Growth hormone receptors in the atherinid Odontesthes bonariensis: characterization and expression profile after fasting-refeeding and growth hormone administration

Food deprivation reduces sensitivity of liver Igf1 synthesis pathways to growth hormone in juvenile gopher rockfish (Sebastes carnatus)

Growth hormone (Gh) regulates growth in part by stimulating the liver to synthesize and release insulin-like growth factor-1 (Igf1), which then promotes somatic growth. However, for fish experiencing food limitation, elevated blood Gh can occur even with low circulating Igf1 and slow growth, suggesting that nutritional stress can alter the sensitivity of liver Igf1 synthesis pathways to Gh. Here, we examined how recent feeding experience affected Gh regulation of liver Igf1 synthesis pathways in juvenile gopher rockfish (Sebastes carnatus) to illuminate mechanisms underlying the nutritional modulation of Igf1 production. Juvenile gopher rockfish were maintained under conditions of feeding or complete food deprivation (fasting) for 14 d and then treated with recombinant sea bream (Sparus aurata) Gh or saline control. Gh upregulated hepatic igf1 mRNA levels in fed fish but not in fasted fish. The liver of fasted rockfish also showed a lower relative abundance of gene transcripts encoding teleost Gh receptors 1 (ghr1) and 2 (ghr2), as well as reduced protein levels of phosphorylated janus tyrosine kinase 2 (pJak2) and signal transducer and activator of transcription 5 (pStat5), which function to induce igf1 gene transcription following Gh binding to Gh receptors. Relative hepatic mRNA levels for suppressors of cytokine signaling (Socs) genes socs2, socs3a, and socs3b were also lower in fasted rockfish. Socs2 can suppress Gh activation of Jak2/Stat5, and fasting-related variation in socs expression may reflect modulated inhibitory control of igf1 gene transcription. Fasted rockfish also had elevated liver mRNA abundances for lipolytic hormone-sensitive lipase 1 (hsl1) and Igf binding proteins igfbp1a, -1b and -3a, reduced liver mRNAs encoding igfbp2b and an Igfbp acid labile subunit-like (igfals) gene, and higher transcript abundances for Igf1 receptors igf1ra and igf1rb in skeletal muscle. Together, these findings suggest that food deprivation impacts liver Igf1 responsiveness to Gh via multiple mechanisms that include a downregulation of hepatic Gh receptors, modulation of the intracellular Jak2/Stat5 transduction pathway, and possible shifts in Socs-inhibitory control of igf1 gene transcription, while also demonstrating that these changes occur in concert with shifts in liver Igfbp expression and muscle Gh/Igf1 signaling pathway components.

Insulin-like growth factor-1 (Igf1) signaling responses to food consumption after fasting in the Pacific rockfish Sebastes carnatus

Fish adjust rates of somatic growth in the face of changing food consumption. As in other vertebrates, growth in fish is regulated by the growth hormone (Gh)/insulin-like growth factor-1 (Igf1) endocrine axis, and changes in food intake impact growth via alterations to Gh/Igf1 signaling. Understanding the time course by which the Gh/Igf1 axis responds to food consumption is crucial to predict how rapidly changes in food abundance might lead to altered growth dynamics. Here, we looked at the response times of plasma Igf1 and liver Igf1 signaling-associated gene expression to refeeding after food deprivation in juvenile gopher rockfish (Sebastes carnatus), one of several species of northern Pacific Ocean Sebastes rockfishes targeted by fisheries or utilized for aquaculture. Gopher rockfish were fasted for 30 d, after which a subset was fed to satiation for 2 h, while other rockfish continued to be fasted. Refed fish exhibited higher hepatosomatic index (HSI) values and increased Igf1 after food consumption. Gene transcripts for Gh receptor 1 (ghr1), but not ghr2, increased in the liver after eating. Transcripts encoding igf1 also increased in the liver of refed fish 2-4 d after feeding, only to return to levels similar as continually fasted rockfish by 9 d after feeding. Liver mRNA abundances for Igf binding protein (Igfbp) genes igfbp1a, igfbp1b, and igfbp3a declined within 2 d of feeding. These findings provide evidence that circulating Igf1 in rockfish reflects a fish's feeding experience within the previous few days, and suggest that feeding-induced increases in Igf1 are being mediated in part by altered liver sensitivity to Gh due to upregulated Gh receptor 1 expression.

