Structural, gene expression, and functional analysis of the fugu (Takifugu rubripes) insulin-like growth factor binding protein-4 gene

Current Animal Model Systems for Ovarian Aging Research

Ovarian aging leads to menopause, loss of fertility and other disorders in multiple organs, which brings great distress to women. For ethical reasons, it is impossible to use humans as direct study subjects for aging research. Therefore, biomedical researchers have employed different non-human organisms to study ovarian aging, including worms, fruit flies, fishes, amphibians, birds, mice, rats, cavies, rabbits, pigs, sheep, cows, horses, monkeys, and apes. Because each of these model organisms has its own features, multiple factors, such as size, anatomical structure, cost, ease of operation, fertility, generation time, lifespan, and gene heredity, should be carefully considered when selecting a model system to study ovarian aging. An appropriate model organism would help researchers explore the risk factors and elucidate molecular mechanisms underlying declined ovarian functions, which might be conducive to preventing or delaying the ovarian aging process. This article will offer an overview on several currently available and commonly used model organisms for ovarian aging research by comparing their pros and cons. In doing so, we hope to provide useful information for ovarian aging researchers.

Insulin-like growth factor signalling and its significance as a biomarker in fish and shellfish research

The insulin-like growth factor signalling system comprises insulin-like growth factors, insulin-like growth factor receptors and insulin-like growth factor-binding proteins. Along with the growth hormones, insulin-like growth factor signalling is very pivotal in the growth and development of all vertebrates. In fishes, insulin-like growth factors play an important role in osmoregulation, besides the neuroendocrine regulation of growth. Insulin-like growth factor concentration in plasma can assess the growth in fishes and shellfishes and therefore widely applied in nutritional research as an indicator to evaluate the performance of selected nutrients. The present review summarizes the role of insulin-like growth factor signalling in fishes and shellfishes, its significance in aquaculture and in evaluating growth, reproduction and development, and discusses the utility of this system as biomarkers for early indication of growth in aquaculture.

Forkhead transcription factor O1 (FoxO1) in torafugu pufferfish Takifugu rubripes: Molecular cloning, in vitro DNA binding, and target gene screening in fish metagenome

The fish insulin/insulin-like growth factor (IGF) pathway has weak control over carbohydrate metabolism. To understand the molecular basis for the metabolic diversity, we characterized the forkhead box transcription factor O1A (FoxO1A), a downstream target of the insulin/IGF pathway, in torafugu Takifugu rubripes. The cloned torafugu FoxO1A cDNA contained all conserved features critical for its transcriptional activity and a unique unspliced intron encoding a poly-glutamine stretch. Torafugu FoxO1A showed the IGF-dependent nuclear exclusion and in vitro binding to the well-conserved FoxO1 binding site, DAF-16 binding element (DBE), but failed to bind to the insulin-responsive element by which mammalian FoxO1 mediates insulin effects. The subsequent in silico genomic screening provided a list of 587 potential torafugu FoxO1A target genes containing the DBE. Some carbohydrate metabolic genes regulated by FoxO1 in mammals were not included in the list. We further identified about 250 potential fish FoxO1 target genes by integrating results of the DBE screening against fish metagenome that contained 262 species. Neuronal processes appeared to be the common major function of fish FoxO1, although further annotation of the potential target genes is required. These results provide a part of the molecular basis underlying the weak association between the insulin/IGF pathway and carbohydrate metabolism in fish.

Effects of food deprivation on plasma insulin-like growth factor-1 (Igf1) and Igf binding protein (Igfbp) gene transcription in juvenile cabezon (Scorpaenichthys marmoratus)

