Intrinsic mechanisms to define neuron class-specific dendrite arbor morphology.

The class-specific transcription factors Knot and Cut act during dendrite arbor development to define the characteristic dendrite branching pattern of the Drosophila class IV dendritic arborisation sensory neurons. Knot mediates dendrite arbor outgrowth and branching via a microtubule-based program that includes upregulation of the microtubule severing protein Spastin. On the other hand, Cut promotes dendrite arbor outgrowth and branching through a filamentous-actin based program and additionally promotes filopodia formation. We discuss how differential regulation of the activity of the Rac1 small GTPase by Knot and Cut may underlie some of the different roles these transcription factors play during class-specific dendrite arbor morphogenesis.