Fig. 3: SGN peripheral processes exhibit a variety of outgrowth behaviors.

a A wholemount E14 cochlea, with SGNs genetically labeled red using Bhlhb5^cre and an Ai14 tdTomato reporter. Process outgrowth was imaged in three different regions of E14-E15 cochleae. Region 1 (blue, R1) is immediately adjacent to the ganglion; region 2 (green, R2) is in the developing osseous spiral lamina (OSL), and region 3 (red, R3) is close to the organ of Corti. See Supplementary Movies 2–4. b Representative trajectories of processes imaged as they grew through each region. c All trajectories were collapsed onto a common origin, revealing overall differences in the pattern of growth in each region. N = 3 cochleae for each region with n = 55 R1 trajectories, 64 R2 trajectories, and 44 R3 trajectories. d, e Quantification of the speed (d) and directionality (e) of SGN peripheral process outgrowth in R1, R2, and R3 (shown as raw data with mean ± SEM indicated). Growth is faster and more directed in R2 than in R1 or R3. Within R1, some SGN processes are as directed as those in R2, with directionality indices greater than 0.66. Significance was assessed using ANOVA with Tukey’s multiple comparison test. R1 vs R2 speed, P < 0.0001; R1 vs R2 directionality, P < 0.0001; R1 vs R3 directionality, P = 0.9782; R1 vs R3 speed, P = 0.6107; R2 vs R3 directionality, P < 0.0001; and R2 vs R3 speed, P < 0.0001. f R1 trajectories were grouped according to directionality, from low (0–0.33) to medium (0.33–0.66) to high (0.66–1). The number of trajectories in each group is indicated. Source data are provided as a Source data file. g Frames from a video (Supp. Movie 2) showing a subset of SGN peripheral processes (arrowheads) that grow ahead of the overall wavefront. Time is indicated in hh:mm. Scale bars: 100 µm (a), 10 µm (b, c, g).