The growth hormone (GH)/insulin-like growth factor (Igf) endocrine axis regulates somatic growth in the face of changing environmental conditions. In actinopterygian fishes, food availability is a key modulator of the somatotropic axis, with lower food intake generally depressing liver Igf1 release to diminish growth. Igf1 signaling, however, also involves several distinct IGF binding proteins (Igfbps), and the functional roles of many of these Igfbps in affecting growth during shifting food availability remain uncertain. Here, we tested how complete food deprivation (fasting) affected gene transcription for paralogs of all six types of Igfbps in the liver and fast-twitch skeletal muscle of cabezon (Scorpaenichthys marmoratus), a nearshore marine fish important for recreational fisheries in the eastern North Pacific Ocean. Juvenile cabezon were maintained as either fed (6% mass food⋅g fish wet mass^-1⋅d^-1) or fasted for 14 d. Fasted fish exhibited a lower body condition (K), a depressed mass-specific growth rate (SGR), and reduced plasma concentrations of Igf1. In the liver, fasting reduced the relative abundance of gene transcripts encoding Igfbps igfbp2a and igfbp2b, while significantly elevating mRNA levels for igfbp1a, igfbp1b, igfbp3b, and igfbp4. Fasting also reduced hepatic mRNA levels of GH receptor-1 (ghr1) - but not GH receptor-2 (ghr2) - supporting the idea that changes in liver sensitivity to GH may underlie the decline in plasma Igf1 during food deprivation. In skeletal muscle, fasting downregulated gene transcripts encoding igf1, igfbp2b, igfbp5b, and igfbp6b, while also upregulating mRNAs for igf2 and ghr2. These data demonstrate isoform-specific regulation of Igfbps in liver and skeletal muscle in cabezon experiencing food deprivation and reinforce the idea that the repertoire of duplicated Igfbp genes that evolved in actinopterygian fishes supports a diverse scope of endocrine and paracrine functions.

Insulin-Like Growth Factor-Binding Proteins of Teleost Fishes

The insulin-like growth factor (Igf) binding protein (Igfbp) family has a broad range of physiological functions and a fascinating evolutionary history. This review focuses on the Igfbps of teleost fishes, where genome duplication events have diversified gene repertoire, function, and physiological regulation-with six core Igfbps expanded into a family of over twenty genes in some lineages. In addition to briefly summarizing the current state of knowledge on teleost Igfbp evolution, function, and expression-level regulation, we highlight gaps in our understanding and promising areas for future work.

IGF-Binding Proteins: Why Do They Exist and Why Are There So Many?

Insulin-like growth factors (IGFs) are key growth-promoting peptides that act as both endocrine hormones and autocrine/paracrine growth factors. In the bloodstream and in local tissues, most IGF molecules are bound by one of the members of the IGF-binding protein (IGFBP) family, of which six distinct types exist. These proteins bind to IGF with an equal or greater affinity than the IGF1 receptor and are thus in a key position to regulate IGF signaling globally and locally. Binding to an IGFBP increases the half-life of IGF in the circulation and blocks its potential binding to the insulin receptor. In addition to these classical roles, IGFBPs have been shown to modulate IGF signaling locally under various conditions. Although members of the IGFBP family share significant sequence homology, they each have unique structural features and play distinct roles. These IGFBP genes also have different modes of regulation and distinct expression patterns. Some IGFBPs have been found to bind to their own receptors or to translocate into the interior compartments of cells where they may execute IGF-independent actions. In spite of this functional and regulatory diversity, it has been puzzling that loss-of-function studies have yielded relatively little information about the physiological functions of IGFBPs. In this review, we suggest that evolution has tended to retain an array of IGFBPs in order to facilitate fine-tuning of IGF signaling. We explore the emerging explanation that many IGFBP functions have evolved to allow the targeted adjustment of IGF signaling under stressful or irregular conditions, which would likely not be revealed in a standard laboratory setting.

PAPP-A: a promising therapeutic target for healthy longevity

Pregnancy-associated plasma protein-A (PAPP-A) is a proteolytic enzyme that was discovered to increase local insulin-like growth factor (IGF) availability for receptor activation through cleavage of inhibitory IGF binding proteins (IGFBPs). Reduced IGF signaling has been associated with increased lifespan and healthspan. Therefore, inhibition of PAPP-A represents a novel approach to indirectly decrease the availability of bioactive IGF. Here, we will review data in support of PAPP-A as a therapeutic target to promote healthy longevity.

