Spatiotemporal Control of microRNA-Target Interactions.

MicroRNA-mediated gene regulation occurs within spatially organized intracellular environments and is governed by dynamic molecular interactions that unfold across defined kinetic timescales. Although classical models emphasize sequence complementarity between microRNAs (miRNAs) and their target transcripts, growing evidence indicates that the outcomes of miRNA-target interactions vary widely across cellular contexts and cannot be explained solely by seed pairing or steady-state expression levels. These observations suggest that additional regulatory layers shape the efficiency and fate of miRNA-mediated silencing. In this Review, we examine how the spatial organization of the cell structures miRNA activity across distinct intracellular microenvironments, where the local availability of Argonaute (AGO)-containing RNA-induced silencing complexes (RISCs), target RNAs and regulatory cofactors influences the probability that RISCs encounter and productively engage their targets. We further explore the temporal dimension of miRNA regulation, including Argonaute loading and turnover, the dwell time of RISC-target interactions, miRNA stability and target transcript lifetimes. Recent advances in quantitative and high-resolution approaches for studying RNA dynamics in living cells are beginning to reveal these regulatory processes directly. Together, these observations support a spatiotemporal kinetic model of miRNA regulation, in which intracellular organization and molecular dynamics jointly determine the probability and efficiency of gene silencing. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms.