Evolution of glycoprotein hormone subunit genes in bilateral metazoa: identification of two novel human glycoprotein hormone subunit family genes, GPA2 and 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.

Eyes open on stem cells

Recently, the murine cornea has reemerged as a robust stem cell (SC) model, allowing individual SC tracing in living animals. The cornea has pioneered seminal discoveries in SC biology and regenerative medicine, from the first corneal transplantation in 1905 to the identification of limbal SCs and their transplantation to successfully restore vision in the early 1990s. Recent experiments have exposed unexpected properties attributed to SCs and progenitors and revealed flexibility in the differentiation program and a key role for the SC niche. Here, we discuss the limbal SC model and its broader relevance to other tissues, disease, and therapy.

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.

Undissociable chemically cross-linked and single-chain gonadotropins

Undissociable gonadotropins can be obtained either by chemical cross-linking of the natural heterodimeric hormones or by expressing recombinant single-chain molecules through the fusion of their α and β polypeptide sequences. These undissociable hormones are not more active than their natural heterodimeric counterparts indicating that the β-subunit seatbelt embracing the α-subunit ensures the αβ heterodimer stability in physiological conditions. The main interests of single-chain gonadotropins are that 1/only one single plasmid is required to produce an active recombinant hormone, 2/the two subunits' domains are constantly present in equal amounts and 3/they remain in close proximity even at low concentration for forming the hormone bioactive 3D structure. These undissociable gonadotropins have been shown to exhibit excellent stability and activity but they have not yet been commercialized probably because of immunogenicity risks and cost of production. Nevertheless, they might be used as a basis for the development of chemically simpler and cheaper ligands of LH and FSH receptors.

Gene Editing of the Follicle-Stimulating Hormone Gene to Sterilize Channel Catfish, Ictalurus punctatus, Using a Modified Transcription Activator-like Effector Nuclease Technology with Electroporation

Follicle-stimulating hormone (fsh) plays an important role in sexual maturation in catfish. Knocking out the fsh gene in the fish zygote should suppress the reproduction of channel catfish (Ictalurus punctatus). In this study, transcription activator-like effector nuclease (TALEN) plasmids targeting the fsh gene were electroporated into fertilized eggs with the standard double electroporation technique. Targeted fsh cleavage efficiency was 63.2% in P1fsh-knockout catfish. Ten of fifteen (66.7%) control pairs spawned, and their eggs had 32.3–74.3% average hatch rates in 2016 and 2017. Without hormone therapy, the spawning rates of P1 mutants ranged from 33.3 to 40.0%, with an average egg hatching rate of 0.75%. After confirmation of the low fertility of P1 mutants in 2016, human chorionic gonadotropin (HCG) hormone therapy improved the spawning rates by 80% for female mutants and 88.9% for male mutants, and the mean hatch rate was 35.0% for F1 embryos, similar to that of the controls (p > 0.05). Polymerase chain reaction (PCR) identification showed no potential TALEN plasmid integration into the P1 channel catfish genome. Neither the P1 nor the F1 mutant fish showed any noticeable changes in in body weight, survival rate, and hatching rate when the reproductive gene was knocked out. F1 families had a mean inheritance rate of 50.3%. The results brought us one step closer to allowing implementation of certain genetic techniques to aquaculture and fisheries management, while essentially eliminating the potential environment risk posed by transgenic, hybrid, and exotic fish as well as domestic fish.

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.

GPHB5 Is a Biomarker in Women With Metabolic Syndrome: Results From Cross-Sectional and Intervention Studies

BACKGROUND

Animal studies have found that GPHB5 has a similar effect on system metabolism as TSH. However, the relationship between GPHB5 and metabolic diseases remains unknown. This study investigates the relationship between GPHB5 and MetS in young women.

METHODS

Bioinformatics analysis was undertaken to explore the relationship between GPHB5 and metabolic-related genes and signaling pathways. EHC and OGTT were performed on all individuals. Lipid-infusion, physical activity, and cold-exposure tests were performed on healthy individuals. Serum GPHB5 concentrations were measured by an ELISA kit.

