Rat vasopressin and oxytocin genes are linked by a long interspersed repeated DNA element (LINE): sequence and transcriptional analysis of LINE

Molecular evolution of the neurohypophysial hormone precursors in mammals: Comparative genomics reveals novel mammalian oxytocin and vasopressin analogues

Among vertebrates the neurohypophysial hormones show considerable variation. However, in eutherian mammals they have been considered rather conserved, with arginine vasopressin (AVP) and oxytocin (OT) in all species except pig and some relatives, where lysine vasopressin replaces AVP. The availability of genomic data for a wide range of mammals makes it possible to assess whether these peptides and their precursors may be more variable in Eutheria than previously suspected. A survey of these data confirms that AVP and OT occur in most eutherians, but with exceptions. In a New-World monkey (marmoset, Callithrix jacchus) and in tree shrew (Tupaia belangeri), Pro(8)OT replaces OT, confirming a recent report for these species. In armadillo (Dasypus novemcinctus) Leu(3)OT replaces OT, while in tenrec (Echinops telfairi) Thr(4)AVP replaces AVP. In these two species there is also evidence for additional genes/pseudogenes, encoding much-modified forms of AVP, but in most other eutherian species there is no evidence for additional neurohypophysial hormone genes. Evolutionary analysis shows that sequences of eutherian neurohypophysial hormone precursors are generally strongly conserved, particularly those regions encoding active peptide and neurophysin. The close association between OT and VP genes has led to frequent gene conversion of sequences encoding neurophysins. A monotreme, platypus (Ornithorhynchus anatinus) has genes for OT and AVP, organized tail-to-tail as in eutherians, but in marsupials 3-4 genes are present for neurohypophysial hormones, organized tail-to-head as in lower vertebrates.

Cell-type specific expression of oxytocin and vasopressin genes: an experimental odyssey

The supraoptic nucleus (SON) is a particularly good model for the study of cell-type specific gene expression because it contains two distinct neuronal phenotypes, the oxytocin (OT) and vasopressin (AVP) synthesising magnocellular neurones (MCNs). The MCNs are found in approximately equal numbers and selectively express either the OT or the AVP gene in approximately 97% of the MCN population in the SON. An unresolved issue has been to determine what mechanisms are responsible for the highly selective regulation of the cell-type specific expression of OT and AVP genes in the MCNs. Previous attempts to address this question have used various bioinformatic and molecular approaches, which included using heterologous cell lines to study the putative cis-elements in the OT and AVP genes, and the use of OT and/or AVP transgenes in transgenic rodents. The data from all of the above studies identified a region < 0.6 kbp upstream of OT exon I and approximately 3 kb upstream of AVP exon I as being sufficient to produce cell-specific expression of the OT and AVP genes, respectively, although they failed to identify the specific cis-domains responsible for the MCN-specific gene expression. An alternative experimental approach to perform promoter deletion analysis in vivo (i.e. to use stereotaxic viral vector gene transfer into the SON to further dissect the cis-elements in the OT and AVP genes) will be described here. This in vivo method uses adeno-associated viral (AAV) vectors expressing OT-promoter deletion constructs and utilises the enhanced green fluorescent protein (EGFP) as the reporter. The AAV constructs are stereotaxically injected into the rat brain above the SON and, 2 weeks post injection, the rats are sacrificed and assayed for EGFP expression. Using this method, it has been possible to identify specific regions upstream of the transcription start site in the OT and AVP gene promoters that are responsible for conferring the cell-type specificity of the OT and AVP gene expression in the SON.

Transcriptomic analysis of the osmotic and reproductive remodeling of the female rat supraoptic nucleus

The supraoptic nucleus (SON) of the hypothalamus is an important integrative brain structure that coordinates responses to perturbations in water balance and regulates maternal physiology through the release of the neuropeptide hormones vasopressin and oxytocin into the circulation. Both dehydration and lactation evoke a dramatic morphological remodeling of the SON, a process known as function-related plasticity. We hypothesize that some of the changes seen in SON remodeling are mediated by differential gene expression, and have thus used microarrays to document global changes in transcript abundance that accompany chronic dehydration in female rats, and in lactation. In situ hybridization analysis has confirmed the differential expression of three of these genes, namely TNF-induced protein 6, gonadotropin-inducible transcription factor 1, and ornithine decarboxylase antizyme inhibitor 1. Comparison of differential gene expression patterns in male and female rats subjected to dehydration and in lactating rats has enabled the identification of common elements that are significantly enriched in gene classes with particular functions. Two of these are related to the requirement for increased protein synthesis and hormone delivery in the physiologically stimulated SON (translation initiation factor activity and endoplasmic reticulum-Golgi intermediate compartment, respectively), whereas others are consistent with the concept of SON morphological plasticity (collagen fibril organization, extracellular matrix organization and biogenesis, extracellular structure organization and biogenesis, and homophilic cell adhesion). We suggest that the genes coordinately regulated in the SON as a consequence of dehydration and lactation form a network that mediates the plastic processes operational in the physiologically activated SON.

