In adults previously entrained under 12h:12h light:dark cycles, the constitutive expression of Hr51^{miRNA.Scer\UAS.a} driven by Scer\GAL4^Pdf.PU, or adulthood-only expression driven by Scer\GAL4¹¹¹⁸ and temporally-controlled by Gal80[ts], leads to a severe decrease in the proportion of circadian rhythmic individuals, despite of insignificant changes in the period, upon shift to constant darkness conditions, as compared to controls.

Flies expressing Hr51^{miRNA.Scer\UAS.a} ubiquitously under the control of Scer\GAL4^αTub84B.PL display abnormal activity patterns in LD conditions (12 hours light: 12 hours dark), and a large majority (94.3%) are arrhythmic in DD conditions (constant darkness). When Hr51^{miRNA.Scer\UAS.a} is expressed in the LNvs (ventral Lateral Neurons) under the control of either Scer\GAL4^P2.4.Pdf or Scer\GAL4¹¹¹⁸ the flies display normal activity patterns in LD, but more than 60% of flies are arrhythmic and 10-20% show complex rhythms. A similar effect is seen when Hr51^{miRNA.Scer\UAS.a} is expressed in all clock neurons under the control of Scer\GAL4^tim.PU. Expression of Hr51^{miRNA.Scer\UAS.a} in the majority of mushroom body neurons under the control of Scer\GAL4^ey-OK107 results in only slight phase delays in LD, but otherwise has no major effects in circadian locomotor rhythms in either LD or DD.

Expression of Hr51^{miRNA.Scer\UAS.a} in LNvs only during adulthood (by restricting expression of Scer\GAL4^P2.4.Pdf during development using Scer\GAL80^ts.αTub84B) results in normal rhythmic behavior in both LD and DD, but the average period of the free-running rhythms is slightly longer than in controls. Flies expressing Hr51^{miRNA.Scer\UAS.a} only during development show normal behavior in LD. The majority of these flies are arrhythmic in DD.

Expression using Scer\GAL4^ey-OK107 results in 100% of mushroom body lobes stopping shortly at the end of peduncle.

Scer\GAL4^ey-OK107-mediated expression of Hr51^{miRNA.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\GAL4^ey-OK107-mediated expression of Hr51^{miRNA.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\GAL4^ey-OK107 Hr51^{miRNA.Scer\UAS.a} mid-third instar larvae are grossly normal, although 12% have thinner dorsal lobes.

Scer\GAL4^ey-OK107 Hr51^{miRNA.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 Hr51^{miRNA.Scer\UAS.a} in mature larval gamma neurons using Scer\GAL4^Tab2-201Y results in missing adult gamma lobes despite presence of other mushroom body lobes. Pruning of the larval-specific gamma lobes occurs normally.

Expression of Hr51^{miRNA.Scer\UAS.a} in most, if not all, post-mitotic mushroom body neurons using Scer\GAL4^Mef2.247 results in selective loss of the adult gamma lobe.

Expression of Hr51^{miRNA.Scer\UAS.a} in newborn neurons using Scer\GAL4^ase.neuro does not affect larval gamma axon projections but drastically arrests the nascent alpha'/beta' or alpha/beta axon bundles around the peduncle.

Scer\GAL4^ey-OK107-mediated induction of Hr51^{miRNA.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\GAL4^ey-OK107 Hr51^{miRNA.Scer\UAS.a} mushroom bodies wander around in the ball-like truncated lobes, often making unusual back turns or loops.

Single Scer\GAL4^ey-OK107 Hr51^{miRNA.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\GAL4^ey-OK107 Hr51^{miRNA.Scer\UAS.a} mushroom bodies show ectopic Fas2-positive axon bundles extending through the calyx into abnormal targets rather than migrating along the peduncle.