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Neurobiology of Disease �-Internexin Is Structurally and Functionally Associated with the Neurofilament Triplet Proteins in the Mature CNS

By Aidong Yuan, Mala V. Rao, Takahiro Sasaki, Yuanxin Chen, Asok Kumar, Ronald K. H. Liem, Joel Eyer, Alan C. Peterson, Jean-pierre Julien and Ralph A. Nixon


�-Internexin, a neuronal intermediate filament protein implicated in neurodegenerative disease, coexists with the neurofilament (NF) triplet proteins (NF-L, NF-M, and NF-H) but has an unknown function. The earlier peak expression of �-internexin than the triplet during brain development and its ability to form homopolymers, unlike the triplet, which are obligate heteropolymers, have supported a widely held view that �-internexin and neurofilament triplet form separate filament systems. Here, we demonstrate, however, that despite a postnatal decline in expression, �-internexin is as abundant as the triplet in the adult CNS and exists in a relatively fixed stoichiometry with these subunits. �-Internexin exhibits transport and turnover rates identical to those of triplet proteins in optic axons and colocalizes with NF-M on single neurofilaments by immunogold electron microscopy. �-Internexin also coassembles with all three neurofilament proteins into a single network of filaments in quadruple-transfected SW13vim(�) cells. Genetically deleting NF-M alone or together with NF-H in mice dramatically reduces �-internexin transport and content in axons throughout the CNS. Moreover, deleting �-internexi

Year: 2013
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