Presence of GH-dependent IGF-II mRNA in the diffuse pancreatic tissue of a teleost

Effects of feeding frequency on juvenile Chinese sturgeon Acipenser sinensis

In this study, the effects of different feeding frequencies on the growth and the expression of genes in the GH/IGF axis were assessed in juvenile Chinese sturgeon. The newly hatched Chinese sturgeons were bred for 38 days at three different feeding frequencies groups (feeding frequency of two times a day, TWD; three times a day, THD; and four times a day, FOD), and the expression levels of the GH/IGF axis responses to feeding frequency were determined by quantitative real-time PCR. In addition, the full-length of the Coding Sequences of IGF I and IGF II genes (489-bp and 660-bp, respectively), were cloned and analyzed from Chinese sturgeon the first time. Multiple sequence alignments of IGFs revealed that Chinese sturgeon are high sequence identity to IGFs from other species. The phylogenetic relationships based on the IGF I and IGF II amino acid sequences were consistent with the traditional classification. After 38 days of growth, the three different feeding frequencies groups of Chinese sturgeon had no significant difference of body length, body weight, specific growth rate, the survival rate, the rate of weight gain and the condition factor. However, the relative expression of Chinese sturgeon GH in the pituitary decreased with increasing feeding frequency. The relative expression of Chinese sturgeon GHR in liver and skeletal muscle was deceased with increasing feeding frequency, while the relative expression of GHR in stomach and intestines at THD group was significantly higher than that of at TWD group and FOD group (p < 0.05). The relative expression of Chinese sturgeon IGF I in liver increased significantly with increasing feeding frequency (p < 0.05). The relative expression of IGF I in stomach and skeletal muscle was similar at the three groups. The relative expression of IGF I in intestines was significantly higher at FOD group than at TWD group and THD group (p < 0.05). The relative expression of Chinese sturgeon IGF II in liver at TWD group was significantly higher than that at THD group and FOD group (p < 0.05). However, the relative expression of IGF II in stomach, intestines and skeletal muscle at THD group was higher than that at TWD group and FOD group. Based on these previous studies that liver IGF I is regarded as a biomarker of growth performance, this result suggested that the juvenile Chinese sturgeon is better for growth when feeding four times daily compared to twice and thrice daily.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Of all divalent metals, mercury (Hg^II) has the highest affinity for metallothioneins. Hg^II is considered to be enclosed in the α and β domains as tetrahedral α‐type Hg₄Cys_11‐12 and β‐type Hg₃Cys₉ clusters similar to Cd^II and Zn^II. However, neither the four‐fold coordination of Hg nor the existence of Hg–Hg atomic pairs have ever been demonstrated, and the Hg^II partitioning among the two protein domains is unknown. Using high energy‐resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two‐coordinate Hg‐thiolate complex and four‐coordinate Hg‐thiolate cluster with a metacinnabar‐type (β‐HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster‐forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

Metallothionein from Pseudosciaena crocea: expression and response to cadmium-induced injury in the testes

Metallothioneins (MTs) are a family of stress proteins that are involved in the process of detoxification and anti-oxidation. Previous studies have focused mostly on the expression and functions of MTs in the non-reproductive tissues of aquatic vertebrates. However, there have been only a few reports regarding the functions of MTs in the reproductive tissues of such vertebrates. In order to investigate the function of MTs during spermatogenesis in Pseudosciaena crocea, reverse-transcription polymerase chain reaction (PCR) and rapid amplification of cDNA ends were performed to obtain the P. crocea MT complete cDNA sequence from the total RNA of the testes for the first time. MT was detected in the liver, kidneys, testes, spleen, gill and muscle of P. crocea by tissue-specific expression analysis. Meanwhile, immunohistochemistry staining indicated that the MT protein was localized in germ cells, Sertoli cells and the peripheral connective tissues in P. crocea testes. Furthermore, acute toxicity tests were conducted with cadmium (Cd) to determine the 96 h-medial lethal concentration value. The toxic effects of Cd on the microstructure and ultrastructure of the testes were observed. In addition, the changes in MT mRNA expression levels in the testes after Cd exposure were measured using real-time quantitative PCR. Consequently, we suggest that MTs play an important role in spermatogenesis and testes protection against Cd toxicity in P. crocea.

