Expression and distribution of octopus gonadotropin-releasing hormone in the central nervous system and peripheral organs of the octopus (Octopus vulgaris) by in situ hybridization and immunohistochemistry

Water temperature effects on embryonic development and GnRH-like expression in kisslip cuttlefish (Sepia lycidas) hinting the potential role of GnRH-like peptide

Gonadotropin-releasing hormone (GnRH)-like peptides are multifunctional neuropeptides involved in cardiac control, early ontogenesis, and reproduction in cephalopods. However, the precise role of GnRH-like peptides in embryonic development and juvenile growth in cephalopods remains unknown. In this study, we showed that GnRH-like peptides are involved in the embryonic development of kisslip cuttlefish (Sepia lycidas). We confirmed that higher water temperatures induced early hatching. Simultaneously, we found that brain GnRH-like peptide gene expression gradually increased with increasing hatching speed. However, the rise in water temperature within a suitable range had no effect on the juvenile sex ratio or early gonadal development. Our results indicate that GnRH-like peptides may play an accelerating role in embryonic development; however, they are not involved in sex determination or early gonadal development in kisslip cuttlefish.

Unusual coexistence of restrictive heart disease and Kallmann syndrome: a case report

BACKGROUND

Kallmann-Morsier syndrome is a rare disease characterized by the association of congenital gonadotropic deficiency and anosmia or hyposmia. The cardiac manifestations associated with this syndrome are little known. Through this case, we will characterize the cardiac involvement of this disease in the light of what is already described in the literature.

CASE PRESENTATION

We report the case of a young patient who presented with a picture of cardiac decompensation revealing restrictive heart disease. In her exploration, she was found to have primary amenorrhea, leading to the diagnosis of Kallmann syndrome. Medical treatment was optimized for the management of her cardiac decompensation as well as hormonal replacement treatment for her delayed puberty and growth.

CONCLUSIONS

Cardiac manifestations in Kallmann-Morsier syndrome are few reported in the literature, and restrictive heart disease is uncommon with no cases report till now. This association suggests a possible common genetic origin that should be explored in the future.

Functional Characterization of Gonadotropin-Releasing Hormone and Corazonin Signaling Systems in Pacific Abalone: Toward Reclassification of Invertebrate Neuropeptides

INTRODUCTION

The proposed evolutionary origins and corresponding nomenclature of bilaterian gonadotropin-releasing hormone (GnRH)-related neuropeptides have changed tremendously with the aid of receptor deorphanization. However, the reclassification of the GnRH and corazonin (CRZ) signaling systems in Lophotrochozoa remains unclear.

METHODS

We characterized GnRH and CRZ receptors in the mollusk Pacific abalone, Haliotis discus hannai (Hdh), by phylogenetic and gene expression analyses, bioluminescence-based reporter, Western blotting, substitution of peptide amino acids, in vivo neuropeptide injection, and RNA interference assays.

RESULTS

Two Hdh CRZ-like receptors (Hdh-CRZR-A and Hdh-CRZR-B) and three Hdh GnRH-like receptors (Hdh-GnRHR1-A, Hdh-GnRHR1-B, and Hdh-GnRHR2) were identified. In phylogenetic analysis, Hdh-CRZR-A and -B grouped within the CRZ-type receptors, whereas Hdh-GnRHR1-A/-B and Hdh-GnRHR2 clustered within the GnRH/adipokinetic hormone (AKH)/CRZ-related peptide-type receptors. Hdh-CRZR-A/-B and Hdh-GnRHR1-A were activated by Hdh-CRZ (pQNYHFSNGWHA-NH2) and Hdh-GnRH (pQISFSPNWGT-NH2), respectively. Hdh-CRZR-A/-B dually coupled with the Gαq and Gαs signaling pathways, whereas Hdh-GnRHR1-A was linked only with Gαq signaling. Analysis of substituted peptides, [I2S3]Hdh-CRZ and [N2Y3H4]Hdh-GnRH, and in silico docking models revealed that the N-terminal amino acids of the peptides are critical for the selectivity of Hdh-CRZR and Hdh-GnRHR. Two precursor transcripts for Hdh-CRZ and Hdh-GnRH peptides and their receptors were mainly expressed in the neural ganglia, and their levels increased in starved abalones. Injection of Hdh-CRZ peptide into abalones decreased food consumption, whereas Hdh-CRZR knockdown increased food consumption. Moreover, Hdh-CRZ induced germinal vesicle breakdown in mature oocytes.

CONCLUSION

Characterization of Hdh-CRZRs and Hdh-GnRHRs and their cognate peptides provides new insight into the evolutionary route of GnRH-related signaling systems in bilaterians.

Brain compartmentalization based on transcriptome analyses and its gene expression in Octopus minor

Coleoid cephalopods have a high intelligence, complex structures, and large brain. The cephalopod brain is divided into supraesophageal mass, subesophageal mass and optic lobe. Although much is known about the structural organization and connections of various lobes of octopus brain, there are few studies on the brain of cephalopod at the molecular level. In this study, we demonstrated the structure of an adult Octopus minor brain by histomorphological analyses. Through visualization of neuronal and proliferation markers, we found that adult neurogenesis occurred in the vL and posterior svL. We also obtained specific 1015 genes by transcriptome of O. minor brain and selected OLFM3, NPY, GnRH, and GDF8 genes. The expression of genes in the central brain showed the possibility of using NPY and GDF8 as molecular marker of compartmentation in the central brain. This study will provide useful information for establishing a molecular atlas of cephalopod brain.

Identification of GnRH-like peptide and its potential signaling pathway involved in the oocyte meiotic maturation in the Chinese mitten crab, Eriocheir sinensis

Gonadotropin-releasing hormone (GnRH) plays a pivotal role in reproductive regulation in vertebrates. However, GnRH was rarely isolated and its function remains poorly characterized in invertebrates. The existence of GnRH in ecdysozoa has been controversial for a long. Here, we isolated and identified two GnRH-like peptides from brain tissues in Eriocheir sinensis. Immunolocalization showed that the presence of EsGnRH-like peptide in brain, ovary and hepatopancreas. Synthetic EsGnRH-like peptides can induce germinal vesicle breakdown (GVBD) of oocyte. Similar to vertebrates, ovarian transcriptomic analysis revealed a GnRH signaling pathway in the crab, in which most genes exhibited dramatically high expression at GVBD. RNAi knockdown of EsGnRHR suppressed the expression of most genes in the pathway. Co-transfection of the expression plasmid pcDNA3.1-EsGnRHR with reporter plasmid CRE-luc or SRE-luc into 293T cells showed that EsGnRHR transduces its signal via cAMP and Ca²⁺ signaling transduction pathways. In vitro incubation of the crab oocyte with EsGnRH-like peptide confirmed the cAMP-PKA cascade and Ca²⁺ mobilization signaling cascade but lack of a PKC cascade. Our data present the first direct evidence of the existence of GnRH-like peptides in the crab and demonstrated its conserved role in the oocyte meiotic maturation as a primitive neurohormone.

Peptidergic modulation of a multi-functional central pattern generator in the pulmonate snail

Egg laying in pulmonate snails is a well-orchestrated process that involves a period of reduced locomotion, followed by substrate cleaning with rhythmic rasping of the surface to make tiny grooves, into which eggs are deposited. Although the neurohormonal control of initiating egg laying has been well established, the signals that modulate the buccal central pattern generator to substrate cleaning during egg laying are not known. Neuropeptides of the invertebrate gonadotropin-releasing hormone/corazonin family (invGnRH/CRZ) have been shown to be involved in reproduction and allied behaviors in many vertebrates and invertebrates. Here, we show that the buccal motor pattern underlying substrate cleaning during egg laying is altered by a vertebrate GnRH agonist. Signals from the intestinal nerve innervating reproductive structures, previously shown to be both necessary and sufficient for egg-laying behaviors, are blocked by a vertebrate GnRH antagonist. Further, the vertebrate GnRH-triggered response elicits rhythmic, phase 2 and non-phase 2 activity in the buccal motor pattern, with a shutdown of phase 3, indicative of repetitive rasping without accompanied swallowing behavior. Using immunohistochemistry, intracellular electrophysiology and extracellular nerve stimulation, we show that a member of the invGnRH/CRZ family of neuropeptides could be the signal that contextually switches the multifunctional buccal CPG to a biphasic rasping rhythm that underlies substrate cleaning behavior during egg laying in the pulmonate snail Planorbella (Helisoma) trivolvis.

