Regulation of dendrite growth, placement, and patterning in Drosophila melanogaster class 4 dendrite arborization neurons

Abstract

The directional flow of information in neurons depends on compartmentalization: dendrites receive inputs whereas axons transmit them. Axons and dendrites likewise contain structurally and functionally distinct subcompartments. Axon/dendrite compartmentalization can be attributed to neuronal polarization, but the developmental origin of subcompartments in axons and dendrites is less well understood. To identify the developmental bases for compartment-specific patterning in dendrites, we screened for mutations that affect discrete dendritic domains in Drosophila sensory neurons. From this screen, we identified mutations that affected distinct aspects of terminal dendrite development with little or no effect on major dendrite patterning. Mutations in tubulin assembly proteins including Tubulin specific chaperone C showed a phenotype that was preferentially affecting the terminal dendrite placement to be shifted towards the soma via controlling compartmentalization specific growth. We performed a detailed analysis of tubulin dynamics to establish a profile of developmental regulation in tubulin cytoskeleton in subcompartments of the dendritic arbor, and we suggest Tbcc as a local, positive regulator of growth in terminal dendrites. Mutation of another gene, raw, affected multiple aspects of terminal dendrite patterning, suggesting that Raw might coordinate multiple signaling pathways to shape terminal dendrite growth. Consistent with this notion, Raw localizes to branch-points and promotes dendrite stabilization together with the Tricornered (Trc) kinase via effects on cell adhesion. Raw independently influences terminal dendrite elongation through a mechanism that involves modulation of the cytoskeleton, and this pathway is likely to involve the RNA-binding protein Argonaute 1 (AGO1), as raw and AGO1 genetically interact to promote terminal dendrite growth but not adhesion. Thus, Raw defines a potential point of convergence in distinct pathways shaping terminal dendrite patterning.