FUS controls muscle differentiation and structure through LLPS mediated recruitment of MEF2 and ETV5 [RNA-Seq]

FUS, a major RNA binding protein with prominent roles in transcription and splicing, is mutated in agressive forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by muscle weakness and motor neuron degeneration. We show here that ALS-associated FUS mutations lead to ultrastructural defects in muscle biopsies of ALS-FUS patients, in particular in sarcomeres and mitochondria, that are recapitulated in iPSC-derived myocytes. Studies in mouse and Drosophila models demonstrate an evolutionary-conserved cell autonomous function of FUS in muscle development. Mechanistically, FUS is required for transcription of MEF2 dependent pathways and directly binds to the promoter of a subset of genes with binding sites for PEA3 family ETS transcription factors, in particular ETV5. We further show that FUS co-activates transcription of MEF2 dependent genes with ETV5. Importantly, FUS phase separates with ETV5 and MEF2A, and MEF2A binding to FUS is potentiated by ETV5. Last, Etv5 haploinsufficiency exacerbates muscle weakness in a knock-in model of ALS-FUS. Thus, FUS is required for muscle structure through its phase separation-dependent recruitment of ETV5 and MEF2, and this pathway is compromised in ALS-FUS.