Oviducal gland transcriptomics of Octopus maya through physiological stages and the negative effects of temperature on fertilization

Background

Elevated temperatures reduce fertilization and egg-laying rates in the octopus species. However, the molecular mechanisms that control the onset of fertilization and egg-laying in the octopus' oviducal gland are still unclear; and the effect of temperature on the expression of key reproductive genes is unknown. This study aims to better understand the molecular bases of octopus fertilization and egg-laying, and how they are affected by elevated temperatures.

Method

RNA-seq of oviducal glands was performed for samples before, during, and after fertilization and their transcriptomic profiles were compared. Also, at the fertilization stage, the optimal and thermal-stress conditions were contrasted. Expression levels of key reproductive genes were validated via RT-qPCR.

Results

In mated females before egg-laying, genes required for the synthesis of spermine, spermidine, which may prevent premature fertilization, and the myomodulin neuropeptide were upregulated. Among the genes with higher expression at the fertilization stage, we found those encoding the receptors of serotonin, dopamine, and progesterone; genes involved in the assembly and motility of the sperm flagellum; genes that participate in the interaction between male and female gametes; and genes associated with the synthesis of eggshell mucoproteins. At temperatures above the optimal range for reproduction, mated females reduced the fertilization rate. This response coincided with the upregulation of myomodulin and APGW-amide neuropeptides. Also, genes associated with fertilization like LGALS3, VWC2, and Pcsk1 were downregulated at elevated temperatures. Similarly, in senescent females, genes involved in fertilization were downregulated but those involved in the metabolism of steroid hormones like SRD5A1 were highly expressed.

Functional characterization and related evolutionary implications of invertebrate gonadotropin-releasing hormone/corazonin in a well-established model species

In vertebrates, gonadotropin-releasing hormone (GnRH) peptide is the central mediator of reproduction. Homologous peptides have previously also been identified in molluscan species. However, emerging evidence suggests that these molecules might serve diverse regulatory functions and proposes to consider them as corazonin (CRZ). We previously isolated the full-length cDNA of the invGnRH/CRZ peptide (termed ly-GnRH/CRZ) in the well-established invertebrate model species, the great pond snail Lymnaea stagnalis; however, its predicted functions remain to be verified. In this study, we first confirmed the presence of the deduced active peptide from the central nervous system of L. stagnalis. Further, we performed in vivo and in vitro studies to explore the functions of ly-GnRH/CRZ. Injection of sexually mature specimens with synthetic active peptide had an inhibitory effect on locomotion and an acceleratory effect on egg-laying, but had no effect on feeding. The previously predicted modulatory effect of ly-GnRH/CRZ was supported by its identified co-localization with serotonin on the surface of the heart atria. Lastly, we demonstrated not only the presence of ly-GnRH/CRZ in the penial complex but also that ly-GnRH/CRZ-containing neurons project to the efferent penis nerve, suggesting ly-GnRH/CRZ may directly modulate the motor output of this peripheral tissue. Overall, our findings strongly support that ly-GnRH/CRZ is a multifunctional neuropeptide. These results contribute to the understanding of the GnRH superfamily and, more broadly, disciplines such as comparative endocrinology and neurobiology.

Expression profile of GnRH-like peptide during gonadal sex differentiation in the cephalopod kisslip cuttlefish, Sepia lycidas

Gonadotropin-releasing hormone (GnRH) is one of the most important neuroendocrine regulators for animal reproduction. GnRH-like peptide (GnRH-like) has recently been shown to play a critical reproductive role mainly in gametogenesis or steroidogenesis in the gonads of some molluscs, including cephalopods. However, its involvement in gonadal sex differentiation remains unknown. Here, we show the expression profile of GnRH-like in the brain of the cephalopod kisslip cuttlefish, Sepia lycidas, throughout gonadal sex differentiation, by quantitative real time RT-PCR and immunohistochemistry. We found that GnRH-like could be detected in the brain at a sexually undifferentiated stage, and its expression level significantly increased upon initiation of gonadal sex differentiation. However, no significant difference in GnRH-like expression levels was observed between sexes during gonadal sex differentiation. Additionally, we demonstrated immunoreactivity of GnRH-like in glial cells or immature neurons, which are mainly distributed in the non-reproductive related area of the cephalopod brain, suggesting the immature function of the reproductive endocrine axis during early ontogenesis. Our results demonstrate for the first time, the expression profile of GnRH-like during early ontogenesis in cephalopods.

Identification, presence, and possible multifunctional regulatory role of invertebrate gonadotropin-releasing hormone/corazonin molecule in the great pond snail (Lymnaea stagnalis)

In the last years, our interpretation of the origin and function of the gonadotropin-releasing hormone (GnRH) neuropeptide superfamily has changed substantially. A main driver for these conceptual changes came from increased investigations into functions and evolutionary lineage of previously identified molluscan GnRH molecules. Emerging evidence suggests not only reproductive, but also diverse biological effects of these molecules and proposes they should most likely be called corazonin (CRZ). Clearly, a more global understanding requires further exploration of species-specific functions and structure of invGnRH/CRZ peptides. Towards this goal, we have identified the full-length cDNA of invGnRH/CRZ peptide in an invertebrate model species, the great pond snail Lymnaea stagnalis, termed ly-GnRH/CRZ, and characterized the transcript and peptide distribution in the central nervous system (CNS) and peripheral organs. Our results are consistent with previous data that molluscan GnRHs are more related to CRZs and serve diverse functions. Hence, our findings support the notion that peptides originally termed molluscan GnRH are multifunctional modulators and that nomenclature change should be taken into consideration.

Invertebrate Gonadotropin-Releasing Hormone Receptor Signaling and Its Relevant Biological Actions

Gonadotropin-releasing hormones (GnRHs) play pivotal roles in reproduction via the hypothalamus-pituitary-gonad axis (HPG axis) in vertebrates. GnRHs and their receptors (GnRHRs) are also conserved in invertebrates lacking the HPG axis, indicating that invertebrate GnRHs do not serve as “gonadotropin-releasing factors” but, rather, function as neuropeptides that directly regulate target tissues. All vertebrate and urochordate GnRHs comprise 10 amino acids, whereas amphioxus, echinoderm, and protostome GnRH-like peptides are 11- or 12-residue peptides. Intracellular calcium mobilization is the major second messenger for GnRH signaling in cephalochordates, echinoderms, and protostomes, while urochordate GnRHRs also stimulate cAMP production pathways. Moreover, the ligand-specific modulation of signal transduction via heterodimerization between GnRHR paralogs indicates species-specific evolution in Ciona intestinalis. The characterization of authentic or putative invertebrate GnRHRs in various tissues and their in vitro and in vivo activities indicate that invertebrate GnRHs are responsible for the regulation of both reproductive and nonreproductive functions. In this review, we examine our current understanding of and perspectives on the primary sequences, tissue distribution of mRNA expression, signal transduction, and biological functions of invertebrate GnRHs and their receptors.

Association of olfactory neuropathy spectrum disorder and Wolff-Parkinson-White syndrome: A Report of a case

Olfactory neuropathy spectrum disorder is characterized by hyposmia or anosmia and hypoplastic or absent olfactory bulbs. There may be an association between olfactory neuropathy spectrum disorder and Wolff-Parkinson-White syndrome.

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.

