Gold glitters everywhere: nucleus microRNAs and their functions

As a highly conserved class of endogenous small (∼22 nucleotides) non-coding RNAs, microRNAs (miRNAs) regulate a broad spectrum of biological processes. Increasing evidences suggested that miRNAs generally regulated gene expression at the posttranscriptional stage via inhibiting the translational process or degrading mRNA. Recent studies have also revealed that there is extensive amount of miRNA, as well as miRNA function-related proteins, in the cell nucleus. Although the molecular basis underneath the biogenesis and function of nucleus miRNAs remains largely unknown, the presence of various miRNAs and miRNA function-related proteins in the nucleus strongly argue that miRNAs may execute their role throughout the whole gene expression pathway. Here we review the recent advances in the researches about the nucleus miRNAs, including the biosynthesis pathways, biological functions and potential regulation machinery of nucleus miRNAs.