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Synapse formation and maturity through planar cell polarity pathway

Periodic Reporting for period 1 - SynPCP (Synapse formation and maturity through planar cell polarity pathway)

Reporting period: 2018-03-01 to 2020-02-29

In the brain, most excitatory synapses are located in small, mushroom shaped membrane extensions called dendritic spines, which formation and specification both depends on actin remodeling. Because Planar cell polarity (PCP) signalling sculpt cell morphology by inducing polarized changes in the cytoskeleton, they are strong candidates to regulate F-actin networks in dendritic spines. My specific goal was to decrypt and monitor at the nanoscale level the organization and dynamics of Scribble, a PCP associated proteins, and a scaffolding protein important for neuronal development, notably at the synaptic and post-synaptic level, that was reported mutated in some spina bifida and Autism Spectrum Disorder patients. One in six people suffers from neurological disorders. Many neurological disorders, including Autism Spectrum disorder and other intellectual disabilities, have been linked to alterations in dendritic spines, the cellular compartment that enclose the postsynapse. Many things remain to be understood in the formation, maintenance and functioning of dendritic spines. It is of the utmost importance to better understand these processes in order to develop new therapeutic strategies. Moreover in the hippocampus, spine morphology, along with post-synaptic density (PSD), varies along the dendrite. Indeed, proximal spines are bigger than distal spines. In the PSD, where receptors are anchored, PSD-95 concentrate glutamatergic receptors into nanodomains, which are crucial for synaptic transmission. This structural organization is modified during plasticity.
Here, we used single molecule super-resolution microscopy combined with tessellation-based analysis to quantify the molecular organization and dynamics of various dendritic spine proteins at the single-molecule level. We show a very specific spatial correlation of Scribble with specific components of the dendritic spines. Expression of mutated forms of Scribble found in ASD and spina bifida modified PSD-95 nanoscale organization in spines along dendrites. These Scribble mutations affect PSD-95 clustering and nano-clustering in terms of size and number differently. Altogether, we identify a critical role for Scribble in PSD95 nanoscale organization that regulate the accumulation of AMPAR and spine plasticity.
With this project we have shown that :
1. Scrib levels regulate differently PSD95 organization in proximal and distal spine
2. Scrib mutations studied disrupt the link between Scrib and actin structure,
3. Scrib mutations disrupt the organization on dendritic spines through the disruption of clustering and nanoclustering of postsynaptic proteins
Results of this project have not yet been published in a peer-reviewed journal
This project provides novel conceptual insights into the role of Scrib in the nanoscale organization of spines along the dendritic tree and how Scrib controls the actin cytoskeleton to build functional synapses. This project offers a multilevel and interdisciplinary approach to understand the consequences of mutations of Scrib-dependent PCP signaling at the nanoscale level, on the maturation and function of the basic functional unit of neuronal integration in the complex circuit of the hippocampus: the dendritic spine helping to lead the way to novel therapeutic strategies.
dSTORM image of spines showing GFP-Scrib (green) and PSD-95 (red)