SC segregation is axon dependent. (A–D) Single-cell labeling of an NMJ 31 h after transection of the intercostal nerve. (A and B) Terminal SCs overlap but remain restricted within the synaptic gutter (labeled in B with BTX). (C and D) Time-lapse recording spanning 1 h demonstrates rapid growth (C) and retraction (D) of terminal SC processes within the synaptic gutter (depicted areas boxed in A). (E–G) 5 d after nerve transcection, terminal SCs have started to sprout beyond the synapse. (F and G) Terminal SCs exhibit extrasynaptic growth cone–like structures, which grow (F) and collapse (G) rapidly over a period of 1–2 h (depicted areas boxed in E). The timers shown represent hours/minutes. Bars, 5 µm.