Scer\GAL4ey-OK107-mediated expression of Hr51miRNA.Scer\UAS.a results in loss of the five adult mushroom body-characteristic axon lobes in all cases. Instead, a ball-like structure is present around the end of the peduncle. The mushroom bodies were otherwise grossly normal. Scer\GAL4ey-OK107-mediated expression of Hr51miRNA.Scer\UAS.a in a Df(2R)ED2426/+ background does not affect the severity of this mushroom body axonal lobe defect.
Most mushroom bodies of Scer\GAL4ey-OK107 Hr51miRNA.Scer\UAS.a mid-third instar larvae are grossly normal, although 12% have thinner dorsal lobes.
Scer\GAL4ey-OK107 Hr51miRNA.Scer\UAS.a mushroom bodies display no obvious morphological defect at 6 hr APF. By contrast, at 18 hr APF when the larval gamma lobes are largely pruned, alpha'/beta' lobes do not exist. At 24 hr APF, no axon extends beyond the peduncle end, indicating defects in both gamma axon re-extension and alpha/beta bundle formation. By 48 hr APF, instead of seeing all five mushroom body lobes, a ball-like structure bulges around the terminus of the peduncle - axons elaborate locally but fail to project into discrete domains.
Expression of Hr51miRNA.Scer\UAS.a in mature larval gamma neurons using Scer\GAL4Tab2-201Y results in missing adult gamma lobes despite presence of other mushroom body lobes. Pruning of the larval-specific gamma lobes occurs normally.
Expression of Hr51miRNA.Scer\UAS.a in most, if not all, post-mitotic mushroom body neurons using Scer\GAL4Mef2.247 results in selective loss of the adult gamma lobe.
Expression of Hr51miRNA.Scer\UAS.a in newborn neurons using Scer\GAL4ase.neuro does not affect larval gamma axon projections but drastically arrests the nascent alpha'/beta' or alpha/beta axon bundles around the peduncle.
Scer\GAL4ey-OK107-mediated induction of Hr51miRNA.Scer\UAS.a from mid-3rd instar and prior to birth of most alpha'/beta' neurons (using the Scer\GAL80[ts] system) disrupts all mushroom body lobes. In contrast, inducing expression after adult eclosion leaves the gross mushroom body morphology intact. When induced around puparium formation after the production of alpha'/beta' neurons, the alpha'/beta' lobes are grossly normal but the Fas2-positive alpha/beta lobes are malformed.
The axonal processes of flip-out clones in Scer\GAL4ey-OK107 Hr51miRNA.Scer\UAS.a mushroom bodies wander around in the ball-like truncated lobes, often making unusual back turns or loops.
Single Scer\GAL4ey-OK107 Hr51miRNA.Scer\UAS.a gamma neurons (generated by MARCM) exhibit abnormal axon trajectories within grossly normal mushroom bodies. These misguided axons are not stalled at the peduncle end.
About 10% of the strongest Scer\GAL4ey-OK107 Hr51miRNA.Scer\UAS.a mushroom bodies show ectopic Fas2-positive axon bundles extending through the calyx into abnormal targets rather than migrating along the peduncle.