Localization of IGF-I, IGF-I receptor, and IGFBP-2 in developing Umbrina cirrosa (Pisces: Osteichthyes)

Unveiling the hidden effects of hypoxia: Pituitary damage and hormonal imbalance in fat greenling (Hexagrammos otakii)

BACKGROUND

In fisheries, hypoxia stress is one of the most common environmental stresses that often lead to the death of large numbers of fish and cause significant economic losses. The pituitary, an important endocrine gland, lies below the hypothalamus region of the brain. It plays a crucial part in controlling vital physiological functions in fish, such as growth, reproduction, and responses to stress. However, the detailed mechanisms of how hypoxia affects these physiological processes via the pituitary remain largely unknown.

METHODS

Fat greenlings (Hexagrammous otakii) were exposed to different dissolved oxygen (DO = 7. 6 mg/L and DO = 2 mg/L) for 24 h. miRNA-mRNA association analysis of H. otakii pituitary after hypoxia stress. Detecting apoptosis in H. otakii pituitary using Tunel and qPCR. Subsequent detection of hormones in H. otakii liver, gonads and serum by ELISA.

RESULTS

In this study, hypoxia causes immune system disorders and inflammatory responses through the combined analysis of miRNAs and mRNAs. Subsequent verification indicated a significant accumulation of reactive oxygen species (ROS) subsequent to hypoxia treatment. The overproduction of ROS cause oxidative stress and apoptosis in the pituitary, ultimately causing pituitary damage and reduced growth hormone and luteinising hormone release.

CONCLUSIONS

According to the association study of miRNA-mRNA, apoptosis problems caused by hypoxia stress result in H. otakii pituitary damage. In the meantime, this work clarifies the possible impact of hypoxia-stress on the pituitary cells, as well as on the gonadal development and growth of H. otakii.

Igf signaling couples retina growth with body growth by modulating progenitor cell division

How the body and organs balance their relative growth is of key importance for coordinating size and function. This is of particular relevance in organisms, which continue to grow over their entire life span. We addressed this issue in the neuroretina of medaka fish (Oryzias latipes), a well-studied system with which to address vertebrate organ growth. We reveal that a central growth regulator, Igf1 receptor (Igf1r), is necessary and sufficient for proliferation control in the postembryonic retinal stem cell niche: the ciliary marginal zone (CMZ). Targeted activation of Igf1r signaling in the CMZ uncouples neuroretina growth from body size control, and we demonstrate that Igf1r operates on progenitor cells, stimulating their proliferation. Activation of Igf1r signaling increases retinal size while preserving its structural integrity, revealing a modular organization in which progenitor differentiation and neurogenesis are self-organized and highly regulated. Our findings position Igf signaling as a key module for controlling retinal size and composition, with important evolutionary implications.

Highlighted Article: Targeted activation of Igf1r signaling in the retinal stem cell niche increases retina size through expanding the progenitor but not stem cell population.

Salinity, Temperature and Ammonia Acute Stress Response in Seabream (Sparus aurata) Juveniles: A Multidisciplinary Study

The present study aimed to investigate the acute response of gilthead seabream (Sparus aurata) juveniles exposed to temperature, salinity and ammonia stress. Radioimmunoassay was used to evaluate cortisol levels, whereas insulin-like growth factors (igf1 and igf2), myostatin (mstn), heat-shock protein 70 (hsp70) and glucocorticoid receptor (gr) gene expression was assessed trough Real-Time PCR. The presence and localization of IGF-I and HSP70 were investigated by immunohistochemistry. In all the stress conditions, a significant increase in cortisol levels was observed reaching higher values in the thermic and chemical stress groups. Regarding fish growth markers, igf1 gene expression was significantly higher only in fish subjected to heat shock stress while, at 60 min, igf2 gene expression was significantly lower in all the stressed groups. Temperature and ammonia changes resulted in a higher mstn gene expression. Molecular analyses on stress response evidenced a time dependent increase in hsp70 gene expression, that was significantly higher at 60 min in fish exposed to heat shock and chemical stress. Furthermore, the same experimental groups were characterized by a significantly higher gr gene expression respect to the control one. Immunostaining for IGF-I and HSP70 antibodies was observed in skin, gills, liver, and digestive system of gilthead seabream juveniles.