Neuroendocrine immune-regulatory of a neuropeptide ChGnRH from the Hongkong oyster, Crassostrea Hongkongensis

It is increasingly appreciated that neuroendocrine-immune interactions hold the key to understand the complex immune system. In this study, we explored the role of a reproductive regulation-related hormone, GnRH, in the regulation of immunity in Hong Kong oysters. We found that vibrio bacterial strains injection increased the expression of ChGnRH. Moreover, ChGnRH neuropeptide promotes the phagocytic ability and bacterial clearance effect of hemocytes which regarded to be the central immune organ. The content of cAMP after incubation with ChGnRH peptide was increased, which could be blocked by adenylyl cyclase inhibitor SQ 22,536. Furthermore, the stimulated effect of ChGnRH peptide on the phagocytosis and bacterial clearance was also blocked by SQ 22,536, H89 and enzastaurin, strongly demonstrating that cAMP dependent PKA and PKC signaling pathway was involved in ChGnRH mediated immune regulation. In conclusion, this study confirms the presence of neuroendocrine-immune regulatory system in marine invertebrates, which contributes to understand the complexity of oyster immune defense system.

Functional characterization of an invertebrate gonadotropin-releasing hormone receptor in the Yesso scallop Mizuhopecten yessoensis

The neuropeptide control of bivalve reproduction with particular reference to gonadotropin-releasing hormone (invGnRH) is a frontier yet to be investigated. Bivalves are unique because they have two forms of the invGnRH peptide; however, there has been no functional characterization of the peptide-receptor pair. Therefore, the identification of a cognate receptor is a preliminary step toward exploring the biological roles of invGnRHs in bivalves. In this study, we functionally characterize an invGnRH receptor (invGnRHR) of a bivalve, the Yesso scallop Mizuhopecten yessoensis. In the receptor assay, HEK293 cells were transfected to transiently express the M. yessoensis invGnRHR (my-invGnRHR), which was found to be localized on the plasma membrane, confirming that my-invGnRHR, similar to other G-protein-coupled receptors, functions as a membrane receptor. Using both forms of invGnRH as ligands in a function-receptor assay, my-invGnRH11aa-NH₂ stimulated intracellular Ca²⁺ mobilization but not cyclic AMP production, whereas my-invGnRH12aa-OH did not induce increase in Ca²⁺ levels. Therefore, we concluded that my-invGnRHR is an endogenous receptor specific to my-invGnRH11aa-NH₂ which is hypothesized to be the mature peptide. To the best of our knowledge, this is the first study reporting the functional characterization of a bivalve invGnRHR.

RFRP3 influences basal lamina degradation, cellular death, and progesterone secretion in cultured preantral ovarian follicles from the domestic cat

The hypothalamic neuropeptide RFRP3 can suppress hypothalamic GnRH neuron activation and inhibit gonadotropin release from the anterior pituitary. RFRP3 is also produced locally in the ovary and can inhibit steroidogenesis and follicle development in many vertebrates. However, almost nothing is known about the presence and regulatory action of RFRP3 in gonads of any carnivore species. Such knowledge is important for developing captive breeding programs for endangered carnivores and for inhibiting reproduction in feral species. Using the domestic cat as a model, our objectives were to (1) demonstrate the expression of feline RFRP3 (fRFRP3) and its receptor in the cat ovary and (2) assess the influence of fRFRP3 on ovarian follicle integrity, survival, and steroidogenesis in vitro. We first confirmed that fRFRP3 and its receptors (NPFFR1 and NPFFR2) were expressed in cat ovaries by sequencing PCR products from ovarian RNA. We then isolated and cultured preantral ovarian follicles in the presence of 10 or 1 µM fRFRP3 + FSH (1 µg/mL). We recorded the percentage of morphologically viable follicles (basal lamina integrity) over 8 days and calculated percentage survival of follicles on Day 8 (using fluorescent markers for cell survival and death). Last, we quantified progesterone accumulation in media. 10 µM fRFRP3 had no observable effect on viability, survival, or steroid production compared to follicles exposed to only FSH. However, 1 µM fRFRP3 decreased the percentage of morphologically viable follicles and the percentage of surviving follicles on Day 8. At the same time, 1 µM fRFRP3 increased the accumulation of progesterone in media. Our study shows, for the first time, direct action of RFRP3 on the follicle as a functional unit, and it is the first in a carnivore species. More broadly, our results support a conserved, inhibitory action of RFRP3 on ovarian follicle development and underscore the importance of comparative functional studies.

Identification and Function of GnRH-like Peptide in the Pacific Abalone, Haliotis discus hannai

Gonadotropin-releasing hormone (GnRH) is an important regulator of reproductive function in various vertebrates and invertebrates. In the present study, we have identified the GnRH-like peptide cDNA and peptide from the cerebral ganglion (CG) of the Pacific abalone, Haliotis discus hannai. Pacific abalone GnRH-like peptide (hdhGnRH-like peptide) cDNA encodes precursor, which possesses the typical organization of the known mollusk GnRH-like peptide precursors, including a hydrophobic signal peptide, GnRH-like peptide, and a cleavage site followed by a GAP-like peptide region. Three hdhGnRH-like peptides, pQNYHFSNGWHAamide (hdhGnRH-11amide), pQNYHFSNGWHA (hdhGnRH-11OH), and pQNYHFSNGWHAG (hdhGnRH-12OH), were determined from the acid/acetone extract of the CG by mass spectrometry (LC-MS/MS) analysis. The hdhGnRH-like peptide mRNA expression was detected not only in the CG but also in gonads, and hdhGnRH-11amide was also detected in the extract of gonads. The mRNA expression of hdhGnRH-like peptide in the CG was lower in spawned males than in non-spawned animals, while no change in hdhGnRH-like peptide mRNA expression was shown in both ovulated and non-ovulated abalone. The hdhGnRH-11amide induces spawning and ovulation of both mature males and females in a concentration-dependent fashion following intramuscular injection. These results indicate that three hdhGnRH-like peptides are yielded from a single hdhGnRH-like peptide precursor, and that at least hdhGnRH-11amide is involved in the control of reproduction of the Pacific abalone.

Adipokinetic Hormone Receptor Mediates Trehalose Homeostasis to Promote Vitellogenin Uptake by Oocytes in Nilaparvata lugens

Adipokinetic hormones (AKHs) are well known to mobilize lipids and carbohydrates for energy-consuming activities in insects. These neuropeptides exert their functions by interacting with AKH receptors (AKHRs) located on the plasma membrane of fat body cells, which regulates energy mobilization by stimulating lipolysis of triacylglycerols (TAG) to diacylglycerols (DAG) and conversion of glycogen into trehalose. Here, we investigated the roles of AKH/AKHR signaling system in trehalose metabolism and vitellogenesis during female reproduction in the brown planthopper, Nilaparvata lugens. Knockdown of AKHR expression by RNA interference (RNAi) resulted in a decrease of the circulating trehalose in hemolymph and significantly increased levels of two trehalases in fat bodies, indicating that the modulation of hemolymph trehalose levels by AKHR may be mediated by regulating trehalose degradation. In addition, adult females that had been injected with double-stranded RNA (dsRNA) for AKHR exhibited delayed oocyte maturation, prolonged pre-oviposition period, as well as decline in egg number and reduction in fecundity. Considering that these phenotypes resulting from AKHR silencing are similar to those of vitellogenin receptor (VgR) RNAi, we further analyzed a possible connection between AKHR and vitellogenesis. Knockdown of AKHR showed no effects on the Vg synthesis in fat bodies, whereas it significantly reduced the levels of VgR in ovaries. With RNAi-females, we observed an increase of Vg accumulation in hemolymph and a decrease of Vg deposition in ovaries. Moreover, the decrease in VgR expression and Vg incorporation by developing oocytes could be partially rescued by injection of trehalose into AKHR RNAi females. The present study has implicated trehalose in the AKH/AKHR signaling-mediated control of reproduction and provided new insight into mechanisms of AKH/AKHR regulation of trehalose metabolism in insect vitellogenesis, oocyte maturation and fecundity.

