Transcriptome reveals insights into hepatic nutritional metabolism and gill immune responses adapted to cold stress in genetically improved farmed tilapia (GIFT: Oreochromis niloticus)

To reveal the hepatic nutritional metabolism and gill immune responses adapted to cold stress in genetically improved farmed tilapia, four libraries were constructed and sequenced using Illumina sequencing technology. The results showed that sequencing generated a total of 556,770,992 raw reads, and approximately 40.9-45.6 M clean reads were obtained from each library. In the liver, 3757 differentially expressed genes (DEGs) were identified under cold stress, among which 1764 genes were upregulated and 1993 genes were downregulated. In the gill, a total of 3933 differentially expressed genes (DEGs) were identified under cold stress, among which 1847 genes were upregulated and 2086 genes were downregulated. Twenty-two DEGs were randomly selected for quantitative RT-PCR (qRT-PCR) analysis, and the results confirmed the reliability of the transcriptome analysis. Furthermore, the DEGs were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and the results showed that most of the DEGs were involved in protein, lipid and carbohydrate metabolism in the liver and immune and apoptotic pathways in the gill. Moreover, plasma total protein (TP) and triglyceride (TG) contents were significantly lower, and plasma glucose (GLU), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly higher at lower tem-peratures compared with the control. In summary, these results indicated that cold stress activates hepatic gluconeogenesis and inhibits lipolysis to provide energy to the body, while reducing the efficiency of protein synthesis. Furthermore, the immune and apoptotic pathways were activated in the gill to enhance anti-apoptotic capacity when exposed to cold stress.