Identifying the Related Genes of Muscle Growth and Exploring the Functions by Compensatory Growth in Mandarin Fish (Siniperca chuatsi)

How organisms display many different biochemical, physiological processes through genes expression and regulatory mechanisms affecting muscle growth is a central issue in growth and development. In Siniperca chuatsi, the growth-related genes and underlying relevant mechanisms are poorly understood, especially for difference of body sizes and compensatory growth performance. Muscle from 3-month old individuals of different sizes was used for transcriptome analysis. Results showed that 8,942 different expression genes (DEGs) were identified after calculating the RPKM. The DEGs involved in GH-IGF pathways, protein synthesis, ribosome synthesis and energy metabolisms, which were expressed significantly higher in small individuals (S) than large fish (L). In repletion feeding and compensatory growth experiments, eight more significant DEGs were used for further research (GHR2, IGFR1, 4ebp, Mhc, Mlc, Myf6, MyoD, troponin). When food was plentiful, eight genes participated in and promoted growth and muscle synthesis, respectively. Starvation can be shown to inhibit the expression of Mhc, Mlc and troponin, and high expression of GHR2, IGFR1, and 4ebp inhibited growth. Fasting promoted the metabolic actions of GHR2, IGFR1, and 4ebp rather than the growth-promoting actions. MyoD can sense and regulate the hunger, which also worked with Mhc and Mlc to accelerate the compensatory growth of S. chuatsi. This study is helpful to understand the regulation mechanisms of muscle growth-related genes. The elected genes will contribute to the selective breeding in future as candidate genes.

How different rearing temperatures affect growth and stress status of Siberian sturgeon Acipenser baerii larvae

Environmental temperature is one of the critical factors affecting fish development. The aim of this study was to examine the impact of three different rearing temperatures (16, 19 and 22°C) throughout the endogenous feeding phase of the Siberian sturgeon Acipenser baerii. This was performed by assessing (a) larval survival and growth; (b) immunofluorescence localization and expression of genes involved in muscle development and growth - myog and Igf1; and (c) stress status through the expression of thermal stress genes - Hsp70, Hsp90α and Hsp90β - and whole body cortisol. Overall survival rate and larval weight did not differ significantly across temperatures. Larvae subjected to 22°C showed faster absorption of the yolk-sac than larvae subjected to 19 or 16°C. Both at schooling and at the end of the trial, larvae reared at 16°C showed significantly lower levels of cortisol than those reared at 19 or 22°C. IGF-1 immunopositivity was particularly evident in red muscle at schooling stage in all temperatures. The expression of all Hsps as well as the myog and Igf1 genes was statistically higher in larvae reared at 16°C but limited to the schooling stage. Cortisol levels were higher in larvae at 22°C, probably because of the higher metabolism demand rather than a stress response. The observed apparent incongruity between Hsps gene expression and cortisol levels could be due to the lack of a mature system. Further studies are necessary, especially regarding the exogenous feeding phase, in order to better understand if this species is actually sensitive to thermal stress.

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.

Insulin-like growth factors I and II in starry flounder (Platichthys stellatus): molecular cloning and differential expression during embryonic development

In order to elucidate the possible roles of insulin-like growth factors I and II (IGF-I and IGF-II) in the embryonic development of Platichthys stellatus, their cDNAs were isolated and their spatial expression pattern in adult organs and temporal expression pattern throughout embryonic development were examined by quantitative real-time PCR assay. The IGF-I cDNA sequence was 1,268 bp in length and contained an open reading frame (ORF) of 558 bp, which encoded 185 amino acid residues. With respect to IGF-II, the full-length cDNA was 899 bp in length and contained a 648-bp ORF, which encoded 215 amino acid residues. The amino acid sequences of IGF-I and IGF-II exhibited high identities with their fish counterparts. The highest IGF-I mRNA level was found in the liver for both sexes, whereas the IGF-II gene was most abundantly expressed in female liver and male liver, gill, and brain. The sex-specific and spatial expression patterns of IGF-I and IGF-II mRNAs are thought to be related to the sexually dimorphic growth and development of starry flounder. Both IGF-I and IGF-II mRNAs were detected in unfertilized eggs, which indicated that IGF-I and IGF-II were parentally transmitted. Nineteen embryonic development stages were tested. IGF-I mRNA level remained high from unfertilized eggs to low blastula followed by a significant decrease at early gastrula and then maintained a lower level. In contrast, IGF-II mRNA level was low from unfertilized eggs to high blastula and peaked at low blastula followed by a gradual decrease. Moreover, higher levels of IGF-I mRNA than that of IGF-II were found from unfertilized eggs to high blastula, vice versa from low blastula to newly hatched larva, and the different expression pattern verified the differential roles of IGF-I and IGF-II in starry flounder embryonic development. These results could help in understanding the endocrine mechanism involved in the early development and growth of starry flounder.

