Molecular evolution of neurohypophysial hormone precursors

An evolutionary timeline of the oxytocin signaling pathway

Oxytocin is a neuropeptide associated with both psychological and somatic processes like parturition and social bonding. Although oxytocin homologs have been identified in many species, the evolutionary timeline of the entire oxytocin signaling gene pathway has yet to be described. Using protein sequence similarity searches, microsynteny, and phylostratigraphy, we assigned the genes supporting the oxytocin pathway to different phylostrata based on when we found they likely arose in evolution. We show that the majority (64%) of genes in the pathway are 'modern'. Most of the modern genes evolved around the emergence of vertebrates or jawed vertebrates (540 - 530 million years ago, 'mya'), including OXTR, OXT and CD38. Of those, 45% were under positive selection at some point during vertebrate evolution. We also found that 18% of the genes in the oxytocin pathway are 'ancient', meaning their emergence dates back to cellular organisms and opisthokonta (3500-1100 mya). The remaining genes (18%) that evolved after ancient and before modern genes were classified as 'medium-aged'. Functional analyses revealed that, in humans, medium-aged oxytocin pathway genes are highly expressed in contractile organs, while modern genes in the oxytocin pathway are primarily expressed in the brain and muscle tissue.

Role of Habenula in Social and Reproductive Behaviors in Fish: Comparison With Mammals

Social behaviors such as mating, parenting, fighting, and avoiding are essential functions as a communication tool in social animals, and are critical for the survival of individuals and species. Social behaviors are controlled by a complex circuitry that comprises several key social brain regions, which is called the social behavior network (SBN). The SBN further integrates social information with external and internal factors to select appropriate behavioral responses to social circumstances, called social decision-making. The social decision-making network (SDMN) and SBN are structurally, neurochemically and functionally conserved in vertebrates. The social decision-making process is also closely influenced by emotional assessment. The habenula has recently been recognized as a crucial center for emotion-associated adaptation behaviors. Here we review the potential role of the habenula in social function with a special emphasis on fish studies. Further, based on evolutional, molecular, morphological, and behavioral perspectives, we discuss the crucial role of the habenula in the vertebrate SDMN.

Neuropeptide precursors and neuropeptides in the sea cucumber Apostichopus japonicus: a genomic, transcriptomic and proteomic analysis

The sea cucumber Apostichopus japonicus is a foodstuff with very high economic value in China, Japan and other countries in south-east Asia. It is at the heart of a multibillion-dollar industry and to meet demand for this product, aquaculture methods and facilities have been established. However, there are challenges associated with optimization of reproduction, feeding and growth in non-natural environments. Therefore, we need to learn more about the biology of A. japonicus, including processes such as aestivation, evisceration, regeneration and albinism. One of the major classes of molecules that regulate physiology and behaviour in animals are neuropeptides, and a few bioactive peptides have already been identified in A. japonicus. To facilitate more comprehensive investigations of neuropeptide function in A. japonicus, here we have analysed genomic and transcriptomic sequence data and proteomic data to identify neuropeptide precursors and neuropeptides in this species. We identified 44 transcripts encoding neuropeptide precursors or putative neuropeptide precursors, and in some instances neuropeptides derived from these precursors were confirmed by mass spectrometry. Furthermore, analysis of genomic sequence data enabled identification of the location of neuropeptide precursor genes on genomic scaffolds and linkage groups (chromosomes) and determination of gene structure. Many of the precursors identified contain homologs of neuropeptides that have been identified in other bilaterian animals. Precursors of neuropeptides that have thus far only been identified in echinoderms were identified, including L- and F-type SALMFamides, AN peptides and others. Precursors of several peptides that act as modulators of neuromuscular activity in A. japonicus were also identified. The discovery of a large repertoire of neuropeptide precursors and neuropeptides provides a basis for experimental studies that investigate the physiological roles of neuropeptide signaling systems in A. japonicus. Looking ahead, some of these neuropeptides may have effects that could be harnessed to enable improvements in the aquaculture of this economically important species.

