Transcriptome Profiling of Gene Expression in Atlantic Salmon (Salmo salar) at Early Stage of Development.

For Atlantic salmon development, the most critical phase is the early development stage from egg to fry through alevin. However, the studies investigating the early development of Atlantic salmon based on RNA-seq are scarce and focus only on one stage of development. Therefore, using the RNA-seq technology, the assessment of different gene expressions of various early development stages (egg, alevin, and fry) was performed on a global scale. Over 22 GB of clean data was generated from 9 libraries with three replicates for each stage with over 90% mapping efficiency. A total of 5534 genes were differentially expressed, among which 19, 606, and 826 genes were specifically expressed in each stage, respectively. The transcriptome analysis showed that the number of differentially expressed genes (DEGs) increased as the Atlantic salmon progressed in development from egg to fry stage. In addition, gene ontology enrichment demonstrated that egg and alevin stages are characterized by upregulation of genes involved in spinal cord development, neuron projection morphogenesis, axonogenesis, and cytoplasmic translation. At the fry stage, upregulated genes were enriched in the muscle development process (muscle cell development, striated muscle cell differentiation, and muscle tissue development), immune system (defense response and canonical NF-kappaB signal transduction), as well as epidermis development. These results suggest that the early development of Atlantic salmon is characterized by a dynamic shift in gene expression and DEGs between different stages, which provided a solid foundation for the investigation of Atlantic salmon development.