The evolution of neuroendocrine peptides

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

A combined strategy of neuropeptide prediction and tandem mass spectrometry identifies evolutionarily conserved ancient neuropeptides in the sea anemone Nematostella vectensis

Neuropeptides are a class of bioactive peptides shown to be involved in various physiological processes, including metabolism, development, and reproduction. Although neuropeptide candidates have been predicted from genomic and transcriptomic data, comprehensive characterization of neuropeptide repertoires remains a challenge owing to their small size and variable sequences. De novo prediction of neuropeptides from genome or transcriptome data is difficult and usually only efficient for those peptides that have identified orthologs in other animal species. Recent peptidomics technology has enabled systematic structural identification of neuropeptides by using the combination of liquid chromatography and tandem mass spectrometry. However, reliable identification of naturally occurring peptides using a conventional tandem mass spectrometry approach, scanning spectra against a protein database, remains difficult because a large search space must be scanned due to the absence of a cleavage enzyme specification. We developed a pipeline consisting of in silico prediction of candidate neuropeptides followed by peptide-spectrum matching. This approach enables highly sensitive and reliable neuropeptide identification, as the search space for peptide-spectrum matching is highly reduced. Nematostella vectensis is a basal eumetazoan with one of the most ancient nervous systems. We scanned the Nematostella protein database for sequences displaying structural hallmarks typical of eumetazoan neuropeptide precursors, including amino- and carboxyterminal motifs and associated modifications. Peptide-spectrum matching was performed against a dataset of peptides that are cleaved in silico from these putative peptide precursors. The dozens of newly identified neuropeptides display structural similarities to bilaterian neuropeptides including tachykinin, myoinhibitory peptide, and neuromedin-U/pyrokinin, suggesting these neuropeptides occurred in the eumetazoan ancestor of all animal species.

Tachykinin-3 Genes and Peptides Characterized in a Basal Teleost, the European Eel: Evolutionary Perspective and Pituitary Role

In mammals, neurokinin B (NKB) is a short peptide encoded by the gene tac3. It is involved in the brain control of reproduction by stimulating gonadotropin-releasing hormone (GnRH) neurons, mainly via kisspeptin. We investigated tac3 genes and peptides in a basal teleost, the European eel, which shows an atypical blockade of the sexual maturation at a prepubertal stage. Two tac3 paralogous genes (tac3a and tac3b) were identified in the eel genome, each encoding two peptides (NKBa or b and NKB-related peptide NKB-RPa or b). Amino acid sequence of eel NKBa is identical to human NKB, and the three others are novel peptide sequences. The four eel peptides present the characteristic C-terminal tachykinin sequence, as well as a similar alpha helix 3D structure. Tac3 genes were identified in silico in 52 species of vertebrates, and a phylogeny analysis was performed on the predicted TAC3 pre-pro-peptide sequences. A synteny analysis was also done to further assess the evolutionary history of tac3 genes. Duplicated tac3 genes in teleosts likely result from the teleost-specific whole genome duplication (3R). Among teleosts, TAC3b precursor sequences are more divergent than TAC3a, and a loss of tac3b gene would have even occurred in some teleost lineages. NKB-RP peptide, encoded beside NKB by tac3 gene in actinopterygians and basal sarcopterygians, would have been lost in ancestral amniotes. Tissue distribution of eel tac3a and tac3b mRNAs showed major expression of both transcripts in the brain especially in the diencephalon, as analyzed by specific qPCRs. Human NKB has been tested in vitro on primary culture of eel pituitary cells. Human NKB dose-dependently inhibited the expression of lhβ, while having no effect on other glycoprotein hormone subunits (fshβ, tshβ, and gpα) nor on gh. Human NKB also dose-dependently inhibited the expression of GnRH receptor (gnrh-r2). The four eel peptides have been synthesized and also tested in vitro. They all inhibited the expression of both lhβ and of gnrh-r2. This reveals a potential dual inhibitory role of the four peptides encoded by the two tac3 genes in eel reproduction, exerted at the pituitary level on both luteinizing hormone and GnRH receptor.

TAC1 Gene Products Regulate Pituitary Hormone Secretion and Gene Expression in Prepubertal Grass Carp Pituitary Cells

Tachykinin-1 (TAC1) is known to have diverse functions in mammals, but similar information is scarce in fish species. Using grass carp as a model, the pituitary actions, receptor specificity and postreceptor signaling of TAC1 gene products, namely substance P (SP) and neurokinin A (NKA), were examined. TAC1 encoding SP and NKA as well as tachykinin receptors NK1R and NK2R were cloned in the carp pituitary. The newly cloned receptors were shown to be functional with properties similar to mammalian counterparts. In carp pituitary cells, SP and NKA could trigger luteinizing hormone (LH), prolactin (PRL), and somatolactin α (SLα) secretion, with parallel rises in PRL and SLα transcripts. Short-term SP treatment (3 hours) induced LH release, whereas prolonged induction (24 hours) could attenuate LHβ messenger RNA (mRNA) expression. At pituitary cell level, LH, PRL, and SLα regulation by TAC1 gene products were mediated by NK1R, NK2R, and NK3R, respectively. Apparently, SP- and NKA-induced LH and SLα secretion and transcript expression were mediated by adenylyl cyclase/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholiphase C (PLC)/inositol 1,4,5-triphosphate/protein kinase C (PKC), and Ca2+/calmodulin (CaM)/CaM-dependent protein kinase-II pathways. The signal transduction for PRL responses was similar, except for the absence of a PKC component. Regarding SP inhibition of LHβ mRNA expression, the cAMP/PKA- and PLC/PKC-dependent (but not Ca2+/CaM-dependent) cascades were involved. These results, as a whole, suggest that TAC1 gene products play a role in LH, PRL, and SLα regulation via overlapping postreceptor signaling coupled to different subtypes of tachykinin receptor expressed in the carp pituitary.

