The effect of online and in-person team-based learning (TBL) on undergraduate endocrinology teaching during COVID-19 pandemic

BACKGROUND

Team-based learning (TBL) combines active and collaborative learning, while incorporating aspects of the flipped classroom approach and problem-based learning. The COVID-19 pandemic presented certain challenges in the delivery of TBL in class. In this study, we investigated the impact of TBL on the academic performance of final year Biomedical Sciences' undergraduate students in the context of an "Endocrine Disorders" study block. We did so by comparing the classical in-person approach and online delivery due to the COVID-19 pandemic.

METHODS

A non-compulsory TBL session was introduced to the curriculum of this block, which followed the traditional 2-h lecture delivery. Comparative analysis was performed for the exam and coursework performance of students who attended the TBL sessions (online and in-person) and those that did not.

RESULTS

Both cohorts of students who attended either in-person (n = 66) or online TBL sessions (n = 109) performed significantly better in their exams (p < 0.05) and a related coursework (p < 0.001 and p < 0.05, respectively) when compared to those that did not attend. For both these cohorts the exam mark distribution was much narrower compared to those that did not attend the TBL sessions where the majority of fails and "no shows" were recorded.

CONCLUSIONS

Online and in-person TBL, can successfully supplement traditional lecture-based teaching and enhance the learning/performance, for complex medical subjects/topics. Our findings demonstrate that it is possible to deliver these sessions online with demonstrable benefit for students suggesting that there is greater flexibility in the use of TBL in higher education.

Testing the Translational Power of the Zebrafish: An Interspecies Analysis of Responses to Cardiovascular Drugs

The zebrafish is rapidly emerging as a promising alternative in vivo model for the detection of drug-induced cardiovascular effects. Despite its increasing popularity, the ability of this model to inform the drug development process is often limited by the uncertainties around the quantitative relevance of zebrafish responses compared with nonclinical mammalian species and ultimately humans. In this test of concept study, we provide a comparative quantitative analysis of the in vivo cardiovascular responses of zebrafish, rat, dog, and human to three model compounds (propranolol, losartan, and captopril), which act as modulators of two key systems (beta-adrenergic and renin–angiotensin systems) involved in the regulation of cardiovascular functions. We used in vivo imaging techniques to generate novel experimental data of drug-mediated cardiovascular effects in zebrafish larvae. These data were combined with a database of interspecies mammalian responses (i.e., heart rate, blood flow, vessel diameter, and stroke volume) extracted from the literature to perform a meta-analysis of effect size and direction across multiple species. In spite of the high heterogeneity of study design parameters, our analysis highlighted that zebrafish and human responses were largely comparable in >80% of drug/endpoint combinations. However, it also revealed a high intraspecies variability, which, in some cases, prevented a conclusive interpretation of the drug-induced effect. Despite the shortcomings of our study, the meta-analysis approach, combined with a suitable data visualization strategy, enabled us to observe patterns of response that would likely remain undetected with more traditional methods of qualitative comparative analysis. We propose that expanding this approach to larger datasets encompassing multiple drugs and modes of action would enable a rigorous and systematic assessment of the applicability domain of the zebrafish from both a mechanistic and phenotypic standpoint. This will increase the confidence in its application for the early detection of adverse drug reactions in any major organ system.

Testing the "read-across hypothesis" by investigating the effects of ibuprofen on fish

Human pharmaceuticals present in the environment have the potential to cause adverse effects on non-target organisms. The "read-across hypothesis" stipulates that pharmaceuticals will exhibit similar biological effects across species (e.g. human and fish) if the molecular target has been conserved and the effective drug concentrations are reached (Cmax). We tested this hypothesis by evaluating if ibuprofen, a non-selective inhibitor of prostaglandins and the cyclooxygenase (COX) enzyme, can mimic its primary effect in humans, on fish, at comparable plasma concentrations. The endpoints, prostaglandin E metabolite (PGEM) levels and the mRNA expression of COX (ptgs) gene, were measured in the gills of control and exposed fathead minnows (Pimephales promelas), using enzyme-immunoassay and quantitative real-time PCR (qPCR). Fish were exposed, for 24-72 h, to measured water concentrations of 9 (n = 12), 370 (n = 40) and 470 μg ibuprofen/L (n = 12). Water and blood plasma concentrations were determined using LC-MS/MS. Results showed that PGEM levels in fish exposed to 370 and 470 μg ibuprofen/L were significantly decreased compared to control fish, when mean plasma ibuprofen concentrations were 1.8-5.6-fold below the Cmax. The plasma ibuprofen concentrations and PGEM levels varied greatly between individuals. In fish exposed to 9 μg ibuprofen/L, when the mean plasma ibuprofen concentration was 224-fold below Cmax, no change in PGEM levels was observed. These data provide evidence for the read-across hypothesis, but suggest establishing a direct dose-response between internal plasma and PGEM is difficult, and would require significantly larger numbers of fish to overcome the inter-individual variation.

Internal exposure dynamics drive the Adverse Outcome Pathways of synthetic glucocorticoids in fish

The Adverse Outcome Pathway (AOP) framework represents a valuable conceptual tool to systematically integrate existing toxicological knowledge from a mechanistic perspective to facilitate predictions of chemical-induced effects across species. However, its application for decision-making requires the transition from qualitative to quantitative AOP (qAOP). Here we used a fish model and the synthetic glucocorticoid beclomethasone dipropionate (BDP) to investigate the role of chemical-specific properties, pharmacokinetics, and internal exposure dynamics in the development of qAOPs. We generated a qAOP network based on drug plasma concentrations and focused on immunodepression, skin androgenisation, disruption of gluconeogenesis and reproductive performance. We showed that internal exposure dynamics and chemical-specific properties influence the development of qAOPs and their predictive power. Comparing the effects of two different glucocorticoids, we highlight how relatively similar in vitro hazard-based indicators can lead to different in vivo risk. This discrepancy can be predicted by their different uptake potential, pharmacokinetic (PK) and pharmacodynamic (PD) profiles. We recommend that the development phase of qAOPs should include the application of species-specific uptake and physiologically-based PK/PD models. This integration will significantly enhance the predictive power, enabling a more accurate assessment of the risk and the reliable transferability of qAOPs across chemicals.

