MicroRNAs (miRNAs), small non-coding RNAs, participate in the transcriptional and post-transcriptional regulation of eukaryotic genes, and are potential biomarkers for diseases. Mature miRNAs can be located in both the nucleus and cytoplasm, where they perform their regulatory function. The discovery of new miRNAs and the identification of their targets and functions are fundamental to understanding the biological processes regulated by them, as well as the role they play in diseases. This present study researched miRNAs function at nuclear level and as circulating molecules.