The evolution and nomenclature of GnRH-type and corazonin-type neuropeptide signaling systems

Gonadotropin-releasing hormone (GnRH) was first discovered in mammals on account of its effect in triggering pituitary release of gonadotropins and the importance of this discovery was recognized forty years ago in the award of the 1977 Nobel Prize for Physiology or Medicine. Investigation of the evolution of GnRH revealed that GnRH-type signaling systems occur throughout the chordates, including agnathans (e.g. lampreys) and urochordates (e.g. sea squirts). Furthermore, the discovery that adipokinetic hormone (AKH) is the ligand for a GnRH-type receptor in the arthropod Drosophila melanogaster provided evidence of the antiquity of GnRH-type signaling. However, the occurrence of other AKH-like peptides in arthropods, which include corazonin and AKH/corazonin-related peptide (ACP), has complicated efforts to reconstruct the evolutionary history of this family of related neuropeptides. Genome/transcriptome sequencing has revealed that both GnRH-type receptors and corazonin-type receptors occur in lophotrochozoan protostomes (annelids, mollusks) and in deuterostomian invertebrates (cephalochordates, hemichordates, echinoderms). Furthermore, peptides that act as ligands for GnRH-type and corazonin-type receptors have been identified in mollusks. However, what has been lacking is experimental evidence that distinct GnRH-type and corazonin-type peptide-receptor signaling pathways occur in deuterostomes. Importantly, we recently reported the identification of two neuropeptides that act as ligands for either a GnRH-type receptor or a corazonin-type receptor in an echinoderm species - the common European starfish Asterias rubens. Discovery of distinct GnRH-type and corazonin-type signaling pathways in this deuterostomian invertebrate has demonstrated for the first time that the evolutionarily origin of these paralogous systems can be traced to the common ancestor of protostomes and deuterostomes. Furthermore, lineage-specific losses of corazonin signaling (in vertebrates, urochordates and nematodes) and duplication of the GnRH signaling system in arthropods (giving rise to the AKH and ACP signaling systems) and quadruplication of the GnRH signaling system in vertebrates (followed by lineage-specific losses or duplications) accounts for the phylogenetic distribution of GnRH/corazonin-type peptide-receptor pathways in extant animals. Informed by these new insights, here we review the history of research on the evolution of GnRH/corazonin-type neuropeptide signaling. Furthermore, we propose a standardized nomenclature for GnRH/corazonin-type neuropeptides wherein peptides are either named "GnRH" or "corazonin", with the exception of the paralogous GnRH-type peptides that have arisen by gene duplication in the arthropod lineage and which are referred to as "AKH" (or red pigment concentrating hormone, "RCPH", in crustaceans) and "ACP".

Cephalopod Brains: An Overview of Current Knowledge to Facilitate Comparison With Vertebrates

Cephalopod and vertebrate neural-systems are often highlighted as a traditional example of convergent evolution. Their large brains, relative to body size, and complexity of sensory-motor systems and behavioral repertoires offer opportunities for comparative analysis. Despite various attempts, questions on how cephalopod 'brains' evolved and to what extent it is possible to identify a vertebrate-equivalence, assuming it exists, remain unanswered. Here, we summarize recent molecular, anatomical and developmental data to explore certain features in the neural organization of cephalopods and vertebrates to investigate to what extent an evolutionary convergence is likely. Furthermore, and based on whole body and brain axes as defined in early-stage embryos using the expression patterns of homeodomain-containing transcription factors and axonal tractography, we describe a critical analysis of cephalopod neural systems showing similarities to the cerebral cortex, thalamus, basal ganglia, midbrain, cerebellum, hypothalamus, brain stem, and spinal cord of vertebrates. Our overall aim is to promote and facilitate further, hypothesis-driven, studies of cephalopod neural systems evolution.

Neural Versus Gonadal GnIH: Are they Independent Systems? A Mini-Review

Based on research in protochordates and basal vertebrates, we know that communication across the first endocrine axes likely relied on diffusion. Because diffusion is relatively slow, rapid responses to some cues, including stress-related cues, may have required further local control of axis outputs (e.g., steroid hormone production by the gonads). Despite the evolution of much more efficient circulatory systems and complex nervous systems in vertebrates, production of many "neuro"transmitters has been identified outside of the hypothalamus across the vertebrate phylogeny and these neurotransmitters are known to locally regulate endocrine function. Our understanding of tissue-specific neuropeptide expression and their role coordinating physiological/behavioral responses of the whole organism remains limited, in part, due to nomenclature and historic dogma that ignores local regulation of axis output. Here, we review regulation of gonadotropin-inhibitory hormone (GnIH) across the reproductive axis in birds and mammals to bring further attention to context-dependent disparities and similarities in neuropeptide production by the brain and gonads. We find that GnIH responsiveness to cues of stress appears conserved across species, but that the response of specific tissues and the direction of GnIH regulation varies. The implications of differential regulation across tissues remain unclear in most studies, but further work that manipulates and contrasts function in different tissues has the potential to inform us about both organism-specific function and endocrine axis evolution.

Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

Neuropeptides play essential roles in regulation of reproduction and growth in marine molluscs. But their function in marine bivalves – a group of animals of commercial importance – is largely unexplored due to the lack of systematic identification of these molecules. In this study, we sequenced and analyzed the transcriptome of nerve ganglia of Yesso scallop Patinopecten yessoensis, from which 63 neuropeptide genes were identified based on BLAST and de novo prediction approaches, and 31 were confirmed by proteomic analysis using the liquid chromatography-tandem mass spectrometry (LC-MS/MS). Fifty genes encode known neuropeptide precursors, of which 20 commonly exist in bilaterians and 30 are protostome specific. Three neuropeptides that have not yet been reported in bivalves were identified, including calcitonin/DH31, lymnokinin and pleurin. Characterization of glycoprotein hormones, insulin-like peptides, allatostatins, RFamides, and some reproduction, cardioactivity or feeding related neuropeptides reveals scallop neuropeptides have conserved molluscan neuropeptide domains, but some (e.g., GPB5, APGWamide and ELH) are characterized with bivalve-specific features. Thirteen potentially novel neuropeptides were identified, including 10 that may also exist in other protostomes, and 3 (GNamide, LRYamide, and Vamide) that may be scallop specific. In addition, we found neuropeptides potentially related to scallop shell growth and eye functioning. This study represents the first comprehensive identification of neuropeptides in scallop, and would contribute to a complete understanding on the roles of various neuropeptides in endocrine regulation in bivalve molluscs.

Identification, Characterization, and Expression Analysis of a FMRFamide-Like Peptide Gene in the Common Chinese Cuttlefish (Sepiella japonica)

The peptide FMRFamide is one of the well-known peptides involved in multiple physiological processes in the phylum Mollusca. In this study, a FMRFamide gene (GenBank accession No. KJ933411) was identified in a cuttlefish species called Sepiella japonica and was designated as SjFMRFamide. The total length of the SjFMRFamide sequence was found to be 1880 bp while the open reading frame contained 996 bp encoding a protein of 331 amino acid residues with a predicted isoelectric point (pI) and molecular weight (MW) of 9.18 and 38.8 kDa along with a 333 bp 5'-untranslated region (UTR) and 551 bp 3'-UTR. The deduced SjFMRFamide precursor protein contains one signal peptide and expresses four kinds FMRFamide-related peptides including a single copy of FLRFamide, ALSGDAFLRFamide, and FIRFamide and multiple copies of FMRFamide. Results of phylogenetic relation analysis strongly indicated that the sequence of this gene shares high identity with the genes of known FMRFamides. Spatial expression analysis indicated the highest mRNA expression of SjFMRFamide in the brain of male and female cuttlefishes among the eight tissues analyzed. An in situ hybridization assay of the brain indicated that SjFMRFamide was transcribed in several functional lobes, which suggests that it might be related to many physiological regulatory mechanisms. This is the first study describing FMRFamide in S. japonica and the results may contribute to future studies of neuropeptide evolution or may prove useful for the development of aquaculture methods for this cuttlefish species.

