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

Genomic structures of insulin-like growth factor from golden pompano (Trachinotus ovatus) and their expression responses to the feed types

Golden pompano is an important aquaculture product in the coastal regions of southern China, which is highly dependent on insulin-like growth factor (IGF) for various biological processes. The cDNAs of ToIGF1, ToIGF2, and ToIGF3 are 1718 bp, 1658 bp, and 2272 bp in length, respectively, with corresponding amino acid sequences of 185 aa, 215 aa, and 194 aa. These sequences consist of 5 parts, including the signal peptide, the B domain, the C domain, the A domain, the D domain, and the E domain, which are also found in other species. While ToIGF1 has no SSR polymorphism, ToIGF2 and ToIGF3 have 3 and 1 SSR polymorphism sites, respectively. In terms of tissue expression, ToIGF1 is predominantly expressed in the liver, ToIGF2 shows its highest expression in the gills, and ToIGF3 also shows its highest expression in the gills, but no expression in the liver and spleen. These tissue distribution results suggest that ToIGFs are not only present in growth-related tissues such as the brain, muscle, and liver, but also in reproductive tissues, tissues that regulate osmotic pressure, and tissues related to food intake. This observation is consistent with other bony fish species and highlights the extensive biological functions of ToIGFs that need to be further explored and exploited. In addition, the expression levels of ToIGFs were found to be different in the different dietary groups, including the pelleted food group, the frozen squid group, and the frozen fish group. In the pelleted diet group, ToIGF1 and ToIGF2 were highly expressed in the liver and intestinal tissues, followed by the frozen fish group. These results suggest that the type of diet can affect the body's energy metabolism by influencing tissue expression of growth-related genes, which in turn affects individual growth.

Molecular cloning and expression profiling of insulin-like growth factor 2 and IGF-binding protein 6 in Clarias magur (Hamilton 1822)

Growth is an important trait in aquaculture and the major genes that regulate it are Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs). In this study, the full-length coding sequences of IGF2 and IGFBP6 genes in the Indian catfish Clarias magur were cloned and characterized. The full-length cDNA sequences of IGF2 and IGFBP6 were 885 bp (ORF 642 bp) and 928 bp (ORF 600 bp), encoding 213 and 199 amino acids, respectively. Bioinformatics analyses revealed that the magur IGF2 and IGFBP6 proteins are hydrophilic and secretory in nature. Sequence alignment with other teleosts and mammalian orthologues shows conservation of the functional domains. Gene expression analysis in 6 individuals each of high (298 ± 5.0 g) and low (210 ± 6.0 g) growth performing families showed significantly (p < 0.05) higher expression (2.5-3 fold) of IGF2, and lower expression (∼2.5 fold) of IGFBP6 in liver and muscle of fast-growing fish. This study suggests that IGF2 could be playing a major role in the growth regulation of magur. These genes and their expression patterns could be developed into growth-associated markers for magur and other catfishes.

Involvement of glycolysis activation in flatfish sexual size dimorphism: Insights from transcriptomic analyses of Platichthys stellatus and Cynoglossus semilaevis

The starry flounder (Platichthys stellatus), a flatfish cultured at the margins of the North Pacific, displays an obvious female-biased growth advantage, similar to many other fish species. To reveal the molecular mechanism underlying sexual size dimorphism, a comparative transcriptomic analysis of the somatotropic and reproductive axes was conducted. In total, 156, 67, 3434, and 378 differentially expressed genes (DEGs) between female and male samples were obtained in the brain, liver, gonad, and muscle tissues (q < 0.05). These DEGs were significantly enriched for various GO terms, including ion channel activity, protein binding, lipid transporter activity, and glycolytic process. The significantly enriched KEGG pathways included insulin secretion, axon guidance, and glycolysis/gluconeogenesis. In a detailed analysis of DEGs in these significantly enriched pathways, 35 genes showed higher expression levels in female muscle tissues than in male muscle tissues. A protein-protein interaction network further revealed specific interactions involving the glycolysis related-protein enolase (ENO), triosephosphate isomerase (TPI), Bisphosphoglycerate mutase (BPGM), fructose-bisphosphate aldolase (ALDO), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Interestingly, the role of glycolysis/gluconeogenesis was supported by an analysis of common DEGs between P. stellatus and Chinese tongue sole (Cynoglossus semilaevis). These results indicate that the activation of glycolysis in female muscle tissues contributes to flatfish sexual size dimorphism.