Expression of insulin-like growth factor I receptors at mRNA and protein levels during metamorphosis of Japanese flounder (Paralichthys olivaceus)

Insulin-like growth factor I (IGF-I) is an important regulator of fish growth and development, and its biological actions are initiated by binding to IGF-I receptor (IGF-IR). Our previous study has revealed that IGF-I could play an important role during metamorphosis of Japanese flounder, Paralichthys olivaceus. The analysis of IGF-IR expression thus helps further elucidate the IGF-I regulation of metamorphic processes. In this study, the spatial-temporal expression of two distinct IGF-IR mRNAs was investigated by real-time RT-PCR. The spatial distribution of two IGF-IR mRNAs in adult tissues is largely overlapped, but they exhibit distinct temporal expression patterns during larval development. A remarkable decrease in IGF-IR-2 mRNA was detected during metamorphosis. In contrast, a significant increase in IGF-IR-1 mRNA was determined from pre-metamorphosis to metamorphic completion. These indicate that they may play different function roles during the flounder metamorphosis. The levels and localization of IGF-IR proteins during larval development were further studied by Western blotting and immunohistochemistry. Immunoreactive IGF-IRs were detected throughout larval development, and the IGF-IR proteins displayed a relatively abundant expression during metamorphosis. Moreover, the IGF-IR proteins appeared in key tissues, such as thickened skin beneath the migrating eye, developing intestine, gills and kidney during metamorphosis. These results further suggest that the IGF-I system may be involved in metamorphic development of Japanese flounder.

Molecular cloning of IGF-1 and IGF-1 receptor and their expression pattern in the Chilean flounder (Paralichthys adspersus)

Insulin-like growth factor-1 and insulin-like growth factor-1 receptor (IGF-1 and IGF-1R) play main roles in vertebrate growth and development. In fish, besides contributing to somatic growth, both molecules exhibit pleiotropic functions. We isolated complete cDNAs sequences encoding for both IGF-1 and IGF-1R in the Chilean flounder by using RT-PCR and rapid amplification of cDNAs ends (RACE) techniques. We analyzed gene expression in pre-metamorphic larvae and different organs of juvenile fish through whole mount in situ hybridization and RT-PCR, respectively. In addition, we studied the presence of calcified skeletal structures in pre-metamorphic larvae through the fluorescent chromophore calcein. The IGF-1 cDNA sequence displays an open reading frame of 558 nucleotides, encoding a 185 amino acid preproIGF-1. Moreover, IGF-1R contains an open reading frame spanning 4239 nucleotides, rendering a 702 amino acid subunit alpha and a 676 amino acid subunit beta. The deduced mature IGF-1 and IGF-1R exhibited high sequence identities with their corresponding orthologs in fishes, especially those domains involved in biological activity. RT-PCR showed expression of IGF-1 and IGF-1R transcripts in all studied tissues, consistent with their pleiotropic functions. Furthermore, we observed IGF-1 expression in notochord and IGF-1R expression in notochord, somites and head in larvae of 8 and 9 days post fertilization. Complementarily, we detected in larvae of 8 days post fertilization the presence of calcified skeletal structures in notochord and head. Interestingly, both mRNAs and calcified structures were found in territories such as notochord, an embryonic midline structure essential for the pattern of surrounding tissues as nervous system and mesoderm. Our results suggest that IGF-1 and its receptor play an important role in the development of the nervous system, muscle and bone-related structures during larval stages.

Immunohistochemical localization of IGF-I, IGF-II and MSTN proteins during development of triploid sea bass (Dicentrarchus labrax)

The cellular localization of IGF-I, IGF-II and MSTN proteins was investigated during ontogenesis of triploid sea bass (Dicentrarchus labrax) by an immunohistochemical approach. The results were compared with those observed in diploids. IGF-I immunostaining was mainly observed in skin, skeletal muscle, intestine and gills of both diploids and triploids. From day 30 of larval life, IGF-I immunoreactivity observed in skeletal muscle, intestine, gills and kidney was stronger in triploids than in diploids. At day 30, triploids exhibited a standard length significantly higher than the one of diploids. Although IGF-II and MSTN immunoreactivity was detectable in different tissues and organs, no differences between diploids and triploids were observed. The spatial localization of IGF-I, IGF-II and MSTN proteins detected in this study is in agreement with previous findings on the distribution of these proteins in diploid larvae and fry. The highest IGF-I immunoreactivity observed in triploids suggests a possible involvement of ploidy in their growth performance.