Microcystin-LR exposure to adult zebrafish (Danio rerio) leads to growth inhibition and immune dysfunction in F1 offspring, a parental transmission effect of toxicity

Microcystins (MCs) are algal toxins produced intracellularly within the cyanobacteria cells. MCs exposure exerts great harm to the reproductive system of fish and deteriorates the quality of eggs and sperms, and has further adverse effects on early developmental stages of fish. Whether the MC toxicity can be parentally transmitted to offspring, even though the embryos and larvae are free of MC exposure? In the present study, adult zebrafish were continuously exposed to MC-LR (with dose of 1, 5 and 20 μg/L) for 30 days. After MC-LR exposure, fertilized eggs were collected and the following F1 generation was reared in water containing no MC-LR until 60 days post fertilization (dpf). In F1 offspring, both body weight and body length were evidently dropped. Some growth and immune related genes were detected using the real-time PCR. The transcriptional levels of these genes significantly decreased in F1 offspring of zebrafish whose parents were treated with 5 and 20 μg/L MC-LR. The activities of some antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) significantly dropped in 5 and 20 μg/L MC-LR groups, and the malondialdehyde (MDA) levels markedly increased in all the three treatment groups. Furthermore, distinct pathological changes in liver were observed in F1 zebrafish. Our findings show that the MC-LR exposure to parental zebrafish results in liver damage and evidently influences the growth and immune function in F1 offspring. We consider this damage as a parental transmission effect of microcystin toxicity. Further mechanism studies are necessary to elucidate this transmission effect.

Metallothioneins, unconventional proteins from unconventional animals: a long journey from nematodes to mammals

Metallothioneins (MTs) are ubiquitous low molecular weight cysteine-rich proteins characterized by high affinity for d10 electron configuration metals, including essential (Zn and Cu) and non-essential (Cd and Hg) trace elements. The biological role of these ancient and well-conserved multifunctional proteins has been debated since MTs were first discovered in 1957. Their main hypothesized functions are: (1) homeostasis of Zn and Cu; (2) detoxification of Cd, and Hg; and (3) free radical scavenging. This review will focus on MTs in unconventional animals, those not traditionally studied in veterinary medicine but of increasing interest in this field of research. Living in different environments, these animals represent an incredible source of physiological and biochemical adaptations still partly unexplored. The study of metal-MT interactions is of great interest for clinicians and researchers working in veterinary medicine, food quality and endangered species conservation.

Effect of pollution history on immunological responses and organ histology in the marine mussel Mytilus edulis exposed to cadmium

The effect of previous toxicant exposure (i.e., exposure history) on an organism's response to re-exposure to the toxicant is of considerable interest. The marine mussel Mytilus edulis was collected from reference and polluted sites in southwest England, and groups of mussels from each site were exposed to 20 μg/L CdCl2 for 0, 1, 4, and 8 days and compared with unexposed controls. End points evaluated were tissue metal and electrolyte concentrations, haemolymph chemistry, haemocyte characteristics [counts, neutral red uptake (NRU), and phagocytosis], histology, and expression of metallothionein gene (mt10) expression in digestive glands. Field-collected animals differed by collection site for some end points at time zero, at which time tissue Fe and Pb concentrations were greater and NRU and condition index lower in mussels from the polluted site. Subsequent exposure to cadmium (Cd) in the laboratory caused Cd accumulation mainly in digestive gland, but there were no site-specific effects on tissue trace-metal concentrations. NRU, phagocytosis, and haemolymph Na(+) and K(+) concentrations differed among sites and Cd treatment, but there were no clear trends. Exposure to Cd resulted in lower Ca(2+) concentrations in gill, digestive gland, and haemolymph in animals from the polluted site compared with controls (Kruskal-Wallis, p ≤ 0.05). Lesions, including necrosis, inflammation, and neoplasia, were observed in animals from the polluted site, but the frequency of these lesions appeared to decrease unexpectedly after Cd exposure. Expression of mt10 increased 3-fold in Cd-exposed animals from the polluted site compared with all other groups (Kruskal-Wallis, p = 0.01). We conclude that Cd exposure affected some immune responses in M. edulis, but pre-exposure history influenced toxicological outcomes of Cd exposure in the laboratory.