Quantitative cross-species extrapolation between humans and fish: the case of the anti-depressant fluoxetine

Fish are an important model for the pharmacological and toxicological characterization of human pharmaceuticals in drug discovery, drug safety assessment and environmental toxicology. However, do fish respond to pharmaceuticals as humans do? To address this question, we provide a novel quantitative cross-species extrapolation approach (qCSE) based on the hypothesis that similar plasma concentrations of pharmaceuticals cause comparable target-mediated effects in both humans and fish at similar level of biological organization (Read-Across Hypothesis). To validate this hypothesis, the behavioural effects of the anti-depressant drug fluoxetine on the fish model fathead minnow (Pimephales promelas) were used as test case. Fish were exposed for 28 days to a range of measured water concentrations of fluoxetine (0.1, 1.0, 8.0, 16, 32, 64 µg/L) to produce plasma concentrations below, equal and above the range of Human Therapeutic Plasma Concentrations (H_TPCs). Fluoxetine and its metabolite, norfluoxetine, were quantified in the plasma of individual fish and linked to behavioural anxiety-related endpoints. The minimum drug plasma concentrations that elicited anxiolytic responses in fish were above the upper value of the H_TPC range, whereas no effects were observed at plasma concentrations below the H_TPCs. In vivo metabolism of fluoxetine in humans and fish was similar, and displayed bi-phasic concentration-dependent kinetics driven by the auto-inhibitory dynamics and saturation of the enzymes that convert fluoxetine into norfluoxetine. The sensitivity of fish to fluoxetine was not so dissimilar from that of patients affected by general anxiety disorders. These results represent the first direct evidence of measured internal dose response effect of a pharmaceutical in fish, hence validating the Read-Across hypothesis applied to fluoxetine. Overall, this study demonstrates that the qCSE approach, anchored to internal drug concentrations, is a powerful tool to guide the assessment of the sensitivity of fish to pharmaceuticals, and strengthens the translational power of the cross-species extrapolation.

The read-across hypothesis and environmental risk assessment of pharmaceuticals

Pharmaceuticals in the environment have received increased attention over the past decade, as they are ubiquitous in rivers and waterways. Concentrations are in sub-ng to low μg/L, well below acute toxic levels, but there are uncertainties regarding the effects of chronic exposures and there is a need to prioritise which pharmaceuticals may be of concern. The read-across hypothesis stipulates that a drug will have an effect in non-target organisms only if the molecular targets such as receptors and enzymes have been conserved, resulting in a (specific) pharmacological effect only if plasma concentrations are similar to human therapeutic concentrations. If this holds true for different classes of pharmaceuticals, it should be possible to predict the potential environmental impact from information obtained during the drug development process. This paper critically reviews the evidence for read-across, and finds that few studies include plasma concentrations and mode of action based effects. Thus, despite a large number of apparently relevant papers and a general acceptance of the hypothesis, there is an absence of documented evidence. There is a need for large-scale studies to generate robust data for testing the read-across hypothesis and developing predictive models, the only feasible approach to protecting the environment.

No substantial changes in estrogen receptor and estrogen-related receptor orthologue gene transcription in Marisa cornuarietis exposed to estrogenic chemicals

Estrogen receptor orthologues in molluscs may be targets for endocrine disruptors, although mechanistic evidence is lacking. Molluscs are reported to be highly susceptible to effects caused by very low concentrations of environmental estrogens which, if substantiated, would have a major impact on the risk assessment of many chemicals. The present paper describes the most thorough evaluation to-date of the susceptibility of Marisa cornuarietis ER and ERR gene transcription to modulation by vertebrate estrogens in vivo and in vitro. We investigated the effects of estradiol-17β and 4-tert-Octylphenol exposure on in vivo estrogen receptor (ER) and estrogen-related receptor (ERR) gene transcription in the reproductive and neural tissues of the gastropod snail M. cornuarietis over a 12-week period. There was no significant effect (p>0.05) of treatment on gene transcription levels between exposed and non-exposed snails. Absence of a direct interaction of estradiol-17β and 4-tert-Octylphenol with mollusc ER and ERR protein was also supported by in vitro studies in transfected HEK-293 cells. Additional in vitro studies with a selection of other potential ligands (including methyl-testosterone, 17α-ethinylestradiol, 4-hydroxytamoxifen, diethylstilbestrol, cyproterone acetate and ICI182780) showed no interaction when tested using this assay. In repeated in vitro tests, however, genistein (with mcER-like) and bisphenol-A (with mcERR) increased reporter gene expression at high concentrations only (>10(-6)M for Gen and >10(-5)M for BPA, respectively). Like vertebrate estrogen receptors, the mollusc ER protein bound to the consensus vertebrate estrogen-response element (ERE). Together, these data provide no substantial evidence that mcER-like and mcERR activation and transcript levels in tissues are modulated by the vertebrate estrogen estradiol-17β or 4-tert-Octylphenol in vivo, or that other ligands of vertebrate ERs and ERRs (with the possible exception of genistein and bisphenol A, respectively) would do otherwise.

Crucial cross-talk of interleukin-1β and progesterone in human choriocarcinoma

Choriocarcinoma is a highly malignant epithelial tumour that is most often associated with hydatidiform mole and presents the most common emergency medical problem in the management of trophoblast disease. We hypothesise that the hormones/cytokines present within the tumour microenvironment play key roles in the development of choriocarcinoma. In this study we assessed the effects of interleukin-1β (IL-1β) on cell death in the presence or absence of the sex hormone progesterone using two choriocarcinoma cell lines (BeWo and JEG-3) as in vitro experimental models. Although IL-1β induced cell death in both cell lines, the effect was more pronounced in JEG-3 cells, where cell death reached 40% compared to 15% in BeWo cells. Cell death of JEG-3 cells in response to IL-1β was significantly decreased by co-treatment with 100 nM and 1000 nM progesterone and completely abolished at a progesterone concentration of 1000 nM. Progesterone was also able to induce phosphorylation of ERK1/2 in these cells. Pretreatment of JEG-3 cells with a specific MAPK inhibitor (UO126) inhibited progesterone's inhibitory effect on cell death. Collectively, these data provide evidence of cross-talk between progesterone and IL-1β in this aggressive and poorly understood tumour that involves activation of a MAPK pathway and involvement of numerous progesterone receptors.

Characterisation and expression of β1-, β2- and β3-adrenergic receptors in the fathead minnow (Pimephales promelas)

Complimentary DNAs for three beta-adrenergic receptors (βARs) were isolated and characterised in the fathead minnow. The encoded proteins of 402 (β(1)AR), 397 (β(2)AR) and 434 (β(3)AR) amino acids were homologous to other vertebrate βARs, and displayed the characteristic seven transmembrane helices of G Protein-coupled receptors. Motifs and amino acids shown to be important for ligand binding were conserved in the fathead minnow receptors. Quantitative RT-PCR revealed the expression of all receptors to be highest in the heart and lowest in the ovary. However, the β(1)AR was the predominant subtype in the heart (70%), and β(3)AR the predominant subtype in the ovary (53%). In the brain, β(1)AR expression was about 200-fold higher than that of β(2)- and β(3)AR, whereas in the liver, β(2)AR expression was about 20-fold and 100-fold higher than β(3)- and β(1)AR expression, respectively. Receptor gene expression was modulated by exposure to propranolol (0.001-1mg/L) for 21 days, but not in a consistent, concentration-related manner. These results show that the fathead minnow has a beta-adrenergic receptor repertoire similar to that of mammals, with the molecular signatures required for ligand binding. An exogenous ligand, the beta-blocker propranolol, is able to alter the expression profile of these receptors, although the functional relevance of such changes remains to be determined. Characterisation of the molecular targets for beta-blockers in fish will aid informed environmental risk assessments of these drugs, which are known to be present in the aquatic environment.

