Since the American scientist Victor Ambros found the first miRNA (short for microRNA) lin-4 in C.elegans in 1993, the research for miRNA has been elapsed more than twenty years. miRNAs are a group of small non-coding RNAs of approximately 22 nucleotides in length which are endogenous and single-stranded. Existed evidence showed that miRNAs are involved in the proliferation, migration and invasion of many tumor cells, hence it is of great theoretical and applicable significance to understand the molecular mechanism of miRNA for the clinical diagnosis purpose. Traditionally, miRNAs are thought to inhibit mRNA translation
or degradation and then play a negative regulatory role in gene expression by binding the targeted 3’UTR in the cytoplasm. However, it is difficult to explain many miRNAs located in the nucleus which may play a positive role in regulating gene expression. Does miRNA localization affect the function of miRNAs? What are the differences between miRNA located in the nucleus and cytoplasm respectively?