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

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

The fifth neurohypophysial hormone receptor is structurally related to the V2-type receptor but functionally similar to V1-type receptors

The neurohypophysial peptides of the vasopressin (VP) and oxytocin (OT) families regulate salt and water homeostasis and reproduction through distinct G protein-coupled receptors. The current thinking is that there are four neurohypophysial hormone receptors (V1aR, V1bR, V2R, and OTR) in vertebrates, and their evolutionary history is still debated. We report the identification of a fifth neurohypophysial hormone receptor (V2bR) from the holocephalan elephant fish. This receptor is similar to conventional V2R (V2aR) in sequence, but induced Ca(2+) signaling in response to vasotocin (VT), the non-mammalian VP ortholog; such signaling is typical of V1-type receptors. In addition, V1aR, V1bR and OTR were also isolated from the elephant fish. Further screening revealed that orthologous V2bRs are widely distributed throughout the jawed vertebrates, and that the V2bR family is subdivided into two subfamilies: the fish specific type-1, and a type-2 that is characteristically found in tetrapods. Analysis suggested that the mammalian V2bR may have lost its function. Based on molecular phylogenetic, synteny and functional analyses, we propose a new evolutionary history for the neurohypophysial hormone receptors in vertebrates as follows: the first duplication generated V1aR/V1bR/OTR and V2aR/V2bR lineages; after divergence from the V2bR lineage, the V2aRs evolved to use cAMP as a second messenger, while the V2bRs retained the original Ca(2+) signaling system. Future studies on the role of V2bR in the brain, heart, kidney and reproductive organs, in which it is highly expressed, will open a new research field in VP/VT physiology and evolution.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Diversity of the hypothalamo-neurohypophysial system and its hormonal genes

The hypothalamic neurosecretory cells (NSCs) which produce and release neurohypophysial hormones are involved in controls of diverse physiological phenomena including homeostatic controls of unconscious functions and reproduction. The far and wide distribution of neurosecretory processes in the discrete brain loci and the neurohypophysis is appropriate for coordination of neural and endocrine events that are required for the functions of NSCs. The presence of dye couplings and intimate contacts among NSCs supports harmonious production and release of hormone to maintain the plasma level within a certain range which is adequate for a particular physiological condition. Neurosecretory cells integrate diverse input signals from internal and external sources that define this particular physiological condition, although reactions of NSCs vary among different species, and among different cell types. An input signal to NSC is received by specific receptors and transduced as unique intracellular signals, important for the various functions of neurohypophysial hormones. Orchestration of multiple intracellular signaling systems, activities of which are individually modulated by input signals, determines the rates of synthesis and release of hormone through regulation of gene expression. The first step of gene expression, i.e., transcription, is amenable for diverse reaction of NSCs, because the 5' upstream regions of genes encoding neurohypophysial hormones are highly variable.

Identification and characterization of mesotocin and V1a-like vasotocin receptors in a urodele amphibian, Taricha granulosa

The cDNA sequences encoding the mesotocin receptor (MTR) and vasotocin 1a receptor (VTR-1a) were identified in a urodele amphibian, the rough-skinned newt, Taricha granulosa. Saturation binding of [(3)H]oxytocin (OT) to the Taricha MTR (tMTR) was best fit by a two-state model; a high affinity-low abundance site and a lower affinity-high abundance site. Competition-binding studies found the following rank-order affinities for the tMTR: mesotocin (MT)>OT≈vasotocin (VT)>vasopressin (VP)>isotocin (IT). Inositol phosphate (IP) accumulation studies demonstrated functional activity of both the tMTR and Taricha VTR-1a (tVTR-1a) in a heterologous cell culture system. The rank-order potencies for the tMTR were MT>OT>VT≈VP>IT. The combined binding and IP results indicate that VT may act as a partial agonist of the tMTR. Rank-order potencies for the tVTR-1a were VT>VP>MT≈OT>IT. For both receptors, stimulation of IP accumulation was blocked by d(CH(2))(5)[Tyr(Me)(2)]AVP (Manning compound) and d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2)]OVT (OTA). OTA was a more potent antagonist for the transiently expressed tMTR while Manning compound was relatively more potent at inhibiting IP accumulation in tVTR-1a expressing cells. In contradiction to earlier assumptions, the absolute IC(50) of Manning compound was lower for the tMTR (27nM±13) than the tVTR-1a (586nM±166) indicating its potential higher affinity for the tMTR, a finding with special relevance to interpretation of comparative studies investigating the behavioral and physiological actions of neurohypophysial peptides in non-mammalian species.

