Arginine Vasopressin-neurophysin II Research Articles

Diabetes: Candidate Genes and Its Variants

Diabetes being one the fastest occurring disease globally and leading to the increase in death rates. In this review we identified the prevalence, epidemiology, types, diagnosis, management and mainly focusing on all the genes and their variants responsible for diabetes mellitus and diabetes insipidus studied and found till date. It was found that there are 18 regions/60 genes are involved in Type 1 diabetes mellitus (T1D) by use of genome-wide association study (GWAS) studies combined with new technologies such as Single nucleotide polymorphisms (SNPs) array genotyping, meta-analysis, taq sequencing etc. The gene that have higher risk in developing T1D is found to be in the region of Insulin dependent diabetes mellitus 1 (IDDM1) containing Human leukocyte antigens (HLA) gene and it’s haplotypes HLA-DQ, HLA-DR, and HLA-DP while several other genes has been also discussed but the mechanisms of pathogenesis still unclear. In Type 2 diabetes mellitus (T2D) many genes have been put forward as candidate genes through (GWAS) and large meta-analysis, but only few susceptibility genes have shown convincing association in several studies, includes Peroxisome Proliferator-Activated Receptor-γ (PPARG γ), Potassium Inwardly Rectifying Channel Subfamily J Member 11( KCNJ11), Transcription Factor7-Like 2 (TCF7L2) and WFS1.In contrast gene responsible for hereditary, central and nephrogenic diabetes insipidus are mutated Arginine Vasopressin-Neurophysin II (AVP-NPII) gene and either The Arginine Vasopressin Receptor 2 (AVPR2) or Aquaporin 2 (AQP2) gene respectively and studied through sequence analysis.

Functional analyses of three different mutations in the AVP-NPII gene causing familial neurohypophyseal diabetes insipidus.

Familial neurohypophyseal diabetes insipidus (FNDI), a rare disorder, which is clinically characterized by polyuria and polydipsia, results from mutations in the arginine vasopressin-neurophysin II (AVP-NPII) gene. The aim of this study was to perform functional analyses of three different mutations (p.G45C, 207_209delGGC, and p.G88V) defined in the AVP-NPII gene of patients diagnosed with FNDI, which are not included in the literature. For functional analysis studies, the relevant mutations were created using PCR-based site-directed mutagenesis and restriction fragment replacement strategy and expressed in Neuro2A cells. AVP secretion into the cell culture medium was determined by radioimmunoassay (RIA) analysis. Fluorescence imaging studies were conducted to determine the differences in the intracellular trafficking of wild-type (WT) and mutant AVP-NPII precursors. Molecular dynamics (MD) simulations were performed to determine the changing of the conformational properties of domains for both WT and 207-209delGGC mutant structures and dynamics behavior of residues. Reduced levels of AVP in the supernatant culture medium of p.G45C and p.G88V transfected cells compared to 207_209delGGC and WT cells were found. Fluorescence imaging studies showed that a substantial portion of the mutant p.G45C and p.G88V AVP-NPII precursors appeared to be located in the endoplasmic reticulum (ER), whereas 207_209delGGC and WT AVP-NPII precursors were distributed throughout the cytoplasm. The mutations p.G45C and p.G88V cause a failure in the intracellular trafficking of mutant AVP-NPII precursors. However, 207_209delGGC mutation does not result in impaired cellular trafficking, probably due to not having any significant effect in processes such as the proper folding, gain of three-dimensional structure, or processing. These results will provide valuable information for understanding the influence of mutations on the function of the AVP precursor hormone and cellular trafficking. Therefore, this study will contribute to elucidate the mechanisms of the molecular pathology of AVP-NPII mutations.

Autosomal dominant familial neurohypophyseal diabetes insipidus caused by a novel nonsense mutation in AVP-NPII gene.

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare single-gene disorder caused by mutations of the arginine vasopressin-neurophysin II (AVP-NPII) gene. These changes impair the release of vasopressin from the posterior pituitary gland. In the present study, the AVP-NPII gene of a Chinese adult patient with central diabetes insipidus, the patient's symptomatic mother and an asymptomatic sister of the patient was sequenced. Examination of the family history revealed cases of FNDI across four generations. Gene sequencing analysis revealed a novel heterozygous mutation, c.268A>T (p.Lys90Ter), in exon 2 of the AVP-NPII gene, in the patient and the patient's mother, which led to the loss of 6 cysteine residues and aberrant disulfide bonds, which is predicted to alter the mature protein structure. The present study identified a novel heterozygous nonsense mutation of the AVP-NPII gene associated with FNDI, which broadens the spectrum of known mutations associated with this disorder and contributes to the understanding of its molecular basis.