The cellular basis of compensatory muscle growth in the teleost Odontesthes bonariensis

This study evaluates white muscle growth and in vivo cell proliferation during a fasting and refeeding trial, using pejerrey Odontesthes bonariensis as animal model, in order to better understand the cellular basis governing catch-up growth. Experiments consisted in two groups of fish, a control one continuously fed ad libitum, and a group fasted for 2 weeks and then fed for another 2 weeks. We examined how the formation of new muscle fibers and their increase in size were related to muscle precursor cell (MPC) proliferation under both experimental conditions. During fasting, the number of 5-ethynyl-2'-deoxyuridinepositive (EdU+) cells decreased along with myogenic regulatory factors (MRF) mRNA levels related to myoblast proliferation and differentiation, and the muscle stem cell-markerPax7 mRNA level increased. Analysis of myomere cross-sectional area, distribution of muscle fiber sizes and number of fibers per myomere showed that muscle hypertrophy but not hyperplasia was inhibited during fasting. Both higher igf2 mRNA level and the persistence of cell proliferation could be supporting new myofibre formation. On the other hand, an exacerbated MPC proliferation occurred during catch-up growth, and this increase in cell number could be contributing to the growth of both pre-existing and newly form small fibers. The finding that some MPCs proliferate during fasting and that muscle growth mechanisms, hyperplasia and hypertrophy, are differentially regulated could help to explain why re-fed fish could growth at higher rates, and why they return to the lost growth trajectory.

Molecular identification and developmental expression patterns of growth hormone and its receptors in yellowtail kingfish (Seriola lalandi)

In fish and other vertebrates, growth hormone (GH) is an essential polypeptide required for normal growth and development. In an attempt to understand growth regulation in yellowtail kingfish (YTK), the full-length cDNA sequences encoding gh and its receptors (ghr1 and ghr2) were cloned, characterized and the expression profiles of these three genes were investigated during embryonic development. The full-length cDNA sequences of GH and its receptors were obtained by RT-PCR combined with RACE methord. YTK gh cDNA sequence was 852 base pairs (bp) that comprised an open reading frame (ORF) of 615 bp encoding a 204-amino acids (aa) precursor. The preprohormone compassed a signal peptide (17 aa) and the mature peptide (187 aa). YTK GHR1 protein consisted of a signal peptide (28 aa), an extracellular domain (222 aa), a single transmembrane domain (23 aa) and an intracellular domain (361 aa). GHR2 protein included 18 aa, 223 aa, 23 aa, and 321 aa, respectively. Tissue distribution analysis showed that the maximal level of gh expression was observed in the pituitary, and ghr1 mRNA was mainly detected in the liver, while ghr2 transcripts were most abundant in the gonad. Moreover, both ghr1 and ghr2 mRNAs were expressed in all embryonic stages and displayed different gene expression profiles. Overall, these results provide initial evidences for the involvement of the GH/GHR system in the early ontogeny of yellowtail kingfish.

