensive identification of neuropeptide precursor proteins in an echinoderm to date, yielding new insights into the evolution of neuropeptide signalling systems. Furthermore, these data provide a basis for experimental analysis of neuropeptide function in the unique context of the decentralized, pentaradial echinoderm bauplan.

Functional role of the heterodimeric glycoprotein hormone, GPA2/GPB5, and its receptor, LGR1: An invertebrate perspective

In vertebrates, follicle-stimulating hormone (FSH), luteinizing hormone (LH), chorionic gonadotropin (CG) and thyroid-stimulating hormone (TSH) are glycoprotein hormones that play central roles in metabolism, reproduction and development. Recently, a novel heterodimeric glycoprotein hormone, called GPA2/GPB5, was discovered in humans; however, contrary to its vertebrate glycoprotein hormone relatives, the physiological role of GPA2/GPB5 has not yet been fully elucidated in any vertebrate or invertebrate. Moreover, it is unclear as to whether GPA2/GPB5 functions as a heterodimer or as individual GPA2 and GPB5 monomers in these organisms. GPA2- and GPB5-like subunits have been identified or predicted in a wide array of animal phyla including the nematodes, chordates, hemichordates, arthropods, molluscs, echinoderms and annelids. So far, molecular studies on transcript expression of the GPA2/GPB5 subunits and its putative receptor, the leucine-rich repeat-containing G protein-coupled receptor 1 (LGR1), suggests this glycoprotein hormone system plays a developmental role and may also function in hydromineral balance in invertebrates. This mini-review summarizes the current state of knowledge on the physiological actions and activity of this evolutionarily ancient heterodimeric glycoprotein hormone with a particular focus on its known functions in the invertebrates.

Minireview: Insights Into the Structural and Molecular Consequences of the TSH-β Mutation C105Vfs114X

Naturally occurring thyrotropin (TSH) mutations are rare, which is also the case for the homologous heterodimeric glycoprotein hormones (GPHs) follitropin (FSH), lutropin (LH), and choriogonadotropin (CG). Patients with TSH-inactivating mutations present with central congenital hypothyroidism. Here, we summarize insights into the most frequent loss-of-function β-subunit of TSH mutation C105Vfs114X, which is associated with isolated TSH deficiency. This review will address the following question. What is currently known on the molecular background of this TSH variant on a protein level? It has not yet been clarified how C105Vfs114X causes early symptoms in affected patients, which are comparably severe to those observed in newborns lacking any functional thyroid tissue (athyreosis). To better understand the mechanisms of this mutant, we have summarized published reports and complemented this information with a structural perspective on GPHs. By including the ancestral TSH receptor agonist thyrostimulin and pathogenic mutations reported for FSH, LH, and choriogonadotropin in the analysis, insightful structure function and evolutionary restrictions become apparent. However, comparisons of immunogenicity and bioactivity of different GPH variants is hindered by a lack of consensus for functional analysis and the diversity of used GPH assays. Accordingly, relevant gaps of knowledge concerning details of GPH mutation-related effects are identified and highlighted in this review. These issues are of general importance as several previous and recent studies point towards the high impact of GPH variants in differential signaling regulation at GPH receptors (GPHRs), both endogenously and under diseased conditions. Further improvement in this area is of decisive importance for the development of novel targeted therapies.

Identification and expression profiles of neuropeptides and their G protein-coupled receptors in the rice stem borer Chilo suppressalis

In insects, neuropeptides play important roles in the regulation of multiple physiological processes by binding to their corresponding receptors, which are primarily G protein-coupled receptors (GPCRs). The genes encoding neuropeptides and their associated GPCRs in the rice stem borer Chilo suppressalis were identified by a transcriptomic analysis and were used to identify potential targets for the disruption of physiological processes and the protection of crops. Forty-three candidate genes were found to encode the neuropeptide precursors for all known insect neuropeptides except for arginine-vasopressin-like peptide (AVLP), CNMamide, neuropeptide-like precursors 2-4 (NPLP2-4), and proctolin. In addition, novel alternative splicing variants of three neuropeptide genes (allatostatin CC, CCHamide 1, and short neuropeptide F) are reported for the first time, and 51 putative neuropeptide GPCRs were identified. Phylogenetic analyses demonstrated that 44 of these GPCRs belong to the A-family (or rhodopsin-like), 5 belong to the B-family (or secretin-like), and 2 are leucine-rich repeat-containing GPCRs. These GPCRs and their likely ligands were also described. qRT-PCR analyses revealed the expression profiles of the neuropeptide precursors and GPCR genes in various tissues of C. suppressalis. Our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in Lepidoptera and aid in the design of peptidomimetics, pseudopeptides or small molecules capable of disrupting the physiological processes regulated by these signaling molecules and their receptors.

