Fig. 1.

Sensory pioneer axons contact the dorsal root entry zone (DREZ) before arrival of boundary cap cells. a Diagram of the dorsal root ganglia (DRG) and DREZ following pioneer axon entry. Measurements are taken from (b). b Distance from the soma-ensheathing glia to the DREZ and length of the pioneer axon at 72 h post fertilization (hpf). c Confocal z-projection frames of a Tg(ngn1:gfp); Tg(gfap:nsfb-mcherry) zebrafish stained for Sox10 at 56 hpf showing absence of Sox10 staining at the DREZ. d Quantification of the number of Sox10⁺ cell bodies located in the DRG and at the DREZ at 56 hpf. SEM is shown, n = 25 DRG. e Confocal z-projection frames from a 24-h time-lapse starting at 48 hpf of a Tg(sox10:gal4); Tg(uas:mcherry); Tg(ngn1:gfp) animal before, during, and after pioneer axon entry. The mCherry⁺/GFP^- glia do not extend with the mCherry⁺/GFP⁺ neuron to the DREZ. Green brackets denote length of axon. Red brackets denote length of glia. f Growth cone insets and rendering from (e) confirming absence of glial processes at the DREZ. White arrows denote growth cone. White arrowheads denote glial leading edge. Green drawing denotes axon tracing. Red drawing denotes glial tracing. g Quantification of the distance between the pioneer axon (red) and associated glia (green) during axon extension, demonstrating DREZ contact by the pioneer axon before glial DREZ arrival. Dashed black line denotes the location of the DREZ. h Quantification of the time between axon initiation and axonal or glial contact of the DREZ. The axon consistently contacts the DREZ before associated glia, n = 9 DRG. Unpaired Student’s t-test (h). Scale bars denote 10 µm