Ancestral genomic duplication of the insulin gene in tilapia: An analysis of possible implications for clinical islet xenotransplantation using donor islets from transgenic tilapia expressing a humanized insulin gene

Tilapia, a teleost fish, have multiple large anatomically discrete islets which are easy to harvest, and when transplanted into diabetic murine recipients, provide normoglycemia and mammalian-like glucose tolerance profiles. Tilapia insulin differs structurally from human insulin which could preclude their use as islet donors for xenotransplantation. Therefore, we produced transgenic tilapia with islets expressing a humanized insulin gene. It is now known that fish genomes may possess an ancestral duplication and so tilapia may have a second insulin gene. Therefore, we cloned, sequenced, and characterized the tilapia insulin 2 transcript and found that its expression is negligible in islets, is not islet-specific, and would not likely need to be silenced in our transgenic fish.

Neurokinin B and reproductive functions: "KNDy neuron" model in mammals and the emerging story in fish

In mammals, neurokinin B (NKB), the gene product of the tachykinin family member TAC3, is known to be a key regulator for episodic release of luteinizing hormone (LH). Its regulatory actions are mediated by a subpopulation of kisspeptin neurons within the arcuate nucleus with co-expression of NKB and dynorphin A (commonly called the "KNDy neurons"). By forming an "autosynaptic feedback loop" within the hypothalamus, the KNDy neurons can modulate gonadotropin-releasing hormone (GnRH) pulsatility and subsequent LH release in the pituitary. NKB regulation of LH secretion has been recently demonstrated in zebrafish, suggesting that the reproductive functions of NKB may be conserved from fish to mammals. Interestingly, the TAC3 genes in fish not only encode the mature peptide of NKB but also a novel tachykinin-like peptide, namely NKB-related peptide (or neurokinin F). Recent studies in zebrafish also reveal that the neuroanatomy of TAC3/kisspeptin system within the fish brain is quite different from that of mammals. In this article, the current ideas of "KNDy neuron" model for GnRH regulation and steroid feedback, other reproductive functions of NKB including its local actions in the gonad and placenta, the revised model of tachykinin evolution from invertebrates to vertebrates, as well as the emerging story of the two TAC3 gene products in fish, NKB and NKB-related peptide, will be reviewed with stress on the areas with interesting questions for future investigations.

Novel pituitary actions of TAC3 gene products in fish model: receptor specificity and signal transduction for prolactin and somatolactin α regulation by neurokinin B (NKB) and NKB-related peptide in carp pituitary cells

TAC3 is a member of tachykinins, and its gene product neurokinin B (NKB) has recently emerged as a key regulator for LH through modulation of kisspeptin/GnRH system within the hypothalamus. In fish models, TAC3 not only encodes NKB but also a novel tachykinin-like peptide called NKB-related peptide (NKBRP), and the pituitary actions of these TAC3 gene products are still unknown. Using grass carp as a model, the direct effects and postreceptor signaling for the 2 TAC3 products were examined at the pituitary level. Grass carp TAC3 was cloned and confirmed to encode NKB and NKBRP similar to that of other fish species. In carp pituitary cells, NKB and NKBRP treatment did not affect LH release and gene expression but up-regulated prolactin (PRL) and somatolactin (SL)α secretion, protein production, and transcript expression. The stimulation by these 2 TAC3 gene products on PRL and SLα release and mRNA levels were mediated by pituitary NK2 and NK3 receptors, respectively. Apparently, NKB- and NKBRP-induced SLα secretion and transcript expression were caused by adenylate cyclase/cAMP/protein kinase A, phospholipase C/inositol 1,4,5-triphosphate/protein kinase C and Ca(2+)/calmodulin/Ca(2+)/calmodulin-dependent protein kinase II activation. The signal transduction for the corresponding responses on PRL release and mRNA expression were also similar, except that the protein kinase C component was not involved. These findings suggest that the 2 TAC3 gene products do not play a role in LH regulation at the pituitary level in carp species but may serve as novel stimulators for PRL and SLα synthesis and secretion via overlapping postreceptor signaling mechanisms coupled to NK2 and NK3 receptors, respectively.

A review of piscine islet xenotransplantation using wild-type tilapia donors and the production of transgenic tilapia expressing a "humanized" tilapia insulin

Most islet xenotransplantation laboratories have focused on porcine islets, which are both costly and difficult to isolate. Teleost (bony) fish, such as tilapia, possess macroscopically visible distinct islet organs called Brockmann bodies which can be inexpensively harvested. When transplanted into diabetic nude mice, tilapia islets maintain long-term normoglycemia and provide human-like glucose tolerance profiles. Like porcine islets, when transplanted into euthymic mice, they are rejected in a CD4 T-cell-dependent manner. However, unlike pigs, tilapia are so phylogenetically primitive that their cells do not express α(1,3)Gal and, because tilapia are highly evolved to live in warm stagnant waters nearly devoid of dissolved oxygen, their islet cells are exceedingly resistant to hypoxia, making them ideal for transplantation within encapsulation devices. Encapsulation, especially when combined with co-stimulatory blockade, markedly prolongs tilapia islet xenograft survival in small animal recipients, and a collaborator has shown function in diabetic cynomolgus monkeys. In anticipation of preclinical xenotransplantation studies, we have extensively characterized tilapia islets (morphology, embryologic development, cell biology, peptides, etc.) and their regulation of glucose homeostasis. Because tilapia insulin differs structurally from human insulin by 17 amino acids, we have produced transgenic tilapia whose islets stably express physiological levels of humanized insulin and have now bred these to homozygosity. These transgenic fish can serve as a platform for further development into a cell therapy product for diabetes.

