Primary motor neuron morphogenesis defects in the Sox2 knockout zebrafish. (A) Confocal imaging analysis of primary motor neurons in control and Sox2 knockout groups at 24, 48, and 72 hpf. The dotted diagonal line marked the boundary of the myosepta. Scale bar = 50 μm. (B) The length of CaP axons in control and Sox2 knockout zebrafish at 48 hpf (n = 21 and 33, respectively) and 72 hpf (n = 13 and 29, respectively). (C) The variability of CaP phenotype across segments in controls and Sox2 mutants at 48 and 72 hpf. Circle means control and triangle means Sox2 mutant. (D) The number of branches per 1-mm CaP axon in control and Sox2 knockout zebrafish at 48 hpf (n = 11 and 9, respectively) and 72 hpf (n = 8 and 12, respectively). Each bar represents the mean ± SD. Values with *, **, and *** above the bars are significantly different (P < 0.05, P < 0.01, and P < 0.001, respectively). (E) The schematic for three different primary motoneurons (CaP, MiP, and RoP) in the whole fish and a specific myotome segment.