Editors' ChoiceNeuroscience

Pruning a Dendritic Tree

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Science's STKE  03 Oct 2006:
Vol. 2006, Issue 355, pp. tw338
DOI: 10.1126/stke.3552006tw338

During development, the dendritic arborization undergoes pruning to eliminate unnecessary or inappropriate processes. Noting that dendritic pruning of the Drosophila dendritic arborizing sensory neuron ddaC during metamorphosis resembled apoptosis in some respects (including fragmentation and clearance of cellular debris by phagocytes), Williams et al. looked to see whether components of the apoptotic machinery played a role. ddaC pruning was suppressed in flies lacking functional Drosophila Nedd2-like caspase (DRONC, which is the only initiator caspase required for apoptosis in flies) and when dominant-negative forms of DRONC were selectively expressed in ddaC. Overexpression of Drosophila inhibitor of apoptosis protein 1 (DIAP1), which inhibits DRONC, or of p35, which inhibits effector caspases, suppressed the removal of dendritic branches. Expression of HID (head involution defective) in ddaC, which antagonizes DIAP1 and is therefore proapoptotic, elicited cell death. A probe for caspase activity (consisting of the mouse CD8 extracellular and transmembrane domain, fused to a portion of the caspase substrate PARP fused to a fluorescent protein) revealed that caspase activity was confined to the dendrites of ddaC undergoing pruning, whereas HID expression elicited caspase activity throughout the cell. Experiments in which engulfment was suppressed suggested that caspase activation took place after dendritic branches had been severed. Thus, dendritic pruning of ddaC during Drosophila metamorphosis appears to depend on localized activation of caspases within dendrites.

D. W. Williams, S. Kondo, A. Krzyzanowska, Y. Hiromi, J. W. Truman, Local caspase activity directs engulfment of dendrites during pruning. Nat. Neurosci. 9, 1234-1236 (2006). [PubMed]

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