Influences of the environment on the endocrine and paracrine fish growth hormone-insulin-like growth factor-I system

Insulin-like growth factor-I (IGF-I) is a key component of the complex system that regulates differentiation, development, growth and reproduction of fishes. The IGF-I gene is mainly expressed in the liver that represents the principal source of endocrine IGF-I but also in numerous other organs where the hormone most probably acts in an autocrine-paracrine manner. The primary stimulus for synthesis and release of IGF-I is growth hormone (GH) from the anterior pituitary. Thus, in analogy to mammals, it is usual to speak of a fish 'GH-IGF-I axis'. The GH-IGF-I system is affected by changes in the environment and probably represents a target of endocrine disrupting compounds (EDC) that impair many physiological processes in fishes. Thus, the review deals with the influences of changes in different environmental factors, such as food availability, temperature, photoperiod, season, salinity and EDCs, on GH gene expression in pituitary, IGF-I gene expression in liver and extrahepatic sites and the physiological effects resulting from the evoked alterations in endocrine and local IGF-I. Environmental influences certainly interact with each other but for convenience of the reader they will be dealt with in separate sections. Current trends in GH-IGF-I research are analysed and future focuses are suggested at the end of the sections.

Common carp (Cyprinus carpio) insulin-like growth factor binding protein-2 (IGFBP-2): molecular cloning, expression profiles, and hormonal regulation in hepatocytes

In the present study, we cloned IGFBP-2 cDNA from common carp (Cyprinus carpio) liver. The 1879 bp full-length cDNA encodes 274 amino acid residues containing a putative signal peptide of 22 residues. Two IGFBP-2 transcripts with estimated sizes of 2.2 and 1.5 kb have been detected with Northern blot analysis in liver. Relatively high levels of IGFBP-2 mRNA were observed in all regions of brain, liver, pituitary, ovary and testis. Intermediate levels were observed in white muscle, thymus gland and head kidney, while in retina, heart and other tissues IGFBP-2 mRNA levels were very low. A significant level of IGFBP-2 mRNA was firstly detected at lens formation stage, and it continued to increase to the highest level at blood cycling stage, and fell to a relatively high level until hatching. The expression pattern of IGFBP-2 mRNA was similar during different stages of testis and ovary. At recrudescing stage the expression level was extremely low, but it sharply increased to a high level at matured stage, and finally brought back to the very low level at regressed stage. Hepatocytes IGFBP-2 mRNA was greatly reduced by growth hormone but increased by insulin. PD-98059 and LY-294002, the specific inhibitor of MEK and PI3K, increased IGFBP-2 mRNA expression level and completely blocked the inhibitory effect of GH. It is suggested that the MAPK and PI3 kinase-signaling pathways were involved in the decrease of IGFBP-2 mRNA expression induced by GH in primary cultured hepatocytes.

Direct actions of cortisol, thyroxine and growth hormone on IGF-I mRNA expression in sea bream hepatocytes

The present study aims to investigate potential regulatory effect of different growth-related hormones including growth hormone (GH), human insulin-like growth factor-I (hIGF-I), thyroxine (T(4)), triiodothyronine (T(3)) and cortisol, on insulin-like growth factor-I (IGF-I) mRNA expression of hepatocytes isolated from silver sea bream. By using real-time PCR, IGF-I mRNA expression profiles of hepatocytes in response to individual hormones were determined in vitro. Hepatocytes incubated with GH at concentrations of 10-1000 ng/mL showed significantly higher IGF-I expression, but the elevation was attenuated at high concentration of GH (1000 ng/mL). IGF-I expression remained unchanged in hepatocytes after incubation with hIGF-I. Hepatocytes incubated with T(4) at concentration of 1000 ng/mL exhibited a significant elevation in IGF-I expression, whereas no difference in IGF-I expression was demonstrated in hepatocytes after incubation with T(3). Upon incubation with cortisol (1-1000 ng/mL), IGF-I expression was significantly decreased in hepatocytes in a dose-dependent manner. Our study demonstrated that GH, T(4), and cortisol had direct modulatory effects on IGF-I expression in fish hepatocytes in vitro.

