Finally, we examined the function of Sema-2a and Sema-2b in PNs that normally target dendrites to the ventromedial antennal lobe. We focused on VM2 PNs, the only ventromedial-targeting PN classes we can label with a specific GAL4 driver (NP5103) ( Komiyama et al., 2007). In sema-2a−/− Selleck Lumacaftor or sema-2b−/− single mutants, VM2 PN targeting appeared normal compared to controls ( Figures 7A–7C). However, in sema-2a−/− sema-2b−/− double mutant flies, VM2 PNs exhibited significant dorsolateral mistargeting ( Figures 7D, quantified in Figure 7E and Figure S6A). These experiments indicate that Sema-2a and Sema-2b also act redundantly to direct
ventromedial-targeting PN dendrites to their normal positions. Next, we attempted to determine the cellular source for this additional function of Sema-2a and Sema-2b. Because we needed to use the GAL4/UAS system to label VM2 PNs, we could not use GAL4/UAS again to ablate larval ORNs or perform tissue specific knockdown and rescue as we did for MZ19+ PNs. However, since PNs themselves made a significant contribution to Sema-2a expression (Figures 4E and 4F), and because ventromedial-targeting PNs should express high levels
of Sema-2a and Sema-2b given their distribution patterns (Figure 2), Rucaparib we tested whether PN-derived Sema-2a and Sema-2b contribute to VM2 dendrite targeting. We used NP5103-GAL4 based MARCM to label anterodorsal neuroblast clones from which VM2 PNs are derived ( Jefferis et al., 2001).
When we induced MARCM neuroblast clones in early larvae such that Sema-2a and Sema-2b were eliminated from all larval-born PNs in the anterodorsal lineage, including VM2 PNs ( Figure 7F, left), VM2 PN dendrites exhibited significant dorsolateral mistargeting ( Figure 7H, compared with Figure 7G; quantified in Figure 7J and Figure S6B). In contrast, dorsolateral-targeting DL1 PN dendrites were unaffected by removal of Sema-2a/2b from this same neuroblast lineage ( Figure S7). These experiments indicate that Sema-2a/2b derived from PNs are essential for VM2 dendrite targeting but not for DL1 dendrite targeting. PN-derived Sema-2a and Sema-2b can affect VM2 dendrite targeting through two mechanisms. First, they could act cell-autonomously, for example over by modifying the cell surface presentation of a targeting receptor. Second, they could act cell-nonautonomously as ligands to mediate dendrite-dendrite interactions among PNs. To distinguish between these two possibilities, we took advantage of the fact that VM2 PNs are produced late in the anterodorsal lineage, and induced smaller MARCM neuroblast clones that contained VM2 PNs but few other PNs within the same lineage (Figure 7F, right). We found that VM2 dendrite targeting in these smaller sema-2a−/− sema-2b−/− neuroblast clones was largely normal ( Figure 7I, quantified in Figure 7J). Thus, Sema-2a/2b act nonautonomously for VM2 dendrite targeting.