A60, an Axonal Membrane-Skeletal Spectrin-Binding Protein

A60 is a 60 kDa protein which is associated with the axonal cortical cytoskeleton in adult central nervous system neurons. It was originally defined by the use of a monoclonal antibody which showed that it was closely associated with the cytoplasic face of axonal plasma membranes. A60 appears to be neuron-specific and biochemical studies show that it is tightly bound to brain membranes. Affinity chromatography has revealed that A60 interacts with brain spectrin but not with erythrocyte spectrin. As erythrocyte spectrin is closely related to the isotype of spectrin that is localized in dendrites this raises the possibility that A60 is restricted to axons by interaction with the isotype of spectrin that is found in axons. During post-natal cerebellar development (days 1-13) A60 is initially located in the perikarya of precursor Purkinje cells and is then localized in the initial dendrites of these cells as well as in the white matter. In contrast, in the adult cerebellum the location of A60 is exclusively axonal. These data indicate that A60 has a spectrin-binding activity in the adult axonal membrane skeleton which is only required after initial axon growth has occurred. A60 is transiently expressed during embryonic and post-natal development of rat dorsal root ganglia (DRG). It is located in the large light DRG cells but is essentially absent from the small dark DRG cells.