NGFFFamide and echinotocin: structurally unrelated myoactive neuropeptides derived from neurophysin-containing precursors in sea urchins

The myoactive neuropeptide NGIWYamide was originally isolated from the holothurian (sea cucumber) Apostichopus japonicus but there is evidence that NGIWYamide-like peptides also occur in other echinoderms. Here we report the discovery of a gene in the sea urchin Strongylocentrotus purpuratus that encodes two copies of an NGIWYamide-like peptide: Asn-Gly-Phe-Phe-Phe-(NH(2)) or NGFFFamide. Interestingly, the C-terminal region of the NGFFFamide precursor shares sequence similarity with neurophysins, carrier proteins hitherto uniquely associated with precursors of vasopressin/oxytocin-like neuropeptides. Thus, the NGFFFamide precursor is the first neurophysin-containing neuropeptide precursor to be discovered that does not contain a vasopressin/oxytocin-like peptide. However, it remains to be determined whether neurophysin acts as a carrier protein for NGFFFamide. The S. purpuratus genome also contains a gene encoding a precursor comprising a neurophysin polypeptide and 'echinotocin' (CFISNCPKGamide) - the first vasopressin/oxytocin-like peptide to be identified in an echinoderm. Therefore, in S. purpuratus there are two genes encoding precursors that have a neurophysin domain but which encode neuropeptides that are structurally unrelated. Furthermore, both NGFFFamide and echinotocin cause contraction of tube foot and oesophagus preparations from the sea urchin Echinus esculentus, consistent with the myoactivity of NGIWYamide in sea cucumbers and the myoactivity of vasopressin/oxytocin-like peptides in other animal phyla. Presumably the NGFFFamide precursor acquired its neurophysin domain following partial or complete duplication of a gene encoding a vasopressin/oxytocin-like peptide, but it remains to be determined when in evolutionary history this occurred.

Identification of mesotocin and vasotocin nucleotide sequences in two species of urodele amphibian

We amplified and identified, for the first time in urodele amphibians, cDNA sequences that encode preprovasotocin (preproVT) and prepromesotocin (preproMT) from two distinct urodelian species, Taricha granulosa (the rough-skinned newt) and Plethodon shermanii (the spotted salamander). Each of these cDNA sequences encoded proteins that contained the characteristics of known neurohypophysial peptide precursors; each sequence consisting of (1) a signal peptide, (2) VT- or MT-like peptides, (3) neurophysin, and for the preproVTs, (4) copeptin. In T. granulosa, cDNA sequences encoded for the nine amino acids that define VT or MT. In P. shermani, cDNA sequences encoded for the VT peptide and a previously unidentified isoform of MT, ([Val(4)]-MT).

Structure of neurohypophysial hormone genes and changes in the levels of expression during spawning season in grass puffer (Takifugu niphobles)

Vasotocin (VT) has been shown to influence various aspects of social and sexual behaviors in a broad range of vertebrate species, but less is known about the mechanisms through which this peptide modulates behavior. Additionally, much less is known about roles of isotocin (IT) in regulation of behavior. Grass puffer, Takifugu niphobles, has unique spawning behavior; spawning occurs on beach only for several days around the spring tide and is conducted by a group of 10-60 individuals, of which one is female. As a first step toward investigating the roles of VT and IT in this species' spawning behavior, we determined the structures of the VT and IT genes from grass puffer using the genome resources of the closely related tiger puffer and green puffer. We then used these sequences to develop real-time PCR assays and examined changes in expression of the VT and IT genes over the spawning season. The structures of VT and IT genes are well conserved among three puffer species. Particularly, the sequence similarities between grass and tiger puffers were very high not only in the coding region (85-99%), but also in the non-coding regions (92-98%) that include the 5'-upstream regions. The levels of expression of VT gene increased in the brain of pre-spawning females. The levels of VT mRNA in the spawning females tended to be higher than that in the spawning males. In contrast, the levels of IT mRNA did not show such variation. The present results suggest that VT gene expression augments in the brain of females during the spawning period. The unique spawning behavior of grass puffer provides a useful model for studying the molecular mechanism of sexual behavior utilizing the genome resources of tiger puffer.

