We showed that elevation of Ik2 activity during dendrite pruning promotes Ik2/Spindle-F/dynein complex moving along the microtubules. Here, we identified Spindle-F that mediates Ik2-dependent pruning activity in the dendrites by linking Ik2 to the microtubule motor dynein complex. We reasoned that the distinctive microtubule polarity in dendrites and axons might be involved and factors are required to regulate the pruning activity in the dendrites through their interaction with microtubules. Certain Drosophila sensory neurons that undergo dendrite pruning, specifically eliminating the dendrites but leaving the axons intact, provide us an opportunity to study the mechanism of how pruning activity is regulated in the dendrites. Pruning that removes specific parts of neuronal branches without causing cell death is a self-destruct process, thus requiring precise regulation to prevent undesired damage to the nervous systems. In Drosophila, the nervous systems undergo extensive neuronal remodeling during metamorphosis, as many larval neurons die and adult neurons are generated while some larval neurons survive and prune their branches. Our findings reveal a novel regulatory mechanism for dendrite pruning achieved by temporal activation of Ik2 kinase and dynein-mediated redistribution of Ik2/Spn-F complex in neurons. Spn-F is a key component to link Ik2 kinase to dynein motor complex, and the formation of Ik2/Spn-F/dynein complex is critical for Spn-F redistribution and for dendrite pruning. The redistribution of Spn-F from puncta in pupal neurons requires the phosphorylation of Spn-F by Ik2 kinase to decrease Spn-F self-association, and depends on the function of microtubule motor dynein complex. Spn-F exhibits a punctate pattern in larval neurons, whereas these Spn-F puncta become redistributed in pupal neurons, a step that is essential for dendrite pruning. Spn-F acts downstream of IKK-related kinase Ik2 in the same pathway for dendrite pruning. Here, we identify a coiled-coil protein Spindle-F (Spn-F) that is required for dendrite pruning in Drosophila sensory neurons. How these neurons regulate pruning activity in the dendrites remains unknown. During development, certain Drosophila sensory neurons undergo dendrite pruning that selectively eliminates their dendrites but leaves the axons intact.
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