Trigeminal sensory neurons sense touch, temperature and pain in the head of vertebrate animals. These neurons are bipolar—they receive sensory information via an elaborate peripheral axon that arborizes extensively under the skin, and transmit that information to the brain through a simple unbranched central axon. They are among the first vertebrate neurons to develop and become functional. Trigeminal neurons are thus faced with the task of rapidly elaborating peripheral axon arbors that blanket the skin with a dense network of fibers, making every part of the head sensitive to touch.

In our previous work, we uncovered a mechanism that limits the extent of trigeminal axon arborization. Using a GFP transgene and a combination of embryological and imaging techniques, we showed that developing trigeminal peripheral axons repel one another. These repulsive interactions allow the partitioning of the epidermis and thus impose an orderly functional organization to the peripheral sensory system. In the absence of competition, trigeminal sensory neurons appear to have an unlimited capacity for growth—a single isolated neuron that lacks neighbors is capable of growing and arborizing to encompass the entire head. These results suggest a simple model for the control of peripheral sensory neuron arborization, in which neurons need only be endowed with two properties: an undirected drive to grow and branch, and a requirement to stop when another neuron is encountered. This strategy can create a highly organized and efficient system of sensory fiber innervation throughout the epidermis. Thus, only one simple rule is required to create order out of a chaotic process.

Our results raise more questions and make possible new avenues for research that will occupy us for the next few years. Click on the links to the left to find out more about four specific projects we have initiated or plan to develop in the near future.