Abstract:The reasonable selection of salinity acclimation is one of the most important problems in Oncorhynchus mykiss culture. Calcium metabolism in fish varies with changing environmental salinity, and is a crucial component of salt metabolism. The scale compartment constitutes a significant, readily accessible calcium source in fish, as it can contain up to 20% of the body´s total calcium. In terms of complexity, scales resemble bone better than cultured osteoblast or osteoclast cell lines. Therefore, scales are ideal models for calcium metabolism and bone research. To provide more reliable data to decipher the bone metabolism at the molecular level, an analysis of the transcriptomic response to salinity acclimation was performed on rainbow trout scales. Fish were subjected to seawater (salinity 28) acclimation or freshwater maintenance for seven days. RNA sequencing (RNA-Seq) was performed using the Illumina HiSeq 4000 sequencing platform. By setting the screening conditions for the significant differentially expressed genes (DEGs) as log2|fold change|≥1 and P<0.05, 1714 DEGs were identified, whereof 484 and 1230 were significantly upregulated and downregulated, respectively. Gene Ontology function annotation analysis showed that the DEGs were primarily annotated in biological functions such as cell membrane, cytoplasm, nucleus, transportation, signal transduction, metal ion binding, and ATP binding. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the DEGs were significantly enriched in pathways such as oxidative phosphorylation, drug metabolism-cytochrome P450, proteasome, p53 signaling pathway, and myocardial contraction. Furthermore, quantitative real-time PCR (RT-qPCR) was used to examine the expression of eight randomly-selected DEGs, and the results of the RT-qPCR and RNA-Seq were consistent, indicating the reliability of the RNA-Seq data. Unigene in rainbow trout scales are predominantly enriched in bone metabolism-related pathways, such as the MAPK, Wnt, and calcium signaling pathways, indicating that scales can be used as a model for bone metabolism research. The results of this study showed that the salinity acclimation of O. mykiss was carried out at a rate of salinity 4 per day; bone metabolism-related genes, such as Mmp-2, Mmp-9, Acp5b, Alpl, Osteocalcin, OPG and Col12a1; and bone metabolism-related signaling pathways, such as NF-kB, MAPK-(JNK, p38, ERK1/2, STAT3), Wnt/β-catenin, BMP/Smads, and OPG-RANK-RANKL, did not have a significant influence, indicating that the acclimation model adopted in this study was reasonable. The results could help clarify the regulatory mechanism of O. mykiss bone metabolism in response to altered salinity, and lay a theoretical foundation for aquaculture industry development.
