GFP expression to identify and track neurons. (A) Left: confocal image showing a repeating pattern of GFP-labeled neurons along the anterior-posterior axis of the abdominal region of a ventral ganglion at 8 h-APF. Grey brackets denote neuromeres. For this and all subsequent confocal images, abdominal neuromeres are shown with anterior up, h denotes h-APF, and RP2s, aCCs and pCCs are marked by arrows, filled arrowheads, and open arrowheads, respectively (see key below inset). The dashed box outlines the enlarged inset at right, illustrating GFP labeling in bilateral pairs of aCCs, RP2s and more faintly labeled pCCs. aCC axons (single asterisks) project posteriorly to join ipsilateral intersegmental nerves (ISNs) while RP2 axons (double asterisks) project anteriorly to join the ISNs. pCC axons are not indicated. (B) Comparison of RP2/aCC-enhanced (B1) and RP2-enhanced (B2) GFP labeling patterns (see Results) at 8 h-APF. The RP2/aCC-enhanced pattern was used to track neurons through metamorphosis; the RP2-enhanced pattern was used for cell culture experiments. Scale bars: 15 μm.