Glandular kallikreins in the teleost Cyprinus carpio: tissue distribution, possible involvement in prolactin processing, and effect of 17 beta-estradiol in vivo

Differential response of two somatolactin genes to zinc or estrogen in pituitary of Cyprinus carpio

Environmental changes affect gene expression that we addressed in the pituitary, a central regulatory organ at the interface between the central nervous system and the endocrine system. With the aim to reveal effects of changes in the aquatic environment on the expression of hypothalamo-hypophyseal factors, we characterized somatolactin (SL) in Cyprinus carpio. SL, a fish specific pituitary hormone belonging to the prolactin (PRL) superfamily, is involved in background adaptation, osmoregulation, reproduction and fatty acid metabolism. Two sl genes, α and β, were discovered in carp and transcripts of both were detected in pituitaries. Clearly, expression of slα and slβ was modulated significantly in pituitary of male adult carp in response to treatment with ZnCl2 (Zn), but only slβ responded to 17β-estrogen (E2), relative to control carp as shown by RT-qPCR analyses. Furthermore, the amount of mRNA of related factors was assessed revealing variable effects on prl, growth hormone (gh), and factors involved in sl regulation: the pituitary transcription factor pit1 and hypothalamic pituitary adenylase cyclase activating peptide (pacap). In parallel, the physiological response of the experimental animals to Zn or E2 was confirmed by showing a significant increase of metallothionein (mt) or vitellogenin (vg) gene expression in liver, classical sentinels for exposure to heavy metal or estrogens. These data suggest that the sl genes seem to be involved in the response to Zn, as well as to estrogen, and could contribute to evaluate biological relevant changes in the aquatic environment.

An immune responsive complement factor D/adipsin and kallikrein-like serine protease (PoDAK) from the olive flounder Paralichthys olivaceus

The cDNA encoding of a complement factor D/adipsin and kallikrein-like serine protease, designated PoDAK, was isolated from the olive flounder Paralichthys olivaceus. PoDAK cDNA encodes a polypeptide with 277 amino acids containing conserved catalytic triad residues of serine proteases. The amino acid sequence of PoDAK showed high similarity to the kallikrein-like protein of medaka, mammalian adipsin/complement factor D and tissue kallikrein homolog, KT-14 of trout, complement factor D of zebrafish, and shared 31.6-36.8% homology with complement factor D/adipsin known from other species, including mammals. Phylogenetic analysis revealed that PoDAK clustered with the kallikrein-like protein of medaka and mammalian adipsin/complement factor D and tissue kallikrein homolog KT-14 of trout. The expression of PoDAK mRNA was high in the gills and heart, moderate in muscle, liver, intestine, stomach, kidney, and spleen of healthy flounder, and increased in the kidney, liver, and spleen of flounder challenged by the viral hemorrhagic septicemia virus (VHSV) or Streptococcus iniae. In situ hybridization confirmed that PoDAK mRNA is localized in the kidney and heart of individuals infected with VHSV. Further investigations are needed to clarify the function of PoDAK in vivo and in vitro.

Purification, structural characterization, and myotropic activity of a peptide related to des-Arg(9)-bradykinin from an elasmobranch fish, the little skate, Leucoraja erinacea

A bradykinin (BK)-related peptide was isolated from heat-denaturated plasma from an elasmobranch fish, the little skate, Leucoraja erinacea after incubation with porcine pancreatic kallikrein. The primary structure of the peptide (H-Gly-Ile-Thr-Ser-Trp-Leu-Pro-Phe-OH; skate BK) shows limited structural similarity to the mammalian B1 receptor agonist, des-Arg(9)-BK. The myotropic activities of synthetic skate BK, and the analog skate [Arg(9)]BK, were examined in isolated skate vascular and intestinal smooth muscle preparations. Skate BK produced a concentration-dependent constriction of the mesenteric artery (EC(50)=4.37x10(-8)M; maximum response=103.4+/-10.23% of the response to 60mM KCl) but the response to skate [Arg(9)]BK was appreciably weaker (response to 10(-6)M=73.0+/-23.4% of the response to 60mM KCl). Neither the first branchial gill arch nor the ventral aorta responded to either purified peptide. Skate BK also produced a concentration-dependent constriction of intestinal smooth muscle preparations (EC(50)=2.74x10(-7)M; maximum response 31.0+/-12.2% of the response to 10(-5)M acetylcholine). Skate [Arg(9)]BK was without effect on the intestinal preparation. The data provide evidence for the existence of the kallikrein-kinin system in a phylogenetically ancient vertebrate group and the greater potency of skate BK compared with the analog skate [Arg(9)]BK suggests that the receptor mediating vascular responses resembles the mammalian B1 receptor more closely than the B2 receptor.

