Biomedical subjects

S A Sower

Publications and source records attributed to S A Sower.

At least 37 records · Page 2Linked to original sources

PubMed1997

Characteristics of GnRH binding in the gonads and effects of lamprey GnRH-I and -III on reproduction in the adult sea lamprey.

In the present study, both lamprey GnRH-I and -III stimulated steroidogenesis and induced ovulation in adult female sea lampreys during their final reproductive stage. One injection of lamprey GnRH-III at 0.1 or 0.2 microg/g lamprey stimulated plasma estradiol levels in lampreys held at each of three water temperatures, 13 degrees , 17 degrees , and 19 degrees , corresponding to increasing stages of maturation. Four successive injections, 3 to 4 days apart, of lamprey GnRH-III at 0.1 or 0.2 microg/g body weight induced ovulation in 100 or 88% of lampreys, respectively, compared to 21% in controls by Day 31. Lamprey GnRH-III also had a direct stimulatory effect on estradiol production in the sea lamprey gonads in vitro. Lamprey GnRH-III at 100 or 1000 ng/ml stimulated estradiol levels in media incubated with either lamprey ovaries or testes. In contrast to a previous finding in which lamprey GnRH-III was more potent than lamprey GnRH-I in inducing spermiation in adult male sea lampreys (Deragon and Sower, 1994), the results from the present study indicate that lamprey GnRH-I and -III are equally potent in inducing ovulation and stimulating steroidogenesis in female sea lampreys. In addition, GnRH binding sites have been demonstrated for the first time in both the testis and the ovary of the adult sea lamprey using an analog of mammalian GnRH ([D-Lys6] mammalian GnRH) as a labeled ligand. Scatchard analysis suggested the presence of a high affinity binding site in both the testis and the ovary. In summary, lamprey GnRH-III is biologically active in stimulating the pituitary-gonadal axis in adult female sea lampreys. This is the first report demonstrating the presence of a GnRH binding site in the gonads of an Agnathan. The evidence for a direct stimulatory effect of lamprey GnRH in the gonads, the presence of GnRH binding site, and the absence of GnRH in the plasma suggest that, like other vertebrates including rat, rabbit, teleost fish, and human, there may be a GnRH-like factor produced in the gonads of the lamprey and it may act as a paracrine/autocrine modulator of gonadal function. This study further strengthens the paracrine regulatory role of GnRH peptides in the gonads of vertebrates, which appear to be evolutionarily conserved.

Animals↗

PubMed1997

Gonadotropin-releasing hormone containing neurons and olfactory fibers during development: from lamprey to mammals.

Gonadotropin releasing-hormone (GnRH) regulates the hypothalamo-pituitary-gonadal axis in all vertebrates. The vast majority of GnRH neurons are thought to be derived from progenitor cells in medial olfactory placodes. Several antibodies and lectins that recognize cell surface carbohydrates have been useful for delineating the migratory pathway from the olfactory placodes and vomeronasal organ, through the nasal compartment, and across the cribriform plate into the brain. In rats, alpha-galactosyl-linked glycoconjugates (immunoreactive with the CC2 monoclonal antibody) are expressed on fibers along the GnRH migration pathway and approximately 10% of the GnRH neuronal population. In lamprey, the alpha-galactosyl binding lectin, Grifonia simplicifolia-I (GS-1), identifies cells and fibers of the developing olfactory system. In contrast to the CC2 immunoreactive GnRH neurons in rats, the GS-1 does not label a subpopulation of presumptive GnRH neurons in lamprey. Results from these and other experiments suggest that GnRH neurons in developing lamprey do not originate within the olfactory placode, but rather within proliferative zones of the diencephalon. However, the overlap of olfactory- and GnRH-containing fibers from prolarval stages to metamorphosis, suggest that olfactory stimuli may play a major role in the regulation of GnRH secretion in lamprey throughout life. By contrast, olfactory fibers are directly relevant to the migration of GnRH neurons from the olfactory placodes in mammalian species. Primary interactions between olfactory fibers and GnRH neurons are likely transient in mammals, and so in later life olfactory modulation of GnRH secretion is likely to be indirect.

Aging↗

PubMed1996

Relationship of gonadotropin-releasing hormone (GnRH) neurons to the olfactory system in developing lamprey (Petromyzon marinus).

