Fig. 1

Biogenesis and function of circRNAs. a. The main product of gene transcription, pre-mRNA. b. In vivo, chromosomal translocations and other reasons may cause CircRNAs to be produced by exons of different genes, which are called fusion CircRNAs(f-circRNAs). c. Two adjacent gene exons on the same DNA chain can form circRNAs, read through circRNA (rt-circRNAs). d. During pre-mRNA transcription to produce a lariat structure containing exons, which is then spliced internally to release introns and form EciRNAs composed of exons. e. the tail end of the downstream 3′ splicing donor site in the exon binds to the upstream 5′ splicing receptor site, resulting in base pairing of the donor and receptor sites, which mediates exon circularization to form circRNAs or EciRNA. It is regulated by Alu, RBPs, and parental gene exons. f. The interconnections of introns cause the formation of CiRNAs after the lariat structure undergoes internal reverse splicing. g. Liner mRNA: single-stranded ribonucleic acids are carrying genetic information. h. Interaction between CiRNA and Pol II promotes parental gene transcription. i. EIciRNAs interact with U1-SNP and Pol II to enhance gene expression. j. CircRNAs can affect the occurrence and development of diseases as competitive binding miRNA of ceRNA. k. CircRNAs act as RBPs scaffold sponge to regulate variable splicing of transcripts, transcription of parent genes, and post-transcriptional translation. l. CircRNAs can be modified with IRES sequence and m⁶A to facilitate the translation of circRNAs