Environmentally relevant concentrations of 17alpha-ethinylestradiol (EE2) interfere with the growth hormone (GH)/insulin-like growth factor (IGF)-I system in developing bony fish

The aim of this study was to evaluate whether effects of environmental estrogens on fish growth and reproduction may be mediated via modulating the growth hormone (GH)/insulin-like growth factor I (IGF-I) system. To this end, developing male and female monosex populations of tilapia were exposed to 17alpha-ethinylestradiol (EE2) at 5 and 25 ng EE2/l water from 10-day postfertilization (DPF) until 100 DPF. Under exposure to both EE2 concentrations, sex ratio shifted toward more females and body length, and weight were significantly reduced in males. The growth-reducing effect was associated with significant changes in hepatic IGF-I expression, both in males and females and with significant alterations of IGF-I mRNA and GH mRNA in the brain. The changes in IGF-I and GH mRNA were accompanied by altered estrogen receptor alpha (ERalpha) expression in brain and liver. These findings point to an influence of estrogenic exposure on the endocrine GH/IGF-I axis. In addition, the EE2 treatment resulted in significant changes of ERalpha and IGF-I expression in ovaries and testis, suggesting that the estrogens interact not only with the endocrine but also with the autocrine/paracrine part of the IGF-I system. Overall, our results provide evidence that EE2 at environmentally relevant concentrations is able to interfere with the GH/IGF-I system in bony fish and that the impairing effects of estrogens reported on fish growth and reproductive functions may rather result from a cross talk between the sex steroid and the IGF-I system than be toxicological.

Real-time polymerase chain reaction, in situ hybridization and immunohistochemical localization of insulin-like growth factor-I and myostatin during development of Dicentrarchus labrax (Pisces: Osteichthyes)

The distribution of insulin-like growth factor-I (IGF-I) and myostatin (MSTN) was investigated in sea bass (Dicentrarchus labrax) by real-time polymerase chain reaction (PCR), in situ hybridization (ISH) and immunohistochemistry. Real-time PCR indicated that IGF-I mRNA increased from the second day post-hatching and that this trend became significant from day 4. ISH confirmed a strong IGF-I mRNA expression from the first week post-hatching, with the most abundant expression being detected in the liver of larvae and adults. Real-time PCR also showed that the level of MSTN mRNA increased significantly from day 25. The expression of MSTN mRNA was higher in muscle and almost absent in other anatomical regions in both larvae and adults. Interestingly, the lateral muscle showed a quantitative differential expression of IGF-I and MSTN mRNAs in red and white muscle, depending on the developmental stage examined. IGF-I immunoreactivity was detected in developing intestine at hatching and in skeletal muscle, skin and yolk sac. MSTN immunostaining was evident in several tissues and organs in both larvae and adults. Both IGF-I and MSTN proteins were detected in the liver from day 4 post-hatching and, subsequently, in the kidney and heart muscle from day 10. Our results suggest, on the basis of a combined methodological approach, that IGF-I and MSTN are involved in the regulation of somatic growth in the sea bass.

IGF-I and branchial IGF receptor expression and localization during salinity acclimation in striped bass

The initial response of the IGF-I system and the expression and cellular localization of IGF type-I receptor (IGF-IR) were studied in the gill of a euryhaline teleost during salinity acclimation. Exposure of striped bass ( Morone saxatilis) to hyperosmotic and hypoosmotic challenges induced small, transitory (<24 h) deflections in hydromineral balance. Transfer from freshwater (FW) to seawater (SW) induced an initial decrease in plasma IGF-I levels after 24 h in both fed and fasted fish. There was an overall decrease in liver IGF-I mRNA levels after SW transfer, suggesting that decreased plasma levels may be due to a decline in hepatic IGF-I synthesis. No changes were observed in gill IGF-I mRNA, but SW transfer induced an increase in gill IGF-IR mRNA after 24 h. Transfer from SW to FW induced an increase in plasma IGF-I levels in fasted fish. In fed fish, no significant changes were observed in either plasma IGF-I, liver, or gill IGF-I mRNA, or gill IGF-IR mRNA levels. In a separate experiment, FW-acclimated fish were injected with saline or IGF-I prior to a 24-h SW challenge. Rapid regain of osmotic balance following SW transfer was hindered by IGF-I. Immunohistochemistry revealed for the first time in teleosts that IGF-IR and Na+-K+-ATPase are localized in putative chloride cells at the base of the lamellae, identifying these cells in the gill as a target for IGF-I and IGF-II. Overall the data suggest a hyperosmoregulatory role of IGF-I in this species.

