Editors' ChoiceNeuroscience

Pruning Dendrites with Calcium

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Sci. Signal.  25 Jun 2013:
Vol. 6, Issue 281, pp. ec142
DOI: 10.1126/scisignal.2004441

Highly branched dendritic trees form during neural development and subsequently undergo selective pruning to establish proper connectivity. Kanamori et al. report that transient calcium (Ca2+) waves localized to specific dendrites occurred before pruning during maturation of a subset of sensory neurons in Drosophila melanogaster pupae. The authors visualized changes in Ca2+ concentration in intact pupae using a fluorescent Ca2+ indicator and observed Ca2+ transients in groups of dendrites, but not in axons or cell bodies, before dendrite severing and fragmentation. The Ca2+ waves were not coordinated between different groups of dendrites, and dendrites were pruned in the same temporal order in which the Ca2+ transients appeared: Dendrites with the earliest Ca2+ transients were pruned first, followed by dendrites that initiated Ca2+ waves later. The formation of Ca2+ transients correlated with increased dendrite excitability before pruning, and voltage-gated Ca2+ channels (VGCCs) were required for Ca2+ influx and efficient pruning. Normal pruning required the Ca2+-activated protease calpain. Whereas animals individually heterozygous for loss-of-function mutations in genes encoding a VGCC β subunit, calpainA, or calpainB exhibited normal pruning, triple heterozygotes showed impaired pruning. Thus, the authors proposed that localized increases in dendrite excitability produce Ca2+ transients that initiate dendrite death through compartmentalized activation of calpain.

T. Kanamori, M. I. Kanai, Y. Dairyo, K.-i. Yasunaga, R. K. Morikawa, K. Emoto, Compartmentalized calcium transients trigger dendrite pruning in Drosophila sensory neurons. Science 340, 1475–1478 (2013). [Abstract] [Full Text]