Influence of target RNA topology on miRNA stability

JERÓNIMO LUKIN; MANUEL DE LA MATA; SEBASTIAN A GIUSTI; FEDERICO F WIGHTMAN; DAMIAN REFOJO

Salta

Congreso; Joint XIV PABMB Congress and LV Annual SAIB Meeting; 2019

PABMB & SAIB

MicroRNAs function by fine tuning gene expression throughout different tissues and cell types, conferring an important layer of post-transcriptional control. Consequently, regulation of miRNAs levels themselves is of crucial importance. Accordingly, the mechanisms of microRNA biogenesis and function have been studied extensively, while their degradation mechanisms remain less explored. Nevertheless, several cases of specific miRNAs that decay quickly under certain conditions such as viral infections or particular stages of the cell cycle, suggested that active miRNA degradation takes place. Indeed, in the past few years, endogenous instances of miRNA active degradation have been described. One of the pathways responsible for this phenomenon is known as TDMD, which stands for Target Directed MicroRNA Degradation. TDMD was first described in Drosophila and in mammalian cells, where it was shown that target RNAs can themselves trigger specific miRNA degradation. Unlike the canonical miRNA silencing pathway, TDMD is characterized by a different target-miRNA architecture. While target repression is achieved by a complementarity limited to the 5? seed region of the miRNA, a more extensive base pairing of a target RNA to both the 5? seed and 3? regions can lead to miRNA destabilization. In the past few years, circular RNA molecules (circRNAs) have attracted a lot of interest. CircRNAs are produced through backsplicing of pre-mRNAs by the spliceosome, they are highly stable molecules and tend to accumulate in the cytoplasm. Some circRNAs can be translated and more recently they have been associated to the innate immune response during viral infections, yet the functions for most circRNAs remain largely unknown. CircRNAs were initially proposed as ?sponges? that can titrate and block miRNA function and since then a plethora of publications seems to support this phenomenon. Nevertheless, a systematic approach exploring which impact, if any, circRNAs have on miRNA stability is still lacking. To shed light into this matter, we are studying an endogenous instance of this kind of interaction, namely the miR-7/CDR1as/Cyrano network, where a circRNA (CDR1as) prevents degradation of a specific miRNA (miR-7). Furthermore, we are developing tools capable of expressing artificial circRNAs in an exclusive manner, by selectively degrading the linear form ?leaked? by the construct. We are currently studying the effects of the artificial circRNAs on their cognate miRNAs.