Dendrites and axons show extremely diverse forms, with important implications for nervous system wiring and neuronal function. How neurons acquire their morphology is a question of great importance for understanding neuronal development and regeneration. In this project, we will explore how the innervation of the epidermis, the major sensory organ for detecting mechanical stimuli, is achieved during embryogenesis. Specifically, we will study the development of the sensory cells that respond to pressure (P) on the skin of the medicinal leech, which are uniquely advantageous for this project because their large size and small number. Their sensory arbors innervate domains (“tiles”) that are organized in very regular patterns. Hence, it is easy to detect morphological changes produced experimentally. Moreover, following crush or axotomy these neurons can regenerate their branches and synaptic connections. Previous work showed that cell-cell interactions are fundamental for setting up sensory tiling. Our preliminary results indicate that molecular cues, such as the axon guidance cue netrin, which are heterogeneously distributed in the skin, play a key role in setting up sensory tiling. The overall goal of this proposal is to formulate a new developmental scheme for sensory neurons and to implement it to promote reinnervation of transplanted skin post trauma. In the proposed study, we will modulate the expression of factors, such as leech netrin, using a novel technology that enables the delivery of reagents into live tissue accurately. The technology, a pneumatic capillary gene gun, has been recently developed at UCSD (the P.I. with colleagues) and will be brought into the lab for the proposed project. We will affect gene expression in individual cells or in small groups of cells in skin to manipulate neuronal growth. We expect that our results on the leech will illuminate the phenomenon of sensory tiling in other systems, including vertebrates.