Long-term culture of muscle explants from Sparus aurata

Although there are mammalian myoblast cell lines, no fish myoblast cell line has been developed so far. The aim of this study was to develop a culture system of muscle explants for fish, as explants provide an approximation of the in vivo conditions for cell proliferation and differentiation, and enable a close comparison with events in muscle regenerating in vivo. Here we describe the main features of a long-term in vitro culture system for muscle explants from Sparus aurata fry. At the time of sampling, the original fibres were damaged and subsequently degenerated as shown by the loss of parvalbumin (PV) and presence of apoptotic nuclei. This mechanical damage provoked a myogenic response by activation of myogenic precursor cells. After a few days, new mononucleate cells aligned with the original fibres were seen in the explants, some with proliferating cell nuclear antigen (PCNA-) and Myf-5-positive nuclei, indicating proliferation and their myogenic fate. By 1 week, multinucleate cells with desmin immunoreactivity but PCNA- and Myf5-negative nuclei were present, equivalent to differentiated, postmitotic myotubes. Some of these myotubes were also immunoreactive for PV and insulin-like growth factors (IGFs). By 11 days, many of the myotubes were also immunoreactive for myostatin (MSTN). By 23 days, many of the myotubes had increased in diameter, were packed with myofibrils, and were strongly PV-positive and immunoreactive for MSTN, IGF-I and IGF-I receptor. This study shows that a proliferative process occurs in the explants despite the death of the original muscle fibres, and new muscle fibres expressing growth regulators are formed by regeneration from myogenic precursors present in the explants at the time of sampling.

Differential expression of IGF-I mRNA and peptide in the male and female gonad during early development of a bony fish, the tilapia Oreochromis niloticus

Insulin-like growth factor I (IGF-I) plays a key role in the complex system that regulates bony fish growth, differentiation, and reproduction. The major source of circulating IGF-I is liver, but IGF-I-producing cells also occur in other organs, including the gonads. Because no data are available on the potential production sites of IGF-I in gonad development, developmental stages of monosex breedings of male and female tilapia from 0 day postfertilization (DPF) to 90 DPF were investigated for the production sites of IGF-I at the peptide (immunohistochemistry) and mRNA (in situ hybridization) level. IGF-I mRNA first appeared in somatic cells of the male and female gonad anlage at 7 DPF followed by IGF-I peptide around 9-10 DPF. Gonad anlagen were detected from 7 DPF. Starting at 7 DPF, IGF-I peptide but no IGF-I mRNA was observed in male and female primordial germ cells (PGCs) provided that IGF-I mRNA was not under the detection level, this observation may suggest that IGF-I originates from the somatic cells and is transferred to the PGCs or is of maternal origin. While in female germ cells IGF-I mRNA and peptide appeared at 29 DPF, in male germ cells both were detected as late as at 51-53 DPF. It is assumed that the production of IGF-I in the germ cells is linked to the onset of meiosis that in tilapia ovary starts at around 28 DPF and in testes at around 52-53 DPF. In adult testis, IGF-I mRNA and peptide occurred in the majority of spermatogonia and spermatocytes as well as in Leydig cells, the latter indicating a role of IGF-I in the synthesis of male sex steroids. In adult ovary, IGF-I mRNA and IGF-I peptide were always present in small and previtellogenic oocytes but only IGF-I peptide infrequently occurred in oocytes at the later stages. IGF-I expression appeared in numerous granulosa and some theca cells of follicles at the lipid stage and persisted in follicles with mature oocytes. The results suggest a crucial role of local IGF-I in the formation, differentiation and function of tilapia gonads.

Organ-specific expression of IGF-I during early development of bony fish as revealed in the tilapia, Oreochromis niloticus, by in situ hybridization and immunohistochemistry: indication for the particular importance of local IGF-I

The cellular sites of insulin-like growth factor I (IGF-I) synthesis in the early developing tilapia (0-140 days post fertilization, DPF) were investigated. IGF-I mRNA and peptide appeared in liver as early as 4 DPF and in gastro-intestinal epithelial cells between 5-9 DPF. In exocrine pancreas, the expression of IGF-I started at 4 DPF and continued until 90 DPF. IGF-I production was detected in islets at 6 DPF in non-insulin cells and occurred throughout life. In renal tubules and ducts, IGF-I production started at 8 DPF. IGF-I production in chondrocytes had its onset at 4 DPF, was more pronounced in growing regions and was also found in adults. IGF-I mRNA and peptide appeared in the cytoplasm of skeletal muscle cells at 4 DPF. In gill chloride cells, IGF-I production started at 6 DPF. At 13 DPF, IGF-I was detected in cardiac myocytes. IGF-I-producing epidermal cells appeared at 5 DPF. In brain and ganglia, IGF-I was expressed in virtually all neurones from 6 to 29 DPF, their number decreasing with age. Neurosecretory IGF-I-immunoreactive axons were first seen in the neurohypophysis around 17 DPF. Endocrine cells of the adenohypophysis exhibited IGF-I mRNA at 28 DPF and IGF-I immunoreactivity at 40 DPF. Thus, IGF-I appeared early (4-5 DPF), first in liver, the main source of endocrine IGF-I, and then in organs involved in growth or metabolism. The expression of IGF-I was more pronounced during development than in juvenile and adult life. Local IGF-I therefore seems to have a high functional impact in early growth, metabolism and organogenesis.

