Circular intronic RNAs emerges from genomic “dark matter”

High-throughput sequencing data combined with new computational algorithms exploring the “dark matter” of mammalian genomes have recently revealed different classes of long noncoding RNAs. Very recently, researchers from Chinese Academy of Sciences (CAS) demonstrate a group of previously unannotated circular RNAs derived from lariat introns (circular intronic RNAs, ciRNAs).

As shown on the cartoon image, the ciRNA (the golden ring) represents this group of noncoding RNAs emerging from genomic “dark matter” (background). Dr. ZHANG Yang, Dr. ZHANG Xiao-ou and their colleagues, under the supervision of Prof. CHEN Lingling from State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology and Prof. YANG Li from Key Laboratory of Computational Biology, CAS-MPG Partner Institute for Computational Biology, CAS, found that Introns containing consensus motifs (golden nucleotides on the ring) near the 5’ splice site and the branch point are resistant to debranching, leading to the formation of ciRNAs carrying a 2’,5’ -phosphodiester bond.

Some abundant ciRNAs partially accumulate to their sites of transcription, associate with Pol II machinery and act as positive regulators of transcription. This study suggests a cis-regulatory role of circular noncoding intronic transcripts on their parent coding genes.

The study entitled “Circular Intronic Long Noncoding RNAs” ^[1] was published online in Mol Cell on Sep 27^th, 2013, and highlighted by Mol Cell ^[2] and Nature ^[3]. This work was supported by the National Natural Science Foundation of China, Chinese Ministry of Science and Technology, the Chinese Academy of Sciences and Committee of Science and Technology in Shanghai.

Reference
1. Zhang Y, Zhang XO, Chen T, Xiang JF, Yin QF, Xing YH, Zhu S, Yang L and Chen LL. Circular intronic long noncoding RNAs. Mol Cell, 2013, 51: 792-806
2. Bolisetty TM and Graveley BR. Circuitous route to transcription regulation. Mol Cell, 2013, 51: 705-706
3. Research highlights: RNA boosts genes on a loop. Nature, 2013, 501: 464