Fig 2

Target-selective regeneration of motor axons.

(A) Schematic of a lateral view of pectoral fin abductor muscle motor innervation. An example trajectory of a single axon is shown in magenta. DP labels dorsal plexus, motor nerves in the body wall are labeled 1–4. (B, C) A timecourse of sparsely labeled axon(s) showing the innervation pattern pre-transection, after axon degeneration, and at 2 dpt. Sparsely labeled axons are labeled in white (B) and magenta (C) and all adductor motor axons are labeled in green (C). The white arrow points to a fascicle that did not degenerate and the orange arrow points to ectopic growth during regeneration. (D) Quantification of the muscle localization of sparsely labeled axons pre-transection compared to where these labeled axons innervated after regeneration. Small numbers on pre-transection data represent n. Diagonal lines indicate the axon mistargeted during regeneration. (E) Schematic defining domains for axon domain scoring. For category 3, which are the minority, axons entered the fin at the DP but innervated the ventral region of the fin, overlapping with domain 4 (like the sparsely labeled axon in A). The domains used to quantify sparsely labeled axon targeting are a broader categorization than the topographic territories schematized in Fig 1A. (F) Quantification of fin domain localization of sparsely labeled axons pre-transection compared to where these labeled axons innervated after regeneration. Small numbers on pre-transection data represent n. (G) Example of sparsely labeled axons (magenta) that form new trajectories and reestablish previous trajectories during regeneration with both motor axons (mnx1:GFP) and muscle fibers (α-actin:GFP) labeled. (H) The original (green) and regenerated (orange) trajectories of the sparsely labeled axons in G. Here, part of the pre-injury and regenerated trajectory can be overlayed precisely (arrows). Additionally, an axon does not follow its original trajectory (double arrows) but instead is mistargeted along the base of the fin (triangle). Original data for panels D and F are in S1 Data. DP, dorsal plexus; dpt, day post transection; GFP, green fluorescent protein.