Identification of five novel arginine vasopressin gene mutations in patients with familial neurohypophyseal diabetes insipidus.

Familial neurohypophyseal diabetes insipidus(FNDI) is a genetic disorder presenting with polyuria and polydipsia and is caused by mutations in the arginine vasopressin-neurophysinII(AVP-NPII) gene. The clinical manifestations of this disorder vary greatly depending on different mutations. The present study reports the genetic, clinical and biochemical characteristics of patients with FNDI caused by five novel mutations. Ten patients encompassing two pedigrees and four individual cases diagnosed with FNDI were included. Biochemical markers and magnetic resonance imaging(MRI) were evaluated and genomic DNA was sequenced. The results revealed that age at onset ranged from 1.0to 11.0years. Daily urine volumes ranged from 2.0to 12.0liters. One patient had mental retardation and three patients had puberty retardation; one patient had nausea, vomiting and mental retardation; and two patients had fever. Treatments, if given, included desmopressin and vasopressin tannate. Posterior pituitary T1-weighted MRI high-intensity signals were absent in two cases and present in four cases. Sequencing revealed five novel mutations in the AVP-NPII gene. On the whole, the findings of the present study indicate that FNDI exhibits different clinical manifestations and a diverse age at onset. Posterior pituitary MRI does not provide a definite diagnosis of FNDI. We also identified five novel AVP-NPII mutations. Thus, an enhanced understanding of FNDI pathogenesis may provide a basis for the development of presymptomatic FNDI diagnotic tools.

AVP-NPII gene mutations and clinical characteristics of the patients with autosomal dominant familial central diabetes insipidus.

Familial central diabetes insipidus (DI), usually an autosomal dominant disorder, is caused by mutations in arginine vasopressin-neurophysin II (AVP-NPII) gene that leads to aberrant preprohormone processing and gradual destruction of AVP-secreting cells. To determine clinical and molecular characteristics of patients with familial central DI from two different Turkish families. The diagnosis of central DI was established by 24-h urine collection, water deprivation test, and desmopressin challenge. To confirm the diagnosis of familial central DI, the entire coding region of AVP-NPII gene was amplified and sequenced. A total of eight affected patients and three unaffected healthy relatives from two families were studied. Genetic analysis revealed a previously reported heterozygous mutation (p.C98X) in family A, and a heterozygous novel mutation (p.G45C) in family B, both detected in exon 2 of AVP-NPII gene. When we compared the clinical characteristics of the two families, it was noticed that as the age of onset of symptoms in family A ranges between 4 and 7years, it was <1year in family B. Additionally, pituitary bright spot was present in the affected siblings, but absent in their affected parents. Familial central DI is a progressive disease, and age of onset of symptoms can differ depending on the mutation. Bright spot on pituitary MRI might be present at onset, but become invisible over time. Genetic testing and appropriate counseling should be given in familial cases of central DI to ensure adequate treatment, and to avoid chronic water deprivation that might result in growth retardation in childhood.

A missense mutation in the arginine‐vasopressin neurophysin‐II gene causes autosomal dominant neurohypophyseal diabetes insipidus in a Chinese family

