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The sizes of nuclear bodies and other nuclear structures are normally no more than a few hundred nanometers. This size is below the resolution limit of light microscopy and thus requires electron microscopy for direct observation. Recent developments in super-resolution microscopy have extended the resolution of light microscopy to beyond 100 nm. Here, we describe a super-resolution technique, gated STED, for the analysis of the structure of nuclear bodies, with emphasis on the sample preparation and other technical tips that are important to obtain high-quality super-resolution images.

Recent immunofluorescent (IF) studies have discovered a variety of nuclear foci that have no known ultrastructurally defined counterpart. Using antibodies as ligands, immuno-electron microscopy (I-EM) is the method of choice for high-resolution recognition of these newly described nuclear compartments. However, noncoding RNAs (ncRNAs) have also been shown to be frequent components, sometimes essential, of nuclear bodies so that electron microscopic in situ hybridization (EM-ISH) can be used as an alternative means to characterize nuclear foci at the EM level. Among the array of protocols available, Lowicryl embedding of chemically fixed cells allows for high preservation of both nuclear structures and antigenicity and provides stable cell and tissue samples that can be re-probed whenever new antibodies or probes become available. Rapid and robust protocols are available for both I-EM and EM-ISH post-embedding techniques so that they can be combined on the same sections, providing ultrastructural and molecular insights into newly "emerging" nuclear bodies.

Fluorescence microscopy is a powerful technique that has become central in the study of the structure and function of biological specimens. This is due in large part to its specificity and versatility. Although an understanding of structure-typically through high-resolution imaging of fixed material-has proved an important tool to understanding function, fluorescence microscopy also offers a mechanism to interrogate cells in the living state, providing a means to explore dynamic process within the specimen over long time periods at high temporal resolution. The cell nucleus is a highly compartmented environment whose components are often highly motile and in a constant state of flux. The ability to monitor the dynamic behavior of nuclear bodies by live-cell imaging provides the researcher with important information regarding underlying mechanistic processes relating to their formation and maintenance. Two techniques have proved particularly valuable to our study of cellular dynamics and molecular mobility, namely, time-lapse imaging and fluorescence recovery after photobleaching (FRAP). Time-lapse microscopy allows for qualitative and quantitative analysis of a wide range of events at the cellular and subcellular level. FRAP provides a mechanism to study the mobility of a population of proteins in a range of conditions within discrete areas of the biological specimen. Therefore, fluorescence microscopy is unique in its ability to provide data at high temporal resolution and in such exquisite detail.

Fluorescence microscopy (FM) and electron microscopy (EM) are powerful tools for observing molecular components in cells. FM can provide temporal information about cellular proteins and structures in living cells. EM provides nanometer resolution images of cellular structures in fixed cells. We have combined FM and EM to develop a new method of correlative light and electron microscopy (CLEM), called "Live CLEM." In this method, the dynamic behavior of specific molecules of interest is first observed in living cells using fluorescence microscopy (FM) and then cellular structures in the same cell are observed using electron microscopy (EM). Following image acquisition, FM and EM images are compared to enable the fluorescent images to be correlated with the high-resolution images of cellular structures obtained using EM. As this method enables analysis of dynamic events involving specific molecules of interest in the context of specific cellular structures at high resolution, it is useful for the study of nuclear structures including nuclear bodies. Here we describe Live CLEM that can be applied to the study of nuclear structures in mammalian cells.

The cell nucleus contains many distinct subnuclear compartments, domains, and bodies that vary in their composition, structure, and function. While the cellular constituents that occupy the subnuclear regions may be well known, defining the structural details of the molecular assembly of the constituents has been more difficult. A correlative fluorescence and energy-filtering transmission electron microscopy (EFTEM) imaging method has the ability to provide these details. The correlative microscopy method described here allows the tracking of subnuclear structures from specific cells by fluorescence microscopy and then, using electron energy loss imaging in the transmission electron microscope, reveals the ultrastructural features of the nuclear components along with endogenous elemental information that relates directly to the biochemical composition of the structure. The ultrastructural features and composition of well-characterized PML bodies and interchromatin granule clusters are compared to those of ligand-activated glucocorticoid receptor (GR) foci, with GR foci containing fibrogranular nucleic acid-containing features and PML bodies being devoid of nucleic acid.