TorsinA and Neuronal Nuclear Pore Complex Biogenesis

Nuclear pore complexes (NPCs) are large multiprotein assemblies essential for macromolecular transport between the nucleus and cytosol. Mutations in NPC components cause early onset neurological disorders, and NPC defects are implicated in several nervous system diseases including DYT-TOR1A dystonia (DYT1), a neurodevelopmental movement disorder caused by a loss-of-function mutation in the AAA+ protein torsinA. Yet, little is known about NPC biogenesis and dynamics, and the biological function of torsinA and the molecular defects underlying DYT1 dystonia remain largely unknown. Using super-resolution microscopy, we observe a striking upregulation in NPC density in maturing mouse primary neurons, identifying neuronal maturation as a novel, physiological context of NPC biogenesis. While NPCs are uniformly distributed in wild-type (WT) neurons, torsinA-knockout (KO) neurons develop severe clusters of NPCs. In contrast to the drastic difference in distribution between WT and torsinA-KO neurons, NPC density is normal in torsinA-KO neurons, suggesting that torsinA is essential for NPC spatial organization, but not total number. To elucidate the dynamics of NPC formation and localization, we developed a HaloTag-Nup107 mouse line and conducted pulse-chase studies of existing and newly-formed NPCs. Abnormal clusters arise in torsinA-KO neurons due to aberrant localization of nascent NPCs, indicating that torsinA is a novel determinant of sites of neuronal NPC biogenesis. Scanning transmission electron microscopy tomography reveals that mislocalized NPCs in torsinA-KO neurons spatially correlate with abnormal blebbing of the nuclear envelope (NE). These findings are consistent with a model in which absence of torsinA causes continued budding of the inner nuclear membrane at sites of new NPC formation, resulting in NE blebs and stalling NPC assembly. Interestingly, while NPC clusters persist, NE blebs are transient, allowing NPC assembly to resume in mature neurons. Collectively, our work highlights the significance of torsinA function during a discrete developmental window and advances the understanding of fundamental mechanisms underlying NPC biogenesis and spatial organization.PHDCellular & Molecular BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/178110/1/suminkim_1.pd