Identification, characterization and feeding response of peptide YYb (PYYb) gene in grass carp (Ctenopharyngodon idellus)

The peptide YYb (PYYb) is a fish-specific peptide belonging to the neuropeptide Y (NPY) family. In the present study, the full-length cDNA sequence and genomic structure of PYYb (gcPYYb) from Ctenopharyngodon idellus have been isolated and characterized. The gcPYYb gene consists of three exons interspaced by two introns, opposing to the typical architecture of most NPY-family genes as well as its paralogs. Alignment of deduced amino acid sequence indicates that the fish PYYb is more variable compared to NPY and PYY as shown by more residue changes in teleosts lineage, suggesting mild selective pressure imposed on the peptide. Real-time quantitative PCR analysis shows the gcPYYb mRNA in developing larvae is increased during the mixed endo- and exogenous-feeding period and is widely distributed throughout the intestine of fully grown individuals. Following a single meal, the gcPYYb mRNA in foregut is increased at 3 h post-feeding and subsequently decreased before the foregut contents are cleared. These results suggest that the gcPYYb has an important role in the early life stages of grass carp and is involved in food intake by transmitting feeding-related signals.

Peptidomic analysis of human reflex tear fluid

Tear fluid is a complex mixture of biological compounds, including carbohydrates, lipids, electrolytes, proteins, and peptides. Despite the physiological importance of tear fluid, little is known about the identity of its endogenous peptides. In this study, we analyzed and identified naturally occurring peptide molecules in human reflex tear fluid by means of LC-MALDI-TOF-TOF. Tandem MS analyses revealed 30 peptides, most of which have not been identified before. Twenty-six peptides are derived from the proline-rich protein 4 and 4 peptides are derived from the polymeric immunoglobulin receptor. Based on their structural characteristics, we suggest that the identified tear fluid peptides contribute to the protective environment of the ocular surface.

Cloning and expression of tachykinins and their association with kisspeptins in the brains of zebrafish

The tachykinins are a family of neuropeptides, including substance P (SP), neurokinin A (NKA), and neurokinin B (NKB), that are encoded by the tac1 (SP and NKA) or tac2/3 (NKB) genes. Tachykinins are widely distributed in the central nervous system and have roles as neurotransmitters and/or neuromodulators. Recent studies in mammals have demonstrated the coexpression of NKB and kisspeptin and their comodulatory roles over the control of reproduction. We have recently identified two kisspeptin-encoding genes, kiss1 and kiss2, in teleosts. However, such relationship between tachykinins and kisspeptins has not been demonstrated in non-mammalian species. To determine the involvement of tachykinins in the reproduction in teleosts, we identified tac1 and two tac2 (tac2a and tac2b) sequences in the zebrafish genome using in silico data mining. Zebrafish tac1 encodes SP and NKA, whereas the tac2 sequences encode NKB and an additional peptide homologous to NKB (NKB-related peptide). Digoxigenin in situ hybridization in the brain of zebrafish showed tac1 mRNA-containing cells in the olfactory bulb, telencephalon, preoptic region, hypothalamus, mesencephalon, and rhombencephalon. The zebrafish tac2a mRNA-containing cells were observed in the preoptic region, habenula, and hypothalamus, whereas the tac2b mRNA-containing cells were predominantly observed in the dorsal telencephalic area. Furthermore, we examined the coexpression of tachykinins and two kisspeptin genes in the brain of zebrafish. Dual fluorescent in situ hybridization showed no coexpression of tachykinins mRNA with kisspeptins mRNA in hypothalamic nuclei or the habenula. These results suggest the presence of independent pathways for kisspeptins and NKB neurons in the brain of zebrafish.

Endocrine archeology: do insects retain ancestrally inherited counterparts of the vertebrate releasing hormones GnRH, GHRH, TRH, and CRF?

Vertebrate releasing hormones include gonadotropin releasing hormone (GnRH), growth hormone releasing hormone (GHRH), corticotropin releasing hormone (CRF), and thyrotropin-releasing hormone (TRH). They are synthesized in the hypothalamus and stimulate the release of pituitary hormones. Here we review the knowledge on hormone releasing systems in the protostomian lineage. We address the question: do insects have peptides that may be phylogenetically related to an ancestral GnRH, GHRH, TRH, and CRF? Such endocrine archeology has become possible thanks to the growing list of fully sequenced genomes as well as to the continuously improving bioinformatic tool set. It has recently been shown that the ecdysozoan (nematodes and arthropods) adipokinetic hormones (AKHs), the lophotrochozoan (annelids and mollusks) GnRHs as well as the protochordate GnRHs are structurally related. The adipokinetic hormone precursor-related peptides (APRPs), in locusts encoded by the same gene that contains the AKH-coding region, have been forwarded as the structural counterpart of GHRH of vertebrates. CRF is relatively well conserved in insects, in which it functions as a diuretic hormone. Members of TRH-receptor family seem to have been conserved in some arthropods, but other elements of the thyroid hormone signaling system are not. A challenging idea is that in insects the functions of the thyroid hormones were taken over by juvenile hormone (JH). Our reconstruction suggests that, perhaps, the ancestral releasing hormone precursors played a role in controlling energy metabolism and water balance, and that releasing hormone functions as present in extant vertebrates were probably secondarily acquired.

Molecular Coevolution of Neuropeptides Gonadotropin-Releasing Hormone and Kisspeptin with their Cognate G Protein-Coupled Receptors

The neuropeptides gonadotropin-releasing hormone (GnRH) and kisspeptin (KiSS), and their receptors gonadotropin-releasing hormone receptor (GnRHR) and kisspeptin receptor (KiSSR) play key roles in vertebrate reproduction. Multiple paralogous isoforms of these genes have been identified in various vertebrate species. Two rounds of genome duplication in early vertebrates likely contributed to the generation of these paralogous genes. Genome synteny and phylogenetic analyses in a variety of vertebrate species have provided insights into the evolutionary origin of and relationship between paralogous genes. The paralogous forms of these neuropeptides and their receptors have coevolved to retain high selectivity of the ligand–receptor interaction. These paralogous forms have become subfunctionalized, neofunctionalized, or dysfunctionalized during evolution. This article reviews the evolutionary mechanism of GnRH/GnRHR and KiSS/KiSSR, and the fate of the duplicated paralogs in vertebrates.

