Characterization of GHRs, IGFs and MSTNs, and analysis of their expression relationships in blunt snout bream, Megalobrama amblycephala

Molecular Characterization of LKB1 of Triploid Crucian Carp and Its Regulation on Muscle Growth and Quality

Liver Kinase B1 (LKB1) is a serine/threonine kinase that can regulate energy metabolism and skeletal muscle growth. In the present study, LKB1 cDNA of triploid crucian carp (Carassius auratus) was cloned. The cDNA contains a complete open reading frame (ORF), with a length of 1326 bp, encoding 442 amino acids. Phylogenetic tree analysis showed that the LKB1 amino acid sequence of the triploid crucian carp had a high sequence similarity and identity with carp (Cyprinus carpio). Tissue expression analysis revealed that LKB1 was widely expressed in various tissues. LKB1 expressions in the brain were highest, followed by kidney and muscle. In the short-term LKB1 activator and inhibitor injection experiment, when LKB1 was activated for 72 h, expressions of myogenic differentiation (MyoD), muscle regulatory factor (MRF4), myogenic factor (MyoG) and myostatin 1 (MSTN1) were markedly elevated and the content of inosine monophosphate (IMP) in muscle was significantly increased. When LKB1 was inhibited for 72 h, expressions of MyoD, MyoG, MRF4 and MSTN1 were markedly decreased. The long-term injection experiment of the LKB1 activator revealed that, when LKB1 was activated for 15 days, its muscle fibers were significantly larger and tighter than the control group. In texture profile analysis, it showed smaller hardness and adhesion, greater elasticity and chewiness. Contrastingly, when LKB1 was inhibited for 9 days, its muscle fibers were significantly smaller, while the gap between muscle fibers was significantly larger. Texture profile analysis showed that adhesion was significantly higher than the control group. A feeding trial on triploid crucian carp showed that with dietary lysine-glutamate dipeptide concentration increasing, the expression of the LKB1 gene gradually increased and was highest when dipeptide concentration was 1.6%. These findings may provide new insights into the effects of LKB1 on fish skeletal muscle growth and muscle quality, and will provide a potential application value in improvement of aquaculture feed formula.

Effects of Dietary Paper Mulberry (Broussonetia papyrifera) on Growth Performance and Muscle Quality of Grass Carp (Ctenopharyngodon idella)

Simple Summary

The quality of muscle plays an important role in improving the economic benefit of aquatic products. The paper mulberry (Broussonetia papyrifera, BP) grows wildly in the south of Asia. In this experiment, grass carps (initial weight: 50.0 ± 0.5 g) were fed diets with the addition of 0%, 5%, 10%, 15% and 20% BP in a control diet (crude protein: 31%, crude fat: 3.8%) for 8 weeks. In conclusion, adding 5% BP did not affect the growth of grass carp. However, the supplementation of 10% BP could improve muscle quality through improving muscle hardness, reducing fat accumulation and muscle fiber diameter, at the cost of reducing growth performance.

Abstract

The present study investigated the effects of dietary paper mulberry (Broussonetia Papyrifera, BP) on growth performance, muscle quality and muscle growth-related mRNA expressions of grass carp. Fish (initial weight: 50.0 ± 0.5 g) were fed diets supplemented with 0% (control diet), 5%, 10%, 15% and 20% BP for 8 weeks. The results showed that increasing levels of paper mulberry linearly and quadratically decreased the special gain rate (SGR) and increased the feed conversion rate (FCR) of grass carp (p < 0.05). Significantly positive quadratic trends were found between paper mulberry levels and muscle crude fat or crude protein of grass carp (p < 0.05). In comparison to the control diet, the 10%BP and 15%BP groups had significantly decreased muscle crude fat and increased crude protein (p < 0.05). The levels of paper mulberry resulted in a linear and quadratic increase in water loss of grass carp muscle (p < 0.05), and all groups with paper mulberry supplementation were significantly higher than the control group (p < 0.05). Significant positive linear and quadratic trends were found between the paper mulberry levels and muscle fiber diameter or density of grass carp (p < 0.05). In comparison to the control diet, the significant differences were found in the 15%BP and 20%BP groups (p < 0.05). The muscle adhesiveness and hardness linearly and quadratically increased with the increasing levels of paper mulberry (p < 0.05), and both of which increased significantly when the level of paper mulberry reached 10% (p < 0.05). In addition, the increase in paper mulberry linearly and quadratically improved the expressions of myoblast determination protein (MyoD), myogenin (MyoG), paired box protein 7 (Pax7) and myostatin 1 (MSTN1) (p < 0.05). When the supplementation of paper mulberry reached 15%, the expressions of all these mRNAs were significantly higher than those of the control group (p < 0.05). In summary, adding 5% paper mulberry did not affect the growth of grass carp. However, the supplementation of 10% paper mulberry could improve muscle quality through improving muscle hardness, reducing fat accumulation and muscle fiber diameter, at the cost of reducing growth performance.

