Axonal transport of tubulin and actin

Axonal transport is responsible for supplying the axonal processes with pro teins that are synthesized in the cell body. Among the proteins that are mo ved by this mechanism are tubulin and actin, two major components of the cy toskeleton. Observation of the movement of metabolically labeled tubulin an d actin in-vivo has demonstrated that tubulin and actin transport are reduc ed in various diseases and with age, but transport is increased during axon al growth and regeneration. These metabolic studies have also raised questi ons about the underlying mechanisms of slow axonal transport such as: what is the polymerization state of tubulin and actin during transport, what mot ors and tracks are responsible for their movement down the axon, and how ar e the transport motors coupled to tubulin and actin during transport ? Sinc e experiments using metabolically labeled tubulin and actin have not effect ively addressed these questions, a variety of new in-vitro fluorescent micr oscopy techniques have been devised to investigate these questions. These f luorescent microscopy experiments have suggested that tubulin can be transp orted in the unpolymerized soluble state and that such transport of soluble tubulin relies on the presence of formed microtubule tracks. It is not yet known what motor or motors are responsible for tubulin or actin transport in axons or how such a motor(s) might be coupled to such an abundant solubl e cargo.