Transcriptome analysis of the Larimichthys polyactis under heat and cold stress.

The small yellow croaker (Larimichthys polyactis) is an economically important marine fish that is widely distributed in the East Sea, Yellow Sea and Bohai of China. However, the wild populations of L. polyactis are severely depleted, and there is currently a developing large-scale artificial propagation of this fish for aquaculture. However, the current variety of L. polyactis that is cultivated is not capable to coping with large fluctuations in temperature. Therefore, it is important to understand the molecular mechanisms that are activated in response to temperature stress in the L. polyactis. Here, we conducted transcriptomic analysis of the liver of L. polyactis under heat and cold stress. A total of 270,844,888, 265,727,006 and 259,666,218 clean reads were generated from high temperature group, low temperature group and control group, respectively, and comparing expression of genes in these transcriptomes, 10,878 unigenes that were differential expressed were identified. Seventeen of the differentially expressed unigenes were validated by qRT-PCR. Pathway enrichment analysis identified that the ER pathway, immune signaling pathway and metabolic response pathway were affected by temperature stress. The results of this study provide a comprehensive overview of temperature stress-induced transcriptional patterns in liver tissues of the L. polyactis. In addition, these results can guide future molecular studies of heat and cold stress response in this species for improving the stock used for aquaculture.

iTRAQ-based quantitative phosphoproteomics provides insights into the metabolic and physiological responses of a carnivorous marine fish (Nibea albiflora) fed a linseed oil-rich diet.

The limited production of fish oil (FO) cannot meet the increasing demand of the aqua-feed industry. Accordingly, the replacement of FO with sustainable alternatives such as vegetable oils has become imperative. Linseed oil (LO), which has an abundance of α-linolenic acid (ALA), is a promising FO alternative. Nevertheless, high dietary LO inclusion generally causes abnormal hepatic lipid accumulation and growth retardation across carnivorous marine fish species. Previous studies have attempted to elucidate the mechanisms with regard to gene and protein levels; however, little is known about posttranslational modifications. In the present study, iTRAQ phosphoproteomics was conducted to investigate the metabolic and physiological responses of the yellow drum (Nibea albiflora) fed an LO-rich or FO-rich diet. Identification and analyses of differentially abundant phosphorylated proteins in hepatic tissue were conducted with parallel reaction monitoring (PRM) verification in reference to the genome sequences of the yellow drum. Among the specific peptides that passed the threshold, 203 hyperphosphorylated and 182 hypophosphorylated peptides were identified. Several functional categories and pathways were associated with these proteins that were mostly related to lipid, amino acid, and carbohydrate metabolism. In particular, the AMP-activated protein kinase (AMPK) pathway, mechanistic target of rapamycin (mTOR) pathway, and citrate (TCA) cycle are discussed. STATEMENT OF SIGNIFICANCE: Dietary LO caused abnormal hepatic lipid accumulation and retarded growth performance. The abnormal hepatic lipid accumulation in the fish fed the LO-rich diet might have arisen from AMPK signaling pathway-mediated de novo synthesis of fatty acids and the synthesis of phospholipids. An mTOR signaling pathway-mediated reduction in ribosome protein synthesis could have been a factor in the growth retardation. Changes in UPS and autophagy proteins phosphorylation and aminotransferase activity levels were related to the flux of amino acids into the TCA cycle for ATP production. The results of PRM were highly correlated with the phosphoproteomics results. These findings will contribute to a better understanding of the mechanisms of abnormal hepatic lipid accumulation and retarded growth performance in carnivorous marine fish fed linseed oil-rich diets.