Gonadotropin releasing-hormone (GnRH) regulates the hypothalamo-pituitary-gonadal axis in vertebrates. The regulation of GnRH is intimately related to information from the olfactory system. Additionally, GnRH neurons are thought to be derived from progenitor cells in medial olfactory placodes. The present experiments were conducted to characterize the earliest development of GnRH neurons in lamprey and to determine their relationship to cells and fibers derived from the olfactory system. Eggs from fertile adult sea lamprey were fertilized in the laboratory, and larvae were maintained for up to 100 days. GnRH neurons were visualized within the lamprey preoptic area and hypothalamus as soon as GnRH was detectable (22 days after fertilization). The number of neurons increased with age through day 100. GnRH neurons were never seen within the olfactory system. The cells and fibers of the olfactory system were identified using the lectin, Grifonia Simplicifolia-1 (GS-1). Overlap between the olfactory and GnRH systems were at the level of fiber projections. GS-1 reactive cells of apparent placodal origin did not enter the region of the preoptic area or hypothalamus that contained GnRH neurons. Recently divided cells were labeled with the thymidine analog, bromodeoxyuridine (BrdU). The positions of BrdU-labeled cells after different survival times suggest a predominant medial-lateral radial neuron migration with a small number in positions suggestive of migration between the olfactory epithelium and the telencephalic lobes. Regardless of survival time, these cells were always found close to their entry point into the brain, suggesting minimal rostral-caudal migration. Based on these results, we hypothesize that GnRH neurons in developing lamprey originate within proliferative zones of the diencephalon and not in the olfactory system. Based on the overlap of olfactory- and GnRH-containing fibers from prolarval stages to metamorphosis, olfactory stimuli may play a major role in the regulation of GnRH secretion in lamprey.

Aging↗

PubMed1996

Isolation of a peptide structurally related to mammalian corticostatins from the lamprey Petromyzon marinus.

Peptides in an extract of skin from the agnathan Petromyzon marinus (sea lamprey) were purified by reversed-phase high-performance liquid chromatography and characterized by Edman degradation. The primary structure of a cysteine- and arginine-rich peptide (termed lamprey corticostatin-related peptide [LCRP]) was established as Cys-Pro-Cys-Gly-Arg-Arg-Arg-Cys-Cys-Val-Arg-Gly-Leu-Asn-Val-Tyr-Cys-Cys- Phe. Mass spectrometry indicated that all cysteine residues are intramolecularly linked. This amino acid sequence shows structural similarity to rat corticostatin R4 and rabbit corticostatin R1. In particular, LCRP contains the polyarginine sequence at the N-terminus of the peptide that is believed to mediate both the inhibition of ACTH stimulated steroidogenesis and the antimicrobial (defensin-like) actions of the corricostatins.

Amino Acid Sequence↗

PubMed1995

Melanotropin and corticotropin are encoded on two distinct genes in the lamprey, the earliest evolved extant vertebrate.

In the lamprey, which is a member of the oldest extant class of vertebrates, the agnathans, melanotropins (MSH) and corticotropin (ACTH) were found to be encoded on two distinct genes. In all other vertebrates, a single precursor gene, proopiomelanocortin (POMC), encodes MSH and ACTH, as well as beta-endorphin (END). Two different cDNAs were cloned from a lamprey pituitary lambda gt11 cDNA library using antisera against lamprey MSH-B and ACTH(1-16). One cDNA encoded MSH-B, MSH-A and beta-END, while the other cDNA encoded nasohypophysial factor (NHF), ACTH and a different beta-END, but not MSH-A and MSH-B. Northern blot analysis demonstrated that in the adult lamprey pituitary, genes for MSH and ACTH are expressed in the pars intermedia (PI) and pars distalis (PD), respectively.

Adrenocorticotropic Hormone↗

PubMed1995

The occurrence and distribution of GnRH in the brain of Atlantic hagfish, an agnatha, determined by chromatography and immunocytochemistry.