Identification of the cDNA Encoding the Growth Hormone Receptor (GHR) and the Regulation of GHR and IGF-I Gene Expression by Nutritional Status in Reeves' Turtle (Chinemys reevesii)

Chinemys reevesii (Reeves’ turtle) is a slow-growing reptile that is distributed widely across China. Prior to this study, the cDNA sequence of the growth hormone receptor (GHR) in the Reeve’s turtle, or how periods of starvation might influence the gene expression of GHR and insulin-like growth factor I (IGF-I) in this species, were unknown. Here, we identified the full-length sequence of the cDNA encoding GHR in Reeves’ turtle by using RT-PCR and RACE. The full-length GHR cDNA was identified to be 3936 base-pairs in length, with a 1848 base-pair open reading frame (ORF) that encodes a 615 amino acid protein. Analysis showed that GHR mRNA was detectable in a wide range of tissues; the highest and lowest levels of expression were detected in the liver and the gonad, respectively. IGF-I was also expressed in a range of tissues, but not in the gonad; the highest levels of IGF-I expression were detected in the liver. After 4 weeks of fasting, the expression levels of GHR and IGF-I in the liver had decreased significantly; however, these gradually returned to normal after refeeding. We report the first cloned cDNA sequence for the GHR gene in the Reeve’s turtle. Our findings provide a foundation from which to investigate the specific function of the GHR in Reeve’s turtle, and serve as a reference for studying the effects of different nutrient levels on GHR expression in this species.

Genomic structure and characterization of growth hormone receptors from golden pompano Trachinotus ovatus and their expression regulation by feed types

In this study, sequence analysis showed that ToGHR1 and ToGHR2 encoded polypeptides of 577 and 588 amino acids, respectively. Bioinformatics analysis showed that both ToGHR1 and ToGHR2 contain FN3 domains and transmembrane domains, which have glycosylation and phosphorylation sites. The exons of ToGHR1 and exons 4-10 of ToGHR2 are homologous to exons 2 and 4-9 in Homo sapiens genes, respectively. Only 3 SSR sites in ToGHR1 have SSR polymorphisms, and ToGHR2 has no SSR polymorphisms. ToGHR1 and ToGHR2 have high homology with GHR1 and GHR2 of many fish by BLAST. qRT-PCR was used to examine the expression profile of ToGHR mRNA in 12 normal liver and intestine tissue samples from 3 feed-type groups. The results showed that ToGHR is expressed in all 12 tissues, especially liver and muscle tissues, which showed higher ToGHR expression than that in other tissues (p < 0.05). Experiments on feed-type groups may indicate that high levels of LC-PUFA in squid bait can promote ToGHR1 expression and simultaneously inhibit ToGHR2 expression in the liver tissue. In addition, the high levels of LC-PUFA in food could inhibit intestinal ToGHR1 expression, and the intermediate levels may promote intestinal ToGHR1 expression. However, the unsaturated fatty acid content in the food does not affect the expression of intestinal ToGHR2.

Direct actions of macronutrient components on goldfish hepatopancreas in vitro to modulate the expression of ghr-I, ghr-II, igf-I and igf-II mRNAs

In mammals and fish, somatic growth and metabolism are coordinated by the GH-IGF axis, composed of growth hormone (GH), growth hormone receptors I and II (GHR-I and GHR-II), and the insulin-like growth factors I and II (IGF-I and IGF-II). In order to determine if dietary macronutrients regulate the hepatopancreatic expression of ghr-I, ghr-II, igf-I and igf-II independently of circulating GH, organ culture experiments were conducted. Briefly, goldfish hepatopancreas sections were incubated with different doses of glucose; L-tryptophan; oleic acid; linolenic acid (LNA); eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). After two and four hours of treatment, the expression of ghr-I, ghr-II, igf-I and igf-II mRNAs was quantified. We found that glucose and L-tryptophan globally upregulate the mRNA expression of ghr-I; ghr-II; igf-I and igf-II. Duration of exposure, and unsaturation level of fatty acids differentially modulate ghr-I, ghr-II and igf-II mRNA expression. Additionally, we found that fatty acids increase the expression of igf-I depending on incubation time and fatty acid class. In conclusion, here we present evidence for GH-independent, direct effects exerted by dietary macronutrients on GHR and IGF in goldfish hepatopancreas.