Polycomb group genes are required for neuronal pruning in Drosophila

Abstract

Background Pruning that selectively eliminates unnecessary or incorrect neurites is required for proper wiring of the mature nervous system. During Drosophila metamorphosis, dendritic arbourization sensory neurons (ddaCs) and mushroom body (MB) γ neurons can selectively prune their larval dendrites and/or axons in response to the steroid hormone ecdysone. An ecdysone-induced transcriptional cascade plays a key role in initiating neuronal pruning. However, how downstream components of ecdysone signalling are induced remains not entirely understood. Results Here, we identify that Scm, a component of Polycomb group (PcG) complexes, is required for dendrite pruning of ddaC neurons. We show that two PcG complexes, PRC1 and PRC2, are important for dendrite pruning. Interestingly, depletion of PRC1 strongly enhances ectopic expression of Abdominal B (Abd-B) and Sex combs reduced, whereas loss of PRC2 causes mild upregulation of Ultrabithorax and Abdominal A in ddaC neurons. Among these Hox genes, overexpression of Abd-B causes the most severe pruning defects, suggesting its dominant effect. Knockdown of the core PRC1 component Polyhomeotic (Ph) or Abd-B overexpression selectively downregulates Mical expression, thereby inhibiting ecdysone signalling. Finally, Ph is also required for axon pruning and Abd-B silencing in MB γ neurons, indicating a conserved function of PRC1 in two types of pruning. Conclusions This study demonstrates important roles of PcG and Hox genes in regulating ecdysone signalling and neuronal pruning in Drosophila. Moreover, our findings suggest a non-canonical and PRC2-independent role of PRC1 in Hox gene silencing during neuronal pruning.

Recent progress in dendritic pruning of Drosophila C4da sensory neurons

“…Polycomb group (PcG) proteins are key chromatin modulators that keep lineage-inappropriate genes repressed and are thereby essential for the determination of a cell’s destiny [ 2 ]. Recent research shows that PcG and Hox genes play a crucial role in modulating ecdysone signaling and dendrite pruning in C4da neurons [ 60 ]. Polycomb repressive complex-1 and-2 (PRC1 and PRC2) are two PcG complexes [ 10 , 61 ], the core PRC1 component Polyhomeotic (Ph) selectively promotes Mical expression might partially by silencing the Hox gene abdominal B ( abd-B ) [ 60 ].…”

“…Recent research shows that PcG and Hox genes play a crucial role in modulating ecdysone signaling and dendrite pruning in C4da neurons [ 60 ]. Polycomb repressive complex-1 and-2 (PRC1 and PRC2) are two PcG complexes [ 10 , 61 ], the core PRC1 component Polyhomeotic (Ph) selectively promotes Mical expression might partially by silencing the Hox gene abdominal B ( abd-B ) [ 60 ]. Nevertheless, further research is needed to identify the other downstream target genes of PcG proteins involved in the regulation of dendritic pruning.…”