Comprehensive physiological and transcriptomic analysis revealing the responses of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) to the replacement of fish meal with soy protein concentrate

Plant proteins are suitable and alternative to fish meals (FMs), with less cost compared with that of all other types of fish feeds. In recent years, soy protein concentrate (SPC) has emerged as a cost-effective alternative to FM; however, little is known regarding the effects of dietary SPC on general fish physiology and well-being. This study aimed to perform comprehensive physiological and transcriptomic analysis for testing the applicability of SPC as fish feeds in hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) [SPC replaced 0% (CK), 30% (SPC30), and 75% (SPC75) of FM protein]. Generally, SPC30 promoted fish survival and had less effects on the phenotype, while SPC75 reduced fish survival, promoted inflammation, and regulated multiple physiological responses. Thousands of differentially expressed genes (DEGs) by SPC were identified in the intestine, liver, and muscle, which were enriched in biological regulation, cellular process, metabolic process, single-organism process, cell, cell part, membrane, binding, and catalytic activity based on RNA-seq. Notably, some DEGs involved in amino acid and lipid metabolism in the digestive system highlighted the modulatory effect of SPC on these metabolic processes, consistent with the physiological responses including enzyme activities. The enriched aspects of these predominant DEGs might be directly related to the different effects of SPC30 and SPC75 on fish growth, digestibility, and underlying enzyme activities and histology. In conclusion, the comprehensive physiological and transcriptomic comparative analysis of CK, SPC30, and SPC75 was also effective in testing the applicability of SPC as fish feeds and in designing a proper diet with the best impact on the growth performance and health of fish in hybrid grouper.

Insulin-like growth factor I of Yellow catfish (Pelteobagrus fulvidraco): cDNA characterization, tissue distribution, and expressions in response to starvation and refeeding

The full-length cDNA coding IGF-I was cloned from the liver of Yellow catfish Pelteobagrus fulvidraco. The tissue distributions of IGF-I in adults were then analyzed by using real-time PCR. The effects of starvation (3 weeks) and subsequent refeeding (3 weeks) on the compensatory growth performance in juvenile fish weighing 3.80 ± 0.78 g and hepatic IGF-I mRNA expressions were also investigated. The cDNA obtained covered 884 bp with an open reading frame of 480 bp encoding 159 amino acids. It is composed of a signal peptide with 41 amino acids (AAs), a mature peptide comprising the B, C, A, and D domains (71 AAs) and E domain of 47 AAs. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (71-87%) among the species of Siluriformes and some closely related species. In adults, the highest IGF-I expression was observed in the liver, followed by the brain, whereas relatively low expressions were detected in muscle and stomach. Both body weight and length increased significantly in fish fed to satiation continuously. Body weight, body length, condition factor, and hepatic IGF-I expressions were all decreased remarkably with increasing starvation times, but increased significantly after refeeding. The results showed that the expression of IGF-I was positively correlated with feed intakes and IGF-I may play a key regulatory role for somatic growth induced by compensatory growth in Yellow catfish.

Molecular characterization and expression profiles of insulin-like growth factors in yellowtail kingfish (Seriola lalandi) during embryonic development

In this study, to understand the role of the insulin-like growth factor (IGF) system in the regulation of early development in yellowtail kingfish (YTK, Seriola lalandi), an economically important marine fish species with a high potential for aquaculture, we first cloned the full-length cDNAs for igf1 and igf2 from the liver. YTK igf1 cDNA was 1946 base pairs (bp) in length with an open reading frame (ORF) of 558 bp encoding preproIGF1 of 185 amino acids (aa). The preproIGF1 consisted of 44 aa for the signal peptide, 68 aa for the mature peptide comprising B, C, A, and D domains, and 73 aa for the E domain. YTK igf2 cDNA had an ORF of 648 bp that encoded a total of 215 aa spanning the signal peptide (47 aa), the mature peptide (70 aa), and the E domain (98 aa). At the protein level, both YTK IGF1 and IGF2 exhibited high sequence identities with their corresponding fish counterparts, respectively. Subsequently, quantitative RT-PCR analysis indicated that the highest level of igf1 mRNA expression was recorded in the gonad and liver, while the igf2 mRNA expression was most abundant in the gill and liver. In addition, both igf1 and igf2 were detected in all stages of embryonic development and exhibited different gene expression patterns, supporting that IGF1 and IGF2 could be functional and play important roles during YTK embryogenesis. Overall, this initial study of IGF1 and IGF2 provides an insight into the endocrine mechanism involved in the early development of yellowtail kingfish.