Use of metallothioneins as biomarkers for environmental quality assessment in the Gulf of Gabès (Tunisia)

Detection and assessment of the impact of pollution on biological resources imply increasing research on early-warning markers such as metallothioneins (MTs) in metal exposure. In this paper, we have collated published information on the use of metallothioneins and metallothionein-like proteins (MTLPs) as biomarkers for environmental quality assessment in the Gulf of Gabès. In this area, some species of fish and bivalve were used as bioindicators of pollution. In these species, an induction of MTs/MTLPs by the essential metals such as Cu and Zn and the non-essential metals such as Cd was observed by different authors who suggest the potential use of these proteins as biomarkers. However, MT concentrations can be influenced by many biotic (sex, maturity stages, and tissues) and abiotic factors (temperature, salinity, and pH). This is essentially the case in field studies where many parameters can randomly affect MT levels, so the endogeneous regulation of MTs must be considered before using MTs as an indicator of heavy metal exposure. Moreover, the use of biomarker cannot be examined independently of the evaluation of techniques that enable its quantification. Therefore, the approach to the use of MTs/MTLP as biomarkers of exposure for an assessment of the physiological status of aquatic organisms is discussed in this paper.

Application of two SH-based methods for metallothionein determination in mussels and intercalibration of the spectrophotometric method: laboratory and field studies in the Mediterranean Sea

Metallothionein (MT) induction is widely used as a biomarker of exposure to metals in mussels. The aims of the present work were first to compare the suitability of spectrophotometry and differential pulse polarography (DPP) for MT detection in mussels exposed to 200 ppb cadmium for 9 days in a laboratory experiment and in mussels sampled in different seasons from expected pollution gradients along the Mediterranean Sea; second, to intercalibrate the widely used spectrophotometric method using mussels from Saronikos Gulf. In the intercalibration of the spectrophotometric method, similar results (p>0.05) were obtained by two different research teams indicating a good reproducibility of the technique. However, polarographic and spectrophotometric methods gave significantly (p<0.05) different results in laboratory and field studies. In the laboratory experiment, MT values detected with DPP were nine times higher than with spectrophotometry. The results obtained by the two methods were significantly correlated. Both methods could discriminate between control and exposed mussels. In field studies, MT values obtained by DPP were 34-38-fold higher than with spectrophotometry, and MT concentrations measured by both methods were not correlated. This discrepancy could be due to several factors, including the low levels of bioavailable metals in the studied areas and the possibility that the different methods can measure MT isoforms differentially. Further work is needed to decipher the functions of MT isoforms in mussels. This information is relevant for the application of MT as a biomarker in biomonitoring programmes.

The metal-binding features of the recombinant mussel Mytilus edulis MT-10-IV metallothionein

