Marie-Thérèse Chauvet

Phylogeny of neurophysins: partial amino acid sequence of a sheep neurophysin.

Neurophysins [ 1 ] are proteins which are apparently associated with neurohypophysial hormones in the posterior pituitary gland and stable protein-hormone complexes have been isolated [2,3]. The components can be separated and reassociated for giving a complex similar to the native one [3] . In the mammalian species so far investigated, several neurophysin components have often been disclosed by electrophoresis but the real number of native neurophysins can hardly be determined by this procedure because of the possible presence of partially degraded forms [4]. Up to now the complete or partial amino acid sequences of two bovine [5-71, two porcine [8,9] and one human [ 10,l l] neurophysins have been determined. Our research on sheep neurophysins has revealed that a major neurophysin (about 70% of crude neurophysin) is present in the gland (M. T. Chauvet, G. Coffe, J. Chauvet and R. Acher unpublished results). This report deals with the determination of the Nterminal sequence of the major ovine neurophysin.

The complete amino acid sequence of the major ovine neurophysin (MSEL-neurophysin); comparison with a re-investigated bovine MSEL-neurophysin

Neurophysins [l] are proteins which have been subjected to extensive studies [2] because of their binding properties towards neurohypophysial hormones. Hormone . protein complexes have been purified from posterior pituitary powders of ox [3], pig [4], sheep [5], horse [6], whale [7], man [8] and cross associations between hormones of a species and neurophysins of another have been carried out [ 51. The neurophysins of the sheep have been purified through a hormone . protein complex [ 51 and recently isolated by molecular sieving and ion exchange chromatography [9]. A major neurophysin (MSELneurophysin) accounting for about 70% of the neurophysin material, has been partially sequenced [lo] . We present now data permitting the determination of the complete amino acid sequence of this protein. On the other hand a comparative investigation was carried out on bovine and porcine MSELneurophysins purified under similar conditions.

Unique evolution of neurohypophysial hormones in cartilaginous fishes: possible implications for urea-based osmoregulation.

Most bony vertebrate species display a great evolutionary stability of their two neurohypophysial hormones, so that two molecular lineages, isotocin-mesotocin-oxytocin and vasotocin-vasopressin, have been traced from bony fishes to mammals. Chondrichthyes, in contrast, show a striking diversity of their oxytocin-like hormones, yet show a substantial decrease in vasotocin stored in neurohypophysis when compared to nonmammalian bony vertebrates. In the rays, glumitocin ([Ser(4),Gln(8)]-oxytocin) has been identified. In the spiny dogfish, aspargtocin ([Asn4]-oxytocin) and valitocin ([Val(8)]-oxytocin) have been characterized whereas in the spotted dogfish, asvatocin ([Asn(4),Val(8)]-oxytocin) and phasvatocin ([Phe(3),Asn(4),Val(8)]-oxytocin) have been found. Finally, in the holocephalian Pacific ratfish, oxytocin, the typical peptide of placental mammals, has been discovered. The duplication of the oxytocin-like hormone gene found in dogfishes has been observed only in some Australian and American marsupials. Cartilaginous fishes have developed an original urea-based osmoregulation involving a glutamine-dependent urea synthesis and blood urea retention through renal urea transporters. Furthermore, marine species use a rectal salt gland for sodium chloride excretion. Although vasopressin, in mammals, and vasotocin, in nonmammalian tetrapods, are clearly implied in water and salt homeostasis, the hormones involved in the blood osmotic pressure regulation of elasmobranchs are still largely unknown. It is suggested that the great diversity of oxytocin-like hormones in elasmobranchs expresses a release from an evolutionary receptor-binding constraint, so that amino-acid substitutions reflect neutral evolution. In contrast, the preservation of vasotocin suggests a selective pressure, which may be related to the regulation of renal urea transporter-recruitment mechanisms, as it has been shown for vasopressin in mammals. J. Exp. Zool. 284:475-484, 1999.

The neurohypophysial hormones of the amphibians: Comparison of the hormones of Rana esculenta and Xenopus laevis☆

Abstract Neurohypophysial extracts from frogs ( Rana esculenta ) and Xenopus ( Xenopus laevis ) have been chromatographed on microcolumns of Amberlite CG-50. In each case two hormones have ben found. Xenopus -active principles are very similar to those of Rana esculenta in their chromatographic and pharmacologic properties. The posterior pituitary of Xenopus laevis contains a hormone which, when assayed for three biological activities (oxytocie, pressor, and hydro-osmotic assays), seems identical to arginine-vasotocin which has been chemically characterized from frog glands.