RESULTS

PPI network showed that 11 genes interacted with GPHB5, in which POMC and KISS1R were involved in glucose and lipid metabolism. GO analysis showed 56 pathways for BP and 16 pathways for MF, in which OPRM1 and MCR families were related to energy metabolism. KEGG analysis found that GPHB5 is associated with lipolysis and neuroactive ligand-receptor interaction pathways. The levels of circulating GPHB5 were significantly increased, while serum adiponectin levels were lower in MetS women compared with healthy women. Obese/overweight individuals had lower adiponectin levels and higher GPHB5 levels. Circulating GPHB5 levels were positively correlated with BMI, WHR, blood pressure, FBG, 2 h-BG, HbA1c, FIns, 2h-Ins, LDL-C, FFA, HOMA-IR, and AUCg, etc. but negatively correlated with HDL-C, adiponectin, and M-values. Serum GPHB5 levels did not change significantly during the OGTT, EHC, and lipid infusion. Physical activity and cold-exposure tests did not lead to changes in GPHB5 levels. GLP-1RA treatment resulted in a significant decrease in serum GPHB5 levels.

CONCLUSIONS

GPHB5 may be a biomarker for MetS.

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.

Elevated circulating GPHB5 levels in women with insulin resistance and polycystic ovary syndrome: A cross-sectional study and multiple intervention studies

OBJECTIVE

GPHB5 has been found to be associated with glucose and lipid metabolism in animal studies. However, the association of GPHB5 with IR and metabolic disorders remains unknown, and there is a lack of research in humans. Our aim in this study was to investigate the relationship between circulating GPHB5 and metabolic disorders in humans.

METHODS

Bioinformatics analysis was performed to understand the relationship between GPHB5 and metabolic disorders. GPHB5 mRNA expression in mice and rats was determined using RT-qPCR. Circulating GPHB5 concentrations were measured with an ELISA kit. EHC and OGTT were performed in humans.

RESULTS

Bioinformatics analysis shows that GPHB5 is associated with metabolic disorders and PCOS. GPHB5 mRNA expression levels in the metabolic-related tissues of HFD-fed mice, db/db and ob/ob mice, and PCOS rats were significantly higher than those of WT mice or rats. In human studies, we find that circulating GPHB5 levels were significantly higher in women with IR and PCOS. GPHB5 levels were positively correlated with age, BMI, WHR, BP, FBG, 2 h-BG, FIns, 2 h-Ins, TC, LDL-C, HbA1c, and FFA, but negatively correlated with adiponectin. Furthermore, GPHB5 was positively correlated with DHEAS and FAI, while negatively correlated with SHBG, FSH, SHBG and FSH. The increased GPHB5 concentration was related to IR and PCOS. After the treatment of metformin, GLP-1RA (Lira), and TZDs, circulating GPHB5 levels were decreased.

CONCLUSIONS

Our results reveal that circulating GPHB5 could be a biomarker and potential therapeutic target for IR and PCOS in women.

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.

Hormone-like conopeptides - new tools for pharmaceutical design

Conopeptides are a diverse family of peptides found in the venoms of marine cone snails and are used in prey capture and host defence. Because of their potent activity on a range of mammalian targets they have attracted interest as leads in drug design. Until recently most focus had been on studying conopeptides having activity at ion channels and related neurological targets but, with recent discoveries that some conopeptides might play hormonal roles, a new area of conopeptide research has opened. In this article we first summarize the canonical pharmaceutical families of Conus venom peptides and then focus on new research relating to hormone-like conopeptides and their potential applications. Finally, we briefly examine methods of chemically stabilizing conopeptides to improve their pharmacological properties. A summary is presented of conopeptides in clinical trials and a call for future work on hormone-like conopeptides.

Potential GnRH and steroidogenesis pathways in the scallop Patinopecten yessoensis

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on GnRH and steroidogenesis pathways is still limited. In this study, we first identified two gonadotropin receptor like genes (LGR and LGR5L) and four steroidogenesis-related genes (CYP17A, HSD17B12, HSD3B1 and HSD3B2) in the scallop Patinopecten yessoensis. By examining the expression of 11 genes in the ganglia and/or gonad as well as the concentration of progesterone, testosterone and estradiol in the gonad, we postulate that a potential GnRH signaling pathway (GnRH-GnRHR-GPB5-LGR/LGR5L) in the cerebral and pedal ganglia (CPG) and steroidogenesis pathway (CYP17A, HSD17B12 and HSD3B1) in the gonad are involved in regulating sex steroid hormones. E₂/T index that indicates aromatase activity is higher in the ovary than testis and is positively correlated with the expression of FOXL2 in the gonad, implying the presence of aromatase in the scallop. In addition, we confirmed that expression of most of the downstream genes in the two pathways was significantly elevated after injection of mature py-GnRH peptide. This study would contribute to a new understanding of the molecular basis underlying reproduction regulation by GnRH in mollusks.

