Figure 1.

The synthetic pathways of noncoding RNAs. Cytoplasmic lncRNAs are transcribed from its corresponding parent gene. CircRNAs are reverse-spliced from precursor mRNAs and form three types, namely, exon circRNAs, intron circRNAs, and exon–intron circRNAs. MiRNAs are transcribed by RNA polymerase II to generate pre-miRNA and then cut into pre-miRNA through the DGCR8–Drosha enzyme complex. Exprotin 5 transports pre-miRNA out of the nucleus. Dicer and other enzymes cut pre-miRNA into unstable double-stranded RNA outside of the nucleus. One single-stranded miRNA is degraded, and the other is integrated into RISC (ribonuclein complex containing members of AGO histones).