Microscopic memories: Visualizing plasticity of synaptic nanoscale organization

Abstract

The brain makes lasting memories by strengthening neuronal connections. This process is called synaptic plasticity. During synaptic plasticity, receptors are anchored in the synapse to strengthen the signal transmission between neurons. However, the receptors need to be within a couple of nanometers from the signal to be activated. Therefore, receptor placement inside the synapse determines the strength of signal transmission. The precise location of receptors inside synapses can be visualized using single-molecule localization microscopy. This technique is highly sensitive to artefacts and requires genetic labeling of receptors. In this thesis, we have improved the usability of existing genetic labeling techniques and extended their function to label multiple proteins at once. Using genetic labeling and single-molecule microscopy, we found that receptors and their scaffolding proteins reorganize into dense nanoscale clusters during synaptic plasticity. Furthermore, we showed that interactions between scaffolding proteins and the cytoskeleton are required for this nanoscale reorganization. The cytoskeleton supports the structure of synapses and increases their size during synaptic plasticity. Future research will try to elucidate how the cytoskeleton can reorganize the synapse and what other proteins are involved in this process. Auxiliary proteins of the receptors also influence the location of receptors in the synapse. We observed nanoclusters of auxiliary proteins in synapses. However, we did not identify what specific auxiliary protein is required for the nanoscale positioning of receptors during synaptic plasticity. All in all, this thesis has revealed that the cytoskeleton and scaffolding proteins guide the nanoscale reorganization of receptors during synaptic plasticity.