Cloning and expression of insulin-like growth factors I and II in the shi drum (Umbrina cirrosa)

Insulin-like growth factors (IGFs) are evolutionarily ancient polypeptides, with potent metabolic actions, affecting cell development and growth. The IGF system consists of two ligands: IGF-I and IGF-II, several binding proteins and high-affinity transmembrane receptors. To understand growth regulation in the teleost shi drum, Umbrina cirrosa, we cloned IGF-I and IGF-II cDNAs, studied their expression and determined the cellular localization of IGF-II peptide by immunohistochemistry. A fragment of 1110 nucleotides, coding for U. cirrosa IGF-I (ucIGF-I), was cloned from liver by PCR. It includes an open reading frame of 561 nucleotides, encoding a 187 amino acid preproIGF-I. A fragment of 938 nucleotides that includes part of the coding sequence and the 3' UTR of IGF-II (ucIGF-II) was cloned as well. Sequence analysis of ucIGF-I and ucIGF-II showed a high degree of homology with known fish IGF-I and IGF-II. Real-Time PCR showed a higher expression of IGF-I and IGF-II in liver, compared to all other tissues analysed. IGF-II peptide was detected in larval liver, intestine, gills and heart musculature. After metamorphosis, reactivity was particularly evident in the kidney and in red fibres of skeletal muscle. These results add novel information on the nucleotide sequence of IGF-I and IGF-II in a marine teleost, the shi drum, that was recently introduced to the mariculture industry in southern Europe and emphasizes the conservation in the 5' UTR of IGF-I among teleosts. Furthermore, this study suggests, on the basis of a combined approach of RT-PCR, Real-Time PCR and immunohistochemistry that IGF-I and IGF-II are involved in the regulation of somatic growth in the shi drum.

A Survey on the Expression of IGF-I in the Early Developing Bony Fish with Special Emphasis on the Tilapia,Oreochromis niloticus

The present study investigates the expression of IGF-I in the early developing tilapia (Oreochromis niloticus). IGF-I was detected very early in ontogeny (4-5 days postfertilization, DPF), first in liver and in organs involved in growth and metabolism, thus suggesting a high physiological impact of IGF-I in growth, metabolism, and organogenesis.

Regulation of adult olfactory neurogenesis by insulin-like growth factor-I

Insulin-like growth factor-I (IGF-I) has multiple effects within the developing nervous system but its role in neurogenesis in the adult nervous system is less clear. The adult olfactory mucosa is a site of continuing neurogenesis that expresses IGF-I, its receptor and its binding proteins. The aim of the present study was to investigate the roles of IGF-I in regulating proliferation and differentiation in the olfactory mucosa. The action of IGF-I was assayed in serum-free culture combined with bromodeoxyuridine-labelling of proliferating cells and immunochemistry for specific cell types. IGF-I and its receptor were expressed by globose basal cells (the neuronal precursor) and by olfactory neurons. IGF-I reduced the numbers of proliferating neuronal precursors, induced their differentiation into neurons and promoted morphological differentiation of neurons. The evidence suggests that IGF-I is an autocrine and/or paracrine signal that induces neuronal precursors to differentiate into olfactory sensory neurons. These effects appear to be similar to the cellular effects of IGF-I in the developing nervous system.

Differential gene expression of IGF-I, IGF-II, and toll-like receptors 3 and 5 during embryogenesis in hybrid (channel x blue) and channel catfish

Insulin-like growth factors-I and-II (IGF-I and IGF-II) play important roles in growth and development of mammals. Toll-like receptors (TLRs) are pattern recognition molecules that orchestrate the induction of early innate immune response by recognition of specific sequences. Evidence is growing that suggests a relationship between growth and immune function. The objective of the study was to examine changes in gene expression of IGF-I, IGF-II, TLR3, and TLR5 during embryogenesis and early larval development in hybrid (channel catfishxblue catfish) and channel catfish. Egg samples were taken pre- and post-fertilization; embryos were collected at two stages of embryogenesis, at hatch, and at swim-up. All genes were detected in unfertilized catfish eggs. Expression levels of TLR5 and IGF-I mRNA in channel catfish and expression levels of TLR3, IGF-I, and IGF-II mRNA in hybrids increased over time (P<0.01). Effect of time was not significant for expression of IGF-II or TLR3 mRNA in channel catfish and for TLR5 mRNA in hybrid catfish. Results of this study suggest growth (IGF-I and IGF-II) and immune (TLR3 and TLR5) associated genes could be functional and play important roles during embryogenesis and early development of hybrid and channel catfish.