In contrast with the paradigmatic mammalian metallothioneins (MTs), mollusc MT systems consist at least of a high-cadmium induced form, possibly involved in detoxification, and another isoform either constitutive or regulated by essential metals and probably associated with housekeeping metabolism. With the aim of providing a deeper characterization of the coordination features of a molluscan MT peptide of the latter kind, we have analyzed here the metal-binding abilities of the recombinant MeMT-10-IV isoform of Mytilus edulis (MeMT). Also, comparison with other MTs of this type has been undertaken. A synthetic complementary DNA was constructed, cloned and expressed into two Escherichia coli systems. Upon zinc coordination, MeMT folds in vivo into highly chiral and stable Zn(7) complexes, with an exceptional reluctance to fully substitute cadmium(II) and/or copper(I) for zinc(II). In vivo cadmium binding leads to homometallic Cd(7) complexes that structurally differ from any of the in vitro prepared Cd(7) complexes. Homometallic Cu-MeMT can only be obtained in vitro from Zn(7)-MeMT after a great molar excess of copper(I) has been added. In vivo, two different heterometallic Zn,Cu-MeMT complexes are recovered, which nicely correspond to two distinct stages of the in vitro zinc/copper replacement. These MeMT metal-binding features are consistent with a physiological role related to basal/housekeeping metal, mainly zinc, metabolism, and confirm the correspondence between the MeMT gene response pattern and the functional properties of the encoded protein.

Assessment of heavy metal contamination using real-time PCR analysis of mussel metallothionein mt10 and mt20 expression: a validation along the Tunisian coast

In mussel Mytilus galloprovincialis tissues, metallothionein belongs to two different gene classes, mt10 and mt20, showing differential expression at both basal conditions and under heavy metal challenge. In this study, a new more highly sensitive technique, expression analysis of mt10 and mt20 mRNA levels by quantitative reverse transcription polymerase chain reaction, was used to assess the effects of heavy metal contamination in the digestive glands of mussels caged along the Tunisian coast. To validate the new assay, total metallothionein protein, amount of heavy metals (zinc, copper, cadmium), and a biomarker of oxidative stress such as malondialdehyde content, were assessed in the same tissues. At the investigated sites, the molecular assay showed variations of mt20 relative gene expression levels within one or two orders of magnitude, with maximum values at two sites severely polluted with cadmium, Mahres (100-fold) and Menzel Jemile (165-fold). Changes in mt10 expression were recorded at all sites where copper had significantly accumulated, although fold induction levels were less pronounced than those of mt20. In this paper, gene expression data are discussed in relation to the studied biomarkers, demonstrating that the molecular technique based on the differential expression of mt10 and mt20 genes represents (i) a useful and robust tool for studying and monitoring heavy metal pollution under field conditions, and (ii) an improvement in the application of metallothionein as a biomarker of response to exposure to heavy metals in marine mussels.

Molecular characterization and function analysis of MT-10 and MT-20 metallothionein isoforms from Mytilus galloprovincialis

Structure and function of molluscan metallothioneins (MTs) are still poorly understood. The sea mussel Mytilus galloprovincialis displays two MT isoforms which differ in both primary sequences and physiological functions. MT-10 is the constitutive isoform, whereas MT-20 is mainly induced by cadmium (Cd). Both MTs were produced as recombinant proteins and showed identical Cd content and similar Cd-binding properties. Conversely, circular dichroism disclosed marked differences in the secondary conformations of the two Cd(7)-MTs. The possible relapses of these structural differences on protein stability and function were assessed. MT-10 presented a higher thermal stability and a more compact structure than MT-20, as it was inferred by absorption and emission spectroscopy studies. Moreover, the kinetics of Cd-release clearly indicated that MT-10 is much more sensitive to oxidation than is MT-20. The observed differences between MT-10 and MT-20 are discussed in terms of the different physiological roles exerted by the two isoforms in mussel.

Effects of aquaculture related stressors and nutritional restriction on circulating growth factors (GH, IGF-I and IGF-II) in Atlantic salmon and rainbow trout