Identification, tissue distribution and orexigenic activity of neuropeptide F (NPF) in penaeid shrimp

The neuropeptide Fs (NPFs) are an invertebrate subgroup of the FMRFamide-like peptides, and are proposed by some to be the homologs of vertebrate neuropeptide Y. Although there is some information about the identity, tissue distribution and function of NPFs in insects, essentially nothing is known about them in crustaceans. We have identified and characterized NPF-encoding transcripts from the penaeid shrimp Litopenaeus vannamei and Melicertus marginatus. Two transcripts were identified from each species. For each shrimp species, the two transcripts differed from one another by the presence or absence of an insert in the portion of the open reading frame that encodes the NPF peptide. The two NPF isoforms are identical in L. vannamei and M. marginatus, with their predicted structures being KPDPSQLANMAEALKYLQELDKYYSQVSRPRFamide and KPDPSQLANMAEALKYLQELDKYYSQVSRPSPRSAPGPASQIQALENTLKFLQLQELGKLYSLRARPRFamide. RT-PCR tissue profiling showed both transcripts are broadly distributed within the nervous system of each species. The transcript encoding the shorter NPF was detected in some, but not all, midgut samples. The transcript encoding the longer NPF was absent in the midgut of both species, and neither transcript was detected in their skeletal muscle. Juvenile L. vannamei fed on a diet supplemented with the shorter NPF exhibited a marked increase in food intake relative to control individuals that did not receive the supplement; the NPF-fed shrimp also showed a significant increase in growth relative to the control group. Our data suggest that NPF is present in both the nervous system and midgut of penaeid shrimp, functioning, at least in part, as a powerful orexigenic agent.

Evolution of the gonadotropin-releasing hormone (GnRH) gene family in relation to vertebrate tetraploidizations

The neuropeptide gonadotropin-releasing hormone (GnRH) plays an important role in the control of reproductive functions. Vertebrates possess multiple GnRH isoforms that are classified into three main groups, namely GnRH1, GnRH2 and GnRH3. In the present study, we show that the chromosomal organization of the three GnRH loci is very well conserved among gnathostome species. We analyzed genes belonging to several other multigenic families that are present in the vicinity of GnRH genes. Five of them were seen to occur in four chromosomal regions that clearly form a paralogon. Moreover, we show that the homologous regions in the amphioxus genome are present on a single locus. Taken together, these observations indicate that GnRH1, GnRH2 and GnRH3 genes represent three paralogous genes that resulted from the two rounds of tetraploidization that took place early in vertebrate evolution. They confirm that the GnRH3 gene which is currently known only in teleost has most likely been lost in the tetrapod lineage. Finally, they suggest the existence of a fourth GnRH gene, named GnRH4. Whether the GnRH4 gene still exists in extant vertebrates is currently unknown. A search for this putative gene would be particularly useful in basal groups such as agnathans and cartilaginous fish.

Neuropeptide localization in nonmammalian vertebrates

Neuropeptides are particularly suited to comparative and evolutionary studies, since they have been highly conserved during evolution. Based on primary amino-acid structure, neuropeptides can be arranged into families and synthesized as multiple molecular variants. They may play different functional roles in different organs or tissues of the same species, but also among species and classes. Immunohistochemistry (IHC) is powerful technique for localizing the molecular expression of proteins in tissues and cells of different classes of vertebrates and has been fully exploited in the study of the mammalian brain. The present chapter provides a detailed description of the protocols routinely used in our laboratory to analyze the presence and distribution of neuropeptides in nonmammalian vertebrate tissues. Single labeling protocols performed by both light and fluorescein IHC, and double labeling protocols using primary antisera raised in different species or in the same species are described. Antibody and method specificity are also discussed in detail.

Molecular coevolution of kisspeptins and their receptors from fish to mammals

Kisspeptin and its receptor, GPR54, play a pivotal role in vertebrate reproduction. Recent advances in bioinformatic tools combined with comparative genomics have led to the identification of a large number of kisspeptin and GPR54 genes in a variety of vertebrate species. Genome duplications may have produced at least two isoforms of both ligand (KiSS1 and KiSS2) and receptor (GPR54-1 and GPR54-2). Additional isoforms of kisspeptin (KiSS1b) and GPR54 (GPR54-1b) have been found in an amphibian species, Xenopus (Silurana) tropicalis. Here, we describe the evolutionary lineages of these kisspeptin and GPR54 isoforms using genome synteny and phylogenetic analyses, and possible molecular interactions between kisspeptin and GPR54 subtypes based on ligand-receptor selectivity. Together, kisspeptin and GPR54 provide an excellent model for understanding molecular coevolution of the peptide ligand and GPCR pairs.

Concomitant duplications of opioid peptide and receptor genes before the origin of jawed vertebrates

Background

The opioid system is involved in reward and pain mechanisms and consists in mammals of four receptors and several peptides. The peptides are derived from four prepropeptide genes, PENK, PDYN, PNOC and POMC, encoding enkephalins, dynorphins, orphanin/nociceptin and beta-endorphin, respectively. Previously we have described how two rounds of genome doubling (2R) before the origin of jawed vertebrates formed the receptor family.

Methodology/Principal Findings

Opioid peptide gene family members were investigated using a combination of sequence-based phylogeny and chromosomal locations of the peptide genes in various vertebrates. Several adjacent gene families were investigated similarly. The results show that the ancestral peptide gene gave rise to two additional copies in the genome doublings. The fourth member was generated by a local gene duplication, as the genes encoding POMC and PNOC are located on the same chromosome in the chicken genome and all three teleost genomes that we have studied. A translocation has disrupted this synteny in mammals. The PDYN gene seems to have been lost in chicken, but not in zebra finch. Duplicates of some peptide genes have arisen in the teleost fishes. Within the prepropeptide precursors, peptides have been lost or gained in different lineages.

Conclusions/Significance

The ancestral peptide and receptor genes were located on the same chromosome and were thus duplicated concomitantly. However, subsequently genetic linkage has been lost. In conclusion, the system of opioid peptides and receptors was largely formed by the genome doublings that took place early in vertebrate evolution.