Dopamine D1, D2 and mu-opioid receptors are co-expressed with adenylyl cyclase 5 and phosphodiesterase 7B mRNAs in striatal rat cells

Intracellular cAMP levels are regulated by cAMP synthesis and degradation rate. Nine isoforms of cAMP-synthesizing enzymes called adenylyl-cyclases (ACs) and eleven phosphodiesterases (PDEs) that degrade cyclic nucleotides have been identified. Both types of enzymes exhibit variations not only in their expression pattern distribution throughout the brain, but also in their regulatory characteristics. Different isoforms of ACs and PDEs may be co-expressed in a single cell, thus a gradient of cAMP intracellular levels is formed, which accounts for the diversity of cell responses. Among these isoforms, AC5 and PDE7B are highly expressed in striatum, where the cAMP pathway is implicated in diverse behavioural functions. Striatal AC5 is involved in drug reinforcing actions and motor activity. Less is known about the role of the PDE7B isoenzyme. We performed a double in situ hybridization analysis of the co-expression patterns of AC5 and PDE7B with mu-opioid-receptor (MOR), D1- and D2-receptor mRNAs to contribute to a better understanding in the regulation of cAMP levels under dopamine or opioidergic pathway activation in striatum. We found co-expression of AC5 and PDE7B mRNAs in caudate-putamen and nucleus accumbens; we also encountered that more than 50% of MOR, D2- and D1-expressing cells contained AC5 and PDE7B mRNAs. The presence of AC5 and PDE7B mRNAs in D1- and D2-containing cells suggests the participation of these enzymes in striatal functions involving dopaminergic pathways. Co-localization of both isoenzyme mRNAs with MOR expressing cells suggests their involvement in opioid reinforcing effects.

Sequence and organization of coelacanth neurohypophysial hormone genes: evolutionary history of the vertebrate neurohypophysial hormone gene locus

BACKGROUND

The mammalian neurohypophysial hormones, vasopressin and oxytocin are involved in osmoregulation and uterine smooth muscle contraction respectively. All jawed vertebrates contain at least one homolog each of vasopressin and oxytocin whereas jawless vertebrates contain a single neurohypophysial hormone called vasotocin. The vasopressin homolog in non-mammalian vertebrates is vasotocin; and the oxytocin homolog is mesotocin in non-eutherian tetrapods, mesotocin and [Phe2]mesotocin in lungfishes, and isotocin in ray-finned fishes. The genes encoding vasopressin and oxytocin genes are closely linked in the human and rodent genomes in a tail-to-tail orientation. In contrast, their pufferfish homologs (vasotocin and isotocin) are located on the same strand of DNA with isotocin gene located upstream of vasotocin gene separated by five genes, suggesting that this locus has experienced rearrangements in either mammalian or ray-finned fish lineage, or in both lineages. The coelacanths occupy a unique phylogenetic position close to the divergence of the mammalian and ray-finned fish lineages.

RESULTS

We have sequenced a coelacanth (Latimeria menadoensis) BAC clone encompassing the neurohypophysial hormone genes and investigated the evolutionary history of the vertebrate neurohypophysial hormone gene locus within a comparative genomics framework. The coelacanth contains vasotocin and mesotocin genes like non-mammalian tetrapods. The coelacanth genes are present on the same strand of DNA with no intervening genes, with the vasotocin gene located upstream of the mesotocin gene. Nucleotide sequences of the second exons of the two genes are under purifying selection implying a regulatory function. We have also analyzed the neurohypophysial hormone gene locus in the genomes of opossum, chicken and Xenopus tropicalis. The opossum contains two tandem copies of vasopressin and mesotocin genes. The vasotocin and mesotocin genes in chicken and Xenopus, and the vasopressin and mesotocin genes in opossum are linked tail-to-head similar to their orthologs in coelacanth and unlike their homologs in human and rodents.

CONCLUSION

Our results indicate that the neurohypophysial hormone gene locus has experienced independent rearrangements in both placental mammals and teleost fishes. The coelacanth genome appears to be more stable than mammalian and teleost fish genomes. As such, it serves as a valuable outgroup for studying the evolution of mammalian and teleost fish genomes.

Hypertension and exercise training differentially affect oxytocin and oxytocin receptor expression in the brain

We have previously shown that exercise training activates nucleus tractus solitarii (NTS) oxytocinergic projections, resulting in blunted exercise tachycardia. The objective of this study was to determine the effects of hypertension and training on oxytocin (OT) and OT receptor expression in the hypothalamic paraventricular nucleus (PVN) and projection areas (dorsal brain stem [DBS]). Male, normotensive, Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were trained (55% maximal exercise capacity, 3 months) or kept sedentary, and pressure was measured weekly. DBS sections were processed for immunohistochemistry (polyclonal guinea pig anti-OT) or in situ hybridization for OT and OT receptor (35S-oligonucleotide probes). Other groups of rats had brains removed and frozen to isolate the DBS and PVN; samples were processed for OT and OT receptor cDNA reverse transcription-polymerase chain reaction amplification with beta-actin as the housekeeping gene. Training was equally effective in improving running distance in both groups, with pressure reduction only in SHR (-10%, P<0.05). In trained WKY, baseline bradycardia (P<0.05) occurred simultaneously with increased NTS OT immunostaining and mRNA expression (+3.5-fold), without any change in OT receptor mRNA expression. PVN OT mRNA and DBS OT receptor mRNA expressions were significantly lower in SHR versus WKY (-39% and -56%, respectively). Training did not alter DBS OT receptor density in the SHR group but increased OT mRNA in both PVN and DBS areas (+78% and +45%, respectively). Our results show a marked hypertension-induced reduction in OT receptor mRNA expression, not altered by training. In contrast, training increased OT mRNA expression in sedentary and hypertensive rats, which may facilitate training-induced cardiac performance.

