Circular RNAs: molecules with past and future

Circular RNAs (circRNAs) are a class of recently identified RNAs highly expressed in eukaryotes and conservedbetween species. The biogenesis of circRNAs is a product of the backsplicing process that occurs duringpre‐mRNA maturation, where the binding 3’ donor and 5’ acceptor sites produce a circular molecule.The closed loop structure of circRNAs provides greater stability and increases resistance to the activityof some RNAses when compared to linear RNA. Different functions of circRNAs have been postulated suchas splicing competition against the gene from which they derive, miRNA sponges, regulators of CpG islandmethylation, or mediators in pAKT migration to the nucleus. Therefore, circRNAs are considered importantpost‐transcriptional regulators for cell survival and have been used as biomarkers in cancer diseases. Theabundance of circRNA in neural tissue also implicates them in the development of different nervous systempathologies including those found in geriatric patients. The aim of this review is to summarize the currentknowledge of circRNAs in eukaryotes by presenting possible functions and highlighting their importance incardiac, nervous, endocrine, and digestive systems. Moreover, the impact on cardiogenesis, neurodegenera tion, and cancer are discussed to understand why circRNAs are considered as an important tool in molecularbiology research field.