Schematic representation of the functions of each transcription factor group in dendritic patterning of type I DA neurons in the Drosophila peripheral nervous system. Subtypes of DA neurons have simple and stereotyped branching patterns (the black neuron represents the ddaD subtype and the gray neuron the ddaE subtype). (a) Group A genes fall into two different subgroups. One group (19 genes) promotes overall dendrite outgrowth (left), whereas the other (20 genes) inhibits overall outgrowth (right). (b) Group B also includes genes with opposing functions. Most of this group (19 genes) promote dendritic branching and inhibit primary dendrite extension (left). The other two members inhibit dendritic branching and promote primary dendrite extension (right). (c) Group C genes (10 genes) influence the routing, or direction of growth, of dendrites. The normal branching pattern is shown on the left. The abnormal routing of dendrite lateral branches observed when a group C gene is downregulated is shown on the right.