The dynamics of postsynaptic receptor scaffold formation and remodeling at inhibitory synapses remain largely unknown. Gephyrin, which is a multimeric scaffold protein, interacts with cytoskeletal elements and stabilizes glycine receptors (GlyRs) and individual subtypes of γ-aminobutyric acid A receptors at inhibitory postsynaptic sites. We report intracellular mobility of gephyrin transports packets over time. Gephyrin units enter and exit active synapses within several minutes. In addition to previous reports of GlyR–gephyrin interactions at plasma membranes, we show cosedimentation and coimmunoprecipitation of both proteins from vesicular fractions. Moreover, GlyR and gephyrin are cotransported within neuronal dendrites and further coimmunoprecipitate and colocalize with the dynein motor complex. As a result, the blockade of dynein function or dynein–gephyrin interaction, as well as the depolymerization of microtubules, interferes with retrograde gephyrin recruitment. Our data suggest a GlyR–gephyrin–dynein transport complex and support the concept that gephyrin–motor interactions contribute to the dynamic and activity-dependent rearrangement of postsynaptic GlyRs, a process thought to underlie the regulation of synaptic strength.

Neuroligins are postsynaptic cell adhesion molecules that associate with presynaptic neurexins. Both factors form a transsynaptic connection, mediate signalling across the synapse, specify synaptic functions and play a role in synapse formation. Neuroligin dysfunction impairs synaptic transmission, disrupts neuronal networks and is thought to participate in cognitive diseases. Here we report that chemical treatment designed to induce LTP or LTD induces neuroligin 1/3 turnover, leading to either increased or decreased surface membrane protein levels, respectively. Despite its structural role at a crucial transsynaptic position, GFP-neuroligin 1 leaves synapses in hippocampal neurons over time with chemical LTD-induced neuroligin internalization depending on an intact microtubule cytoskeleton. Accordingly, neuroligin 1 and its binding partner PSD-95 associate with components of the dynein motor complex and undergo retrograde co-transport with a dynein-subunit. Transgenic depletion of dynein function in mice causes postsynaptic NLG1/3 and PSD-95 enrichment. In parallel, postsynaptic density (PSD) lengths and spine head sizes are significantly increased, a similar phenotype as observed upon transgenic overexpression of NLG1 (Dahlhaus et al., 2009). Moreover, application of a competitive PSD-95 peptide or neuroligin 1 C-terminal mutagenesis, specifically alter neuroligin 1 surface membrane expression and interfere with its internalization. Our data suggest the concept that synaptic plasticity regulates neuroligin turnover through active cytoskeleton transport.

No abstract