Mesenchymal stem cells and myoblast differentiation under HGF and IGF-1 stimulation for 3D skeletal muscle tissue engineering

Background

Volumetric muscle loss caused by trauma or after tumour surgery exceeds the natural regeneration capacity of skeletal muscle. Hence, the future goal of tissue engineering (TE) is the replacement and repair of lost muscle tissue by newly generating skeletal muscle combining different cell sources, such as myoblasts and mesenchymal stem cells (MSCs), within a three-dimensional matrix. Latest research showed that seeding skeletal muscle cells on aligned constructs enhance the formation of myotubes as well as cell alignment and may provide a further step towards the clinical application of engineered skeletal muscle.

In this study the myogenic differentiation potential of MSCs upon co-cultivation with myoblasts and under stimulation with hepatocyte growth factor (HGF) and insulin-like growth factor-1 (IGF-1) was evaluated. We further analysed the behaviour of MSC-myoblast co-cultures in different 3D matrices.

Results

Primary rat myoblasts and rat MSCs were mono- and co-cultivated for 2, 7 or 14 days. The effect of different concentrations of HGF and IGF-1 alone, as well as in combination, on myogenic differentiation was analysed using microscopy, multicolour flow cytometry and real-time PCR. Furthermore, the influence of different three-dimensional culture models, such as fibrin, fibrin-collagen-I gels and parallel aligned electrospun poly-ε-caprolacton collagen-I nanofibers, on myogenic differentiation was analysed. MSCs could be successfully differentiated into the myogenic lineage both in mono- and in co-cultures independent of HGF and IGF-1 stimulation by expressing desmin, myocyte enhancer factor 2, myosin heavy chain 2 and alpha-sarcomeric actinin. An increased expression of different myogenic key markers could be observed under HGF and IGF-1 stimulation. Even though, stimulation with HGF/IGF-1 does not seem essential for sufficient myogenic differentiation. Three-dimensional cultivation in fibrin-collagen-I gels induced higher levels of myogenic differentiation compared with two-dimensional experiments. Cultivation on poly-ε-caprolacton-collagen-I nanofibers induced parallel alignment of cells and positive expression of desmin.

Conclusions

In this study, we were able to myogenically differentiate MSC upon mono- and co-cultivation with myoblasts. The addition of HGF/IGF-1 might not be essential for achieving successful myogenic differentiation. Furthermore, with the development of a biocompatible nanofiber scaffold we established the basis for further experiments aiming at the generation of functional muscle tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0131-2) contains supplementary material, which is available to authorized users.

Variation in branchial expression among insulin-like growth-factor binding proteins (igfbps) during Atlantic salmon smoltification and seawater exposure

Background

In preparation for migration from freshwater to marine habitats, Atlantic salmon (Salmo salar L.) undergo smoltification, a transformation that includes the acquisition of hyposmoregulatory capacity. The growth hormone (Gh)/insulin-like growth-factor (Igf) axis promotes the development of branchial ionoregulatory functions that underlie ion secretion. Igfs interact with a suite of Igf binding proteins (Igfbps) that modulate hormone activity. In Atlantic salmon smolts, igfbp4,−5a,−5b1,−5b2,−6b1 and−6b2 transcripts are highly expressed in gill. We measured mRNA levels of branchial and hepatic igfbps during smoltification (March, April, and May), desmoltification (July) and following seawater (SW) exposure in March and May. We also characterized parallel changes in a broad suite of osmoregulatory (branchial Na⁺/K⁺-ATPase (Nka) activity, Na⁺/K⁺/2Cl⁻cotransporter 1 (nkcc1) and cystic fibrosis transmembrane regulator 1 (cftr1) transcription) and endocrine (plasma Gh and Igf1) parameters.

Results

Indicative of smoltification, we observed increased branchial Nka activity, nkcc1 and cftr1 transcription in May. Branchial igfbp6b1 and -6b2 expression increased coincidentally with smoltification. Following a SW challenge in March, igfbp6b1 showed increased expression while igfbp6b2 exhibited diminished expression. igfbp5a,−5b1 and−5b2 mRNA levels did not change during smolting, but each had lower levels following a SW exposure in March.

