Lineage and birth date specify motor neuron targeting and dendritic architecture in adult Drosophila

Locomotion in adult Drosophila depends on motor neurons that target a set of multifibered muscles in the appendages. Here, we describe the development of motor neurons in adult Drosophila, focusing on those that target the legs. Leg motor neurons are born from at least 11 neuroblast lineages, but two lineages generate the majority of these cells. Using genetic single-cell labeling methods, we analyze the birth order, muscle targeting, and dendritic arbors for most of the leg motor neurons. Our results reveal that each leg motor neuron is born at a characteristic time of development, from a specific lineage, and has a stereotyped dendritic architecture. Motor axons that target a particular leg segment or muscle have similar dendritic arbors but can derive from different lineages. Thus, although Drosophila uses a lineage-based method to generate leg motor neurons, individual lineages are not dedicated to generate neurons that target a single leg segment or muscle type.