Expression of membrane and nuclear progesterone receptors in two human placental choriocarcinoma cell lines (JEG-3 and BeWo): Effects of syncytialization

A vital function of the human placenta is to produce steroid hormones such as progesterone, which are essential for the maintenance of pregnancy and the onset of parturition. Although choriocarcinoma cell lines are valuable placental models for investigations of steroid hormone actions, little is known about the expression of progesterone receptors (PRs) in these cell lines. Therefore, in this study, the expression of membrane and nuclear PRs was investigated in cultures of fusigenic (BeWo) and non-fusigenic (JEG-3) human choriocarcinoma cell lines. In addition, the effects of an inducer of syncytialization (forskolin) on the PR expression in BeWo cells were assessed. Quantitative RT-PCR revealed that in fully syncytialized BeWo cells (treated with 50 µM forskolin for 72 h) there was a significant down-regulation of mPRα and up-regulation of mPRβ and of the progesterone membrane component-1 (PGRMC1) when compared with non-syncytialized BeWo cells. Expression of all the mPR and PGRMC1 mRNAs was significantly lower in JEG-3 cells compared to non-syncytialized BeWo cells. Interestingly, expression of PR-B was unaltered between the two BeWo states but was significantly higher in JEG-3 cells. Immunofluorescence analysis revealed that mPR proteins are differentially expressed in these choriocarcinoma cell lines as well as in the human placenta. The data demonstrate that human choriocarcinoma cell lines have a complex system of progesterone signalling involving multiple classes of PRs. The finding that syncytialization is accompanied by changes in the expression of these receptors may suggest that this process influences progesterone signalling.

Chronic effects assessment and plasma concentrations of the beta-blocker propranolol in fathead minnows (Pimephales promelas)

The presence of many human pharmaceuticals in the aquatic environment is now a worldwide concern, yet little is known of the chronic effects that these bioactive substances may be having on aquatic organisms. Propranolol, a non-specific beta adrenoreceptor blocker (beta-blocker), is used to treat high blood pressure and heart disease in humans. Propranolol has been found in surface waters worldwide at concentrations ranging from 12 to 590ng/L. To test the potential for ecologically relevant effects in fish in receiving waters, short-term (21 days) adult reproduction studies were conducted, in which fathead minnows were exposed to nominal concentrations of propranolol hydrochloride [CAS number 318-98-9] ranging from 0.001 to 10mg/L (measured concentrations typically from 78 to 130%). Exposure of fish to 3.4mg/L (measured) over 3 days caused 100% mortality or severe toxicity requiring euthanasia. The most sensitive endpoints from the studies were a decrease in hatchability (with regard to the number of days to hatch) and a concentration-related increase in female gonadal somatic index (GSI), giving LOEC(hatchability) and LOEC(female GSI) values of 0.1mg/L. Concentration-related decreases in weights of male fish were also observed, with LOEC(male wet weight value) of 1.0mg/L, and the LOEC(reproduction) value was 1.0mg/L. Collectively, these data do not suggest that propranolol was acting as a reproductive toxin. Plasma concentrations of propranolol in male fish exposed to nominal concentrations of 0.1 and 1.0mg/L were 0.34 and 15.00mg/L, respectively, which constitutes 436 and 1546% of measured water concentrations. These compare with predicted concentrations of 0.07 and 0.84mg/L, and thus to a degree support the use of partition coefficient models for predicting concentrations in plasma in fish. In addition, propranolol plasma concentrations in fish exposed to water concentrations of 0.1 and 1.0mg/L were greater than the human therapeutic plasma concentration and hence these data very strongly support the fish plasma model proposed by Huggett et al. [Huggett, D.B., Cook, J.C., Ericson, J.F., Williams, R.T., 2003a. A theoretical model for utilizing mammalian pharmacology and safety data to prioritize potential impacts of human pharmaceuticals to fish. Hum. Ecol. Risk Assess. 9, 1789-1799].

Novel estrogen receptor-related Transcripts in Marisa cornuarietis; a freshwater snail with reported sensitivity to estrogenic chemicals

We have isolated novel molluskan steroid receptor transcripts orthologous to vertebrate estrogen receptors (ERs) and estrogen receptor-related receptors (ERRs) from the freshwater snail Marisa cornuarietis. Radiolabeled ligand binding analyses showed that neither recombinant receptor protein specifically bound 17beta-estradiol over the range applied (0.3-9.6 nM). These novel receptor transcripts have thus been designated mcER-like and mcERR respectively. Quantitative PCR revealed mcER-like to be expressed ubiquitously throughout a range of male and female structures studied, including neural and reproductive tissues. Highest absolute levels were seen in the male penis-sheath complex. The mcERR mRNA was also expressed ubiquitously throughout all male and female tissues analyzed here, with very low absolute transcript numbers in female accessory sex structures compared to other tissues.

Overwinter fasting and re-feeding in rainbow trout: plasma growth hormone and cortisol levels in relation to energy mobilisation

This study investigated the roles of cortisol and growth hormone (GH) during a period of fasting in overwintering salmonid fish. Indices of carbohydrate (plasma glucose, liver glycogen), lipid (plasma free fatty acids (FFAs)) and protein metabolism (plasma protein, total plasma amino acids) were determined, together with plasma GH, cortisol and somatolactin (SL) levels at intervals in three groups of rainbow trout (continuously fed; fasted for 9 weeks then fed; fasted for 17 weeks). In fasted fish, a decline in body weight and condition factor was accompanied by reduced plasma glucose and hepatic glycogen and increased plasma FFA. No consistent elevation of plasma GH occurred until after 8 weeks of fasting when plasma GH levels increased ninefold. No changes were observed in plasma total protein and AA until between weeks 13 and 17 when both were reduced significantly. When previously fasted fish resumed feeding, plasma glucose and FFA, and hepatic glycogen levels rapidly returned to control values and weight gain resumed. No significant changes in plasma cortisol levels, related to feeding regime, were evident at any point during the study and there was no evidence that SL played an active role in the response to fasting. The results suggest that overwinter fasting may not represent a significant nutritional stressor to rainbow trout and that energy mobilisation during fasting may be achieved without the involvement of GH, cortisol or SL.

