Behavior of neurites. A. A total of 5.5 hours following photoconversion of the entire diameter of the E12.5 colon (hashed box), 600 μm from the wavefront. Numerous neurites (white arrows) were present on the caudal side. More cells migrated caudally than rostrally. B. A neuron with a circumferentially projecting neurite in the E12.5 proximal colon. C. Neurites do not normally explore outside of the ENCC network. Growth cone of a neurite in the E12.5 colon, which was often bifurcated (arrows), and only explored within the ENCC network. The main shaft of the neurite is marked by an asterisk. D. Polar frequency histogram showing the direction of neurite advance (n = 9) and migrating ENCCs (n = 6) measured at 10-minute intervals. The directions of neurite advance were significantly different from ENCC migration direction (Watson’s U2 test for angles). E. Close association between a growing neurite and an individual ENCC. The growing tip (white arrow) of the neurite (orange) initially extends circumferentially and then the neurite extends caudally. It grew in close association with a photoconverted (red) ENCC (yellow arrow) for over 2.5 hours. The neuron cell body (asterisk) also migrates. F. Segments of Ednrb-hKikGR small intestine were placed at both ends of an explant of RetTGM/TGM small intestine, which lacks ENCCs. When ENCCs from the two populations were approximately 100 μm apart, the rostrally migrating population was photoconverted (time = 0). When the two populations collided, chains of intermingled cells formed (arrow, 2.5 h). Both populations then ceased to advance, although red neurites (open arrows) continue to grow rostrally for over 15 hours, well beyond the most rostral ENCC (arrow). G. Tracings of two ENCCs in the initial stages of neurite projection that were imaged for 12 hours (top cell) and 7 hours (bottom). ENCCs, enteric neural crest-derived cells.