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Lipid metabolism is a key biological process involving the synthesis and degradation of lipids in organisms. In the liver, triglyceride (TG) synthesis mediates the storage of fats for energy, which is catalysed by diacylglycerol acyltransferase‐2 (DGAT2). Herein, we compared TG‐related indexes in serum from Nile tilapia (Oreochromis niloticus), blue tilapia (O. aureus) and hybrid offspring (Nile tilapia ♀ × blue tilapia ♂). The results showed that serum TG levels were significantly higher in the hybrid tilapia (6.95 ± 1.48 mmol/L) than that in blue tilapia (4.39 ± 1.02 mmol/L). Tissue distribution analysis suggested that DGAT2 was mainly expressed in the liver and muscle. Furthermore, hybrid tilapia exhibited higher mRNA expression of DGAT2 in the liver than the parents. Additionally, the allelic gene expression assay indicated that the alleles of DGAT2 gene from the two parental species were expressed at equal levels. To elucidate the epigenetic regulation of DGAT2 gene expression, the DNA methylation levels at the putative promoter region of DGAT2 in hybrid tilapia and its parents were compared. We found lower DNA methylation levels at the putative promoter region of DGAT2 in hybrid tilapia as compared to the paternal species in liver. DNA methylation levels in the putative promoter region were negatively correlated with DGTA2 expression in tilapia. Three CpG sites were significantly correlated with DGAT2 expression in tilapia. Overall, the present evidence suggests that DNA methylation is associated with the elevated expression of DGAT2 in hybrid tilapia. These results provide new evidence for epigenetic regulation of genes in hybrids, which may aid to understanding of heterosis for fish hybridization breeding and superiorities of nutrient utilization in hybrids. [ABSTRACT FROM AUTHOR]

This study was explored the supplementary of vitamin E on reproduction of tilapia. Five vitamin E supplements (0, 40, 80, 120 and 160 mg/kg) were tested for 90 days. Results: The SGR, GSI and ovarian maturity of female were the highest at Group 120 mg/kg, and the FCR was the lowest. The SGR, GSI and testis maturity of male were the highest at Group 160 mg/kg, and the FCR was the lowest. The levels of FSH and P were significantly increased at Group 120 mg/kg in female, and the levels of E2 reached the maximum. The levels of T and GnRH were increased at Group 160 mg/kg in male. The expression of FSHR in female liver was the highest at Group 160 mg/kg, and the expression of FSHR in ovary was the highest at Group 40 mg/kg. The expression of FSHR and pgr in female kidney was significantly increased at Group 40 and 80 mg/kg. The expression of FSHR and pgr in testis was the highest at Group 160 mg/kg. In conclusion, vitamin E can regulate the secretion levels of reproductive hormones and the expression levels of FSHR and pgr during different developmental stages in tilapia, and thus promote tilapia reproduction and growth. Among them, the reproductive and growth performance of female tilapia were the greatest at Group 120 mg/kg, and for male tilapia, these parameters were the greatest at Group160 mg/kg. [ABSTRACT FROM AUTHOR]

DGAT2 (acyl CoA:diacylglycerol acyltransferase 2) is a key and rate-limiting enzyme that catalyzes the final step of triglyceride (TG) synthesis. In this study, hybrid tilapia were generated from Nile tilapia (♀) and blue tilapia (♂) crossing. The TG content levels in the liver of these tilapia were measured. The results showed that the TG content was higher in the hybrid tilapia. In addition, protein and mRNA expression levels in the tilapia livers were determined. Higher hepatic mRNA and protein expression of DGAT2 in the hybrid fish was found. A luciferase reporter assay with HEK293T cells revealed that miRNA-19a-5p targeted the 3′UTR of DGAT2, suggesting a direct regulatory mechanism. Using qRT-PCR, we found that DGAT2 mRNA levels had a negative correlation with miRNA-19a-5p expression in Nile tilapia and hybrid. Taken together, these findings provide evidence that miRNA-19a-5p is involved in TG synthesis in the regulation of lipid metabolism in tilapia. • Hybrid had higher expression of DGAT2 to blue tilapia; • miR-19a-5p could bind to the 3′ UTR of DGAT2 in tilapia; • Low expression of miR-19a-5p was correlated with the high expression of DGAT2. [ABSTRACT FROM AUTHOR]