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.

Diet Affects Muscle Quality and Growth Traits of Grass Carp (Ctenopharyngodon idellus): A Comparison Between Grass and Artificial Feed

Fish muscle, the main edible parts with high protein level and low fat level, is consumed worldwide. Diet contributes greatly to fish growth performance and muscle quality. In order to elucidate the correlation between diet and muscle quality, the same batch of juvenile grass carp (Ctenopharyngodon idellus) were divided into two groups and fed with either grass (Lolium perenne, Euphrasia pectinata and Sorghum sudanense) or artificial feed, respectively. However, the different two diets didn't result in significant differences in all the detected water quality parameters (e.g., Tm, pH, DO, NH3/[Formula: see text]-N, [Formula: see text]-N, [Formula: see text], TN, TP, and TOC) between the two experimental groups. After a 4-month culture period, various indexes and expression of myogenic regulatory factor (MRFs) and their related genes were tested. The weight gain of the fish fed with artificial feed (AFG) was nearly 40% higher than the fish fed with grass (GFG). Significantly higher alkaline phosphatase, total cholestrol, high density cholestrol and total protein were detected in GFG as compared to AFG. GFG also showed increased hardness, resilience and shear force in texture profile analysis, with significantly bigger and compact muscle fibers in histologic slices. The fat accumulation was most serious in the abdomen muscle of AFG. Additionally, the expression levels of MyoG, MyoD, IGF-1, and MSTNs were higher, whereas Myf-5, MRF4, and IGF-2 were lower in most positional muscles of GFG as compared to AFG. Overall, these results suggested that feeding grass could promote muscle growth and development by stimulating muscle fiber hypertrophy, as well as significantly enhance the expression of CoL1As. Feeding C. idellus with grass could also improve flesh quality by improving muscle characteristics, enhancing the production of collagen, meanthile, reducing fat accumulation and moisture in muscle, but at the cost of a slower growth.

Effects of zearalenone on the localization and expression of the growth hormone receptor gene in the uteri of post-weaning piglets

OBJECTIVE

In this study, we investigated the adverse effects of dietary zearalenone (ZEA) (0.5 to 1.5 mg/kg diet) on the localization and expression of the growth hormone receptor (GHR) in the uteri of post-weaning gilts and explored alternative mechanism of the reproductive toxicity of ZEA on piglets.

METHODS

A total of forty healthy piglets (Duroc×Landrace×Large White) aged 28 d were selected for study. Piglets were transferred to single cages after 10 days' adaptation on an obstetric table. The animals were allocated to one of four treatments: a normal basal diet supplemented with 0 (Control), 0.5 (ZEA0.5), 1.0 (ZEA1.0), or 1.5 (ZEA1.5) mg/kg purified ZEA, and fed for 35 d after the 10-d adaptation. Analyzed ZEA concentrations in the diets were 0, 0.52±0.07, 1.04±0.03, and 1.51±0.13 mg/kg, respectively. At the end of the feeding trial, piglets were euthanized after being fasted for 12 h. Two samples of uterine tissue from each pig were rapidly collected, one of which was stored at -80°C for analysis of the relative mRNA and protein expression of GHR, and the second was promptly fixed in Bouin's solution for immunohistochemical analysis.

RESULTS

The relative weight of the uteri and thickness of the myometrium and endometrium increased linearly (p<0.001) and quadratically (p<0.001) with an increasing level of ZEA. The results of immunohistochemical analysis indicated that GHR immunoreactive substance was mainly localizated in the cytoplasm of uterine smooth muscle, glandular epithelial, luminal epithelial, stromal, and vascular endothelial cells. In contrast, nuclear staining was rarely observed. The immunoreactive integrated optic density of GHR in the myometrium, luminal epithelium, glandular epithelium, and whole uteri of weaning gilts increased linearly (p<0.001) and quadratically (p<0.05) with an increasing level of ZEA. The mRNA and protein expression of GHR in the uteri of weaning gilts increased linearly (p<0.001) and quadratically (p<0.05) with an increasing level of ZEA.