Thyrostimulin-TSHR signaling promotes the proliferation of NIH:OVCAR-3 ovarian cancer cells via trans-regulation of the EGFR pathway

Gonadotropin signaling plays an indispensable role in ovarian cancer progression. We previously have demonstrated that thyrostimulin and thyroid-stimulating hormone receptor (TSHR), the most ancient glycoprotein hormone and receptor pair that evolved much earlier than the gonadotropin systems, co-exist in the ovary. However, whether thyrostimulin-driven TSHR activation contributes to ovarian cancer progression in a similar way to gonadotropin receptors has never been explored. In this study, we first found that TSHR is expressed in both rat normal ovarian surface epithelium and human epithelial ovarian cancers (EOCs). Using human NIH:OVCAR-3 as a cell model, we demonstrated that thyrostimulin promotes EOC cell proliferation as strongly as gonadotropins. Thyrostimulin treatment not only activated adenylyl cyclase and the subsequent PKA, MEK-ERK1/2 and PI3K-AKT signal cascades, but also trans-activated EGFR signaling. Signaling dissection using diverse inhibitors indicated that EOC cell proliferation driven by thyrostimulin-TSHR signaling is PKA independent, but does require the involvement of the MEK-ERK and PI3K-AKT signal cascades, which are activated mainly via the trans-activation of EGFR. Thus, not only have we proved that this ancient glycoprotein hormone system is involved in NIH:OVCAR-3 cell proliferation for the first time, but also that it may possibly become a novel oncotarget when studying ovarian cancer.

In silico prediction of the G-protein coupled receptors expressed during the metamorphic molt of Sagmariasus verreauxi (Crustacea: Decapoda) by mining transcriptomic data: RNA-seq to repertoire

Against a backdrop of food insecurity, the farming of decapod crustaceans is a rapidly expanding and globally significant source of food protein. Sagmariasus verreauxi spiny lobster, the subject of this study, are decapods of underdeveloped aquaculture potential. Crustacean neuropeptide G-protein coupled receptors (GPCRs) mediate endocrine pathways that are integral to animal fecundity, growth and survival. The potential use of novel biotechnologies to enhance GPCR-mediated physiology may assist in improving the health and productivity of farmed decapod populations. This study catalogues the GPCRs expressed in the early developmental stages, as well as adult tissues, with a view to illuminating key neuropeptide receptors. De novo assembled contiguous sequences generated from transcriptomic reads of metamorphic and post metamorphic S. verreauxi were filtered for seven transmembrane domains, and used as a reference for iterative re-mapping. Subsequent putative GPCR open reading frames (ORFs) were BLAST annotated, categorised, and compared to published orthologues based on phylogenetic analysis. A total of 85 GPCRs were digitally predicted, that represented each of the four arthropod subfamilies. They generally displayed low-level and non-differential metamorphic expression with few exceptions that we examined using RT-PCR and qPCR. Two putative CHH-like neuropeptide receptors were annotated. Three dimensional structural modelling suggests that these receptors exhibit a conserved extracellular ligand binding pocket, providing support to the notion that these receptors co-evolved with their ligands across Decapoda. This perhaps narrows the search for means to increase productivity of farmed decapod populations.

The LH/CG receptor activates canonical signaling pathway when expressed in Drosophila

G-protein coupled receptors (GPCRs) and their ligands provide precise tissue regulation and are therefore often restricted to specific animal phyla. For example, the gonadotropins and their receptors are crucial for vertebrate reproduction but absent from invertebrates. In mammals, LHR mainly couples to the PKA signaling pathway, and CREB is the major transcription factor of this pathway. Here we present the results of expressing elements of the human gonadotropin system in Drosophila. Specifically, we generated transgenic Drosophila expressing the human LH/CG receptor (denoted as LHR), a constitutively active form of LHR, and an hCG analog. We demonstrate activation-dependent signaling by LHR to direct Drosophila phenotypes including lethality and specific midline defects; these phenotypes were due to LHR activation of PKA/CREB pathway activity. That the LHR can act in an invertebrate demonstrates the conservation of factors required for GPCR function among phylogenetically distant organisms. This novel gonadotropin model may assist the identification of new modulators of mammalian fertility by exploiting the powerful genetic and pharmacological tools available in Drosophila.

Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development

The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

Vertebrate cranial placodes as evolutionary innovations--the ancestor's tale

Evolutionary innovations often arise by tinkering with preexisting components building new regulatory networks by the rewiring of old parts. The cranial placodes of vertebrates, ectodermal thickenings that give rise to many of the cranial sense organs (ear, nose, lateral line) and ganglia, originated as such novel structures, when vertebrate ancestors elaborated their head in support of a more active and exploratory life style. This review addresses the question of how cranial placodes evolved by tinkering with ectodermal patterning mechanisms and sensory and neurosecretory cell types that have their own evolutionary history. With phylogenetic relationships among the major branches of metazoans now relatively well established, a comparative approach is used to infer, which structures evolved in which lineages and allows us to trace the origin of placodes and their components back from ancestor to ancestor. Some of the core networks of ectodermal patterning and sensory and neurosecretory differentiation were already established in the common ancestor of cnidarians and bilaterians and were greatly elaborated in the bilaterian ancestor (with BMP- and Wnt-dependent patterning of dorsoventral and anteroposterior ectoderm and multiple neurosecretory and sensory cell types). Rostral and caudal protoplacodal domains, giving rise to some neurosecretory and sensory cells, were then established in the ectoderm of the chordate and tunicate-vertebrate ancestor, respectively. However, proper cranial placodes as clusters of proliferating progenitors producing high-density arrays of neurosecretory and sensory cells only evolved and diversified in the ancestors of vertebrates.

Structure-function relationships of glycoprotein hormones and their subunits' ancestors

Glycoprotein hormones (GPHs) are the most complex molecules with hormonal activity. They exist only in vertebrates but the genes encoding their subunits' ancestors are found in most vertebrate and invertebrate species although their roles are still unknown. In the present report, we review the available structural and functional data concerning GPHs and their subunits' ancestors.

Functional neuropeptidomics in invertebrates

Neuropeptides are key messengers in almost all physiological processes. They originate from larger precursors and are extensively processed to become bioactive. Neuropeptidomics aims to comprehensively identify the collection of neuropeptides in an organism, organ, tissue or cell. The neuropeptidome of several invertebrates is thoroughly explored since they are important model organisms (and models for human diseases), disease vectors and pest species. The charting of the neuropeptidome is the first step towards understanding peptidergic signaling. This review will first discuss the latest developments in exploring the neuropeptidome. The physiological roles and modes of action of neuropeptides can be explored in two ways, which are largely orthogonal and therefore complementary. The first way consists of inferring the functions of neuropeptides by a forward approach where neuropeptide profiles are compared under different physiological conditions. Second is the reverse approach were neuropeptide collections are used to screen for receptor-binding. This is followed by localization studies and functional tests. This review will focus on how these different functional screening methods contributed to the field of invertebrate neuropeptidomics and expanded our knowledge of peptidergic signaling. This article is part of a Special Issue entitled: Neuroproteomics: Applications in Neuroscience and Neurology.

Molecular analysis of the koala reproductive hormones and their receptors: gonadotrophin-releasing hormone (GnRH), follicle-stimulating hormone β and luteinising hormone β with localisation of GnRH

During evolution, reproductive hormones and their receptors in the brain-pituitary-gonadal axis have been altered by genetic mechanisms. To understand how the neuroendocrine control of reproduction evolved in mammals, it is important to examine marsupials, the closest group to placental mammals. We hypothesised that at least some of the hormones and receptors found in placental mammals would be present in koala, a marsupial. We examined the expression of koala mRNA for the reproductive molecules. Koala cDNAs were cloned from brain for gonadotrophin-releasing hormones (GnRH1 and GnRH2) or from pituitary for GnRH receptors, types I and II, follicle-stimulating hormone (FSH)β and luteinising hormone (LH)β, and from gonads for FSH and LH receptors. Deduced proteins were compared by sequence alignment and phylogenetic analysis with those of other vertebrates. In conclusion, the koala expressed mRNA for these eight putative reproductive molecules, whereas at least one of these molecules is missing in some species in the amniote lineage, including humans. In addition, GnRH1 and 2 are shown by immunohistochemistry to be expressed as proteins in the brain.

Silencing D. melanogaster lgr1 impairs transition from larval to pupal stage

G protein-coupled receptors (GPCRs) play key roles in a wide diversity of physiological processes and signalling pathways. The leucine-rich repeats containing GPCRs (LGRs) are a subfamily that is well-conserved throughout most metazoan phyla and have important regulatory roles in vertebrates. Here, we report on the critical role of Drosophila melanogaster LGR1, the fruit fly homologue of the vertebrate glycoprotein hormone receptors, in development as a factor involved in the regulation of pupariation. Transcript profiling revealed that lgr1 transcripts are most abundant in third instar larvae and adult flies. The tissues displaying the highest transcript levels were the hindgut, the rectum and the salivary glands. Knockdown using RNA interference (RNAi) demonstrated that white pupa formation was severely suppressed in D. melanogaster lgr1 RNAi larvae. Associated with this developmental defect was a reduced ecdysteroid titer, which is in line with significantly reduced transcript levels detected for the Halloween genes shadow (sad) and spookier (spok) in the third instar lgr1 RNAi larvae compared to the control condition.