Nile tilapia (Oreochromis niloticus) is a worldwide farmed fish and has been widely used for the study on comparative immunology in teleosts. It is well known that cadmium (Cd) can cause a variety of adverse effects in fish. However, data on the effects of Cd in fish liver and the defensive mechanisms of these effects using transcriptome approach are relatively scarce to date. In this study, by using an RNA sequencing approach, the gene expression profiling was performed in livers of tilapia exposed to 0 (control), 50, 100, and 200 μg/L of Cd for 2 months. The results showed that exposure to 50 μg/L Cd altered the expressions of 911 genes, while exposure to 100 and 200 μg/L Cd resulted in 4318 and 3737 differentially expressed genes compared to the control. Weighted correlation network analysis (WGCNA) and gene ontology (GO) analysis identified a 14-gene network linked to the immune system development. Further, in a fuzzy analysis, the GO term immune system development was enriched in cluster 3, and gene expression decreased with increasing Cd levels in a concentration-dependent manner. The qPCR and RNA-seq results identified 4 genes, i.e., dnmt3bb.1 , sf3b1 , SMARCAL1 , and zap70 , as convenient potential biological indicators for detecting waterborne Cd. The present results help systematically understand the effects of Cd on the hepatic transcriptome in tilapia. • The accumulation level of Cd in the liver is positively correlated with the concentration of Cd in water. • Hepatic transcriptome affected by Cd were determined. • Four genes in liver of tilapia could be potential indicators for detecting waterborne Cd. [ABSTRACT FROM AUTHOR]

Hybridization is a common breeding technique that can improve germplasm through heterosis in aquaculture. However, the regulation of key gene expression, including the details of transcriptional level changes at the beginning of hybridization events, remains largely undefined, especially in teleosts. In this study, by interspecies crossing between two pure lines of Nile tilapia and blue tilapia, we obtained a hybrid tilapia population as a model to elucidate heterosis, and we traced the molecular outcomes of growth hormone (GH) expression and allele-specific expression (ASE) in hybrids. The hybrids display growth vigor compared to their parents in the 120-day growth trial. GH mRNA expression was uniquely expressed in the pituitary. Higher GH expression was found in the hybrid than the midparent value, in both males and females, showing a nonadditive pattern. We identified four single-nucleotide polymorphism sites between Nile tilapia and blue tilapia. Subsequently, by pyrosequencing, we found asymmetric allelic expression in hybrids with higher maternal allelic transcript ratios in both males and females. Fasting significantly increased GH expression in hybrids, but asymmetric allelic expression was not affected by feeding or fasting conditions. Finally, we identified cis and trans effects via overall expression and ASE values in the hybrid, which showed that the cis and trans effects promoted the expression of maternal subgenome in the hybrid, contributing to the expression superiority of GH in hybrid tilapia. Taken together, the results of our study first illustrated the concept of GH expression superiority and its formation mechanism in hybrid fish with growth vigor. [ABSTRACT FROM AUTHOR]

This study investigated the molecular mechanisms involved in ovarian transcriptomic responses in Nile tilapia under different photoperiod regimes. Histological analysis indicated that ovarian development was significantly affected by photoperiod. The photoperiods tested were as follows: LD (12 h light:12 h dark), LL (24 h light:0 h dark), and DD (0 h light:24 h dark). The longer photoperiod (LL) was shown to induce ovary development earlier than LD and DD. Next, ovary transcriptome levels were sequenced and analyzed. These data indicated that 988, 992, and 1,036 differentially expressed genes (DEGs) were detected by comparing LD–LL, LD–DD, and LL–DD. A number of genes that may be involved in photoperiod-specific regulation of ovarian development were observed. These findings may be useful for investigating the molecular mechanisms underlying light-induced ovarian development in Nile tilapia. [ABSTRACT FROM AUTHOR]

High-throughput sequencing of transcriptome promises a new approach for detecting evolutionary divergence among species. Up to now, the information about evolution of immune genes in cultured fish, especially in tilapias which would aid to understand the molecular basis of immune phenotypic differentiation is still lack. Thus, in the present study, we used high-throughput sequencing to obtain large amount of gene sequences in blue tilapia and characterized the diversity of orthologs among Nile tilapia, blue tilapia and zebrafish. A total of 52,424,506 raw reads, representing 31,404 unigenes were obtained from blue tilapia cDNA library of mixed tissues, including brain, pituitary, gill, heart, liver, spleen, kidney, intestine, muscle, testis and ovary. Based on Ks value, we calculated that the divergence time between Nile tilapia and blue tilapia is 2.93 million years ago. And the tilapias are both apart from zebrafish in 197 million years ago. Furthermore, the positive selected genes were identified by calculating of Ka/Ks ratio. Several immune-related genes were identified as positively selected genes, such as Notch2 and nfatc3b. Considering that these genes play crucial role in immune regulating function, the immune system genes met a great variation under environment selection in tilapias which suggests fast evolution in immune system of cultured tilapias. [ABSTRACT FROM AUTHOR]

