(A–F’) Single-cell MARCM clones show the diverse morphologies of ring neuron axons and pb-eb-gall neuron dendrites in the EB (frontal views in A–F, dorsal views in A’–F’). (G) Schematic depicting a dendritic arbor from a single pb-eb-gall neuron (red) overlapping with axons from multiple types of R neuron. Only axons from one R4m (yellow) and one R3 (blue) are shown here as examples. (H) R19G02-GAL4 was used to express pre-synaptic (Syt-GFP) and dendritic (DenMark) markers in small-field pb-eb-gall neurons. Syt-GFP, but not DenMark, was enriched in the gall, demonstrating that these gall projections are largely pre-synaptic. PB and EB projections were filled by both Syt-GFP and DenMark, suggesting that these projections include both pre- and post-synaptic terminals. (I–J) Native GFP fluorescence is reconstituted between pb-eb-gall dendrites and R neuron axons (R1/R3/R4d in panel I, R2/R4m in panel J) in GRASP (GFP reconstitution across synaptic partners) experiments. CD4-spGFP1-10 was expressed in R1/R3/R4d and R2/R4m neurons by R15B07-GAL4 and EB1-GAL4, respectively. CD4-spGFP11 and mCherry were expressed in pb-eb-gall neurons by R19G02-lexA in both cases. No GFP fluorescence was observed in control animals in which either GAL4 or lexA driver was not present (data not shown). (K and L) R19G02-GAL4-driving CD8-GFP and R19G02-lexA-driving mCherry label pb-eb-gall neuron projections in K and L (in green), respectively. At 24 hr APF, the pb-eb-gall neuron dendrites overlap with R2/R4m axons (labeled by R32H08-lexA-driving mCherry in panel K, red arrows), but not with R3/R4d axons (labeled by R15F02-GAL4-driving CD8-GFP in panel L, red arrow). At 48 hr APF, the pb-eb-gall dendrites have expanded toward the EB canal and overlap with both R2/R4m and R3/R4d axons. Scale bars are: 20 μm in panels A–F’; 50 μm in panels H–L.