Characterization and spatiotemporal expression of gonadotropin-releasing hormone in the Pacific abalone, Haliotis discus hannai

Gonadotropin-releasing hormone (GnRH) is a key neuropeptide regulating reproduction in humans and other vertebrates. Recently, GnRH-like cDNAs and peptides were reported in marine mollusks, implying that GnRH-mediated reproduction is an ancient neuroendocrine system that arose prior to the divergence of protostomes and deuterostomes. Here, we evaluated the reproductive control system mediated by GnRH in the Pacific abalone Haliotis discus hannai. We cloned a prepro-GnRH cDNA (Hdh-GnRH) from the pleural-pedal ganglion (PPG) in H. discus hannai, and analyzed its spatiotemporal gene expression pattern. The open reading frame of Hdh-GnRH encodes a protein of 101 amino acids, consisting of a signal peptide, a GnRH dodecapeptide, a cleavage site, and a GnRH-associated peptide. This structure and sequence are highly similar to GnRH-like peptides reported for mollusks and other invertebrates. Quantitative polymerase chain reaction demonstrated that Hdh-GnRH mRNA was more strongly expressed in the ganglions (PPG and cerebral ganglion [CG]) than in other tissues (gonads, gills, intestine, hemocytes, muscle, and mantle) in both sexes. In females, the expression levels of Hdh-GnRH mRNA in the PPG and branchial ganglion (BG) were significantly higher at the ripe and partial spent stages than at the early and late active stages. In males, Hdh-GnRH mRNA levels in the BG showed a significant increase in the partial spent stage. Unexpectedly, Hdh-GnRH levels in the CG were not significantly different among the examined stages in both sexes. These results suggest that Hdh-GnRH mRNA expression profiles in the BG and possibly the PPG are tightly correlated with abalone reproductive activities.

Invertebrate Gonadotropin-Releasing Hormone-Related Peptides and Their Receptors: An Update

Gonadotropin-releasing hormones (GnRHs) play pivotal roles in reproductive functions via the hypothalamus, pituitary, and gonad axis, namely, HPG axis in vertebrates. GnRHs and their receptors (GnRHRs) are likely to be conserved in invertebrate deuterostomes and lophotrochozoans. All vertebrate and urochordate GnRHs are composed of 10 amino acids, whereas protostome, echinoderm, and amphioxus GnRH-like peptides are 11- or 12-residue peptide containing two amino acids after an N-terminal pyro-Glu. In urochordates, Halocynthia roretzi GnRH gene encodes two GnRH peptide sequences, whereas two GnRH genes encode three different GnRH peptides in Ciona intestinalis. These findings indicate the species-specific diversification of GnRHs. Intriguingly, the major signaling pathway for GnRHRs is intracellular Ca²⁺ mobilization in chordates, echinoderms, and protostomes, whereas Ciona GnRHRs (Ci-GnRHRs) are endowed with multiple GnRHergic cAMP production pathways in a ligand-selective manner. Moreover, the ligand-specific modulation of signal transduction via heterodimerization among Ci-GnRHR paralogs suggests the species-specific development of fine-tuning of gonadal functions in ascidians. Echinoderm GnRH-like peptides show high sequence differences compared to those of protostome counterparts, leading to the difficulty in classification of peptides and receptors. These findings also show both the diversity and conservation of GnRH signaling systems in invertebrates. The lack of the HPG axis in invertebrates indicates that biological functions of GnRHs are not release of gonadotropins in current invertebrates and common ancestors of vertebrates and invertebrates. To date, authentic or putative GnRHRs have been characterized from various echinoderms and protostomes as well as chordates and the mRNAs have been found to be distributed not only reproductive organs but also other tissues. Collectively, these findings further support the notion that invertebrate GnRHs have biological roles other than the regulation of reproductive functions. Moreover, recent molecular phylogenetic analysis suggests that adipokinetic hormone (AKH), corazonin (CRZ), and AKH/CRZ-related peptide (ACP) belong to the GnRH superfamily but has led to the different classifications of these peptides and receptors using different datasets including the number of sequences and structural domains. In this review, we provide current knowledge of, and perspectives in, molecular basis and evolutionary aspects of the GnRH, AKH, CRZ, and ACP.

Gonadotropin-releasing hormone and adipokinetic hormone/corazonin-related peptide in the female prawn

Crustacean neuropeptides (NPs) play important roles in the regulation of most physiological activities, including growth, molting and reproduction. In this study, we have performed an in silico analysis of female prawn (Macrobrachium rosenbergii) neural transcriptomes to identify NPs not previously identified. We predict that approximately 1309 proteins are destined for the secretory pathway, many of which are likely post-translationally processed to generate active peptides. Within this neural secretome, we identified a gene transcript that encoded a precursor protein with striking similarity to a gonadotropin-releasing hormone (GnRH). We additionally identified another GnRH NP superfamily member, the adipokinetic hormone/corazonin-related peptide (ACP). M. rosenbergii GnRH and ACP were widespread throughout the nervous tissues, implicating them as potential neuromodulators. Furthermore, GnRH was found in non-neural tissues, including the stomach, gut, heart, testis and ovary, in the latter most prominently within secondary oocytes. The GnRH/corazonin receptor-like gene is specific to the ovary, whereas the receptor-like gene expression is more widespread. Administration of GnRH had no effect on ovarian development and maturation, nor any effect on total hemolymph lipid levels, while ACP administration decreased oocyte proliferation (at high dose) and stimulated a significant increase in total hemolymph lipids. In conclusion, our targeted analysis of the M. rosenbergii neural secretome has revealed the decapod GnRH and ACP genes. We propose that ACP in crustaceans plays a role in the lipid metabolism and the inhibition of oocyte proliferation, while the role of the GnRH remains to be clearly defined, possibly through experiments involving gene silencing.

Functional Authentication of a Novel Gastropod Gonadotropin-Releasing Hormone Receptor Reveals Unusual Features and Evolutionary Insight

A gonadotropin-releasing hormone (GnRH)-like molecule was previously identified in a gastropod, Aplysia californica, and named ap-GnRH. In this study, we cloned the full-length cDNA of a putative ap-GnRH receptor (ap-GnRHR) and functionally authenticated this receptor as a bona fide ap-GnRHR. This receptor contains two potential translation start sites, each accompanied by a Kozak sequence, suggesting the translation of a long and a short form of the receptor is possible. The putative ap-GnRHR maintains the conserved structural motifs of GnRHR-like receptors and shares 45% sequence identity with the octopus GnRHR. The expression of the putative ap-GnRHR short form is ubiquitous in all tissues examined, whereas the long form is only expressed in parts of the central nervous system, osphradium, small hermaphroditic duct, and ovotestis. The cDNA encoding the long or the short receptor was transfected into the Drosophila S2 cell line and subject to a radioreceptor assay using ¹²⁵I-labeled ap-GnRH as the radioligand. Further, the transfected cells were treated with various concentrations of ap-GnRH and measured for the accumulation of cAMP and inositol monophosphate (IP1). Radioreceptor assay revealed that only the long receptor bound specifically to the radioligand. Further, only the long receptor responded to ap-GnRH with an increased accumulation of IP1, but not cAMP. Our studies show that despite the more prevalent expression of the short receptor, only the long receptor is the functional ap-GnRHR. Importantly, this is only the second report on the authentication of a protostome GnRHR, and based on the function and the phylogenetic grouping of ap-GnRHR, we suggest that this receptor is more similar to protostome corazonin receptors than chordate GnRHRs.

Identification and Expression Profile of the Gonadotropin-Releasing Hormone Receptor in Common Chinese Cuttlefish, Sepiella japonica

Gonadotropin-releasing hormone (GnRH) plays a vital role in the regulation of reproduction through interaction with a specific receptor (the GnRH receptor). In this study, the GnRH receptor gene from the cuttlefish Sepiella japonica (SjGnRHR) was identified and characterized. The cloned full-length SjGnRHR cDNA was 1,468 bp long and contained a 1,029 bp open reading frame encoding 342 amino acid residues, 8 bp of 5' untranslated regions (UTR), and 431 bp of 3' UTR. The putative protein was predicted to have a molecular weight of 38.75 kDa and an isoelectric point of 9.47. In addition, this protein was identified as belonging to the rhodopsin-type (class A) G protein-coupled receptor family. The predicted amino acid sequence contained two N-linked glycosylation sites and 18 phosphorylation sites. Multiple sequence alignment, phylogenetic tree analysis, and three-dimensional structure modeling were conducted to clarify SjGnRHR bioinformatics characteristics. In vitro SjGnRHR expression was carried out using HEK293 cells and the pEGFP-N1 plasmid, to verify the transmembrane properties of this protein. The interaction between the S. japonica GnRH receptor and its ligand was clarified using internalization analysis. SjGnRHR transcriptional quantification confirmed the wide distribution of SjGnRHR in various S. japonica mature tissues. In addition, the transcriptional profile of SjGnRHR in the female brain and ovary during gonadal development was analyzed. Results indicate that GnRHR may be involved in diverse S. japonica physiological functions, especially in the control of reproduction.

