The PI3K Class III Complex Promotes Axon Pruning by Downregulating a Ptc-Derived Signal via Endosome-Lysosomal Degradation

Developmental axon pruning is essential for wiring the mature nervous system, but its regulation remains poorly understood. Here we show that the endosomal-lysosomal pathway regulates developmental pruning of Drosophila mushroom body γ neurons. We demonstrate that the UV radiation resistance-associated gene (UVRAG) functions together with all core components of the phosphatidylinositol 3-kinase class III (PI3K-cIII) complex to promote pruning via the endocytic pathway. By studying several PI(3)P binding proteins, we found that Hrs, a subunit of the ESCRT-0 complex, required for multivesicular body (MVB) maturation, is essential for normal pruning progression. Thus, we hypothesized the existence of an inhibitory signal that needs to be downregulated. Finally, our data suggest that the Hedgehog receptor, Patched, is the source of this inhibitory signal likely functioning in a Smo-independent manner. Taken together, our in vivo study demonstrates that the PI3K-cIII complex is essential for downregulating Patched via the endosomal-lysosomal pathway to execute axon pruning. [Display omitted] •UVRAG and the PI3K-cIII are required for developmental axon pruning•UVRAG is required to generate PI(3)P during normal development•The PI3K-cIII mediates the endosome-lysosomal pathway to promote axon pruning•The endolysosomal pathway downregulates Ptc signaling to prime MB neurons for pruning Issman-Zecharya and Schuldiner find that the endolysosomal pathway is required for developmental axon pruning of mushroom body neurons. The PI3K class III complex is required to downregulate a Patched-derived signal via endolysosomal degradation. Interestingly, it seems that the Patched-derived signal that inhibits pruning is independent of Smoothened and Hedgehog.