Differential mRNA splicing and precursor processing of neurokinin B in neuroendocrine tissues

The tachykinin neurokinin B which is encoded on the tachykinin 3 precursor, has prominent roles in both neuronal and endocrine systems, yet little is known about its evolution, potential splice variants and the manner in which it is processed. Here, we deduce the diversity within the vertebrate tachykinin 3 precursors, and identify novel tachykinin 3 splice variants and precursors. A total of 35 different tachykinin 3 precursors were identified in mammals, birds and reptiles. Nine additional alternatively spliced tachykinin 3 mRNA transcripts were also discovered in humans leading to the formation of three tachykinin 3 precursors (named alpha, beta and gamma tachykinin 3), but no novel tachykinin. gamma tachykinin 3, albeit rarer, was not found to encode neurokinin B. Differential processing of the tachykinin 3 precursor in the human placenta leads to the formation of potential NH2-terminally extended forms of neurokinin B. Moreover, we found increased proteolytic cleavage of the tachykinin 3 precursor during the pregnancy syndrome of pre-eclampsia. We have established neurokinin B to be an evolutionarily conserved peptide, nonetheless the significance of the three different tachykinin 3 precursors is not clear, but could represent an evolutionarily redundant splicing mechanism once employed by an ancestral gene that encoded two tachykinins. Our results indicate that differential mRNA splicing and precursor processing is likely to play an important role in differentiating the actions of the tachykinin 3 gene products in both neuronal and endocrine tissues.

Melanocortin peptides affect the motivation to feed in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the effects of one melanocortin receptor (MCR) agonist and two antagonists on food intake in juvenile rainbow trout. Baseline food intake was established prior to 1 microl intracerebroventricular injection (ICV) of the non-specific agonist MTII, the MC4R antagonist HS024 and the MC3/4R antagonist SHU9119 at concentrations of 0.3, 1 or 3 nM. Saline-injected fish and untreated fish served as controls. Changes in food intake were observed 1h after the ICV injections. Our results showed that treatment with MTII significantly decreased food intake at 3 nM compared to control, HS024 significantly increased food intake at 3 nM compared to control and saline-treated fish, and SHU9119 significantly increased food intake at 3 nM compared to saline-treated fish. In conclusion, our study provides further evidence, and hence strengthens the hypothesis, that MC4R participates in the control of energy balance in fish in the same manner as in mammals. Our findings that HS024 is more potent than SHU9119 in increasing food intake suggest that the effects of melanocortin on energy balance in rainbow trout are mainly regulated by activation of MC4R. Hence, HS024 seems an excellent tool as a MC4R antagonist in rainbow trout.

Molecular evolution of neuropeptides in the genus Drosophila

The first genomic and chemical characterization of fruit fly neuropeptides outside Drosophila melanogaster provides insights into the evolution of the neuropeptidome in this genus.

Background

Neuropeptides comprise the most diverse group of neuronal signaling molecules. They often occur as multiple sequence-related copies within single precursors (the prepropeptides). These multiple sequence-related copies have not arisen by gene duplication, and it is debated whether they are mutually redundant or serve specific functions. The fully sequenced genomes of 12 Drosophila species provide a unique opportunity to study the molecular evolution of neuropeptides.

Results

We data-mined the 12 Drosophila genomes for homologs of neuropeptide genes identified in Drosophila melanogaster. We then predicted peptide precursors and the neuropeptidome, and biochemically identified about half of the predicted peptides by direct mass spectrometric profiling of neuroendocrine tissue in four species covering main phylogenetic lines of Drosophila. We found that all species have an identical neuropeptidome and peptide hormone complement. Calculation of amino acid distances showed that ortholog peptide copies are highly sequence-conserved between species, whereas the observed sequence variability between peptide copies within single precursors must have occurred prior to the divergence of the Drosophila species.

Conclusion

We provide a first genomic and chemical characterization of fruit fly neuropeptides outside D. melanogaster. Our results suggest that neuropeptides including multiple peptide copies are under stabilizing selection, which suggests that multiple peptide copies are functionally important and not dispensable. The last common ancestor of Drosophila obviously had a set of neuropeptides and peptide hormones identical to that of modern fruit flies. This is remarkable, since drosophilid flies have adapted to very different environments.

New insight into the molecular evolution of the somatostatin family

The present review describes the molecular evolution of the somatostatin family and its relationships with that of the urotensin II family. Most of the somatostatin sequences collected from different vertebrate species can be grouped as the products of at least four loci. The somatostatin 1 (SS1) gene is present in all vertebrate classes from agnathans to mammals. The SS1 gene has given rise to the somatostatin 2 (SS2) gene by a segment/chromosome duplication that is probably the result of a tetraploidization event according to the 2R hypothesis. The somatostatin-related peptide cortistatin, first identified in rodents and human, is the counterpart of SS2 in placental mammals. In fish, the existence of two additional somatostatin genes has been reported. The first gene, which encodes a peptide usually named somatostatin II (SSII), exists in almost all teleost species investigated so far and is thought to have arisen through local duplication of the SS1 gene. The second gene, which has been characterized in only a few teleost species, encodes a peptide also named SSII that exhibits a totally atypical structure. The origin of this gene is currently unknown. Nevertheless, because the two latter genes are clearly paralogous genes, we propose to rename them SS3 and SS4, respectively, in order to clarify the current confusing nomenclature. The urotensin II family consists of two genes, namely the urotensin II (UII) gene and the UII-related peptide (URP) gene. Both UII and URP exhibit limited structural identity to somatostatin so that UII was originally described as a "somatostatin-like peptide". Recent comparative genomics studies have revealed that the SS1 and URP genes, on the one hand, and the SS2 and UII genes, on the other hand, are closely linked on the same chromosomes, thus confirming that the SS1/SS2 and the UII/URP genes belong to the same superfamily. According to these data, it appears that an ancestral somatostatin/urotensin II gene gave rise by local duplication to a somatostatin ancestor and a urotensin II ancestor, whereupon this pair was duplicated (presumably by a segment/chromosome duplication) to give rise to the SS1-UII pair and the SS2-URP pair.

