CORRELATED IMAGING OF SUPRAMOLECULAR COMPLEXES ANDCELLULAR COMPARTMENTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. At NCMIR, we seek to understand how proteins map onto complex cellular microdomains like synapses, and how these domains in turn relate to higher orders of structure. Although cryo-tomography of unstained material offers the opportunity to study native molecular structure in situ, this approach is not often feasible for many of the most interesting questions in cell biology, particularly in the nervous system. NCMIR has pioneered the use of fluorescence photooxidation as a staining technique for correlated light and electron microscopic imaging. Reactive oxygen, generated when fluorescent compounds are strongly excited, drives the oxidation of diaminobenzidine (DAB) into an insoluble polymer that can be rendered electron-dense by treatment with osmium tetroxide. We made fluorescence photooxidation compatible with both immunolabeling and in situ hybridization using the fluorophore eosin, a brominated derivative of fluorescein. This method has the advantage of correlating low resolution analysis at the light microscope to the finer ultrastructural details obtainable at the electron microscope. The specificity of the photooxidation-generated labeling and localization was outstanding compared to enzymebased methods because the reactive oxygen species are relatively short-lived and do not diffuse far from the site of production and the extensive cross-linking of tissue minimizes the spread of the reaction product. We are applying selective contrasting methods, including tetracysteine (TC) technology, immunocytochemical and histological staining techniques, to highlight and dissect areas of macromolecular specialization in cells and tissues and map the three dimensional arrangement with electron tomography. We are developing methods for high pressure freezing of fragile nervous tissue and for photoconverted samples. Using the capabilities of our energy filtering microscope and computational methods for improving the alignment and segmentation of tomographic reconstructions, we continually push the resolution of our imaging techniques to bridge the gap between light microscopic imaging of cellular dynamics and direct visualization of macromolecular structure.