Injection of 1.6MO altered SMN axons although Mauthner axons projected normally. (A-F) Zn-8 immunoreactivity revealed differences in SMN axon outgrowth between morphants and controls. Between 48 and 66 hpf (A-D), innervation of the dorsal musculature was reduced in 1.6MO morphants (B,D) versus control (A,C). Arrows and arrowheads in C,D,F indicate the rostral and dorsal projections. Asterisks in C indicate ventral projections. At 78 hpf (E,F), substantial recovery had occurred in 1.6MO morphants (F) and the majority of dorsal somites were innervated. (G) Although 1.6MO morphants (squares) initially displayed no innervation of the dorsal musculature, this phenotype recovered. Recovery began at 3 dpf and was nearly complete by 5 dpf. Circles represent data from control embryos. (H) In ventral muscle at 66 hpf, extra ventrally projecting axons (asterisks) were present in 28.8±3.6% of segments in 1.6MO morphants but were not present in controls. (I,J) At 78 hpf, the axons of ventrally projecting SMNs in 1.6MO morphants branched more (J) compared with controls (I), consistent with results obtained with the znp-1 antibody (cf. Fig. 5C,D). (K-N) Injection of 1.6MO did not affect Mauthner cell axonal morphology. (K,L) Mauthner cell axons projected caudally into spinal cord in 48 hpf 1.6MO morphants (L) and controls (K). (M,N) Mauthner axons of 72 hpf 1.6MO morphants (N) displayed morphologies similar to those of controls (M). Scale bars: in F, 40 μm for A-F; in H, 40 μm for H and 20 μm for I,J; in L 40 μm for K,L; in N, 40 μm for M,N.
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