MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate gene expression by complementary binding to target mRNAs. Virus-encoded miRNAs play important roles in virus life cycle and virus-host interactions. Viruses from the Megalocytivirus genus, family Iridoviridae, infect a wide range of fishes, bringing great challenges to aquaculture. Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the Megalocytivirus genus. In this study, using Illumina sequencing coupled with miRNA precursor prediction and stem-loop real-time PCR, 14 putative ISKNV-encoded miRNAs were preliminarily identified from ISKNV-infected mandarin fish MFF-1 cells. To initially study their functions, inhibitors of the 14 viral miRNAs were synthesized and transfected into MFF-1 cells, which were further infected with ISKNV. The results showed that these viral miRNAs could affect the virus titers in the supernatant of ISKNV-infected cells and the expression of major capsid protein (MCP). Moreover, we observed that inhibition of several ISKNV miRNAs had different effects on MCP expression and on titer of released virus, suggesting complex roles of viral miRNAs in ISKNV infection. The current study may provide a fundamental information for further identification and functional studies on miRNAs encoded by Megalocytivirus.

MicroRNA（miRNA）是小的非编码RNA，通过与靶mRNA的互补结合在转录后调节基因表达。病毒编码的miRNA在病毒生命周期和病毒-宿主相互作用中起重要作用。巨轮虫病毒属虹膜病毒科的病毒感染多种鱼类，给水产养殖带来了巨大挑战。传染性脾肾坏死病毒（ISKNV）是的类型种类Megalocytivirus属。在这项研究中，使用Illumina测序结合miRNA前体预测和茎环实时PCR，从感染ISKNV的man鱼MFF-1细胞中初步鉴定出14种假定的ISKNV编码的miRNA。为了初步研究其功能，合成了14种病毒miRNA的抑制剂并将其转染到MFF-1细胞中，再用ISKNV感染。结果表明，这些病毒miRNA可能影响ISKNV感染细胞上清中的病毒滴度和主要衣壳蛋白（MCP）的表达。此外，我们观察到对几种ISKNV miRNA的抑制对MCP表达和释放病毒的滴度有不同的影响，表明病毒miRNA在ISKNV感染中具有复杂的作用。巨轮病毒。