In Atlantic hagfish (Myxine glutinosa), chromatographic and immunocytochemical evidence showed that the brain contains a gonadotropin-releasing hormone (GnRH)-like molecule that is closely related to lamprey GnRH-III. The chromatographic studies (HPLC) used specific antisera directed against mammalian GnRH and lamprey GnRH-I. In addition to these antisera, other specific antisera were tested in immunocytochemical studies, including chicken GnRH-I, chicken-GnRH-II, salmon GnRH, and lamprey GnRH-III. Using a lamprey GnRH-I antiserum, an early eluting GnRH form coeluted on HPLC with lamprey GnRH-III standard and an unknown form coeluted with the chicken GnRH-II standard. Radioimmunoassay of brain tissue detected GnRH immunoreactivity only when the lamprey GnRH-I antibody was used. A GnRH-like immunoreactivity was also obtained immunocytochemically in the neurohypophysis with the use of antisera against chicken GnRH-II, salmon GnRH, lamprey GnRH-I, and lamprey GnRH-III. These studies indicate that, contrary to earlier reports, hagfish do have a GnRH-like molecule that is more closely related, in terms of immunological determinants, to lamprey GnRH-III than to other currently known vertebrate GnRH molecules.

Amino Acid Sequence↗

PubMed1995

Distribution of lamprey adrenocorticotropin and melanotropins in the pituitary of the adult sea lamprey, Petromyzon marinus.

Three peptides containing the melanotropin (MSH)-core sequence, YXMXHFRWG, have been isolated recently from the pituitary glands of adult sea lampreys (Petromyzon marinus) and were tentatively assigned as lamprey adrenocorticotropin (ACTH), MSH-A, and MSH-B, respectively. Both MSHs differed significantly from gnathostome MSHs and cannot be assigned as alpha-MSH, beta-MSH, or gamma-MSH. The aim of the present study was to localize these peptides in the lamprey pituitary using antisera generated against synthetic lamprey ACTH1-16, MSH-A, and MSH-B. ACTH-like immunoreactivity was found in most cells of the rostal pars distalis (RPD) and in a few scattered cells of the proximal pars distalis (PPD). MSH-A-like immunoreactivity was found in most cells of the RPD, a few scattered cells of the PPD, and almost all cells of the pars intermedia (PI). MSH-B-like immunoreactivity was found only in the PI, where almost all cells were stained. Thus, the topographic distributions of ACTH and MSHs in the lamprey pituitary were similar to those in gnathostome vertebrates.

Adrenocorticotropic Hormone↗

PubMed1995

The appearance of proopiomelanocortin early in vertebrate evolution: cloning and sequencing of POMC from a Lamprey pituitary cDNA library.

A proopiomelanocortin (POMC)-like hormone has been cloned and sequenced from a pituitary cDNA library of upstream migrant (prespawning) sea lamprey, Petromyzon marinus. The clone, designated LPP-1, consisted of 986 nucleotides, with an open reading frame of 277 amino acids, including a signal peptide of 22 amino acids. Like POMCs from more recently evolved vertebrates, lamprey POMC contained domains which corresponded to alpha-MSH, ACTH, and beta-endorphin. However, sequences corresponding to gamma- and beta-MSH are absent or likely nonfunctional, respectively, in this cDNA. Northern blot analyses showed low but detectable expression levels of LPP-1 in larvae and strong expression in parasitic adults and prespawning animals. These observations indicate that a recognizable POMC, distinct from proenkephalin, has an ancient lineage within subphylum Vertebrata, likely dating back to the last common ancestor of the lamprey and gnathostome lines.

Adrenocorticotropic Hormone↗

PubMed1995

In vivo effects of lamprey GnRH-I and cyclized analogs: a structure-activity study.

Lamprey GnRH-I and lamprey GnRH-III are the only two members of the GnRH family to have substitutions in the sixth position, Glu6 and Asp6, respectively; all other GnRH peptides have Gly in the sixth position suggesting a different conformational structure. Thus, a structure-activity study of lamprey GnRH-I or analogs that were cyclized or with sixth position substitutions were determined in vivo in adult female sea lamprey, Petromyzon marinus. The following analogs which were tested, ([D-Glu6]-GnRH-I; cyclo-[D-Glu6-Trp7-Lys8]-GnRH-I; or cyclo-[Glu6-Trp7-Lys8]-GnRH-I), significantly elevated plasma estradiol compared to controls. However, [D-Glu6]-lamprey GnRH-I was the only analog to significantly stimulate ovulation while another analog [Gly6]-lamprey GnRH-I significantly delayed ovulation. These data suggest that the sixth position of lamprey GnRH is critical for function.

Amino Acid Sequence↗

PubMed1995

A novel glycoprotein in the olfactory and pituitary systems of larval and adult lampreys.

