Gene structure and seasonal expression of carp fish prolactin short receptor isoforms

Effects of Osmotic Stress on the mRNA Expression of prl, prlr, gr, gh, and ghr in the Pituitary and Osmoregulatory Organs of Black Porgy, Acanthopagrus schlegelii

In euryhaline teleost black porgy, Acanthopagrus schlegelii, the glucocorticoid receptor (gr), growth hormone receptor (ghr), prolactin (prl)-receptor (prlr), and sodium–potassium ATPase alpha subunit (α-nka) play essential physiological roles in the osmoregulatory organs, including the gill, kidney, and intestine, during osmotic stress. The present study aimed to investigate the impact of pituitary hormones and hormone receptors in the osmoregulatory organs during the transfer from freshwater (FW) to 4 ppt and seawater (SW) and vice versa in black porgy. Quantitative real-time PCR (Q-PCR) was carried out to analyze the transcript levels during salinity and osmoregulatory stress. Increased salinity resulted in decreased transcripts of prl in the pituitary, α-nka and prlr in the gill, and α-nka and prlr in the kidney. Increased salinity caused the increased transcripts of gr in the gill and α-nka in the intestine. Decreased salinity resulted in increased pituitary prl, and increases in α-nka and prlr in the gill, and α-nka, prlr, and ghr in the kidney. Taken together, the present results highlight the involvement of prl, prlr, gh, and ghr in the osmoregulation and osmotic stress in the osmoregulatory organs (gill, intestine, and kidney). Pituitary prl, and gill and intestine prlr are consistently downregulated during the increased salinity stress and vice versa. It is suggested that prl plays a more significant role in osmoregulation than gh in the euryhaline black porgy. Furthermore, the present results highlighted that the gill gr transcript’s role was solely to balance the homeostasis in the black porgy during salinity stress.

Cloning and molecular characterization of PRL and PRLR from turbot (Scophthalmus maximus) and their expressions in response to short-term and long-term low salt stress

The pituitary hormone prolactin (PRL) regulates salt and water homeostasis by altering ion retention and water uptake through peripheral osmoregulatory organs. To understand the role of PRL and its receptor (PRLR) in hypoosmoregulation of turbot (Scophthalmus maximus), we characterized the PRL and PRLR gene and analyzed the tissue distribution of the two genes and their gene transcriptional patterns in the main expressed tissues under long-term and short-term low salt stress. The PRL cDNA is 1486 bp in length, incorporating an ORF of 636 bp with a putative primary structure of 211 residues. And the PRLR cDNA is 2849 bp in length, incorporating an ORF of 1944 bp with a putative primary structure of 647 residues. The deduced amino acid sequences of these two genes shared highly conserved structures with those from other teleosts. Quantitative real-time PCR results showed that PRL transcripts were strongly expressed in the pituitary and very weakly in brain, but were hardly expressed in other tissues. PRLR transcripts were most abundant in the kidney, to a lesser extent in the gill, intestine, brain, and spleen, and at low levels in the pituitary and other tissues examined. The expression of PRL in the pituitary increased after short-term or long-term low salt stress, and the highest expression level appeared 12 h after stress (P < 0.05). And there is no significant difference between both low salt group (5 ppt and 10 ppt) at each sampling point. The variation of PRLR expression in gill under short-term low salt stress is similar to that of PRL gene in pituitary, with highest value in 12 h (P < 0.05). However, the expression under long-term low salt stress was significantly higher than control group even than 12 h group under 5 ppt (P < 0.05). The expression of PRLR in the kidney increased first and then decreased after low salt stress, and the highest value also appeared in 12 h after stress and there was no significant difference between the salinity groups. After long-term low salt stress, the expression level also increased significantly (P < 0.05), but it was flat with 24 h, which was lower than 12 h. The variation of PRLR expression in the intestine was basically consistent with that in the kidney. The difference was that the expression level of 24 h after stress in the 5 ppt group was significantly higher than that of the 10 ppt group (P < 0.05). After a comprehensive analysis of the expression levels of the two genes, it can be found that the expression level increased and peaked at 12 h after short-term low salt stress, indicating that this time point is the key point for the regulation of turbot in response to low salt stress. This also provides very important information for studying the osmotic regulation of turbot. In addition, our results also showed that the expression of PRLR was stable in the kidney and intestine after long-term low salt stress, while the expression in the gill was much higher than short-term stress. It suggested that PRL and its receptors mainly exert osmotic regulation function in the gill under long-term low salt stress. At the same time, such a result also brings a hint for the low salt selection of turbot, focusing on the regulation of ion transport in the gill.