The obesity gene, FTO, is of ancient origin, up-regulated during food deprivation and expressed in neurons of feeding-related nuclei of the brain

Gene variants of the FTO (fatso) gene have recently been strongly associated with body mass index and obesity. The FTO gene is well conserved and found in a single copy in vertebrate species including fish and chicken, suggesting that the ancestor of this gene was present 450 million years ago. Surprisingly, the FTO gene is present in two species of algae but not in any other invertebrate species. This could indicate that this gene has undergone a horizontal gene transfer. Quantitative real-time PCR showed that the gene is expressed in many peripheral and central rat tissues. Detailed in situ hybridization analysis in the mouse brain showed abundant expression in feeding-related nuclei of the brainstem and hypothalamus, such as the nucleus of the solitary tract, area postrema, and arcuate, paraventricular, and supraoptic nuclei as well as in the bed nucleus of the stria terminalis. Colabeling showed that the FTO gene is predominantly expressed in neurons, whereas it was virtually not found in astrocytes or glia cells. The FTO was significantly up-regulated (41%) in the hypothalamus of rats after 48-h food deprivation. We also found a strong negative correlation of the FTO expression level with the expression of orexigenic galanin-like peptide, which is mainly synthesized in the arcuate nucleus. These results are consistent with the hypothesis that FTO could participate in the central control of energy homeostasis.

A 'reverse' phylogenetic approach for identification of novel osmoregulatory and cardiovascular hormones in vertebrates

Vertebrates expanded their habitats from aquatic to terrestrial environments during the course of evolution. In parallel, osmoregulatory and cardiovascular systems evolved to counter the problems of desiccation and gravity on land. In our physiological studies on body fluid and blood pressure regulation in various vertebrate species, we found that osmoregulatory and cardiovascular hormones have changed their structure and function during the transition from aquatic to terrestrial life. In fact, Na(+)-regulating and vasodepressor hormones play essential roles in fishes, while water-regulating and vasopressor hormones are dominant in tetrapods. Accordingly, Na(+)-regulating and vasodepressor hormones, such as natriuretic peptide (NP) and adrenomedullin (AM), are much diversified in teleost fishes compared with mammals. Based on this finding, new NPs and AMs were identified in mammals and other tetrapods. These hormones have only minor roles in the maintenance of normal blood volume and pressure in mammals, but their importance seems to increase when homeostasis is disrupted. Therefore, such hormones can be used for diagnosis and treatment of body fluid and cardiovascular disorders such as cardiac/renal failure and hypertension. In this review, we introduce a new approach for identification of novel Na(+)-regulating and vasodepressor hormones in mammals based on fish studies. Until recently, new hormones were first discovered in mammals, and then identified and applied in fishes. However, chances are increasing in recent years to identify new hormones first in fishes then in mammals, based on the difference in the regulatory systems between fishes and tetrapods. As the direction is opposite from the traditional phylogenetic approach, we added 'reverse' to its name. The 'reverse' phylogenetic approach offers a typical example of how comparative fish studies can contribute to the general and clinical endocrinology.

PACAP, VIP and their receptors in the metazoa: insights about the origin and evolution of the ligand-receptor pair

The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions.

Molecular evolution of neuropeptide receptors with regard to maintaining high affinity to their authentic ligands

Recently, we cloned many of the bullfrog neuropeptide G protein-coupled receptors (GPCRs), including receptors for vasotocin (VT), mesotocin, gonadotropin-releasing hormone (GnRH), neurotensin, apelin, and metastin. Bullfrog GPCRs usually have high affinity for bullfrog ligands but relatively low affinity for mammalian ligands. Reciprocally, synthetic agonists and antagonists developed based upon mammalian ligands display lower affinity at bullfrog receptors. Studies using chimeric or domain-swapped receptors indicate that the motifs responsible for differential ligand selectivity usually reside within transmembrane domain 6 (TMD6)-extracellular loop 3 (ECL3)-transmembrane domain 7 (TMD7). Triple mutation of mammalian V1aR (Phe(6.51) to Tyr, Ile(6.53) to Thr, and Pro(7.33) to Thr) increases VT affinity but greatly reduces arginine vasopressin affinity. This binding profile is similar to that of bullfrog VT1R. Changing just three amino acids in the bullfrog GnRH receptor-1 (i.e. Ser-Gln-Ser in the ECL3) to those found in the type-I mammalian GnRH receptor (i.e. Ser-Glu-Pro) reverses GnRH selectivity. In conclusion, specific receptor motifs that govern ligand selectivity can be determined by comparative molecular analyses of GPCRs and their ligands. Such analysis provides clues for understanding how GPCRs maintain high affinity to their authentic ligands.

Modular changes of cis-regulatory elements from two functional Pit1 genes in the duplicated genome of Cyprinus carpio

The pituitary-specific transcription factor Pit1 is involved in its own regulation and in a network of transcriptional regulation of hypothalamo-hypophyseal factors including prolactin (PRL) and growth hormone (GH). In the ectotherm teleost Cyprinus carpio, Pit1 plays an important role in regulation of the adaptive response to seasonal environmental changes. Two Pit1 genes exist in carp, a tetraploid vertebrate and transcripts of both genes were detected by RT-PCR analysis. Powerful comparative analyses of the 5'-flanking regions revealed copy specific changes comprising modular functional units in the naturally evolved promoters. These include the precise replacement of four nucleotides around the transcription start site embedded in completely conserved regions extending upstream of the TATA-box, an additional transcription factor binding site in the 5'-UTR of gene-I and, instead, duplication of a 9 bp element in gene-II. Binding of nuclear factors was assessed by electro mobility shift assays using extracts from rat pituitary cells and carp pituitary. Binding was confirmed at one conserved Pit1, one conserved CREB and one consensus MTF1. Interestingly, two functional Pit1 sites and one putative MTF1 binding site are unique to the Pit1 gene-I. In situ hybridization experiments revealed that the expression of gene-I in winter carp was significantly stronger than that of gene-II. Our data suggest that the specific control elements identified in the proximal regulatory region are physiologically relevant for the function of the duplicated Pit1 genes in carp and highlight modular changes in the architecture of two Pit1 genes that evolved for at least 12 MYA in the same organism.

