Circular RNA: New Regulatory Molecules.

Circular RNA are a family of covalently closed circular RNA molecules, formed from pre-mRNA of coding genes by means of splicing (canonical and alternative noncanonical splicing). Maturation of circular RNA is regulated by cis- and trans-elements. Complete list of biological functions of these RNA is not yet compiled; however, their capacity to interact with specific microRNA and play a role of a depot attracts the greatest interest. This property makes circular RNA active regulatory transcription factors. Circular RNA have many advantages over their linear analogs: synthesis of these molecules is conservative, they are universal, characterized by clearly determined specificity, and are resistant to exonucleases. In addition, the level of their expression is often higher than that of their linear forms. It should be noted that expression of circular RNA is tissue-specific. Moreover, some correlations between changes in the repertoire and intensity of expression of circular RNA and the development of some pathologies have been detected. Circular RNA have certain advantages and can serve as new biomarkers for the diagnosis, prognosis, and evaluation of response to therapy.