Slow components of axonal transport: two cytoskeletal networks.

Abstract

Two slowly moving groups of axonally transported proteins in guinea pig retinal ganglion cell axons were identified. The slowest group of proteins, designated slow component a (SCa), has a transport rate of 0.25 mm/d [day] and consists of tubulin and neurofilament protein. The other slowly transported group of proteins, designated slow component b (SCb), has a transport rate of 2-3 mm/d and consists of many polypeptides, one of which is actin. The transport kinetics of the individual polypeptides of SCa and SCb indicate that the polypeptides of SCa are transported coherently in the optic axons, the polypeptides of SCb are also transported coherently but completely separately from the SCa polypeptides and the polypeptides of SCa differ completely from those comprising SCb. Slow axonal transport may represent the movements of structural complexes of proteins. SCa may correspond to the microtubule-neurofilament network, and SCb may represent the transport of the microfilament network together with the proteins complexed with microfilaments.