Neuron dendrite branching is carefully controlled to build a complex nervous system. Using Drosophila sensory neurons as a model, we previously described a network of class-specific and regional transcription factors that define dendrite arbor shape. We have now investigated the genetic pathways controlled by these factors. Our analysis reveals a transcriptional-effector system for dendrite complexity based on the selection and orientation of microtubule nucleation sites. This mechanism has surprising parallels to the nucleation of the mitotic spindle in dividing cells. We also have developed time-lapse microscopy of branching dendrites in vivo followed by automated computer vision analysis. With this we carried out a live-imaging based genetic screen. Isolated from this screen, we find that the atypical myosin (MyosinVI) creates actin tracks within the dendritic growth cone that guide microtubule growth into nascent branches. These two new findings converge to emphasize how the nucleation and orientation of dendrite microtubule growth regulates branching.