Comparison of genomic and cDNA sequences of guinea pig CYP2B18 and rat CYP2B2: absence of a phenobarbital-responsive enhancer module in the upstream region of the CYP2B18 gene

Potential mechanisms were investigated whereby CYP2B18, a cytochrome P450 gene exhibiting high constitutive expression but only low levels of phenobarbital-inducibility in the guinea pig liver, may be differentially regulated versus the highly inducible rat CYP2B2 gene. To comparatively assess potential regulatory sequences associated with CYP2B18, a guinea pig genomic library was screened enabling isolation of the CYP2B18 gene. The genomic screening process resulted in the identification of at least four closely-related CYP2B18 genes, designated here as CYP2B18A-D. Of these isolates, CYP2B18A exhibited sequence identical to that of the CYP2B18 cDNA. Further, the deduced amino acid sequence of the CYP2B18 cDNA was identical to that of N-terminal and internally-derived peptide sequences obtained in this investigation from CYP2B18 protein isolated from guinea pig liver. Genomic structural sequences were derived for CYP2B18A, together with the respective 5'-upstream and intronic regions of the gene. Comparison of the CYP2B18A and CYP2B2 gene sequences revealed the lack of repetitive LINE gene sequences in CYP2B18A, putative silencing elements that effect neighboring genes, although these sequences were present in both 5'-upstream and 3'-downstream regions of CYP2B2. We determined that the phenobarbital-responsive enhancer module was absent from the 5'-upstream region as well as the intronic regions of CYP2B18A gene. We hypothesize that the compromised phenobarbital inducibility of CYP2B18A stems from its lack of a functional phenobarbital responsive enhancer module.

Deciphering the mechanisms of homeostatic plasticity in the hypothalamo-neurohypophyseal system—genomic and gene transfer strategies

The hypothalamo-neurohypophyseal system (HNS) is the specialised brain neurosecretory apparatus responsible for the production of a peptide hormone, vasopressin, that maintains water balance by promoting water conservation at the level of the kidney. Dehydration evokes a massive increase in the regulated release of hormone from the HNS, and this is accompanied by a plethora of changes in morphology, electrical properties and biosynthetic and secretory activity, all of which are thought to facilitate hormone production and delivery, and hence the survival of the organism. We have adopted a functional genomic strategy to understand the activity dependent plasticity of the HNS in terms of the co-ordinated action of cellular and genetic networks. Firstly, using microarray gene-profiling technologies, we are elucidating which genes are expressed in the HNS, and how the pattern of expression changes following physiological challenge. The next step is to use transgenic rats to probe the functions of these genes in the context of the physiological integrity of the whole organism.

Neurone-specific expression and regulation of the pufferfish isotocin and vasotocin genes in transgenic mice

We used comparative genetics to investigate the location, structure and evolution of the oxytocin and vasopressin gene regulatory regions. The pufferfish, Fugu rubripes, is an attractive vertebrate model for comparison because of its maximal evolutionary distance from mammals and short intergenic regions. To determine whether regulatory DNA is conserved between oxytocin and vasopressin, and their Fugu homologs, isotocin and vasotocin, we generated transgenic mice bearing overlapping Fugu cosmids that contained the isotocin and/or vasotocin genes as well as short isotocin (5 kb) and vasotocin (9 kb) constructs. Our study shows that the Fugu isotocin and vasotocin genes express specifically in the mouse oxytocinergic and vasopressinergic neurones, respectively, and that the cis-regulatory elements which mediate neurone-specific expression are located within the short transgene constructs tested. Thus, the neurone-specific expression of the oxytocin and vasopressin gene families, and the mechanisms mediating the cell-specificity, evolved before the divergence of the fish and mammalian lineages. Salt-loading of transgenic mice induced an increase in abundance of isotocin, but not vasotocin mRNA in the cognate neurones. It appears that either the vasotocin gene does not respond to osmotic perturbations or the vasotocin transgene construct tested lacks osmotic response elements. Comparisons of homologous flanking sequences of the Fugu and mouse genes identified several short matching sequences, which are candidate regulatory elements.

Vasopressin-SV40 T antigen expression in transgenic mice induces brain tumor and lymphoma

In order to understand the importance of various cis-acting elements in regulating VP gene expression, transgenic mice regulated by VP constructs were produced containing 3.8 kb of the 5' flanking region and all the exons and introns in the mouse VP gene, which was fused at the end of exon 3 to an SV40 T antigen (Tag). In the transgenic mice by the pVPSV.IGR3.6 construct, all the six transgenic mice died at the age of 2-6 weeks. In the transgenic mice by pVPSV.IGR2.1, 21% of them had brain tumors at 5 weeks and 100% of the mice had brain tumors after 24 weeks. Histological analysis of the transgenic mice revealed primitive neuroectodermal tumors (PNET) in the brain and lymphoma in the spleen and lymph nodes. The phenotype differences between the two transgenic mice suggest that tissue-specific expression might be regulated by cis-acting elements in the 1.5-kb of the 3(') flanking region, which are not contained in pVPSV.IGR2.1. In conclusion, pVPSV.IGR2.1 mice will be a valuable mouse model system for investigating PNET tumorigenesis in the brain and lymphoma in the lymph nodes and spleen.

