Fig. 3

The biogenesis and functions of miRNAs, lncRNAs, and circRNAs. a Biogenesis and functions of miRNA. After transcription by RNA polymerase II in the nucleus, primary miRNA (pri-miRNA) is cleaved by DGCR8 and the Drosha complex into precursor-miRNA (pre-miRNA). The pre-miRNA is subsequently transported from the nucleus to the cytoplasm, where it is further processed by Dicer and TRBP to a miRNA duplex. Next, the guide strand (mature miRNA) remains to form RISC protein complexes and ultimately mediates translation repression and mRNA degradation. b Biogenesis and functions of lncRNA. Several primary transcripts undergo inefficient splicing to generate lncRNAs with a 5′ cap and a 3′ poly-(A) tail structure. In the nucleus, lncRNAs are associated with chromatin remodeling and gene transcription regulation. In the cytoplasm, they can exert their function by acting as miRNA sponges, binding with proteins, or encoding regulatory peptides. c Biogenesis and functions of circRNA. circRNA forms a closed-loop structure primarily produced from pre-mRNAs via back-splicing. Based on the original sources, circRNAs can be divided into ciRNAs, EIciRNAs, and exonic ecircRNAs. ciRNAs and EIciRNAs are involved in the transcriptional modulation of their parent genes, while ecircRNAs primarily reside in the cytoplasm and can interact with miRNAs and proteins or be translatable. DGCR8 DiGeorge syndrome critical region 8, TRBP TAR RNA-binding protein, RISC RNA-induced silencing complex, ciRNAs circular intronic RNAs, EIciRNAs exon-intron circRNAs, ecircRNAs exonic circRNAs