Optical Control of Synaptic Function via Adhesion Molecules

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 understanding of neurological disorders, is to shed light on the mechanisms that wire up, sculpt and maintain synaptic connections. Neuronal adhesion molecules, such as pre- synaptic neurexins (NRXs) and post-synaptic neuroligins (NLGs), play important roles in these processes. In this project, we will control synaptic nanoscale organization and function by optogenetic tuning of the oligomerization and the signaling of the adhesion proteins NRX and NLG. To achieve this goal, this joint ANR/FWF application brings together two teams with highly complementary background: The team of 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. The team of H. Janovjak (Klosterneuburg) established optogenetic methods to control the signaling and behavior of mammalian cells with a focus on the regulation of membrane protein oligomerization. This combination of state-of-the art methods and the emergence of a new line of research will allow both the dynamic and quantitative description as well as regulation of adhesion protein clustering and function at synapses towards an understanding of synaptic development and function. 1

Nerve cells in the brain are assembled into a complex network whose activity enables control of body functions and higher brain functions, such as thought and memory. Tissue complexity is illustrated by the sheer number of nerve cells, approximating 86 billions in the human brain. It is further illustrated by the fact that each nerve cell receives information from a large number of other cells at synapses, processes it, and transmits it further. Optical microscopy methods play a central role in the analysis of brain tissue structure, as they allow visualizing specific molecules and investigating living systems. However, the spatial resolution of conventional light microscopes is limited to about half the wavelength of light or a few hundred nanometers, such that the detailed architecture of brain tissue or of synapses cannot be resolved. Novel optical "super-resolution" microscopy tools with much better resolution hold promise for analyzing living brain tissue to the level of the synaptic connection between nerve cells. In this FWF project, light microscopy technologies were developed that allow analyzing brain tissue with detail that has not been reached previously. In particular, these techniques allow to visualize the cellular context comprehensively in the tissue with high resolution, rather than just single cells. One approach, tailored towards living tissue, can decode dynamic processes. A second approach for fixed tissues visualizes specific molecules, e.g. at synapses, in their structural context. These technologies will aid in addressing a series of questions in neuroscience in the context of synaptic connectivity and the cellular architecture of brain tissue. This will be of value for studying fundamental aspects of the biology of brain tissue and for studying the alterations of brain tissue in disease processes, such that ultimately, together with complementary approaches, they will help understand the underlying mechanisms better.