Conclusions

Salmonids express an especially large suite of igfbps. Our data suggest that dynamic expression of particular igfbps accompanies smoltification and SW challenges; thus, transcriptional control of igfbps may provide a mechanism for the local modulation of Igf activity in salmon gill.

Molecular characterization of exon 3 of caprine myostatin gene in Marwari goat

AIM

To estimate genetic variability in exon 3 of caprine myostatin gene in Marwari goats.

MATERIALS AND METHODS

A total of 120 blood samples from unrelated Marwari goats were randomly collected from different villages of Bikaner (Rajasthan), India. Genomic DNA was extracted from whole blood using blood DNA isolation kit (Himedia Ltd.) as per manufacturer's protocol. The quality of extracted genomic DNA was checked on 0.8% agarose gel. Specifically designed a primer set for caprine myostatin (MSTN) gene (Genebank accession no. DQ167575) was used to amplify the exon 3 region of MSTN gene in Marwari goat. The genetic variability in exon 3 of MSTN gene in Marwari goat was assessed on 8% polyacrylamide gel electrophoresis to detect single strand conformation polymorphism (SSCP) pattern.

RESULTS

The exon 3 of MSTN gene in Marwari goat showed two types of conformation patterns on 8% polyacrylamide gel. One of the patterns showed only two bands and was considered as genotype AA, whereas another pattern having an extra band was designated as genotype AB. The frequencies of AA and AB genotype for exon 3 region of MSTN gene were calculated as 0.90 and 0.10, respectively.

CONCLUSION

Low level of polymorphism was observed at exon 3 region of MSTN gene in Marwari goat through SSCP analysis. This information could be utilized in future breeding plan to exploit the unique characteristics of Marwari goat of Rajasthan.

Effects of phytoestrogens on growth-related and lipogenic genes in rainbow trout (Oncorhynchus mykiss)

This study determined whether estradiol (E2) or the phytoestrogens genistein and daidzein regulate expression of growth-related and lipogenic genes in rainbow trout. Juvenile fish (5 mon, 65.8±1.8 g) received intraperitoneal injections of E2, genistein, or daidzein (5 μg/g body weight) or a higher dose of genistein (50 μg/g body weight). Liver and white muscle were harvested 24h post-injection. In liver, expression of vitellogenin (vtg) and estrogen receptor alpha (era1) increased in all treatments and reflected treatment estrogenicity (E2>genistein (50 μg/g)>genistein (5 μg/g)=daidzein (5 μg/g)). Estradiol and genistein (50 μg/g) reduced components of the growth hormone (GH)/insulin-like growth factor (IGF) axis in liver, including increased expression of IGF binding protein-2b1 (igfbp2b1) and reduced igfbp5b1. In liver E2 and genistein (50 μg/g) affected expression of components of the transforming growth factor beta signaling mechanism, reduced expression of ppar and rxr transcription factors, and increased expression of fatty acid synthesis genes srebp1, acly, fas, scd1, and gpat and lipid binding proteins fabp3 and lpl. In muscle E2 and genistein (50 μg/g) increased era1 and erb1 expression and decreased erb2 expression. Other genes responded to phytoestrogens in a manner that suggested regulation by estrogen receptor-independent mechanisms, including increased ghr2, igfbp2a, igfbp4, and igfbp5b1. Expression of muscle regulatory factors pax7 and myod was increased by E2 and genistein. These data indicate that genistein and daidzein affect expression of genes in rainbow trout that regulate physiological mechanisms central to growth and nutrient retention.

Global gene expression patterns of grass carp following compensatory growth

BACKGROUND

Compensatory growth is accelerated compared with normal growth and occurs when growth-limiting conditions are overcome. Most animals, especially fish, are capable of compensatory growth, but the mechanisms remain unclear. Further investigation of the mechanism of compensatory growth in fish is needed to improve feeding efficiency, reduce cost, and explore growth-related genes.

