Lack of Colocalization between Gephyrin and Tubulin at the Inhibitory Post-Synapse

Idil Arioz1, Albert Becker2, Dirk Dietrich3, Susanne Schoch2

1 Institute of Neuropathology, University of Bonn Medical Cente�r
2 Institute of Neuropathology, University of Bonn Medical Center
3 Institute of Neurosurgery, University of Bonn Medical Center

Disruption of excitation inhibition balance of neuronal circuits contributes to various brain pathologies. Despite the importance of inhibitory synaptic transmission, the mechanisms underlying the inhibitory synaptic transmission, stabilization, and maintenance are poorly understood. Gephyrin is a multifunctional protein that plays a role in clustering of glycine and GABAA receptors at the inhibitory post-synapses. Biochemical studies in the literature show a direct interaction of polymerized tubulin with gephyrin. In contrast, there is also evidence in a previous study, that gephyrin was not affected by the depolymerization of microtubules or actin. Therefore, differences in the modes of interaction are suspected of gephyrin to the cytoskeleton. Moreover, the nanoscale architecture of cytoskeletal elements is not resolved in inhibitory post-synapses. To characterize the underlying structure, we have started with establishing super-resolution microscopy (dSTORM) of microtubules and the inhibitory post-synapse scaffold gephyrin. Our first results, imaging the laterally located inhibitory-postsyapses, suggest that tubulin lacks direct contact with gephyrin, although the number of dendritic microtubule filaments was found to be a critical indicator of the occurrence of inhibitory synapses. Moreover, single filament-containing dendrites were devoid of gephyrin punctae. These experiments will help us gain further insight into how cytoskeletal organization elements are involved in inhibitory post-synapses.