A novel homodimeric glycoprotein was isolated and characterized from the pituitaries of adult sea lampreys, Petromyzon marinus, modern representatives of the earliest vertebrates. The monomer consists of 121 amino-acid residues in a sequence that has no resemblance to any known pituitary hormone. Whereas this protein is localized in most cells of the rostral pars distalis of adult lampreys, we have chosen to name it, nasohypophysial factor (NHF), because it first appears in the olfactory system of developing larval lampreys. Not only may NHF be a new pituitary hormone but a useful probe for examining the ontogenetic and phylogenetic relationships of the pituitary and olfactory systems in vertebrates.

Amino Acid Sequence↗

PubMed1994

Purification of a neuropeptide Y-related peptide from the brain of the sea lamprey and its effect on steroidogenesis.

A peptide with neuropeptide Y-like immunoreactivity was identified by radioimmunoassay in an extract of the brain of the sea lamprey, Petromyzon marinus using an antiserum raised against the conserved COOH-terminal region of mammalian neuropeptide Y. Purification of the peptide and determination of its primary structure showed that it was identical to peptide methionine-tyrosine (PMY), previously isolated from the intestine of the same species. Intraperitoneal injection of synthetic PMY (0.15 micrograms/g) into female lampreys undergoing final maturation before spawning produced a significant (P < 0.05) decrease in plasma concentrations of estradiol compared with control lampreys injected with vehicle only. These data suggest the hypothesis that the observed decrease in the concentration of PMY-containing cells in the intestines of lampreys during upstream migration may correlate with the increase in circulating estradiol concentrations and final maturational processes.

Amino Acid Sequence↗

PubMed1994

Effects of lamprey gonadotropin-releasing hormone-III on steroidogenesis and spermiation in male sea lampreys.

The biological activities of lamprey gonadotropin-releasing hormone-III (GnRH-III) were determined in the adult male sea lamprey, Petromyzon marinus. One injection of lamprey GnRH-III at 0.1 or 0.2 microgram/g body wt stimulated plasma estradiol and progesterone levels in adult male sea lampreys undergoing final maturation. Four successive injections of lamprey GnRH-III at 0.1 microgram/g of lamprey GnRH-1 at 0.2 microgram/g induced spermiation in 78 or 30% of the lampreys, respectively, compared to 0% in controls by Day 16. In summary, lamprey GnRH-III is biologically active in stimulating the pituitary-gonadal axis in adult male lampreys.

Animals↗

PubMed1994

Diffusion between the neurohypophysis and the adenohypophysis of lampreys, Petromyzon marinus.

Horseradish peroxidase (HRP), a protein that can be visualized by appropriate histochemical procedures, was injected into the third ventricle of the brain of adult lampreys, Petromyzon marinus. Within 5 to 15 min HRP had passed through the neurohypophysis, which forms the floor of the third ventricle. It appeared at this time to have diffused throughout the connective tissue separating the adenohypophysial follicles from the neurohypophysis and from each other. This observation would indicate that it is possible for neurosecretory peptides like gonadotropin-releasing hormone to diffuse from the brain (neurohypophysis) to the adenohypophysis and thus regulate its secretory activity in lampreys.

Animals↗

PubMed1994

Polygenic expression of somatostatin in lamprey.

Previous studies have led to the identification of three biosynthetically related molecular forms of somatostatin (somatostatin-14, -34 and -37) from the pancreas of the sea lamprey (Petromyzon marinus). We have now isolated from the brain of the same species a second form of somatostatin-14 that is identical to mammalian somatostatin-14 and differs from lamprey pancreatic somatostatin-14 by the substitution Ser12 to Thr. Larger forms of somatostatin were not identified in lamprey brain in this study. These data suggest that the two molecular forms of lamprey somatostatin-14 are the products of different genes that are expressed in a tissue-specific manner.

Amino Acid Sequence↗

PubMed1994

Characterization and localization of gonadotropin-releasing hormone receptors in the adult female sea lamprey, Petromyzon marinus.

