A striking number of genes, including TDP-43, FUS and ATXN2 implicated in ALS pathogenesis encode proteins with functions in RNA metabolism. Also, preliminary results suggest that miRNAs are aberrantly expressed in spinal motor neurons, and that mRNAs encoding neurofilament proteins are a disease relevant target and represent the most reliable prognostic biomarker for ALS patients. To address the mechanisms involved and identify common therapeutic targets, we developed zebrafish models, which allows large-scale drug screening and in vivo assessment of biological processes, combined with a wide range of genetic tools: gene overexpression (DNA or RNA injection), knock-down (antisense morpholino injection) or knock out (CRISPR/Cas9 and deletion mutants) to define in vivo the functions of miRNAs and neurofilament proteins, as well as the consequences of their disruption. We identified and characterized the zebrafish homologues for the low molecular weight neurofilament protein (Nefl) and assessed its expression within physiological and ALS pathological conditions. We also established that down regulation of a specific Nefl isoform in zebrafish using antisense oligonucleotides results in a strong ALS-like motor phenotype (motor axon atrophy combined to a paralysis reflected by deficits in the evoked swimming response). We are currently developing long-term Nefl KO using the CRISPR/Cas9 genome editing tools and obtained zebrafish lines from EZRC carrying mutations in the Nefl orthologues. We also assessed by Western Blot the expression of Nefl within ALS zebrafish models, and revealed that TDP43 knock- down leads to a strong decrease in Nefl protein. Our collaborators, Drs. Strong and Hornstein identified specific miRNAs that affect Nefl expression and aggregation in vitro and are known to be aberrantly expressed in ALS patients. In parallel, we are performing down regulations of these miRNAs of interest in zebrafish embryos to assess their biological consequences. Inhibition of two of these miRNAs led to motor deficits and aberrant branching of axonal projections from motor neurons in live zebrafish larvae, associated with a strong disruption of Nefl expression. These animal models will allow us to elucidate the role of these key actors in ALS pathogenesis and will provide relevant endpoints for future studies to identify novel therapeutics targets for ALS. Funding provided by the ERA-NET E-rare (ANR) project RNA-ALS and the ERC project ALS-Networks.