Single C4 da neurons homozygous for Dscam118, exhibit markedly reduced presynaptic arbor growth.
Dscam118/Dscam118 late pupal MB neuron clones exhibit abnormal additional axon branches and failure in the segregation of sister branches.
Adult single-cell Dscam18 clones of DL-1 PNs exhibit reduced dendritic elaboration in the DL-1 glomeruli and reduced axon arborization in the mushroom body calyces and lateral horns.
Single cell clones of mushroom body α/β neurons that are homozygous for Dscam18 show axon branching defects, such as lack of segregation of sister branches (35%) and generation of additional branches at the bifurcation points (42%).
When homozygous somatic clones are made in the mushroom body neuroblasts, normal looking γ lobes are seen, but the α/β lobes are abnormal. Being much thicker and denser than in wild-type clones, the core α/β lobes seem to be composed of many more axons. But unlike wild-type α/β axons, most mutant core α/β processes appear to fail to reach the ends of the lobes. Because no change in the number of cell bodies can be detected, the morphological changes observed in mutant bundles imply that individual α/β axons acquire supernumerary but short-ending branches in mutant clones. In addition, dramatic changes in the configuration of the α/β lobes are observed in 38% of mutant neuroblast clones. Instead of bifurcating axons at a right angle, these mutant clones project all of their α/β axons only in one direction, either dorsal or medially. These processes can exist as two distinct bundles running side by side, or can be fasciculated into a single bundle. In about 20% of clones, differences in the thickness of then axon bundles exist between the dorsal and medial fascicles. These clones also have a non cell-autonomous effect on axon guidance: When the mutant core α/β lobes extend as two distinct bundles side by side, all the wild-type α/β axons are seen to project in the same direction as mutant ones. Consistent abnormalities are observed in the projections of both α/β and α'/β' axons. If clones are induced around mid 3rd instar stage, changes in the α/β lobe configuration are found when mutant clones contain γ axons. If clones are induced after initiation of α'/β' neuron production, normal organisation of α/β lobes is observed despite uneven segregation of axonal branches. When single cell clones are made in the γ neuron, they are indistinguishable from wild-type. However mutant α'/β' and α/β axons develop abnormalities in the axon branching and projecting patterns. Axons often give rise to supernumerary branches which branch towards the termini of Mushroom body clones. In addition, these extra branches still acquire their cell type-specific morphological features, and mutant α/β axons are never incorporated into the α', β' or γ lobes. Individual neurons sometimes fail to send processes into both dorsal and medial lobes. All mutant α/β axons, when examined as isolated single axons in neuroblast clones yield multiple branches that extend randomly into the accessible lobes. Each individual axon frequently sens most or all of their supernumerary branches into only one of the lobes. In addition the multifurcation of mutant axons at the original branching point persists even when the α/β fascicle is not bifurcated. When single cell clones are made in the ellipsoid body, mutant neurons fail to elaborate their axon projections within the ellipsoid body despite normal initial pathfinding.