摘要：SummaryCircular RNAs (circRNAs) are stable non-coding RNAs with a closed circular structure. One of the best studied circRNAs is ciRS-7 (CDR1as), which acts as a regulator of the microRNA miR-7; however, its biosynthetic pathway has remained an enigma. Here we delineate the biosynthetic pathway of ciRS-7. The back-splicing events that form circRNAs are often facilitated by flanking inverted repeats of the primate-specificAluelements. The ciRS-7 gene lacks these elements, but, instead, we identified a set of flanking inverted elements belonging to the mammalian-wide interspersed repeat (MIR) family. Splicing reporter assays in HEK293 cells demonstrated that these inverted MIRs are required to generate ciRS-7 through back-splicing, and CRISPR/Cas9-mediated deletions confirmed the requirement of the endogenous MIR elements in SH-SY5Y cells. Using bioinformatic searches, we identified several other MIR-dependent circRNAs and confirmed them experimentally. We propose that MIR-mediated RNA circularization is used to generate a subset of mammalian circRNAs.Graphical AbstractDisplay OmittedHighlights•The circular RNA, ciRS-7 (CDR1as), functions as a regulator of miR-7•ciRS-7 is generated by back-splicing, not via intra-lariat splicing•Back-splicing of ciRS-7 is promoted by the flanking inverted MIR elements•The biosynthesis of a subset of mammalian circRNAs could be mediated by MIRsBiological Sciences; Molecular Biology
