Molecular architecture of synapses
We combine immunohistochemistry, high resolution light microscopy and electron microscopy to study the molecular architecture of synapses and how structure relates to function. In general, synapses comprise several morphological and functional distinguishable compartments as the presynaptic cytomatrix at the active zone (CAZ), a mesh of proteins, essential for synaptic vesicle docking and release and the postsynaptic density (PSD) containing a matrix of cell-adhesion molecules, receptors and cytoskeletal elements.
The sensory inner hair cell (IHC) ribbon synapses are of particular interest for us. They exhibit an elaborated ellipsoid ribbon surrounded by a halo of synaptic vesicles. This characteristic structure allows ribbon synapses to support sustained exocytosis over long time periods. Using electron microscopic techniques as electron tomography and high-pressure freezing/freeze-substitution (HPF/FS) we study morphological aspects of wild-type and mutant synapses qualitatively and quantitatively. Electron tomography enables the visualization of fine molecular structures due to its high z-resolution. HPF/FS is a special preparation method avoiding chemical fixation of the tissue. Under high pressure and low temperature samples become immobilized within milliseconds and preserved in a near native state. The combination of electron tomography and HPF/FS allows us to determine synaptic vesicle pools, docking or tethering of synaptic vesicles in high spatio-temporal resolution under different conditions (resting or stimulated). Further, we want to construct a coherent picture of the localization of synaptic proteins at IHC ribbon synapses using immunofluorescence and immunogold labeling methods in combination with high resolution light microscopy and electron tomography or serial 3D reconstructions.
In addition, we have a longstanding interest in the ultrastructure of presynapses and their postsynaptic counterparts in general.