What happens after a blood meal? A transcriptome analysis of the main tissues involved in egg production in Rhodnius prolixus, an insect vector of Chagas disease

The blood-sucking hemipteran Rhodnius prolixus is a vector of Chagas disease, one of the most neglected tropical diseases affecting several million people, mostly in Latin America. The blood meal is an event with a high epidemiological impact since adult mated females feed several times, with each meal resulting in a bout of egg laying, and thereby the production of hundreds of offspring. By means of RNA-Sequencing (RNA-Seq) we have examined how a blood meal influences mRNA expression in the central nervous system (CNS), fat body and ovaries in order to promote egg production, focusing on tissue-specific responses under controlled nutritional conditions. We illustrate the cross talk between reproduction and a) lipids, proteins and trehalose metabolism, b) neuropeptide and neurohormonal signaling, and c) the immune system. Overall, our molecular evaluation confirms and supports previous studies and provides an invaluable molecular resource for future investigations on different tissues involved in successful reproductive events. These analyses serve as a starting point for new investigations, increasing the chances of developing novel strategies for vector population control by translational research, with less impact on the environment and more specificity for a particular organism.

The Molecular Function and Clinical Role of Thyroid Stimulating Hormone Receptor in Cancer Cells

The thyroid stimulating hormone (TSH) and its cognate receptor (TSHR) are of crucial importance for thyrocytes to proliferate and exert their functions. Although TSHR is predominantly expressed in thyrocytes, several studies have revealed that functional TSHR can also be detected in many extra-thyroid tissues, such as primary ovarian and hepatic tissues as well as their corresponding malignancies. Recent advances in cancer biology further raise the possibility of utilizing TSH and/or TSHR as a therapeutic target or as an informative index to predict treatment responses in cancer patients. The TSH/TSHR cascade has been considered a pivotal modulator for carcinogenesis and/or tumor progression in these cancers. TSHR belongs to a sub-group of family A G-protein-coupled receptors (GPCRs), which activate a bundle of well-defined signaling transduction pathways to enhance cell renewal in response to external stimuli. In this review, recent findings regarding the molecular basis of TSH/TSHR functions in either thyroid or extra-thyroid tissues and the potential of directly targeting TSHR as an anticancer strategy are summarized and discussed.

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.

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.

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.

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.

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.

Evolutionarily conserved TRH neuropeptide pathway regulates growth in Caenorhabditis elegans

In vertebrates thyrotropin-releasing hormone (TRH) is a highly conserved neuropeptide that exerts the hormonal control of thyroid-stimulating hormone (TSH) levels as well as neuromodulatory functions. However, a functional equivalent in protostomian animals remains unknown, although TRH receptors are conserved in proto- and deuterostomians. Here we identify a TRH-like neuropeptide precursor in Caenorhabditis elegans that belongs to a bilaterian family of TRH precursors. Using CRISPR/Cas9 and RNAi reverse genetics, we show that TRH-like neuropeptides, through the activation of their receptor TRHR-1, promote growth in Celegans TRH-like peptides from pharyngeal motor neurons are required for normal body size, and knockdown of their receptor in pharyngeal muscle cells reduces growth. Mutants deficient for TRH signaling have no defects in pharyngeal pumping or isthmus peristalsis rates, but their growth defect depends on the bacterial diet. In addition to the decrease in growth, trh-1 mutants have a reduced number of offspring. Our study suggests that TRH is an evolutionarily ancient neuropeptide, having its origin before the divergence of protostomes and deuterostomes, and may ancestrally have been involved in the control of postembryonic growth and reproduction.

Multigenic Delineation of Lower Jaw Deformity in Triploid Atlantic Salmon (Salmo salar L.)

