Isolation and characterization of carp prolactin

Small GTPase control of pituitary hormone secretion: Evidence from studies in the goldfish (Carassius auratus) neuroendocrine model

The secretion of vertebrate pituitary hormones is regulated by multiple hypothalamic factors, which, while generally activating unique receptor systems, ultimately propagate signals through interacting intracellular regulatory elements to modulate hormone exocytosis. One important family of intracellular regulators is the monomeric small GTPases, a subset of which (Arf1/6, Rac, RhoA, and Ras) is highly conserved across vertebrates and regulates secretory vesicle exocytosis in many cell types. In this study, we investigated the roles of these small GTPases in basal and agonist-dependent hormone release from dispersed goldfish (Carassius auratus) pituitary cells in perifusion experiments. Inhibition of these small GTPases elevated basal LH and GH secretion, except for Ras inhibition which only increased basal LH release. However, variable responses were observed with regard to LH and GH responses to the two goldfish native gonadotropin-releasing hormones (GnRH2 and GnRH3). GnRH-dependent LH release, but not GH secretion, was mediated by Arf1/6 GTPases. In contrast, inhibition of Rac and RhoA GTPases selectively enhanced GnRH3- and GnRH2-dependent GH release, respectively, while Ras inhibition only enhanced GnRH3-evoked LH secretion. Together, our results reveal novel divergent cell-type- and ligand-specific roles for small GTPases in the control of goldfish pituitary hormone exocytosis in unstimulated and GnRH-evoked release.

Production, characterization, and applications of mouse monoclonal antibodies against gonadotropin, somatolactin, and prolactin from common carp (Cyprinus carpio)

The gonadotropin alpha subunit (cGTH alpha), gonadotropin II beta subunit (cGTHII beta), somatolactin (cSL), and prolactin (cPRL) were isolated from the pituitaries of common carps, purified by traditional chromatographic analysis, identified by mass-chromatographic analysis, and used as immunogens in the B-lymphocyte hybridoma technique. Totally, 7, 11, 17, and 8 hybridoma cell lines were established, which were able to stably secrete monoclonal antibodies (mAbs) against cGTH alpha, cGTHII beta, cSL, and cPRL, and designated as FMU-cGTH alpha 1-7, FMU-cGTHII beta 1-11, FMU-cSL 1-17, and FMU-cPRL 1-8, respectively. The isotype, titer, and specificity were identified by enzyme-linked immunosorbent assay (ELISA), Western blot, and immunohistochemical staining, respectively, and application of these mAbs in the aforementioned tests has been proved. Furthermore, sensitive sandwich-ELISA systems for quantitative detection of the hormones mentioned above were also developed.

Isolation and characterization of two distinct gonadotropins, GTHI and GTHII, from bonito (Katsuwonus plelamis) pituitary glands

Two distinct glycoproteins homologous to chum salmon GTHI and GTHII were isolated from the pituitary glands of a marine fish, the bonito (Katsuwonus plelamis), and characterized by amino acid sequence analysis in order to obtain additional evidence for duality of teleost GTHs. Glycoproteins were extracted from the pituitary glands, and intact GTHI and GTHII, consisting of two distinct subunits, were purified by ion-exchange chromatography on DEAE-cellulose, rpHPLC on Asahipak C4P-50 in alkaline buffer, and gel filtration on Superdex 75. The association of the subunits was stable in GTHI (39 kD) and unstable in GTHII (30 kD) in acidic conditions. Immunoblotting revealed that antisera against beta subunits of chum salmon GTHs reacted with GTHII, but not with GTHI. In addition, none of the GTHs was stained with antiserum against human TSH beta. Sequence analysis demonstrated that bonito GTHI beta is homologous to salmon GTHI beta with 43% sequence identity, and bonito GTHII beta is homologous to salmon GTHII beta with 67% identity. Sequence identity between bonito GTHI beta and GTHII beta was only 28%. Thus, it is evident that the bonito pituitary gland produces two chemically distinct gonadotropins homologous to chum salmon GTHs.