Evidences for involvement of growth hormone and insulin-like growth factor in ovarian development of starry flounder (Platichthys stellatus)

Although gonadotrophins are major regulators of ovarian function in teleosts and other vertebrates, accumulating evidence indicates that the growth hormone (GH)-insulin-like growth factor (IGF) axis also plays an important role in fish reproduction. As a first step to understand the physiological role of the GH-IGF system in the ovarian development of starry flounder (Platichthys stellatus), the expression profiles of GH and IGF messenger RNAs (mRNAs) and plasma GH, IGF-I, estradiol-17β (E2), and testosterone (T) levels during the ovarian development were investigated. The developmental stages of ovaries were divided into five stages (II, III, IV, V, and VI) by histological analysis. The hepatosomatic index (HSI) and gonadosomatic index (GSI) values increased and peaked at stage IV and stage V, respectively, and then declined at stage VI. Pituitary GH mRNA levels decreased sharply at stage III and raised to top level at stage VI. The hepatic IGF-I mRNA levels ascended to maximum value at stage V and then declined significantly at stage VI. However, the hepatic IGF-II mRNA levels remained stable and increased significantly at stage VI. In contrast, the ovarian IGF-I mRNA levels increased gradually and peaked at stage VI. The ovarian IGF-II mRNA levels were initially stable and increased significantly at stage V until the top level at stage VI. Consistent with the pituitary GH mRNA levels, plasma GH levels reduced sharply at stage III and remained depressed until stage V and then raised remarkably at stage VI. Plasma IGF-I level peaked at stage V and then declined to initial level. Plasma E2 level peaked at stage IV and then dramatically descended to the basal level. Plasma T level peaked at stage V and then declined significantly back to the basal level. Based on statistical analysis, significant positive correlations between hepatic IGF-I mRNA and GSI, ovarian IGF-II mRNA and hepatic IGF-II mRNA, ovarian IGF-I mRNA and ovarian IGF-II mRNA, and plasma IGF-I and plasma T were observed, respectively. These results suggest that the GH-IGF system may be involved in the ovarian development of starry flounder; GH and IGFs appear to play distinct roles in the regulation of the ovarian development in paracrine/autocrine manners. These findings extend our knowledge of the roles of the GH-IGF axis on reproduction regulation in fish.

Insulin-like growth factor I (IGF-I) in Chinese alligator, Alligator sinensis: Molecular characterization, tissue distribution and mRNA expression changes during the active and hibernating periods

The Chinese alligator Alligator sinensis is an endangered species endemic to China, up to date, little is known about the regulation of its growth and development. Insulin-like growth factor I (IGF-I) plays a vital role in regulating vertebrate growth and development. In this study, the full-length cDNA of IGF-I in Chinese alligator (caIGF-I) was obtained for the first time, it contains 890-bp nucleotides encoding a 153-amino acid precursor, the mature caIGF-I consists of 70 amino acids by cleaving the signal peptide and C-terminal extension (E domain). The caIGF-I contains all the features of IGF-I peptide with B, C, A, and D domains and the six conservative cysteine residues involved in the stable tertiary structure. Multiple alignment analysis showed that the amino acid sequence of caIGF-I shares high identity with American alligator Alligator mississippiensis (100%) and birds (95-97%). Phylogenetic tree analysis of the IGF-I amino acid sequences indicated that alligators cluster into the bird branch. Real-time quantitative PCR technique showed that caIGF-I is widely expressed in all the examined tissues with the highest expression level in liver, higher in pancreas and oviduct while lower in heart, spleen, lung, kidney, stomach, intestines, ovary and muscles. During hibernation, the caIGF-I expression level decreased significantly in liver, pancreas, oviduct and kidney, while did not significantly change in heart, spleen, lung, stomach, small intestine, ovary and muscles. The mRNA expression changes during the two periods implicate that caIGF-I might play an important role in the regulation of feeding and growth in the Chinese alligator.

Feed restriction and insulin-like growth factor-I (IGF-I) affect the oocyte maturation in matrinxã Brycon amazonicus

