Past, present, and future of circ RNA s

Exonic circular RNA s (circ RNA s) are covalently closed RNA molecules generated by a process named back‐splicing. circ RNA s are highly abundant in eukaryotes, and many of them are evolutionary conserved. In metazoans, circular RNA s are expressed in a tissue‐specific manner, are highly stable, and accumulate with age in neural tissues. circ RNA biogenesis can regulate the production of the linear RNA counterpart in cis as back‐splicing competes with linear splicing. Recent reports also demonstrate functions for some circ RNA s in trans : Certain circ RNA s interact with micro RNA s, some are translated, and circ RNA s have been shown to regulate immune responses and behavior. Here, we review current knowledge about animal circ RNA s and summarize new insights into potential circ RNA functions, concepts of their origin, and possible future directions in the field.