Mass spectrometric identification of pEGFYSQRYamide: a crustacean peptide hormone possessing a vertebrate neuropeptide Y (NPY)-like carboxy-terminus

In invertebrates, peptides possessing the carboxy (C)-terminal motif -RXRFamide have been proposed as the homologs of vertebrate neuropeptide Y (NPY). Using matrix assisted laser desorption/ionization mass spectrometry, in combination with sustained off-resonance irradiation collision-induced dissociation and chemical and enzymatic reactions, we have identified the peptide pEGFYSQRYamide from the neuroendocrine pericardial organ (PO) of the crab Pugettia producta. This peptide is likely the same as that previously reported, but misidentified, as PAFYSQRYamide in several earlier reports (e.g. [Li, L., Kelley, W.P., Billimoria, C.P., Christie, A.E., Pulver, S.R., Sweedler, J.V., Marder, E. 2003. Mass spectrometric investigation of the neuropeptide complement and release in the pericardial organs of the crab, Cancer borealis. J. Neurochem. 87, 642-656; Fu, Q., Kutz, K.K., Schmidt, J.J., Hsu, Y.W., Messinger, D.I., Cain, S.D., de la Iglesia, H.O., Christie, A.E., Li, L. 2005. Hormone complement of the Cancer productus sinus gland and pericardial organ: an anatomical and mass spectrometric investigation. J. Comp. Neurol. 493, 607-626.]). The -QRYamide motif contained in pEGFYSQRYamide is identical to that present in many vertebrate members of the NPY superfamily. Mass spectrometric analysis conducted on the POs of several other decapods showed that pEGFYSQRYamide is present in three other brachyurans (Cancer borealis, Cancer irroratus and Cancer productus) as well as in one species from another decapod infraorder (Lithodes maja, an anomuran). Thus, our findings show that at least some invertebrates possess NPY-like peptides in addition to those exhibiting an -RXRFamide C-terminus, and raise the question as to whether the invertebrate -QRYamides are functionally and/or evolutionarily related to the NPY superfamily.

Gastroenteropancreatic hormones and metabolism in fish

Metabolism of vertebrates integrates a vast array of systems and processes, including the pursuit and capture of food, feeding and digestion of ingested food, absorption and transport of nutrients, assimilation, partitioning and utilization of energy, and the processing and elimination of wastes. Fish, which are the most diverse group of vertebrates and occupy a wide range of habitats and display numerous life history patterns, have proven to be important models for the study of the structure, biosynthesis, evolution, and function of gastroenteropancreatic (GEP) hormones. Food intake is promoted by galanin, neuropeptide Y, and pancreatic polypeptide (PP), while cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) inhibit food intake. Digestion of ingested food is facilitated by CCK, PP, and secretin by coordinating gastrointestinal tract motility and regulation of exocrine secretion. Somatostatins (SS), on the other hand, generally inhibit exocrine secretions. Insulin facilitates assimilation by promoting the uptake of nutrient molecules (e.g., glucose, amino acids, and fatty acids) into cells. Insulin also is generally anabolic and stimulates the synthesis and deposition of energy reserves (e.g., glycogen, triacylglycerol) as well as of proteins, thereby facilitating organismal growth. Insulin-like growth factors (e.g., IGF-1) also promote cell proliferation and organismal growth. Breakdown and mobilization of stored energy reserves is stimulated by glucagon, GLP-1, and SS. Somatostatins also affect metabolism and reproduction via their effects on the thyroid axis as well as growth via effects on growth hormone (GH) release and perhaps directly via modulation of GH sensitivity. Studies in fish have revealed that GEP hormones play an important role in coordinating the various aspects of metabolism with each other and with the physiological and developmental status of the animal as well as with the environment.

The fish endocrine pancreas: review, new data, and future research directions in ontogeny and phylogeny

The literature on the ontogeny and phylogeny of the endocrine pancreas of ray-finned fishes is summarized since the latest review in fish [Youson, J.H., Al-Mahrouki, A.A., 1999. Review. Ontogenetic and phylogenetic development of the endocrine pancreas (islet organ) in fishes. Gen. Comp. Endocrinol. 116, 303-335]. A basic description and a demonstration of the diversity of the fish islet organ is provided through new immunohistochemical data on islet tissue from a basal teleost, an osteoglossomorph, and a more derived teleost, a perciforme. Unlike the previous review, the present report provides a review and discussion of the utility of sequence data of insulin, somatostatin, and NPY- and glucagon-family peptides in phylogenetic analyses of jawed and jawless fishes. The present study also provides the first comparative analysis of sequences of preprohormones of endocrine peptides from closely related basal teleost species. Some nucleotide and deduced amino acid sequence data for preprosomatostatins (PPSS-I and/or -II) are compared for four species of bonytongues, Osteoglossomorpha, and with PPSSs of the white sucker, Catostomus commersoni, representing Cypriniformes, a more generalized teleost order. Phylogenetic analysis of deduced amino acid sequences of the PPSSs of these species and others from databases indicates good support for the monophyly of Osteoglossomorpha and some support for the present taxonomic grouping of the osteoglossomorphs examined, and also the white sucker. However, PPSS may have limited phylogenetic utility due to the relative short sequence, particularly in resolving relationships among lineages that diverged over a short period of time. Since in the few fish species examined we have just touched the surface in describing the diversity of structure of the islet organ, and likely the nature of the products of its cells, this report promotes the continued study of this organ.

