INFLUENCE OF CIRCULAR TARGET RNA TOPOLOGY ON microRNA STABILITY AND FUNCTION

FUCHS WIGHTMAN F., DE LA MATA M.; LUKIN J., GIUSTI S., REFOJO D.

Virtual

Conferencia; Bay Area RNA Conference; 2020

MicroRNAs are small regulatory RNAs which confer cells the possibility of fine-tuning gene expression at apost-transcriptional level. Consequently, regulation of miRNAs levels themselves is of crucial importance.Accordingly, the mechanisms of microRNA biogenesis and function have been studied extensively, whiletheir degradation mechanisms remain less explored.On the one hand, a mechanism called TDMD (for Target Directed MicroRNA Degradation) has emerged asone of the processes affecting miRNA turnover. During TDMD, targets with extensive base-paircomplementarity towards the 3? end lead to miRNA degradation, contrary to the canonical target silencing.A number of examples of this mechanism have arisen in the past few years, including both endogenoustargets capable of destabilizing specific miRNAs and viral transcripts which in doing so facilitate infection.On the other hand, there have been reports proposing circular RNAs as microRNA sponges. CircRNAsoriginate from pre-mRNA back-splicing and, despite most of them lack a functional annotation, recentfindings have showed that many may be important for gene regulation through miRNAs. However,although a plethora of publications claim to have expressed circRNAs as sponges that prevent miRNAs fromexerting their typical function, their capability of cleanly and exclusively over-expressing exogenouscircRNAs without suffering from a linear isoform ?leak? remains questionable. Thus, assigning the observedeffects to the circRNAs while ignoring the potential participation of the counterpart linear transcripts mightseem far-fetched.In this study, we aimed at shedding light on whether linear versus circular topologies of targets can producedifferent effects on both miRNA stability and function. We started by examining the well described CDR1as/miR-7/Cyrano network of noncoding RNAs, where the lncRNA Cyrano destabilizes miR-7-5p through TDMD,while the circRNA CDR1as yields an apparent protection by sponging it, leaving it unavailable fordegradation. By expressing a linear version of CDR1as in combination with knocking the endogenouscircRNA, we show that the circular topology of CDR1as is crucial for its function. Furthermore, using astrategy in which we expressed an artificial circRNA aimed at binding miR-132, designed in way that itminimizes the linear counterpart leak, we showed that the differences between topologies are notcircumscribed to CDR1as. Finally, we analyzed publicly available sequencing data to show that this kind ofregulation is potentially widespread through a number of miRNAs and circRNAs during neuron-likedifferentiation.