Modulation of the microRNA-induced silencing complex loading through a specific interaction with a J-domain co-chaperone

MicroRNAs (miRNAs) are essential regulators of several biological processes. To achieve their repressive function, they are loaded onto Argonaute (AGO) proteins, forming the microRNA Induced Silencing Complex (miRISC). Thus, regulating this loading step is essential for miRNA-dependent gene regulation. In this study, we identified the co-chaperone DNJ-12 as a new interactor of ALG-1, one of the two major miRNA-specific AGOs in Caenorhabditis elegans (C. elegans). Importantly, DNJ-12 does not interact with other AGOs, making it a specific regulator of miRNA function. Furthermore, the loss of DNJ-12 leads to developmental phenotypes previously shown to be dependent on miRNA function. Using the Auxin Inducible Degron (AID) system, a powerful tool to study the spatiotemporal effects of DNJ-12 depletion on miRNA function, we show that DNJ-12 depletion hampers ALG-1 interaction with HSP70, a chaperone required for miRISC loading in vitro. Moreover, DNJ-12 depletion leads to a decrease in the levels of several miRNAs and prevents their loading onto ALG-1. This study highlights for the first time the requirement of a co-chaperone for the loading of miRNAs in vivo, provides a potential mechanism explaining AGO differential loading by small RNA, and therefore helps expand our understanding of the miRISC function in animals. Overall design: We compared the effect of DNJ-12 depletion on microRNA expression in different C. elegans tissues