CONCLUSION

In conclusion, ZEA at a concentration of 0.5 mg/kg was sufficient to significantly thicken the myometrium and endometrium, and at a concentration of 1.0 mg/kg induced a high level of GHR expression to promote growth and development of the uteri. This revealed an alternative molecular mechanism whereby ZEA induces growth and development of the uteri and provides a theoretical basis for the revision of Chinese feed hygiene standards.

Construction of a high-density linkage map and fine mapping of QTLs for growth and gonad related traits in blunt snout bream

High-density genetic maps based on SNPs are essential for fine mapping loci controlling specific traits for fish species. Using restriction-site associated DNA tag sequencing (RAD-Seq) technology, we identified 42,784 SNPs evenly distributed across the Megalobrama amblycephala genome. Based on 2 parents and 187 intra-specific hybridization progenies, a total of 14,648 high-confidence SNPs were assigned to 24 consensus linkage groups (LGs) of maternal and paternal map. The total length of the integrated map was 3,258.38 cM with an average distance of 0.57 cM among 5676 effective loci, thereby representing the first high-density genetic map reported for M. amblycephala. A total of eight positive quantitative trait loci (QTLs) were detected in QTL analysis. Of that, five QTL explained ≥35% of phenotypic variation for growth traits and three QTL explained ≥16% phenotypic variation for gonad related traits. A total of 176 mapped markers had significant hits in the zebrafish genome and almost all of the 24 putative-chromosomes of M. amblycephala were in relatively conserved synteny with chromosomes of zebrafish. Almost all M. amblycephala and zebrafish chromosomes had a 1:1 correspondence except for putative-chromosome 4, which mapped to two chromosomes of zebrafish caused by the difference in chromosome numbers between two species.

Growth hormone reverses excitotoxic damage induced by kainic acid in the green iguana neuroretina

It is known that growth hormone (GH) is expressed in extrapituitary tissues, including the nervous system and ocular tissues, where it is involved in autocrine/paracrine actions related to cell survival and anti-apoptosis in several vertebrates. Little is known, however, in reptiles, so we analyzed the expression and distribution of GH in the eye of green iguana and its potential neuroprotective role in retinas that were damaged by the intraocular administration of kainic acid (KA). It was found, by Western blotting, that GH-immunoreactivity (GH-IR) was expressed as two isoforms (15 and 26kDa, under reducing conditions) in cornea, vitreous, retina, crystalline, iris and sclera, in varying proportions. Also, two bands for the growth hormone receptor (GHR)-IR were observed (70 and 44kDa, respectively) in the same tissues. By immunofluorescence, GH-IR was found in neurons present in several layers of the neuroretina (inner nuclear [INL], outer nuclear [ONL] and ganglion cell [GCL] layers) as determined by its co-existence with NeuN, but not in glial cells. In addition, GH and GHR co-expression was found in the same cells, suggesting paracrine/autocrine interactions. KA administration induced retinal excitotoxic damage, as determined by a significant reduction of the cell density and an increase in the appearance of apoptotic cells in the INL and GCL. In response to KA injury, both endogenous GH and Insulin-like Growth Factor I (IGF-I) expression were increased by 70±1.8% and 33.3±16%, respectively. The addition of exogenous GH significantly prevented the retinal damage produced by the loss of cytoarchitecture and cell density in the GCL (from 4.9±0.79 in the control, to 1.45±0.2 with KA, to 6.35±0.49cell/mm(2) with KA+GH) and in the INL (19.12±1.6, 10.05±1.9, 21.0±0.8cell/mm(2), respectively) generated by the long-term effect of 1mM KA intraocular administration. The co-incubation with a specific anti-GH antibody, however, blocked the protective effect of GH in GCL (1.4±0.23cell/mm(2)) and INL (11.35±1.06), respectively. Furthermore, added GH induced an increase of 90±14% in the retinal IGF-I concentration and the anti-GH antibody also blocked this effect. These results indicate that GH and GHR are expressed in the iguana eye and may be able to exert, either directly of mediated by IGF-I, a protective mechanism in neuroretinas that suffered damage by the administration of kainic acid.