Quantitative in vitro autoradiography was used to characterize and localize putative GnRH receptors in the anterior pituitary of the adult female sea lamprey, Petromyzon marinus. Pituitaries were sectioned at 20 microns and incubated for 3 h at 4 C with DAla6,Pro9 NEt mammalian GnRH as both the labeled and unlabeled ligand. Scatchard analysis revealed two classes of high affinity binding sites with Kds of 1.5 x 10(-12) M and 5 x 10(-9) M. Binding to the GnRH receptors was saturable, reversible, tissue specific, and time and temperature dependent. Displacement studies showed that labeled peptide could be displaced by chicken GnRH-I, chicken GnRH-II, synthetic mammal, salmon, lamprey GnRH-I, lamprey GnRH-III, DAla6,Pro9 NEt mammalian GnRH and DPhe2,6,Pro3 lamprey GnRH. The proximal pars distalis region of the anterior pituitary contained most of the GnRH binding sites with slight binding in the rostral pars distalis. These data provide direct evidence of GnRH activity on the Agnathan pituitary and are the first to demonstrate that a vertebrate pituitary contains two high affinity binding sites for GnRH.

Animals↗

PubMed1993

Primary structure and biological activity of a third gonadotropin-releasing hormone from lamprey brain.

Previous studies have led to the identification of two molecular forms of GnRH (GnRH-I and II) in the brain of the sea lamprey, Petromyzon marinus. From analysis of these two forms, the primary structure of GnRH-I and the amino acid composition of GnRH-II were determined. We have now isolated a third molecular form of GnRH (GnRH-III) from the brain of this species that is different from GnRH-I and -II. The primary structure of GnRH-III is pGlu-His-Trp-Ser-His-Asp-Trp-Lys- Pro-Gly-NH2. A synthetic decapeptide with this amino acid sequence was chromatographically identical to natural GnRH-III. Intraperitoneal injection of synthetic lamprey GnRH-III (0.1 microgram/g) produced a significant (P < 0.05) elevation of plasma progesterone (31% over basal values) in female lampreys that was comparable to that produced by the same dose of lamprey GnRH-I (36% over basal). The elevation in plasma estradiol produced by lamprey GnRH-III (244% over basal) was significantly (P < 0.05) less than the elevation produced by GnRH-I (322% over basal). We propose based on the biological activity of lamprey GnRH-III in these studies and the occurrence of this peptide during metamorphosis in lampreys, that both lamprey GnRH-I and -III are neurohormones involved in reproduction in lampreys.

Amino Acid Sequence↗

PubMed1993

Two molecular forms of gonadotropin-releasing hormone from the brain of the frog, Rana ribibunda: purification, characterization, and distribution.

The molecular forms of GnRH in amphibia have not been characterized structurally. An antiserum to mammalian GnRH that shows appreciable cross-reactivity with chicken GnRH-I ([Gln8]GnRH), chicken GnRH-II ([His5,Trp7,Tyr8]GnRH), and salmon GnRH ([Trp7, Leu8]GnRH) was used in a RIA to detect GnRH-related peptides in an extract of the brain of the European green frog, Rana ridibunda. Two peptides were purified to apparent homogeneity, and determination of their primary structures showed that they are identical to mammalian GnRH and chicken GnRH-II. Salmon GnRH and lamprey GnRH-I ([Tyr3,Leu5,Glu6,Trp7,Lys8]GnRH) were not identified in this species of frog. Immunocytochemical analysis using specific antisera has identified regions of the frog diencephalon and telencephalon in which chicken GnRH-II and mammalian GnRH are localized to different populations of neurons. This differential distribution suggests distinct physiological roles for the two forms of GnRH in amphibia.

Animals↗

PubMed1992

Changes in brain gonadotropin-releasing hormone, plasma estradiol 17-beta, and progesterone during the final reproductive cycle of the female sea lamprey, Petromyzon marinus.

Changes in ovarian morphology, brain gonadotropin-releasing hormone (GnRH), plasma estradiol, and progesterone were examined during the 1988 and 1989 spawning migrations of the adult female sea lamprey, Petromyzon marinus. There were significant increases through time in brain GnRH (1989) and plasma estradiol (1988 and 1989), with progesterone levels fluctuating (1988 and 1989) during the freshwater phase of the spawning migrations. In 1989, brain GnRH and plasma estradiol levels gradually increased through time until just prior to spawning when levels decreased. During 1988, there were no significant changes in GnRH, which may reflect lower temperatures in that year. These data provide new information on brain GnRH during the final maturational processes in the female sea lamprey.

Amino Acid Sequence↗