Lower jaw deformity (LJD) is a skeletal anomaly affecting farmed triploid Atlantic salmon (Salmo salar L.) which leads to considerable economic losses for industry and has animal welfare implications. The present study employed transcriptome analysis in parallel with real-time qPCR techniques to characterise for the first time the LJD condition in triploid Atlantic salmon juveniles using two independent sample sets: experimentally-sourced salmon (60 g) and commercially produced salmon (100 g). A total of eleven genes, some detected/identified through the transcriptome analysis (fbn2, gal and gphb5) and others previously determined to be related to skeletal physiology (alp, bmp4, col1a1, col2a1, fgf23, igf1, mmp13, ocn), were tested in the two independent sample sets. Gphb5, a recently discovered hormone, was significantly (P < 0.05) down-regulated in LJD affected fish in both sample sets, suggesting a possible hormonal involvement. In-situ hybridization detected gphb5 expression in oral epithelium, teeth and skin of the lower jaw. Col2a1 showed the same consistent significant (P < 0.05) down-regulation in LJD suggesting a possible cartilaginous impairment as a distinctive feature of the condition. Significant (P < 0.05) differential expression of other genes found in either one or the other sample set highlighted the possible effect of stage of development or condition progression on transcription and showed that anomalous bone development, likely driven by cartilage impairment, is more evident at larger fish sizes. The present study improved our understanding of LJD suggesting that a cartilage impairment likely underlies the condition and col2a1 may be a marker. In addition, the involvement of gphb5 urges further investigation of a hormonal role in LJD and skeletal physiology in general.

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.

Editing of the Luteinizing Hormone Gene to Sterilize Channel Catfish, Ictalurus punctatus, Using a Modified Zinc Finger Nuclease Technology with Electroporation

Channel catfish (Ictalurus punctatus) is the most important freshwater aquaculture species in the USA. Genetically enhanced fish that are sterile could both profit the catfish industry and reduce potential environmental and ecological risks. As the first step to generate sterile channel catfish, three sets of zinc finger nuclease (ZFN) plasmids targeting the luteinizing hormone (LH) gene were designed and electroporated into one-cell embryos, different concentrations were introduced, and the Cel-I assay was conducted to detect mutations. Channel catfish carrying the mutated LH gene were sterile, as confirmed by DNA sequencing and mating experiments. The overall mutation rate was 19.7 % for 66 channel catfish, and the best treatment was ZFN set 1 at the concentration 25 μg/ml. To our knowledge, this is the first instance of gene editing of fish via plasmid introduction instead of mRNA microinjection. The introduction of the ZFN plasmids may have reduced mosaicism, as mutated individuals were gene edited in every tissue evaluated. Apparently, the plasmids were eventually degraded without integration, as they were not detectable in mutated individuals using PCR. Carp pituitary extract failed to induce spawning and restoration of fertility, indicating the need for developing other hormone therapies to achieve reversal of sterility upon demand. This is the first sterilization achieved using ZFN technology in an aquaculture species and the first successful gene editing of channel catfish. Our results will help understand the roles of the LH gene, purposeful sterilization of teleost fishes, and is a step towards control of domestic, hybrid, exotic, invasive, and transgenic fishes.

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.

Initial description of primate-specific cystine-knot Prometheus genes and differential gene expansions of D-dopachrome tautomerase genes

Using eutherian comparative genomic analysis protocol and public genomic sequence data sets, the present work attempted to update and revise two gene data sets. The most comprehensive third party annotation gene data sets of eutherian adenohypophysis cystine-knot genes (128 complete coding sequences), and d-dopachrome tautomerases and macrophage migration inhibitory factor genes (30 complete coding sequences) were annotated. For example, the present study first described primate-specific cystine-knot Prometheus genes, as well as differential gene expansions of D-dopachrome tautomerase genes. Furthermore, new frameworks of future experiments of two eutherian gene data sets were proposed.

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.

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.

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.