In vivo gene transfer studies on the regulation and function of the vasopressin and oxytocin genes

Novel genes can be introduced into the germline of rats and mice by microinjecting fertilized one-cell eggs with fragments of cloned DNA. A gene sequence can thus be studied within the physiological integrity of the resulting transgenic animals, without any prior knowledge of its regulation and function. These technologies have been used to elucidate the mechanisms by which the expression of the two genes in the locus that codes for the neuropeptides vasopressin and oxytocin is confined to, and regulated physiologically within, specific groups of neurones in the hypothalamus. A number of groups have described transgenes, derived from racine, murine and bovine sources, in both rat and mouse hosts, that mimic the appropriate expression of the endogenous vasopressin and genes in magnocellular neurones (MCNs) of the supraoptic and paraventricular nuclei. However, despite considerable effort, a full description of the cis-acting sequences mediating the regulation of the vasopressin-oxytocin locus remains elusive. Two general conclusions have nonetheless been reached. First, that the proximal promoters of both genes are unable to confer any cell-specific regulatory controls. Second, that sequences downstream of the promoter, within the structural gene and/or the intergenic region that separates the two genes, are crucial for appropriate expression. Despite these limitations, sufficient knowledge has been garnered to specifically direct the expression of reporter genes to vasopressin and oxytocin MCNs. Further, it has been shown that reporter proteins can be directed to the regulated secretory pathway, from where they are subject to appropriate physiological release. The use of MCN expression vectors will thus enable the study of the physiology of these neurones through the targeted expression of biologically active molecules. However, the germline transgenic approach has a number of limitations involving the interpretation of phenotypes, as well as the large cost, labour and time demands. High-throughput somatic gene transfer techniques, principally involving the stereotaxic injection of hypothalamic neuronal groups with replication-deficient adenoviral vectors, are now being developed that obviate these difficulties, and which enable the robust, long-lasting expression of biologically active proteins in vasopressin and oxytocin MCNs.

Further delineation of the sequences required for the expression and physiological regulation of the vasopressin gene in transgenic rat hypothalamic magnocellular neurones

We have introduced transgenes into rats with a view to defining genomic regions that mediate the cell-specific and physiological regulation of the vasopressin gene. These transgenes consist of the rat vasopressin structural gene with a reporter inserted into exon III, flanked by different lengths of upstream and downstream sequences. 11-VCAT-3 is flanked by 11 kbp of upstream sequences and 3 kbp of downstream sequences. The previously described 5-VCAT-3 is flanked by 5 kbp of upstream and 3 kbp of downstream sequences. 3-VCAT-3 has 3 kbp of upstream and 3 kbp of downstream sequences, and 3-VCAT-0.2 is flanked by 3 kbp of upstream and 0.2 kbp of downstream sequences. All four transgenes elicit the same expression patterns; low basal expression is seen in the magnocellular supraoptic and paraventricular nuclei, and is negligible in the suprachiasmatic nucleus. Expression increases markedly in vasopressin magnocellular cells following dehydration. The sequences responsible for the cell-specific expression and physiological regulation of our transgenes thus reside within the confines of the smallest construct studied, 3-VCAT-0.2.

Conophysin-R, a Conus radiatus venom peptide belonging to the neurophysin family

A novel Conus peptide, conophysin-R, was purified from the venom of Conus radiatus. The distinctive disulfide framework and sequence indicates that it is a member of the neurophysin peptide family. The complete sequence of the peptide is HPTKPCMYCSFGQCVGPHICCGPTGCEMGTAEANMCSEEDEDPIPCQVFGSDCALNNPDNIHGHCVADGICCVDDTCTTHLGCLThis is the first time a neurophysin-like peptide has been found in any venom. In addition, conophysin-R is the first neurophysin family member isolated and biochemically characterized from an invertebrate source.

The vasopressin gene non-canonical Hogness box: effect on protein binding and promoter function

Comparison of the promoter sequences of the genes encoding the neuropeptide hormone vasopressin from a number of organisms has revealed that they do not contain a classical Hogness box. In all vertebrate species examined, the canonical TATA box is replaced with a CATA sequence. We hypothesised that this conserved modified sequence may play a role in the regulation of vasopressin promoter activity. We used electrophoretic mobility shift assays to show that TATA and CATA sequences generate different complexes with SON nuclear proteins. Further, the transfection of wild-type (CATA) and mutated (TATA) VP promoter-reporter constructs into a heterologous cell line demonstrated a sequence-specific effect on transcriptional activity. The CATA sequence contributes to weaker promoter activity than a TATA box, but is able to interact with the upstream elements to increase the efficacy of an enhancer. The CATA box may thus be involved in the cell-specific and physiological regulation of the VP gene.

Vasopressin gene expression: experimental models and strategies

The intergenic region (IGR) separating the genes for vasopressin (VP) and oxytocin (OT) has been shown to be critical for the cell-specific expression of these peptide genes in hypothalamic neurons. To date, the most relevant information about the putative cis-elements in the IGR that might determine cell-specific gene expression has come from studies in transgenic models. As a first step toward increasing the efficiency of the IGR sequence deletion studies in transgenic animals, a comparative genomics approach comparing the IGR sequence in humans versus mice was used to identify conserved sequences that might be candidate regulatory elements. The nucleotide sequence of the IGR between the human VP and OT genes was determined and compared to the mouse IGR, and 26 conserved sequences in three distinct clusters were found. These conserved sequences and motifs may be important for the cell-specific expression of the VP and OT genes. However, before further significant progress can be made, a "high-throughput" method for the analysis of deletion constructs in relevant cell types in vitro is needed. It is proposed here that organotypic culture models combined with the use of particle-mediated gene transfer methods may provide an effective, general strategy for the study of cell-specific expression in the central nervous system.