Familial neurohypophyseal diabetes insipidus, an autosomal dominant disorder, is mostly caused by mutations in the genes that encode AVP or its intracellular binding protein, neurophysin-II. The mutations lead to aberrant preprohormone processing and progressive destruction of AVP-secreting cells, which gradually manifests a progressive polyuria and polydipsia during early childhood, and a disorder of water homeostasis. We characterized the clinical and biochemical features, and sequenced the AVP neurophysin-II(AVP-NPII) gene of the affected individuals with autosomal dominant neurohypophyseal diabetes insipidus(ADNDI)to determine whether this disease was genetically determined. We obtained the histories of eight affected and four unaffected family individuals. The diagnosis of ADNDI was established using a water deprivation test and exogenous AVP administration. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified using polymerase chain reaction and sequenced. The eight affected individuals showed different spectra of age of onsets (7-15 years) and urine volumes (132-253 ml/kg/24 h). All affected individuals responded to vasopressin administration, with a resolution of symptoms and an increase in urine osmolality by more than 50%. The characteristic hyperintense signal in the posterior pituitary on T1-weighted magnetic resonance imaging was absent in six family members and present in one. Sequencing analysis revealed a missense heterozygous mutation 1516G > T (Gly17Val) in exon 2 of the AVP-NPII gene among the ADNDI individuals. We identified a missense mutation in the AVP-NPII gene and the same mutation showed different spectra of age of onsets and urine volumes in a new Chinese family with ADNDI. The mutation may provide a molecular basis for understanding the characteristics of NPII and add to our knowledge of the pathogenesis of ADNDI, which would allow the presymptomatic diagnosis of asymptomatic subjects.

Mutations in the AVPR2, AVP-NPII, and AQP2 genes in Turkish patients with diabetes insipidus

The aim of this study was to identify mutations in three different genes, the arginine-vasopressin-neurophysin II (AVP-NPII) gene, the arginine-vasopressin receptor 2 (AVPR2) gene, and the vasopressin-sensitive water channel aquaporin-2 (AQP2) gene in Turkish patients affected by central diabetes insipidus or nephrogenic diabetes insipidus. This study included 15 patients from unrelated families. Prospective clinical data were collected for all patients including the patients underwent a water deprivation-desmopressin test. The coding regions of the AVPR2, AQP2, and AVP-NPII genes were amplified by polymerase chain reaction and submitted to direct sequence analysis. Of the 15 patients with diabetes insipidus referred to Gulhane Military Medical Academy, Department of Endocrinology and Metabolism, eight patients have AVPR2 mutations, five patients have AQP2 mutations and two patients have AVP-NPII mutations. Of the patients, which have AVPR2 mutations, one is compound heterozygous for AVPR2 gene. Seven of these mutations are novel. Comparison of the clinical outcomes of these mutations may facilitate in understanding the functions of AVP-NPII, AQP2, and AVPR2 genes in future studies.

Clinical and molecular analysis of a Chinese family with autosomal dominant neurohypophyseal diabetes insipidus associated with a novel missense mutation in the vasopressin–neurophysin II gene

The objective of this study is to identify the genetic defects in a Chinese family with autosomal dominant familial neurohypophyseal diabetes insipidus. Complete physical examination, fluid deprivation, and DDAVP tests were performed in three affected and three healthy members of the family. Genomic DNA was extracted from leukocytes of venous blood of these individuals for polymerase chain reaction amplification and direct sequencing of all three coding exons of arginine vasopressin-neurophysin II (AVP-NPII) gene. Seven members of this family were suspected to have symptomatic vasopressin-deficient diabetes insipidus. The water deprivation test in all the patients confirmed the diagnosis of vasopressin-deficient diabetes insipidus, with the pedigree demonstrating an autosomal dominant inheritance. Direct sequence analysis revealed a novel mutation (c.193T>A) and a synonymous mutation (c.192C>A) in the AVP-NPII gene. The missense mutation resulted in the substitution of cysteine by serine at a highly conserved codon 65 of exon 2 of the AVP-NPII gene in all affected individuals, but not in unaffected members. We concluded that a novel missense mutation in the AVP-NPII gene caused neurohypophyseal diabetes insipidus in this family, due to impaired neurophysin function as a carrier protein for AVP. The Cys65 is essential for NPII in the formation of a salt bridge with AVP. Presence of this mutation suggests that the portion of the neurophysin peptide encoded by this sequence is important for the normal expression of vasopressin.

