Identification and characterization of microRNAs in the liver of rainbow trout in response to heat stress by high-throughput sequencing.

MicroRNAs (miRNAs) play key roles in the stress response in animals. The rainbow trout is a widely cultivated cold-water fish species that usually encounters heat stress, which affects its growth and may cause diseases. However, there is limited information on the miRNAs involved in heat stress in this species. To identify the heat-responsive miRNAs at the genome level in rainbow trout, we conducted high-throughput sequencing of 6 small RNA libraries from the liver tissues of rainbow trout specimens under control and heat-treated conditions. A total of 363 conserved miRNAs and 638 novel miRNAs were identified, among which 39 (21 conserved and 18 novel) miRNAs were differentially expressed in response to heat stress. Eight important miRNAs were further validated using quantitative real-time PCR. GO enrichment and KEGG pathway analyses of the potential target genes of the DE miRNAs, revealed DNA replication and protein folding and unfolding were affected by heat stress. Several key pathways involved in the heat stress response were characterized, such as protein processing in the endoplasmic reticulum, NOD-like receptor signaling pathway, and progesterone-mediated oocyte maturation. In addition, 20 important functional interaction pairs among the 65 negatively correlated miRNA-mRNA pairs were identified using integrated miRNA-mRNA analysis and miRNA prediction algorithms, which including potential important miRNAs and target genes such as miR-301a, miR-301d, let-7c, novel_1181 and HSP90BA, HSP90BB, HSP40, PDIA3. This study showed that the identified miRNAs probably play important roles in the heat stress response and lay a foundation for further studies on the thermal adaptation mechanisms in rainbow trout.