RESULTS

In the study, grass carp, an important farmed fish in China, were subjected to a compensatory growth experiment followed by transcriptome analysis by RNA-sequencing. Samples of fish from starved and re-feeding conditions were compared with the control. Under starved conditions, 4061 and 1988 differentially expressed genes (DEGs) were detected in muscle and liver tissue when compared the experimental group with control group, respectively. After re-feeding, 349 and 247 DEGs were identified in muscle and liver when the two groups were compared. Moreover, when samples from experimental group in starved and re-feeding conditions were compared, 4903 and 2444 DEGs were found in muscle and liver. Most of these DEGs were involved in metabolic processes, or encoded enzymes or proteins with catalytic activity or binding functions, or involved in metabolic and biosynthetic pathways. A number of the more significant DEGs were subjected to further analysis. Under fasting conditions, many up-regulated genes were associated with protein ubiquitination or degradation, whereas many down-regulated genes were involved in the metabolism of glucose and fatty acids. Under re-feeding conditions, genes participating in muscle synthesis and fatty acid metabolism were up-regulated significantly, and genes related to protein ubiquitination or degradation were down-regulated. Moreover, Several DEGs were random selected for confirmation by real-time quantitative PCR.

CONCLUSIONS

Global gene expression patterns of grass carp during compensatory growth were determined. To our knowledge, this is a first reported for a teleost fish. The results will enhance our understanding of the mechanism of compensatory growth in teleost fish.

Association between intraarticular cytokine levels and clinical parameters of osteochondritis dissecans in the ankle

Background

Reliable data about in vivo regulation of cytokines in osteochondritis dissecans (OCD) of the ankle are still missing. Disease-specific regulation patterns were hypothesized.

Methods

28 patients with a mean age of 30.7 ± 14.8 years undergoing an arthroscopy of the ankle because of OCD were prospectively included in a clinical trial. Lavage fluids were analyzed by ELISA for levels of aggrecan, BMP-2, BMP-7, IGF-1, IGF-1R, bFGF, endoglin, MMP-13, and IL-1β. Additionally, clinical parameters and scores (FFI, CFSS, AOFAS) were evaluated and supplemented by the Kellgren Lawrence Score (KLS) for conventional X-rays and the Ankle Osteoarthritis Scoring System (AOSS) for MRI.

Results

Grading of OCD lesions statistically significant increased with age and was higher in case of previously performed operations (p < 0.03). A worse clinical function reflected by low AOFAS and CFSS scores or high FFI was associated with high grading of cartilage damage or OCD (p < 0.03). Similarly, high radiological scores (KLS and AOSS) indicating progress of OA positively correlated with grading of cartilage damage and OCD. The concordance between the MRI and arthroscopic classification was overall moderate (κ = 0.52). Biochemically, only IGF/IGF-1R levels were consistently negatively associated with OCD grading, ICRS score, FFI and KLS (p < 0.05). Correlation data is supported by post hoc statistics.

Conclusions

Radiological and clinical parameters in association with synovial IGF-1/IGF-1R levels indicated an increasing joint degeneration with rising OCD stage.

Trial registration

German Clinical Trials Register DRKS00000365, 11/03/2008.

Biochemical characterization of early osteoarthritis in the ankle

Purpose. Reliable data about in vivo regulation of cytokines in early ankle osteoarthritis (OA) are still missing. Methods. 49 patients with a mean age of 33 ± 14 years undergoing an arthroscopy of the ankle with different stages of chronic OA were prospectively included in a clinical trial. Lavage fluids were analyzed by ELISA. Additionally, clinical parameters and scores (FFI, CFSS, and AOFAS) were evaluated and supplemented by the Kellgren Lawrence Score (KLS) and the ankle osteoarthritis scoring system (AOSS). Results. ICRS grading of cartilage damage, previous operations, and duration of complains were strong indicators for OA progress and showed correlations to age, clinical scores, validated KLS, and AOSS (P < 0.04). Systemic and intraarticular inflammatory parameters were low in all patients. Biochemically, aggrecan and BMP-7 positively indicated OA with statistically significant associations with duration of symptoms, FFI, AOFAS, and KLS (P < 0.04). In contrast, BMP-2 levels showed statistically significant negative correlations to aggrecan or BMP-7 concentrations, which is in line with the negative association with ICRS score and KLS and the positive correlation with FFI (P < 0.03). Conclusions. We were able to identify different key markers of OA in the ankle as aggrecan, BMP-7, and BMP-2, offering starting points for new ways in diagnostics and interventional strategies.