Identification of a novel mutation in the arginine vasopressin-neurophysin II gene affecting the sixth intrachain disulfide bridge of the neurophysin II moiety

Most mutations of the arginine vasopressin-neurophysin II (AVP-NPII) gene cause autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI). Such mutations are predicted to alter the three-dimensional structure of the prohormone, which accumulates in the cell body, ultimately leading to neuronal degeneration and hormonal deficit. In this study we describe the case of a 26-year-old female reporting a long-lasting history of polyuria/polydipsia. The father of the patient was affected by diabetes insipidus and was under desmopressin treatment until the time of his death. Nevertheless, the patient had never been subjected to endocrine evaluation. Clinical and genetic studies were performed. An 8-h fluid deprivation test plus desmopressin challenge and a 5% saline solution test were performed, in order to confirm the diagnosis. DNA was extracted from peripheral blood lymphocytes and subjected to direct sequencing of the entire coding region of the AVP-NPII gene. Clinical assessment of the patient confirmed the diagnosis of neurohypophyseal diabetes insipidus. Desmopressin treatment was started, which effectively reversed the polyuria/ polydipsia syndrome. Genetic analysis revealed a novel mutation (1665T>A) in exon 2 of the AVP-NPII gene, disrupting one of the disulfide bonds present in the NPII moiety which play a fundamental role in determining the proper folding of the molecule. In summary, in the present study we have described a novel mutation of the AVP-NPII gene, which is consistent with the malfolding/toxicity hypothesis underlying the pathogenesis of adFNDI.

A missense mutation encoding Cys73Phe in neurophysin II is associated with autosomal dominant neurohypophyseal diabetes insipidus

Autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) is an inherited disease caused by progressive deficiency of the hormone arginine vasopressin (AVP) that typically becomes clinically apparent in the first decade of life. The genetic locus of ADNDI is the arginine vasopressin-neurophysin II (AVP-NPII) gene and mutations that cause ADNDI have been found in the nucleotides encoding the signal peptide, vasopressin, and neurophysin II peptides. In this study we have analyzed the AVP-NPII gene in a 20-year-old female who was diagnosed with ADNDI at 2 years of age. A heterozygous missense mutation (1684G>T) was found in exon 2 that predicts replacement of cysteine with phenylalanine at position 73 of neurophysin II. The mutation was confirmed by subcloning exon 2 PCR products to sequence each allele independently. Two out of four clones were found to have the missense mutation and two have the normal sequence, confirming the presence of the mutation and heterozygosity. Neurophysin II is an intracellular carrier protein for AVP during axonal transport from the hypothalamus to the posterior pituitary and contains 14 cysteine residues forming 7 disulfide bonds. This mutation is predicted to disrupt the disulfide bridge between Cys73 and Cys61 within the neurophysin II moiety. This finding of a novel mutation substituting cysteine with phenylalanine in one AVP-NPII gene allele supports the hypothesis that inability to form normal disulfide bonds in neurophysin II leads to ADNDI.

A Patient with Familial Diabetes Insipidus and Idiopathic Hypoparathyroidism.

A 17 9/12-year-old female with familial diabetes insipidus (FDI) and idiopathic hypoparathyroidism is described. We analyzed the arginine vasopressin-neurophysin II (AVP-NPII) gene in her family, and a novel heterozygous mutation in exon 2 of the AVP-NPII gene was noted in the patient and her mother. This deletion mutation results in a frame shift beginning at codon 70 and a premature termination at codon 80. Only two cases of non-FDI and idiopathic hypoparathyroidism have been reported so far, but there has been no report on the association of FDI and idiopathic hypoparathyroidism. The causes of this association are not known and it is not known whether it is accidental or not.

A Missense Mutation Encoding Cys67 → Gly in Neurophysin II Is Associated with Early Onset Autosomal Dominant Neurohypophyseal Diabetes Insipidus

Autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) is an inherited disorder in which progressive degeneration of magnocellular neurons of the hypothalamus impairs production of arginine vasopressin (AVP). ADNDI is caused by mutations in the arginine vasopressin-neurophysin II (AVP-NPII) gene. These mutations are hypothesized to trigger neurodegeneration via disruption of preproAVP-NPII processing. Affected individuals usually develop diabetes insipidus between 1 and 6 years of age. Here we report a novel mutation of the AVP-NPII gene in a family with unusually early presentation of ADNDI. The index case developed symptoms of diabetes insipidus at 1 month of age, her mother at 9 months of age, and the maternal grandfather in early childhood. Each was found to be heterozygous for the missense mutation 1665T > G encoding the amino acid substitution C67G within NPII. This mutation helps to define two homologous regions of the AVP-NPII precursor bounded by disulfide bridges between C13 and C27 and between C61 and C73 that have structural homology and contain the majority of amino acid substitutions associated with ADNDI. The early onset of symptomatic diabetes insipidus in this family suggests that the C67G substitution may be particularly deleterious to magnocellular neurons and may provide a valuable model for study of dominantly inherited neurodegeneration.