The feeding and nutrition of breeders are crucial aspects in the reproductive process. During the maturation period, metabolic changes occur aiming at mobilizing energy for growth and follicular development. The involvement of IGF-1 in metabolic and reproductive events is important. The aim of this work was to evaluate if alternate feed restriction and re-feeding have permissive effects on in vitro actions of IGF-1 on oocytes development of matrinxã. In vivo experiments were performed during vitellogenesis period. Females (n = 60) were fed with a commercial feed (2% of biomass) and they were divided into two treatments: fish receiving food daily (control - fed), and fish submitted to cycles of 3 days of feed restriction and 2 days of re-feeding (no-fed group). For the in vitro experiments, oocytes (n = 20) were obtained from the ovaries removed at the end of the in vivo experiment and were divided into four groups: fed -IGF-1; fed +IGF-1; no-fed -IGF-1 and no-fed +IGF-1. Fish under restriction had lower body weights, decreased plasma glucose, increased triglycerides levels, and their final maturation and mature oocyte were reduced and the atresic ones were in higher number. Moreover, IGF-1, in vitro, increased the percentage of mature oocytes in fed females and decreased the atresic ones. In no-fed females, IGF-1 increased the final maturation and mature oocytes and reduced the atresic ones. This study demonstrates the importance of the feeding management of female breeders of matrinxã during the vitellogenesis period.

Evolution and Function of the Insulin and Insulin-like Signaling Network in Ectothermic Reptiles: Some Answers and More Questions

The insulin and insulin-like signaling (IIS) molecular network regulates cellular growth and division, and influences organismal metabolism, growth and development, reproduction, and lifespan. As a group, reptiles have incredible diversity in the complex life history traits that have been associated with the IIS network, yet the research on the IIS network in ectothermic reptiles is sparse. Here, we review the IIS network and synthesize what is known about the function and evolution of the IIS network in ectothermic reptiles. The primary hormones of this network-the insulin-like growth factors 1 and 2 (IGFs) likely function in reproduction in ectothermic reptiles, but the precise mechanisms are unclear, and likely range from influencing mating and ovulation to maternal investment in embryonic development. In general, plasma levels of IGF1 increase with food intake in ectothermic reptiles, but the magnitude of the response to food varies across species or populations and the ages of animals. Long-term temperature treatments as well as thermal stress can alter expression of genes within the IIS network. Although relatively little work has been done on IGF2 in ectothermic reptiles, IGF2 is consistently expressed at higher levels than IGF1 in juvenile ectothermic reptiles. Furthermore, in contrast to mammals that have genetic imprinting that silences the maternal IGF2 allele, in reptiles IGF2 is bi-allelically expressed (based on findings in chickens, a snake, and a lizard). Evolutionary analyses indicate some members of the IIS network are rapidly evolving across reptile species, including IGF1, insulin (INS), and their receptors. In particular, IGF1 displays extensive nucleotide variation across lizards and snakes, which suggests that its functional role may vary across this group. In addition, genetic variation across families and populations in the response of the IIS network to environmental conditions illustrates that components of this network may be evolving in natural populations. The diversity in reproductive physiology, metabolic plasticity, and lifespan among reptiles makes the study of the IIS network in this group a potentially rich avenue for insight into the evolution and function of this network. The field would benefit from future studies that discern the respective functions of IGF1 and IGF2 and how these functions vary across taxa, perfecting additional assays for measuring IIS components, and determining the role of IIS in different tissues.

Insulin-like growth factor 1 (IGF-1) regulates prolactin, growth hormone, and IGF-1 receptor expression in the pituitary gland of the gilthead sea bream Sparus aurata

The role of insulin-like growth factor 1 (IGF-1) on regulation of growth hormone (GH) and prolactin (PRL) as well as the possible involvement of IGF-1 receptor subtype a (IGF-1Ra) mRNA was assessed in juvenile specimens of Sparus aurata. IGF-1Ra was successfully cloned, and active receptor domains were localized in its mRNA precursor. Also, phylogenetic analysis of the protein sequence indicated a closer proximity to IGF-1Ra isoform found in zebrafish and other teleosts, than to the isoform IGF-1Rb. The most abundant presence of IGF-1Ra mRNA was detected in white muscle, whereas head kidney showed the lowest gene expression among 24 different studied tissues. Pituitaries of juvenile specimens of S. aurata were incubated in vitro with different doses of IGF-1 (0, 1, 100, and 1000 ng mL(-1)) during a period of 10 h. Total RNA with a high quality could be obtained from these pituitaries. PRL mRNA expression significantly increased with increasing IGF-1 doses. Similarly, IGF-1Ra mRNA increased its expression in response to IGF-1. However, GH mRNA levels decreased in a dose-dependent manner after IGF-1 treatment. The contradictory responses of GH and PRL expressions to IGF-1 in our experiment are possibly mediated by IGF-1Ra presence on the somatotrophs and prolactotrophs. The increase in IGF-1Ra mRNA levels may be related to the proper activation of the PI3-K/Akt signal transduction pathways which are normally involved in GH and PRL regulation.