Regulation of skeletal muscle growth in fish by the growth hormone--insulin-like growth factor system

The growth hormone (GH)-insulin-like growth factor (IGF) system is the key promoter of growth in vertebrates; however, how this system modulates muscle mass in fish is just recently becoming elucidated. In fish, the GH induces muscle growth by modulating the expression of several genes belonging to the myostatin (MSTN), atrophy, GH, and IGF systems as well as myogenic regulatory factors (MRFs). The GH controls the expression of igf1 via Janus kinase 2 (JAK2)/signal transducers and activators of the transcription 5 (STAT5) signaling pathway, but it seems that it is not the major regulator. These mild effects of the GH on igf1 expression in fish muscle seem to be related with the presence of higher contents of truncated GH receptor1 (tGHR1) than full length GHR (flGHR1). IGFs in fish stimulate myogenic cell proliferation, differentiation, and protein synthesis through the MAPK/ERK and PI3K/AKT/TOR signaling pathways, concomitant with abolishing protein degradation and atrophy via the PI3K/AKT/FOXO signaling pathway. Besides these signaling pathways control the expression of several genes belonging to the atrophy and IGF systems. Particularly, IGFs and amino acid control the expression of igf1, thus, suggesting other of alternative signaling pathways regulating the transcription of this growth factor. The possible role of IGF binding proteins (IGFBPs) and the contribution of muscle-derived versus hepatic-produced IGF1 on fish muscle growth is also addressed. Thus, a comprehensive overview on the GH-IGF system regulating fish skeletal muscle growth is presented, as well as perspectives for future research in this field.

Comparative analysis of a teleost skeleton transcriptome provides insight into its regulation

An articulated endoskeleton that is calcified is a unifying innovation of the vertebrates, however the molecular basis of the structural divergence between terrestrial and aquatic vertebrates, such as teleost fish, has not been determined. In the present study long-read next generation sequencing (NGS, Roche 454 platform) was used to characterize acellular perichondral bone (vertebrae) and chondroid bone (gill arch) in the gilthead sea bream (Sparus auratus). A total of 15.97 and 14.53Mb were produced, respectively from vertebrae and gill arch cDNA libraries and yielded 32,374 and 28,371 contigs (consensus sequences) respectively. 10,455 contigs from vertebrae and 10,625 contigs from gill arches were annotated with gene ontology terms. Comparative analysis of the global transcriptome revealed 4249 unique transcripts in vertebrae, 4201 unique transcripts in the gill arches and 3700 common transcripts. Several core gene networks were conserved between the gilthead sea bream and mammalian skeleton. Transcripts for putative endocrine factors were identified in acellular gilthead sea bream bone suggesting that in common with mammalian bone it can act as an endocrine tissue. The acellular bone of the vertebra, in contrast to current opinion based on histological analysis, was responsive to a short fast and significant (p<0.05) down-regulation of several transcripts identified by NGS, osteonectin, osteocalcin, cathepsin K and IGFI occurred. In gill arches fasting caused a significant (p<0.05) down-regulation of osteocalcin and up-regulation of MMP9.

Two origins of blastemal progenitors define blastemal regeneration of zebrafish lower jaw