Familial neurohypophyseal diabetes insipidus associated with a novel mutation in the vasopressin-neurophysin II gene.

Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant disorder of renal water conservation due to deficiency of arginine vasopressin as the result of mutations in the arginine vasopressin-neurophysin II (AVP-NPII) gene that encodes the hormone or its carrier protein. Thirty-one different mutations have been reported. In this study, we evaluated the AVP-NPII gene in a family with FNDI and identified a new mutation (1911Gright curved arrow A) in the coding sequence for NPII in affected family members. This mutation substitutes Tyr for 74 Cys in the NPII moiety. NPII is an intracellular carrier protein for AVP during the axonal transport from the hypothalamus to the posterior pituitary and contains 14 conserved cysteine residues forming 7 disulfide bonds. Because the mutation cosegregates with the phenotype, it is possible that this mutation causes neurohypophyseal diabetes insipidus in this family.

A Novel Arginine Vasopressin-Neurophysin II Mutation Causes Autosomal Dominant Neurohypophyseal Diabetes insipidus and Morphologic Pituitary Changes

To determine the genetic basis of autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) in a Cypriot family, we ascertained and studied a large, four-generation kindred in which all participating family members had arginine vasopressin-neurophysin II (AVP-NP-II) gene analyses done. A G to A transition was found by DNA sequence analysis at position 1773 (G1773A) of the AVP-NPII gene which is predicted to encode a substitution of tyrosine for cysteine in codon 59 (CYS59TYR). The mutation was confirmed by restriction endonuclease analysis of PCR amplification products that contain the corresponding segment of the AVP-NPII gene. To clarify the morphologic status of the pituitaries of family members, 12 affected and 3 nonaffected members had magnetic resonance imaging (MRI) studies. The bright spot of the posterior pituitary lobe was completely absent in 75% and faintly identified in 25% of the affected members who were examined with MRI. We conclude that (1) a novel G1773A transition in exon 2 of the AVP-NPII gene causes ADNDI in the large Cypriot kindred studied, (2) this mutation is predicted to encode a CYS59TYR substitution in NPII, and (3) MRI studies of the posterior pituitary lobes of affected family members show either a decreased intensity or a complete absence of the bright spot in all cases studied.

Heterogeneity in clinical manifestation of autosomal dominant neurohypophyseal diabetes insipidus caused by a mutation encoding Ala-1-->Val in the signal peptide of the arginine vasopressin/neurophysin II/copeptin precursor.

Autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) is a familial form of diabetes insipidus due to progressive vasopressin deficiency with onset typically at 1-6 yr of age. Affected individuals demonstrate specific degeneration of the vasopressinergic magnocellular neurons in the hypothalamic supraoptic and paraventricular nuclei and loss of the posterior pituitary bright spot on magnetic resonance imaging. The genetic locus of ADNDI is the arginine vasopressin-neurophysin II (AVP-NPII) gene. Mutations that cause ADNDI have been found to occur both within the signal peptide of the prepro-AVP-NPII precursor and within the coding sequence for neurophysin II, but not within the coding sequence for AVP itself. We evaluated the AVP-NPII genes in two independent families with ADNDI and identified a mutation (C280-->T) in the coding sequence for the signal peptide of the prepro-AVP-NPII precursor in both families. This mutation encodes an Ala-->Val substitution at the C-terminus of the signal peptide (-1 amino acid). This mutation predicts the complete inability of signal peptidase to cleave the signal peptide from the preproprecursor and supports the hypothesis that the progressive neural degeneration that underlies ADNDI is caused by accumulation of malprocessed precursor. However, considerable heterogeneity in the age of onset (1-28 yr of age) and the severity of diabetes insipidus among affected members of these two families suggests that additional factors modulate the rate and extent of progression of the neurodegeneration that results from this one specific ADNDI mutation.

A single base substitution in the coding region for neurophysin II associated with familial central diabetes insipidus.

