MicroRNAs (miRNA) are small regulatory RNAs that exist in all multicellular eukaryotes. Mature miRNAs are bound by Argonaute proteins to form the miRNA induced silencing complex (miRISC), which post-transcriptionally regulates target gene expression. Recently, multiple de novo coding variants in human Argonaute gene AGO1 have been reported to cause neurodevelopmental disorders with intellectual disability (ID). Interestingly, most of the altered amino acids are conserved between the miRISC Argonautes of H. Sapiens and C. elegans, suggesting evolutionarily conserved function in the miRNA pathway. To understand how the human AGO1 mutations may affect miRNA biogenesis and/or function, we chose a set of mutations that were identified as associated with ID in independent families, and used CRISPR/Cas9 genome engineering to introduce the identical mutations in C. elegans
alg-1 gene. We found that several mutations resulted in phenotypes known to be characteristic of
alg-1 loss-of-function. These phenotypes were remarkably enhanced in the absence of
alg-2, the C. elegans
alg-1 paralog, suggesting that the impaired functions in
alg-1 are partially redundant among Argonaute genes. Intriguingly, some mutations resulted in retarded heterochronic phenotypes with penetrance greater than that of
alg-1 null mutation, indicating that these modelled human AGO1 mutations have antimorphic effects on
alg-1 function in C. elegans. To characterize how the mutations impact post-transcriptional gene regulation, we performed ribosome profiling of the mutants and observed perturbation of the translational levels of dozens to hundreds of genes, depend on the mutations. Combining the ribosome profiling analysis with RNAseq, we found that these
alg-1 mutations can affect gene expression levels by perturbing translational efficiency and/or mRNA stability. Interestingly, a large proportion of the genes perturbed by the modelled mutations are known to be expressed in C. elegans nervous system, and many of them have human homologs whose dysfunction is known to cause neuronal disorder diseases, including the homeobox gene
alr-1/ARX which is highly related with intellectual disability. We are currently working on understanding how the modelled human AGO1 mutations may affect miRNA biogenesis and/or miRISC association in C. elegans, and exploring how the C. elegans modelling may help illuminate the mechanisms of the corresponding human disorders. We also anticipate that these cross-clade genetic studies may advance the understanding of fundamental Argonaute functions, and provide insights into the conservation of miRNA-mediated post-transcriptional regulatory mechanisms.