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SIM-less SMN fails to rescue motor axon deficits in a zebrafish model of SMA.a 250 pg of WT or 2 VA human SMN RNA was injected into one-cell stage mz-smn mutants zebrafish embryos and western blot analysis showed that both WT and mutant SMN protein are expressed at comparable levels. b Representative images of motor neuron phenotype for each group. Scale bar 50 μm. Truncated motor axons (white arrows) and branched motor axons (red arrowheads) occur, in relation to SMN levels reduction, with increasing degrees of severity determining the classification in one phenotypic class. c Animals were scored as having severe, moderate, mild or no defects in their motor axons at 28 h post fertilization (hpf). Data represent means and SEM. Three independent experiments were performed with 14–21 animals per experiment. Statistics were performed with two tailed Mann–Whitney non-parametric rank test (wt vs mz-smnp p < 0.0001; wt vs mz-smn + WT RNA p = 0.865; wt vs mz-smn + 2 VA SMN RNA p < 0.0001; mz-smn vs mz-smn + WT SMN RNA p < 0.0001; mz-smn vs mz-smn + 2 VA SMN RNA p = 0.624; mz-smn + WT SMN RNA vs mz-smn + 2 VA SMN RNA p < 0.0001).
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