Glycoprotein hormones and their receptors emerged at the origin of metazoans

The cystine knot growth factor (CKGF) superfamily includes important secreted developmental regulators, including the families of transforming growth factor beta, nerve growth factor, platelet-derived growth factor, and the glycoprotein hormones (GPHs). The evolutionary origin of the GPHs and the related invertebrate bursicon hormone, and their characteristic receptors, contributes to an understanding of the endocrine system in metazoans. Using a sensitive search method with hidden Markov models, we identified homologs of the hormones and receptors, along with the closely related bone morphogenetic protein (BMP) antagonists in basal metazoans. In sponges and a comb jelly, cystine knot hormones (CKHs) with mixed features of GPHs, bursicon, and BMP antagonists were identified using primary sequence and phylogenetic analysis. Also, we identified potential receptors for these CKHs, leucine-rich repeat-containing G protein-coupled receptors (LGRs), in the same species. Cnidarians, such as the sea anemone, coral, and hydra, diverged later in metazoan evolution and appear to have duplicated and differentiated CKH-like peptides resulting in bursicon/GPH-like peptides and several BMP antagonists: Gremlin (Grem), sclerostin domain containing (SOSD), neuroblastoma suppressor of tumorigenicity 1 (NBL1), and Norrie disease protein. An expanded cnidarian LGR group also evolved, including receptors for GPH and bursicon. With the appearance of bilaterians, a separate GPH (thyrostimulin) along with bursicon and BMP antagonists were present. Synteny indicates that the GPHs, Grem, and SOSD have been maintained in a common gene neighborhood throughout much of metazoan evolution. The stable and highly conserved CKGFs are not identified in nonmetazoan organisms but are established with their receptors in the basal metazoans, becoming critical to growth, development, and regulation in all animals.

Neuropeptides and polypeptide hormones in echinoderms: new insights from analysis of the transcriptome of the sea cucumber Apostichopus japonicus

Echinoderms are of special interest for studies in comparative endocrinology because of their phylogenetic position in the animal kingdom as deuterostomian invertebrates. Furthermore, their pentaradial symmetry as adult animals provides a unique context for analysis of the physiological and behavioral roles of peptide signaling systems. Here we report the first extensive survey of neuropeptide and peptide hormone precursors in a species belonging to the class Holothuroidea. Transcriptome sequence data obtained from the sea cucumber Apostichopus japonicus were analyzed to identify homologs of precursor proteins that have recently been identified in the sea urchin Strongylocentrotus purpuratus (class Echinoidea). A total of 17 precursor proteins have been identified in A. japonicus, including precursors of peptides related to thyrotropin-releasing hormone, pedal peptide/orcokinin-type peptides, AN peptides/tachykinins, luqins, corticotropin-releasing hormone (CRH), GPA2-type glycoprotein hormone subunits and bursicon. In addition, an unusual finding was an A. japonicus calcitonin-type precursor protein (AjCTLPP), the first to be discovered that comprises two calcitonin-like peptides; this contrasts with the products of the alternatively-spliced calcitonin/CGRP gene in vertebrates, which comprise either calcitonin or CGRP. Collectively, the data obtained provide new insights on the evolution and diversity of neuropeptides and polypeptide hormones. Furthermore, because A. japonicus is one of several sea cucumber species that are used for human consumption, our findings may have practical and economic impact by providing a basis for neuroendocrine-based strategies to improve methods of aquaculture.

The evolutionary history of vertebrate cranial placodes--I: cell type evolution

Vertebrate cranial placodes are crucial contributors to the vertebrate cranial sensory apparatus. Their evolutionary origin has attracted much attention from evolutionary and developmental biologists, yielding speculation and hypotheses concerning their putative homologues in other lineages and the developmental and genetic innovations that might have underlain their origin and diversification. In this article we first briefly review our current understanding of placode development and the cell types and structures they form. We next summarise previous hypotheses of placode evolution, discussing their strengths and caveats, before considering the evolutionary history of the various cell types that develop from placodes. In an accompanying review, we also further consider the evolution of ectodermal patterning. Drawing on data from vertebrates, tunicates, amphioxus, other bilaterians and cnidarians, we build these strands into a scenario of placode evolutionary history and of the genes, cells and developmental processes that underlie placode evolution and development.