MicroRNA Alternations in the Testes Related to the Sterility of Triploid Fish

The knowledge of understanding the molecular traits of the sterile triploid fish is sparse. Herein, we analyzed the microRNA (miRNA) alternations in the testes of the sterile triploid fish produced by crossing the tetraploid fish with the diploid fish, compared with those of tetraploids and diploids used as the controls. A total of 136, 134, and 142 conserved miRNAs and 105, 112, and 119 novel miRNAs were identified in the diploid, triploid, and tetraploid fish, respectively. The genes targeted by the differentially expressed miRNAs were identified and were enriched in the GO term cell surface receptor signaling pathway, cellular process, G-protein coupled receptor signaling pathway, and metabolic process. KEGG pathway enrichment was also assessed to evaluate the target genes with differentially expressed miRNAs and these genes were enriched in four pathways (synthesis and degradation of ketone bodies, pentose and glucuronate interconversions, cyanoamino acid metabolic process, and ascorbate and aldarate metabolism). Nine differentially expressed miRNAs were verified by quantitative real-time PCR analysis (qPCR). The upregulated miRNAs in triploids, including miR-101a, miR-199-5p, miR-214, miR-222, and miR-193a, showed the same results with high-throughput sequencing. Among the selected downregulated miRNAs, miR-7b and miR-153b had significantly lower expression levels in triploids. Dnah3 and Tekt1 genes targeted by miR-199-5p showed lower expression in triploids by qPCR. These verified differentially expressed miRNAs may participate in testicular development and sperm activity by targeting functional genes, which were identified with differential expression in the triploid. This evidence provides insights into the epigenetic regulatory mechanisms of sterility in triploid cyprinids.