Determination of RNAs bound by wildtype and P525L mutant FUS in human iPSC-derived motoneurons using PAR-CLIP (Photoactivatable Ribonucleoside-Enhanced Crosslinking and Immunoprecipitation) Overall design: First, endogeneous FUS was immunoprecipitated from wildtype and FUS-P525L mutant motoneurons. Second, FUS wildtype or the P525L mutant was ectopically expressed as a flag-fusion protein and immunoprecipitated using an anti-flag antibody.