Brain spectrin(240/235A): a novel astrocyte specific spectrin isoform.

We have previously demonstrated the existence of two distinct isoforms of spectrin in mammalian brain (23). Brain spectrin(240/235) is found primarily in neuronal axons and presynaptic terminals, and brain spectrin(240/235E) is located in neuronal cell bodies, dendrites and postsynaptic terminals, and oligodendrocytes. These isoforms are thought to play important roles in controlling the early events of synaptic transmission, axonal transport of organelles and vesicles, and lateral mobility of integral membrane proteins. In this study, we have utilized a panel of monoclonal antibodies to identify a novel astrocyte specific isoform(240/235A) with subunits of 240 kDa and 235 kDa in a 1:1 ratio. Double label indirect immunofluorescence has indicated that brain spectrin (240/235A) is distinct from brain spectrin (240/235E). This novel isoform located in the soma and processes of astrocytes may play a role in actin-membrane attachment, cellular architecture, strengthening of the membrane fabric, and translocation of cytoplasmic organelles and vesicles.

Brain spectrin(240/235) and brain spectrin(240/235E): conservation of structure and location within mammalian neural tissue.

We demonstrate that the brain spectrin isoforms (240/235) and (240/235E) are present in all mammalian species studied (human, bovine, mouse, and rat). Immunohistochemistry with a panel of eleven polyclonal antibodies have indicated an identical localization of the brain spectrin isoforms in all mammalian species. Brain spectrin(240/235) is found primarily in axons, and brain spectrin(240/235E) primarily in cell bodies and dendrites. Immunoprecipitation and Western blotting studies have indicated that the subunit molecular weights of brain spectrin(240/235) and (240/235E) are identical in all mammalian species. We demonstrate that when proteolysis is not completely blocked during immunoprecipitation studies, the 235 kDa subunits are converted to a 230 kDa polypeptide [brain spectrin(240/235)] and a 232 kDa polypeptide [brain spectrin(240/235E)]. Finally, we show that both the alpha and beta subunits of brain spectrin(240/235) and brain spectrin(240/235E) are antigenically distinct in every species examined. These studies indicate that previous findings on the structure, location, and function of mouse brain spectrin isoforms can now be generalized to all mammalian species.