Isolation and characterization of glycosylated and non-glycosylated prolactins from alligator and crocodile

Two molecular forms of prolactin (PRL), glycosylated and non-glycosylated, were isolated from pituitary glands of two reptiles, alligator and crocodile. The reptilian PRLs were extracted under alkaline conditions from the precipitate obtained after pituitaries were first extracted with 0.25 M sucrose, 1 mM NH4HCO3, pH 6.3. Purification was performed by ion exchange chromatography on DE-52, gel filtration on Sephadex G-75 superfine, and reversed phase high performance liquid chromatography. Two forms of both alligator and crocodile PRL, designated PRLI and PRLII, with molecular weights of 26,000 and 24,000 were isolated. Alligator and crocodile PRLI and PRLII were stained specifically in immunoblots with anti-sea turtle PRL and anti-ostrich PRL. Sequence analysis revealed that both forms of alligator and crocodile PRLs consisted of 199 amino acid residues with a glycosylation consensus sequence (Asn-Ala-Ser) at position 60 in alligator and crocodile PRLs with a molecular weight of 26,000 (PRLI). In contrast, Thr was substituted for Asn at position 60 in the PRLs with a molecular weight of 24,000 (PRLII). The sequences of alligator PRLs differed from crocodile PRLs only in position 134: Val for alligator PRLs and Ile for crocodile PRLs. There is a high degree of structural conservation between the reptilian PRLs isolated in this study and avian PRL; each showed 92% sequence identity with chicken PRL and 89% with turkey PRL.

Properties of common carp gonadotropin I and gonadotropin II

Two gonadotropins, GtH I and GtH II, were extracted with 35% ethanol-10% ammonium acetate, pH 6.1, from female common carp pituitary glands and purified by ion-exchange chromatography on a DE-52 column followed by gel filtration on a Sephadex G-75 column. Molecular weights of GtH I and GtH II as determined by SDS-PAGE were 45,000 and 35,000, respectively. Both GtHs dissociate into two subunits following reduction with beta-mercaptoethanol. These subunits contain different N-terminal amino acids (Tyr and Gly for GtH I; Tyr and Ser for GtH II). GtH I was acid stable and did not dissociate into subunits following treatment with 0.1% trifluoroacetic acid; GtH II readily dissociated into subunits by this treatment. GtH I and GtH II have distinct elution profiles on reverse-phase HPLC. The N-terminal amino acid sequence of the beta-subunit of GtH II was identical to that of common carp maturational GtH described by other workers suggesting that GtH I is a newly identified molecule. This was supported by radioimmunoassay analysis. GtH II and a common carp maturational GtH preparation (F11 cGtH; Peter et al., 1982, J. Interdiscipl. Cycle Res. 13, 229-239) had similar immunological activity in tests with antisera to the beta-subunit of maturational GtH whereas GtH I had low (less than 6%) cross-reactivity. GtH I, GtH II, and F11 cGtH were equipotent in tests with antisera to the alpha-subunit of maturational GtH suggesting these molecules contain a similar alpha-subunit. In vitro bioassays using goldfish revealed that GtH I and GtH II share the same spectrum of biological activities causing stimulation of ovarian and testicular steroidogenesis and induction of oocyte final maturation. The demonstration of two chemically distinct GtHs in common carp is similar to what has been described for chum and coho salmon.

Demonstration of gonadotropin releasing-hormone receptors on gonadotrophs and somatotrophs of the goldfish: an electron microscope study

Dispersed pituitary cells of the goldfish were incubated with biotinylated [D-Lys6, Pro9-N-ethylamide] salmon gonadotropin-releasing hormone (sGnRH-A) then avidingold (10 nm), and were fixed, embedded and sectioned. Cells were identified as gonadotrophs, somatotrophs, or prolactin cells using specific hormone antisera and protein-A gold (20 nm) as a marker. Attachment of the biotinylated sGnRH-A to the pituitary cell sections was determined by scanning cell surfaces for the smaller gold particles using the transmission electron microscope. Attachment was observed on gonadotrophs and somatotrophs, but was negligible on prolactin cells. Preincubation with unlabelled salmon gonadotropin-releasing hormone or chicken II gonadotropin-releasing hormone, or omission of the salmon gonadotropin-releasing hormone analog, prevented the reaction. The direct visualization of specific gonadotropin-releasing hormone receptors on gonadotrophs and somatotrophs supports the existence of direct stimulatory actions of gonadotropin-releasing hormone on gonadotropin and somatotropin release in gold-fish.

Isolation and characterization of Japanese eel prolactins

A highly purified prolactin (PRL) was isolated from the pituitary of the Japanese eel (Anguilla japonica) by extraction with acid-acetone, gel filtration on Sephadex G-75, and reversed-phase HPLC on TSK-gel ODS 120T and on TSK-gel TMS 250. Eel PRL is comprised of two variants (ePRL I and II), which were separated by HPLC on an ODS column. The two PRLs were also secreted by organ-cultured pituitaries in a defined medium. After being dialyzed against distilled water and lyophilized, the medium was dissolved in 0.01 M ammonium acetate (pH 9.0), and then the insoluble fraction was subjected to HPLC on an ODS column to isolate the secreted PRLs. The ePRL I and II were equipotent in retaining plasma Na in the hypophysectomized killifish, Fundulus heteroclitus, transferred from sea-water to fresh water. The putative PRL-producing cells in the rostral pars distalis of the eel pituitary were specifically stained with the antiserum against the mixture of ePRL I and II. Both PRLs had a molecular weight of 22 kDa in SDS-PAGE, an isoelectric point of 10.1 by gel electrofocusing, and an N-terminal residue of valine. Amino acid compositions and the partial amino acid sequences of ePRL I and II show that they are highly homologous with a limited number of substitutions, and that they are more closely related to those of teleostean PRLs than to those of mammalian PRLs.