On the biological significance of neurophysins: Presence of a major neurophysin in the sheep

Neurophysins [ 1 ] are proteins which are usually found associated with neurohypophysial hormones in the posterior pituitary gland. The components of the complex can be separated [2] and reassociated [3] to give a complex similar to the native one. Because of that, a role of neurophysins either in the biosynthesis of hormones or in their carriage from hypothalamus to the posterior pituitary lobe has often been postulated [4,5]. Two neurohypophysial hormones are generally present in the gland and it is assumed that a stoichiometric amount of a particular neurophysin is associated to each hormone. If such an assumption is correct, two neurophysins should be isolated in the same proportions as those found for the two hormones. Actually two major neurophysins have been characterized in ox (6-8) and pig [9,10], species in which oxytocin and vasopressin are present in approximately equal amount [ 111. However in the sheep, despite the fact that oxytocin and arginine vasopressin exist in equal molar amounts in the posterior pituitary gland [ 121, we have found a single major neurophysin representing about 60-70% of the ‘crude neurophysin’.

Reptilian neurohypophyseal hormones: the active peptides of a Saurian, Iguana iguana

Abstract The neurohypophyseal hormones of a saurian, Iguana iguana , have been isolated. Mesotocin ([8-isoleucine]oxytocin) has been characterized by its amino acid composition and biological properties. Arginine vasotocin ([8-arginine]oxytocin) has been identified from its chromatoelectrophoretic migrations and pharmacological activities. These peptides have been demonstrated previously in snakes so the Ophidia and the Sauria , which belong to the same order, Squamata, seem to have the same neurohypophyseal hormones.

Évolution des hormones neurohypophysaires : isolement des principes actifs du lapin et du rat

Summary The neurohypophysial hormones of one species of Lagomorpha, the rabbit, and one species of Rodentia, the rat, have been isolated and characterized by amino acid composition, chromatographic and electrophoretic migrations and pharmacological properties. Oxytocin and arginine vasopressin have been identified in both cases. The same neurohypophysial hormones have so far been found in seven species belonging to six orders of eutherian mammals : Primates, Cetacea, Lagomorpha, Rodentia, Perissodactyla and Artiodactyla. In an eighth species belonging to Artiodactyla, the pig, lysine vasopressin replaces arginine vasopressin. In contrast the non-mammalian tetrapods (birds, reptiles, amphibians) have two different hormones, mesotocin (Ile 8 -oxytocin) and arginine vasotocin (Arg 8 -oxytocin) so that a double change has probably occurred somewhere between mammalian reptiles or primitive mammals and the present-day eutherian species.

Non-compact conformation of ovine MSEL-neurophysin

Neurophysins [ 1 ] are proteins which bind specifically the neurohypophysial hormones (for reviews, see [2-51). In mammals, two types of neurophysins, called MSEL-neurophysins and VLDVneurophysins according to the amino acids in position 2, 3,6 and 7, have been distinguished [6-81. The amino acid sequences of ovine [7-81 and bovine [S-9 ] MSEL-neurophysins have recently been determined. The molecules, nearly identical, comprise 95 residues arranged in a single polypeptide chain. Apparently, in solution at physiological pH values neurophysins are present as dimers rather than monomers [3]. We describe here experiments suggesting a non-compact or flexible conformation for neurophysins at pH about 8.0. In contrast to many native proteins, all the basic residues of ‘native’ neurophysin are accessible to trypsin; on the other hand, all the disulfide bridges are virtually reduced by dithiothreitol without the help of urea.

Ontogeny and phylogeny of neuropeptides: Protein precursors and enzymic processing

Abstract Neurohypophysial hormones are nonapeptides derived from precursors containing two or three domains, namely the hormonal moiety, a small protein, neurophysin (93/95 residues) and occasionally a glycopeptide, copeptin (39 residues). Enzymic processing of the precursors is very fast and separate domains are usually found in neurohypophysis. These fragments can be used on one hand to trace two phylogenetic lineages in vertebrates, on the other hand to follow expression of the precursor genes during the early stages of development. Regarding the hormonal domains, whereas mammalian species possess virtually always vasopressin and oxytocin, nonmammalian tetrapods have vasotocin ([Ile3]-vasopressin) and mesotocin ([Ile8]-oxytocin). Concerning the neurophysin domains, the two types MSEL-neurophysin (vasopressin-associated) and VLDV-neurophysin (oxytocin-associated) identified in mammals, have been also detected in nonmammalian tetrapods suggesting the association of MSEL-neurophysin with vasotocin and VLDV-neurophysin with mesotocin. About copeptin, recognition in lower vertebrates is difficult, likely because of a high number of substitutions. The three distinct domains correspond roughly to separate coding regions within the genes and could therefore have had autonomous evolutionary histories. Studies carried out with bovine fetus at the ages of 3 and 7 months reveal the same neuropeptides as those identified in the adult, but vasopressin gene is expressed 3 and 4 times more than oxytocin gene whereas in the adult both genes are roughly equally productive. This research fails, however, to identify vasotocin in fetus and to demonstrate a molecular recapitulation of neurohypophysial hormones, as previously suggested on the basis of pharmacological and immunological data.