Fig. 7. Poxn expression pattern in the developing brain. (A,B) Bilateral-symmetric expression of Poxn in the two brain hemispheres (arrows) of a stage 16 wild-type embryo (A) or third instar larva (B), shown in dorsal views (anterior upwards) under Nomarski optics at a resolution of 20x magnification. (B) Note that no Poxn is detectable in the ventral ganglion. (C) Bilateral-symmetric Poxn expression in the brain of a wild-type adult male, visualized as frontal view by bright field microscopy at a resolution of 16x magnification. Arrows indicate the dorsolateral cluster of about 200 Poxn expressing cells and the ventral cluster of about 100 Poxn expressing cells, which forms an arc around the region where the antennal nerve (an) enters the brain. (D,E) Frontal views of Poxn expression in brains of 2-day-old w; Poxn-Gal4-13-1 UAS-GFP (D) and w; Poxn^M22-B5; Poxn-Gal4-13-1 UAS-GFP (E) males, visualized by GFP expression and confocal fluorescence microscopy at a resolution of 20x magnification and with maximum projection of Z-stacks. (D) The majority of cells in both GFP expressing clusters have the morphology of neurons, which project into different regions of the brain. The ventral clusters project mainly into the antennal lobes. The dorsal clusters have the ellipsoid body (eb) as major target and arborize in the lateral triangle (ltr) and in at least one additional region of the brain. The arborizations in the subesophageal ganglion (sog) of the chemosensory neurons of the labellar taste bristles and the LSO are also labeled by GFP. The arborization in the antennal lobe (al) and the antennal nerve (an) are indicated by arrows. (E) The projection pattern of the dorsal clusters has changed dramatically, the ellipsoid body is not targeted and hence not visible, and the arborizations do not reveal the striking symmetry of the wild-type pattern. Note that the disturbance of the projection pattern, as revealed by the Gal4-driven GFP expression, is completely rescued by two copies, but not by a single copy of PK6. This effect is presumably caused by the presence of Gal4 because the GFP pattern is not entirely wild-type even in a Poxn^M22-B5/+ background, whereas the Poxn pattern of a Poxn^M22-B5 mutant is completely rescued to wild-type by XBs if visualized by anti-Poxn and histochemical staining. (F,G) Poxn expression in the brain of a 2-day-old w; Poxn-Gal4-9/+; UAS-GFP/+ male, visualized as in D,E, but with average projection of the Z-stack. The Poxn-Gal4-9 driver shows a very strong GFP expression in the Poxn expression domains of the brain with some ectopic expression, mainly in the medulla. The enhanced GFP expression combined with the average Z-stack projection produces a clearer image of the arborizations of the Poxn expressing neuronal clusters. (F) The major targets of the projections from the dorsal cluster (dc) of neurons are marked by asterisks. (G) Same specimen as F, but with inverted Z-stack, which offers a posterior view of the GFP expressing neuronal clusters and of the extensive arborizations of the ventral cell cluster (vc) expressing Poxn. The major neurite bundles are marked by arrows and the target areas by asterisks.