Growth hormone and insulin-like growth factors in fish: where we are and where to go

This communication summarizes viewpoints, discussion, perspectives, and questions, put forward at a workshop on "Growth hormone and insulin-like growth factors in fish" held on September 7th, 2004, at the 5th International Symposium on Fish Endocrinology in Castellon, Spain.

Insulin-like growth factor signaling in fish

The insulin-like growth factor (IGF) system plays a central role in the neuroendocrine regulation of growth in all vertebrates. Evidence from studies in a variety of vertebrate species suggest that this growth factor complex, composed of ligands, receptors, and high-affinity binding proteins, evolved early during vertebrate evolution. Among nonmammalian vertebrates, IGF signaling has been studied most extensively in fish, particularly teleosts of commercial importance. The unique life history characteristics associated with their primarily aquatic existence has fortuitously led to the identification of novel functions of the IGF system that are not evident from studies in mammals and other tetrapod vertebrates. Furthermore, the emergence of the zebrafish as a preferred model for development genetics has spawned progress in determining the requirements for IGF signaling during vertebrate embryonic development. This review is intended as a summary of our understanding of IGF signaling, as revealed through research into the expression, function, and evolution of IGF ligands, receptors, and binding proteins in fish.

Ontogeny of osmoregulation in postembryonic fish: a review

Salinity and its variations are among the key factors that affect survival, metabolism and distribution during the fish development. The successful establishment of a fish species in a given habitat depends on the ability of each developmental stage to cope with salinity through osmoregulation. It is well established that adult teleosts maintain their blood osmolality close to 300 mosM kg(-1) due to ion and water regulation effected at several sites: tegument, gut, branchial chambers, urinary organs. But fewer data are available in developing fish. We propose a review on the ontogeny of osmoregulation based on studies conducted in different species. Most teleost prelarvae are able to osmoregulate at hatch, and their ability increases in later stages. Before the occurrence of gills, the prelarval tegument where a high density of ionocytes (displaying high contents of Na+/K+-ATPase) is located appears temporarily as the main osmoregulatory site. Gills develop gradually during the prelarval stage along with the numerous ionocytes they support. The tegument and gill Na+/K+-ATPase activity varies ontogenetically. During the larval phase, the osmoregulatory function shifts from the skin to the gills, which become the main osmoregulatory site. The drinking rate normalized to body weight tends to decrease throughout development. The kidney and urinary bladder develop progressively during ontogeny and the capacity to produce hypotonic urine at low salinity increases accordingly. The development of the osmoregulatory functions is hormonally controlled. These events are inter-related and are correlated with changes in salinity tolerance, which often increases markedly at the metamorphic transition from larva to juvenile. In summary, the ability of ontogenetical stages of fish to tolerate salinity through osmoregulation relies on integumental ionocytes, then digestive tract development and drinking rate, developing branchial chambers and urinary organs. The physiological changes leading to variations in salinity tolerance are one of the main basis of the ontogenetical migrations or movements between habitats of different salinity regimes.

Cellular localisation of insulin-like growth factor binding protein-2 (IGFBP-2) during development of the marine fish, Sparus aurata

The spatial localisation of insulin-like growth-factor-binding protein-2 (IGFBP-2) and its mRNA was investigated during larval and post-larval developmental stages of the gilthead seabream ( Sparus aurata) by immunohistochemistry and in situ hybridisation with specific antisera and riboprobes. During larval development, immunoreactivity was found in skin, muscle, gills, pharynx, intestine, liver and olfactory epithelium. After metamorphosis, immunoreactivity was found in the oesophageal epithelium (the strongest reaction) and in red skeletal muscle, heart muscle, the thymus and the epithelium of renal tubules. In the adult, immunostaining with IGFBP-2 antibody was also found in the saccus vasculosus, ovary and testis. IGFBP-2 mRNA was detected by in situ hybridisation mainly in the intestine, skeletal musculature and ovary. These results show that IGFBP-2 protein and mRNA are expressed in a variety of seabream tissues, suggesting that IGFBP-2 regulates the actions of IGFs on these tissues during development and growth.