Ectopic expression of Hr39^GS9939 driven by Scer\GAL4^Tab2-201Y in developing γ neurons blocks pruning. Although some γ neurons seem pruned normally, 100% of the mushroom bodies predominantly display γ neurons that retain their larval characteristics. In mutant neuroblast clones, there is a mixture of unpruned and apparently pruned &gr; neurons. Similarly, in two-cell mutant clones, two mutant neurons are clearly unpruned whereas two others appear normal. Only γ neurons appear affected by Hr39^GS9939 ectopic expression in adult mushroom body neurons.