The effects of aquaculture related stressors on circulating levels of GH, IGF-I and for the first time, IGF-II in Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, circulating growth factor levels were measured in four different experiments. Two 24 h confinement stressor procedures, (one with Atlantic salmon, the other with rainbow trout); following a hypo-osmotic stressor (freshwater bath) in salt water acclimated, adult, Atlantic salmon; and during a 22 day starvation and re-feeding protocol with juvenile Atlantic salmon. Handling and confinement resulted in significant decreases in circulating levels of all three growth factors in Atlantic salmon, and IGF-I and IGF-II (but not GH) in rainbow trout. A 2-3 h freshwater bath to remove gill parasites on a commercial Atlantic salmon aquaculture operation caused a significant decrease in circulating GH and IGF-I concentrations, but no significant change in IGF-II concentration, 2 days post bathing. Starvation for a period of 15 days in Atlantic salmon resulted in a significant increase in circulating GH levels and a significant decrease in circulating IGF-I and IGF-II. Re-feeding of starved fish for 7 days resulted in a significant decrease in GH to the concentration measured in continually fed fish, however re-feeding did not change plasma levels of IGF-I and IGF-II relative to continually starved fish. The results presented here confirm previously observed handling and confinement stressor induced effects on GH and IGF-I and, for the first time, on IGF-II in salmonids. Furthermore this study confirms the nutritional regulation of GH, IGF-I and IGF-II in juvenile Atlantic salmon.

Small metallothionein MT-10 genes in coastal and hydrothermal mussels

Metallothioneins (MTs) are important proteins in the intracellular regulation of metals. In the Mytilidae family, which includes many economically important species, 2 major forms of MTs have been reported: MT-10 (10 kDa) and MT-20 (20 kDa). Many different MT-10 proteins have been isolated from the common species Mytilus edulis, which suggests that distinct MT-10 genes may occur in a single specimen. Some MT genes, involving 3 exons and 2 large introns, have been isolated in Mytilidae. Our aim was to determine whether intron-free forms of the MT-10 genes can exist, which could allow rapid transcription in response to exposure to metals. Our study focused on 2 species living under very different environmental conditions: Mytilus edulis (a coastal mussel) and Bathymodiolus thermophilus (a hydrothermal mussel). We report here the first description of small, intron-free MT-10 genes, possessing a correct open reading frame in these 2 species.

IGF-I and IGF-II mRNA expression in slow and fast growing families of USDA103 channel catfish (Ictalurus punctatus)

The objective of this study was to examine insulin-like growth factor (IGF)-I and IGF-II mRNA levels in fast and slow growing families of catfish. Relative levels of IGF-I and IGF-II mRNA were determined by real-time PCR. Family A exhibited a specific growth rate (SGR) of 3.6 and was designated as fast growing, while family H exhibited a SGR of 3.1 and was designated as slow growing (P=0.017). Levels of IGF-II mRNA were 3.3-fold greater (P=0.006) in muscle for the fast growing family compared to the slow growing family. Levels of IGF-II mRNA were 1.8-fold greater (P=0.049) in liver for the fast growing family compared to the slow growing family. Levels of IGF-II mRNA from both fast and slow families were 12.2-fold greater (P<0.001) in muscle and 5.8-fold greater (P=0.021) in liver, respectively, compared to levels of IGF-I mRNA. Muscle and liver levels of IGF-I mRNA were similar between families. Elevated levels of IGF-II mRNA in muscle and liver compared to IGF-I mRNA, as well as differences in levels of IGF-II mRNA between fast and slow growing families of fish suggests a role of IGF-II in growth of channel catfish.

Effects of environmental temperature on IGF1, IGF2, and IGF type I receptor expression in rainbow trout (Oncorhynchus mykiss)