Zebrafish possess a remarkable ability to regenerate complicated structures by formation of a mass of undifferentiated mesenchymal cells called blastema. To understand how the blastema retains the original structural form, we investigate cellular transitions and transcriptional characteristics of cell identity genes during all stages of regeneration of an amputated lower jaw. We find that mesenchymal blastema originates from multiple sources including nucleated blood cells, fibroblasts, damaged muscle cells and pigment cells. These cells are transformed into two populations of blastemal progenitors: foxi1-expression and isl1-expression, before giving rise to cartilage, bone, and muscle. Time point- based transcriptomal analysis of 45 annotated Hox genes reveal that five 3′-end Hox genes and an equal number of 5′-end Hox genes are activated largely at the stage of blastema reformation. RNA in situ hybridization shows that foxi1 and pax3a are respectively expressed in the presumptive mandible skeletal region and regenerating muscle at 5 dpa. In contrast, hoxa2b and hoxa11b are widely expressed with different domain in chondrogenic blastema and blastema mesenchyme. Knockdown foxi1 changes the expression patterns of sox9a and hoxa2b in chondrogenic blastema. From these results we propose that two origins of blastemal progenitors define blastema skeleton and muscle respecifications through distinct signaling pathways. Meanwhile, the positional identity of blastema reformation is implicated in mesenchymal segmentation and characteristic expression pattern of Hox genes.

Dynamic transcriptional regulation of autocrine/paracrine igfbp1, 2, 3, 4, 5, and 6 in the skeletal muscle of the fine flounder during different nutritional statuses

The IGF-binding proteins (IGFBPs) play a dual role in the regulation of the activity and bioavailability of IGFs in different tissues. Diverse evidence has shown that IGFBPs can inhibit and/or potentiate IGF actions. In this study, igfbp1, 2, 3, 4, 5, and 6 were isolated in the fine flounder, a flat fish species that shows slow growth and inherent Gh resistance in muscle. Subsequently, the expression of all igfbps was assessed in the skeletal muscle of flounder that underwent different nutritional statuses. igfbp1 was not expressed in muscle during any of the nutritional conditions, whereas igfbp3 and igfbp5 were the lowest and the highest igfbps expressed respectively. A dynamic expression pattern was found in all the igfbps expressed in skeletal muscle, which depended on the nutritional status and sampling period. During the fasting period, igfbp2, 4, and 5 were downregulated, whereas igfbp3 was upregulated during part of the fasting period. The restoration of food modulated the expression of the igfbps dynamically, showing significant changes during both the long- and short-term refeeding. igfbp3 and igfbp6 were downregulated during short-term refeeding, whereas igfbp5 was upregulated, and igfbp2 and igfbp4 remained stable. During long-term refeeding, the expression of igfbp2, 4, 5, and 6 increased, while igfbp3 remained unchanged. In conclusion, this study shows for the first time the isolation of all igfbps in a single fish species, in addition to describing a dynamic nutritional and time-dependent response in the expression of igfbps in the skeletal muscle of a nonmammalian species.

Evolution of the insulin-like growth factor binding protein (IGFBP) family

The evolution of the IGF binding protein (IGFBP) gene family has been difficult to resolve. Both chromosomal and serial duplications have been suggested as mechanisms for the expansion of this gene family. We have identified and annotated IGFBP sequences from a wide selection of vertebrate species as well as Branchiostoma floridae and Ciona intestinalis. By combining detailed sequence analysis with sequence-based phylogenies and chromosome information, we arrive at the following scenario: the ancestral chordate IGFBP gene underwent a local gene duplication, resulting in a gene pair adjacent to a HOX cluster. Subsequently, the gene family expanded in the two basal vertebrate tetraploidization (2R) resulting in the six IGFBP types that are presently found in placental mammals. The teleost fish ancestor underwent a third tetraploidization (3R) that further expanded the IGFBP repertoire. The five sequenced teleost fish genomes retain 9-11 of IGFBP genes. This scenario is supported by the phylogenies of three adjacent gene families in the HOX gene regions, namely the epidermal growth factor receptors (EGFR) and the Ikaros and distal-less (DLX) transcription factors. Our sequence comparisons show that several important structural components in the IGFBPs are ancestral vertebrate features that have been maintained in all orthologs, for instance the integrin interaction motif Arg-Gly-Asp in IGFBP-2. In contrast, the Arg-Gly-Asp motif in IGFBP-1 has arisen independently in mammals. The large degree of retention of IGFBP genes after the ancient expansion of the gene family strongly suggests that each gene evolved distinct and important functions early in vertebrate evolution.

