Some cellular transcripts are converted to circular form by splicing reactions, which results in circular RNA. Although the significance of the circular RNA has been enigmatic in animal cells, recently some scientists revealed that the circular RNA is involved in the regulation of cellular gene expression by acting as a "sponge" for several microRNAs. Basically, microRNA contributes to the inhibition of protein production from mRNA by forming a direct base-pairing to target site of mRNA. The scientists discovered that circular RNA has many microRNA binding sites within its sequence. This fact means that the circular RNA behaves as a decoy for microRNAs, and hampers their biological function. Indeed, they demonstrated such mechanism by biochemical experiments.
Animal genome expresses thousand of circular RNAs in tissue-, cell type-, developmental stage-specific manner. The balance of circular RNA expression and microRNA action may determine the posttransciprtional fate of mRNA transcriptome.
http://www.nature.com/nature/journal/v495/n7441/full/nature11928.html
http://www.nature.com/nature/journal/v495/n7441/full/nature11993.html
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