Reciprocal localization of Nod and kinesin fusion proteins indicates microtubule polarity in the Drosophila oocyte, epithelium, neuron and muscle. Larvae were further immobilized by pressing a cover slip on top of two lines of vacuum grease spacers flanking the animal. The NudE C-terminus is not required for dendrite branching Next, we sought to determine whether we could identify which domains of NudE are crucial for its activity in dendrite growth and branching. These results suggest that NudE specifically regulates the polarity of axonal, but not dendritic, microtubules and that NudE has a role in modulating microtubule dynamics in both compartments. Ndel1-derived peptides modulate bidirectional transport of injected beads in the squid giant axon. Confocal optical sectioning revealed that these fine branches were indeed derived from the axons and were not just dendrite branches that bundled with the axons data not shown.
The fly dendritic arborization da neurons that we employ as a model do not migrate, which enables us to clearly analyze whether NudE has a role in establishing the mature structure of a neuron.
Dendrite arborization requires the dynein cofactor NudE
Cortical dynein controls microtubule dynamics to generate pulling forces that position microtubule asters. Moreover, although the orientation of the dendritic microtubules is similar to that of wild type, axonal microtubules are no longer organized in a uniform plus-end-distal array; instead, they display a mixed polarity in the absence of NudE. Mixed microtubules steer dynein-driven cargo transport into dendrites. These results suggest that NudE specifically regulates the polarity of axonal, but not dendritic, microtubules and that NudE has a role in modulating microtubule dynamics in both compartments. Our data support a model in which NudE promotes dendrite growth and branching by facilitating an interaction between dynein and Lis1, another key dynein cofactor that frequently interacts with NudE and dynein as part of a tripartite complex.