Regulatory domains in the intergenic region of the oxytocin and vasopressin genes that control their hypothalamus-specific expression in vitro

Previous studies of oxytocin (OT) and vasopressin (VP) cell-specific gene expression in the hypothalamus using transgenic mouse and rat models focused attention on the intergenic region (IGR) as the site of critical enhancer elements. In this study, we used organotypic slice-explant cultures of rat hypothalamus as in vitro models, and particle-mediated gene transfer (biolistics) transfection methods to identify critical DNA sequences in the IGR between the OT and VP genes responsible for hypothalamic-specific gene expression. Reducing the 5' flanking region in the mouse VP gene from 3.5 kbp to 288 bp did not alter the efficacy of its expression in hypothalamic slices. All subsequent VP constructs were based on this 288 bp VP gene construct with changes made only to the IGR. These studies, which used various constructs with OT and VP promoters driving enhanced green fluorescent protein reporter gene expression, demonstrated that the IGR is necessary for OT and VP gene expression in hypothalamic slices in vitro. The DNA sequences in the IGR responsible for both OT and VP gene expression were located in a 178 bp domain immediately downstream of exon 3 of the VP gene. In addition, another domain in the IGR, 430 bp immediately downstream of exon 3 of the OT gene, contained a positive regulatory element for OT gene expression in the hypothalamus. Alignment of the DNA sequences in the 178 and 430 bp domains reveals four common sequences (motifs) that may be candidates for the putative enhancers in the IGR that regulate OT and VP gene hypothalamic-specific expression.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Mammalian mesotocin: cDNA sequence and expression of an oxytocin-like gene in a macropodid marsupial, the tammar wallaby

The oxytocin (OT)-like peptide of most Australian marsupials is mesotocin (MT), which differs from OT by substitution of isoleucine for leucine at position 8. To date, the only information on the evolution of the OT peptide in marsupials is based on the sequence of the 9-amino acid peptide itself. The main objective of this study was to obtain the nucleotide and derived amino acid sequences of a marsupial MT precursor for comparison with known OT and MT precursors of eutherians and nonmammalian vertebrates. The structural organization and sequence of the MT gene and its specific transcript were established in a macropodid marsupial, the tammar wallaby, using PCR strategies with a combination of genomic DNA and reverse-transcribed hypothalamic RNA. A consensus genomic sequence of 1221 bp was produced which, by comparison with the expressed cDNA sequence, included two intron sequences of 480 and 188 bp. The tammar MT precursor molecule consists of a 32-amino acid signal peptide, followed by the MT-encoding region and the Gly-Lys-Arg carboxy-terminal cleavage and amidation signal which separates the nonapeptide from the 92-amino acid neurophysin. At the amino acid level, the MT precursor is more similar to eutherian OT precursors than to nonmammalian MT, isotocin, or vasotocin precursors. Northern analysis demonstrated a single transcript of approximately 0.6 kB in the hypothalamus. Mesotocin mRNA is also present in several tissues of the reproductive tract, including the corpus luteum, follicle, uterus, and placenta. Within the ovary, MT transcripts are localized predominantly in the granulosa cells of antral follicles with some positive hybridization signals in cells of the theca interna. This pattern of MT gene expression in marsupials is very similar to that of OT in eutherians and suggests a conserved physiology in the mammalian ovary.

