Liver comparative transcriptome analysis reveals the mechanism of the Hainan medaka, Oryzias curvinotus , to adapt to salinity

To explore the adaptation mechanism of Hainan medaka, Oryzias curvinotus, to salinity, this study performed a histological and RNA-Seq comparative analysis of female medaka liver with different salinities (0, 15 and 30 practical salinity unit [psu]). In the 30 psu group, the volume of hepatocytes was increased and cytoplasmic fat accumulated. A total of 83,758 unigenes were assembled by RNA-Seq, of which 31,147 were annotated. In total, 922 differentially expressed genes (DEGs) were obtained, and the detection results of 24 DEGs by quantitative polymerase chain reaction (qPCR) were consistent with the RNA-Seq data. Gene ontology (GO) enrichment showed that DEGs were mainly involved in biological processes, such as substance synthesis and transport, energy metabolism, signal transduction, and had catalytic activity and binding functions. Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that DEGs were significantly enriched in steroid biosynthesis, glycerophospholipid metabolism, peroxisome proliferator-activated receptor signaling pathway, and insulin signaling pathway that regulate lipid metabolism. The results of this study highlight the response of the liver transcriptome to long-term environmental salinity changes and provide a basis for the application of the medaka genetic resources.