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.