Cloning and gene expression of P450 17alpha-hydroxylase,17,20-lyase cDNA in the gonads and brain of the fathead minnow Pimephales promelas

P450 17alpha-hydroxylase,17,20-lyase (P450c17) is a key steroidogenic enzyme in the production of androgens and, therefore, is also indispensable for the production of oestrogens (that are produced from the aromatisation of androgens). In this study, P450c17 cDNA was cloned from the ovary of the fathead minnow (FHM) and its gene expression was examined in the gonads and brains of male and female FHM at different stages of gonadal development with a view to developing an understanding of its involvement in the reproductive physiology in this species. The FHM-P450c17 cDNA sequence cloned was 1812 bp in length, with an open reading frame of 1554 nucleotides encoding a protein of 518 amino acids. Amino acid identity of FHM-P450c17 with P450c17s in other animals was up to 81.8% in other teleosts (channel catfish), 62% in elasmobranches (spiny dogfish), 64% in birds (chicken), and up to 48.8% in mammals (human). FHM-P450c17 gene expression occurred in the ovary, testis, and also in the brain (both male and female) at all stages of sexual development studied. Expression in the brain was at least 30-fold lower than in the gonads, but consistent in all fish life stages studied. In the testis, FHM-P450c17 gene expression was negatively correlated with gonadal development, but there was no obvious association between P450c17 gene expression and sexual development in the ovary, or brain (in both males and females). The results from this study demonstrate the expression of P450c17 in the brain for the first time in fish. Enzymatic studies are now needed to investigate the possible role of P450c17 in neurosteroid production in teleosts.

Exposure to exogenous 17beta-oestradiol disrupts p450aromB mRNA expression in the brain and gonad of adult fathead minnows (Pimephales promelas)

Oestrogens are key regulators in sexual differentiation and development in higher vertebrates. P450 aromatase (p450arom) is the steroidogenic enzyme responsible for the synthesis of oestrogens from aromatisable androgens. Effects of endocrine disrupting chemicals on steroidogenic enzyme gene expression have received little attention so far, yet it is potentially a major pathway for sexual disruption. In this 14-day study the effects of exogenous 17beta-oestradiol (E2) at environmentally relevant concentrations were assessed on gene expression of p450aromB in the gonad and brain of maturing male and female fathead minnows (FHM). Exposure to E2 resulted in an oestrogenic response as shown by a dose-dependent induction of plasma vitellogenin (VTG) in female and male fish and a dose-dependent inhibition of testis growth. There was an effect of exposure to E2 on p450aromB mRNA expression in the gonads; E2 up-regulated p450aromB mRNA expression in the testis and ovary in a dose-response manner after 14 days of exposure. In male brain, p450aromB mRNA concentrations were significantly reduced in fish exposed to 100 and 320 ng E2/l on day 4, but on day 14 were elevated in males exposed to both 32 and 100 ng E2/l. No effects of E2 on p450aromB mRNA expression occurred in the brain of females. The results of this study show that concentrations of E2 found in the environment can have disruptive effects on key steroidogenic enzyme pathways that control sexual development in fish.

Follicle-stimulating hormone and its alpha and beta subunits in rainbow trout (Oncorhynchus mykiss): purification, characterization, development of specific radioimmunoassays, and their seasonal plasma and pituitary concentrations in females

Gonad development in fish, as in mammals, is regulated by two gonadotropins (GTHs), FSH and LH. The function of LH in fish has been clearly established; however, the function(s) of FSH is less certain. The lack of specific and sensitive assays to quantify FSH and its alpha and beta subunits has hindered studies to assess physiological function. In this study, gel filtration chromatography, ion exchange chromatography, and HPLC were employed to purify FSH and its subunits from pituitary glands of rainbow trout (Oncorhynchus mykiss), and the identities of the isolates were confirmed by amino acid analysis. Polyclonal antibodies were raised against the free GTHalpha2 and free FSHbeta subunits to develop specific RIAs. The sensitivities of the intact FSH, GTHalpha2, and FSHbeta assays were 1 ng/ml, 0.2 ng/ml, and 0.1 ng/ml, respectively, and the cross-reaction of these molecules with each other and with intact LH in the heterologous assays was <10.4% throughout. Pituitary and plasma samples diluted in parallel with the standards in all three assays and spiked sample recoveries were >90% throughout. Measurement of plasma and pituitary concentrations of intact FSH in female rainbow trout confirmed the established seasonal profiles. Concentrations of free GTHalpha2 subunit were elevated both in the plasma and in the pituitary in females at ovulation (maximum concentrations: 34.93 +/- 6.3 ng/ml in plasma; 37.63 +/- 5.79 microg/pituitary). In both the plasma and the pituitary, free FSHbeta subunit was present throughout the reproductive cycle but at very low concentrations when compared with both free GTHalpha2 and intact FSH. The presence of free GTHalpha2 subunit in the plasma similarly occurs in mammals, but its functional significance in fish has yet to be established.

Molecular characterisation of a putative Atlantic salmon (Salmo salar) odorant receptor

The olfactory system of fish is extremely important as it is able to recognise and distinguish a vast array of odorous molecules that are involved in behaviours paramount to survival. This is achieved by the activation of a diverse multigene family of G-protein coupled receptors through odorous ligand binding. Using molecular techniques, the nucleotide sequence of the cDNA coding for an Atlantic salmon (Salmo salar) odorant receptor (ASOR1) has been determined. The full-length cDNA (1260 nt) encodes a protein of 320 amino acid residues, including one potential N-linked glycosylation site, within the short extracellular amino terminal of the receptor. Hydrophobicity analysis revealed seven hydrophobic regions within the amino acid sequence, corresponding to possible positions of the transmembrane domains characteristic of the G-protein coupled receptor superfamily. Several conserved motifs unique to odorant receptors were also present. Through characterisation of this receptor, we hope to increase the understanding of the mechanisms underlying olfaction in salmonid species.

Molecular characterization of the first non-mammalian p73 cDNA

The p53 gene is believed to be mutated or deficient in over 50% of human tumours, and is therefore considered to be instrumental in the process of carcinogenesis. Recently in humans, homologues of p53 (such as p73 and p63) have been isolated. In our studies in fish, we have been isolating tumour suppressor genes with a view to their potential use to study genotoxins in the aquatic environment. In this paper, we report the characterisation of the first non-mammalian p73 cDNA, isolated from barbel (Barbus barbus), a freshwater cyprinid fish indigenous to UK rivers. The deduced barbel p73 amino acid sequence has a high homology with human p73 alpha: the proteins are 641 and 636 aa in length, respectively, and there is a 72% identity over the entire sequence length of the protein (over 90% in the putative DNA binding domain). The level of conservancy for p73 is considerably higher across class (from man to fish), than for p53 and it may therefore have particular value in studies on environmental mutagenesis. Northern analysis showed expression of three p73 mRNA transcripts/homologues. The patterns of p73 tissue expression in the barbel differed from the expression of p53 mRNA, suggesting specific functional roles for the two genes.