Acute handling disturbance modulates plasma insulin-like growth factor binding proteins in rainbow trout (Oncorhynchus mykiss)

The effects of acute stressor exposure on proximal (growth hormone [GH]) and distal (insulin-like growth factor-I [IFG-I] and insulin-like growth factor-binding proteins [IFGBPs]) components of the somatotropic axis are poorly understood in finfish. Rainbow trout (Oncorhynchus mykiss) were exposed to a 5-min handling disturbance to mimic an acute stressor episode, and levels of plasma GH, IGF-I, and IGFBPs at 0, 1, 4, and 24 h post-stressor exposure were measured. An unstressed group was also sampled at the same clock times (09:00, 10:00, 13:00, and 08:00 [the following day]) as acute stress sampling to determine temporal changes in the above somatotropic axis components. The acute stressor transiently elevated plasma cortisol and glucose levels at 1 and 4 h post-stressor exposure, whereas no changes were seen in the unstressed group. Plasma GH levels were not affected by handling stress or sampling time in the unstressed animals. Plasma IGF-I levels were significantly depressed at 1 and 4 h post-stressor exposure, but no discernible temporal pattern was seen in the unstressed animals. Using a western ligand blotting technique, we detected plasma IGFBPs of 21, 32, 42, and 50 kDa in size. The plasma levels of the lower-molecular-weight IGFBPs (21 and 32 kDa) were unaffected by handling stressor, nor were there any discernible temporal patterns in the unstressed animals. By contrast, the higher-molecular-weight IGFBPs (42 and 50 kDa) were affected by stress or time of sampling. Levels of the 42-kDa IGFBP levels significantly decreased over the sampling period in unstressed control animals, but this temporal drop was eliminated in stressed animals. Levels of the 50-kDa IGFBPs also decreased significantly over the sampling time in unstressed trout, whereas handling disturbance transiently increased levels of this IGFBP at 1 h but not at 4 and 24 h post-stressor exposure compared with the control group. Overall, our results suggest that acute stress adaptation involves modulation of plasma IGF-1 and high-molecular-mass IGFBP levels (42 and 50 kDa) in rainbow trout.

Transcriptional regulation of the IGF signaling pathway by amino acids and insulin-like growth factors during myogenesis in Atlantic salmon

The insulin-like growth factor signalling pathway is an important regulator of skeletal muscle growth. We examined the mRNA expression of components of the insulin-like growth factor (IGF) signalling pathway as well as Fibroblast Growth Factor 2 (FGF2) during maturation of myotubes in primary cell cultures isolated from fast myotomal muscle of Atlantic salmon (Salmo salar). The transcriptional regulation of IGFs and IGFBP expression by amino acids and insulin-like growth factors was also investigated. Proliferation of cells was 15% d⁻¹ at days 2 and 3 of the culture, increasing to 66% d⁻¹ at day 6. Three clusters of elevated gene expression were observed during the maturation of the culture associated with mono-nucleic cells (IGFBP5.1 and 5.2, IGFBP-6, IGFBP-rP1, IGFBP-2.2 and IGF-II), the initial proliferation phase (IGF-I, IGFBP-4, FGF2 and IGF-IRb) and terminal differentiation and myotube production (IGF2R, IGF-IRa). In cells starved of amino acids and serum for 72 h, IGF-I mRNA decreased 10-fold which was reversed by amino acid replacement. Addition of IGF-I and amino acids to starved cells resulted in an 18-fold increase in IGF-I mRNA indicating synergistic effects and the activation of additional pathway(s) leading to IGF-I production via a positive feedback mechanism. IGF-II, IGFBP-5.1 and IGFBP-5.2 expression was unchanged in starved cells, but increased with amino acid replacement. Synergistic increases in expression of IGFBP5.2 and IGFBP-4, but not IGFBP5.1 were observed with addition of IGF-I, IGF-II or insulin and amino acids to the medium. IGF-I and IGF-II directly stimulated IGFBP-6 expression, but not when amino acids were present. These findings indicate that amino acids alone are sufficient to stimulate myogenesis in myoblasts and that IGF-I production is controlled by both endocrine and paracrine pathways. A model depicting the transcriptional regulation of the IGF pathway in Atlantic salmon muscle following feeding is proposed.