Cloning, expression of, and evidence of positive selection for, the prolactin receptor gene in Chinese giant salamander (Andrias davidianus)

Prolactin receptor (PRLR) is a protein associated with reproduction in mammals and with osmoregulation in fish. In this study, the complete length of Chinese giant salamander Andrias davidianus prolactin receptor (AD-prlr) was cloned. Andrias davidianus prlr expression was high in the kidney, pituitary, and ovary and low in other examined tissues. The AD-prlr levels were higher in ovary than in testis, and increased in ovaries with age from 1 to 6 years. To determine effect of exogenous androgen and aromatase inhibitor on AD-prlr expression, methyltestosterone (MT) and letrozole (LE) were injected, resulting in decreased AD-prlr in both brain and ovary, with MT repressing prlr transcription more rapidly than did LE. The molecular evolution of prlr was assessed, and found to have undergone a complex evolution process. The obranch-site test detected four positively selected sites in ancestral lineages prior to the separation of mammals and birds. Fourteen sites underwent positive selection in ancestral lineages of birds and six were positively selected in amphibians. The site model showed that 16, 7, and 30 sites underwent positive selection in extant mammals, amphibians, and birds, respectively. The positively selected sites in amphibians were located outside the transmembrane domain, with four in the extracellular and three in the intracellular domain, indicating that the transmembrane region might be conserved and essential for protein function. Our findings provide a basis for further studies of AD-prlr function and molecular evolution in Chinese giant salamander. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 707-719, 2015. © 2015 Wiley Periodicals, Inc.

Diverse mechanisms for body fluid regulation in teleost fishes

Teleost fishes are the major group of ray-finned fishes and represent more than one-half of the total number of vertebrate species. They have experienced in their evolution an additional third-round whole genome duplication just after the divergence of their lineage, which endowed them with an extra adaptability to invade various aquatic habitats. Thus their physiology is also extremely diverse compared with other vertebrate groups as exemplified by the many patterns of body fluid regulation or osmoregulation. The key osmoregulatory organ for teleosts, whose body fluid composition is similar to mammals, is the gill, where ions are absorbed from or excreted into surrounding waters of various salinities against concentration gradients. It has been shown that the underlying molecular physiology of gill ionocytes responsible for ion regulation is highly variable among species. This variability is also seen in the endocrine control of osmoregulation where some hormones have distinct effects on body fluid regulation in different teleost species. A typical example is atrial natriuretic peptide (ANP); ANP is secreted in response to increased blood volume and acts on various osmoregulatory organs to restore volume in rainbow trout as it does in mammals, but it is secreted in response to increased plasma osmolality, and specifically decreases NaCl, and not water, in the body of eels. The distinct actions of other osmoregulatory hormones such as growth hormone, prolactin, angiotensin II, and vasotocin among teleost species are also evident. We hypothesized that such diversity of ionocytes and hormone actions among species stems from their intrinsic differences in body fluid regulation that originated from their native habitats, either fresh water or seawater. In this review, we summarized remarkable differences in body fluid regulation and its endocrine control among teleost species, although the number of species is still limited to substantiate the hypothesis.

Scuticociliatosis and its recent prophylactic measures in aquaculture with special reference to South Korea Taxonomy, diversity and diagnosis of scuticociliatosis: Part I Control strategies of scuticociliatosis: Part II

Scuticociliatosis caused by about 20 species belonging to the Phylum Ciliophora has been recognized as an emerging problem inflicting significant economic loss in aquaculture industry in the world. Among these Philasterides dicentrarchi, Miamiensis avidus, and Uronema marinum are the three species responsible for scuticociliatosis in olive flounder farms of South Korea. Some of the parasites living or scavenger ciliates also have become parasites of aquaculture fish. The major clinico-pathological manifestations of scuticociliatosis infected fishes are anemia, weight loss, dark coloration, enteritis, excessive body mucus, yellowish intestinal mucus, loss of scales, hemorrhagic and/or bleached spots on the skin, and dermal necrotic lesions that finally destroy tissues lead to high mortalities. Affected fish exhibit organ-specific pathological changes in the brain, eyes, muscle, gills, liver, kidney, intestine, and stomach that lead to severe mortality. At present, farmers in South Korea manage scuticociliatosis by using therapeutic measures, such as application of antibiotics like oxytetracycline, gentamycine, tetracycline, amoxycililin, and cefazolin and chemicals, such as formalin, hydrogen peroxide, malachite green, and jenoclean at a concentration of 350 +/- 150 ppm. However till date, no systematic scientific study has been conducted under field condition on the efficacy of these management measures. Under laboratory condition the ciliate can be effectively controlled with the antibiotics and chemicals while on the host, but on entering the host no systemic chemotherapeutic treatment has been yet proven effective. Furthermore the indiscriminate uses of harmful chemicals in aquaculture are increasingly becoming a cause of concern. Recently formalin and malachite green, the most widely used chemicals have been banned in food fish production by FDA as not consumer friendly and being carcinogenic respectively. Vaccines and immunostimulants can induce good immune response and protect against scuticociliatosis as it has been proved in the case of freshwater Ich. Now a days a number of probiotics and herbal formulations are in use against freshwater bacterial and fungal diseases, while, little information is available regarding the different prophylactic measures against marine scuticociliatosis. This review attempts to provide information on the various prophylaxic measures practiced against scuticociliatosis with special reference to olive flounder farms in South Korea.