Fish p53 as a possible biomarker for genotoxins in the aquatic environment

The p53 gene is a tumour suppressor gene which has a fundamental role in cell cycle control and division, and in mammals certain genotoxic agents induce specific mutations in p53, leading to tumourigenesis. Fish have been investigated as models for studying carcinogens, but as yet very little data exists that links exposure to specific chemicals with the aetiology of tumours found in wild populations. In this study, p53 was sequenced from five species of fish with a view to the possible use of mutations in the highly conserved domains of p53 to identify genotoxins in the aquatic environment. A 0.8 kb fragment of the cDNA encompassing the conserved DNA-binding domain of p53 was sequenced in three Oncorhynchus salmonid fish: coho (O. kisutch), chum (O. keta), and chinook (O. tshawytscha) and full-length p53 cDNAs were sequenced in the puffer fish (Tetraodon miurus) and the barbel (Barbus barbus). The full-length puffer fish and barbel p53 cDNAs were 1834 bp and 1790 bp in length, encoding a 367 aa protein and a 369 aa protein, respectively. The deduced aa sequences of the p53 cDNA in the Oncorhynchus salmon shared a 100% identity in the five conserved regions (I-V). Comparisons of the deduced aa sequences for puffer fish and barbel p53 with other fish p53s revealed a high homology within the conserved DNA binding domain (68-86% for puffer fish and between 66-88% for barbel). "Conserved" domain I was not highly conserved in fish, as it is in mammals, and, therefore, conserved domains II-V are most likely to provide the valuable sequences in fish p53 for use in mutational studies to fingerprint genotoxins in the aquatic environment.

Studies on the GH/SL gene family: cloning of African lungfish (Protopterus annectens) growth hormone and somatolactin and toad (Bufo marinus) growth hormone

The lungfishes (lobe-finned fish) occupy a unique position in vertebrate phylogeny, being regarded as the closest extant relatives to the tetrapods. The putative pituitary hormone somatolactin (SL) has hitherto been found only in teleost fishes, and the presence of this protein in tetrapods or lobe-finned fishes has not been ascertained. It was therefore of interest to determine the structure of SL in the African lungfish (Protopterus annectens), as this information would be useful for designing probes to facilitate the detection of SL genes in amphibians and other tetrapods. The structural relationships between SL, growth hormone (GH), and prolactin (PRL) strongly suggest that these proteins evolved from a common ancestor. To obtain a more complete picture of the evolution of these hormones in lungfish, African lungfish GH has been cloned and sequenced. The cDNA sequence of a toad (Bufo marinus) GH was determined to facilitate maximum parsimony analysis of GH sequences. Cladistic analysis confirmed that lungfish and amphibian GH sequences form a clade distinct from the GH sequences of ray-finned fishes. A distance matrix analysis of SL sequences indicated that lungfish SL had the lowest primary sequence identity with goldfish SL (47%) and the highest with flounder SL (66%). The detection of SL in a lungfish indicates that the gene duplication within the SL/GH/PRL family, which gave rise to SL, must have occurred in a common ancestor of the ray-finned fishes (Actinopterygii) and the lungfishes (Sarcopterygii) and tetrapods.

Identification and modulation of a growth hormone-binding protein in rainbow trout (Oncorhynchus mykiss) plasma during seawater adaptation

A soluble protein that specifically bound 125I-human growth hormone (hGH) was identified in rainbow trout plasma, using HPLC-gel filtration. The binding affinity of the protein for hGH was 1.2 x 10(9)M-1. 125I-rainbow trout GH (tGH) was also able to bind to the protein albeit with a lower affinity (6.6 x 10(7)M-1) than hGH. Crosslinking experiments using 125I-hGH revealed two specific bands of 150 and 130 kDa. The complex 125I-hGH-BP could be precipitated by a monoclonal anti-GH receptor antibody, suggesting a close relationship between the plasma GH-BP and the GH receptor. A fourfold increase in the hGH binding to the GH-BP was shown 48 h after transfer of the fishes from freshwater to seawater. The increase in binding was related to a high binding capacity without significant changes in binding affinity. These results suggest a potential role of this related GH-BP as an index of GH effects during seawater adaptation in salmonids.

Effects of gonadectomy and steroids on plasma and pituitary levels of somatolactin in Atlantic salmon, Salmo salar

Somatolactin (SL) is a hormone recently isolated and characterized from fish pituitaries. Although the functions of SL are still largely unknown, it has been implicated in reproduction. In this study, the effects of gonadal steroids on SL secretion were investigated in Atlantic salmon male parr in two experiments. In both, mature males were gonadectomized in the autumn and implanted with Silastic capsules containing testosterone (T), 11-ketoandrostenedione (11kA), or 17 alpha,20 beta-dihydroxy-4-pregnene-3-one (20-P), gonadectomized alone, or sham-operated. In addition, immature males were implanted with T or 11kA in experiment 1. After 4-5 weeks pituitaries and plasma were sampled and SL levels measured by radioimmunoassay (RIA). Plasma levels of T, 11-ketotestosterone, and 20-P were also measured by RIA. In experiment 1, initial immature males had lower (0.7 +/- 0.4 ng/ml) plasma SL levels than initial mature males (3.3 +/- 0.4 ng/ml), whereas pituitary content was not influenced. Gonadectomy significantly reduced both plasma SL levels (experiment 1, sham controls 5.6 +/- 0.5 ng/ml, castrated 1.6 +/- 0.5 ng/ml; experiment 2, sham controls 6.5 +/- 1.1 ng/ml, castrated 3.3 +/- 0.4 ng/ml) and the pituitary content of SL (experiment 1, sham controls 1206 +/- 187 ng/pituitary, castrated 663 +/- 104 ng/pituitary; experiment 2, sham controls 1043 +/- 199 ng/pituitary, castrated 629 +/- 70 ng/pituitary), suggesting that the testes stimulated the synthesis and release of pituitary SL. Overall, the effects of steroid replacement were inconsistent between the experiments, although in experiment 2 castrated males receiving the highest dose of T had significantly higher plasma SL levels (8.2 +/- 1.2 ng/ml) than all other castrated groups (1.8-4.3 ng/ml).

Isolation and characterisation of mRNA encoding the salmon- and chicken-II type gonadotrophin-releasing hormones in the teleost fish Rutilus rutilus (Cyprinidae)

The complementary DNAs (cDNA) encoding the [Trp7,Leu8]-gonadotrophin-releasing hormone (salmon-type GnRH; sGnRH:GeneBank accession no. u60667) and the [His5,Trp7,Tyr8]-GnRH (chicken-II-type GnRH; cGnRH-II: GeneBank accession no. u60668) precursor in the roach (Rutilus rutilus) were isolated and sequenced following reverse transcription and rapid amplification of cDNA ends (RACE). The sGnRH and cGnRH-II precursor cDNAs consisted of 439 and 628 bp, and included open reading frames of 282 and 255 bp respectively. The structures of the encoded peptides were the same as GnRHs previously identified in other vertebrates. The sGnRH and cGnRH-II precursor cDNAs, including the non-coding regions, had 88.6 and 79.9% identity respectively, to those identified in goldfish (Carassius auratus). However, significant similarity was not observed between the non-coding regions of the GnRH cDNAs of Cyprinidae and other fish. The presumed third exon, encoding partial sGnRH associated peptide (GAP) of roach, demonstrated significant nucleotide and amino acid similarity with the appropriate regions in the goldfish, but not with other species, and this may indicate functional differences of GAP between different families of fish. cGnRH-II precursor cDNAs from roach had relatively high nucleotide similarity across this GnRH variant. Cladistic analysis classified the sGnRH and cGnRH-II precursor cDNAs into three and two groups respectively. However, the divergence between nucleotide sequences within the sGnRH variant was greater than those encoding the cGnRH-II precursors. Consistent with the consensus developed from previous studies, Northern blot analysis demonstrated that expression of sGnRH and cGnRH-II was restricted to the olfactory bulbs and midbrain of roach respectively. This work forms the basis for further study on the mechanisms by which the tapeworm, Ligula intestinalis, interacts with the pituitary-gonadal axis of its fish host.

