CSDE1 promotes passenger strand cleavage of miR-486

Strand separation of the RNA duplex is vital for miRNA maturation, enabling the guide strand to form miRISC. The erythroid miRNA miR-486-5p requires AGO2-mediated catalytic cleavage of its passenger strand, miR-486-3p, but the regulatory factors remain unclear. We identify CSDE1 as a cofactor that facilitates AGO2-dependent removal of the passenger strand and the maturation of miR-486-5p. Loss of CSDE1 increases miR-486-3p levels in leukaemia cells, decreases cleavage efficiency in vitro, and derepresses miR-486-5p targets. Reintroducing the full-length CSDE1 restores AGO2-dependent duplex cleavage in vitro, a function that depends on its N-terminal cold-shock domain (CSD1) for interaction with AGO2. Overall, these findings indicate that CSDE1 contributes to AGO2-mediated miR-486 strand separation, with implications for target gene silencing in leukaemia.