Abstract: Growth hormone (GH) and its receptors are critical regulators of somatic growth and metabolism. It has been shown in mammals that the methylation of cytosines within the GH promoter plays a key role in regulating transcripts expression. In the present study, the GH, GHR1 and GHR2 proximal promoters were identified and the methylation levels of these genes in corresponding tissues were assayed. The results suggested that significant arising of GH putative promoter methylation levels in pituitary was observed in females compared with males. However, no such sex-specific changes were found in GHR1 and GHR2 promoters. The GH mRNA expression also was influenced by GH promoter methylation levels in pituitary, which resulted in the higher growth rate of Nile tilapia males. Meanwhile, the methylation levels of GH putative promoter were negatively correlated with growth rate as well as mRNA expression of GH. Furthermore, the methylation of specific E-Box CpG site is also negatively related to the mRNA expression of GH in pituitary. Taken together, our data provide an epigenetic mechanism of explicating the sex duality in phenotypic plasticity of growth rate in male and female of Nile tilapia. [Copyright &y& Elsevier]

MicroRNAs (miRNAs) are endogenous non-coding small RNAs which play important roles in the regulation of gene expression by cleaving or inhibiting the translation of target gene transcripts. Thereinto, some specific miRNAs show regulatory activities in gonad development via translational control. In order to further understand the role of miRNA-mediated posttranscriptional regulation in Nile tilapia (Oreochromis niloticus) ovary and testis, two small RNA libraries of Nile tilapia were sequenced by Solexa small RNA deep sequencing methods. A total of 9,731,431 and 8,880,497 raw reads, representing 5,407,800 and 4,396,281 unique sequences were obtained from the sexually mature ovaries and testes, respectively. After comparing the small RNA sequences with the Rfam database, 1,432,210 reads in ovaries and 984,146 reads in testes were matched to the genome sequence of Nile tilapia. Bioinformatic analysis identified 764 mature miRNA, 209 miRNA-5p and 202 miRNA-3p were found in the two libraries, of which 525 known miRNAs are both expressed in the ovary and testis of Nile tilapia. Comparison of expression profiles of the testis, miR-727, miR-129 and miR-29 families were highly expressed in tilapia ovary. Additionally, miR-132, miR-212, miR-33a and miR-135b families, showed significant higher expression in testis compared with that in ovary. Furthermore, the expression patterns of the miRNAs were analyzed in different developmental stages of gonad. The result showed different expression patterns were observed during development of testis and ovary. In addition, the identification and characterization of differentially expressed miRNAs in the ovaries and testis of Nile tilapia provides important information on the role of miRNA in the regulation of the ovarian and testicular development and function. This data will be helpful to facilitate studies on the regulation of miRNAs during teleosts reproduction. [ABSTRACT FROM AUTHOR]

In this study, the effect of Lycium barbarum polysaccharides (LBP) on immunological parameters, apoptosis, and growth performance of Nile tilapia (Oreochromis niloticus) was investigated. Dietary supplementation with LBP significantly increased complement 3 (C3) activity and promoted interleukin IL-1β gene expression in spleen tissue, significantly reduced apoptosis in spleen tissue, increased the specific growth rate (SGR), relative length gain (LG), and relative weight gain (WG) of Nile tilapia. However, dietary supplementation with LBP did not have a significant effect on serum alkaline phosphatase (AKP), malondialdehyde (MDA), and superoxide dismutase (SOD), blood constituents, apoptosis, or gene expression of IL-1β in liver tissue. Overall, the results showed that dietary supplementation with LBP increased the nonspecific immunity of Nile tilapia and reduced the apoptosis rate to promote growth and development. Thus, LBP has potential for use as a new immunostimulant in aquaculture. • Dietary supplementation with LBP to feed tilapia. • Supplementation of LBP can increase non-specific immunity of Nile tilapia and reduce apoptosis rate. • Supplementation of LBP can improve the growth and development of Nile tilapia. [ABSTRACT FROM AUTHOR]

Lycium barbarum polysaccharide (LBP) is one of the main active ingredients in the fruit of L. barbarum L. It has been used as herbal medicine for thousands of years in China. In this study, Nile tilapia (Oreochromis niloticus) was taken as the research object. After feeding tilapia with 5 different doses of LBP (0 mg/kg, 500 mg/kg, 1000 mg/kg, 1500 mg/kg, 2000 mg/kg) for 55 d, it was found that LBP could promote the growth of tilapia, and this effect was the strongest at Group 1500 mg/kg. Apoptosis analysis in the liver and spleen showed that dietary supplementation with 1000 mg/kg LBP had the best protective effect on the spleen and liver in tilapia. Combined transcriptomics and metabolomics of the spleen in tilapia at Group 0 mg/kg and 1000 mg/kg showed that the differentially expressed genes (DEGs) such as NT5C2L1, pmm1, FasL and the differentially metabolites such as xanthine, dGMP, guanine and glutamate were mainly concentrated in signaling pathways such as Purine metabolism and FoxO signaling pathway. In conclusion, LBP regulates the metabolic waste levels of tilapia mainly through Purine metabolism and the FoxO signaling pathway, thereby inhibiting cell apoptosis, improving the utilization of nutrients, and promoting the growth of tilapia. This study not only provides a theoretical basis for the application of LBP in aquatic animals but also provides useful information for the healthy development of the aquaculture. • LBP can improve the growth parameters of tilapia. • LBP has a protective effect on the spleen and liver of tilapia. • Combined transcriptomics and metabolomics showed that LBP regulates the apoptosis of tilapia spleen. [ABSTRACT FROM AUTHOR]

Estradiol (E2) is a sex steroid hormone that modulates multiple physiological processes in teleosts. The aim of this study was to explore the role of E2 in the hepatic lipid metabolism of hybrid tilapia. The hybrid tilapias were injected with different concentrations of E2 (0 mg/kg, 10 mg/kg, 25 mg/kg and 50 mg/kg) and ICI 182,780 (ICI) (35 mg/kg) (an E2 receptor antagonist). Subsequently, the liver lipid depositions were analyzed by tissue sections with oil red O staining. Serum total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and nonesterified fatty acids (NEFAs) were assayed from the fish in different groups. Genes related to very low-density lipoprotein (VLDL) assembly, lipoprotein lipase and lipoprotein receptors, fatty acid uptake and triacylglycerol metabolism were determined by quantitative RT-PCR. The results showed that 50 mg/kg E2 injections enlarged the lipid droplets significantly. Simultaneously, the E2 injections tended to upregulate TC, TG, LDL, and HDL in the serum. The 50 mg/kg E2 group showed a significantly higher expression of the VLDL assembly genes but depressed levels of LDLR and LRP1. In addition, FABP3, FABP11a and DGAT2 were significantly elevated, while CD36 and ACO1 decreased in the 50 mg/kg E2 injection. The ICI injection inhibited the expression of MTP, LPL, LRP1, CD36, FABP11a, ACO1 and FAS in tilapia livers. These results demonstrated that by stimulating the expression of genes associated with the VLDL assembly, inhibiting lipoprotein lipase and lipoprotein receptor-related genes and promoting the rate-limiting enzyme in the synthesis of the TG, E2 induced deposition of lipids in the livers of hybrid tilapia. Overall, the results suggest a role for E2 in fish lipid metabolisms that provide new clues to illustrate the sex steroid function in energy metabolism in livers. Unlabelled Image • E2 promoted lipid depositions in liver of hybrid tilapia. • Triglyceride levels in serum were increased by E2 injection. • Lipid metabolism related genes in liver were regulated by E2. [ABSTRACT FROM AUTHOR]

Streptococcus agalactiae is a common pathogen in aquatic animals, especially tilapia, that hinders aquaculture development and leads to serious economic losses. Previously, a S. agalactiae strain named HN016 was identified from infected tilapia, and the attenuated strain YM001 was subsequently obtained by continuous passaging in Tryptic Soy Broth (TSB) medium. YM001 has been demonstrated as a safe vaccine for S. agalactiae infection in tilapia. To understand the molecular bases of the virulence of these two strains, we performed proteomic and transcriptomic analysis to reveal the protein and gene expression changes in the liver and intestine during the infection process. HN016 significantly decreased the contents of white blood cells (WBCs), neutrophils (NEUs), red blood cells (RBCs) and hematocrit (HCT) and increased the levels of total protein (TP), albumin (ALB) and globulin (GLO), while no such significant differences were observed when comparing the control with YM001. During the infection process, pathogenic peptidoglycan hydrolase, CSPA and membrane proteins were significantly differentially expressed between YM001 and HN016. Furthermore, both proteome and transcriptome data showed that the complement and coagulation cascades pathway and the antigen processing and presentation pathway were stimulated in the liver and intestine, respectively, by YM001 infection compared to HN016 infection. The interaction network analysis of key virulence genes from pathogens suggested that CSPA, as a key node, affects the expression of DOLPP1, MIPEP, PA2G4, OCIAD1, G3BP1 and CLIC5 with a positive correlation. The present evidence suggests that during the infection process, CSPA was the key genes contributing to low virulence in YM001. • Differentially expressed genes after infection with low and high virulence strains were identified. • Antigen processing and presentation pathway from intestine was stimulated by YM001. • CSPA contributed to the pathogenicity of Streptococcus agalactiae in tilapia. [ABSTRACT FROM AUTHOR]

