Identification of microRNAs in Silver Carp (Hypophthalmichthys molitrix) Response to Hypoxia Stress

SIMPLE SUMMARY: Hypoxia stress is one of the main problems in silver carp (Hypophthalmichthys molitrix) culture. Severe hypoxia stress can lead to damage and even death of silver carp. Therefore, it is very important to explore how silver carp adapt to and respond to hypoxia stress. MicroRNAs play an important role in a series of important life activities in organisms. In this study, the differentiallyexpressed miRNAs were screened from a mixed pool of liver, brain, heart and gill of silver carp under different levels of hypoxia stress by high-throughput sequencing. Our findings provided new insights to further study the miRNA regulatory mechanism and molecular characteristics of anoxic response in silver carp. ABSTRACT: Hypoxia is one of the serious stresses in fish culture, which can lead to physical and morphological changes, and cause injury and even death to fish. Silver carp (Hypophthalmichthys molitrix) is an important economic fish and widely distributed in China. MicroRNA is a kind of endogenous non-coding single-stranded small RNA, which is involved in cell development, and immune response and gene expression regulation. In this study, silver carp were kept in the closed containers for hypoxia treatment by spontaneous oxygen consumption. The samples of heart, brain, liver and gill were collected, and the total RNAs extracted separately from the four tissues were mixed in equal amounts according to the concentration. Afterwards, the RNA pool was constructed for high-throughput sequencing, and based on the small RNA sequencing, the differentially expressed microRNAs were identified. Furthermore, their target gene prediction and enrichment analyses were carried out. The results showed that a total of 229 known miRNAs and 391 putative novel miRNAs were identified, which provided valuable resources for further study on the regulatory mechanism of miRNAs in silver carp under hypoxia stress. The authors verified 16 differentially expressed miRNAs by qRT-PCR, and the results were consistent with small RNA sequencing (sRNA-seq). The predicted target genes number of differentially expressed miRNAs was 25,146. GO and KEGG functional enrichment analysis showed that these target genes were mainly involved in the adaption of hypoxia stress in silver carp through biological regulation, catalytic activity and apoptosis. This study provides references for further study of interaction between miRNAs and target genes, and the basic data for the response mechanism under hypoxia stress in silver carp.