Leptin Genes in Blunt Snout Bream: Cloning, Phylogeny and Expression Correlated to Gonads Development

To investigate the leptin related genes expression patterns and their possible function during the gonadal development in fish, the cDNA and genomic sequences of leptin, leptin receptor (leptinR), and leptin receptor overlapping transcript like-1 (leprotl1) were cloned and their expression levels were quantified in the different gonadal development stages of Megalobrama amblycephala. The results showed that the full length cDNA sequences of leptin, leptinR and leprotl1 were 953, 3432 and 1676 bp, coding 168, 1082, and 131 amino acid polypeptides, and the genomic sequences were 1836, 28,528 and 5480 bp, which respectively had 3, 15 and 4 exons, respectively. The phylogenetic analysis revealed that three genes were relatively conserved in fish species. Quantitative real-time PCR results showed that the three genes were ubiquitously expressed in all examined tissues during the different gonadal development stages. The leptin and leptinR took part in the onset of puberty, especially in female M. amblycephala, by increasing the expression levels in brain during the stage I to III of ovary. The expression levels of leptin and leptinR had significant differences between male and female in hypothalamic-pituitary-gonadal (HPG) axis tissues (p < 0.05). The leptinR had the same variation tendency with leptin, but the opposite changes of expression levels were found in leprotl1, which may resist the expression of leptinR for inhibiting the function of leptin in target organ. These findings revealed details about the possible role of these genes in regulating gonadal maturation in fish species.

Polymorphisms and DNA methylation level in the CpG site of the GHR1 gene associated with mRNA expression, growth traits and hormone level of half-smooth tongue sole (Cynoglossus semilaevis)

The objectives of the present study were to estimate the GHR1 gene mutations and methylation status of CpGs, and whether those mutations and methylation were involved in the regulation of GHR1 gene expression, hormone level and growth traits in half-smooth tongue sole (Cynoglossus semilaevis). Identification of single-nucleotide polymorphisms was performed on 43 male fish. Through polymerase chain reaction-single-strand conformation polymorphism and sequencing, two SNPs were found. SNP1 [c.G1357A (p.Val376Ile)] creating one CpG site located in exon 8 was named L1 locus, and SNP2 (c.G1479A) located in exon 9 was named L2 locus. Individuals were divided into three genotypes, AA, AG and GG according to L1 locus (GG genotype had one more CpG site because of the mutation), and into two genotypes, AA- and GG-based on L2 locus. The results showed that only L1 locus was significantly associated with body weight (P < 0.01), gonad weight (P ≤ 0.05), triiodothyronine (T3) level (P ≤ 0.05) and mRNA expression (P < 0.01). At L1 locus, newly created CpG site in GG genotype was highly methylated (93.3 %), while there was no difference of methylation level in the other two CpG sites among three genotypes. AA genotype and AG genotype having higher T3 level were significantly different (P ≤ 0.05) from GG genotype. There were significant differences among body weights of AA, AG and GG genotypes (P < 0.01). Gonad weights of AA genotype and AG genotype were significantly lower than GG genotype. The GHR1 mRNA expression of GG genotype was significantly lower than AA and AG genotypes (P < 0.01). These implied that mutations and methylation status of GHR1 gene might influence the hormone level, growth traits and gene expression in male half-smooth tongue sole and the L1 locus could be regarded as a potential candidate genetic and epigenetic marker in half-smooth tongue sole selection.

Two myostatin genes exhibit divergent and conserved functions in grass carp (Ctenopharyngodon idellus)

Myostatin (MSTN) is an important negative regulator of myogenesis, which inhibits myoblast proliferation and differentiation. Here, we report the isolation and characterization of two mstn genes in grass carp (Ctenopharyngodon idellus). Grass carp mstn-1 and mstn-2 cDNAs are highly divergent, sharing a relatively low amino acid sequence identity of 66%. In adult fish, both orthologs are expressed in numerous tissues and they are differentially regulated during a fasting/refeeding treatments. During embryogenesis, the mRNA levels of both mstn-1 and -2 were upregulated significantly at the beginning of somitogenesis, and maintained at high levels until hatching. Using in situ hybridization, grass carp mstn-1 mRNA was found to ubiquitously express at 12hpf, with strong signals in the notochord, and in the eyes, brain and tailbud at 24hpf, and in brain and notochord at 36hpf. In comparison, the mstn-2 mRNA can be detected in the eyes, brain and notochord at 24hpf, and in the notochord and hindbrain at 36hpf. Further overexpression of mstn-1 mRNA caused a strongly ventralized phenotype by inhibiting dorsal tissue development, while injection of mstn-2 mRNA resulted in obvious embryonic abnormalities in grass carp. These results provide some new insights into the functional conservation and divergence of mstn genes in teleost species.