Fig. 1. svp mutant R1 and R6 axons terminate in either the R8 or R7 target layer. Adult medullas in which the axon terminals of individual homozygous R1s, R6s and R7s created by GMR-FLP-mediated mitotic recombination were labeled with the synaptic vesicle marker synaptotagmin-GFP (green) using MARCM. All R axons were labeled with mAb24B10 (red). The approximate positions of the R8 recipient layer, M3, and the R7 recipient layer, M6, are indicated by broken lines. (A) Wild-type (FRT82) R7s terminate in the R7 recipient layer (arrows). (B) Some svp mutant R1/R6s terminate in the R8 recipient layer (arrowhead); a wild-type R7 is present in the same column (double arrow). Labeled axons in the R7 recipient layer (arrows) originate from R7s or from R1/R6s. (C,D) We used the sev mutation to remove R7s (residual mAb24B10 staining in the R7 recipient layer is derived from medulla neurons). (C) No wild-type R1/R6s terminate in the medulla. (D) svp mutant R1/R6s terminate in either the R8 (arrowheads) or the R7 recipient layer (arrows) with approximately equal frequency. (E) pros mutant R7s form synaptic boutons at both the R8 and R7 recipient layers (double arrows), but sometimes appear wild-type (not shown) or terminate in the R8 recipient layer (arrowhead). (F) Quantification of A,D,E. Red bars represent homozygous axons that form synaptic boutons in the R7 recipient layer only, blue bars represent those that terminate in the R8 recipient layer, and green bars represent those that form boutons in both the R8 and R7 recipient layers. Scale bar: 10 µm.