Cell-specific expression and subcellular localization of neurophysin-CAT-fusion proteins expressed from oxytocin and vasopressin gene promoter-driven constructs in transgenic mice

The cell-specific expression of both the oxytocin (OT) and vasopressin (VP) genes in magnocellular neurons (MCNs) of the hypothalamus has been proposed to be under the control of cis-elements in an intergenic region downstream of the VP gene. We examined this hypothesis using transgenic mice containing mouse genomic DNA-derived constructs linked to chloramphenicol acetyltransferase (CAT) reporters. VP gene expression was studied using constructs containing 3.8 kbp of the 5' flanking region and all the exons and introns in the mouse VP gene, which was fused at the end of exon 3 to a CAT reporter. The two VP-transgene constructs differed by the lengths of their VP gene 3' flanking regions (2.1 versus 3.6 kbp). A similar construct for the oxytocin CAT transgene was used which contained the full-length (3.6 kbp) downstream intergenic region between the mouse genes. All three transgenic constructs produced cell-specific expression of the CAT-reporter in the magnocellular neurons as determined by CAT-immunoreactivity. Oxytocin transgene expression was restricted to OT cells in two founders, and the two VP transgenes to VP cells in five founders. Electron microscopic immunocytochemistry showed that the CAT fusion proteins produced from the OT- and VP-transgenes were efficiently trafficked through the regulated secretory pathways in their respective magnocellular neurons, packaged into large dense core vesicles, and transported to nerve terminals in the posterior pituitary.

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.

Salt-loading increases vasopressin and vasopressin 1b receptor mRNA in the hypothalamus and choroid plexus

The choroid plexus plays a pivotal role in the production of cerebrospinal fluid (CSF). Messenger RNA (mRNA) transcripts encoding arginine vasopressin (AVP) and the vasopressin 1b receptor (V(1b)R) are found in various structures of the central nervous system, including the choroid plexus. The present study measured AVP and V(1b)R mRNA production in response to plasma hyperosmolality. Compared to rats maintained on water, 2% salt-drinking rats had increased levels of AVP and V(1b)R mRNAs in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus and in the choroid plexus. The increase in V(1b)R mRNA in the SON and PVN as a result of plasma hyperosmolality may reflect changes in receptor production that, in turn, have a role in AVP autoregulation of hypothalamic magnocellular neurons. The increase of AVP and V(1b)R mRNAs in the choroid plexus further shows the involvement of AVP in the regulation of brain water content and cerebral edema.

Species- and tissue-specific physiological regulation of vasopressin mRNA poly(A) tail length

Transgenic experiments can be used to test the extent to which genes from different species can be swapped around, but still retain function, and be appropriately regulated. A vector has been developed that directs the expression of foreign genes to specific groups of vasopressin (VP) hypothalamic neurons in transgenic rats. Using this vector, we have expressed the bovine VP (bVP) RNA in the rat brain. In contrast to the situation in a mouse host, but like its endogenous rat counterpart, the mRNA encoded by the bVP transgene is subject to posttranscriptional physiological regulation in the hypothalamus; its poly(A) tail dramatically lengthens as a consequence of 3 days of dehydration. Transgene expression is also seen in the adrenal cortex, but here, despite a marked increase in transgene RNA levels with dehydration, there is no change in poly(A) tail length. These data suggest that the mouse hypothalamus and the rat adrenal gland do not have the transcript recognition or enzymatic machinery required for the physiologically responsive poly(A) tail length modulation seen in the rat brain.

Differential regulation of vasopressin gene expression in the hypothalamus of endotoxin-treated 14-day-old rat

The E. coli endotoxin 0111 B4, a lipopolysaccharide (LPS), in a dose of 200 ng/kg body weight/50 microl artificial cerebrospinal fluid (CSF) was given intracisternally to 14-day-old rats. Four hours later CSF, blood and urine were sampled, and consecutive brain sections from the hypothalamic area of the brain were prepared for in situ hybridization. The LPS treatment resulted in a significant (p<0.001) pleocytosis and an elevation of the protein content of the CSF. There were no changes observed in the chemical parameters of the CSF, plasma, blood or urine, i.e. vasopressin (VP) levels, osmolality, Na+ and K+ concentrations, glucose level, pH, bicarbonate or PaCO2, PaO2 values. LPS injection, however, resulted in a significantly (p<0.01) increased VP mRNA level (121% of the control value) in the supraoptic nuclei (SON), but not in the paraventricular nuclei (PVN), as compared to controls. Our findings suggest an early effect of LPS on VP gene expression selectively in the SON of 14-days-old rats. This animal model might be suitable for studying the regulation of VP gene expression and the role of this peptide in the pathogenesis of bacterial meningitis in pediatric patients.

