Fig. 1.

Biogenesis and functions of miRNAs and lncRNAs. MiRNAs are transcribed into pri-miRNAs by RNA Pol II, which are then processed into pre-miRNAs by Drosha in the nucleus. After export to the cytoplasm via exportin 5 and further processing by Dicer into mature double-stranded miRNAs in the cytoplasm, the resultant miRNA duplex is then incorporated into AGO proteins, forming the RISC. In this complex, the enzymatically unwound single-strand miRNAs bind to the 3′-UTRs of target mRNAs, resulting in degradation or translational repression. On the other hand, the biogenesis of lncRNAs can occur in both the nucleus and the cytoplasm, with the transcription usually being mediated by Pol II functioning in various manners, such as chromatin modification and transcriptional and post-transcriptional regulation