The second prolactin receptor in Nile tilapia (Oreochromis niloticus): molecular characterization, tissue distribution and gene expression

Prolactin (PRL) is one of the most versatile hormones found in the pituitary of vertebrates and exerts its actions through binding to a specific PRL receptor (PRLR). Here we describe the cloning and characterization of a second prolactin receptor (ntPRLR2), isolated from the ovary of Nile tilapia (Oreochromis niloticus). The newly identified PRLR cDNA was 2011 bp in length and encoded 529 amino acids. It shared 31.6% identity in nucleotide sequence and 29.2% in deduced amino acid sequence with the first PRLR identified in Nile tilapia (ntPRLR1). Both of these ntPRLRs resemble the long form mammalian PRLRs. The nominated ntPRLR2 was further confirmed as a real prolactin receptor based on its competence to transactivate the beta-casein and c-fos promoters in the transiently ntPRLR2-transfected HEK293 cells. The ntPRLR2 gene also found to encode a 864-bp short form transcript in the ovary, which was confirmed by Northern blot analysis. A tissue distribution study by real-time PCR revealed that the mRNA of both receptors (ntPRLR1 and ntPRLR2) was widely expressed in different tissues, with an extremely high abundance in the osmoregulatory organs, including the gills, intestine and kidney. ntPRLR1 mRNA was more abundant than ntPRLR2 in the testis, while the reverse expression pattern was found in the ovary. In the ovary, ntPRLR2 mRNA demonstrated a distinct gonadal development-dependent expression profile, with significantly higher levels at a sexual mature stage than at sexual recrudescent and sexual regressed stages. When challenged with estradiol, ntPRLR2 mRNA expression was up-regulated by E2, whereas E2 had no significant effect on ntPRLR1.

A novel tilapia prolactin receptor is functionally distinct from its paralog

A novel tilapia prolactin (PRL) receptor (OmPRLR2) was identified based on its induction during hyperosmotic stress. OmPRLR2 protein shows 28% identity to tilapia OmPRLR1 and 26% identity to human PRLR. Comparison of OmPRLR1 and OmPRLR2 revealed conserved features of cytokine class I receptors (CKR1): a WS domain and transmembrane domain, two pairs of cysteines and N-glycosylation motifs in the extracellular region, CKR1 boxes I and II, and three tyrosines in the intracellular region. However, OmPRLR2 lacked the ubiquitin ligase and 14-3-3 binding motifs. OmPRLR2 mRNA was present in all tissues analyzed, with highest expression in gills, intestine, kidney and muscle, similar to OmPRLR1. Transfer of fish from fresh water to sea water transiently increased gill OmPRLR2 mRNA levels within 4 h but decreased its protein abundance in the long term. OmPRLR2 is expressed in part as a truncated splice variant of 35 kDa in addition to the 55 kDa full-length protein. Cloning of the mRNA encoding the 35 kDa variant revealed that it lacks the extracellular region. It is expressed at significantly higher levels in males than in females. In stably transfected HEK293 cells over-expressing tetracycline-inducible OmPRLR1 and OmPRLR2, activation of these receptors by tilapia PRL177 and PRL188 triggered different downstream signaling pathways. Moreover, OmPRLR2 significantly increased HEK293 salinity tolerance. Our data reveal that tilapia has two PRLR genes whose protein products respond uniquely to PRL and activate different downstream pathways. Expression of a short PRLR2 variant may serve to inhibit PRL binding during osmotic stress and in male tissues.

Prolactin receptor mRNA is upregulated in discus fish (Symphysodon aequifasciata) skin during parental phase

Prolactin (PRL) has been shown to directly influence parental-care associated behavior in many vertebrate species. The discus fish (Symphysodon aequifasciata) displays extensive parental care behavior through utilization of epidermal mucosal secretion to raise free-swimming fry. Here, we cloned the full-length cDNA sequence of the S. aequifasciata prolactin receptor (dfPRLR) and investigated the mRNA expression pattern in several adult tissues. Bioinformatic analysis showed the dfPRLR shared rather high identity (79 and 67%) with the Nile tilapia PRLR 1 and black seabream PRLR 1, respectively. The presence of dfPRLR in several osmoregulatory tissues including kidney, gill and intestine is consistent with the known role of PRL in mediating hydromineral balance in teleosts. In addition, upregulated expression of PRLR mRNA was observed in skin of parental fish compared to non-parental fish, indicating possibility of a role of the PRL hormonal signaling in regulation of mucus production in relation to parental care behaviour.