Enrichment of voltage-gated sodium channels to nodes of Ranvier is vital for the proper conductance of the nerve impulse in a saltatory manner. While myelination and the interaction of glia with axons facilitates the segregation of ion channels within specific subcellular axonal domains, the exact mechanisms governing the formation, organization and maintenance of the node are elusive. Recently, a group of cell adhesions molecules, known as Neurofascins (Nfasc), have been implicated in the coordination and stabilization of axonal domains. Two major isoforms have been characterized and are shown to be spatio-temporally regulated during development. NfascNF155 (NF155) is expressed specifically in glia within the paranodal myelin loops, while NfascNF186 (NF186), is enriched at the nodes of Ranvier and expressed specifically in neurons. Genetic ablation of Nfasc in mice resulted in the absolute disorganization of axonal domains (the node, paranode, and juxtaparanode), loss of both isoforms, and death at postnatal day 7, which has significantly hindered the examination of the individual roles of each isoform in nodal development, coordination, and stabilization. In this proposal, we seek to use a combination of genetic, cell biological, physiological and biochemical methods to determine the specific role of NF186 in nodal formation and the role of Nfascs during long-term axonal domain organization, axonal integrity and axonal function.
Our specific aims are to: 1. Determine the role of NF86 during nodal biogenesis and development. 2. Determine the role of NF186 in the long-term maintenance and stabilization of axonal domains. 3. Determine whether loss of neurofascins in adults results in axonal degeneration.
The recent implication of Neurofascins in disease progression and pathology in demyelinating diseases, such as multiple sclerosis, has brought considerable focus towards the elucidation of their functions during axonal domain organization, axonal stability and axonal function. The studies proposed here will help to provide considerable insight into the individual and collective functions of Neurofascins to nodal formation and stabilization, as well as overall axonal domain organization and stability. It is likely that these studies will contribute towards the future development of therapeutic strategies that will allow for the treatment of afflicted individuals, through the restoration of the intimate relationship between axons and glia.