Expression of salmon corticotropin-releasing hormone precursor gene in the preoptic nucleus in stressed rainbow trout

The behavior of genes encoding the corticotropin-releasing hormone (CRH) precursor in response to stress has not been extensively studied in teleosts. To clarify this problem, CRH cDNAs were isolated from a hypothalamic cDNA library of sockeye salmon, Oncorhynchus nerka, by screening with PCR products amplified from the hypothalamic mRNA with primers deduced from the sequence of the sucker CRH precursor. Two types of PCR products with a high degree of sequence homology were identified (CRH-I and CRH-II). A cDNA encompassing the entire coding sequence of the salmon CRH-I precursor was isolated. The salmon CRH-I cDNA encodes a 167-amino-acid precursor, which consists of a signal sequence, a cryptic peptide, and the carboxyl terminal 41-amino-acid sequence of CRH. The deduced amino acid sequence of salmon CRH peptide exhibits 66 to 80% homology with mammalian, Xenopus, and sucker CRHs, whereas it shows about 50% homology with sucker, carp, or sole urotensin I, a CRH-related neuropeptide in teleost fish. In situ hybridization histochemistry demonstrated CRH mRNA-positive perikarya in the preoptic nucleus in rainbow trout, Oncorhynchus mykiss, when the fish were stressed by confinement. Adjacent sections hybridized with probes for salmon vasotocin (VT) precursor showed many VT mRNA-positive neurons also in the preoptic nucleus, suggesting a colocalization of CRH and VT mRNAs in the same magnocellular neurons in the rainbow trout brain. The present results suggest that CRH may have important roles in the control of stress responses in salmonid fish.

Structure-function relationships of the vasopressin prohormone domains

1. In this review the structure-function relationships of the different vasopressin prohormone domains are dated and discussed, with special reference to the neurophysin and glycopeptide domains. 2. The primary structures of the currently known neurophysins and glycopeptide sequences are compared and discussed. 3. The hormone-binding and aggregational properties of neurophysin are reviewed and related to a possible function within the regulated secretory pathway. 4. It is proposed, based on the properties reviewed here as well as our own data shown here, that the sorting of the vasopressin prohormone is initiated by hormone binding, which triggers aggregation of the prohormone into the characteristic dense cores of the regulated secretory pathway. 5. This may suggest that prohormone sorting into the regulated secretory pathway is, in general, determined by noncovalent, intramolecular interactions that promote aggregation.

Neuropeptide families: evolutionary perspectives

Examination of neuropeptide families can provide information about phyletic relationships and evolutionary processes. In this article the oxytocin/vasopressin family, growth hormone releasing factor (GRF) superfamily and the substance P/tachykinin family have been considered in detail because they have been isolated from an extraordinarily diverse array of species from several vertebrate classes and invertebrate phyla. More important is that the nucleotide sequence of mRNA or cDNA encoding many of these peptides has been determined, which has allowed evolutionary distances to be estimated based on the DNA mutation rate. The origin of a given family lies in a primordial gene that arose many millions of years ago, and through time, exon duplication and insertion, gene duplication, point mutation and exon loss, the family developed into the forms that are now recognised. For example, in birds, GRF and pituitary adenylate cyclase activating peptide (PACAP) are encoded by the same gene, which probably arose as a result of exon duplication and tandem insertion of the ancestral GRF gene. In mammals GRF is the sole product on one gene, and PACAP is the product of a gene that also produces PACAP-related peptide (PRP), which is homologous to GRF. Thus it appears that between birds and mammals the GRF/PACAP gene duplicated: exon loss gave rise to the mammalian GRF gene, while mutation led to the formation of the mammalian PRP/PACAP gene. The neuropeptide Y superfamily is considered briefly, as is cionin, which is an invertebrate peptide that is closely related to the mammalian gastrin/cholecystokinin family.