Recently, we have demonstrated in rainbow trout that environmental temperature may, independently of nutritional status, directly stimulate plasma growth hormone (GH) that is recognised as being an insulin-like growth factor (IGF) system regulator. The aim of this study was to determine whether temperature may directly regulate the IGF system or indirectly regulate it through plasma GH or nutritional status. For this purpose, rainbow trout were reared at 8, 12, or 16 degrees C and fed either ad libitum (similar nutritional status) to evidence the global effect of temperature, or with the same ration (1.2% body weight/day), to determine the temperature effect in fish with the same growth rate. Endocrine and autocrine/paracrine regulations of the IGF system were determined by measuring plasma IGF1 and IGF2, liver and muscle IGF1 and IGF2 mRNA as well as IGFRIa, IGFRIb mRNA, and the quantity of IGF type I receptor in muscle. Our results show that neither rearing temperature nor the nutritional status of fish affected the expression of both IGF receptor genes in muscle. Nevertheless, the quantity of IGF type I receptor determined by a binding study, appeared to be inversely proportional (P<0.05) to the rearing temperature without any relationship with nutritional status, suggesting a direct effect of temperature on its turnover. After 2 weeks of treatment, the levels of IGF1 mRNA in muscle at 8 degrees C were 2-fold higher (P<0.05) than at 16 degrees C in both ad libitum and restricted feed fish, whereas after 6 weeks, this difference was no longer observed. In both experiments, the levels of plasma IGF2 were 10-fold higher than the levels of plasma IGF1 (mean 105+/-3.0 versus 13.5+/-0.6 ng/ml), and plasma levels were correlated with their respective mRNA liver concentrations (r2=0.14 and 0.25, respectively; P<0.01). In the ad libitum feeding experiment, plasma and mRNA levels of IGF1 were related to the rearing temperature (P<0.05), while for IGF2 no effect was seen. In contrast, in the restricted feeding experiment, plasma and IGF2 mRNA levels were inversely proportional to the rearing temperature (P<0.0001) while plasma IGF1 was unaltered. Levels of plasma IGF1 were related to the growth rate in both experiments, while levels of plasma IGF2 appeared to be associated with the nutritional status of the fish. Our results suggest that the autocrine/paracrine expression of IGF1 and IGF2 in muscle is not a key regulator of the growth promoting effect of temperature. Conversely, temperature seems to promote growth through IGF1 secretion by the liver following GH stimulation, and impairment of nutritional status would prevent the IGF1 stimulation by temperature. In addition, the growth-promoting effect of temperature did not affect plasma IGF2, which appeared to be more related to the metabolic status of the fish.

Novel biological activities of the fish pro-IGF-I E-peptides: studies on effects of fish pro-IGF-I E-peptide on morphological change, anchorage-dependent cell division, and invasiveness in tumor cells

E-peptides of proinsulin-like growth factor-I (pro-IGF-I) are proteolytically cleaved from the prohormone after translation and have long been regarded as biologically inactive. Tian et al. [Endocrinology 140 (1999) 3387-3390] recently demonstrated that recombinant rainbow trout pro-IGF-I E-peptides (rtEa-2-, rtEa-3-, and rtEa-4-peptides), like hIGF-I, exhibited a dose-dependent mitogenic activity in several nontransformed mammalian cell lines. We show in this report that treatment of established human and fish cancer cells (MCF-7, HT-29, HepG2, ZR-75-1, SK-N-F1, and HC) and retroviral transformed human embryonic kidney cells (293GP) with recombinant rtEa-2- or rtEa-4-, but not rtEa-3-peptide, resulted in a dose-dependent induction of morphological change and enhanced cell attachment. The E-peptide-induced morphological changes are sensitive to treatment with alpha-amanitin or cycloheximide, known inhibitors of RNA and protein synthesis. The in vitro colony formation activity of established human tumor cells (HT-29 and MDA-MB-231) is greatly reduced or diminished by treatment with the rtEa-4-peptide. Both morphological change and reduction of colony formation activity in MDA-MB-231 cells were also observed following transfection with an Ea-4 transgene construct. Furthermore, the invasive activity of HT1080 cells, known invasive cancer cells, is reduced three to fourfold by treatment with the rtEa-4-peptide. These results suggest that E-peptides of rainbow trout pro-IGF-I possess novel biological activities controlling malignant properties of cancer cells in vitro.