Selenium is an essential element but toxic at high levels in animals. The effects of Se on growth performance and the immune system in Nile tilapia remain inconclusive. In this study, Nile tilapia Oreochromis niloticus was fed on selenium yeast (Se(Y))- and selenite (Se(IV))-enriched feed at 0, 3, 6, and 12 μg/g (dry wt) for 45 and 90 d. The growth, bioaccumulation, biochemical markers related to antioxidant, immunological, nervous and digestive systems were evaluated in various fish tissues (liver, intestine, kidney, muscle, brain, spleen, gills). The results showed that the accumulation of Se(Y) was 1.3–2 folds of Se(IV) in most tissues. The growth of tilapia was enhanced by both Se(Y) and Se(IV) at 3 μg/g after 90 d, with Se(Y) better than Se(IV) in tilapia feed. After 45 d, the levels of lipid peroxidation, the activity of the antioxidant enzymes, and the transcriptional levels of the immune related genes (IL-1β , IFN-γ and TNF-α) and stress proteins (HSP70 and MT) were enhanced in all treatments, except that of MT in the 12 μg/g Se(Y) group. In addition, both Se species inhibited the activity of acetylcholinesterase (AChE) in the brain and one digestive enzyme α-glucosidase (α-Glu) in the intestine at 12 μg/g. However, after 90 d, the effects on most biochemical markers were less pronounced, implying a possible acclimation after prolonged duration. The results demonstrate Se is beneficial to O. niloticus at low levels and toxic at elevated levels. The immunostimulation by Se might be greatly weakened after long term feeding Se-enriched feed. This study helps to better understand the effects of Se on the antioxidant and immune systems and to establish the optimal Se levels in the feed and duration for O. niloticus. • Se increases the transcripts of IL-1β , IFN-γ and TNF-α in O. niloticus after 45 d feeding. • Se enhances the mRNA levels of the stress proteins HSP70 and MT. • Se(Y) and Se(IV) enhance the growth of tilapia at low level but inhibit it at high level after 90 d of feeding. • High level of Se adversely affects the antioxidant, nervous and digestive systems of O. niloticus. • The immunostimulation of Se might be weakened after prolonged feeding. [ABSTRACT FROM AUTHOR]

Abstract Hybrid Nile tilapia (Oreochromis niloticus , ♀) × blue tilapia (O. aureus , ♂) is a widely cultured tilapia variety due to its growth vigor compared to the parent species. As a peptide hormone, insulin-like growth factor 1 (IGF-1) plays a critical role in regulating somatic growth. The present study focuses on the expression characteristics of IGF-1 in hybrid tilapia. The cloned complete open reading frame of IGF-1 in hybrid tilapia is 549 bp in length, encoding a protein of 182 amino acids. The deduced protein is highly similar to that of Nile tilapia and blue tilapia. IGF-1 was found to be primarily expressed in the liver and muscle in the hybrid; lower expression levels were found in other tissues such as the intestine, spleen, and head-kidney. Increased mRNA expression was observed in the liver and muscle of the hybrid compared to Nile tilapia and blue tilapia, indicating a nonadditive expression pattern in the hybrid. An IGF-1 SNP site (397 site: C in Nile tilapia, G in blue tilapia) for differentiating the Nile tilapia or blue tilapia subgenome in hybrids was identified. Pyrosequencing analysis of the liver transcriptome indicated that most of the hybrids (9 of 10 individuals) predominantly expressed the G allele, demonstrating bias of the blue tilapia subgenome. The present study provides novel data indicating, for the first time, overall gene expression of IGF-1 and allele-specific expression in hybrid tilapia. Highlights • IGF-1 mRNA was mainly expressed in liver and widely distributed in all tissues in hybrid tilapia. • Nonadditive expression pattern of IGF-1 was found in hybrid. • IGF-1 in hybrid predominantly expressed blue tilapia allele in liver. [ABSTRACT FROM AUTHOR]

Highlights: [•] LHRH-A and hCG significantly down-regulated Piwil-1 and Piwil-2 in mRNA expression in testis of tilapia. [•] Piwi expressed in spermatocytes rather than mature sperms. [•] HPG suppresses Piwis in tilapia testis. [ABSTRACT FROM AUTHOR]