Fig. 2. Time course of ORN axon development. (A) The approach used to label ORNs – the restricted expression of the eyeless-FLP construct generates GFP-labelled cells only in the antennal disc and eye disc/optic lobe, not in the central brain. (B_1-2) Developing antennae at 20 hours APF. (left) GAL4-C155 drives expression of membrane targeted mCD8-GFP (green) in all post-mitotic neurons, whereas a monoclonal anti-Elav antibody stains neuronal nuclei (magenta). (right) An antenna containing MARCM clones generated according to the scheme in (A). Up to half of the cells are randomly labelled. In both cases, the upper group of neurons [second antennal segment (2AS)] are auditory mechanoreceptors of the Johnston's organ, whereas the lower group are the ORNs of the third antennal segment (3AS). (C-F) Time course of ORN invasion of the developing ALs. Note that, at 14 hours APF, no axons touch the lobe (C), whereas, at 16 hours APF (D), axons in the left hemisphere just touch the lobe. C-E are stained for GFP (detecting the mCD8-GFP marker ORN axons, green), N-cadherin (which labels the developing AL in red; an example is outlined in C); In C, nc82 is in blue, whereas, in D and E, blue is FasII (which labels axon tracts). F-H are stained with anti-mCD8 (i.e. the mCD8-GFP marker) and anti-Elav antibody. The developing ALs (C-E) are devoid of Elav staining. Unless indicated otherwise, all images in this and subsequent figures are maximum-intensity z projections of confocal stacks; dorsal is uppermost, with the midline indicated by a dashed white line when within the field of view or located to the left of the panel otherwise.