pLL nerve regeneration in larvae totally or partially lacking Schwann cells. Transgenic tg(neuroD:EGFP) or tg(NeuroD:TagRFP) were used to evaluate the impact of Schwann cell absence on pLL nerve regeneration. (A) After 48 hpn, the regrowing nerve of control but neurectomized larvae reaches the tip of the tail. (B-F) Transgenic larvae were treated with AG1478 following two treatments: 5 µM AG1478 from 10 to 58 hpf (B-D) and 3.5 µM AG1478 from 24 to 58 hpf (E, F). In both cases, the drug was washed out at 58 hpf and the larvae were maintained in E3 medium. At 3 dpf, larvae of each treatment were separated into two groups: non-neurectomized AG-treated controls and neurectomized AG-treated larvae. Note that the nerve of control (and treated) larvae deviates from the myoseptum (dotted line) in both treatments (B, E) but deviation is more severe in the longer treatment; insets show larger magnification. In parallel, the pLL nerve of neurectomized larvae fails to regenerate properly as it defasciculates and wanders outside of the horizontal myoseptum (C, D, F), and fails to reach the tip of the tail at 48 hpn under these conditions. (G,H) At 5 dpf we quantified and compared the winding index of the nerve in neurectomized vs. non-neurectomized larvae. In both treatments, the pLL axons of neurectomized larvae have an increased winding index in comparison with their respective controls. ***P <0.001. Scale: A-F: 100 µm.