RESUMEN
MicroRNAs (miRNAs) negatively regulate genes which are involved in various biological processes of metabolism at both transcriptional and post-transcriptional levels. In recent years, the existence and function of miRNAs have been extensively studied in plants and animals with the application of deep sequencing and microarray technology. In this study, small RNAs from leucocytes of Lampetra japonica (L. japonica) were sequenced using the second generation high-throughput sequencing technology. A total of 5 207 787 small RNA sequences were identified, and 4 739 346 of them assembled into 10 989 variants. Based on sequence similarity analysis, the sequences of these variants matched known miRNAs of 306 conserved families, among which 6 conserved miRNA family members expressed at an extremely high level which reflected the conservatism of miRNAs among species. In addition, 70 unannotated sequences were predicted to be new miRNAs, and 34 of them were further verified expressing in antigen-treated L. japonica leucocytes by miRNA microarray assay. Moreover, the minimal folding free energy indexes for 16 of the 34 miRNA precursors exceed 0.85, indicating the existence of species-specific miRNAs in L. japonica which may play important roles in regulating, growth, development and disease response of L. japonica leukocytes.