Modeling neurodevelopmental disorder-associated human mutations in Argonaute .

MicroRNAs (miRNA) associate with Argonaute (AGO) proteins and repress gene expression by base pairing to sequences in the 3' untranslated regions of target genes. De novo coding variants in the human AGO genes and cause neurodevelopmental disorders (NDD) with intellectual disability, referred to as Argonaute syndromes. Most of the altered amino acids are conserved between the miRNA-associated AGO in and , suggesting that the human mutations could disrupt conserved functions in miRNA biogenesis or activity. We genetically modeled four human mutations in by introducing identical mutations into the homologous gene. These NDD mutations cause phenotypes in indicative of disrupted miRNA processing, miRISC (miRNA silencing complex) formation, and/or target repression. We show that the NDD mutations are antimorphic, causing developmental and molecular phenotypes stronger than those of null mutants, likely by sequestrating functional miRISC components into non-functional complexes. The NDD mutations cause allele-specific disruptions in mature miRNA profiles, accompanied by perturbation of downstream gene expression, including altered translational efficiency and/or messenger RNA abundance. The perturbed genes include those with human orthologs whose dysfunction is associated with NDD. These cross-clade genetic studies illuminate fundamental AGO functions and provide insights into the conservation of miRNA-mediated post-transcriptional regulatory mechanisms.