Brain vasotocin pathways and the control of sexual behaviors in the bullfrog

The neurohypophysial peptide arginine vasotocin (AVT) alters the display of several sexually dimorphic behaviors in the bullfrog (Rana catesbeiana). These behaviors include mate calling, release calling, call phonotaxis, and locomotor activity. Populations of AVT-immunoreactive cells are present in six areas of bullfrog brain and fibers are widespread. Neural areas involved in vocalization, in particular, contain AVT cells and fibers. As well, AVT concentrations in a subset of brain areas are sexually dimorphic and steroid sensitive. Effects of gonadectomy and gonadal steroid treatment vary, depending on the brain area and sex of the frog. For example, some anterior areas are sensitive to changes in both dihydrotestosterone (DHT) and estradiol. In some posterior brain areas, on the other hand, AVT levels are affected only by DHT. A similar situation exists for putative AVT receptors in bullfrogs. Receptors are widespread, occurring in many areas that have been linked to behavior. Receptor concentrations are sexually dimorphic in the amygdala pars lateralis, hypothalamus, pretrigeminal nucleus, and dorsolateral nucleus. Estradiol alters AVT receptor level in the amygdala of both sexes of bullfrog and both estradiol and DHT alter the receptor number in the pretrigeminal nucleus, but only in males. The mechanisms responsible for steroid effects on vasotocin neurons and their targets are unknown. Specific AVT cells, fiber terminal fields, and receptor populations are likely influenced by gonadal steroids for effective timing of individual behaviors displayed by bullfrogs.

Two types of cDNAs encoding proopiomelanocortin of sockeye salmon, Oncorhynchus nerka

To investigate regulatory mechanisms of proopiomelanocortin (POMC) gene expression in sockeye salmon, we have isolated and characterized cDNAs encoding two types of sockeye salmon POMC, which are referred to as ssPOMC-A and -B. Two types of PCR products were amplified from total RNA of sockeye salmon pituitaries by use of rainbow trout sequences. Full length cDNA clones encoding ssPOMC-A and ssPOMC-B were obtained from a pituitary cDNA library of sockeye salmon using the PCR products as probes. The ssPOMC-A and -B cDNAs have a length of 1072 and 1709 bps, respectively. Northern blot analysis showed that both ssPOMC-A and -B mRNAs were expressed only in the pituitary, and their sizes were about 1.2 kb and 1.8 kb, respectively. The presence of two ssPOMC genes was confirmed by Southern blot analysis of genomic DNA obtained from a single sockeye salmon. The deduced amino acid sequences of the ssPOMC-A and -B contained 230 and 226 residues, respectively. The amino terminal of beta-endorphin in ssPOMC-B which corresponds to Met-enkephalin domain is YSGFM, which is different from YGGFM of Met-enkephalin found in many other vertebrate species. The homology of nucleotide sequences between ssPOMC-A and -B is 59% in the entire coding region, whereas alpha-MSH coding regions are highly homologous (91%). Although the deduced amino acid sequences of ssPOMs show 43% overall similarity, their hydropathy profiles are coincident with those of several other vertebrate species, particularly the amino terminal of N-terminal peptide (NPP) shows almost the same pattern with other vertebrate NPPs.

The human vasopressin-oxytocin gene family: no evidence for additional neurophysin-related genes

Over the last 20 years several observations at the peptide level have indicated the possible existence of additional members of the vasopressin (VP)-oxytocin (OT) gene family in mammals. In this study, the human genome was analyzed for the existence of genes structurally related to the VP and OT genes. Human genomic blots probed under low stringency conditions with exon B of the human OT gene, that codes for the conserved constant region of neurophysin, revealed the presence of two distinct bands in addition to the known VP and OT gene fragments. Five clones were obtained from a library of genomic EcoRI fragments ranging from 4-8 kb, that comprised both low stringency signals, by low stringency hybridization with the OT exon B probe. One clone of 7 kb hybridized at high stringency conditions to bands of the same size as previously detected with OT exon B on a human genomic blot. However, no similarity was observed between the open reading frames of this clone and the neurophysin portion of the OT gene. Another clone of 4.8 kb was identical to a fragment of the gene for the human bone morphogenetic factor hBMP-6, a member of the TGF-beta family. The hBMP-6 gene was not detected by low stringency hybridization of the human genomic blot with the OT exon B probe. No significant similarity was found between the amino acid sequences of human OT neurophysin and hBMP-6. Therefore, no evidence can be provided that the human genome contains additional neurophysin-related genes.(ABSTRACT TRUNCATED AT 250 WORDS)