CadN^unspecified single R-cell clones show extension defects; 36% of mutant R-cell axons do not extend at all.

Mutant olfactory receptor neurons (ORNs) (generated using the MARCM technique) reach the antennal lobe, project along the periphery in the nerve fiber layer and extend normally through the commissure to the contralateral lobe. However, in contrast to wild type, the mutant ORN axon terminals remain largely on the surface of the antennal lobe, and only a few mutant ORN fibres penetrate the antennal lobe neuropil. There is also severe disruption of the glomerular organisation of the antennal lobe neuropil. Mutant olfactory receptor neurons (ORNs) of particular subclasses (generated using the MARCM technique) typically target to the appropriate region of the antennal lobe (AL) but fail to converge on a single glomerulus. Mutant ORNs of the Or46a-expressing class spread out over the surface of the anterior central region of the AL. Some mutant ORNs of the Or47b-expressing class converge on their appropriate glomeruli while other spread out over the anterior surface of the AL. Mutant ORNs of the Or22a- or Or59c-expressing class spread out over the posterior medial surface of the AL. Mutant ORNs of the Scer\GAL4^GH298-expressing class target to the appropriate glomerulus but do not enter it. Mutant ORNs of the Scer\GAL4^72OK-expressing class spread out over the medial surface of the AL. Studies of mutant ORNs of the Scer\GAL4^72OK-expressing class during development indicates that they do not form protoglomeruli. Mutant olfactory receptor neurons (ORNs) of the Or22a-expressing class branch as in wild type and extend processes to the contralateral side. These contralateral axons largely target the correct region of the AL, but also remain separate, lying above the neuropil and spreading into neighbouring ventral AL regions. Local interneurons (LNs) in animals in which the olfactory receptor neurons are mutant for CadN retain many of the morphological features characteristic of these cells in wild-type animals; they elaborate extensive dendritic fields throughout the antennal lobe neuropil with thickened terminal branches. The projection neuron (PN) dendrites in animals in which the olfactory receptor neurons are mutant for CadN extend processes in localised regions of the antennal lobe (AL) (as occurs in wild type), although in contrast to wild type they often elaborate highly irregular shapes. In addition, PN dendrites in the mosaic animals have poorly defined borders, extend through larger regions of the AL and intermingle with PN dendrites that in wild-type animals innervate different glomeruli.

R1-R6 axons fail to extend out of the ommatidial bundle in the lamina of mosaic flies in which the photoreceptor cells are homozygous. The topographic map of the lamina plexus is severely disrupted. Single homozygous R7 photoreceptor cells in the lamina (induced in a heterozygous background) often fail to terminate at their normal target layer in the medulla. 50% of single homozygous R1-R6 photoreceptor cells in the lamina (induced in a heterozygous background) fail to extend out from the ommatidial bundle before elaborating the presynaptic terminal, producing a presynaptic terminal in an inappropriate position, while the remainder extend normally. The morphology of the presynaptic terminal is only mildly disrupted.