To elucidate the molecular mechanism of familial central diabetes insipidus (FDI), we sequenced the arginine vasopressin-neurophysin II (AVP-NPII) gene in 2 patients belonging to a pedigree that is consistent with an autosomal dominant mode of inheritance. 10 patients with idiopathic central diabetes insipidus (IDI) and 5 normals were also studied. The AVP-NPII gene, locating on chromosome 20, consists of three exons that encode putative signal peptide, AVP, NPII, and glycoprotein. Using polymerase chain reaction, fragments including the promoter region and all coding regions were amplified from genomic DNA and subjected to direct sequencing. Sequences of 10 patients with IDI were identical with those of normals, while in 2 patients with FDI, a single base substitution was detected in one of two alleles of the AVP-NPII gene, indicating they were heterozygotes for this mutation. It was a G----A transition at nucleotide position 1859 in the second exon, resulting in a substitution of Gly for Ser at amino acid position 57 in the NPII moiety. It was speculated that the mutated AVP-NPII precursor or the mutated NPII molecule, through their conformational changes, might be responsible for AVP deficiency.

Molecular Analysis of Autosomal Dominant Neurohypophyseal Diabetes Insipidus*

The status of the arginine vasopressin-neurophysin-II (AVP-NPII) gene was studied in three families with autosomal dominant neurohypophyseal diabetes insipidus (AD-NDI). Restriction fragments of genomic DNA containing AVP-NPII sequences from affected individuals were not detectably different in size from those of normal controls. Thus, these individuals with ADNDI do not have apparent large deletions, insertions, or rearrangements of an AVP-NPII allele. Four restriction fragment length polymorphisms were detected with a probe for the adjacent gene on chromosome 20, oxytocin-neurophysin-I (OT-NPI). Linkage studies in these three families between the restriction fragment length polymorphism haplotypes and ADNDI phenotype strongly suggest cosegregation. This indicates that the genetic locus for ADNDI maps within or near the AVP-NPII locus and suggests that a defective AVP-NPII allele may be the basis of ADNDI.

Localization of arginine vasopressin-neurophysin II messenger ribonucleic acid in the hypothalamus of control and Brattleboro rats by hybridization histochemistry with a synthetic pentadecamer oligonucleotide probe.

By using 32P-labeled oligonucleotide probes for in situ DNA-RNA hybridization, we have defined the distribution of messenger RNA (MRNA) for arginine vasopressin-neurophysin II (AVP-NPII) in the rat hypothalamus. With a specific pentadecamer nucleotide probe, strong specific hybridization is seen in supraoptic, suprachiasmatic, and paraventricular nuclei in both Sprague-Dawley and Brattleboro rats. This finding, of equivalent distribution of AVP-NPII mRNA in Brattleboro and control hypothalami, confirms and extends the recent report of equivalent levels of AVP-NPII mRNA by Northern blot analysis.

Deduced amino acid sequence from the bovine oxytocin-neurophysin I precursor cDNA.

The nonapeptide hormone oxytocin-like arginine-vasopressin (AVP) is synthesized as part of a larger precursor polypeptide. The precursor also includes the neurophysin molecule with which the hormone is associated in the neurosecretory granules of the hypothalamo-pituitary tract. A protein of molecular weight (Mr) approximately 20,000 has been isolated from supraoptic nuclei of rat hypothalami which, after tryptic cleavage, released a neurophysin-like molecule of Mr approximately 10,000 and an oligopeptide related to oxytocin. This result was complemented by in vitro translation of bovine hypothalamic mRNA. Among the primary translation products a single polypeptide of Mr approximately 16,500 was shown to contain antigenic determinants recognized by specific antisera against bovine neurophysin I and oxytocin. Here we report the amino acid sequence of the bovine oxytocin-neurophysin I (OT-NpI) precursor which was derived from sequence analysis of the cloned cDNA. As is the case for the bovine arginine-vasopressin-neurophysin II (AVP-NpII) precursor, the signal sequence of the OT-NpI precursor is immediately followed by the nonapeptide hormone which is connected to neurophysin I by a Gly-Lys-Arg sequence. A striking feature of the nucleic acid sequence is the 197-nucleotide long perfect homology with the AVP-NpII precursor mRNA sequence encoding the conserved middle part of neurophysins I and II.