Copeptin, derived from isotocin precursor, is a probable prolactin releasing factor in carp

Control of prolactin (PRL) release is of crucial importance for the multiple functions exerted by PRL in vertebrates. Recently identified hypothalamic PRL-releasing peptides displayed additional neuromodulatory activities and in fish only few could be detected close to lactotrophs. Here we describe the C-terminal peptide processed from the carp isotocin precursor as probable physiologically relevant regulator of PRL release in carp. The amino acid sequence derived from the complete isotocin precursor gene of Cyprinus carpio, predicted a C-terminal peptide uncleaved between the neurophysin (Np) and copeptin (Cp) domain. Accordingly, antibodies against synthetic Np- and Cp-specific oligopeptides both immunodetected a 13kDa protein (cNpCp) in total pituitary proteins and showed abundant immunoreaction in hypothalamic axons in direct contact with lactotrophs in the rostral pars distalis of carp pituitary gland sections. Finally, incubation of cultured carp pituitary explants with purified carp cNpCp resulted in a potent stimulation of PRL release.

Seasonal modulation of growth hormone mRNA and protein levels in carp pituitary: evidence for two expressed genes

Adaptation of eurythermal fish to naturally varying environmental conditions involves modulation of expressions of various factors in the hypothalamo-hypophyseal axis. Here we used three complementary approaches to assess the seasonal variation of growth hormone (GH) protein and mRNA levels in pituitary glands of acclimatized carp fish. First, a polyclonal antibody raised against an oligopeptide derived from the carp GH sequence was used for immunohistochemistry; second, oligonucleotides specific for GH transcripts were used for in situ hybridization. Specific immunodetection of GH coincides with visualization of GH mRNA in the proximal pars distalis, the specific location of somatotroph cells in carp pituitary gland. Finally, competitive RT-PCR analyses confirmed that GH expression exhibits seasonal cyclical reprogramming with higher levels in summer- than in winter-adapted fish. The expression pattern suggests an important role for GH in the molecular mechanisms underlying the acclimatization process. In parallel, amplification of sequences from the fourth intron and adjacent sites from exons IV and V demonstrates the existence of a new GH gene previously undescribed. The detection of transcripts corresponding to each gene suggests that both GH gene copies are active in the duplicated carp genome and that they are similarly affected by seasonal adaptation.

Seasonal environmental changes modulate the prolactin receptor expression in an eurythermal fish

Eurythermal fish have evolved compensatory responses to the cyclical seasonal changes of the environment. The complex adaptive mechanisms include the transduction of the physical parameters variations into molecular signals. Studies in carp have indicated that prolactin and growth hormone expression is associated with acclimatization, suggesting that the pituitary gland is a relevant physiological node in the generation of the homeostatic rearrangement that occurs in this adaptive process. Here, we report the cloning and characterization of a full-length carp prolactin receptor cDNA, which codes for the long form of the protein resembling that found in mammalian prolactin receptors. We identified up to three receptor transcript isoforms in different tissues of the teleost and assessed cell- and temporal-specific transcription and protein expression in carp undergoing seasonal acclimatization. The distinctive pattern of expression that carp prolactin receptor (cPRLr) depicts upon seasonal acclimatization supports the hypothesis that prolactin and its receptor are clearly involved in the new homeostatic stage that the eurythermal fish needs to survive during the cyclical changes of its habitat.