Production, in vitro characterisation, in vivo clearance, and tissue localisation of recombinant barramundi (Lates calcarifer) insulin-like growth factor II

Recombinant barramundi insulin-like growth-factor-II (bIGF-II) has been produced in Escherichia coli after modification of an expression plasmid that coded for a chicken IGF-II fusion protein. The bIGF-II fusion protein, deposited in bacterial inclusion bodies, was dissolved under reducing conditions, desalted, and refolded. The protein was then released from the fusion protein by cleavage with subtilisin BPN'. Finally the protein was purified to homogeneity with a number of HPLC steps. In vitro analysis of recombinant bIGF-II demonstrated decreased potency in stimulating protein synthesis when compared to human and barramundi IGF-I (bIGF-I). The in vivo distribution of radiolabeled bIGF-II and bIGF-I in the circulation and tissue uptake of radiolabeled bIGF-II was also compared in juvenile barramundi (Lates calcarifer). Analysis of trichloroacetic acid-precipitable radioactivity in sequential samples following bolus injection of radiolabeled IGFs revealed that bIGF-II was degraded faster than bIGF-I. Moreover, neutral gel chromatography of these samples suggested this difference may be due to reduced affinity of bIGF-II, compared to blGF-I, for the IGF-binding proteins (IGFBPs) present in the barramundi circulation. Based on these results, it would appear that elements important in the function of IGFs have been well conserved during vertebrate evolution. However, to clearly define the IGF system in fish it will be necessary to characterise the IGFBPs present and to determine how they influence the biological actions of native IGFs.

The chum salmon insulin-like growth factor II promoter requires Sp1 for its activation by C/EBPbeta

The chum salmon insulin-like growth factor II (IGF-II) gene is highly expressed in liver tissue. In this study we demonstrate that two transcription factors, Sp1 and C/EBPbeta, are involved in the enhanced expression of the salmon IGF-II gene. The presence of the fish homolog for C/EBPbeta in salmon liver RNA was confirmed by Northern blotting. The sIGF-II promoter was activated up to 20-fold by co-transfection with C/EBPbeta. The functional importance of four out of the five putative C/EBPbeta binding sites was demonstrated with mutational analysis in transient transfection assays. The transcription factor Sp1 binds to two sites within the salmon IGF-II promoter. Interestingly, mutation of the Sp1 binding sites decreases not only the basal IGF-II promoter activity but also the C/EBPbeta-induced transactivation. These results demonstrate that liver-enriched C/EBPbeta and ubiquitously expressed Sp1 each activate the sIGF-II promoter and that Sp1 is required for full transactivation of the sIGF-II gene by C/EBPbeta. This suggests that C/EBPbeta and Sp1 act in synergy.

Quantitation of IGF-I, IGF-II, and multiple insulin receptor family member messenger RNAs during embryonic development in rainbow trout

The IGF system has been shown to be important for normal embryonic growth in mice. Characterization of the IGF system in lower vertebrates is still in progress. To gain a greater understanding of the IGF system during embryonic development in teleosts, a competitive reverse transcription-polymerase chain reaction (RT-PCR) assay was developed and used to quantitate the levels of IGF-I and IGF-II mRNAs from rainbow trout embryos isolated from a staged series. The absolute number of molecules of IGF-I mRNA/microg total RNA was significantly lower than the absolute number of molecules of IGF-II mRNA/microg total RNA both during early and late embryonic development. The recent identification of multiple IGF type I receptor (rtIGFR) and insulin receptor (rtIR) cDNAs in rainbow trout has provided us with a tool to investigate the expression of these mRNAs. A relative quantitative RT-PCR assay was used to determine the steady state levels of two forms of rtIGFR and three forms of rtIR mRNAs in rainbow trout embryos. The relative levels of rtIGFR mRNAs were greater in embryos compared to adult tissues while the relative levels of rtIR mRNAs were generally lower. In a RT-PCR based assay, a differential ability to detect rtIGFR and rtIR mRNAs was shown, suggesting developmental regulation of polyadenylation. Our results suggest that IGF-II mRNA is the predominant IGF expressed in rainbow trout embryos. Our characterization of IGF ligand and receptor mRNA levels in rainbow trout embryos suggests that a functional IGF system exists during embryonic development in teleosts.