Delivery to nerve terminals of cytoskeletal proteins synthesized in the cell body is crucial for growth, maintenance and regeneration of neurons. Important questions about this slow transport are by what motors and in what forms are proteins are transported. The movements of fluorescent labeled cytoskeletal proteins injected into the squid giant axon were examined by confocal microscopy. A novel finding is that there is diffusion of these proteins simultaneous with the expected energy dependent movements. Inhibiting the molecular motors: myosin, kinesin, and dynein as well as disrupting specific cytoskeletal tracts pharmacologically, or with a newly developed 2-photon lesioning technique, has begun to elucidate which motors and tracts are responsible for slow transport of axonal proteins. Binding coefficients of proteins within the transport complex are also under investigation. In addition to studying transport, supplemental work on one particular motor, myosin, has shown that it is responsible for the purse-string constriction of the axons that follows axonal transection. Because of this role, as well as its possible role in some aspects of slow transport, the myosins in the giant axon have been sequenced and characterized to produce probes for functional studies.
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