Optical control of synaptic function via adhesion molecules – SyntheSyn

Elucidation of the complex map of neural connectivity in the mammalian brain has become one of the major goals of modern neuroscience. Fundamental to such efforts, and to the comprehension of neurological disorders, is to gain an understanding of the mechanisms that wire up, sculpt and maintain synaptic connections. Neuronal adhesion molecules, including pre-synaptic neurexins (NRXs) and post-synaptic neuroligins (NLGs) play important roles in these processes. For example, genetic mutations of certain NRX and NLG isoforms in humans are associated with autism spectrum disorders, demonstrating a crucial role of these proteins in maintaining a normal balance between excitatory and inhibitory synaptic transmission. In this context, the group of O. Thoumine (Bordeaux) demonstrated that tyrosine phosphorylation of NLG1 leads to a switch in the assembly of excitatory versus inhibitory synapses. However, the precise underlying tyrosine kinase signaling pathway remains to be identified.
Furthermore, an important concept that has emerged from recent progress in super-resolution imaging is that synaptic proteins are not homogeneously distributed in the membrane, but form distinct clusters promoted by lateral oligomerization and interactions with intracellular scaffolding molecules. The Thoumine team recently deciphered the internal nanoscale organization of pre-synaptic NRX1, and its post-synaptic binding partners NLG1 and LRRTM2, organized as small domains in the range of 100 nm. However, the actual function of those protein clusters is completely unknown.
Finally, optogenetic methods have made tremendous progress in the past years now allowing an exquisite control of protein-protein interactions with light, including protein dimerization (for instance, through light–oxygen-sensing (LOV) domains), dissociation (through cobalamin-binding domains), and association and oligomerization (through cryptochromes). The group of H. Janovjak (Klosterneuburg) has pioneered some of these methods, in particular through the engineering of light-gated receptor tyrosine kinases (RTKs) that can be switched on and off with light of different wavelengths. These receptors have already been applied by the Thoumine group in collaboration with the Janovjak group.
In this project, we aim at controlling synaptic nanoscale organization and function by optogenetic tuning of oligomerization and signaling of the adhesion proteins NRXs and NLGs. To reach this aim, this joint ANR/FWF application brings together two scientists with highly complementary background: O. Thoumine (Bordeaux) is a specialist of neuronal adhesion proteins, with expertise in single molecule imaging, computation, and electrophysiology to probe synaptic function and nanoscale organization. H. Janovjak (Klosterneuburg) established new optogenetic methods to control the signaling and behavior of mammalian cells with focus on the regulation of membrane protein oligomerization. We believe that this partnership represents the ideal combination of state-of-the art methods and the emergence of a new line of research towards both the dynamic and quantitative description as well as the regulation of adhesion protein clustering and phosphorylation at synapses. Together, these approaches will provide a better understanding of synaptic development and function. This interdisciplinary project comprises three collaborative Aims, from the control of molecular interactions to synaptic physiology:
AIM1: TO ESTABLISH A PLATFORM FOR REAL-TIME CONTROL OF PROTEIN INTERACTIONS IN NEURONS WITH LIGHT
AIM 2: TO UNDERSTAND THE IMPACT OF PROTEIN OLIGOMERIZATION ON SYNAPTIC PHYSIOLOGY
AIM 3. TO UNDERSTAND THE IMPACT OF NLG PHOSPHORYLATION ON SYNAPTIC DIFFERENTIATION