Besides their shared mechanisms, MB axon pruning and da neuron dendrite pruning also employ distinct mechanisms. In addition, the ubiquitin-proteosome system and caspases play crucial roles in both axon and dendrite pruning, and a few ubiquitylating enzymes and components of the proteasome involved in axon and/or dendrite pruning have been identified ( Kuo et al., 2005 Watts et al., 2003 Kuo et al., 2006 Rumpf et al., 2011 Williams et al., 2006 Wong et al., 2013). EcRB1 promotes axon and dendrite pruning in part by activating Sox14 ( Kirilly et al., 2009). In the MB, TGF-β signaling together with the immunoglobulin protein Plum activates the expression of EcRB1 at early pupal stages ( Zheng et al., 2003 Yu et al., 2013). At the molecular level, both axon and dendrite pruning require ecdysone receptor B1 (EcRB1) and its co-receptor Ultraspiracle (Usp) ( Lee et al., 2000 Kuo et al., 2005). Recent studies also reveal that pruning of MB axons and da neuron dendrites involves endocytosis ( Zhang et al., 2014 Issman-Zecharya and Schuldiner, 2014) and a transient increase in calcium influx ( Kanamori et al., 2013).
Dendrite pruning series#
At the cellular level, both axon and dendrite pruning follow a similar series of cellular events, including breakdown of the microtubule and actin cytoskeleton, blebbing and fragmentation of axons/dendrites, and clearance of axon/dendrite fragments by glial or epidermal cells through phagocytosis ( Watts et al., 2003 Lee et al., 2009 Awasaki et al., 2006 Han et al., 2014 Williams and Truman, 2005). Studies in these two types of neuron have begun to reveal cellular processes and molecular mechanisms underlying axon/dendrite pruning. MB γ neurons prune both their larval axons and dendrites, and then re-grow their axons and dendrites in adult-specific patterns ( Lee et al., 1999), whereas c4da neurons only prune and re-grow their dendrites ( Kuo et al., 2005). These neurons undergo drastic remodeling during metamorphosis. In Drosophila, large-scale axon/dendrite pruning has been well characterized in mushroom body (MB) γ neurons in the brain and class IV dendritic arborization (c4da) sensory neurons in the peripheral nervous system ( Yu and Schuldiner, 2014 Kanamori et al., 2015). Thus, our work not only identifies a novel pathway involved in dendrite pruning and a new downstream target of EcRB1 in c4da neurons, but also reveals that JNK and Ecdysone signaling coordinate to promote dendrite pruning. Interestingly, our data show that JNK activity in c4da neurons remains constant from larval to pupal stages but the expression of Fos is specifically activated by ecdysone receptor B1 (EcRB1) at early pupal stages, suggesting that ecdysone signaling provides temporal control of the regulation of dendrite pruning by JNK signaling. We find that loss of JNK or its canonical downstream effectors Jun or Fos led to dendrite-pruning defects in c4da neurons. Here, we have investigated the function of JNK signaling in dendrite pruning using Drosophila class IV dendritic arborization (c4da) neurons as a model.
Developmental pruning of axons and dendrites is crucial for the formation of precise neuronal connections, but the mechanisms underlying developmental pruning are not fully understood.
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