The Molecular Architecture of Axons in Health and Disease

Project Summary Action potential initiation and propagation in myelinated axons requires high densities of ion channels clustered at axon initial segments (AIS), nodes of Ranvier, and a robust axonal cytoskeleton to help axons resist mechanicial injury. AIS also function to maintain neuronal polarity and regulate the distinction between axonal and somatodendritic domains. Unfortunately, disruption of these domains and the cytoskeleton during disease or after injury dramatically impairs nervous system function. Furthermore, the molecular mechanisms that control the assembly, function, and maintenance of AIS, nodes, and axonal cytoskeleton remain poorly understood. Since any therapeutic approach aimed at nervous system repair or regeneration must include the reassembly or preservation of axons, AIS and nodes of Ranvier, a detailed mechanistic understanding of their structure, mechanisms of assembly, and composition is urgently needed. To this end we developed proteomic approaches to perform a molecular dissection of AIS and nodes of Ranvier; these experiments will yield AIS and node 'interactomes.' To determine the functions of identified proteins we will perform rigorous gain and loss of function studies using modern molecular, imaging, genetic, and electrophysiological methods. Building on our previous research accomplishments and our discovery that mechanisms of node assembly converge on ankyrin and spectrin cytoskeletons, we will also determine the functions of these enigmatic, yet essential, cytoskeletal proteins using conditional knockout mouse models that we have developed. Together, we expect these studies to reveal key molecular mechanisms responsible for the assembly, maintenance, and function of axons. These discoveries may reveal targets and mechanisms that can be used for therapies to repair or preserve axon function.