DESCRIPTION: The general aim of this project is to test the hypothesis that movement of neurofilaments relative to microtubules can be achieved by an ATP-dependent molecule linked to the neurofilament and moving along the microtubules. Neurofilaments are the most abundant intermediate filament type expressed in neurons and are characterized by long sidearm extensions orthogonal to the filament axis that are thought to link neurofilaments to microtubules and other intracellular structures. Neurofilaments in vivo are presumed to provide mechanical stability to the neuron by forming a viscoelastic network characterized by higher resistance to mechanical stress than provided by other cytoskeletal polymers. A second potential cellular function of neurofilaments is to facilitate or organize transport of materials, including microtubules, through the neuron, especially during the slow axonal transport required for neuronal growth, differentiation, and function. The molecular mechanism of slow axonal transport is unknown, but neurofilaments, microtubules, and the microtubule motor dynein are all implicated in this process. This proposal combines in vitro biophysical, biochemical, and cell biologic studies to characterize a novel form of motility in which individual neurofilaments move along microtubules by a mechanism involving cytoplasmic dynein and perhaps other motor proteins. Since dysfunction or loss of neurofilaments is associated with several neuronal pathologies such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy, and neurodegeneration with aging, these studies may reveal molecular interactions that can be targets for neuronal disease prevention or therapy.