Something fishy in the rat brain: molecular genetics of the hypothalamo-neurohypophysial system

The brain peptides vasopressin and oxytocin play crucial roles in the regulation of salt and water balance. The genes encoding these neurohormones are regulated by cell-specific and physiological cues, but the molecular mechanisms remain obscure. New strategies, involving the introduction of rat transgenes into rats, are being used to address these issues, but the complexity of the rat genome has hampered progress. By contrast, the pufferfish, Fugu rubripes, has a "junk-free" genome. The oxytocin homologue from Fugu, isotocin, has been introduced into rats and is expressed in oxytocin neurons, where it is upregulated by physiological perturbations that upregulate the oxytocin gene. The Fugu and rat lineages separated 400 million years ago, yet the mechanisms that regulate the isotocin and oxytocin genes have been conserved. Fugu genome analysis and transgenesis in the physiologically tractable rat host are a powerful combination that will enable the identification of fundamental components of the neural systems that control homeostasis.

Ontogeny of the vasopressin and oxytocin RNAs in the mouse hypothalamus

The single-copy genes encoding the vasopressin and oxytocin prepropeptides are closely linked in mouse genome, being separated by an intergenic region of only 3 kbp. These genes are expressed in anatomically defined hypothalamic neurons--in the adult rodent, vasopressin is synthesised in the paraventricular nucleus and the supraoptic nucleus, and in the dorsomedial region of the suprachiasmatic nucleus, whilst oxytocin is expressed in the supraoptic nucleus and paraventricular nucleus, but not in the suprachiasmatic nucleus. The molecular mechanisms that mediate the cell-specific and developmental expression patterns of the two transcription units within the vasopressin-oxytocin locus remain to be elucidated. As a first step in this process, we have used in situ hybridisation to study the expression of the RNAs encoded by the linked vasopressin and oxytocin genes during the development of the mouse hypothalamus. We have revealed a hierarchy of gene activation events, with vasopressin first being observed in presumptive supraoptic nucleus at day 13.5, and in the paraventricular at day 14.5. Oxytocin is seen first in the paraventricular at day 15.5; expression in the supraoptic nucleus is clearly seen at day 18.5. As early as day 15.5, the vasopressin and oxytocin RNAs are expressed in different groups of neurons.

Round-spotted pufferfish (Tetraodon fluviatilis) snf5 gene is oriented in a tail-to-tail manner with the set gene which encodes an inhibitor of protein phosphatase 2A

The round-spotted pufferfish Tetraodon fluviatilis has a genome size of 380 Mb which is slightly smaller than that of another pufferfish Fugu rubripes rubripes (Fugu). Due to its compact genome and small introns, Fugu has been introduced as a model for genome studies. Recently, the round-spotted pufferfish has also been proposed as a new model for genome studies because of the ease in obtaining material and high-sequence homology to that of Fugu. In this study, we have cloned and characterized the snf5 and set genes from the round-spotted pufferfish. The snf5 gene is composed of 9 exons spanning about 2.9 kb whereas the set gene consists of 8 exons spanning about 2.7 kb. They are linked in a tail-to-tail manner with an intergenic region of about 6.5 kb. So far, the genomic structures of human snf5 and set genes are unknown. Based on our data, the pufferfish SNF5 and SET display high amino acid sequence identity (>90%) with the respective human genes. By primer extension and sequence analysis, we found that putative promoter region of the snf5 gene contains a typical TATA box and numerous potential binding sites for transcription factors including AP1, AP2, AP3, c-Myb, HNF-5, and NF-IL6. As for the set gene, its promoter region does not have any TATA or CCAAT motif and contains a few potential binding sites for transcriptional factors such as c-Myb and gamma-IRE. When these promoter regions were placed upstream of the CAT reporter gene and transfected into a carp CF cell line, the 5'-upstream 1.6-kb DNA fragment of the snf5 gene displayed stronger promoter activity, approximately three-fold higher than that of the 5'-upstream 1.3 kb DNA fragment of the set gene. By transient expression and immunofluorescent staining, we also showed that the pufferfish SNF5 and SET are nuclear proteins, consistent with their postulated roles as transcriptional factors.

Widespread expression and estrogen regulation of PPEIA-3' nuclear RNA in the rat brain

We previously identified a novel nuclear RNA species derived from the preproenkephalin (PPE) gene. This transcript, which we have named PPEIA-3' RNA, hybridizes with probes directed at a region of PPE intron A downstream of an alternative germ-cell transcription start site, but does not contain PPE protein coding sequences. We now report that estrogen treatment of ovariectomized rats increases the expression of conventional PPE heteronuclear RNA, and also induces the expression of PPEIA-3' RNA, apparently in separate cell populations within the ventromedial nucleus of the hypothalamus. Further, we show that cells expressing PPEIA-3' are found in several neuronal groups in the rat forebrain and brainstem, with a distinct topographical distribution. High densities of PPEIA-3' containing cells are found in the reticular thalamic nucleus, the basal forebrain, the vestibular complex, the deep cerebellar nuclei, and the trapezoid body, a pattern that parallels the distribution of atypical nuclear RNAs described by other groups. These results suggest that this diverse neuronal population shares a common set of nuclear factors responsible for the expression and retention of this atypical RNA transcript. The implication of these results for cell-specific gene transcription and regulation in the brain and the possible relationship of PPEIA-3' RNA and other atypical nuclear RNAs is discussed.