cDNA cloning of eel (Anguilla anguilla) somatolactin

The nucleotide sequence of the cDNA coding for eel somatolactin (SL), a pituitary hormone belonging to the growth hormone (GH)/prolactin (PRL) family, has been determined. The full-length eel SL cDNA (1213 bp) encodes a protein of 229 amino acids (aa), with a putative signal peptide of 24 aa and a mature protein of 204 aa. Eel SL contains seven Cys residues found to be characteristic of SLs, and two potential N-glycosylation sites. Significant sequence homology between eel and seven other fish SLs (42% aa identity, 63% aa similarity) reveal SL to be highly conserved. A higher sequence identity of SL to GH than PRL is suggested by the comparison of these hormones in eel and chum salmon.

Pronounced seasonal rhythms in plasma somatolactin levels in rainbow trout

The aim of this study was to establish whether there are seasonal or age-related changes in circulating levels of somatolactin (SL) in rainbow trout (Onchorhynchus mykiss). SL levels were determined in blood sampled at monthly intervals over a 2-year period from a population of rainbow trout maintained under a natural daylength and temperature regime (North-West England, latitude 54 degrees 20' N). SL levels displayed a distinct circannual cycle, with peak levels in summer (17-20 micrograms/l) and lowest levels occurring in winter (0.2-2 micrograms/l). This variation in SL levels was closely correlated with water temperature (P < 0.001) but was out of phase with changes in daylength. Plasma SL levels were significantly higher in both mature male and female fish compared with immature fish. Plasma prolactin levels were determined to provide information on a hormone structurally related to SL, and also because mammalian prolactin is known to show distinct seasonal cycles. However, trout prolactin, in contrast to SL, did not show a pronounced seasonal pattern, although prolactin levels were significantly, but inversely, correlated with water temperature (P < 0.001).

Immunoreactive somatolactin cells in the pituitary of young, migrating, spawning and spent chinook salmon, Oncorhynchus tshawytscha

Immunocytochemical techniques using an antiserum to cod somatolactin (SL) demonstrated the presence of SL cells in the intermediate lobe of the pituitary in Oncorhynchus tshawytscha. The cells were small in yearling fish. Two groups of maturing fish were studied. In the spring run salmon collected in April and May during the upstream migration, the SL cells appeared stimulated. In September, during spawning, SL cell stimulation was maximal with indices of hypertrophy and degranulation often more marked in females than in males. In the other group, salmon of the fall run collected in the Pacific Ocean in August had well developed gonads, large gonadotropes and abundant SL cells. In spawning salmon (September) the SL cells were stimulated, mainly in females. However, the final stimulation was less intense than in spring run spawning fish. The SL cells were smaller, without evident granule release, but still abundant in spent salmon of the fall run caught at the end of November. Various factors (time spent in rivers before spawning, starvation, decalcification, stress, hypothalamic influences) were considered which might explain differences between spring and fall run salmon. These observations suggest that SL may play a role in the control of gonadal maturation in chinook salmon as it may also do in sockeye and chum salmon previously studied, and that SL cells may be sensitive to the ambient salinity.

Immunocytochemical study of the somatolactin cells in the pituitary of Pacific salmon, Oncorhynchus nerka, and O keta at some stages of the reproductive cycle

Cells of the intermediate lobe of salmonids, homologous to the PAS-positive cells of other teleost species, cannot be differentiated by normal staining techniques, but can be immunostained with an antiserum against cod somatolactin (SL). Immunocytochemical techniques were applied to pituitary sections of two Pacific salmon, Oncorhynchus nerka and O. keta. Samples of immature or early maturing fish were collected in the Pacific Ocean and from mature spawning fish from hatcheries near Seattle and Willard (Washington). SL cells were rather small and moderately immunoreactive in immature fish. They were slightly enlarged in the early stages of gonadal development and more often contacted the basal lamina through processes with terminal swellings, suggesting granule release into perivascular spaces. In spawning fish, cells were enlarged and frequently more granulated, showing a wide contact with the basal lamina and a proximodistal transport of granules. In addition, large and more or less degranulated cells were noted, also indicating an active release of SL granules. Spawning females tended to have more SL cells than equivalent males. The gradual stimulation of SL synthesis and release during sexual maturation suggests that SL may be involved in the control of some steps of reproduction as previously shown by the increase in SL plasma levels in maturing coho salmon.

Plasma somatolactin concentrations in salmonid fish are elevated by stress

The preliminary finding that plasma levels of somatolactin (SL) were markedly elevated following stress caused by confinement in chinook salmon (Oncorhynchus tshawytscha) prompted a more detailed study of SL dynamics during stress. SL levels have been determined in the plasma of rainbow trout (Oncorhynchus mykiss) during exposure to acute (0-30 min) and short (0-24 h) periods of stress resulting from handling and confinement. The results show that SL levels increase rapidly within minutes following the onset of stress, reach a peak between 1 and 2 h, decline over the next 3 h, and then show an additional increase again by 24 h. During acute stress caused by confinement, the increase in plasma SL levels occurred within 2 min, thus showing a more rapid response than cortisol. This suggests that the response is mediated directly by the hypothalamus and is not a result of a feedback mechanism. The results also demonstrate that SL secretion in response to stress is at least partially under genetic control. In the short-term stress experiment, progeny of fish selected as high responders or low responders to stress, based on the magnitude of the plasma cortisol levels induced by stress, were used, and these fish showed similarly accentuated or attenuated release of SL following stress. These results clearly demonstrate that non-specific environmental stress causes rapid activation of SL-secreting cells in the pars intermedia, suggesting that this hormone has an important role in the adaptive response of fish to stress.

Plasma somatolactin levels in coho salmon (Oncorhynchus kisutch) during smoltification and sexual maturation

Somatolactin (SL) is a novel pituitary hormone recently characterized in several fish species. Structural analyses have shown that SL belongs to the growth hormone/prolactin family, and that it is a highly conserved protein. SL is synthesized by the periodic acid/Schiff-positive cells in the pars intermedia, but has an as yet unidentified function(s). We have recently developed a homologous radioimmunoassay for coho salmon SL and measured plasma levels of SL during two stages of the coho salmon life cycle, smoltification and sexual maturation. During smoltification, plasma levels of SL changed almost in parallel with plasma levels of thyroxine; levels increased as morphological indices of smoltification appeared and decreased as smoltification was completed. Following this period, SL levels remained low until the spring prior to spawning. In a separate study, plasma levels of SL were measured in sexually maturing coho salmon that remained in fresh water throughout their life cycle. During the year of sexual maturation, plasma levels of SL gradually increased from the spring onward, reaching peak levels at the time of spawning in November and December. These data are similar to those previously reported for sexually maturing coho salmon that were maintained in seawater prior to spawning (Rand-Weaver et al. 1992). Therefore, increases in plasma SL levels occurred in sexually maturing fish irrespective of whether they were maintained in fresh water or seawater. Peak levels at spawning were higher than those observed during smoltification. Possible roles for SL in metabolism and reproduction are discussed.

