Neuronal connectivity depends on the proper development of individual synapses. In this axis, we focus on understanding the molecular mechanisms driving excitatory synapse formation and molecular organization. Our aim is to understand how synaptic cell adhesion proteins dynamically shape synapse organization during neuronal development and maturation. Insight into these fundamental molecular mechanisms is key to understanding brain function and the etiology of neurodevelopmental diseases that involve numerous cell adhesion proteins.

 

 

 

Excitatory synapses contain numerous cell adhesion proteins involved in driving synapse establishment, specification, maintenance, and participating to synapse plasticity. However, how these proteins are co-organized at synapses, how they interact or compete with one another, and how they are differentially regulated during development remains unknown. One of the main limitation to the study of these proteins is the lack of efficient tools to target them in their native environment.

 

 

 

To gain insight into the dynamic molecular organization of synapses, we develop novel fluorescent nanoprobes to target adhesion proteins and study their dynamic organization at the nanoscale using super-resolution microscopy. Nanoprobes are small (~3nm) monomeric ligands that do not induce protein crosslinking, allow efficient targeting of proteins inside synaptic clefts and dense tissue, to observe the dynamic rearrangement of adhesion proteins in situ during neuronal development.

We combine these tools with super-resolution microscopy and conditional mouse genetics to understand the dynamics and nanoscale organization of synaptic proteins and gain insight into the mechanisms driving synapse development, organization, and function. Using these methodologies, we showed that neuroligins and LRRTMs, two major partners of presynaptic neurexins display different dynamic behavior and nanoscale organization at post-synapses, suggesting different functions in synapse organization and function, which we are currently investigating.

 

 

Selected publications

Dynamics, nanoscale organization, and function of synaptic adhesion molecules.
Chamma I, Thoumine O. Mol Cell Neurosci. 2018 Sep;91:95-107. doi:10.1016/j.mcn.2018.04.007. Epub 2018 Apr 17. Review.

Optimized labeling of membrane proteins for applications to super-resolution imaging in confined cellular environments using monomeric streptavidin.
Chamma I, Rossier O, Giannone G, Thoumine O, Sainlos M.
Nat Protoc. 2017 Apr;12(4):748-763. doi: 10.1038/nprot.2017.010. Epub 2017 Mar 9.

Nanoscale organization of synaptic adhesion proteins revealed by single-molecule localization microscopy.
Chamma I, Levet F, Sibarita JB, Sainlos M, Thoumine O.
Neurophotonics. 2016 Oct;3(4):041810. Epub 2016 Nov 3.

Mapping the dynamics and nanoscale organization of synaptic adhesion proteins using monomeric streptavidin.
Chamma I, Letellier M, Butler C, Tessier B, Lim KH, Gauthereau I, Choquet D, Sibarita JB, Park S, Sainlos M, Thoumine O. Nat Commun. 2016 Mar 16;7:10773. doi: 10.1038/ncomms10773.