Abstract
MicroRNAs (miRNAs) are a type of small non-coding RNAs that participate in diverse cellular processes including microbial invasion and immune defense. In a previous study, we identified a large amount of Japanese flounder (Paralichthys olivaceus) miRNAs responsive to megalocytivirus infection. In the present study, we examined the function of one of these miRNAs, pol-miR-194a, in association with the infectivity of Edwardsiella tarda, an intracellular bacterial pathogen to many fish species including flounder. We found that pol-miR-194a was induced in expression to a significant extent in the spleen, liver, and gill of Japanese flounder infected by E. tarda. Transfection of flounder cells with pol-miR-194a mimic significantly enhanced the intracellular replication of E. tarda. pol-miR-194a was able to interact specifically with the 3'UTR of IRF7 in a negative manner, resulting in inhibition of IRF7 expression. Consistently, pol-miR-194a significantly blocked the promoter activity of type Ⅰ interferon. Taken together, these results indicate that pol-miR-194a plays an important role in the regulation of flounder immune response as well as microbial infection, and that pol-miR-194a probably serves as a target for E. tarda to manipulate and escape host immune defense.