Isolation of prolactin and growth hormone from the pituitary of the holostean fish Amia calva

Pituitaries from adult male and female Amia calva (Order Holostei) were acid extracted and fractionated by gel filtration column chromatography and reversed-phase high performance liquid chromatography. This two-step isolation procedure yielded homogeneous pools of Amia prolaction (PRL) and growth hormone (GH). The amino acid composition of both purified polypeptides was determined. Primary sequence analysis of the first 22 positions at the N-terminal of Amia PRL revealed that this region has 63% sequence identity with eel PRL-1. The N-terminal region of Amia PRL lacks the disulfide bridge which is characteristic of tetrapod PRLs. Primary sequence analysis of the first 24 positions at the N-terminal of Amia GH revealed that this region has 62% sequence identity with eel GH and 54% sequence identity with both blue shark GH and sea turtle GH. Based on N-terminal analysis, it appears that Amia PRL and GH are more closely related to teleost PRLs and GHs than they are to tetrapod PRLs and GHs.

Somatolactin stimulates in vitro gonadal steroidogenesis in coho salmon, Oncorhynchus kisutch

Somatolactin (SL), a newly discovered pituitary hormone of the teleost pars intermedia, is structurally similar to prolactin and growth hormone. The function(s) of SL are not yet established, although evidence suggests that it may play a role in reproduction. Possible steroidogenic activity of coho salmon SL was tested and compared with gonadotropin I (GTH I) in incubations of ovarian follicles or testicular fragments. SL stimulated production of 11-ketotestosterone and testosterone by testicular fragments, and production of estradiol by ovarian follicles in a concentration-dependent manner. However, the steroidogenic activity of SL was considerably less than that of GTH I. These results suggest that SL may play a role in regulation of gonadal function in salmon.

Somatolactin, a novel pituitary protein: purification and plasma levels during reproductive maturation of coho salmon

Somatolactin (SL), a newly discovered fish pituitary protein belonging to the GH/prolactin family, was isolated from coho salmon (Oncorhynchus kisutch). Antibodies were raised to purified coho SL, and a homologous radioimmunoassay was developed and validated. The assay was specific for SL as indicated by the absence of cross-reactivity with coho salmon GH, gonadotrophins I and II and less than 0.2% cross-reaction to prolactin. Serial dilutions of plasma and pituitary extracts from Oncorhynchus species including coho salmon, chinook salmon and rainbow trout were parallel to the coho salmon SL standard curve. Displacement curves for dilutions of Atlantic salmon (Salmo salar) plasma, but not pituitary extract were parallel to the standards. Plasma levels of SL were measured in coho salmon throughout the final year of reproductive maturation. During the period of gonadal growth, plasma SL levels increased and were highly correlated to oestradiol levels in females and 11-ketotestosterone levels in males. Peak levels of SL were observed at the time of final maturation and spawning in both sexes. It is hypothesized that SL may regulate some physiological aspect of reproduction.

A rapid procedure for the isolation of bioactive growth hormone

A two-step isolation method is described for the purification of growth hormone and prolactin from rat pituitaries. Following alkaline extraction, the sample was chromatographed on Sephadex G-75. Growth hormone and prolactin, which eluted in the same gel filtration fraction, were separated on a reversed-phase HPLC column. The isolated proteins migrated to the same position as rat growth hormone and prolactin standards. Further confirmation that the purified proteins were indeed growth hormone and prolactin was provided by immunoblotting using several mammalian antisera and N-terminal amino acid sequencing. The purified rat growth hormone was shown to be biologically active when tested in the hypophysectomized rat body weight gain assay. Although rat prolactin remains to be tested, it seems likely that this hormone would also have biological activity. The present procedure is of general applicability and particularly useful when only small amounts of pituitary glands are available for extraction.

Detection of a novel sequence change in the major form of alpha-MSH isolated from the intermediate pituitary of the reptile, Anolis carolinensis

Intermediate pituitaries of the reptile, Anolis carolinensis, were separately pulse labeled with [3H]Trp and [3H]Tyr. The major form of alpha-MSH was purified by immunoprecipitation and isolated by reverse phase HPLC. Tryptic peptide analysis indicated that the [3H]Trp-labeled C-terminal fragment of Anolis alpha-MSH had the same retention time as mammalian ACTH(9-13) amide; however, the [3H]Tyr-labeled N-terminal fragment did not coelute with either mammalian ACTH(1-8) or N-acetyl-ACTH(1-8). Purification of alpha-MSH from 76 Anolis intermediate pituitaries confirmed that a sequence change had occurred in the N-terminal region of Anolis alpha-MSH. The tissues were acid extracted and purified by Sephadex G-25 chromatography and reverse phase HPLC to yield 4.5 micrograms of purified Anolis alpha-MSH for amino acid composition analysis and automated Edman degradation sequence analysis. The major form of Anolis alpha-MSH is nonacetylated and has the following novel primary sequence: Ser-Tyr-Ala-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro(Val-amide). The presence of Val-amide was verified by immunological analysis, tryptic peptide analysis and amino acid composition analysis.

Greater conservation of somatolactin, a presumed pituitary hormone of the growth hormone/prolactin family, than of growth hormone in teleost fish

From pituitary cDNA libraries of Atlantic cod and chum salmon, cDNA clones coding for somatolactin (SL), a presumed pituitary hormone belonging to the growth hormone (GH)/prolactin (PRL) family, were isolated and characterized. The 1.3-kb cod SL mRNA was composed of a greater than 0.25-kb 5' untranslated region, a coding region for the precursor of 235 amino acids (aa), a 0.14-kb 3' untranslated region, and a poly(A) tail. The 2.5-kb salmon SL mRNA had a less than 0.1-kb 5' untranslated region, a precursor (233 aa) coding region, a 1.6-kb 3' untranslated region, and a poly(A) tail. A signal peptide of 26 and 24 aa was found in the SL precursor of cod and salmon, respectively. Thus, the mature SLs of these fish are composed of 209 aa. Two potential N-glycosylation sites were identified in cod SL, whereas no site could be found in the salmon. A comparison of amino acid sequences of the three SLs so far isolated indicated six Cys residues to be in homologous positions to those in GH and PRL, and one Cys residue to be characteristically present in SL. Among cod, salmon, and flounder, greater colinearity of amino acid sequences was noted in SLs than in GHs. The identities of the SL amino acid sequences were between 73 and 81% as compared to 58-62% for the corresponding GHs, indicating greater conservation of SL than GH.

