Résumé :
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Mutations in the gene encoding gigaxonin are causative for the fatal, early-onset recessive neurodegenerative disorder Giant Axonal Neuropathy (GAN). The crucial role of gigaxonin in neuronal maintenance, first assessed by alterations in the motor/sensory tracts of the peripheral nervous system and the impairment of the central nervous systems was subsequently confirmed in the GAN mouse model. Characterized by a generalized aggregation of Intermediate Filaments (IFs), GAN points to the essential role of cytoskeleton architecture in neuronal function, and especially to the implication of IF disorganization in neurodegeneration. Identification of gigaxonin as the substrate adaptor of a new Cul3-ubiquitin ligase E3 and three of its partners (the microtubule associated proteins MAP1B, MAP8 and the tubulin chaperone TBCB) allows now to dissect the mechanisms of neurodegeneration and IFs organization in GAN. We studied here cellular models of GAN A) to develop an alternative diagnostic tool (to nerve biopsies) for GAN patients and B) to assess the role of microtubules (MTS) and tubulin chaperones in IF aggregation. A) Using our new gigaxonin specific monoclonal antibodies and protein extracts from lymphoblast cell lines derived from GAN patients, multiple disease causing mutants are shown to be unstable, demonstrating that GAN is caused by the loss of function of gigaxonin. B) We assessed the implication of MTs and tubulin chaperones in vimentin organization in transfection experiments but also in the GAN cellular model: the patients’s skin derived primary fibroblasts. This allowed us to demonstrate that neither MTs instability nor TBCB overabundance are able to reproduce the vimentin aggregates so characteristic of GAN patients.
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