Molecular cloning, expression analysis and cellular localization of an LFRFamide gene in the cuttlefish Sepiella japonica

Neuropeptides are important regulators of physiological processes in metazoans, such as feeding, reproduction, and heart activities. In this study, an LFRFamide gene was identified from the cuttlefish Sepiella japonica (designated as SjLFRFamide). The full-length sequence of SjLFRFamide cDNA has 841bp, and the open reading frame contains 567bp encoding 188 amino acids, which shared high similarity with precursor SOFaRP2 from Sepia officinalis. The deduced SjLFRFamdie precursor protein contains a signal peptide and four different FLPs (FMRFamide-like peptides): one pentapeptide (TIFRFamide), two hexapeptides (NSLFRFamide and GNLFRFamide) and one heptapeptide (PHTPFRFamide). Multiple sequence alignment showed that SjLFRFamide contains rather conserved mature peptides, which all ended in FRF. The phylogenetic analysis suggests that SjLFRFamide belongs to the LFRFamide subfamily. The tissue distribution analysis through quantitative real-time PCR method showed that SjLFRFamide mRNA is significantly expressed in the brain, and slight trace are detected in female nidamental gland and accessory nidamental gland. In situ hybridization assay of the brain indicated that SjLFRFamide is transcribed in several different functional lobes, suggesting SjLFRFamide might associate with multiple physiological regulations, such as feeding, chromatophore regulation and reproduction. This is the first study describing LFRFamide in S. japonica, which might have great importance for cuttlefish artificial breeding.

Oct-GnRH, the first protostomian gonadotropin-releasing hormone-like peptide and a critical mini-review of the presence of vertebrate sex steroids in molluscs

In protostome and deuterosome invertebrates, neurosecretory cells play major roles in the endocrine system. The optic glands of cephalopods are indicators of sexual maturation. In mature octopuses, optic glands enlarge and secrete a gonadotropic hormone. A peptide with structural features similar to that of vertebrate gonadotropin-releasing hormone (GnRH) was isolated from the octopus, Octopus vulgaris, and was named oct-GnRH. The discovery of oct-GnRH has triggered structural determinations and predictions of other mollusc GnRH-like peptides in biochemical and in silico studies. Interestingly, cephalopods studied so far are characterized by a single molecular form of oct-GnRH with a C-terminal -Pro-Gly-NH2 sequence, which is critical for gonadotropin-releasing activity in vertebrates. Other molluscan GnRH-like peptides lack the C-terminal -Pro-Gly-NH2 sequence but have -X-NH2 or -Pro-Gly although all protostome GnRH-like peptides have yet to be sequenced. In marine molluscs, relationships between GnRH-like peptides and sex steroids have been studied to verify the hypothesis that molluscs have vertebrate-type sex steroid system. However, it is currently questionable whether such sex steroids are present and whether they play endogenous roles in the reproductive system of molluscs. Because molluscs uptake and store steroids from the environment and fishes release sex steroids into the external environment, it is impossible to rule out the contamination of vertebrate sex steroids in molluscs. The function of key enzymes of steroidogenesis within molluscs remains unclear. Thus, evidence to deny the existence of the vertebrate-type sex steroid system in molluscs has been accumulated. The elucidation of substances, which regulate the maturation and maintenance of gonads and other reproductive functions in molluscs will require rigorous and progressive scientific study.

Characterization of GnRH-like peptides from the nerve ganglia of Yesso scallop, Patinopecten yessoensis

There is yet no firm experimental evidence that the evolutionary ancient gonadotropin-releasing hormone GnRH (i.e., GnRH1) also acts in invertebrate gametogenesis. The objective of this paper is to characterize candidate invGnRH peptides of Yesso scallop Patinopecten yessoensis (i.e., peptide identification, immunohistochemical localization, and immunoquantification) in order to reveal their bioactive form in bivalves. Using mass spectrometry (MS), we identified two invGnRH (py-GnRH) peptides from the scallop nerve ganglia: a precursor form of py-GnRH peptide (a non-amidated dodecapeptide; py-GnRH12aa-OH) and a mature py-GnRH peptide (an amidated undecapeptide; py-GnRH11aa-NH2). Immunohistochemical staining allowed the localization of both py-GnRH peptides in the neuronal cell bodies and fibers of the cerebral and pedal ganglia (CPG) and the visceral ganglion (VG). We found that the peptides showed a dimorphic distribution pattern. Notably, the broad distribution of mature py-GnRH in neuronal fibers elongating to peripheral organs suggests that it is multi-functional. Time-resolved fluorescent immunoassays (TR-FIA) enabled the quantification of each py-GnRH form in the single CPG or VG tissue obtained from one individual. In addition, we observed greater abundance of mature py-GnRH in VG compared with its level in CPG, suggesting that VG is the main producing organ of mature py-GnRH peptide and that py-GnRH may play a central regulatory role in neurons of scallops. Our study provides evidence, for the first time, for the presence of precursor and mature forms of invGnRH peptides in the nerve ganglia of an invertebrate.

In Vivo Administration of Scallop GnRH-Like Peptide Influences on Gonad Development in the Yesso Scallop, Patinopecten yessoensis

Existing research on the role of gonadotropin-releasing hormone (GnRH) in bivalve reproduction is inadequate, even though a few bivalve GnRH orthologs have been cloned. The objective of this paper was to elucidate the in vivo effect of GnRH administration in Yesso scallop reproduction. We performed in vivo administration of scallop GnRH (py-GnRH) synthetic peptide into the developing gonad, and analyzed its effect on gonad development for 6 weeks during the reproductive season. The resulting sex ratio in the GnRH administered (GnRH(+)) group might be male biased, whereas the control (GnRH(-)) group had an equal sex ratio throughout the experiment. The gonad index (GI) of males in the GnRH(+) group increased from week 2 to 24.8% at week 6. By contrast the GI of the GnRH(-) group peaked in week 4 at 16.6%. No significant difference was seen in female GI between the GnRH(+) and GnRH(-) groups at any sampling point. Oocyte diameter in the GnRH(+) group remained constant (about 42–45 μm) throughout the experiment, while in the GnRH(-) group it increased from 45 to 68 μm i.e. normal oocyte growth. The number of spermatogonia in the germinal acini of males in the GnRH(+) group increased from week 4 to 6. Hermaphrodites appeared in the GnRH(+) group in weeks 2 and 4. Their gonads contained many apoptotic cells including oocytes. In conclusion, this study suggests that py-GnRH administration could have a potential to accelerate spermatogenesis and cause an inhibitory effect on oocyte growth in scallops.

Immunohistochemical detection of GnRH-like peptides in the neural ganglia and testis of Haliotis asinina

Gonadotropin releasing hormone (GnRH) is a peptide that is conserved in both vertebrate and invertebrate species. In this study, we have demonstrated the distribution pattern of two isoforms of GnRH-like peptides in the neural ganglia and testis of reproductively mature male abalone, H. asinina, by immunohistochemistry and whole mount immunofluorescence. We found octopus (oct) GnRH and tunicate-I (t) GnRH-I immunoreactivities (ir) in type 1 neurosecretory cells (NS1) and they were expressed mostly within the ventral horn of the cerebral ganglion, whereas in pleuropedal ganglia they were localized primarily in the dorsal horn. Furthermore, tGnRH-I-ir were strongly detected in fibers at the caudal part of the cerebral ganglia and both ventral and dorsal horns of the pleuropedal ganglia. In the testis, only octGnRH-ir was found primarily in the granulated cell and central capillaries within the trabeculae. These results suggest that multiple GnRH-like peptides are present in the neural ganglia which could be the principal source of their production, whereas GnRH may also be synthesized locally in the testis and act as the paracrine control of testicular maturation.

