Our studies focus on the cellular and molecular mechanisms underlying the specification of neuronal identity, growth cone motility and navigation, target selection and the generation of neuronal arbors. We work with identified neurons in the medicinal leech, Hirudo medicinalis, a system that has several advantages for our studies. First, we can study a particular neuron at all stages of development, in the animal; second, we can visualize many cells in the intact animal as they differentiate, using time-lapse 2-photon confocal imaging, and operate on them with a laser microbeam to ask very specific questions; and third, we can inject macromolecules into embryonic or adult neurons, which means that we can transform a single cell in a wild-type environment.