Advances in microRNA promoting gene expression.

MicroRNAs (miRNAs) are a class of endogenous, single-stranded, noncoding RNAs ranging from 20~24 nucleotides in length. Traditionally, miRNAs are considered to inhibit mRNA translation or promote mRNA degradation, thereby exerting a negative regulatory effect on gene expression by binding to the 3' untranslated region (UTR) in the cytoplasm. However, this framework cannot fully explain the observed positive roles of certain miRNAs in gene regulation. Recent studies have identified mechanisms such as enhancer- and promoter-mediated transcriptional activation, as well as UTR-mediated translational activation, as key processes underlying the positive regulation of gene expression by miRNAs. Additionally, the subcellular distribution of miRNAs and specific physiological conditions can influence their functions. In this review, we summarize the biological characteristics and functions of miRNAs, with the goal of providing insights for future research in this field.