Embryonic development of gonadotrope cells and gonadotropic hormones--lessons from model fish

Pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are key regulators of vertebrate reproduction. The differential regulation of these hormones, however, is poorly understood and little is known about gonadotrope embryonic development. The different cell types in the vertebrate pituitary develop from common progenitor cells just after gastrulation. Proper development and merging of the anterior and posterior pituitary is dependent upon carefully regulated cell-to-cell interactions, and a suite of signaling pathways with precisely organized temporal and spatial expression patterns, which include transcription factors and their co-activators and repressors. Among the pituitary endocrine cell types, the gonadotropes are the last to develop and become functional. Although much progress has been made during the last decade regarding details of gonadotrope development, the coordinated program for their maturation is not well described. FSH and LH form an integral part of the hypothalamo-pituitary-gonad axis, the main regulator of gonad development and reproduction. Besides regulating gonad development, pre- and early post-natal activity in this axis is thought to be essential for proper development, especially of the central nervous system in mammals. As a means to investigate early functions of FSH and LH in more detail, we have developed a stable transgenic line of medaka with the LH beta subunit gene (lhb) promoter driving green fluorescent protein (Gfp) expression to characterize development of lhb-expressing gonadotropes. The lhb gene is maternally expressed early during embryogenesis. lhb-Expressing cells are initially localized outside the primordial pituitary in the developing gut tube as early as 32 hpf. At hatching, lhb-Gfp is clearly detected in the gut epithelium and in the anterior digestive tract. lhb-Gfp expression later consolidates in the developing pituitary by 2 weeks post-fertilization. This review discusses status of knowledge regarding pituitary morphology and development, with emphasis on gonadotrope cells and gonadotropins during early development, comparing main model species like mouse, zebrafish and medaka, including possible developmental functions of the observed extra pituitary expression of lhb in medaka.

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 heterodimeric glycoprotein hormone, GPA2/GPB5, regulates ion transport across the hindgut of the adult mosquito, Aedes aegypti

A family of evolutionarily old hormones is the glycoprotein cysteine knot-forming heterodimers consisting of alpha- (GPA) and beta-subunits (GPB), which assemble by noncovalent bonds. In mammals, a common glycoprotein hormone alpha-subunit (GPA1) pairs with unique beta-subunits that establish receptor specificity, forming thyroid stimulating hormone (GPA1/TSHβ) and the gonadotropins luteinizing hormone (GPA1/LHβ), follicle stimulating hormone (GPA1/FSHβ), choriogonadotropin (GPA1/CGβ). A novel glycoprotein heterodimer was identified in vertebrates by genome analysis, called thyrostimulin, composed of two novel subunits, GPA2 and GPB5, and homologs occur in arthropods, nematodes and cnidarians, implying that this neurohormone system existed prior to the emergence of bilateral metazoans. In order to discern possible physiological roles of this hormonal signaling system in mosquitoes, we have isolated the glycoprotein hormone genes producing the alpha- and beta-subunits (AedaeGPA2 and AedaeGPB5) and assessed their temporal expression profiles in the yellow and dengue-fever vector, Aedes aegypti. We have also isolated a putative receptor for this novel mosquito hormone, AedaeLGR1, which contains features conserved with other glycoprotein leucine-rich repeating containing G protein-coupled receptors. AedaeLGR1 is expressed in tissues of the alimentary canal such as the midgut, Malpighian tubules and hindgut, suggesting that this novel mosquito glycoprotein hormone may regulate ionic and osmotic balance. Focusing on the hindgut in adult stage A. aegypti, where AedaeLGR1 was highly enriched, we utilized the Scanning Ion-selective Electrode Technique (SIET) to determine if AedaeGPA2/GPB5 modulated cation transport across this epithelial tissue. Our results suggest that AedaeGPA2/GPB5 does indeed participate in ionic and osmotic balance, since it appears to inhibit natriuresis and promote kaliuresis. Taken together, our findings imply this hormone may play an important role in ionic balance when levels of Na⁺ are limited and levels of K⁺ are in excess – such as during the digestion and assimilation of erythrocytes following vertebrate blood-feeding by females.

