velo^LL05209 mutants exhibit projection neuron dendrite targeting defects.

velo^LL05209 mutant neuroblast clones exhibit several defects. First, the number of neurons is reduced from an average of 35 ad projection neurons in wild-type to 5 neurons in velo^LL05209 mutant clones. Second, the overall dendritic mass is reduced and disorganised. Third, dendrites aberrantly innervate the wrong glomeruli within the antennal lobe, or ectopically project outside the antennal lobe.

velo^LL05209 mutant dorsolateral glomerulus DL1 neurons exhibit various dendrite mistargeting defects in the antennal lobe. In adults, these phenotypes can be grouped into five distinct phenotypic classes. In class 1, dendrites innervated DL1 sparsely by spill over into incorrect adjacent areas. In class 2, dendrites are found in the dorsolateral region of the antennal lobe, but excluded from the DL1 glomerulus. Class 3 mutant DL1 projection neurons project to ventromedial regions in the antennal lobe, preferably but not exclusively to the VM6 or VC3 glomeruli. Class 4 mutant DL1 projection neurons mistarget their dendrites outside the antennal lobe mostly into the subesophageal ganglion. Class 5 mutant dendrites innervate multiple glomeruli within the antennal lobe. In 96% of velo^LL05209 mutant DL1 axons 2 or fewer collaterals innervate the mushroom body calyx. In 78% of velo^LL05209 mutant axons the dorsal branch is missing.

velo^LL05209 mutant DL1 projection neurons exhibit defects in axon morphology. Axons extend as wild-type and always reach the end of the lateral horn, but only form 0-2 collaterals in the mushroom body calyx, and often have a missing or shorter dorsal branch in the lateral horn. These axonal phenotypes are independent of the phenotypic class of dendrite mistargeting.

Approximately 38% of velo^LL05209 DL1 projection neurons exhibit ventromedially mistargeted dendrites.