Molecular evolution of proadrenomedullin N-terminal 20 peptide (PAMP): evidence for gene co-option

Posttranslational processing of proadrenomedullin generates two biologically active peptides, adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP). Sequence comparison of homologous proadrenomedullin genes in vertebrate evolution shows a high degree of stability in the reading frame for AM, whereas PAMP sequence changes rapidly. Here we investigate the functional significance of PAMP phylogenetic variation studying two of PAMP's better characterized physiological activities, angiogenic potential and antimicrobial capability, with synthetic peptides carrying the predicted sequence for human, mouse, chicken, and fish PAMP. All tested peptides induced angiogenesis when compared with untreated controls, but chicken and fish PAMP, which lack terminal amidation, were apparently less angiogenic than their human and mouse homologs. Confirming the role of amidation in angiogenesis, Gly-extended and free acid variants of human PAMP produced responses similar to the natural nonamidated peptides. In contrast, antimicrobial activity was restricted to human PAMP, indicating that this function may have been acquired at a late time during the evolution of PAMP. Interestingly, free acid human PAMP retained antimicrobial activity whereas the Gly-extended form did not. This fact may reflect the need for maintaining a tightly defined structural conformation in the pore-forming mechanism proposed for these antimicrobial agents. The evolution of PAMP provides an example of an angiogenic peptide that developed antimicrobial capabilities without losing its original function.

Neuropeptide Y-family receptors Y6 and Y7 in chicken. Cloning, pharmacological characterization, tissue distribution and conserved synteny with human chromosome region

The peptides of the neuropeptide Y (NPY) family exert their functions, including regulation of appetite and circadian rhythm, by binding to G-protein coupled receptors. Mammals have five subtypes, named Y1, Y2, Y4, Y5 and Y6, and recently Y7 has been discovered in fish and amphibians. In chicken we have previously characterized the first four subtypes and here we describe Y6 and Y7. The genes for Y6 and Y7 are located 1 megabase apart on chromosome 13, which displays conserved synteny with human chromosome 5 that harbours the Y6 gene. The porcine PYY radioligand bound the chicken Y6 receptor with a K(d) of 0.80 +/- 0.36 nm. No functional coupling was demonstrated. The Y6 mRNA is expressed in hypothalamus, gastrointestinal tract and adipose tissue. Porcine PYY bound chicken Y7 with a K(d) of 0.14 +/- 0.01 nm (mean +/- SEM), whereas chicken PYY surprisingly had a much lower affinity, with a Ki of 41 nm, perhaps as a result of its additional amino acid at the N terminus. Truncated peptide fragments had greatly reduced affinity for Y7, in agreement with its closest relative, Y2, in chicken and fish, but in contrast to Y2 in mammals. This suggests that in mammals Y2 has only recently acquired the ability to bind truncated PYY. Chicken Y7 has a much more restricted tissue distribution than other subtypes and was only detected in adrenal gland. Y7 seems to have been lost in mammals. The physiological roles of Y6 and Y7 remain to be identified, but our phylogenetic and chromosomal analyses support the ancient origin of these Y receptor genes by chromosome duplications in an early (pregnathostome) vertebrate ancestor.

The expression of neurokinin-1 and preprotachykinin-1 in breast cancer cells depends on the relative degree of invasive and metastatic potential

Breast cancer has a predilection for metastasis to the bone marrow. The preprotachykinin-I (PPT-I) gene has a central role in the early migration of breast cancer cells into the bone marrow, making this organ a latent repository of the cancer cells. This study investigated whether the invasive and metastatic potential of breast cancer cells correlate with the expression of the PPT-I gene and the receptors for its peptides, neurokinin-1 (NK-1) and NK-2. The studies compared cells that are non-tumorigenic (MCF12A), low metastatic and invasive potential (MCF7), and sublines of MCF with increased invasive and metastatic potential (LCC1 and LCC2). LCC2, but not LCC1 is tamoxifen resistant. Quantitative RT-PCR showed increased expression of PPT-I, NK-1 and NK-2 mRNA LCC1 and LCC2. MCF7 required stimulation by phorbol ester for NK-1 induction. The levels of NK-2 mRNA were significantly increased in LCC2. Clonogenic assays with specific receptor antagonists showed a predominant role for NK-2 in the proliferation of both LCC1 and LCC2. While the growth rate of LCC1 and LCC2 were similar, the latter showed increased migration. Use of a nude mouse model confirmed higher metastatic potential of LCC2, including increased migration to regions of the endosteum. Overall, these studies show a correlation between three neuroendocrine-related genes: PPT-I, NK-1 and NK-2 and the metastatic potential of specific breast cancer cells. These cells provide a model for future studies on bone marrow metastasis.

Adult tissue-specific expression of a Dppa3-derived retrogene represents a postnatal transcript of pluripotent cell origin

Processed pseudogenes emerge by reverse transcription of spliced mRNAs followed by incorporation of the resultant cDNA into the genome. Their genesis requires that retrotransposition occurs within the germ line, a provision that significantly limits random distribution of source genes. We previously identified embryonic stem cell-specific genes as an enriched source of retropseudogene origin. Nanog, Oct4, and Dppa3 (Stella/PGC7) presented as source genes for >30 processed pseudogenes within the human genome. In the current study, we extended our previous analysis and focused on the pluripotent cell-specific Dppa gene family. Of the five Dppa genes characterized, four were associated with putative retropseudogenes as determined by nucleotide BLAST (basic local alignment sequence tool) searches of the respective mRNA transcripts against the human genome. A subset of the 11 Dppa3-derived hits were then screened against a human adult tissue cDNA panel for evidence of transcriptional activity. One of the putative Dppa3-derived retropseudogenes, Dppa3(d), located on human chromosome 16p13, tested positive for mRNA transcript in bone marrow, peripheral blood, pancreas, adrenal gland, and thyroid gland. Specificity against the source Dppa3 gene expression was sequence verified, and independent human tissue samples were obtained to confirm Dppa3(d) expression. These data substantiate the existence of human adult tissue-specific transcripts that originate via retrotransposition of the pluripotent cell-specific gene, Dppa3. Further studies may reveal an evolutionary role for this example of genetic diversity, but in the short term our observations serve a cautionary purpose regarding the use of Dppa3 transcripts in adult tissue-derived cells as a potential marker of pluripotency.