Exogenous FMRP rescues NMJ and locomotion defects caused by mutant FUS. a Western blot analysis of 72 hpf zebrafish embryo lysates using antibodies against human FUS or FMRP following injection of FUS WT, FUS R521C and/or FMR1 RNAs. Tubulin is used as a loading control. NIC non-injected control. b Representative images of neuromuscular junctions (NMJ) in 72 hpf NIC zebrafish embryos or following injection of FUS WT, FUS R521C, and FUS R521C and FMR1 RNAs. Anti-synaptic vesicles 2 (SV2) and anti-bungarotoxin (BTX) were used to label the pre- and postsynaptic compartments. Arrowheads indicate absence of colocalization between SV2 and BTX staining. c Quantification of the Pearson’s correlation coefficient for overlap between immunolabeling for pre- and post-synaptic markers, as shown in b. n = 20 per condition. IB immunoblot. d Quantification of touch-evoked escape responses (TEER) in zebrafish embryos at 72 hpf following injection of the indicated RNAs. Data is obtained over five experiments with n = 267 for NIC, n = 182 for FUS WT, n = 163 for FUS R521C and n = 111 for FUS R521C + FMR1. *p < 0.05, **p < 0.01, Fisher’s exact test. Scale bar 20 µm