Transgenic rats reveal functional conservation of regulatory controls between the Fugu isotocin and rat oxytocin genes

We have asked whether comparative genome analysis and rat transgenesis can be used to identify functional regulatory domains in the gene locus encoding the hypothalamic neuropeptides oxytocin (OT) and vasopressin. Isotocin (IT) and vasotocin (VT) are the teleost homologues of these genes. A contiguous stretch of 46 kb spanning the Fugu IT-VT locus has been sequenced, and nine putative genes were found. Unlike the OT and vasopressin genes, which are closely linked in the mammalian genome in a tail-to-tail orientation, Fugu IT and VT genes are linked head to tail and are separated by five genes. When a cosmid containing the Fugu IT-VT locus was introduced into the rat genome, we found that the Fugu IT gene was specifically expressed in rat hypothalamic oxytocinergic neurons and mimicked the response of the endogenous OT gene to an osmotic stimulus. These data show that cis-acting elements and trans-acting factors mediating the cell-specific and physiological regulation of the OT and IT genes are conserved between mammals and fish. The combination of Fugu genome analysis and transgenesis in a mammal is a powerful tool for identifying and analyzing conserved vertebrate regulatory elements.

A systematic survey of the intergenic region between the murine oxytocin- and vasopressin-encoding genes

The genomic region between the oxytocin (OT) and vasopressin (VP) genes in the two strains of mice was independently sequenced by our two groups. In this report, we present our collated sequence data and analyses. The mouse intergenic region (MUIGR) was aligned to that of the rat, which has been reported to contain 6.4-kb long interspersed nuclear element (LINE). The MUIGR sequences in the two mice strains did not contain any LINE sequences. This suggests that the approximately 3.5-kb sequence that is conserved between the rat and mouse intergenic regions is likely to be involved in the regulation of OT and VP expression. We also observed several conserved putative transcription factor recognition sequences. Analysis of the MUIGR revealed the lack of any significant ORFs, but the presence of several repetitive elements.

Selective binding of specific mouse genomic DNA fragments by mouse vimentin filaments in vitro

Mouse vimentin intermediate filaments (IFs) reconstituted in vitro were analyzed for their capacity to select certain DNA sequences from a mixture of about 500-bp-long fragments of total mouse genomic DNA. The fragments preferentially bound by the IFs and enriched by several cycles of affinity binding and polymerase chain reaction (PCR) amplification were cloned and sequenced. In general, they were G-rich and highly repetitive in that they often contained Gn, (GT)n, and (GA)n repeat elements. Other, more complex repeat sequences were identified as well. Apart from the capacity to adopt a Z-DNA and triple helix configuration under superhelical tension, many fragments were potentially able to form cruciform structures and contained consensus binding sites for various transcription factors. All of these sequence elements are known to occur in introns and 5'/3'-flanking regions of genes and to play roles in DNA transcription, recombination and replication. A FASTA search of the EMBL data bank indeed revealed that sequences homologous to the mouse repetitive DNA fragments are commonly associated with gene-regulatory elements. Unexpectedly, vimentin IFs also bound a large number of apparently overlapping, AT-rich DNA fragments that could be aligned into a composite sequence highly homologous to the 234-bp consensus centromere repeat sequence of gamma-satellite DNA. Previous experiments have shown a high affinity of vimentin for G-rich, repetitive telomere DNA sequences, superhelical DNA, and core histones. Taken together, these data support the hypothesis that, after penetration of the double nuclear membrane via an as yet unidentified mechanism, vimentin IFs cooperatively fix repetitive DNA sequence elements in a differentiation-specific manner in the nuclear periphery subjacent to the nuclear lamina and thus participate in the organization of chromatin and in the control of transcription, replication, and recombination processes. This includes aspects of global regulation of gene expression such as the position effects associated with translocation of genes to heterochromatic centromere and telomere regions of the chromosomes.

Bovine oxytocin transgenes in mice. Hypothalamic expression, physiological regulation, and interactions with the vasopressin gene

To gain insights into the molecular mechanisms that restrict the expression of the oxytocin gene to anatomically defined groups of neurons in the hypothalamus, we generated transgenic mice bearing bovine oxytocin genomic fragments. Appropriate neuron-specific and physiological regulation was observed in mice bearing transgene bOT3.5, which consists of the oxytocin structural gene flanked by 0.6 kilobase pair (kbp) of upstream and 1.9 kbp of downstream sequences. bOT3.5 is expressed in oxytocin magnocellular neurons in the mouse supraoptic nucleus and paraventricular nucleus, but transgene RNAs are excluded from vasopressin neurons. Replacement of the drinking diet of the transgenic mice with 2% (w/v) NaCl for 7 days significantly increased the abundance of bovine oxytocin transcripts in the supraoptic nucleus, but not in the paraventricular nucleus, in parallel with the endogenous mouse oxytocin RNA. Surprisingly, mimicry of the endogenous oxytocin gene expression pattern was lost with larger transgenes. Addition of 0.7 kbp of contiguous downstream sequences (transgene bOT) or linkage to the bovine vasopressin gene (transgene VP-B/bOT3.5) repressed hypothalamic expression. No mice were derived bearing transgene bOT6.4, which consists of the oxytocin structural gene flanked by 3 kbp of upstream and 2.6 kbp of downstream sequences, suggesting that the presence of this DNA is detrimental to normal embryonic development. These data suggest that while bOT3.5 contains sufficient cis-acting sequences to mediate expression to particular subsets of hypothalamic neurons, the overall regulation of the oxytocin gene is governed by multiple interacting enhancers and repressors.

