Alpha-Internexin: The Fourth Subunit of Neurofilaments in the Mature CNS

Abstract

Because α-internexin is expressed in embryonic brain and can form homopolymers in vitro, it was originally considered to be an independent filament system critical mainly during brain development and distinct from that assembled in neurons from neurofilament (NF) triplet proteins. Analysis of mice engineered to eliminate individual or different combinations of NF triplet or α-internexin has proved that α-internexin and NF proteins are constituents of the same NF and functionally interdependent. α-Internexin satisfies all criteria previously used to establish the NF triplet proteins as subunits of a single intermediate filament and can now be considered to be a fourth subunit of NF in the adult CNS. Its role as a subunit of CNS NF explains the close relationship of α-internexin with the pathology of CNS diseases associated with NF accumulation.