Graphical abstract. Credit: Nucleic Acids Research (2026). DOI: 10.1093/nar/gkaf1510 MicroRNAs, whose discovery was recognized with the 2025 Nobel Prize in Physiology or Medicine, are central regulators of gene expression, yet a fundamental question has remained unanswered: how cells choose between the two strands produced from each microRNA precursor. A study published in Nucleic Acids Research reveals that this decision follows conserved, programmable ru