Localization of a molluscan gonadotropin-releasing hormone in Aplysia californica by in situ hybridization and immunocytochemistry

Gonadotropin-releasing hormone (GnRH) plays important roles in vertebrate reproduction. Recently, molecules structurally similar to vertebrate GnRH were discovered in mollusks, including a gastropod, Aplysia californica. As an important step toward understanding the function of A. californica GnRH (ap-GnRH), the present study examined the localization of ap-GnRH peptide and transcript in the central and peripheral tissues. Reverse transcription polymerase chain reaction (RT-PCR) revealed wide expression of ap-GnRH in all ganglia (abdominal, buccal, cerebral, and pedal ganglia) of the central nervous system (CNS) and in multiple peripheral organs. However, in situ hybridization (ISH) revealed that cells positive for ap-GnRH are detectable only in the CNS, with the pedal ganglia containing the highest number of ap-GnRH-positive neurons, followed by the cerebral and abdominal ganglia. Most neurons positive for the transcript were simultaneously positive for the peptide, although some discrepancies were observed in cerebral and abdominal ganglia. Overall, our data suggest the de novo synthesis of ap-GnRH is restricted to the CNS, with the pedal ganglia being the primary source of ap-GnRH. Our results support the notion that ap-GnRH is a bona-fide neuropeptide that may assume diverse central functions, including those unrelated to reproduction.

Molluscan GnRH associated with reproduction

Gonadotropin-releasing hormone (GnRH) is a neuropeptide that has an essential role in the neural regulation of vertebrate reproduction. Over the past two decades there has been increasing evidence strongly indicating that members of the GnRH superfamily, which includes GnRH, adipokinetic hormone (AKH), corazonin (Crz) and adipokinetic hormone/corazonin-related peptides (ACP), are almost ubiquitous amongst bilateral animals. Moreover GnRH possibly has origins in even more ancient, non-bilateral ancestors. Current knowledge about molluscan GnRH has been accumulated regarding immunological identification, physiological function and sequence analysis. In the present review we summarized a current status of molluscan GnRH research and focus on its role in the reproduction of the molluscs. In cephalopods and gastropods the presence of a GnRH-like peptide was detected with heterologous antibodies and the identified GnRH was suggested to be involved with behavior and reproduction. Reproductive roles for GnRH have been confirmed in both bivalve and cephalopod molluscs. These findings will provide useful insights into the evolution of reproductive endocrinology.

Gonadotropin-releasing hormone in protostomes: insights from functional studies on Aplysia californica

Several protostomian molecules that structurally resemble chordate gonadotropin-releasing hormone (GnRH) have been identified through cloning, biochemical purification or data mining. These molecules share considerable sequence and structural similarities with chordate GnRH, leading to the current belief that protostomian and chordate forms of GnRH share a common ancestor. However, the physiological significance of these protostomian GnRH-like molecules remains poorly understood. This knowledge gap hampers our understanding of how GnRH has evolved functionally over time. This review provides a summary of our recent functional characterization of a GnRH-like molecule (ap-GnRH) in a gastropod mollusk, Aplysia californica, and presents preliminary proof for a cognate ap-GnRH receptor (ap-GnRHR). Our data reveal that ap-GnRH is a general neural regulator capable of exerting diverse central and motor effects, but plays little or no role in reproductive activation. This notion is supported by the abundance of a putative ap-GnRHR transcript in the central nervous system and the foot. Comparing these results to the available functional data from a cephalopod mollusk, Octopus vulgaris, we surmise that protostomian GnRH-like molecules are likely to assume a wide range of physiological roles, and reproductive activation is not an evolutionarily conserved role of these molecules. Future functional studies using suitable protostomian models are required to identify functional changes in protostomian GnRH-like molecules that accompany major taxa-level transitions.

Mollusc gonadotropin-releasing hormone directly regulates gonadal functions: a primitive endocrine system controlling reproduction

Gonadotropin-releasing hormone (GnRH) is central to the control of vertebrate reproductive cycles and since GnRH orthologs are also present in invertebrates, it is likely that the common ancestor of bilateral animals possessed a GnRH-like peptide. In order to understand the evolutionary and comparative biology of GnRH peptides we cloned the cDNA transcripts of prepro GnRH-like peptides from two species of bivalve molluscs, the Yesso scallop Patinopecten yessoensis and the Pacific oyster Crassostrea gigas. We compared their deduced uncleaved and mature amino acid sequences with those from other invertebrates and vertebrates, and determined their sites of expression and biological activity. The two molluscan GnRH sequences increased the number of known protostome GnRHs to six different forms, indicating the current classification of protostome GnRHs requires further revision. In both molluscs, RT-PCR analysis showed that the genes were highly expressed in nervous tissue with lower levels present in peripheral tissues including the gonads, while immunocytochemistry, using anti-octopus GnRH-like peptide, demonstrated the presence of GnRH-like peptide in neural tissue. Putative scallop GnRH-like peptide stimulated spermatogonial cell division in cultured scallop testis, but the scallop GnRH-like peptide did not stimulate LH release from cultured quail pituitary cells. This is the first report of the cloning of bivalve GnRH-like peptide genes and of molluscan GnRH-like peptides that are biologically active in molluscs, but not in a vertebrate.

Characterization of GnRH-related peptides from the Pacific oyster Crassostrea gigas

Gonadotropin-releasing hormone (GnRH), a key neuropeptide regulating reproduction in vertebrates has now been characterized in a number of non-vertebrate species. Despite the demonstration of its ancestral origin, the structure and the function of this family of peptides remain poorly known in species as distant as lophotrochozoans. In this study, two GnRH-related peptides (Cg-GnRH-a and CgGnRH-G) were characterized by mass spectrometry from extracts of the visceral ganglia of the Pacific oyster Crassostrea gigas. These peptides showed a high degree of sequence identity with GnRHs of other mollusks and annelids and to a lesser extent with those of vertebrates or with AKH and corazonins of insects. Both the mature peptides and the transcript encoding the precursor protein were exclusively expressed in the visceral ganglia. Significant differences in transcriptional activity of Cg-GnRH encoding gene were recorded in the ganglia along the reproductive cycle and according to trophic conditions with a higher level in fed animals compared to starved animals. This suggests the involvement of Cg-GnRHs as synchronizers of nutritional status with energy requirements during reproduction in oyster. Evidence for a role of Cg-GnRHs as neuroregulators and as neuroendocrine factors in bivalve is discussed.

Evidence for differential regulation of GnRH signaling via heterodimerization among GnRH receptor paralogs in the protochordate, Ciona intestinalis

The endocrine and neuroendocrine systems for reproductive functions have diversified as a result of the generation of species-specific paralogs of peptide hormones and their receptors including GnRH and their receptors (GnRHR), which belong to the class A G protein-coupled receptor family. A protochordate, Ciona intestinalis, has been found to possess seven GnRH (tGnRH-3 to -8 and Ci-GnRH-X) and four GnRHR (Ci-GnRHR1 to -4). Moreover, Ci-GnRHR4 (R4) does not bind to any Ciona GnRH and activate any signaling pathways. Here we show novel functional diversification of GnRH signaling pathways via G protein-coupled receptor heterodimerization among Ciona GnRHR. R4 was shown to heterodimerize with R2 specifically in test cells of vitellogenic oocytes by coimmunoprecipitation. The R2-R4 heterodimerization in human embryonic kidney 293 cells cotransfected with R2 and R4 was also observed by coimmunoprecipitation and fluorescent energy transfer analyses. Of particular interest is that the R2-R4 heterodimer decreases the cAMP production in a nonligand-selective manner via shift of activation of Gs protein to Gi protein by R2, compared with R2 monomer/homodimer. Considering that the R1-R4 heterodimer elicits 10-fold more potent Ca²⁺ mobilization than R1 monomer/homodimer in a ligand-selective manner but does not affect cAMP production, these results indicate that R4 regulates differential GnRH signaling cascades via heterodimerization with R1 and R2 as an endogenous allosteric modulator. Collectively, the present study suggests that the heterodimerization among GnRHR paralogs, including the species-specific orphan receptor subtype, is involved in rigorous and diversified GnRHergic signaling of the protochordate, which lacks a hypothalamus-pituitary gonad axis.

RNA interference unveils functions of the hypertrehalosemic hormone on cyclic fluctuation of hemolymph trehalose and oviposition in the virgin female Blattella germanica

Hypertrehalosemic hormone (HTH) is a neuropeptide within the adipokinetic hormone (AKH) family that induces a release of trehalose from fat body into hemolymph in a number of insects. In this study, we first showed that female adult German cockroach, Blattella germanica, displayed a cyclic fluctuation of hemolymph trehalose levels correlated to the maturation of oocytes in the reproductive cycle. After cloning the HTH cDNA from the German cockroach (Blage-HTH), expression studies indicated that Blage-HTH mRNA showed the cyclic changes during the first reproductive cycle, where peak values occurred in 8-day-old virgin female cockroaches, which were going to produce oothecae. The functions of Blage-HTH were studied using RNA interference (RNAi) to knockdown its expression. Adult virgin females of B. germanica injected with Blage-HTH dsRNA increased hemolymph trehalose levels in the late period of vitellogenesis more slowly than control. Furthermore, RNAi of Blage-HTH delayed oviposition time and some (10%) individuals did not produce the first ootheca until 15 days after eclosion, whereas the control group produced ootheca before 9 days in all cases.

The heart: a novel gonadotrophin-releasing hormone target

Gonadotrophin-releasing hormone (GnRH) is a hypothalamic hormone transported by the hypophyseal portal bloodstream to the pituitary gland, where it binds to GnRH receptors. However, GnRH receptors are expressed in multiple extrapituitary tissues, although their physiological relevance is not fully understood. GnRH agonists are employed extensively in steroid deprivation therapy, especially to suppress testosterone in prostate cancer. Because GnRH agonist treatment is associated with increased coronary heart disease and myocardial infarction, we investigated the impact of GnRH on cardiomyocyte contractile function. Cardiomyocytes were isolated from mouse hearts and mechanical and intracellular Ca(2+) properties were evaluated, including peak shortening amplitude (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90) ), maximal velocity of shortening/relengthening (± dLdt), electrically-stimulated rise in Fura-2 fluorescence intensity (ΔFFI) and Ca(2+) decay. GnRH (1 ng/ml) increased PS, ± dL/dt, resting FFI and ΔFFI, and prolonged TPS, TR(90) and Ca(2+) decay time, whereas 1 pg/ml GnRH affected all these cardiomyocyte variables, except TPS, resting FFI and ΔFFI. A concentration of 1 fg/ml GnRH and the GnRH cleavage product, GnRH-[1-5] (300 pg/ml), had no effect on any cardiomyocyte parameter. The 1 pg/ml GnRH-elicited responses were attenuated by the GnRH receptor antagonist cetrorelix (10 μm), the protein kinase A (PKA) inhibitor H89 (1 μm) but not the protein kinase C inhibitor chelerythrine chloride (1 μm). These data revealed that GnRH is capable of regulating cardiac contractile function via a GnRH receptor/PKA-dependent mechanism. If present in the human heart, dysfunction of such a system may play an important role in cardiac pathology observed in men treated with GnRH agonists for prostate cancer.

Existence and distribution of gonadotropin-releasing hormone-like peptides in the central nervous system and ovary of the Pacific white shrimp, Litopenaeus vannamei

We used antibodies against octopus gonadotropin-releasing hormone (octGnRH) and tunicate GnRH (tGnRH-I) in order to investigate the existence and distribution of GnRH-like peptides in the central nervous system (CNS) and in the ovary during various stages of the ovarian cycle of the white shrimp, Litopenaeus vannamei. OctGnRH-immunoreactive and tGnRH-I-immunoreactive neurons and fibers were present in several regions of the supraesophageal ganglion (brain), subesophageal ganglion (SEG), thoracic ganglia, and abdominal ganglia. In the brain, both octGnRH immunoreactivity (ir) and tGnRH-I-ir were detected in neurons of clusters 6, 11, 17, and associated fibers, and the anterior medial protocerebral, posterior medial protocerebral, olfactory, and tegumentary neuropils. In the SEG and thoracic ganglia, octGnRH-immunoreactive and tGnRH-I-immunoreactive neurons and fibers were present in dorsolateral and ventromedial cell clusters and in surrounding fibers. Only immunoreactive fibers were detected in the abdominal ganglia. In the ovary, both octGnRH and tGnRH-I were detected at medium intensity in the cytoplasm of early step oocytes (Oc2) and, at high intensity, in Oc3. Furthermore, octGnRH-ir and tGnRH-I-ir were intense in follicular cells surrounding Oc2 and Oc3. The presence of GnRH-ir in the CNS and ovary indicates that GnRH-like peptides occur in the white shrimp, and that GnRHs are involved in the reproductive process, especially ovarian maturation and the differentiation of oocytes, as reported in other species.

A gonadotropin-releasing hormone-like molecule modulates the activity of diverse central neurons in a gastropod mollusk, aplysia californica

In vertebrates, gonadotropin-releasing hormone (GnRH) is a crucial decapeptide that activates the hypothalamic-pituitary-gonadal axis to ensure successful reproduction. Recently, a GnRH-like molecule has been isolated from a gastropod mollusk, Aplysia californica. This GnRH (ap-GnRH) is deduced to be an undecapeptide, and its function remains to be explored. Our previous study demonstrated that ap-GnRH did not stimulate a range of reproductive parameters. Instead, it affected acute behavioral and locomotive changes unrelated to reproduction. In this study, we used electrophysiology and retrograde tracing to further explore the central role of ap-GnRH. Sharp-electrode intracellular recordings revealed that ap-GnRH had diverse effects on central neurons that ranged from excitatory, inhibitory, to the alteration of membrane potential. Unexpectedly, extracellular recordings revealed that ap-GnRH suppressed the onset of electrical afterdischarge in bag cell neurons, suggesting an inhibitory effect on female reproduction. Lastly, using immunocytochemistry coupled with nickel backfill, we demonstrated that some ap-GnRH neurons projected to efferent nerves known to innervate the foot and parapodia, suggesting ap-GnRH may directly modulate the motor output of these peripheral tissues. Overall, our results suggested that in A. californica, ap-GnRH more likely functioned as a central modulator of complex behavior and motor regulation rather than as a conventional reproductive stimulator.

The existence of gonadotropin-releasing hormone-like peptides in the neural ganglia and ovary of the abalone, Haliotis asinina L

Gonadotropin-releasing hormone (GnRH) is a neuropeptide that is conserved in both vertebrate and invertebrate species. In this study, we have demonstrated the presence and distribution of two isoforms of GnRH-like peptides in neural ganglia and ovary of reproductively mature female abalone, Haliotis asinina, using immunohistochemistry. We found significant immunoreactivities (ir) of anti-lamprey(l) GnRH-III and anti-tunicate(t) GnRH, but with variation of labeling intensity by each anti-GnRH type. lGnRH-III-ir was detected in numerous type 1 neurosecretory cells (NS1) throughout the cerebral and pleuropedal ganglia, whereas tGnRH-I-ir was detected in only a few NS1 cells in the dorsal region of cerebral and pleuropedal ganglia. In addition, a small number of type 2 neurosecretory cells (NS2) in cerebral ganglion showed lGnRH-III-ir. Long nerve fibers in the neuropil of ventral regions of the cerebral and pluropedal ganglia showed strong tGnRH-I-ir. In the ovary, lGnRH-III-ir was found primarily in oogonia and stage I oocytes, whereas tGnRH-ir was observed in stage I oocytes and some stage II oocytes. These results indicate that GnRH produced in neural ganglia may act in neural signaling. Alternatively, GnRH may also be synthesized locally in the ovary where it could induce oocyte development.