Disruption of the PAR3/INSC/LGN complex causes microtubule instability and peripheral neuropathy

PAR3/INSC/LGN form an evolutionarily conserved complex required for asymmetric cell division in the developing brain, but its post-developmental function and disease relevance in the peripheral nervous system (PNS) remains unknown. We mapped a new locus for axonal Charcot-Marie-Tooth disease (CMT2) and identified a missense mutation c.209T>G (p.Met70Arg) in the INSC ( INSC ) gene. Modelling the INSCM70R variant in Drosophila , we showed that it caused proprioceptive defects in adult flies, leading to gait defects resembling those in CMT2 patients. Cellularly, PAR3/INSC/LGN dysfunction caused tubulin aggregation and necrotic neurodegeneration, with microtubule-stabilizing agents rescuing both morphological and functional defects of the INSCM70R mutation in the PNS. Our findings underscore the critical role of the PAR3/INSC/LGN machinery in the adult PNS and highlights a potential therapeutic target for INSC-associated CMT2. One-Sentence Summary PAR3/INSC/LGN dysfunction causes peripheral neuropathy and is potentially treatable by stabilizing the microtubule network. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by grants from the National Science and Technology Council of Taiwan (111-2320-B-002-049-MY3 and 112-2314-B-002-016 to C.-C.C;109-2314-B-075-044-MY3 and 112-2314-B-075-034-MY3 to Y.-C.L), National Health Research Institutes (EX112-11228NI to C.-C.C), National Taiwan University (112L895403), and Brain Research Center, National Yang Ming Chiao Tung University from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: the study was approved by the Institutional Review Board of Taipei Veterans General Hospital, Taiwan (TPEVGH IRB No.:2020-02-016B). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data are available in the manuscript or the supplementary material. All fly strains, cell lines, and DNA vectors are readily available through the corresponding author. Antibodies are commercially available.