Development and validation of a competitive enzyme immunoassay for chum salmon prolactin: a comparison to radioimmunoassay

An enzyme immunoassay (EIA), based on a competitive assay system, for the measurement of prolactin (PRL) in the pituitary of salmonid fishes and of hormone released in medium from incubated pituitary was developed using a rabbit antiserum to chum salmon PRL (PRL, a combination of PRL I and PRL II). Chum salmon PRL was coupled to horseradish peroxidase (HRP). The incubation procedure for the antigen-antibody reaction was analogous to that in the radioimmunoassay (RIA) for PRL. The antibody-bound HRP-PRL was separated by a double antibody method. The enzyme activity in the precipitate was followed by a colorimetric method, in which 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and o-phenylenediamine were used as substrates. PRL, PRL I, and PRL II showed exactly the same competitive curves in the EIA system. PRL (127-158) showed the highest cross-reactivity among the fragments of PRL examined. Low cross-reactivity was seen with other hormones isolated from chum salmon pituitary. The displacement curves for pituitary extracts from several salmonids, including chum salmon, coho salmon, and rainbow trout, were parallel to that of the PRL standard, whereas those from the carp and tilapia showed negligible cross-reactivity. A parallel displacement curve to the PRL standard was also seen with incubation medium of the pars distalis of the chum salmon pituitary. Plasma from chum salmon, coho salmon, and rainbow trout gave nonspecific HRP activity in the EIA. The values of PRL-EIA were significantly correlated (y = 0.99x + 1.06, r = 0.942, P less than 0.05, n = 24) with those obtained in PRL-RIA.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone-dependent potentiation of gonadotropin-stimulated steroid production by ovarian follicles of the goldfish

The possible involvement of growth hormone (GH) in the regulation of ovarian function in the goldfish was investigated by determining the effects of common carp GH on steroid production by vitellogenic and preovulatory ovarian follicles incubated in vitro. Carp GH acts in a dose-dependent manner to potentiate the actions of common carp gonadotropin (GtH) on the production of 17 beta-estradiol and testosterone by vitellogenic ovarian follicles and the actions of human chorionic gonadotropin (hCG) on testosterone production by preovulatory ovarian follicles. Carp GH alone had no effect on basal steroid secretion by either class of ovarian follicles. Chum salmon GH but not bovine GH also enhanced carp GtH-induced production of 17 beta-estradiol by vitellogenic ovarian follicles. Common carp prolactin had no effects on basal or GtH-stimulated steroid production by vitellogenic or preovulatory ovarian follicles. The actions of carp GH on preovulatory follicles were not apparent when tested with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, suggesting that GH may act to enhance either the formation or actions of cAMP. In summary, these data demonstrate that GH has a direct modulatory effect on GtH-stimulated steroid production and suggest that GH may be an important regulator of follicular development in the goldfish.

Isolation and characterization of growth hormone from a marine fish, bonito (Katsuwonus pelamis)

Growth hormone (GH) was extracted under alkaline conditions (pH 10) from pituitary glands (6.3 g) of bonito (Katsuwonus pelamis), and subsequently purified by gel filtration, ion exchange chromatography, and reversed-phase HPLC. The GH was monitored by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and by immunoblotting with yellowtail GH antiserum at each step of purification. GH activity was determined by an in vivo bioassay. The yield of this hormone was 4.8 mg/g wet tissue. Intraperitoneal injection of bonito GH at doses of 0.1 and 1 micrograms/g body wt at 7-day intervals resulted in a significant increase in body weight and length of juvenile rainbow trout. Bonito GH antiserum exhibited both species and hormone specificity in radioimmunoassay. However, the bonito GH antiserum as well as yellowtail GH antiserum exhibited hormone specificity but not species specificity in immunoblotting. A molecular weight of 21,000 and an isoelectric point of 7.0 for bonito GH were estimated by SDS-PAGE and gel electrofocusing, respectively. The complete amino acid sequence of 185 residues was determined by sequencing fragment peptides prepared by chemical and enzymatic cleavages. Sequence comparison of bonito GH with other GHs revealed that there is a significant deletion in the middle of the molecule.