Gene structure of chum salmon somatolactin, a presumed pituitary hormone of the growth hormone/prolactin family

From a chum salmon genomic DNA library, clones coding for somatolactin (SL), a presumed pituitary hormone belonging to the GH/PRL family, were isolated and analyzed. The salmon SL gene was 16 kilobases (kb) in length, this being the largest among mammalian GH (approximately 2 kb) and PRL (approximately 10 kb) and fish GH (approximately 4 kb) genes. As in the case of mammalian GH/PRL genes, the salmon SL gene was comprised of five exons in contrast to rainbow trout and Atlantic salmon GH genes, which each have six exons. Upstream from the transcriptional initiation site were found one TATA box identical to those of mammalian PRL genes and four consensus sequences corresponding to the Pit-1/GHF-1 binding element which is essential to the expression of mammalian GH and/or PRL genes. The similarity in amino acid sequences and organization of the SL gene with mammalian GH/PRL genes indicates that the SL gene is quite likely produced from an ancestral gene common to GH/PRL genes by gene duplication. Based on these considerations, an evolutionary model for the GH/PRL/SL gene family was made and shows the common ancestral gene to originate not from duplication of a primordial gene but from shuffling of independent exons and a regulatory sequence.

Isolation and characterization of somatolactin, a new protein related to growth hormone and prolactin from Atlantic cod (Gadus morhua) pituitary glands

The characterization of cod somatolactin (SL), a new pituitary protein belonging to the growth hormone/prolactin family, is described. Cod SL has a molecular weight of 26 kDa and consists of 209 amino acids, of which eight are Cys. The protein has three disulfide bonds between residues Cys5-Cys15, Cys65-Cys181, and Cys198-Cys206. The Cys residues at positions 42 and 180 are not involved in disulfide bonding. The positions of these disulfide bonds are homologous to those found in prolactin and growth hormone. Cod SL has two possible N-glycosylation sites, but only one appears to have carbohydrate units attached. Chemical analysis showed the following sugars to be present: galactose, mannose, N-acetylneuramic acid, and glucosamine. A smaller variant (23 kDa) of SL has been isolated, which is believed to be deglycosylated. Sequence comparison revealed cod SL to be similarly related to both GH and PRL, but slightly higher identity was observed to the tetrapod hormones (27-33%) than to the teleost hormones (21-27%).

The complete amino acid sequences of two variants of growth hormone from Atlantic cod (Gadus morhua)

The complete amino acid sequences of two variants of cod growth hormone (GH) have been determined. The GHs, which have apparent molecular weights of 20K and 22K in SDS-PAGE, consist of 185 amino acids and have calculated molecular weights of 20,733 and 20,805, respectively. Comparison of the two sequences showed only one amino acid difference between the variants, with Lys at position 151 in the 22K GH changed to Gly in the 20K GH. The substitution of a charged amino acid by one which contains no sidechain might be expected to be reflected in the isoelectric point of the molecule. However, the observed pI for both the 20K and 22K GHs was 5.8. The difference in apparent molecular weights by SDS-PAGE suggests the existence of a conformational difference between the variants which is attributable to the observed substitution. This conclusion is in agreement with our previous data obtained from radioimmunoassay studies where the 20K GH shows only 25% cross-reactivity in an assay developed for the 22K GH. Alignment of the cod GH sequence with those of other teleost GHs reveals cod GH to be most similar to advanced marine fish such as tuna, sea bream, bonito, and yellowtail (76-83% identity), whereas it is 62-66% identical to flounder and chum salmon GH.

cDNA cloning of somatolactin, a pituitary protein related to growth hormone and prolactin

From a flounder pituitary cDNA library, cDNA clones encoding a 28-kDa glycoprotein produced by the pars intermedia of the pituitary were isolated and characterized. Nucleotide sequencing demonstrated a precursor of the 28-kDa protein, which consisted of 231 amino acid residues, to be cleaved into a signal peptide (24 amino acids) and a mature protein (207 amino acids) containing one N-glycosylation site. By comparison of amino acid sequences, the 28-kDa protein was found to be distantly and similarly related to growth hormone and prolactin. Consequently, it was named somatolactin. Somatolactin mRNAs were specifically expressed as 1.2 and 1.8 kb poly(A)+ RNAs in flounder pituitary.

Isolation and characterization of growth hormone from Atlantic cod (Gadus morhua)

Growth hormone was purified from cod pituitary extract by a simple two-step procedure involving gel filtration and reversed-phase high-performance liquid chromatography (rpHPLC). At each stage of purification, fractions were monitored by rpHPLC, SDS-polyacrylamide gel electrophoresis, and immunoblotting using anti-chum salmon growth hormone (GH) antiserum. The yield of purified hormone was 1.3 mg/g pituitary. Cod GH was found to exist in two monomeric forms (Mr = 20K and 22K) and dimeric forms (Mr = 40K and 42K). The two monomeric forms have a pI of 5.8, an identical amino acid composition, histidine as the N-terminal residue, and an identical lysyl endopeptidase peptide map. Staining with concanavalin A was observed on the 20K component only, but analysis for total reducing sugar did not confirm these results. Cod GH was found to be a potent stimulator of growth in juvenile rainbow trout which received intraperitoneal injections of the hormone. The partial amino acid sequence has been determined.

Aminomethyl coumarin acetic acid: a new fluorescent labelling agent for proteins

A new fluorescent protein labelling agent, 7-amino-4-methyl coumarin-3-acetic acid (AMCA), emits in the blue region (440-460 nm) on activation with UV light (350 nm). The active reagent is the N-hydroxysuccinimide ester which reacts with lysine residues under mild conditions to form photostable amide links. The Stokes shift of 100 nm compared to 30 nm for Fluorescein isothiocyanate (FITC) allows easy filter discrimination of exciting and emitting radiation. The agent has been demonstrated in use for fluorohistochemical examination of human kidney glomeruli, using the sandwich technique and compared with the same procedure using FITC-labelled antibodies. The good quantum yield coupled with convenient emission lines in the mercury spectrum allows photographic exposure time of fluorescent labelled sections to be reduced to a quarter of that required for a corresponding FITC conjugate. AMCA-immunoglobulin conjugates were not susceptible to photobleaching and have a storage life at -20 degrees C of more than two years.

Fluorescent and radiolabelling of pepsin-digested human glomerular basement membrane with a newly developed hydroxy-coumarin derivative (CASE)

The labelling of pepsin-digested human glomerular basement membrane (pHGBM) with a newly developed fluorescent iodine acceptor 7-hydroxy-coumarin-3-acetic acid N-hydroxysucciniimydyl ester (CASE) is described. The binding of a monoclonal antibody to pHGBM was assessed by radiobinding assays, and when directly iodinated pHGBM was used there was no apparent binding. When CASE was conjugated to pHGBM prior to iodination 11% binding was achieved. CASE acting as an iodine acceptor may be useful for proteins containing few or inaccessible tyrosine residues or which are destroyed by introduction of 125I. Since CASE is fluorescent, small amounts of material can be detected during isolation prior to iodination.