Constitutive activities in the thyrotropin receptor: regulation and significance

The thyroid-stimulating hormone receptor (TSHR, or thyrotropin receptor) is a family A G protein-coupled receptor. It not only binds thyroid-stimulating hormone (TSH, or thyrotropin) but also interacts with autoantibodies under pathological conditions. The TSHR and TSH are essential for thyroid growth and function and thus for all thyroid hormone-associated physiological superordinated processes, including metabolism and development of the central nervous system. In vitro studies have found that the TSHR permanently stimulates ligand-independent (constitutive) activation of Gs, which ultimately leads to intracellular cAMP accumulation. Furthermore, a vast variety of constitutively activating mutations of TSHR-at more than 50 different amino acid positions-have been reported to enhance basal signaling. These lead in vivo to a "gain-of-function" phenotype of nonautoimmune hyperthyroidism or toxic adenomas. Moreover, many naturally occurring inactivating mutations are known to cause a "loss-of-function" phenotype, resulting in resistance to thyroid hormone or hyperthyrotropinemia. Several of these mutations are also characterized by impaired basal signaling, and these are designated here as "constitutively inactivating mutations" (CIMs). More than 30 amino acid positions with CIMs have been identified so far. Moreover, the permanent TSHR signaling capacity can also be blocked by inverse agonistic antibodies or small drug-like molecules, which both have a potential for clinical usage. In this chapter, information on constitutive activity in the TSHR is described, including up- and downregulation, linked protein conformations, physiological and pathophysiological conditions, and related intracellular signaling.

Novel insights on thyroid-stimulating hormone receptor signal transduction

The TSH receptor (TSHR) is a member of the glycoprotein hormone receptors, a subfamily of family A G protein-coupled receptors. The TSHR is of great importance for the growth and function of the thyroid gland. The TSHR and its endogenous ligand TSH are pivotal proteins with respect to a variety of physiological functions and malfunctions. The molecular events of TSHR regulation can be summarized as a process of signal transduction, including signal reception, conversion, and amplification. The steps during signal transduction from the extra- to the intracellular sites of the cell are not yet comprehensively understood. However, essential new insights have been achieved in recent years on the interrelated mechanisms at the extracellular region, the transmembrane domain, and intracellular components. This review contains a critical summary of available knowledge of the molecular mechanisms of signal transduction at the TSHR, for example, the key amino acids involved in hormone binding or in the structural conformational changes that lead to G protein activation or signaling regulation. Aspects of TSHR oligomerization, signaling promiscuity, signaling selectivity, phenotypes of genetic variations, and potential extrathyroidal receptor activity are also considered, because these are relevant to an understanding of the overall function of the TSHR, including physiological, pathophysiological, and pharmacological perspectives. Directions for future research are discussed.

Extended and structurally supported insights into extracellular hormone binding, signal transduction and organization of the thyrotropin receptor

The hormone thyrotropin (TSH) and its receptor (TSHR) are crucial for the growth and function of the thyroid gland. The TSHR is evolutionary linked with the receptors of follitropin (FSHR) and lutropin/choriogonadotropin (LHR) and their sequences and structures are similar. The extracellular region of TSHR contains more than 350 amino acids and binds hormone and antibodies. Several important questions related to functions and mechanisms of TSHR are still not comprehensively understood. One major reason for these open questions is the lack of any structural information about the extracellular segment of TSHR that connects the N-terminal leucine-rich repeat domain (LRRD) with the transmembrane helix (TMH) 1, the hinge region. It has been shown experimentally that this segment is important for fine tuning of signaling and ligand interactions. A new crystal structure containing most of the extracellular hFSHR region in complex with hFSH has recently been published. Now, we have applied these new structural insights to the homologous TSHR and have generated a structural model of the TSHR LRRD/hinge-region/TSH complex. This structural model is combined and evaluated with experimental data including hormone binding (bTSH, hTSH, thyrostimulin), super-agonistic effects, antibody interactions and signaling regulation. These studies and consideration of significant and non-significant amino acids have led to a new description of mechanisms at the TSHR, including ligand-induced displacements of specific hinge region fragments. This event triggers conformational changes at a convergent center of the LRRD and the hinge region, activating an “intramolecular agonistic unit” close to the transmembrane domain.

