Fig 4

Schwann cells tightly associate with axons in the pectoral fin.

(A) Schematic of a dorsal view of a larval zebrafish. In the SC, motor axons that sort at the DP to innervate the abductor (green) or adductor (orange) muscle are mixed within nerves 1–3. Nerve 4 axons sort at the VP (not labeled). The C and D boxes denote the regions included in the maximum projections shown in C and D. The lateral view shows the arrangement of nerves 1–4 in the body wall (magenta) and innervation in the fin (green) as it is shown in C and D. The dashed line indicates where nerve 4 grows in the body wall behind the fin. (B) Quantification of number of Schwann cells on the abductor or adductor muscle or associated with the plexus; n = 8 pectoral fins. Data are represented as mean ± 95% CI. (C) Maximum projection of abductor innervation labeled with Tubb:dsRed and 37a> EGFP to label Schwann cells. VP labels ventral plexus. Inset shows Schwann cell membranes that surround axon fascicles within the pectoral fin. Arrows point to axons that are not associated with Schwann cells. (D) Maximum projection of body wall innervation of the same larvae shown in C. Nerves 3 and 4 are labeled. Inset shows DP expanded in E and F. Asterisks label the dorsal region of abductor and adductor innervation. The rest of the fin innervation is not included in this maximum projection. (E) Maximum projection of the dorsal plexus with a single plane shown in (F). Abductor (Ab) and adductor (Ad) innervation and nerves 1/2 and 3 are labeled. The arrow in F points to Schwann cell membranes that completely wrap axonal fascicle in the plexus. Scale bars are 25 microns for C and D and 10 microns for the inset in C, E, and F. Original data for panel B is in S1 Data. DP, dorsal plexus; SC, spinal cord; VP, ventral plexus.