Cell specific expression of a vasopressin transgene in rats

A transgene consisting of the rat vasopressin structural gene containing a reporter in exon III, flanked by 5 kb of upstream and 3 kb of downstream sequences, is expressed in vasopressinergic, but not oxytocinergic, magnocellular neurons of rats. Functionally appropriate physiological stimuli increase transgene expression in magnocellular neurons in an exaggerated fashion; the magnitude of the transgene response to osmotic challenge exceeds that of the endogenous gene by 10-15 fold. Magnocellular vasopressinergic neurons in the rat are now accessible to rational and precise genetic perturbation of function and regulation.

Nucleotide sequence and genomic structure of duck acyl-CoA binding protein/diazepam-binding inhibitor: co-localization with S-acyl fatty acid synthase thioesterase

A computer-aided homology search of the GenBank nucleotide database using the amino acid sequence of human acyl CoA-binding protein (ACBP)/diazepam-binding inhibitor (DBI)-endozepine as a probe revealed that a genomic fragment containing the gene encoding the mallard duck (Anas platyrhynchos) S-acyl fatty acid synthase thioesterase also contains sequences which encode the duck homolog of ACBP/DBI. The duck ACBP/DBI gene is positioned downstream of the thioesterase gene in a tail-to-tail orientation separated from the 3' end of the thioesterase gene by only several hundred nucleotides. Three exons were identified that have strong homology to the published cDNA sequences of human and bovine ACBP/DBI. These exons define all of the coding region except for the amino-terminal domain, which was subsequently cloned by polymerase chain reaction (PCR) amplification. The encoded amino acid sequence of the duck ACBP/DBI is 62-68% homologous to mammalian ACBP/DBI sequences. While the mammalian ACBP/DBI is expressed mainly in the liver, with smaller amounts in the brain and heart, mRNA transcripts of duck ACBP/DBI were detected only in the brain with no evidence for expression in the liver or heart. The close proximity of the genes for ACBP/DBI and S-acyl fatty acid synthase thioesterase raises the possibility of co-regulation of expression.

DNA sequences tightly bound to proteins in mouse chromatin: identification of murine MER sequences

The finding of stably (tightly) associated DNA-protein complexes in eukaryotic chromatin has provoked many hypotheses and speculations concerning their possible role. While the answer of this question is not envisaged yet, it is clear that elucidation of the nature of the individual components involved in such complexes is a necessary step in this direction. Here, the nature of several mouse DNA sequences in the vicinity of a putative stably attached protein is studied. Eight independently isolated clones containing such sequences were compared to known sequences in GenBank. Two clones were found to belong to different subfamilies of repetitive sequences, organized into a larger family--the L1md family. One clone harbors a sequence that is a member of the Alu-type family. Four of the cloned sequences are preset in low copy numbers, but the computer search found similar sequences in various genomic regions of different rodents. These facts, together with the finding that regions homologous to the above clones often flank other repetitive elements in the genome, suggest that the cloned sequences belong to new, not yet described families of repeats in the murine genome. It is possible that they correspond to the medium reiteration frequency sequences, MER-sequences, discovered recently in the human genome (Jurka, 1990; Kaplan and Duncan, 1990). Particularly intriguing is the homology found at the integration sites of polyoma virus in two transformed cell lines with two of these clones.

Two orphan receptors binding to a common site are involved in the regulation of the oxytocin gene in the bovine ovary

The peptide hormone oxytocin is highly expressed in the hypothalamus within only a small number of magnocellular neurons. However, it is also expressed in a much larger number of cells in the bovine corpus luteum at high levels in an estrous cycle-dependent manner. By using nuclear extracts from this tissue for in vitro binding studies, two protein complexes have been shown to bind to a common site in the bovine oxytocin promoter. One of these proteins has been identified as the bovine homologue of the chicken ovalbumin upstream promoter transcription factor (COUP-TF). The second protein is here characterized as the bovine homologue of a tissue-specific transcription factor, steroidogenic factor 1 (SF-1). The relative expression of these two factors during luteal development correlates with the level of luteal oxytocin gene expression, with SF-1 being the factor binding to the promoter of the oxytocin gene when this promoter is activated. Cotransfection experiments using the murine testicular cell line TM4 show that SF-1 can stimulate the expression of a transfected oxytocin gene, suggesting that SF-1 may be involved in upregulation of the oxytocin gene in vivo, possibly by transducing a stimulatory signal to the RNA polymerase.

Cell-specific expression of preproenkephalin intronic heteronuclear RNA in the rat forebrain

Using in situ hybridization with multiple probes to the rat preproenkephalin gene, we have identified a novel population of cells in the reticular thalamic nucleus and basal forebrain which express RNA derived from the preproenkephalin gene. These cells contain nuclear RNA from downstream of an alternate transcription start site in intron A of the preproenkephalin gene (Kilpatrick et al., Mol. Cell Biol., 10 (1990) 3717-3726), while in the same cells preproenkephalin exon 2 RNA is undetectable. The results suggest that in this population of cells, preproenkephalin gene transcription initiates from the intron A initiation site, and is regulated by an additional mechanism which results in the accumulation of nuclear preproenkephalin intron A-derived heteronuclear RNA. The anatomical distribution of these cells indicates that they may be involved in the control of cerebral cortical function.

Neuropeptide gene expression in transgenic animals

Transgenic animal techniques offer today's neuroscientist the ability to experimentally manipulate neurosecretory systems with a precision undreamt of by our predecessors. The range of techniques now available, building as it does on our growing knowledge of physiological systems at the inter- and intercellular level, allows us to critically define molecular lesions and ask about their consequences to the whole organism. Neuroscientist should grasp the opportunities afforded by these recent developments.