Distinct expression patterns of glycoprotein hormone subunits in the lophotrochozoan Aplysia: implications for the evolution of neuroendocrine systems in animals

Glycoprotein hormones (GPHs) comprise a group of signaling molecules critical for major metabolic and reproductive functions. In vertebrates they include chorionic gonadotropin, LH, FSH, and TSH. The active hormones are characterized by heterodimerization between a common α and hormone-specific β subunit, which activate leucine-rich repeat-containing G protein coupled receptors. To date, genes referred to as GPHα2 and GPHβ5 have been the only glycoprotein hormone subunits identified in invertebrates, suggesting that other GPHα and GPHβ subunits diversified during vertebrate evolution. Still the functions of GPHα2 and GPHβ5 remain largely unknown for both vertebrates and invertebrates. To further understand the evolution and putative function of these subunits, we cloned and analyzed phylogenetically two glycoprotein subunits, AcaGPHα and AcaGPHβ, from the sea hare Aplysia californica. Model based three-dimensional predictions of AcaGPHβ confirm the presence of a complete cysteine knot, two hairpin loops, and a long loop. As in the human GPHβ5 subunit the seatbelt structure is absent in AcaGPHβ. We also found that AcaGPHα and AcaGPHβ subunits are expressed in larval stages of Aplysia, and we present a detailed expression map of the subunits in the adult central nervous system using in situ hybridizations. Both subunits are expressed in subpopulations of pleural and buccal mechanosensory neurons, suggesting a neuronal modulatory function of these subunits in Aplysia. Furthermore it supports the model of a relatively diffuse neuroendocrine-like system in molluscs, where specific primary sensory neurons release peptides extrasynaptically (paracrine secretion). This is in contrast to vertebrates and insects, in which releasing and stimulating factor from centralized sensory regions of the central nervous system ultimately regulate hormone release in peripheral glands.

Mini-review: the evolution of neuropeptide signaling

Neuropeptides and their G protein-coupled receptors (GPCRs) have an early evolutionary origin and are already abundant in basal animals with primitive nervous systems such as cnidarians (Hydra, jellyfishes, corals, and sea anemones). Most animals emerging after the Cnidaria belong to two evolutionary lineages, the Protostomia (to which the majority of invertebrates belong) and Deuterostomia (to which some minor groups of invertebrates, and all vertebrates belong). These two lineages split about 700 million years (Myr) ago. Many mammalian neuropeptide GPCRs have orthologues in the Protostomia and this is also true for some of the mammalian neuropeptides. Examples are oxytocin/vasopressin, GnRH, gastrin/CCK, and neuropeptide Y and their GPCRs. These results implicate that protostomes (for example insects and nematodes) can be used as models to study the biology of neuropeptide signaling.

Emergence and evolution of the glycoprotein hormone and neurotrophin gene families in vertebrates

Background

The three vertebrate pituitary glycoprotein hormones (GPH) are heterodimers of a common α and a specific β subunit. In human, they are located on different chromosomes but in a similar genomic environment. We took advantage of the availability of genomic and EST data from two cartilaginous fish species as well as from two lamprey species to identify their repertoire of neurotrophin, lin7 and KCNA gene family members which are in the close environment of gphβ. Gphα and gphβ are absent outside vertebrates but are related to two genes present in both protostomes and deuterostomes that were named gpa2 and gpb5. Genomic organization and functional characteristics of their protein products suggested that gphα and gphβ might have been generated concomitantly by a duplication of gpa2 and gpb5 just prior to the radiation of vertebrates. To have a better insight into this process we used new genomic resources and tools to characterize the ancestral environment before the duplication occurred.

Results

An almost similar repertoire of genes was characterized in cartilaginous fishes as in tetrapods. Data in lampreys are either incomplete or the result of specific duplications and/or deletions but a scenario for the evolution of this genomic environment in vertebrates could be proposed. A number of genes were identified in the amphioxus genome that helped in reconstructing the ancestral environment of gpa2 and gpb5 and in describing the evolution of this environment in vertebrates.

Conclusion

Our model suggests that vertebrate gphα and gphβ were generated by a specific local duplication of the ancestral forms of gpa2 and gpb5, followed by a translocation of gphβ to a new environment whereas gphα was retained in the gpa2-gpb5 locus. The two rounds of whole genome duplication that occurred early in the evolution of vertebrates generated four paralogues of each gene but secondary gene losses or lineage specific duplications together with genomic rearrangements have resulted in the present organization of these genes, which differs between vertebrate lineages.